Zpvlrsbk Guide E 2019 V1 2 Pdf

Fire safety engineering

The Chartered Institution of Building Services Engineers 222 Balham High Road, London SW12 9BS +44 (0)20 8675 5211 www.cibse.org

CIBSE Guide E

ISBN 978-1-912034-29-1

2019

9 781912 034291

CIBSE Guide E

This publication is supplied by CIBSE for the sole use of the person making the download. The content remains the copyright property of CIBSE

Fire safety engineering

CIBSE Guide E

This publication is supplied by CIBSE for the sole use of the person making the download. The content remains the copyright property of CIBSE

Fire safety engineering

The rights of publication or translation are reserved.

© Fourth edition June 2019 The Chartered Institution of Building Services Engineers London Registered charity number 278104 ISBN 978-1-912034-29-1 (book) ISBN 978-1-912034-30-7 (PDF) This document is based on the best knowledge available at the time of publication. However, no responsibility of any kind for any injury, death, loss, damage or delay however caused resulting from the use of these recommendations can be accepted by the Chartered Institution of Building Services Engineers, the authors or others involved in its publication. In adopting these recommendations for use each adopter by doing so agrees to accept full responsibility for any personal injury, death, loss, damage or delay arising out of or in connection with their use by or on behalf of such adopter irrespective of the cause or reason therefore and agrees to defend, indemnify and hold harmless the Chartered Institution of Building Services Engineers, the authors and others involved in their publication from any and all liability arising out of or in connection with such use as aforesaid and irrespective of any negligence on the part of those indemnified. Layout and typesetting by Alasdair Deas for CIBSE Publications Printed in Great Britain by The Lavenham Press Ltd., Lavenham, Suffolk CO10 9RN

Note from the publisher This publication is primarily intended to provide guidance to those responsible for the design, installation, commissioning, operation and maintenance of building services. It is not intended to be exhaustive or definitive and it will be necessary for users of the guidance given to exercise their own professional judgement when deciding whether to abide by or depart from it. Any commercial products depicted or described within this publication are included for the purposes of illustration only and their inclusion does not constitute endorsement or recommendation by the Institution.

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No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission of the Institution.

Foreword from the Institution of Fire Engineers

We believe that this guide provides a thorough and complete introduction to, and summary of, fire safety engineering for those for whom fire engineering is not their primary activity but who have to work with, or have dealings with, fire engineers or fire engineered buildings, either during construction or in use. The guide also provides a useful concise handbook of fire safety engineering which we know is of proven value to professional fire engineers. It is largely based on existing codes and guidance that professional fire engineers will be familiar with, although additional original material has been included where appropriate. The guide necessarily has a strong UK focus, but is intended for a global readership. Many of the chapters in this guide have been written by Fellows and Members of the IFE who are Chartered Engineers. The IFE is committed to making the world safer from fire, mainly by seeking to ensure that those working in the fire industry, or in conjunction with the fire industry, have the appropriate competency and ethics. On behalf of the IFE we commend this guide as a significant contribution towards that goal. Martin Shipp BSc (Physics) CEng FIFireE CPhys MInstP IFE International President 2017/18 Dr Peter Wilkinson BEng (Hons) MSc EngD CEng FIFireE PMSFPE SIRM IFE Chair of the Board of Trustees 2017

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As officers of the Institution of Fire Engineers (IFE) we welcome this guide – the fourth revision of CIBSE Guide E for Fire Safety Engineering.

Preface

As with the third edition a concerted effort has been made to provide information that can be used internationally. These references include codes, standards and guidance from the USA that are frequently used in the Middle East and Asia. Fire safety engineering can mean many things to many people and covers a wide range of levels of knowledge and competence as well as a diverse range of activities of which developing a package of measures having the objective of reducing the potential for injury, death, property and financial loss to an acceptable level is the area for which this Guide is produced. At the time this guide was going through the final stages of publication the devastating fire at Grenfell tower in Kensington, London occurred. CIBSE considered that it should provide guidance on the design of building facades for tall buildings using the expertise of fire safety consultants and specialist facade engineers within CIBSE. A new chapter on facade fire safety is included in this guide. Fire safety engineering is a continually developing art and science and users are advised to maintain a personal regime of professional development and to make use of new standards and techniques that will be introduced after the publication of this Guide. Finally, I wish to extend my thanks to the authors of the various chapters, all of whom are experienced fire engineers who were at the time practising with well-respected engineering consultancy firms or major organisations internationally. Without their dedication, and the time and expertise they have freely given, this edition of Guide E would not have been produced. Martin J. Kealy CEng BSc (Hons) FIFireE MSFPE MCIBSE Chairman, CIBSE Guide E Steering Committee

Guide E Steering Committee Martin J. Kealy (Chairman), MKA Fire John Barnfield, Tenos Fire Safety Engineering Gary Daniels, Hoare Lea Chris George, Falck Roger Harrison, AECOM Sam Liptrott, Olsson Fire Andrew Nicholson, The Fire Surgery Benjamin O’Regan, Qatar Rail Martin Shipp, BRE Brent Sutherland, AMEC Nick Troth, Arup Martin Weller, Atkins Peter Wilkinson, Pyrology

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This fourth edition of CIBSE Guide E: Fire safety engineering is a fully updated version of the third edition which was published in 2010. The entire text of every chapter has been carefully reviewed.

Principal authors and contributors (fourth edition) Principal author: Martin J. Kealy (Chairman) (MKA Fire)

Chapter 2: Legislation Principal author: Nick Troth (Arup) Contributor: Philip Close (Arup)

Chapter 3: Building designation Principal authors: Sam Liptrott and James Perry (Olsson Fire)

Chapter 4: Performance-based design principles Principal authors: John Barnfield and Andrew Foolkes (Tenos Fire Safety Engineering)

Chapter 5: Application of risk assessment to fire engineering designs Principal authors: Martin Weller (Atkins) and Russell Kirby (FM Global)

Chapter 6: Fire dynamics Principal authors: Roger Harrison (AECOM), Gary Daniels and Chris Hallam (Hoare Lea)

Chapter 7: Means of escape and human factors Principal authors: John Barnfield and Andrew Foolkes (Tenos Fire Safety Engineering) Contributor: Steven Porter (Tenos Fire Safety Engineering)

Chapter 8: Fire detection and alarm Principal author: Benjamin O’Regan (Qatar Rail)

Chapter 9: Emergency lighting Principal author: Benjamin O’Regan (Qatar Rail)

Chapter 10: Smoke ventilation Principal authors: Gary Daniels and Chris Hallam (Hoare Lea)

Chapter 11: Fire suppression Principal authors: Chris George and Paul Watkins (Falck) and Dr Tim Nichols (Tyco Fire Protection)

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Chapter 1: Introduction

Chapter 12: Fire resistance, structural robustness in fire and fire spread

Contributor: Ben McColl (OFR Consultants)

Chapter 13: Firefighting Principal authors: Andrew Nicholson and Matt Ryan (The Fire Surgery)

Chapter 14: Fire safety management Principal author: Martin Shipp (BRE)

Chapter 15: Fire safety on construction sites Principal author: Brent Sutherland (AMEC)

Chapter 16: Fire safety of building facades Principal authors: Martin J. Kealy (MKA Fire) Hywel Davies (CIBSE)

Principal authors and contributors (first, second and third editions) Guide E is a continuing publication and each edition relies on material provided for previous editions. The Institution acknowledges the material provided by previous authors and contributors, including: David Boughen, Peter Bressington, Gordon Butcher, Anna Cockayne, Geoffrey Cox, Mike Dennett, Graham Faulkner, Mick Green, Miller Hannah, Graeme Hansell, John Hopkinson, Harry Hosker, Martin Kealy, John Klote, Margaret Law, Kathryn Lewis, Rodrigo Machado, Hugh Mahoney, Steve Marshall, Frank Mills, Bob Nixon, Su Peace, Alan Porter, Andy Riley, Colin J. Roberts, Linton Rodney, Gerard Sheridan, Jonathan D. Sime, David B. Smith, Shane Tate, Philip Thomas, Chris Trott, Terry M. Watson, Peter Warren, Bob Whiteley, Corinne Williams.

Acknowledgements Permission to reproduce extracts from British Standards is granted by BSI. British Standards can be obtained in PDF or hard copy formats from the BSI online shop: www.bsigroup.com/Shop or by contacting BSI Customer Services for hardcopies only: Tel: +44 (0)20 8996 9001, Email: [email protected] Contains public sector information licensed under the Open Government Licence v3.0. The Institution is grateful to Lynsey Seal (London Fire Brigade), Paul McLaughlin (Chapman BDSP) and Andy Passingham (Buro Happold FEDRA) for kindly reviewing the entire draft prior to publication.

Project manager: Editor: Editorial Manager: CIBSE Head of Knowledge: CIBSE Technical Director:

Sanaz Agha Alasdair Deas Ken Butcher Nicholas Peake Hywel Davies

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Principal authors: Peter Wilkinson (Pyrology) Danny Hopkin (OFR Consultants)

Contents 1-1

2 Legislation

2-1

3

Building designation

3-1

4

Performance-based design principles

4-1

5

Application of risk assessment to fire engineering designs

5-1

6

Fire dynamics

6-1

7

Means of escape and human factors

7-1

8

Fire detection and alarm

8-1

9

Emergency lighting

9-1

10

Smoke ventilation

10-1

11

Fire suppression

11-1

12

Fire resistance, structural robustness in fire and fire spread

12-1

13 Firefighting

13-1

14

Fire safety management

14-1

15

Fire safety on construction sites

15-1

16

Fire safety of building facades

16-1

Index I-1

Important note: potential changes to fire safety legislation Legislation and guidance relating to fire safety is currently undergoing significant changes in the UK and in several other jurisdictions following recent fire events and, in the UK, publication of the Independent Review of Building Regulations and Fire Safety*. Users of this Guide are responsible for ensuring that they are aware of changes in guidance and legislation that may relate to their work in any jurisdiction, including proposed changes that may have a significant effect on designs currently under development. * Hackitt J (2018) Building a Safer Future: Independent Review of Building Regulations and Fire Safety (London: Ministry of Housing, Communities and Local Government)

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1 Introduction

1-1

1 Introduction

About this Guide

CIBSE Guide E: Fire engineering was first published in 1997, and was revised in 2003 and in 2010 to reflect the development of fire safety engineering as a discipline. It has been further updated to take into account the latest fire safety engineering knowledge and techniques. As with the previous editions, the Guide has been updated by experienced fire engineers, all of whom were at the time practising with well-respected engineering consultancy firms or major organisations in the UK and overseas. The Guide is intended to be the ‘go to’ document that provides building services engineers and fire life safety consultants with guidance on a broad range of fire engineering issues.

1.3

There are generally two ways of demonstrating compliance with statutory building codes and regulations. One is to follow the prescriptive guidance given in codes of practice and statutory guidance, and the other is to use a fire safety engineering approach. This is recognised, for example, in the formal guidance that accompanies the Building Regulations in England and Wales. Approved Document B (HM Government, 2013; Welsh Government, 2015) makes the following very clear statement: Fire safety engineering can provide an alternative approach to fire safety. It may be the only practical way to achieve a satisfactory standard of fire safety in some large and complex buildings containing different uses, e.g. airport terminals. Fire safety engineering may also be suitable for solving a problem with an aspect of the building design which otherwise follows the provisions in this [Approved] document.

This Guide aims to give practical advice on fire safety engineering. Since publication of the first edition, Guide E has been widely used and is referred to in British Standards as an authoritative guidance document. The extent of modification to the sections has varied according to need. The committee decided to keep the same structure as the 2010 version. Some sections have had a light update and others have been substantially amended.

1.2

What is fire engineering?

The term ‘fire engineering’ continues to be widely misused and not well understood. It is worth noting at this point that there are two main types of fire engineering: ——

fire protection engineering, where the engineer is responsible for the design of fire systems, such as automatic fire suppression and fire detection systems

——

fire safety engineering, where the engineer is responsible for the design of fire strategies, including the location and number of stairs, design of smoke control regimes and designed structural fire protection measures. The term ‘fire and life safety’ is also commonly used to describe this type of fire engineering

This Guide deals with both types of fire engineering. BS 7974: 2001 Application of fire safety engineering principles to the design of buildings. Code of practice (BSI, 2001) and International Fire Engineering Guidelines (ABCB, 2005) both address fire safety engineering and both provide a framework for an engineering approach to the achievement of fire safety in buildings. Guide E can be used as a set of methodologies within these frameworks.

Use and benefits of a fire safety engineering approach

Formal guidance documents, published standards (such as British Standards, National Fire Protection Association Codes, etc.) and industry codes of practice cannot take into account the peculiarities of every single building design. The larger and more complex the design, the more difficult and more costly it is to ensure that the design meets the requirements of the prescriptive codes. As an example, prescriptive guidance will usually specify maximum travel distances to exits, a situation that could be very difficult to achieve in buildings such as airport terminals and other large buildings without imposing restrictions on building usage and design. A fire safety engineering alternative method would look at the time taken to escape and compare that with the time for conditions to become untenable. This Guide will assist engineers to calculate escape times and tenability criteria, and to make judgments regarding whether the performance criteria required by the locally applicable codes or regulations have been satisfied. There are three main fire safety engineering approaches, as follows: (a)

Equivalency (or comparative approach): whereby it is demonstrated that the design provides a level of safety equivalent to that which would have been obtained by applying prescriptive codes.

(b)

Deterministic approach: in which the objective is to show that, on the basis of the initial (usually ‘worst credible case’) assumptions, some defined set of conditions will not occur. Where there is any doubt regarding the reliability of the input data, a

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1.1

1-2 conservative approach should be adopted. This may require the use of explicit safety factors to compensate for uncertainties in the assumptions.

1.6

Contents of this Guide

Probabilistic approach: the objective of which is to show that the likelihood of a given event occurring is acceptably small. This is usually expressed in terms of the annual probability of occurrence of the unwanted event (e.g. a probability of an individual death through fire of 10−6, or one per million). It must be recognised that, whatever measures are taken, risks can never be reduced to zero.

1.6.1

Chapter 1: Introduction

The main benefits that fire safety engineering alternatives can bring are the following: ——

increased design flexibility

——

reduction in construction and/or running costs

——

measures more suited to the building use.

1.4

The authority having jurisdiction (AHJ)

The ahj is the governmental agency or sub-agency that regulates the construction process and is usually in the municipality where the building is located. Where a fire safety engineering approach is being considered, early consultation with the ahj is essential. Many ahjs will accept a fire safety engineering approach and for large and complex buildings the ahj will frequently expect such an approach to be adopted. However, certain ahjs will not accept a fire safety engineering approach. The likelihood of acceptance will be a function of: ——

the type of building

——

the perceived competence of the design team

——

the

——

individual personalities within the

——

the client/owner’s previous behaviour and history.

1.5

ahj’s

level of experience ahj

Purpose of this Guide

It is intended that this Guide will be used in conjunction with established codes and standards to provide guidance to practitioners. It will also be of interest to designers and ahjs who, while not directly concerned with fire safety engineering, need to understand the advice offered to them by specialists. The Guide will be of value to students embarking on careers in the professions related to fire safety and to practising designers who wish to enhance their knowledge through continuing professional development. Previous editions of this guide were UK-centric; however, this edition has been written by fire safety engineers with international experience or who have international offices or overseas headquarters. This Guide is intended for use worldwide and, where applicable, local statutes, regulations and guidance should be used in place of the quoted UK documentation.

Chapter 1 provides an introduction to the Guide, gives some history about the publication, discusses what fire safety engineering is and the benefits that it offers to designers, provides an overview of its structure and contents, and highlights changes from and additions to the previous edition.

1.6.2

Chapter 2: Legislation

This renamed chapter has changed substantially and provides further information on the concept of fire safety engineering with a focus on that fact that responsibility for a fire safety engineering approach lies with the designer and not the ahj. The chapter considers the high-level overview, early consultation and generic procedures that need to be followed by a designer responsible for the design. Although every ahj is different and it is not possible to cover all ahjs within the Guide, some major geographic regions are addressed. The chapter also details the legislation that applies to a building from design to post-completion.

1.6.3

Chapter 3: Building designation

This chapter addresses the manner in which buildings are classified in the context of fire precautions. It includes extracts from published data and identifies factors that have implications for building types, together with a checklist of items to be considered following purpose group classification. Some additional information is added regarding care homes and risk assessments.

1.6.4

Chapter 4: Performance-based design principles

This chapter provides information on basic principles and draws attention to the need for design to be entrusted to suitably qualified and experienced persons. Design objectives and design scenarios are covered and references made to ‘what if ’ events. The fire safety design process is described and reference is made to both UK and international framework documents, including those of the USA and Australia.

1.6.5

Chapter 5: Application of risk assessment to fire safety engineering designs

This chapter provides a detailed introduction to this complex subject, followed by comprehensive information on the various techniques available. This chapter has been substantially modified and now also addresses business resilience and insurance. Societal concerns and risks to firefighters are considered, and the chapter concludes with guidance on risk assessment pitfalls.

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(c)

Fire safety engineering

Introduction 1-3

1.6.6

Chapter 6: Fire dynamics

1.6.10

Chapter 10: Smoke ventilation

This chapter is renamed simply Smoke ventilation, reflecting a substantial rewrite that simplifies the entire chapter to both bring it up to date and make it more ‘relevant’ to its audience. Elements of the old chapter 6: Fire dynamics have been moved to this section.

There is a section on flame calculations that addresses flame height, flame projection, radiant heat flux calculations and fire resistance.

Chapter 10 describes the objectives of smoke ventilation systems. It then addresses system considerations, tenability criteria, design of systems and the components of the systems.

The old sections on smoke visibility/toxicity and smoke modelling have been moved to chapter 10: Smoke ventilation. Chapter 6 has also been simplified with new diagrams added and smoke control equations updated to reflect current research on smoke control design.

1.6.7

Chapter 7: Means of escape and human factors

This chapter covers the basic principles of designing for escape by using the established prescriptive design codes or an alternative fire safety engineering approach. The chapter gives guidance on means of escape design, including information on escape strategies, occupancy capacities, exit widths, occupant loads, response times, travel speeds and distances, capacities of escape routes, escape for people with disabilities, lifts, escalators and information systems. Additional graphical material has been incorporated on performance-based design using evacuation simulation models.

1.6.8

Chapter 8: Fire detection and alarm

This chapter covers both manual fire alarm systems and automatic fire detection systems, and details the basic requirements for the design and application of fire detection and alarm systems. It has been updated and includes additional advice on managing false alarms. The chapter defines the intentions of the systems in terms of both property protection and life safety, and guidelines are given with respect to types of systems and equipment, together with descriptions of specialist systems, zoning, location and selection of detectors.

1.6.9

Chapter 9: Emergency lighting

This chapter has been lightly updated with additional references to International Code Council (ICC) and National Fire Protection Association (NFPA) codes. It provides detailed practical guidance on the design of emergency escape lighting. Material detailing types of system and modes of operation has been removed, as these aspects are covered in other referenced CIBSE publications.

1.6.11

Chapter 11: Fire suppression

This chapter considers the principal fixed systems for fire suppression within buildings. It has been substantially rewritten and updated. The chapter covers design guidance for automatic sprinkler systems, foam systems, gaseous systems and water mist systems. The chapter contains more detail on the use and value of various systems, makes reference to a wider range of international codes and introduces new or revised guidance, especially on mist, gaseous and foam systems.

1.6.12

Chapter 12: Fire resistance, structural robustness in fire and fire spread

This chapter, originally titled Compartmentation, has been renamed and extensively rewritten and restructured. It provides general guidance on the use and value of fire separation in reducing the potential for fire spread. It describes the purpose of compartmentation, the measurement of fire resistance and the need for good maintenance of all fire-resisting barriers. Additional text has been added on the practical fire separation methods, including fire and smoke dampers, that aligns with the new BS 9999: 2017 code (BSI, 2017). There is also a new section on structural design for fire safety. While this section does not provide detailed calculation techniques, it does set the framework and points the reader to more detailed structural fire safety engineering codes and guides.

1.6.13

Chapter 13: Firefighting

This chapter has been substantially revised in close consultation with the London Fire Brigade and includes references to international practices and codes. The chapter defines common terms in firefighting and stresses the need to include the fire department as a key stakeholder in the building design. It describes general principles of firefighting, equipment (both traditional and state-of-the-art), fire department response to fires, vehicle access and water supplies. It also addresses firefighting timelines and a fire engineered approach as well as firstaid firefighting by the building occupants prior to fire department arrival.

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This new leaner chapter aims to impart a basic understanding of the processes which govern fire and smoke development and to guide the reader through the available techniques for calculating the important parameters, including design fires and smoke production rates.

1-4

1.6.14

Fire safety engineering

Chapter 14: Fire safety management

1.6.15

Chapter 15: Fire safety on construction sites

This chapter has been updated to reflect new industry guidance, current issues and regulations both in the UK and internationally. The chapter addresses fire precaution methods and the responsibilities of designers with respect to fire safety on construction sites. A new section has been added that addresses the use of timber products and timber-framed building structures, which has significantly increased since the last edition.

1.6.16

Chapter 16: Fire safety of building facades

This new chapter has been added as a result of the devastating fire at Grenfell Tower in Kensington, London and other large scale international fires involving external facades that have occurred in the last seven years. However, as a result of the significant regulatory uncertainty at the time of publication of this Guide, the decision has been taken to publish chapter 16 in online form only. This will allow it to be updated in line with anticipated ongoing government announcements and changes to

1.7

Other sources of information

The aim of this Guide is to provide an invaluable reference source for those involved in the design, installation, commissioning, operation and maintenance of buildings when considering fire precautions. However, it does not claim to be exhaustive. It contains many references to other sources of information, which should all be carefully consulted in conjunction with Guide E.

References ABCB (2005) International Fire Engineering Guidelines. Edition 2005 (Canberra: Australian Building Codes Board) BSI (2001) BS 7974: 2001 Application of fire safety engineering principles to the design of buildings. Code of practice (London: British Standards Institution) (Note: BS 7974: 2012 has been replaced by BS 7974: 2019) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Vols 1 and 2 (2006 edition, incorporating 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) Welsh Government (2015) The Building Regulations 2010 Approved Document B: Fire Safety. Vols 1 and 2 (2006 edition, incorporating 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS)

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This chapter reflects the importance that is attached to the proper management of a building with respect to fire safety. It addresses legal obligations, design, maintenance, fire prevention and planning. It has been updated to reflect changes in BS 9999, which was revised in 2017.

legislation. It also removes the potential for erroneous guidance on these matters to be available in a more durable and persistent printed form.

2-1

2

Legislation

2.1.1

Disaster-led regulations

Although the birth of fire safety engineering as a technical design discipline is relatively recent compared to other areas of engineering, UK fire safety regulations stem from as far back as the seventeenth century. The majority of UK fire safety legislation has evolved as a response to specific fire disasters. This still continues to be the case, with legislators reacting to major fire incidents. The Great Fire of London in 1666, involving rapid fire spread between buildings and, ultimately, the destruction of a large part of the city, led to an early ‘building regulations’ requirement to control the types of construction materials used in buildings and define minimum separation distances between buildings to limit the spread of fire. As urbanisation and industrialisation increased over the centuries in many countries, so too did the number of fire incidents, prompting the development of either local or national fire safety legislation, codes and standards. In the UK, the first national building regulations which prescribed fire safety measures, among other aspects of building design, did not come into effect until the 1970s. These were administered by local authority building control. Prior to this there were piecemeal regional byelaws which covered some aspects of fire safety. The Rose and Crown Hotel fire in Saffron Walden in December 1969 prompted the creation of the Fire Precautions Act 1971 in the UK. This legislation required those with a duty of care to implement fire safety measures and controls in certain ‘designated’ premises. However, it did not cover all types of premises. The Fire Precautions Act was administered by the fire and rescue authorities in the UK. In 2004, the Fire and Rescue Services Act came into force. This paved the way for a radical reform of fire safety legislation in the UK. This Act enabled the drafting and implementation of the Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541), which repealed and consolidated several pieces of earlier and historical fire safety legislation and regulations. The most important aspect of this Order was the requirement for all premises to have a valid fire risk assessment, thus moving away from prescriptive regulations towards the adoption of a performance-based approach. The recent disastrous fire at Grenfell Tower, London, on 14 June 2017 resulted in the loss of 72 lives. This prompted the UK government to hold a public inquiry into the fire and also establish an independent review of building regulations and fire safety in England, led by Dame Judith Hackitt DBE FREng, former Chair of the Health and

Safety Executive. Her report, Building a Safer Future: Independent Review of Building Regulations and Fire Safety (Hakitt, 2018), was published in May 2018. It identified systemic problems in construction in England, and called for significant changes to the construction sector. At the time of publication, the Public Inquiry is still in progress and the government’s response to Dame Judith’s report is still being developed. In December 2018, the government introduced changes to Regulation 7 of the Building Regulations, which prohibits the use of combustible materials in the external walls of high-rise buildings at least 18 m above ground level, containing one or more dwellings. In its response to Dame Judith Hackitt’s review in December 2018, the government also announced a full technical review of Part B of the Building Regulations and announced an initial call for evidence, which closed in March 2019. The outcome is almost certain to result in further changes to fire safety and building control legislation. In the meantime, work to more clearly define professional competencies is already underway under the auspices of the Industry Response Group, a body established by the government to compliment the work of the Independent Expert Advisory Panel established in June 2017, and relevant professional bodies in the UK. The Grenfell Tower disaster will inevitably have a significant impact on construction in the UK and around the world, but at the time of publication it would be premature to predict the changes that it may bring about.

2.1.2

The advent of performancebased regulations

In 1985, the first performance-based building regulations were issued in England and Wales. Prior to this, building and fire safety regulations were prescribed. The introduction of these performance-based requirements formally opened up the opportunity for designers to utilise fire engineering as a way of demonstrating compliance with the functional performance requirements. This move prompted the introduction of British Standard DD 240: 1997 Fire safety engineering in buildings: Guide to the application of fire safety engineering principles (BSI, 1997) and the first edition of CIBSE Guide E, which set out a methodology and approaches to undertaking performance-based fire safety design. A number of other countries also introduced performance-based requirements, while others still retain prescriptive requirements.

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2.1 Introduction

2-2

2.1.3

Fire safety engineering

Guidance documents (UK)

These documents make it clear that alternative ways of demonstrating compliance can be adopted. One such method is to utilise fire engineering based on guidance such as CIBSE Guide E. In 2008, in the UK, the British Standards Institution first published BS 9999 Code of practice for fire safety in the design, management and use of buildings (the current version being the 2017 revision (BSI, 2017)). It should be noted that BS 9999 is not a fire engineering guide, unlike CIBSE Guide E. The concept behind BS 9999 is that it sits between the general prescriptive guidance, such as Approved Documents and Technical Handbooks, and performance-based fire engineering guides, such as CIBSE Guide E and BS 7974: 2001 (BSI, 2001). This effectively offers a fire safety designer in the UK the choice of three methods to adopt in terms of fire safety design: (a)

generic or simplified approach (Approved Documents and Technical Handbooks)

(b)

advanced approach (BS 9999)

(c)

performance-based engineering approach.

It is the last of these approaches that this Guide explores in greater detail. However, it is vital that anyone tasked with developing the fire safety design of a building is competent to do so.

2.1.4 Competency It is essential that the fire engineer clearly understands the background of the guidance which they are adopting. This is important to ensure that the guidance and the assumptions made in the guidance are applicable and relevant to the particular design that they are progressing. The responsibility for the fire safety design rests with the person providing that fire safety design advice. It is important to recognise that authorities having jurisdiction (ahjs) do not carry any design responsibility. So a fire engineer developing the fire strategy for a building assumes full responsibility for the elements of design on which they are advising others. Consequently, they must be competent to provide such advice. This applies even if the fire safety design is following the generic or simplified approach referred to above. It is essential that the fire safety designer understands the background to and the reasons for the prescribed solutions. The overall responsibility for a design rests with the lead designer (usually the

The only reliable way to demonstrate that a fire engineer is competent is to ensure that they are a Chartered or Incorporated Engineer with a relevant professional engineering institution, such as the Institution of Fire Engineers (IFE). The IFE, as is the case with all professional engineering institutions licensed by the Engineering Council in the UK, is required to base its assessment of applicants for Chartered or Incorporated Engineer on a standardised set of competency and commitment criteria. This ensures that a consistent definition of competency can be applied to all applicants. Outside the UK, the broadly equivalent professional registrations are Professional Engineer (PE in the USA or PEng. in Canada), Chartered Professional Engineer (CPEng in Australia) and Eur Ing (in Europe, administered by FEANI). There are numerous technician level accreditations that can be sought through industry bodies, for example Certified Fire Protection Specialist (CFPS in the USA, administered by the National Fire Protection Association (NFPA)). The fire engineer may have specialist expertise in a particular aspect of fire engineering (for example, structural fire engineering, smoke movement or human behaviour), but must have a sound knowledge and understanding of the fundamentals of all aspects of fire safety science and design and be technically competent and rigorous in applying this knowledge.

2.1.5

The need for an integrated approach

Fire safety legislation and guidance thus far has been primarily driven by disasters and architectural trends, and has arguably been playing catch-up for a number of years. The growth and consolidation of fire engineering as a profession, fuelled by the demand for more complex building and the use of modern construction methods and materials, has led to a need for the fire engineer to adopt a more holistic, considered approach to design, rather than simply providing specific technical solutions. It is important that, in developing the fire safety design for a building, the fire engineer gives due consideration to how the building will be constructed and how it will be occupied and operated, as well as how it will be managed and maintained once completed. The assumptions about all of these factors should be documented in the fire safety strategy that the fire engineer delivers. At the design stage it is important that the fire engineer, in developing a fire strategy for a building, is cognisant of the potential occupiers and end users and how they will use the building. This can have a fundamental impact on the fire strategy. It is therefore important that during the design stage onerous restrictions on the end user are not imposed or required by the fire strategy. While the fire engineer may not have overall responsibility for design coordination, it is important that the fire engineer ensures that the fire safety solutions which they are proposing can actually be built. This is reflected in the

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With the introduction of performance requirements came the need for supporting guidance. In England and Wales, the Approved Documents, in Scotland, the Technical Handbooks and the Technical Booklets in Northern Ireland are published to provide guidance on some of the more common building situations. In 2009, the Welsh Assembly was granted devolved responsibility for building regulations, and as such the Approved Documents issued by the Welsh Government are now separate from those issued in England.

architect) with assistance from the design team, of which the fire engineer forms an important part.

Legislation 2-3

Another important factor is that the fire engineer should understand the potential materials and components to be used in the building in terms of their fire risk. It is inevitable that fire safety guidance will fall out of date, particularly in relation to the development of modern materials and building products, and these new materials may need careful consideration and assessment to understand how they will perform in a fire. The fire engineer should also ensure that the fire safety design does not assume or require onerous or unsafe fire safety management or maintenance procedures once the building is occupied, Construction (Design and Management) Regulations 2015 for the design to be safely maintainable in use. It is also important for the fire engineer to clearly document any relevant fire safety management or maintenance procedures required as part of the fire strategy that they develop, and for these to be handed over to the client. In England and Wales, for example, this is required to comply with Regulation 38 of the Building Regulations. The advent of Building Information Modelling (bim) and 3D models can greatly assist the fire engineer in understanding the detailing of fire compartmentation and fire-resisting lines and help them to gain an understanding of voids and connections between floors and buildings. Such tools can also enable the fire engineer to gain a better understanding of how people can potentially navigate through the building, especially in an emergency situation. It is only after considering all of these elements or phases that a truly integrated fire safety design can be achieved.

2.1.6

The objectives outline how the goals will be achieved. For example, the goals may be achieved simply by following code recommendations. All the requirements may be met by using a performance-based design approach. It may be that the goals can be accomplished by utilising a combination of code-based approach and performance-based design to verify departures from codes. Whatever methodology is to be adopted, it should be clearly documented. When using code-based approaches it is important that the fire engineer has detailed knowledge of the code to ensure that the use of a given code is valid for the particular building for which the strategy is being developed. When using performance-based approaches it is important that the fire engineer is suitably qualified and competent to undertake the fire engineering design. The fire safety strategy should be robust enough to stand up to any necessary third-party validation. It should also be recognised that prescriptive codes are usually intended for more common, generic types of buildings. In buildings that require a fire engineered approach or performance-based design, a more rigorous audit trail may often be required to document the fire safety solution and the decision-making process that was undertaken to arrive at the solution. Where those tasked with approving the design do not have sufficient competence to check the fire engineering strategy then third-party validation through a competent fire engineer should be sought. 

2.2

Regulatory approvals

Fire engineer responsibilities

The first stage in developing a fire strategy is for the fire engineer, in conjunction with all relevant design team members and stakeholders, to clearly define and understand the objectives and goals of the fire strategy. In the UK, this is defined in BS 7974 as a qualitative design review (qdr); in the International Fire Engineering Guidelines (for Australia, New Zealand, the USA and Canada) this is defined as a fire engineering brief (ABCB, 2005). The fire safety goals are the high-level target that the fire strategy is aiming to meet. They could be life safety goals, but may also include other stakeholder goals, such as providing property, heritage, asset and content protection and business resilience. It is part of the fire engineer’s remit to develop solutions which take into consideration how they can be applied during the construction phase (refer to chapter 15), how they will be implemented during building operation (refer to chapter 14) and how they contribute to sustainable development; requirements which apply to all engineers registered with the Engineering Council. There may also be contractual goals, such as those as outlined in the employer’s requirements, or specific stakeholder goals, which may be dictated by interested parties. Again, these should all be established in conjunction with the project stakeholders and clearly documented.

The approvals process for the fire safety design of buildings varies significantly from country to country and even, in many cases, between regions within a single country. To demonstrate the range of approaches, the approvals processes for a selection of countries are summarised below. A fire engineer should fully understand the approvals process applicable to their project prior to undertaking any fire safety design.

2.2.1 UK In the UK, the approval and enforcement process for fire safety in buildings is effectively split into three distinct parts, with three separate ahjs: (a)

Design and implementation: the ahj for design approval for compliance with the Building Regulations and enforcement of design implementation on site may be normally either a private approved inspector (in England and Wales) or the local building control authority, with the fire and rescue service acting as a statutory consultee in both cases.

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regulatory approach in the UK, i.e. that the fire safety design should meet the functional building regulations requirements and give due consideration to fire safety at the construction stage and throughout the building’s use.

2-4

Fire safety engineering

Construction: the ahj for enforcing construction site fire safety legislation is the Health and Safety Executive (HSE).

(c)

Occupation and use: post-completion, the ahj for enforcing compliance with operational fire safety legislation is the fire and rescue authorities.

2.2.2

Central Europe

In mainland Europe, the building approval process varies between countries and often within federal or municipal states within each country, therefore checking local regulations prior to submitting a design is essential. In France, Germany and Italy, building permits are controlled through local municipal bodies, who require adherence to a compliance certification process in order to meet the local building regulations. This process requires the builder to provide technical information at certain benchmark points throughout the construction process, and allows the relevant authority to undertake inspections. However, in each case it is the responsibility of the appointed architect or engineer to meet the technical requirements of the local laws. In Germany and Italy, an independent engineer may be engaged to undertake technical checks on the project on behalf of the local authority.

2.2.3

Middle East (Gulf States)

In the Middle Eastern states, notably Bahrain, United Arab Emirates, Saudi Arabia and Qatar, the local municipal bodies are responsible for providing a coordinating role in reviewing applications and building plans and undertaking inspections; however, the Civil Defense Department (the fire department) must grant permission for the building fire safety design. The Civil Defense Department will undertake a detailed technical review of the fire safety design; thus early engagement and agreement of the fire safety standards to be adopted for the project (whether NFPA, IBC or British Standards) is essential.

2.2.4 Australia In Australia, a prescriptive approach is provided as a ‘deemed to satisfy’ solution. The ahjs are normally private certifiers, but council certifiers can also be used. A fire engineer is not needed on a project if a ‘deemed to satisfy’ solution is adopted. However, non-standard approaches can be used, in which case a fire engineer would submit a design to demonstrate how the performance requirements have been achieved, often using comparison to the prescriptive solution as a benchmark. One fundamental aspect in Australia is that a fire engineer is required to carry out a final site inspection to confirm that the solution constructed fulfils the requirements.

provincial or national level fire authority, which will commission an expert panel review. The review findings will then be sent to the local fire officer for implementation. The local officer must also inspect to determine whether all requirements raised by the expert panel have been met.

2.2.6 USA In the USA, the regulatory system for building fire safety is fairly complex. The codes and standards, which are developed by numerous organisations in the USA, are adopted on a jurisdiction-by-jurisdiction basis. The building codes and standards that become a model are developed utilising a consensus system of development to minimise the influence of any single constituency. The actual adoption of these codes and standards is through legislation developed at the State or local jurisdiction level. The legislation adopts specific codes and standards, but often with local amendments. Some States require local jurisdictions (cities and counties) to adopt the State-adopted codes without further amendments, while others allow local jurisdictions to make local amendments. There are also entities that are recognised by the Government as exempt from State regulations. These entities typically establish their own regulations. All of the model codes allow for alternative means and methods of design and construction, provided that the alternative can be shown to be equivalent in terms of safety to the prescriptive criteria of the code. These approaches (code modifications) can be developed utilising performance-based engineering methods. Alternative designs are required to be submitted for approval with accompanying justification and are subject to the review of the approving authority. Some States require modifications to be reviewed by a Board of Appeals that is made up of independent individuals. Others allow code modifications to be reviewed and approved by the Building or Fire Officials of the jurisdiction. Facilities owned by the federal government are not subject to local requirements and are typically bound by the requirements of the specific government agency involved in the project. For example, the Department of Defense has its Unified Facilities Criteria, which specify requirements for building design.

2.2.5 China

The ahj is typically the building and fire department within the jurisdiction of the project or, in the case of a Government-owned project, the authority will be a designated individual or department within the agency.

China adopts a prescriptive design approach, with code guidance specifying fire safety requirements and the local fire officer as the ahj. Exceptions to the prescriptive codes can be made for the more unusual building situations, in which case the ahj will file an application to the

It is critical to understand the applicable requirements, based on the location of the project and knowledge of the enforcement mechanisms within the jurisdiction, prior to starting a design project.

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(b)

Legislation 2-5

2.3

During design and construction

It is important that the fire engineer does not rely solely on approval of the fire strategy by the ahj to demonstrate that their design is adequate. It is imperative that a competent professional fire engineer ensures that anything that they are submitting for approval passes their own test of adequacy. It is also important to note that, in many jurisdictions, the ahjs have no design responsibility; the design responsibility for the fire strategy will rest entirely with the fire safety engineer. In the UK, the responsibility for regulatory compliance does not rest with the ahj but with the designer. The ahj has no liability in relation to the design and, while they check for compliance, they are not ultimately responsible for it.  Within the UK, the person carrying out the work, i.e. the client, is responsible for ensuring that it is carried out in accordance with the Building Regulations. Similarly, the building contractor (builder) is responsible for ensuring that the works undertaken comply with the Building Regulations. The quality of the build to meet the design intent and the objectives of the fire strategy are the responsibility of the building contractor. 

to use competency as a selection criterion for those that they employ to undertake construction and design work.  A person who is responsible for appointing others is legally responsible for ensuring that the designer or contractor appointed is competent to fulfil that role. This duty, in turn, means that a contractor or designer appointing another party is therefore responsible for undertaking due diligence to ensure that the performance of the fire safety products or systems is tested to appropriate standards and that their manufacturers can supply sufficient documentation to validate their products’ compliance with those standards.

2.3.2 Handover The building handover phase is critical to ensuring that the fire safety information generated during the design and construction stages is fully completed and provided to the building operators, such that the building can be safely operated and maintained within the constraints of the fire strategy. In England and Wales, Regulation 38 of the Building Regulations 2010 (SI 2010/2214) requires the person carrying out the work (the contractor) to provide this information to the person responsible for fire safety under the operational legislation (the Regulatory Reform (Fire Safety) Order 2005). In general terms, this would include: ——

an as-built fire strategy report

——

as-built fire safety plans, showing fire escapes, fireresisting construction, firefighting provisions and all other pertinent fire safety information

It is also important that all of the relevant information relating to the fire safety design of the building is passed on to the end user of the building, particularly to those responsible for the maintenance and upkeep of the building.

——

cause and effect descriptions/matrix

——

fire safety systems information

——

verification documentation for installed fire safety systems

During the design stage, the responsibility for designing in accordance with statutory regulations usually rests with the lead designer. In terms of fire safety design on more complex buildings, they will usually be supported by a fire engineer. The remit of the fire engineer is defined on a project-by-project basis. More often than not, the fire engineer will define a minimum performance requirement in the fire strategy to be implemented by others on site; however, due to the increasing complexity of fire safety systems and modern construction solutions that can be adopted in buildings, there is an increasing reliance on the fire engineer during the construction stage to provide assistance to ensure that their design is implemented appropriately.

——

operation and maintenance instructions.

This information can then be incorporated into the fire safety manual for the building in the operational phase.

2.3.3 Post-completion

During the construction phase, on-site fire safety is the responsibility of the building contractor; again, they may be assisted and supported by a fire engineer. Further information on fire safety on construction sites can be found in chapter 15.

Within England and Wales, the Regulatory Reform (Fire Safety) Order 2005 places a clear responsibility for ensuring general and process fire precautions in occupied buildings on a nominated person or persons, defined as the ‘Responsible Person’ (or the ‘Duty Holder’ under the Fire (Scotland) Act 2005 in Scotland). The Responsible Person has a duty to ensure that any occupants and visitors within or around the building are protected from the effects of fire, and is required to implement specific actions, as defined in the Regulatory Reform (Fire Safety) Order 2005 for England and Wales and the Fire Safety (Scotland) Regulations 2006 (SSI 2006/456) in Scotland.

In the UK, designers, including fire engineers, are responsible for complying with the Construction (Design and Management) Regulations 2015 (SI 2015/51). This includes identifying and eliminating risks through their design process, and also a duty to take steps to assist others in meeting duties under those Regulations by providing suitable information about their design. Clients are required

In order to coordinate their actions and comply with their various duties under operational fire safety legislation, the Responsible Person will often use a fire safety manual as a general umbrella document for organising their different duties, including fire policy and procedures, staff fire safety training, building fire safety information, testing and maintenance regimes and operational records.

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2.3.1

Legislation throughout the building life cycle

2-6

Further information on the fire safety management processes required in operational buildings can be found in chapter 14. One of the recommendations of Dame Judith Hackitt’s Review (HM Government, 2018) was for information about the building, including the fire safety information, to form part of a ‘golden thread’ of information that is passed down through the life of the building or asset. At the time of publication, the government is considering how this recommendation could be addressed.

References ABCB (2005) International Fire Engineering Guidelines (Canberra: Australian Building Codes Board) BSI (1997) DD 240: 1997 Fire safety engineering in buildings: Guide to the application of fire safety engineering principles (London: British Standards Institution) BSI (2001) BS 7974: 2001 Application of fire safety engineering principles to the design of buildings. Code of practice (London: British Standards Institution) (Note: BS 7974: 2012 has been replaced by BS 7974: 2019) BSI (2017) BS 9999: 2017 Code of practice for fire safety in the design, management and use of buildings (London: British Standards Institution) Hackitt J (2018) Building a Safer Future: Independent Review of Building Regulations and Fire Safety (London: Ministry of Housing, Communities and Local Government) [online] https://www.gov.uk/government/ publications/independent-review-of-building-regulations-and-fire-safetyfinal-report (accessed April 2019)

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The operational legislation in the UK requires the Responsible Person to have a valid fire risk assessment for the premises. The fire risk assessment has to be undertaken by a competent person and is updated regularly (or when there is a need to review due to any changes being made to the fire safety arrangements) to take account of the fire hazards in the building and the occupants exposed to those hazards. This legislation therefore places a legal duty on the building operators themselves to manage their responsibilities and is enforced by the fire and rescue authorities. This is in contrast to the previous framework under the Fire Precautions Act 1971, in which the fire service would undertake the inspection and certification of premises.

Fire safety engineering

3-1

3

Building designation

Fire precautions in buildings can address several aspects, including life safety, contents damage and avoidance of business disruption. The use to which a building or a part thereof is put (i.e. its designation or classification) has implications for all of these aspects. The most important implications for life safety arise from building population and the risk to which the people are exposed, usually related to fire load and ignition risk. The majority of recognised building design guides across the world differentiate fire safety expectations by the occupancy type. For example, in the UK, the Building Regulations 2010 are supported by supplementary documentation (HM Government, 2013) in which buildings are classified according to specific ‘purpose groups’, see Table 3.1. Different fire precautions may be required for the different purpose groups. The means of detecting, controlling and extinguishing a fire, the provisions for evacuating the building, the means of limiting the spread of fire and smoke within the building and their impact on adjacent compartments and structures, as well as the facilities for firefighting, will all be influenced by the building’s use. In essence, building designation is a recognition of the level of risk. Authorities apply different criteria for building designation but, in the context of fire precautions, the main authorities are those concerned with building certification (including firefighting) and building insurance (including business disruption and contents). Examples of systems of building classification in England and Wales are given in Table 3.1, and for sprinklers in Europe in Table 3.2 (BSI, 2015). Section 2 of BS 9999: 2017 outlines a means of establishing building designation based on risk profiles (BSI, 2017). It gives basic factors, occupancy characteristics and fire growth rates, enabling a risk profile to be established. It then gives nearly 70 examples of application of its principles. It is often the case that a single building accommodates more than one occupancy type, and therefore can house numerous risk profiles. The majority of recognised fire design guidance offers advice on how to separate those occupancies, or to not separate and design to the higher risk. This balance is increasingly a feature of the fire safety design, as mixed-use buildings are becoming more common. New occupancy types can emerge, such as apart-hotels and extra-care accommodation, and guidance documents are an inadequate means of keeping up with the realities of commercial developments. The BS 9999 approach goes some way towards addressing this problem by introducing risk categories and fitting occupancy types to those categories based on their characteristics.

Oversimplifying a building into a specific occupancy type is often only truly valid for simple buildings, but for larger or more complex schemes, some assessment of the validity of the occupancy grouping should be carried out.

3.2

Common factors

There are a number of factors that have implications for most building types. In general, the extremes of these factors call for greater protection and increased fire precautions.

3.2.1

Building height

The fire engineering implications of building height are: ——

greater vertical distances through which persons must travel to escape

——

increased challenges for firefighting

——

a longer escape period and increased interaction between evacuees and firefighters

——

greater implications of building collapse and consequential damage.

The height of a building alone does not result in an increased probability of fire occurring, and therefore the height alone should not preclude a building accommodating certain occupancies. However, the level of risk associated with the increased height of a building is higher when compared to low-rise buildings of a similar occupancy type, as the consequences of a fire occurring will be more severe unless suitable mitigation is introduced. In buildings over a certain height, phased evacuation (evacuating certain floors in sequence) can be more practical than simultaneous evacuation (full decant of the whole building). It allows for more efficient staircase width, and may reduce the need for total evacuation. It may not be necessary to fully evacuate a building, subject to the provision of adequate fire precautions to provide a place of relative safety within the building. Where firefighter activities are not possible from the building perimeter due to building height, access within the building can be provided by firefighting shafts. These provide protection for firefighters because they offer safe access, a forward attack point from which to carry out operations and a safe escape route for firefighters. They also include water supply outlets which, in tall buildings, are permanently charged. The interaction between firefighters accessing the building and occupants evacuating is one that needs consideration in high-rise buildings. The provision of firefighting shafts,

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3.1 Introduction

3-2

Fire safety engineering

Table 3.1  Classification by purpose group (HM Government, 2013: 140) Group

Purpose for which the building or compartment of a building is intended to be used

Residential (dwellings)

1(a)*

Flat.

1(b)†

Dwellinghouse which contains a habitable storey with a floor level which is more than 4.5 m above ground level.

1(c)†+

Dwellinghouse which does not contain a habitable storey with a floor level which is more than 4.5 m above ground level.

Residential (Institutional)

2(a)

Hospital, home, school or other similar establishment used as living accommodation for, or for the treatment, care or maintenance of persons suffering from disabilities due to illness or old age or other physical or mental incapacity, or under the age of 5 years, or place of lawful detention, where such persons sleep on the premises.

(Other)

2(b)

Hotel, boarding house, residential college, hall of residence, hostel and any other residential purpose not described above.

Office

3

Offices or premises used for the purpose of administration, clerical work (including writing, book keeping, sorting papers, filing, typing, duplicating, machine calculating, drawing and the editorial preparation of matter for publication, police and fire and rescue service work), handling money (including banking and building society work), and communications (including postal, telegraph and radio communications) or radio, television, film, audio or video recording, or performance (not open to the public) and their control.

Shop and commercial

4

Shops or premises used for a retail trade or business (including the sale to members of the public of food or drink for immediate consumption and retail by auction, self-selection and over-the-counter wholesale trading, the business of lending books or periodicals for gain and the business of a barber or hairdresser and the rental of storage space to the public) and premises to which the public is invited to deliver or collect goods in connection with their hire repair or other treatment, or (except in the case of repair of motor vehicles) where they themselves may carry out such repairs or other treatments.

Assembly and recreation

5

Place of assembly, entertainment or recreation; including bingo halls, broadcasting, recording and film studios open to the public, casinos, dance halls; entertainment, conference, exhibition and leisure centres; funfairs and amusement arcades; museums and art galleries; non-residential clubs, theatres, cinemas and concert halls; educational establishments, dancing schools, gymnasia, swimming pool buildings, riding schools, skating rinks, sports pavilions, sports stadia; law courts; churches and other buildings of worship, crematoria; libraries open to the public, non-residential day centres, clinics, health centres and surgeries; passenger stations and termini for air, rail, road or sea travel; public toilets; zoos and menageries.

Industrial

6

Factories and other premises used for manufacturing, altering, repairing, cleaning, washing, breakingup, adapting or processing any article; generating power or slaughtering livestock.

Storage and other nonresidential+

7(a)

Place for the storage or deposit of goods or materials (other than described under 7(b)) and any building not within any of the Purpose Groups 1 to 6.

7(b)

Car parks designed to admit and accommodate only cars, motorcycles and passenger or light goods vehicles weighing no more than 2500 kg gross.

Notes: This table only applies to Part B. * Includes live/work units that meet the provisions of paragraph 2.52. † Includes any surgeries, consulting rooms, offices or other accommodation, not exceeding 50 m2 in total, forming part of a dwellinghouse and used by an occupant of the dwellinghouse in a professional or business capacity. + A detached garage not more than 40 m2 in area is included in purpose group 1(c); as is a detached open carport of not more than 40 m2, or a detached building which consists of a garage and open carport where neither the garage nor the open carport exceeds 40 m2 in area.

Table 3.2  Classification according to hazard for sprinkler installations (reproduced from BS EN 12845:2015 by permission of BSI.) (a) Light hazard occupancies Schools and other educational institutions (certain areas) Offices (certain areas) Prisons

(b) Ordinary hazard occupancies Occupancy

Ordinary hazard group OH1

OH2

Glass and ceramics Chemicals

Continued

OH3 Glass factories

Cement works

Photographic film factories

Dyers works, soap factories, photographic laboratories, paint applicaton shops with water based paint

OH4

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Title

Building designation

3-3

Table 3.2  (b) continued OH1

OH2

OH3

Engineering

Sheet metal product factories

Metal working

Electronics factories, radio equipment factories, washing machine factories, car workshops

Abattoirs, meat factories, bakeries, biscuit factories, breweries, chocolate factories, confectionery factories, dairies

Animal fodder factories, corn mills, dehydrated vegetable and soup factories, sugar factories

Alcohol distilleries

Broadcasting studios (small), railway stations, plant (technical) rooms, farm buildings

Cinemas and theatres, concert halls, tobacco factories, film and TV production studios

Book binding factories, cardboard factories, paper factories

Waste paper processing

Department stores, shopping centres

Exhibition halls*

Carpet factories (excluding rubber and foam plastics), cloth and clothing factories, fibre board factories, footwear factories (excluding plastics and rubber), knitting factories, linen factories, mattress factories (excluding foam plastics), sewing factories, weaving mills, woollen and worsted mills

Cotton mills, flax preparation plants, hemp preparation plants

Woodworking factories, furniture factories (without foam plastics), furniture showrooms, upholstery (without foam plastics) factories

Saw mills, plywood factories

Food and beverages

Miscellaneous

Hospitals, hotels, libraries Laboratories (physical), (excluding book stores), laundries, car parks, restaurants, schools, offices museums

Paper Shops and offices

Data processing (computer room, excluding tape storage), offices

Textiles and clothing

Leather goods factories

Timber and wood

OH4

Note: Where there is painting or other similar high fire load areas in a OH1 or OH2 occupancy, they should be treated as OH3. *Excessive clearance shall be taken into consideration (c) High hazard process occupancies HHP1

HHP2

HHP3

HHP4

Floor cloth and linoleum manufacture

Fire lighter manufacture

Cellulose nitrate manufacture

Firework manufacture

Resin, lamp black and turpentine manufacture

Tar distilling

Rubber tyres for cars and lorries

Rubber substitute manufacture

Depots for buses, un-laden lorries and railway carriages

Wood wool manufacture

Candle wax and paraffin manufacturers

Match manufacturers

Paper machine halls

Manufacture of material factor M3 (see table b.1) foam plastics, foam rubber and foam rubber goods manufacture (excluding M4 see table b.1)

Paint application shops with solvent

Carpet factories including rubber and foam plastics

Refrigerator factories Printing works Cable factories for PP/PE/PS or similar burning characteristics other than OH3

Saw mill Chipboard manufacturing Paint, colour and varnish manufacture

Injection moulding (plastics) for PP/PE/ PS or similar burning characteristics other than OH3 Plastics factories and plastic goods (excluding foam plastics) for PP/PE/PS or similar burinig characteristics other than OH3 Rubber goods factories, synthetic fibre factories (excluding acrylic) Rope factories Carpet factories including unexpanded plastics Footwear factories including plastics and rubber Note: Additional object projection might be necessary.

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Occupancy

3-4

Fire safety engineering

Engineering of fire safety in high-rise buildings continues to go beyond the well-established lines of assuming a single genuine ‘accidental’ fire outbreak. Tall building fire safety should properly consider the risks arising from the potential for multiple fire seats or multiple floors to be involved. The principle adopted is that any increase in risk arises from the vertical stacking of usable space and hence the focus in tall buildings is on preventing the vertical movement of fire and smoke, therefore overcoming this risk variation.

The potential increased risk to occupants and firefighters below ground can be addressed by provision of smoke and heat ventilation, coupled with fire suppression, as well as sub-compartmentation of basement floors. The movement of people and fire products should ideally be separated, perhaps by smoke and heat venting at source, to keep escape routes clear. People using escape routes in case of fire from upper floors should not have to go below ground level to reach an exit. Separation of some escape stairs at access level, and otherwise suitable signage at exit level, assists safe exit. Basement areas should be separated from the upper floors by suitable fire-resisting structure. Additional facilities to support access for firefighting, including by firefighting shafts (with lifts) in deep basements, may be required in certain circumstances.

The result of fire engineering analysis in tall buildings is generally the provision of phased evacuation via protected stairs, voice alarms, sprinkler protection, firefighting access, compartment floors and increased fire resistance.

3.2.3

3.2.2

——

greater aggregate fire loads

——

greater horizontal distances through which persons may be required to travel to escape

——

increased firefighting challenges, such as potentially greater distance to a point of safety, a large area to search and the inability to reach all areas of a floor plate from outside.

Depth below ground

The implications of depth below ground are: ——

the possibility of products of combustion, escaping occupants and firefighters using the same route

——

the fire hazard traditionally housed below ground is often considered to be greater, with associated increase in risk

——

increased difficulty for firefighters accessing the fire location

——

increased physiological stress during upwards escape

——

under-ventilated fires leading to backdrafts and unpredictable fire behaviours.

The fact that a floor is below ground level does not, of itself, necessarily increase the risk of a fire occurring within it, nor does it directly affect the consequences of a fire. Traditionally, basements have often been put to uses which have a different risk to above-ground floors, such as storage and plant, and access to them may have also been irregular. However, this is not always the case and in many situations the costs of building basements and the need to maximise use of a site mean that basements may well be put to the same uses as above-ground spaces. The overall use of the building needs to be taken into account, as there are many good reasons for locating certain things in basements: in laboratories, for example, basements provide a much higher floor loading capacity and hence can be used for heavy equipment; in scenarios where a lecture space is required, the lack of windows is a benefit; similarly, many arts buildings use basements for acoustically sensitive uses. These uses would offer a significantly different risk to a more traditional basement use, such as storage, and therefore the specific risk of the basement being reviewed should be used to define the fire safety recommendations, as much as the physical location below ground.

Building area

The implications of increased building area are:

Strict adherence to maximum travel distances could be a determining factor for floor area. Where extended distances are preferred, smoke control or other compensating features may need to be provided. These may include internal protected corridors. Sub-compartmentation will divide fire loads but fire control (e.g. venting, fire suppression) may provide an alternative solution. Limitation of firefighting hose lengths may have a bearing on floor area and the practical limit of laying out of hoses is usually taken as the maximum length for design purposes. Guidance for England limits compartment size by area only (except for storage) (HM Government, 2013). Some modern buildings, such as commercial use ‘landscrapers’, are producing floor plate areas which are many times larger than conventional new build developments. Such large areas of floor plate, particularly where open plan, are not adequately addressed by guidance documents in relation to designation of fire size and type. Most guidance documents assume fully involved compartment fires, with uniform temperature generation and limited ventilation. In reality, large floor areas are likely to generate localised fires with relatively unrestrained ventilation, which will move along the floor plate, maintaining a largely stable rate of fire load consumption. Such travelling fires will produce different heating regimes to the standard temperature–time model and will therefore elicit non-standard structural responses. Consideration of their properties is therefore particularly relevant when undertaking structural fire engineering assessments.

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coupled with phased evacuation regimes, or partial evacuation of the building, is part of this consideration. Firefighting shafts can also be used by those with mobility impairment as refuge locations. Other aspects that could be considered are evacuation using lifts, creating refuge floors within the building and managing smoke via pressure differential or smoke extract systems.

Building designation Suitable consideration should therefore be given to the area of the compartment and the likely associated fire types.

Building volume

The main effect of building volume is that, with the presence of sufficient fire load, larger compartments can sustain larger fires, and in some uses extended uncompartmented volumes may result in increased total fire load. In these cases, fire development and spread can be controlled by early detection, smoke venting, oxygen depletion and water suppression. Increased volumes do not, however, necessarily imply increased fire load or risk. Increased volume may, in fact, extend the smoke filling time with the resulting benefit of potentially increased escape times. The implications for means of escape and firefighting are very different in large volume buildings, which is related to the timing of egress versus the entry of firefighters. An increased risk to escape is sometimes considered an increased risk to firefighters, but in the case of large volume buildings this is not necessarily the case. In particular circumstances, the fire load may not be commensurate with the volume (e.g. places of assembly, transport terminals) and lower standards of fire resistance may be appropriate, perhaps coupled with fire containment and smoke control.

3.2.5

Proximity to site boundary and adjacent buildings

The proximity of a building to the site boundary or to adjacent buildings affects the risk of fire spread from one building to another and, to reduce that possibility, may require: ——

increased controls on compartmentation

——

restrictions on unprotected (i.e. non-fire-resisting and combustible) areas of the facade

——

firefighting access via firefighting shafts rather than by perimeter access

UK regulations (the Building Regulations 2010, as amended by the Building (Amendment) Regulations 2018, for England and Wales and the corresponding regulations for Scotland and Northern Ireland) require the external walls of a building to adequately resist the spread of fire over the walls and from one building to another. The proportion of unprotected areas of the façade, provided in the guidance contained in Approved Document B (HM Government, 2013) is determined by proximity to the boundary and, broadly, by the nature of the occupancy based on the fire load. In circumstances where a high life risk is involved, this guidance also requires fire resistance to be provided between buildings on the same site and between certain uses within a single building. The division of buildings into compartments provides a means of restricting the area of radiation at the boundary of the building. Where such compartmentation conflicts with building occupancy,

equivalent provision can be achieved by sprinkler protection, since this restricts the fire size. With a sprinkler system, more refined calculations of fire size can be made and the subsequent benefit to the boundary condition can be anticipated. The approach above is a simple one and takes very little account of the actual size to which a fire may grow. It assumes a fully developed fire throughout the entire compartment volume, and takes only cursory account of the fire load but none of its distribution and potential to result in such a fire. This simplified approach was developed at a time during which building construction types and fire load distributions more closely matched the assumptions of the guidance. The approach was captured in the 1991 BRE publication BR187, which has subsequently been updated in a second volume, released in 2014 (Chitty, 2014); however, the approach in the updated document remains largely the same. Modern buildings typically present fire loads, materials and methods of construction which sit in stark contrast to those built 25 years ago. The guidance should therefore be applied in the context of these changes and rational conclusions drawn from the results of the analyses. A performance-based approach to boundary separation requires looking at the effect of any active systems present, actual fire load density, its distribution and any hazard arising from it.

3.2.6

Fire load

The characteristics that contribute to fire hazard include the quantity of combustible materials, their distribution, flammability, smoke production and surface flame spread rates. Traditionally, various occupancies have identifiable fire loads. The full fire development of these loads results in the standards of fire resistance and limits of compartmentation. Therefore, other measures provided to control fire development and spread should reduce the need for compartmentation while at the same time protecting against losses. Standards of enclosure and separation may differ for life safety and property protection purposes, the latter generally being higher when it is assumed that the occupants will have vacated the building during the early stages of a fire. Clearly, the successful action of fire suppression systems dramatically modifies the impact of fire load on design. Suppression systems include conventional sprinklers, water mist (high and low pressure), gaseous suppression, oxygen depletion and foam, not all of which are applicable for all conditions (see chapter 11).

3.2.7

Numbers of people

Large numbers of people may require more emphasis on management to achieve means of escape. There are currently moves to provide more reliable information to assist people to make the correct decisions in making their exit. This can be achieved by voice alarms or informative displays. Fire engineering provides for accommodating

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3.2.4

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‘over-occupancy’ and extended travel distances by identifying the risk and managing fire development.

Sleeping accommodation

With sleeping accommodation, there is the possibility that occupants become disorientated on hearing the fire alarm, especially when outside their own homes (e.g. in hotels). The response to alarms is affected by the alertness of the occupants at the time that the alarm is sounded and by their knowledge of the building. Therefore, increased detection, protection or fire control can be justified for sleeping accommodation. For example, fire alarms can be suitably located and sufficiently loud to alert sleeping people (see chapter 8). The reliability of an alarm system has a direct bearing on people’s response to it, and more complex systems can be justified in critical circumstances. Increased levels of compartmentation and control of fire development and spread are also justified.

3.2.9

Disadvantaged occupants

Consideration must be given to the needs of disadvantaged occupants. These include those with physical or learning disabilities, young or aged persons, and the infirm. It is recommended that means of escape for disabled people should receive special attention. Guidance on access and exit provision for people with health conditions or impairments is given in Approved Document M (HM Government, 2015) and throughout BS 9999 as inclusive design. Proactive consultation with facilities management teams during the design stages is highly recommended. Doing so allows the specific practicalities of the evacuation of disadvantaged occupants to be properly assessed on a caseby-case basis. From these consultations, the need to provide enhanced features, such as evacuation lifts or chairs, can be fully understood and any changes which are necessary during the design process can be captured effectively.

3.2.10 Multi-tenancy/multi-occupancy Where the whole population of a building is not under the same management, there is the possibility of varying standards of care and attention to fire precautions. It may be necessary to ensure that the other occupancies are warned in the event of a fire being detected. The combination of different purpose groups within the same building may call for additional provisions, including better fire separation and separate means of escape, particularly where the purpose groups include sleeping risks.

3.2.11

Special building features

Such special features include, inter alia, atria, environmental flues, single-stair conditions, open spatial planning and extensive underground spaces. This is a broad categorisation, and each of the examples highlighted above presents its own unique challenges, which will vary across building types. As a result, the scope of this document is not sufficiently wide to deal in

3.2.12

Life safety and property protection

Life safety protection — which includes both occupants and firefighting personnel — requires different levels of fire precautions from those appropriate to property protection and avoidance of business disruption. Property protection (including avoidance of business disruption) generally requires higher standards of fire precautions since it addresses fire behaviour beyond the time required for occupants to vacate the building. This is often reflected in the call for fire suppression, smoke management and higher standards of fire resistance. In providing for life safety, the issues of property protection are often addressed to a significant degree.

3.2.13

Fire precautions during construction

The fire loads, and the associated risks, can be higher during construction than in the completed building (refer to chapter 15). This is especially the case when a building is constructed from combustible material. The consequences can be particularly severe when construction is occurring in part of an operational building. Fires at buildings under construction have emphasised the need to minimise the hazard and for increased vigilance. A code of site fire precautions has been produced by the Fire Protection Association (FPA) (FPA, 2015) and other codes of practice include appropriate information (HSE, 2010; Standing Committee on Fire Precautions, 1995). Standards of construction are also covered by the FPA code (FPA, 2015).

3.3

Risk profiles

The alternative way of defining the risk to persons in buildings, as opposed to the purpose group approach outlined in section 3.2, is to adopt the risk profile approach. The risk to which occupants may be exposed is a combination of their occupancy group and the likely fire development; for example, a sleeping risk in a hotel is greater than one where persons are awake and familiar with the building. This approach is presented more fully in BS 9999. In summary, it divides occupancy into seven life risk categories and fire development into four well-established growth scenarios. From these divisions, most occupancies can be profiled. In terms of building design, more flexibility should be expected from the lower risk categories. It should be noted that some types of occupancy are not addressed at all by the BS 9999 approach, for example transport infrastructure (although some elements will fit into

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3.2.8

detail with the challenges that each could present. It is, however, the actual, rather than perceived, problems that arise as a result of the inclusion of special features which need to be examined carefully to provide life safety protection. Fire engineering identifies the issues and addresses them to ensure that an acceptable level of risk is achieved.

Building designation

The standard of management in a building should also be considered, as highly managed environments with regular maintenance of fire precautions, including critical systems, can be considered a lower risk than facilities in which little or no management is present. Approvers may have concerns over change of risk profile during the life of the building. The potential impacts of a change of risk should be identified and considered in the design.

3.4

Designing the fire precautions

3.4.1

Fire precautions standards in the UK for life safety

For life safety purposes, fire precautions to an appropriate standard are a requirement of the fire design guidance of most building design code regimes. The means of achieving them are broadly common, but the specific details on how to achieve them vary. Most building codes have developed over a considerable period of time, informed by fire incidents within the geographies to which they apply. The codes inform firefighting practices, and are reciprocally informed by established firefighting practices and procedures within that region. As a result, standards are not consistent between one country/region and another. For example, even within the UK there are four systems: (a) England (b) Wales (c) Scotland (d)

Northern Ireland.

It is necessary to contact the appropriate building or fire authority to obtain details of the requirements within a particular country. 3.4.1.1

England and Wales

The requirements of the Building Regulations 2010, as amended, may be satisfied by observing the recommendations contained in Approved Document B: Fire Safety (HM Government, 2013; Welsh Government, 2015). However, the Building Regulations requirements may be met in other ways, such as by observing the recommendations of British Standards, particularly BS 9999, or by adopting a fire safety engineering approach, as explained in Approved Document B: Volume 2, paragraphs 0.30 to 0.34 (England) or 0.28 to 0.32 (Wales).

3.4.1.2 Scotland The criteria for compliance with the Building (Scotland) Regulations 2004 are set out in the Technical Handbook – Domestic and Technical Handbook – Non-Domestic (Scottish Government, 2017a, 2017b). These documents are highly prescriptive. However, the Regulations state that compliance may also be achieved by the alternative approaches explained in Section 2.0.7 of both Handbooks. 3.4.1.3

Northern Ireland

The functional requirements are set down in the Building Regulations (Northern Ireland) 2012. The associated Technical Booklet E: Fire Safety provides ‘deemed-to-satisfy’ measures which, if followed, will ensure compliance with the Regulations (DFPNI, 2012). 3.4.1.4

Alternative approaches

In all three of the above legislative areas, there is provision for the consideration of departures from prescriptive solutions. In England, Wales and Northern Ireland such departures are allowed with the agreement of the local building control officer or by a ‘determination’ by the Department for Communities and Local Government. In Scotland, departures from prescriptive guidance can be agreed with the local building control officer. A ‘relaxation’ from the Regulation in their entirety can also be gained and is sought through the Scottish Ministers. 3.4.1.5

Fire brigades’ requirements

Local fire brigades are concerned with fire precautions in buildings and the approvals process includes provisions for their consultation. In England and Wales, for example, their responsibilities for fire precautions result mainly from the Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541), which deals with occupied buildings (refer to chapter 2). However, they also have consultative responsibilities for many issues under the extensive legislation concerning the various occupancies. In the UK, the extent of this legislation is set down in various publications (Home Office, 2012) and the consultation procedure is outlined in national procedural guidance (DCLG, 2007). In all cases, the building control department of the local authority, an approved inspector (England and Wales only) or the fire prevention department of the fire brigade will advise on these issues. Generally, the building control authority should be consulted initially for new buildings and the fire authority for occupied buildings. The procedural guidance for England requires either authority to alert the applicant of the need to consult the other, and to distinguish between ‘recommendation’ and ‘requirement’ (DCLG, 2007).

3.4.2

Fire precautions standards for life safety outside the UK

Standards and consultation processes vary considerably outside the UK but, in general, the fire authorities have greater powers of approval than they do in the UK (refer

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other occupancy types). Unless alternative codes of practice can be adopted, the risk profile in these types of premises should be carefully considered and the adoption of a performance-based design approach is usually necessary.

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It should also be noted that the phenomenon of regional differences, which is pervasive within the UK, also applies in other nations, and the acceptance of fire engineering often varies according to region. Furthermore, local authorities may not be familiar with the use of fire safety engineering, and they may have adopted particular national code systems that make less or no room for it. The approach to successfully applying fire safety engineering outside the UK usually includes the demonstration that an equivalent level of safety, or an appropriate level, is achieved to that implied by adoption of local codes. Some codes include emphasis beyond life safety. Where necessary, and possible, the particular insurance company should be consulted in the early stages of the design process. However, this may not be possible for speculative developments, since the insurer of the completed property may not have been nominated. The fire insurance industry increasingly accommodates a fire engineered approach; as with other authorities, early consultation is recommended. The benefits of the inclusion of water suppression and fire spread control for insurance purposes can be realised in the overall fire precautions package for life safety purposes.

3.5

Implications of classification by purpose group

The aim of this section is to provide a checklist of items that should be considered for particular occupancies. UK guidance to which this section refers often includes background information in support of the recommendations; the principles can therefore be applied outside the UK. As a typical source of building designation, reference will be made to the classifications given in Table D1 of Approved Document B, reproduced here as in Table 3.1, and in Table 4.3.4 of BS 9999.

3.5.1

Residential (dwellings)

In private dwellings, ongoing control under fire safety legislation is minimal due to a societal desire to maintain the privacy of the individual. The main factors relevant to dwellings are as follows: ——

most deaths by fire occur in dwellings

——

lack of ongoing control by fire authorities

——

need for separation of dwellings by fire-resisting compartmentation

——

well-established and consistent fire load

——

additional risk associated with sleeping accommodation

——

additional risk associated with uncontrolled ignition sources, including cooking, smoking and portable electrical appliances.

Dwellings can be divided into three sub-groups, which also separates high-rise from low-rise dwellings, including houses in multiple occupation: (a)

flat and maisonette

(b)

dwelling which contains a habitable storey with a floor level more than 4.5 m above ground level

(c)

dwelling which does not contain a habitable storey with a floor level more than 7.5 m above ground level.

Except for houses in multiple occupation, controls over low-rise dwellings are minimal and are mainly confined to the separation of dwellings from each other, to control fire spread between them, and the need for smoke detection. Individual dwellings with a habitable storey above 4.5 m and 7.5 m require further control by the provision of a protected escape route (unless there is an alternative exit), escape windows and automatic fire suppression systems. Approved Document B and BS 5839-6: 2013 (BSI, 2013), for example, provide guidance on detection and alarm systems relevant to a wide range of residential buildings, including large houses, houses in multiple occupation and sheltered housing. There is scope for fire safety engineering in unconventional dwellings where protected routes are compromised by an open-plan layout. Provisions may include water suppression and enhanced smoke control; smoke detection is recommended in Approved Document B. Such provisions might also be considered during refurbishment or major alterations. Where dwellings are grouped together, as in flats and maisonettes, a ‘stay put’ or ‘defend in place’ strategy is generally implemented, where only the flat of fire origin evacuates and the remainder of the dwellings in the facility remain in place. This approach calls for increased controls, particularly with respect to vertical and horizontal fire separation (compartmentation) in order to contain a fire within one dwelling and prevent it from spreading to others. Maintaining this separation is important in the provision of common services and has implications for ductwork and fire stopping. Protected stairs and firefighting shafts take on increased importance with increased building height, a higher standard being required in single-stair situations. The venting of common areas is required as a means of keeping escape and rescue routes clear. To accommodate increased travel distances to a storey exit, custom designed means of controlling smoke in common areas are often installed. These include natural, mechanical and hybrid systems, designed specifically for the building. There are controls over wall and ceiling surfaces for common areas, and limits on the fire risks opening onto such areas. There are also controls on the spread of flame over the external walls and in the sub-division of cavities.

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to chapter 2). Some nations do not have the UK equivalent of building control; therefore, the fire authority is always the best starting point for consultation on requirements and procedures. Enquiries should be made concerning the need to also consult other bodies.

Building designation

For all three groups, the fire load is generally predictable. Also, the maximum fire size can be estimated due to the provision of compartmentation. Life safety in tall blocks of flats is further enhanced by the introduction of automatic fire suppression for residential buildings over 18 m high (Scotland) and 30 m high (England and Wales).

3.5.2

Residential (institutional)

For residential (institutional) buildings, the key factors are as follows: ——

high life risk

——

occupants may be asleep

——

occupants may be infirm or in other ways disadvantaged, such as mobility or sensory impaired

——

compartmentation is recommended

——

clear advantage of fire detection (subject to reliability)

——

well-established and consistent fire load

——

trained staff may be present.

Subdivision within this purpose group separates premises intended to house the infirm (group (a), which includes health-care premises) from those intended to house the able-bodied (group (b), which includes hotels and guest houses). Greater controls are recommended for purpose group (a) and these are mainly concerned with progressive horizontal evacuation procedures, compartmentation and fire detection, which should be designed to minimise the number of false alarms. Health-care premises invariably incorporate an abundance of piped and wired services, and the risk of fire affecting more than one compartment has particular repercussions in these premises. It is therefore of critical importance to maintain the integrity of the compartmentation, both internally and in any external cavities. The historical record of fire incidents in health-care premises is generally good, but there is concern over the potential for loss of life. In the upgrading of existing premises, there is a strong case for active fire control and informative detection systems. The major fires have occurred in premises catering for the mobility impaired and learning disabled and extra provision should be considered for such buildings. Fatalities and extensive damage have occurred in premises where undivided cavities have resulted in hidden fire spread. Guidance on fire precautions design for healthcare premises is contained in the series of Health Technical Memoranda: Firecodes, produced by the Department of Health’s Estates and Facilities Division (e.g. NHS Estates, 1996). Since the guidance includes background

information in support of the recommendations, the principles can be applied outside the UK. In the UK, water suppression protection (i.e. active fire control) is not yet widely adopted for this occupancy category, although the benefits are now more forcefully encouraged in guidance. In NFPA domains, sprinklers are more common. Where this approach is adopted there are clear advantages in the control of fire spread and, as a result, increased opportunities for fire safety engineering. There are also areas where damage to the contents would have serious implications, and increased controls are therefore justified. Also, the loss of medical facilities can have serious repercussions. Fire precautions legislation in existing buildings arose largely as a result of multiple-fatality fires within group (b), which includes hotels and boarding houses. Statutory controls for group (b) are lower than those for group (a), mainly falling within the areas of compartmentation and detection. Means of escape are more conventional, with clear advantages if the normal circulation routes are also those which lead to emergency exits. There is increased interest in providing an appropriate level of emergency lighting. The provision of an atrium would require additional controls to offset the loss of passive compartmentation. BS 9999, Annex C includes prescriptive guidance for this occupancy but also allows an engineered approach. Guidance for fire precautions in existing buildings is available from the Department for Communities and Local Government (DCLG, 2006). For new premises in the UK, appropriate guidance is available (HM Government, 2013; Scottish Government, 2017a, 2017b; Welsh Government, 2015; DFPNI, 2012; BAFSA, 2012). Since the guidance includes background information in support of the recommendations, the principles can be applied outside the UK.

3.5.3 Offices The key factors are as follows: ——

historically low occurrence of fires, and low incidence of loss of life

——

desire to maximise design flexibility

——

well-understood and consistent fire load.

This purpose group offers the greatest flexibility for design in that the risk to life is understood to be low. However, the protection of contents and the avoidance of business disruption take on a greater significance. Smoke spread in the early stages of fire development via ventilation and air conditioning distribution ductwork, although a valid concern, has not resulted in fire casualties. Nevertheless, guidance in Approved Document B and BS 9999, for example, recommends that good design should address smoke movement via these systems using smoke detectoroperated fire/smoke dampers. Occupants can be expected to be familiar with the premises and the fire load is well understood. The main emphasis on controls concerns the means of escape. The introduction of an atrium is not always seen as increasing risk, subject to reasonable additional provisions. BS 9999,

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Unconventional designs, particularly in the manner of grouping the dwellings, offer opportunities for fire safety engineering. For example, tall residential blocks in an atrium setting would call for special provisions to offset the loss of physical compartmentation.

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3.5.4

Shops and other commercial premises

The key factors are as follows:

3.5.5

Assembly and recreational buildings

The key factors are: ——

significant serious fires historically

——

high occupancy capacity potentially resulting in high life loss

——

designs may call for large volumes and long travel distances

——

occupants are likely to be unfamiliar with the layout of the premises

——

historically low incidence of life loss

——

potentially high life loss

——

some high fire loads

——

potentially high contents value

——

——

high occupancy capacity

extensive controls based on investigations of historical fires

——

problems with extended height

——

high fire load

——

increased risk in underground conditions.

——

designs often involve large volumes and long travel distances

——

occupants potentially unfamiliar with the layout of the premises

——

significant historic fires.

The above key factors indicate the clear benefits of sprinkler protection (or alternative suppression) with the corresponding scope for fire safety engineering. This group includes shopping malls and complexes, for which specific guidance is available, although designers are not obliged to adopt the principles they contain (BSI, 2017; Morgan and Gardner, 1990). However, it would be prudent to address the items raised. Considerable emphasis is now placed on premises management pertaining both to the means of escape regime and also the general housekeeping (BSI, 2017). Although controls can be placed on occupancies, it is generally in the interest of the building to maximise the number of occupants. It is therefore important to design for times of maximum footfall, and not to rely on management controls to limit occupancies. The benefits of automatic fire suppression systems have been well demonstrated. In shop design, consideration must be given to the fire characteristics: ——

size, growth rate and the effects of selected sprinkler/ nozzle response

——

the implications of suppression systems on other active measures, such as smoke control.

The provision of sprinklers in high areas (i.e. over 15 m) will be ineffective in controlling fire. However, fire control for these areas is possible by the application of systems designed for atrium base protection, either sidewall- or canopy-mounted. Lateral fire spread can now be controlled by fire-resisting curtains and by the combination of window-wetting sprinklers on toughened or laminated glazing that is otherwise not fire-rated.

In the educational sector of this group, extensive fire damage has been caused by arson; there are strong links between security and arson prevention. The inclusion of water suppression largely addresses the concerns. Undivided cavities have also resulted in extensive damage, but these are now restricted by the Building Regulations and associated guidance (HM Government, 2013; Scottish Government, 2017a, 2017b; DFPNI, 2012). In the fire precautions design of this purpose group, the fire development characteristics should be considered, along with their implications for the standard of active measures. Large room volumes should not necessarily imply increased life or property risk, as the fire load may be relatively low. Compartmentation limits can be exceeded without increased risk, and extended travel distances should be possible by the provision of compensating features, including smoke control and sprinklers. More so than with other purpose groups, the occupancies of these facilities can be a function of their operation. During the design it is necessary to look in detail at how a facility will be used and managed in order to calculate the design occupancy. It is also necessary to carefully consider how the operation of the facility may change over time, to ensure that the means of escape facilities allow the building’s operation to evolve. Considerable emphasis is now placed on premises management, and how that can help during means of escape (BSI, 2017). Staffing levels can be higher than in other purpose groups, and the benefit of that can be realised in the means of escape design. The provision of roof-mounted sprinklers in high areas (i.e. over 15 m) will be ineffective in controlling fire. Intelligent side-wall systems mounted on both sides can effectively control fire over areas up to 16 m wide. There may also be scope for alternative water suppression systems, such as water mist, provided that these systems are demonstrated to be suitable for this type of application through testing and compliance with applicable standards (BSI, 2016).

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Annex C is a helpful starting point for design. Note that Approved Document B recommends that the guidance on atria in BS 5588-7: 1997 (BSI, 1997) only applies where an atrium traverses compartment floors. BS 9999 recommends that the guidance is relevant where a void traverses any floor, whether a compartment floor or not.

Building designation

3.5.6

Industrial buildings

The key factors for industrial buildings are as follows: significant historic fires

——

high life risk (but often low number of occupants and few mobility-impaired occupants)

——

hazardous processes requiring special provisions

——

high fire loads, often situated in close proximity to each other

——

firefighting difficulties

——

potentially high commercial losses

——

potential environmental damage from smoke and fire products.

Special controls and requirements appropriate to industrial processes are available in, for example, BS 5908: 2012 (BSI, 2012). The development of technologies and processes generally out-paces the development of Building Regulations, so a fire engineering review of the risks presented by the particular function of the building should be the main focus in design. Designers should not expect the recommendations in the current guidance to apply in isolation (e.g. HM Government, 2013; Scottish Government, 2017a, 2017b; DFPNI, 2012). The fire characteristics should be considered in the design of buildings in this group, with implications for the standard of active measures. The provision of roof-mounted sprinklers in high areas (over 15 m) will be ineffective in controlling fires but fast-response, in-rack systems are available. Care should be taken regarding the differences between approval for shell and core under the Building Regulations and when fitting out. Approving authorities and building insurers have different terms of reference, which can lead to conflicts of interest. Consultation with all relevant stakeholders, including authorities having jurisdiction, is recommended.

3.5.7

Storage and other non-residential buildings

The key factors are: ——

high contents and commercial losses

——

high fire loads

——

low occupancy

——

significant historic fires

——

designs may call for large volumes and long travel distances

——

underground accommodation may be involved

——

firefighting difficulties.

Purpose-designed water suppression systems are available to cope with densely stacked goods on high racks. Compartmentation may be disruptive or difficult to provide but is seen as a means of limiting fire damage. In many cases, fire spread may be limited by the combination of fire suppression and smoke venting.

In car parks, both above and below ground, a fire safety engineering examination of the actual risks may result in a lowering of the traditionally adopted standards, including the likely omission of sprinklers. Their omission, even in underground car parks, is permitted under the Approved Document B guidance (HM Government, 2013). Some fire authorities point out the increased risk where sleeping accommodation is located above car parking. The inclusion of water suppression can allay their concerns, especially in car parks with car stacker systems. Some recognition of the possible increase in fire load/risk associated with car fuels should be made, and reference to the BRE research may be advisable (BRE, 2010a, 2010b). The use of jet fans is an alternative to the more conventional use of ducted smoke control.

References BAFSA (2012) Sprinklers for Safer Living: Residential and domestic applications (Aberfeldy: British Automatic Fire Sprinkler Association) BRE (2010a) BRE Project: Fires in enclosed car parks [online] (Garston: Building Research Establishment) BRE (2010b) Fire Spread in Car Parks BD 2552 (London: Department for Communities and Local Government) BSI (1997) BS 5588-7: 1997 Fire precautions in the design, construction and use of buildings. Code of practice for the incorporation of atria in buildings (London: British Standards Institution) BSI (2012) BS 5908: 2012 Fire and explosion precautions at premises handling flammable gases, liquids and dusts (London: British Standards Institution) BSI (2013) BS 5839-6: 2013 Fire detection and alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of fire detection and alarm systems in domestic premises (London: British Standards Institution) BSI (2015) BS EN 12845: 2015 Fixed firefighting systems. Automatic sprinkler systems. Design, installation and maintenance (London: British Standards Institution) BSI (2016) BS 8489-1: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Code of practice for design and installation (London: British Standards Institution) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) Chitty R (2014) BR187: External Fire Spread: Building separation and boundary distances (Watford: BRE Fire Research Stations) DCLG (2006) Building Safety Risk Assessment: Residential care premises (London: Department for Communities and Local Government) DCLG (2007) Building Regulations and Fire Safety: Procedural guidance (London: Department for Communities and Local Government) DFPNI (2012) Technical Booklet E: Fire Safety (Belfast: Department of Finance and Personnel) FPA (2015) Fire Prevention on Construction Sites: The joint code of practice on the protection from fire of construction sites and buildings undergoing renovation (London: Fire Protection Association) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) HM Government (2015) The Building Regulations 2010 Approved Document M: Access to and use of buildings (Newcastle upon Tyne: NBS)

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——

3-11

3-12 Home Office (2012) Fire safety law and guidance documents for business [online] https://www.gov.uk/government/collections/fire-safety-law-andguidance-documents-for-business (accessed January 2018)

Morgan HP and Gardner JP (1990) Design Principles for Smoke Ventilation in Enclosed Shopping Centres BRE Research Report 186 (Garston: Building Research Establishment) NHS Estates (1996) Health Technical Memorandum 81: Firecode. Fire precautions in new hospitals (HMSO: London)

Scottish Government (2017a) Technical Handbook — Domestic (Livingston: Building Standards Division) Scottish Government (2017b) Technical Handbook — Non-Domestic (Livingston: Building Standards Division) Standing Committee on Fire Precautions (1995) Standard Fire Precautions for Contractors Engaged on Crown Works. Applicable to contractors engaged on works for Crown civil and defence estates (London: HMSO/Standing Committee on Fire Precautions) Welsh Government (2015) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Cardiff)

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HSE (2010) Fire Safety in Construction HSG 168 (London: Health and Safety Executive)

Fire safety engineering

4-1

4

Performance-based design principles

Statutory requirements for fire safety are primarily concerned with the protection of people from death or injury, although in some jurisdictions an element of property protection is also implicit within the requirements. Historically, fire safety measures to meet the life safety requirements have been specified by reference to fire safety design codes that provide ‘deemed to satisfy’ solutions for more typical building types. However, international design codes, such as the National Fire Protection Association’s NFPA 101® Life Safety Code® (NFPA, 2018)1 and BS 7974: 2001 (BSI, 2001) now explicitly recognise the use of fire safety engineering as an alternative means of satisfying statutory requirements. The assessment of risk has a fundamental part to play in the development of designs that provide adequate fire safety (whether in terms of life safety, business continuity or asset protection). Guidance on the risk assessment process is given in chapter 5. The inclusion of fire safety engineering in the risk assessment process provides the flexibility to address a range of design objectives, such as: ——

protection of people

——

prevention of conflagration

——

limiting damage to building structure

——

limiting damage to building contents

——

maintaining business continuity

——

protection of the environment

——

protection of animals.

The fire safety engineer will also need to consider a range of other factors that can have a significant influence on the design solution, such as: ——

security requirements

——

cost

——

aesthetics

——

building function

——

management capabilities

——

sustainability

——

legal framework

——

approach adopted by approvals bodies.

1 Life Safety Code® and 101® are registered trademarks of the National Fire Protection Association, Quincy, MA.

In some large and complex buildings, fire safety engineering may be the only practical way to achieve the required standard of safety, but in other cases it may just be used to vary a single aspect of a design that otherwise follows standard guidance. Indeed, with regard to UK fire safety design guidance for healthcare premises, in Health Technical Memorandum 05-02: Firecode (DoH, 2015) it is recommended that a qualitative design review (qdr), be carried out for very large and complex healthcare buildings by a study team involving one or more fire safety engineers, other members of the design team and the client user group. It also suggests that, if appropriate, representatives of approval bodies or the insurers be included to ensure that their views can be taken into account. Theoretically, it might be possible to establish a design that is based wholly on risk assessment and fire safety engineering techniques without reference to the recommendations of established fire safety design codes. However, these codes embody many years of experience and the most common and practical approach is to use fire engineering techniques to evaluate the effects of one or more departures from these established code(s). The complexity of the interactions between people, buildings and fire is such that no single approach or set of calculation procedures can be applied to all building types in all circumstances. Fire safety engineering thus requires more care, responsibility and experience from the designer than the application of standard guidance documents. It is essential that fire safety engineering design is entrusted to suitably qualified and experienced personnel. Appropriate professional qualifications and experience of fire safety engineering on projects of similar scale and complexity should be considered when appointing a fire engineer. Suitable qualifications include Chartered Membership of the Institution of Fire Engineers (CEng, MIFireE) or, in the USA, the Professional Licensure of Fire Protection Engineers by the Society of Fire Protection Engineers (P.E.).

4.2

Design objectives

4.2.1

Life safety

NFPA 101 Life Safety Code (NFPA, 2018) sets the following life safety goals, which provide a good starting point for any life safety design: A goal of this Code is to provide an environment for the occupants that is reasonably safe from fire and similar emergencies by the following means:

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4.1 Introduction

4-2

Fire safety engineering

(1) Protection of occupants not intimate with the initial fire development

This approach recognises that it may not always be possible to prevent injury to an individual who is located close to the source of fire (e.g. a person falling asleep while smoking in bed) but requires that people who are not in the immediate proximity of the initial seat of the fire are suitably protected and can leave the building in safety.

4.2.2

Other design objectives

The life safety requirements set down in legislation will often also provide a degree of property protection. However, the fire safety engineer should work with the client to establish whether it would be appropriate to consider other objectives, such as the protection of highvalue building contents or the safeguarding of essential electronic data to maintain business continuity. 4.2.2.1

Loss prevention

The effects of a fire on the continuing viability of a business can be substantial and consideration should be given to protecting: ——

the building fabric

——

the building contents

——

business continuity.

4.2.2.2

Environmental impact

A conflagration involving several buildings or the release of hazardous materials, e.g. fire on a waste site or in a chemical process plant, can have a significant environmental impact and consideration should be given to the need to limit:

4.3.2

Fire scenarios

The number of possible fire scenarios in even a relatively simple building is very large and it is not feasible (or necessary) to assess the effects of them all. Therefore, it is usual to identify one or more worst case scenarios for detailed evaluation. In some cases (e.g. a single compartment building), it will be feasible to identify one scenario that clearly represents the worst case. However, in a complex building, it might be necessary to establish several scenarios for detailed assessment. It is prudent and good practice to agree the design scenarios with the approvals bodies before embarking on extensive and potentially expensive modelling. Design fire scenarios should be chosen to reflect credible worst case conditions, taking account of: ——

the initial location of the fire

——

the materials on fire

——

the rate of fire growth and/or severity

——

smoke generation potential.

4.3.3

Multiple safeguards

Any fire safety design that is intended for the protection of people should not normally be wholly dependent on any one fire safety measure. The failure of any single system should not have the potential to lead to a catastrophic event.

——

the effects of fire on adjacent buildings or facilities

——

the release of hazardous materials into the environment

Care should be taken to ensure that a common mode failure will not lead to loss of multiple fire safety systems. In some instances, the failure of one system will have an adverse effect on the efficiency of another fire protection measure. For instance, an open fire door will not only be an ineffective barrier to fire spread but could also undermine the performance of a gaseous extinguishing system due to escape of the extinguishing agent.

——

methods of firefighting (e.g. avoidance of watercourse pollution).

The impact of a system failure should be assessed as part of a ‘what if ’ assessment. 4.3.3.1

4.3

Design scenarios

4.3.1 Occupancy The escape design should be based on the maximum number of people that a room, area or building is likely to contain and should take account of their likely distribution and response characteristics (mobility, wakefulness, familiarity with their surroundings etc.). The design should assume that a proportion of the occupants may have mobility, sensory or cognitive disabilities, except in situations where it would not be practical for disabled people to enter or work (e.g. wheelchair users would

‘What if’ events

An important part of any fire safety design is to carry out a ‘what if ’ assessment to identify system failures or other foreseeable events that might have a significant influence on the outcome of the study. An example would be ‘what if ’ a fire-resisting roller shutter between compartments were to fail to operate. The answer could be that it has no impact on life safety but it would lead to increased property damage. Some examples of typical ‘what if ’ events are: ——

fire door propped open

——

combustible materials introduced into sterile areas

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(2) Improvement of the survivability of occupants intimate with the initial fire development.

not be expected to access or work in a mechanical plant room).

Performance-based design principles

4-3

compartment walls penetrated and not made good

——

use of materials of greater than specified flammability

——

power supply to smoke vents fails

——

sprinklers ineffective due to poor maintenance

——

detection systems adversely affected by ventilation system

——

the fire is located where it will block an exit

——

management fails to adequately implement fire safety procedures

——

fire risk is increased by lack of awareness of fire safety issues.

Start

Qualitative design review (QDR)

Quantitative analysis

Assessment against criteria

Unsatisfactory

4.3.3.2 Uncertainty Any significant uncertainty in the design data should be addressed by choosing suitably conservative design assumptions, applying safety factors or carrying out sensitivity analyses. To assist in the approval process and any future building changes, these should be clearly recorded and referred to in the fire safety strategy report.

Reporting of results

The objective of a sensitivity analysis is to check the robustness of the results and to investigate the criticality of individual input parameters.

End

Common sources of uncertainty that might need to be addressed are: ——

input parameters

——

necessary simplifications techniques

——

limitations of empirical relationships

——

human response.

in

the

modelling

Satisfactory

Figure 4.1  The fire safety design process

During the qdr process, the scope and objectives of the fire safety design are defined, performance criteria are established and one or more potential design solutions (trial designs) are proposed. Key information is also gathered to enable detailed evaluation of the design solutions in a quantitative analysis. The building occupancy and design fire scenarios should also be established during the qdr process.

4.4

Fire safety design process

BS 7974: 2001 (BSI, 2001) and the International Fire Engineering Guidelines (ABCB, 2005) both set out very similar processes for carrying out a fire safety engineering design, which broadly comprise the four main stages illustrated in Figure 4.1:

It is important to ensure that the fire safety design provides for reasonable future flexibility of use and any constraints arising from the design should be reviewed with the client (e.g. unrealistic management procedures should not be imposed on the building operator and the fire engineer should not accept management requests that will be difficult to achieve or maintain).

——

qualitative design review (qdr)

The main stages in the

——

quantitative analysis

——

——

assessment against criteria

review architectural design and occupant characteristics

——

reporting of results.

——

establish fire safety objectives

——

identify fire hazards and possible consequences (see also chapter 5)

——

establish trial fire safety designs

——

carry out ‘what if ’ assessment

——

identify acceptance criteria and methods of analysis

——

establish fire scenarios for analysis.

4.4.1

Qualitative design review (QDR)

The first stage in the design process is to establish the basic parameters of the project. This includes a review of the scheme, identification of any overriding constraints and definition of the design objectives.

qdr

can be summarised as:

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——

4-4

4.4.2

Fire safety engineering

Quantitative analysis

4.4.3

Assessment against criteria

The suitability of the fire safety design needs to be assessed against the objectives and design criteria identified during the qdr process. Three basic approaches are available against which the acceptability of a design can be judged:

The report should set out clearly the basis of the design, the calculation procedures used and any assumptions made during the study. The format of the report will depend on the nature and scope of the fire engineering study and the house style of the particular fire safety engineer, but it would typically contain the following information: (a)

objectives of the study

(b)

building description

(c)

results of the

(d)

design assumptions

(e)

proposed fire safety strategy

qdr

——

comparative

——

deterministic

——

escape provisions

——

probabilistic.

——

internal linings and fire spread

——

compartmentation

——

structural fire resistance

——

fire spread to adjacent buildings

——

fire service access and facilities

——

active and passive fire safety measures

4.4.3.1

Comparative criteria

It can often be difficult to establish the level of safety achieved in absolute terms. However, it can be relatively straightforward to demonstrate that the design provides a level of safety equivalent to that in a building that complies with recognised fire safety design codes. 4.4.3.2

Deterministic criteria

In a deterministic study, the objective is to show that, based on the initial (worst case scenario) assumptions, a defined set of conditions will not occur (e.g. the smoke layer will not fall below head height during the evacuation period). 4.4.3.3

Probabilistic criteria

In a probabilistic study, criteria are set to ensure that the probability of a given event occurring is acceptably low. The risk criteria are usually expressed in terms of the annual probability of the unwanted event occurring (e.g. the probability of death in fire is less than 10–6 per annum). Further guidance on quantified risk assessment is given in Part 7 of PD 7974-7: 2003 Probabilistic risk assessment (BSI, 2003).

4.4.4

Reporting of results

Most buildings designed using fire engineering principles will be subject to review by approvals bodies and other parties that may not be specialists in fire safety engineering. It is therefore essential that the findings of the fire safety engineering study are clearly recorded so that the philosophy and underlying assumptions of the study are clear and are presented in a form that can be easily reviewed by a third party. This information should, ultimately, be included in the fire safety strategy for the premises. It is also important to provide sufficient information for another fire engineer to be able to assess (and if necessary repeat) any calculations and computer modelling that have

(f)

quantified analysis

(g)

comparison with acceptance criteria

(h)

management requirements

(i)

restrictions on use or change of use

(j) conclusions (k) references (l)

qualifications and experience of the fire safety engineer(s).

It is important that the report draws a clear distinction between life safety, property protection and environmental protection so that the building owner, manager and approval body can clearly identify the purpose of the proposed measures.

References ABCB (2005) International Fire Engineering Guidelines. Edition 2005 (Canberra: Australian Building Codes Board) BSI (2001) BS 7974: 2001 Application of fire safety engineering principles to the design of buildings. Code of practice (London: British Standards Institution) (Note: BS 7479: 2012 has been replaced by BS 7479: 2019) BSI (2003) PD 7974-7: 2003 Application of fire safety engineering principles to the design of buildings. Probabilistic risk assessment (London: British Standards Institution) (Note: PD 7974-7: 2003 has been replaced by PD 7974-7: 2019) DoH (2015) Health Technical Memorandum 05-02: Firecode. Guidance in support of functional provisions (Fire safety in the design of healthcare premises) 2015 edition (London: Department of Health) NFPA (2018) NFPA 101 Life Safety Code (Quincy, MA: National Fire Protection Association)

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Following the qdr, a quantified analysis can be carried out, if necessary. Various quantitative methods are available, such as those presented in other chapters of this Guide. However, in many cases the qdr process may generate a satisfactory design solution without the need for quantification.

been used to support the design. A comprehensive report will also enable the inputs and design of the building to be evaluated.

5-1

Application of risk assessment to fire engineering designs

5.1 Introduction Risk assessment often has a fundamental part to play in the development of fire engineering designs, enabling them to describe how adequate fire safety will be achieved in terms of life safety, business resilience and/or asset protection. Used properly, it is a tool that enables the designer to optimise their fire protection solutions while maintaining levels of safety at (or even above) those which could be achieved by straightforward compliance with codes and standards. Legislation generally requires that designers and managers of non-domestic premises assess the life safety risk posed by fire in those premises and that they take suitable measures to reduce the risk to an acceptable level. This can be achieved by: ——

incorporating fire protection in the design of the premises

——

implementing and maintaining effective and appropriate management controls.

In some countries, the assessment of life safety fire risk is an ongoing legal obligation that continues throughout a building’s occupation — this type of routine risk assessment is outside the scope of this Guide. This chapter addresses the role and use of fire risk assessment in the building design process to analyse design solutions, compare design options or justify variations from published codes and standards. Non-life-safety fire risk may also be an important consideration. For example, insurers may advise on fire risk reduction measures as part of a wider risk management strategy, in order to control financial losses for both client and insurer, or to limit large potential loss exposures. Clients may also require designers to incorporate measures to protect assets in case of fire, as a means of ensuring business continuity, enhancing overall business resilience, improving supply chain security and to protect their overall brand. Such measures will augment (but must not reduce) those required for life safety purposes. The findings from a risk assessment can be used to inform decisions regarding whether fire precautions and fire safety management procedures are sufficient to control fire risks to a satisfactory level, or whether additional risk reduction measures are required. Risk assessment can also be used to perform a systematic comparison of different risk control/reduction options, so that the optimal design or management solution can be selected. It is not, however, appropriate to carry out a risk assessment to justify a decision that has already been made. Risk assessment is input to the decision-making process, not output from that process (Gadd et al., 2003).

The techniques used to assess risk vary from very simple qualitative analyses to sophisticated quantitative risk analysis (qra) techniques of the type commonly found in the nuclear, transport and chemical processing industries. No single approach is correct for all applications. For example, qra may be inappropriate for cases where straightforward adherence to good industry practice is reasonable. On the other hand, in more complex environments simple checklists (e.g. ‘tick box’ techniques) are likely to be inappropriate for assessing fire risks. While risk assessment methodologies vary, they are likely to include the following steps: (1)

Identify the hazards.

(2)

Identify the possible consequences and estimate their likelihood.

(3)

Evaluate the risk.

(4)

Take action to reduce risk to an acceptable level.

(5)

Record the findings.

(6)

Monitor and review as appropriate.

Before a risk assessment is undertaken, it is important to determine the scope and purpose of that assessment and, if appropriate, agree that scope with those who will refer to it – this may include clients, managers, premises owners, regulators and insurers. Almost all risk assessment includes an element of judgment, either in identifying the hazards, analysing the possible consequences or estimating their likelihood. For this reason, it is important that the risk assessment is undertaken by persons with skills and experience appropriate to the fire risks being assessed. In cases where the assessment involves a straightforward and unvarying application of good industry practice (e.g. government guidance), the assessor might not require detailed knowledge of fire behaviour. However, where the assessment uses techniques that may result in solutions that depart significantly from guidance, it will be necessary for the assessors to have the relevant competence in fire safety engineering and/or fire safety management to appreciate the consequences of those departures on fire risk in the premises. This will require an understanding of the fire hazards or fire risks that the guidance addresses and the reasons why the guidance recommends a particular controlling measure. It is only with this knowledge that the assessor can make informed decisions regarding the significance of variation from that measure. If considering resilience, rather than safety, then prior to the risk assessment being undertaken the key stakeholders should establish their risk tolerance in terms of how much risk to accept, mitigate or insure against.

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5

5-2

Fire safety engineering

In the context of the built environment it is not usual for the design of premises to be based solely on the results of risk assessment. It is more often used either to address specific risks not foreseen by the good practice guidance or to justify variations from particular recommendations in that guidance, where their application would result in a non-optimum design.

5.2

5.3

A number of definitions are available for hazard, risk and risk assessment, and these concepts are fundamental to any risk assessment process. It is therefore essential to define what is meant by these terms: ——

A hazard is that which has the potential to cause harm or loss.

——

Risk is a function of both the likelihood of a specific hazard being realised and the consequence of that realisation.

——

Risk assessment is the process by which reasonably foreseeable hazards are identified, the likelihood of occurrence of specific undesirable events (the realisation of the identified hazards) is estimated, and the severity of the harm or loss caused is assessed. This may be coupled with a judgment concerning the significance of the results.



In other words, it is through the risk assessment that the risk will be evaluated (using either a qualitative or a quantitative approach).

Risk assessment process

Where the risk assessment input is simple and straightforward, it may not be necessary to consider it as an activity separate from the normal design, review and acceptance/ approval process for the project, especially where the risk of non-approval is judged to be low. For more complex risk assessment, it is good practice to establish and agree how the risk assessment will be conducted and its acceptability criteria before embarking on any significant activity. This reduces the risk of carrying out work that may later prove to be wasted. The following outline process may be applied, to a level appropriate to the complexity of the particular assessment being undertaken: (1)

Establish the need for risk assessment.

(2)

Gain approval to use risk assessment (if necessary).

(3)

Define the scope.

(4)

Agree the methodology.

(5)

Define the key stakeholders and establish roles – especially those who will approve and/or accept the outcome of the analysis.

(6)

Research and review any applicable good practice.

(7)

Agree the acceptability criteria for the risk assessment.

(8)

Undertake the analysis, consulting with key stakeholders as required.

(9)

Present the analysis, either physically or as a document.

(10)

Review, revise and gain approval/acceptance.

(11)

Communicate the results to any affected design disciplines and record the outcome in the project fire safety strategy (if this exists).

In practice, many of the above activities will not be undertaken as separate exercises and will be the natural outcome of a well-managed design process. The precise order may be varied according to need, but it is strongly recommended that commencement of the analysis itself does not proceed until all the activities prior to it in the above list have been completed, to the satisfaction of the key stakeholders.

Hazard, risk and risk assessment

Where the word ‘loss’ is used above, it should be interpreted as describing a non-safety-related consequence of a fire, which is harmful to the business, individual(s) or concern that occupies the premises. The loss normally results in exposure to increased cost and/or risk to the continuance of the activities based within (or supported from) that location. It may also include the loss or damage of items of historic or aesthetic importance. It is essential that all reasonably foreseeable fire risks are identified and considered in the risk assessment process. It is not always necessary to carry out a detailed assessment of all of those risks but exactly which fire risks have been considered, and have been found to be acceptable by all key stakeholders, should be recorded. It is important to note that the fact that a specific fire risk was not foreseen does not automatically mean that it was not ‘reasonably foreseeable’. Those undertaking the hazard analysis should have the competence and knowledge to identify the fire risks that need to be assessed, whether they had been foreseen up to that point in time or not. It is also relevant to point out that a hazard may always exist, but it is usually possible to substantially reduce the risk associated with that hazard. Reducing the risk from fire to zero is almost impossible. However, to moderate it to an acceptable level is possible and, in fact, this should be the aim of a risk assessment.

5.4

Defining the scope of the risk assessment

In some cases, it may be straightforward to define the purpose and scope of the risk assessment, such as where the assessment is aimed only at satisfying fire safety legislation in simple premises. In other cases, the scope may need more careful definition, especially:

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It may not be possible for a fire engineer alone to assess the fire risks associated with certain hazards (e.g. in determining whether certain equipment is ‘critical’ if assessing fire risk to business or process continuity). In this case, it will be both necessary and appropriate to draw on the skills and experience of others in order to undertake an adequate assessment of fire risk.

Application of risk assessment to fire engineering designs when the purpose of the risk assessment is to support the acceptability of the design of complex or novel buildings

——

where fire risks to assets or business continuity are being assessed.

In simple terms, the questions that need to be asked may include the following: ——

Risk ‘of what’ (e.g. fatality, major injury, loss of assets, loss of business, reputation, supply chain interruption etc.)?

——

Risk ‘to what/whom’ (e.g. employees, visitors, members of the public, firefighters, assets or premises)?

——

Risks ‘from what’ (e.g. accidental ignition, the nature and distribution of potential fire load, construction materials, arson, occupancy or process hazards etc.)?

Once the scope and purpose of the risk assessment is defined, this will inform the decision about the most appropriate technique (or combinations of techniques) for undertaking the assessment.

5.5

Acceptability criteria

5.5.1 General When undertaking fire risk assessments, it is important to understand what can be regarded as an acceptable level of risk from fire. As mentioned previously, it is practically impossible to achieve zero fire risk and, in reality, society neither expects nor requires such a high level of safety. However, fire risk does have to be acceptable to those who have an interest in controlling it. In the case of life safety, it will normally be legislation that defines acceptable levels of risk. In the case of insurance requirements, it will be the insurers or their representatives. In terms of risk to business continuity, it will be the management and/or owners of the relevant organisation. In most cases, the objective will be to reduce risks to a level that is ‘as low as is reasonably practicable’ (alarp). An alarp assessment involves analysing fire risk against the effort, time and cost of controlling it. Thus, alarp describes the level to which it is expected that fire risks are controlled. If the fire risk reduction benefit is proportionate to the time, effort and expenditure necessary to implement the relevant risk reduction measure, then that risk reduction measure must usually be implemented. Another term for a very similar process is ‘so far as is reasonably practicable’ (sfairp). Care should be taken to select and use the process relevant to the particular circumstances of the project being worked on, as in some parts of the world the terms are freely interchangeable, whereas elsewhere the processes are different and the terms are not. In fire safety, the practical definition of the level of fire risk that can be regarded as alarp tends to be set by

national guidance. Adherence to such guidance (where relevant and appropriate) is likely to demonstrate that the life safety risks from fire are acceptably controlled. Where duty holders wish to depart from that guidance, then the normal expectation is that they use alternative risk control measures which achieve the same level of safety by other means (HSE, 2001). When considering business resilience, continuity and asset protection, then risk appetite or tolerance will vary on a case-by-case basis, depending on the level of selfinsured retentions, actual client loss history, criticality, values at risk and any potential maximum loss scenario. It is by no means the case that such matters will always need to be considered, but where this is necessary it will be crucially important to establish a means of defining an acceptable level of fire risk at the outset of the process. This is often achieved by means of adopting published guidance on loss prevention (e.g. BS EN 16893: 2018 (BSI, 2018), BS 4971: 2017 (BSI, 2017a), the LPC Design Guide for the Fire Protection of Buildings (LPC, 2000) or more general loss prevention guidance) and applying this in a very similar way to the guidance on life safety (i.e. by either demonstrating compliance or achieving an equivalent level of fire risk by other means).

5.6

Assessment techniques

5.6.1

Application of good industry practice

In many cases, it is possible to assess fire risk using an uncomplicated approach by reference to relevant good industry practice. Indeed, it should be the case that, before any risk assessment is carried out, the assessor should review whether relevant good industry practice exists and, if so, whether it can be straightforwardly applied. It is normally accepted that if good practice can reasonably be applied, it should be adhered to (Gadd et al., 2003). The following would be possible exceptions: ——

If it were to be applied to existing premises, the cost of compliance with the guidance would be grossly disproportionate to the fire risk reduction achieved.

——

The situation under consideration has inherently and significantly lower or greater fire risk than that for which the good practice was developed.

——

The operations or works include alternative means of controlling the risks to a comparable or better level.

Good practice encompasses industry and regulatory codes, ‘approved codes of practice’ (acops), and regulatory guides, as well as practices and guidance adopted successfully by similar organisations. Where life safety is concerned, relevant good practice is likely to reflect the minimum expectations of society and is therefore of use both to those who will use it directly to assess risk and also to those who will assess risk in other ways (whether by quantitative or qualitative methods). As long as it is possible to demonstrate a level of risk

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——

5-3

5-4

Fire safety engineering

In practice, if relevant good practice exists and is adopted for all reasonably foreseeable hazards, further detailed evaluation of risk is not usually necessary; the risk assessment duty is discharged by the appropriate adoption of that good practice. It is therefore very important to ensure that the good practice is: ——

appropriate to the activities being considered

——

up to date

——

both relevant to and able to cover all significant fire risks from the circumstances being considered.

5.6.2

Qualitative risk assessment

Qualitative risk assessment (or analysis) can be defined as the assessment of risk using methods that might be analytical, but are predominantly non-numerical. This includes designers using judgment and experience to argue that non-compliance with a particular standard recommendation does not unacceptably increase fire risk. Similarly, qualitative risk assessment can include the offering of alternative design solutions using qualitative arguments for equivalence (in terms of fire risk). The application of methods for ranking the identified risks according to their potential consequences sometimes forms part of this process. This type of risk assessment relies on the training and experience of the assessor(s) to: ——

identify the relevant hazards

——

make a judgment as to the likelihood of that hazard resulting in harm

——

assess whether the resultant risk is acceptable.

Such risk evaluation processes often use a set of worksheets or questionnaires that incorporate all items that could affect fire risk, such as ignition sources, presence and quantity of combustible materials, flammable liquids and gases, structural features, people at risk, means of escape, fire detection and warning, fire suppression, maintenance and safety management practices. In addition, the likelihood of fire occurrence and potential damage to life and property, and limiting factors, should be considered. The categories described above may be evaluated by a series of questions requiring ‘yes’ or ‘no’ or ‘acceptable’/​ ‘unacceptable’ responses, then ranked or scored within a matrix (an example of which is outlined below). This process will normally be used in conjunction with relevant good industry practice, which the assessor will apply where it is reasonable to do so. Where this is either impracticable, or where alternative solutions offer the same or a better level of safety at lower cost or in a manner more suited to the premises, the assessor should use their judgment to determine the acceptability of those variations from good practice.

Good industry practice sometimes gives guidance on how to assess risk and how to apply that risk assessment in order to influence the design in a qualitative but structured manner. For example, BS 7974: 2001 (BSI, 2001) and the more recent BS 9999: 2017 (BSI, 2017b) introduce the concept of ‘risk profiling’ as a tool to inform the design of such aspects as means of escape and structural fire resistance. They utilise the concept of ‘occupancy characteristics’, considering whether the occupants are likely to be awake and aware of their environment, and whether they will be familiar with it or not. Risk profiling also considers the probable fire growth rate in the premises (this will necessarily be a matter of judgment) and combines the two to produce a ranking of risk. That ranking is used to indicate recommended design criteria (such as maximum means of escape distance, structural fire resistance etc.). In the case of BS 9999, it is important to note that it is the fire growth rate that is the important factor, and this is not the same as the fire load or ultimate fire size. It is entirely possible to have a high fire growth rate in a space with a relatively low fire load, and vice versa. Variation of the risk profile is possible by the application of certain risk reduction measures (such as automatic sprinkler systems or enhanced fire detection and alarm systems), which allows more flexibility in the design of other risk reduction measures. In some cases, this allows risk to be controlled by less costly and/or less intrusive engineering measures than would be demanded by a wholly prescriptive solution. For more details of this approach, reference should be made to the current version of BS 9999. Another example of a qualitative risk assessment is the ‘risk matrix’ technique (commonly called a qualitative risks assessment/analysis matrix). The risk matrix is a comparative table in which the likelihood and the consequence(s) are related to each other according to a qualitative ranking. This will provide a comparative estimation of the level of risk. Table 5.1 shows an example of a risk matrix. The level of risk will be represented in each cell of the matrix and can be expressed by using a colour, code or scale, such as:

E: extreme risk



H: high risk



M: moderate risk



L: low risk.

The risk matrix can also be used in a semi-quantitative sense by assigning nominal values to both likelihood (L) and consequence (C), where the risk factor (R) is the multiple (or sum) of L and C. Although frequently adopted as a technique in the assessment of risks for fire safety management purposes, the application of risk matrices to design risk assessment tends to be less useful because of the inevitable subjectivity involved and the difficulty of agreeing the acceptability criteria (for example: Are ‘medium’ risks ever acceptable?; Are ‘low’ risks always acceptable?). alarp assessment requires more than simply rendering risks ‘low’, and therefore the risk matrix is not appropriate as the sole method of defining design solutions. If fire risk is analysed

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equivalent to that represented by the application of good practice (in premises typical of the type being examined), then that should be acceptable. If it is found that a design or management solution results in a situation where fire risk is higher than would be delivered by the application of good practice, then it is questionable whether that solution could be regarded as acceptable.

Application of risk assessment to fire engineering designs

5-5

Table 5.1 A hypothetical example of a risk matrix Likelihood

Fire detection operation

Consequences Minor (2)

Moderate (3)

Major (4)

Catastrophic (5)

A (almost certain)

M

H

H

E

E

B (likely)

M

M

H

H

E

C (possible)

L

M

M

H

E

D (unlikely)

L

M

M

M

H

E (rare)

L

L

M

M

M

Manual extinguishment

Scenario

Yes

1

Yes Yes

2

No Fire occurs

No Yes No No

3 4

5

Figure 5.1   Time-dependent event tree for probable fire scenario

as being ‘low’, but it can be further reduced in a straightforward manner and at little or no cost, then that potential improvement in fire risk cannot be easily dismissed. It is therefore more useful as a technique for comparing risks than for determining absolute acceptability. In addition to standard and well-known risk matrices, alternative methodologies are starting to be used for the same purpose, such as multi-criteria decision-making models (Tavares et al., 2008). Whichever technique is used, these analyses should be documented in a manner that records how the assessment has been undertaken and which includes the rationale for concluding that risks are acceptable. Where the risk assessment forms part of the design solution for a building, it should be included in the Fire Safety Strategy document (BSI, 2001).

5.6.3

Quantitative risk assessment (QRA) and cost–benefit analysis (CBA)

Quantitative risk assessment (qra) is a technique whereby risks are evaluated by assigning numerical values to hazard (e.g. cases of death or serious injury, damage area or financial loss), to the probability that the hazard will be realised, and to the resultant fire risk. This enables the assessor to either compare risk reduction measures on a ‘like-for-like’ basis or to ascertain whether risks are tolerable in absolute terms. The qra process is well-established and models are essentially non-deterministic (i.e. statistical, probabilistic, stochastic or reliability techniques). These techniques are commonly used in industries such as nuclear power generation and transportation to assess all safety risks in a structured and rigorous way. qra is often used in such cases to determine if it is reasonably practicable to make safety improvements under existing or altered conditions, or to define safety objectives for new works. There are several qra techniques, such as: hazards and operability study (hazops); standard logical trees, such as fault tree analysis (fta) and event tree analysis (eta); and new logical trees (such as the continuum net-value work diagram). The Health and Safety Executive (HSE), the Occupational Safety and Health Administration (OSHA)

Activation of the alarm

The occupants heard the alarm

The occupants did not hear the alarm

The occupants recognised the alarm

The occupants did not recognise the alarm

The occupants accepted the alarm as being a true fire alarm

The occupants did not accept the alarm as being a true fire alarm

The occupants had a response to the alarm

The occupants did not have a response to the alarm

Figure 5.2   Continuum net-value work diagram for a generic fire emergency situation

and the American Institute of Chemical Engineers (AIChE) provide good guidance documents for using such techniques. Figure 5.1 shows an example of an event tree used for describing possible fire scenarios if a fire occurs. Figure 5.2 shows an example of a continuum net-value work diagram, which describes the complexity of human behaviour within fire emergency situations. The two examples shown in Figures 5.1 and 5.2 illustrate graphically how qra techniques can be used. For each

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Insignificant (1)

Sprinkler operation

5-6

Both qra and cba need not be restricted to safety-related decision making; they may be usefully applied to decisions concerning property and asset protection as well. For example, using knowledge regarding the probability of a significant fire during a relevant period of time, its consequences and the potential financial loss (both in terms of assets damaged or destroyed or lost revenue), an informed judgment can be made as to the practicability and desirability of fire protection as a loss control measure. It may commonly be found that the case for inclusion of such engineering is far stronger as protection for assets rather than as a life-safety measure. As an example, increasing fire resistance may reduce the probability of fire spreading beyond a compartment boundary, which may reduce the probable damage area. The additional cost of fire resistance can therefore be offset against the reduction in probable damage. PD 7974-7: 2003 provides a model based on statistical studies for calculating the probability of a fire starting that has a ‘power’ relationship with building area (BSI, 2003); similarly, the probable damaged area can be calculated based on building area and ‘power’ constants derived from real fire statistics and data. The constants are modified for compartments with or without sprinklers. In high-value commercial or industrial premises, the cost of the potential maximum loss scenario can far outweigh the cost of a sprinkler system, especially when factored in to the early design/specification stage of a new building. Factoring in the likelihood of that scenario being realised might make the case for the installation of sprinklers compelling. may use statistical or historical data to inform judgment on probability, or expert judgment may be used to estimate probabilities for the occurrence of hazards. The resultant risk can be expressed as the likelihood that an unwanted and harmful event occurs in a particular period of time; e.g. the probability of a fatality per year of operation might be 1 × 10–7.

qra

or have a higher vpf in order to recognise that society is less tolerant of multiple fatalities than it is of single events. Society also expects lower levels of risk exposure for members of the public than for employees. A further value multiplier is often applied to the cost part of the analysis to define the level at which the risk reduction measures are deemed ‘grossly disproportionate’. Typically, costs (for risk reduction measures) of less than three times the value of risk reduction achieved are regarded as indicating that it is reasonably practicable to implement that risk reduction measure. However, this does not mean that if cost is greater than three times the value of risk reduction that would be achieved, then it is justifiable under the alarp approach not to implement that measure – other criteria (such as societal concern or comparison to relevant good practice) might apply. Guidance on the application of probabilistic risk assessment is given in PD 7974-7. This document advises that it is most straightforward to apply qra and cba where comparisons are being made of alternative risk reduction measures (e.g. a fire engineered solution compared to a ‘code-compliant’ one); but that establishing ‘absolute’ quantified values for acceptability is far less straightforward. If contemplating the use of such an analysis, it is therefore important that the techniques to be used and the input data (including the vpf and application of all relevant ‘value multipliers’) are agreed with all those with an interest in controlling fire risk (including the relevant regulators) before embarking upon the analysis. Where cba is being used to assess whether it is reasonably practicable to implement measures to reduce risk to business, assets or property, it may be more straightforward to quantify the negative benefit of the loss of that property or functionality. However, it is no less important to agree with all stakeholders the input data to be used and the ‘success criteria’ for what residual risk is regarded as being tolerable before embarking upon the analysis. A

cba

on its own: case

——

does not constitute an

——

cannot be used to argue against statutory duties

——

cannot justify risks that are intolerable

——

cannot justify what is evidently poor engineering design.

alarp

In some industries (e.g. transport), guidance exists on the value that society is willing to place on the prevention of a fatality as a result of the operations of that industry (DfT, 2007). It is important to note that this does not constitute the ‘value’ of a life – that is unquantifiable – but it gives an indication of the cost that society is willing to pay to secure an assessed reduction in risk to life, with regard to that industry. This is called the ‘value of preventing a fatality’ (vpf). It can be used in a cba whereby the cost of the risk reduction measure is assessed against the risk reduction it achieves.

If carrying out a cba, it is crucial that the same level of discipline is used in estimating costs as is used in assessing the risk. Only costs directly related to safety can be used in the analysis — costs associated with non-safety requirements (e.g. aesthetic appearance or potential loss of revenue) cannot be considered in a safety-related cba. It is, however, acceptable to include installation, training and any additional maintenance costs, and any business losses that would follow from assets being taken out of service solely for the purpose of putting the measure into place. The corollary of this is that any cost savings that result from the implementation of the risk reduction measure should also be considered — these might include improved availability of assets, for example. These should be offset against the cost of the risk reduction measure(s) in the cba.

Events that could result in multiple fatalities (e.g. death in fire) typically have value multipliers assigned to the vpf,

In terms of life safety, the cost used must be that for the minimum safe solution. Any associated non-safety

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event represented in each diagram, there would be an associated probability and, therefore, as mentioned above, the assessor will need to use their prior knowledge and/or historical data as a basis for estimating the probabilities. For more complex scenarios, such as large spaces, high population density environments etc., the assessor might use numerical optimisation techniques (Tavares and Galea, 2009). It is also relevant to mention that, when using the qra techniques, the assessor can also perform a cba, if necessary and/or requested.

Fire safety engineering

Application of risk assessment to fire engineering designs

5-7 premises, or where those persons might be regarded as particularly ‘vulnerable’ in case of fire, consideration should be given to possible societal concern about the risk or the measures proposed to reduce the risk. The factors to be considered within this determination should include those where:

While qra is a useful and respected tool, there are known pitfalls to its use:

——

the risk arises from a potential failure that could result in a major accident, which society would be unaware of or would assume was already well controlled

——

there might be public aversion to the scale of the injuries should the risk be realised

——

public disquiet and loss of confidence would arise from a key failure occurring within the accident sequence, even if not leading to serious consequence (e.g. a near miss)

——

the risk is inequitably shared, particularly where a vulnerable group (such as children or persons with a disability) may be involved

——

the decision may lead to loss of public trust in the duty holder’s ability to learn from serious incidents and/or adopt good practice

——

the adoption of the risk reduction measure would have a significant adverse effect on the duty holder’s operations, which the public may perceive as being disproportionate to the safety risks.

——

is not always appropriate; it should not be used where established good industry practice exists, is relevant and is straightforwardly applicable.

qra

——

It should be used with caution when considering low frequency and/or serious consequence events (such as a significant fire, in most premises).

——

‘Historical’ data should be used with caution and statistics based on limited sample periods should be used with care. History shows that, even where many years have passed without significant incident, this does not necessarily indicate that risk is acceptable. Indeed, fire safety legislation is often driven by public reaction to infrequent events that would not necessarily have been predicted beforehand using probabilistic assessment techniques.

——

should not be used to justify removal of risk reduction measures on the basis of cost saving alone, unless it can be demonstrated that fire risk is maintained at equivalent or lower levels by other risk reduction measures.

qra

——

Numerical levels of probability might mistakenly be regarded as predictive ‘fact’ and be given undue prominence in the judgment of acceptable risk. This will be especially relevant if it is viewed that their precision implies that they are accurate, whereas in most cases there will be significant uncertainty in the probabilities generated during the assessment process.

——

The quantified ‘success criteria’ for determining whether fire risk is tolerable or not may be difficult to establish.

The last point is particularly relevant where fire risk is being assessed. While general levels of ‘tolerability’ for risk to individuals are reasonably well defined numerically in guidance and standards, where multiple fatalities in fire are concerned, society tends to be much less tolerant of risk. There is a greater than normal expectation of safety from that particular hazard. This is generally known as ‘societal concern’ and is not straightforward to quantify. There is no widely agreed and quantified maximum level of risk that satisfies societal concern – the ‘benchmark’ level can be regarded as being equivalent to that set by means of legislation and the recommendations in national and/or governmental guidance. Therefore, qra should normally only be used to demonstrate acceptable fire safety by comparison with accepted levels of risk against established relevant good practice.

5.6.4

Societal concern

Where a significant number of persons could be affected by the consequences of a particular fire hazard in the

The above will be particularly relevant for public bodies (e.g. health authorities, transport infrastructure providers, education authorities) or those offering access to large numbers of members of the public (managers of sporting and entertainment venues, duty holders in shopping malls etc.). The Villaggio Shopping Mall fire in Doha, Qatar in May 2012, in which 19 people (including 13 young children) were killed, was a tragic incident that serves as an example of where one of the circumstances described above manifested itself. It has resulted in the attitude to fire safety in an entire country (arguably, throughout the entire Gulf region) being re-evaluated, and lengthy prison sentences for those convicted of being at fault.

5.6.5

Risk to firefighters

It is expected that firefighters are likely to be exposed to risk (when carrying out their fire and rescue duties) that would be intolerable for members of the public. Fire and rescue operations are normally undertaken on the basis of a dynamic risk assessment made upon arrival at the incident (based on the type of premises, severity of the fire and whether it is believed that there are persons at risk from the fire). That risk assessment is regularly updated as the incident unfolds and takes into consideration the high levels of training and appropriate personal protective equipment (ppe), such as heat-resistant clothing and/or breathing apparatus that enables firefighters to tolerate severe conditions. It is not, therefore, either practicable or necessary to control risk to firefighters during their fire and rescue activities to levels equivalent to those applicable to other occupants. Having said the above, risk to firefighters undertaking their duties during a fire should be considered when

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requirements may be entirely legitimate, but they are subject to a different cost–benefit case, unrelated to safety, and the cost of these cannot influence the decision as to whether or not the measure is alarp. Only costs that fall on the duty holder should be used — costs to third parties (e.g. members of the public) should not be used.

5-8

Fire safety engineering

Within this perspective, some technological tools can be useful when assessing the fire risks to firefighters within buildings. For instance, the use of evacuation models as well as fire models can assist an assessor when undertaking a risk assessment (Tavares et al., 2008; FSEG, 2017a, 2017b).

5.6.6

Business resilience and insurance considerations

Designing to meet a code or minimum life safety standard is clearly the first consideration for risk assessment. However, within the commercial and industrial world there could be broader considerations around maximum loss potential that may be a low probability/high consequence scenario. Analysis of this normally takes into account the largest possible loss based on an understanding of the overall hazard and associated business impact (FM Global, 2015). Such analyses may assume that certain active fire protection systems (such as sprinklers) are impaired so that the only limiting factors considered are physical barriers or space separation that will adequately prevent fire spread. Credit for a physical barrier is typically only given for specifically engineered fire-resisting structures, which comply with established and agreed technical criteria. The largest loss scenario and values at risk should be considered at the earliest stages of design and during the establishment of project objectives, and an assessment made as to whether the risk is simply too big not to separate (e.g. a warehouse from manufacturing). Such decisions will usually be driven by the client’s appetite for risk, their business impact analysis, resilience needs and business continuity strategy.

5.7

Risk assessment pitfalls

5.7.1 General It is possible that risk assessment could be viewed as an opportunity to dispense completely with ‘prescriptive’ standards and to reduce costs by assessing out established risk reduction measures. If properly applied, risk assessment does allow targeted risk reduction, perhaps resulting in lower risk than the prescriptive solution or the same level of risk at lower cost. However, care should be taken when using risk assessment techniques to depart from established prescriptive codes and some examples of poor practice in risk assessment (taken from Gadd et al., 2003) are included in the following sections.

5.7.2

Considering only the probability of fire

It is unlikely to be legitimate to conclude that fire hazard is so low that the probability of having a fire that can cause harm is negligible. It is expected that, where a low frequency but serious consequence event such as a large fire is concerned, it should be assumed that a fire could occur and the risk should be assessed on that basis. The management controls that would be required to reduce to negligible the probability of a significant fire starting are so demanding that, in most industries, it is not sensible to rely on them being applied throughout the life of a premises.

5.7.3

‘Reverse ALARP’

The removal of existing fire protection measures might be attempted, justified on the basis that the cost of ongoing maintenance or renewal is grossly disproportionate to the risk reduction benefit achieved. This is not acceptable because there is a responsibility to maintain existing fire protection measures (which is usually enshrined in law) and those existing measures reduce risk to what must have been regarded (when they were implemented) as an acceptable level. By providing those measures, the duty holder has demonstrated that it is reasonably practicable to do so, and by so doing has established a particular level of fire risk. Increasing that level of risk can therefore not be alarp. This unacceptable form of argument is commonly known as ‘reverse alarp’. This does not mean that fire protection can never be removed; if one can reasonably argue that fire risk has not been increased at all by that removal, then it may be acceptable to do so. This might be accomplished by applying one or more of the following criteria: ——

the risk reduction measure to be removed or modified addressed a hazard that is no longer present

——

alternative risk reduction measures, no less effective than the measure being removed, will be applied and maintained, so resulting in risk not being increased

——

in all cases the removal of the risk reduction measure does not increase risk beyond that which would be achieved by the application of relevant and current good practice.

5.7.4

Using the cost of remedial works in a CBA

It might be the case that works have been designed and implemented in an unacceptable or inappropriate manner; e.g. it might be discovered that they do not comply with good industry practice or that they fail to offer an equivalent level of safety. In this case, it has been known for cba to be used (in either a qualitative or quantitative risk assessment) to justify why it is acceptable for those variations from acceptable risk to remain. Frequently, those making the case argue that the ‘trouble’ (i.e. cost, disruption or impact on programme) of correcting the issue is the measure against which the risk reduction benefits are to be judged.

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designing a building. It is not acceptable to ignore the fact that their duties under law are likely to include doing all that is reasonable to protect both life and property in case of fire, and the fire protection provided should be such that these duties can be undertaken without exposing the firefighters to unnecessary risks. In practice, this will usually mean ensuring that works either comply with good industry practice or will represent an equivalent level of fire risk (to the firefighters) by incorporating alternative design solutions.

Application of risk assessment to fire engineering designs

5.7.5

Confusion between cost and affordability

While cost is, undoubtedly, a legitimate factor in some forms of risk assessment analysis, affordability is not. Some examples of the latter include the following: ——

——

It is sometimes claimed that it is not practicable to implement a risk reduction measure because there has been no allowance for it in the budget. The argument is sometimes made that unforeseen risk reduction measures are so expensive that their cost may threaten the viability of the project.

These are not acceptable reasons for failing to implement reasonably practicable risk reduction measures. This is because there is a reasonable presumption that before a duty holder embarks upon an activity, they will have determined that they can afford to undertake that activity safely. Failure to do so (for example, by not foreseeing and allowing for the necessary risk reduction measures in a project’s budget) cannot therefore be accepted as a reason for tolerating higher levels of risk. If this situation arises, it is sometimes possible to address the consequences by reducing spend on non-safety-related project requirements, such as certain fixtures, fittings and finishes provided only for aesthetic reasons. Similarly, the enhancement of management procedures is sometimes proposed as a mitigation measure in these circumstances. While this approach may indeed enable acceptable levels of fire risk to be achieved, it is strongly recommended that the practicability of reliably maintaining those procedures (perhaps for many years) is very carefully reviewed in conjunction with the users, occupiers and/or managers of the premises, to ensure that they are satisfied that this is achievable. The ‘whole-life’ operational cost of those measures should also be considered as, if more staff resources are required, then the cost (over the whole life of the assets) may significantly exceed the capital cost of the physical risk reduction measures themselves.

5.7.6

Citing conflicting and contradictory legislative requirements

Other technical or legislative requirements are sometimes advanced as reasons why fire risk reduction measures cannot be implemented. For example, heritage concerns are sometimes offered as justification for avoiding the alteration of properties of historic interest. The question is sometimes asked whether there is a hierarchy of legislative requirements, whereby fire safety may be considered subordinate to other factors.

There is no such hierarchy — the need for compliance with one item of legislation has no bearing on the requirement to comply with any other. The designer has to consider and comply with all legislation equally. Having said this, where non-legislative project requirements are being analysed and there is genuine conflict, then safety-related issues must take precedence. The above necessarily calls for a sensitive approach to be applied to the design process, with due regard being paid to any aspects (such as heritage issues) that are somewhat subordinate to fire safety. This may require the application of sector-specific fire safety solutions to those premises, so that the acceptable level of fire risk is achieved without unnecessary alteration to the historic fabric. Examples might be the use of radio-linked fire detection systems to avoid the need for cables, or the reversible upgrading of the fire resistance of heritage structures.

5.7.7

Incorrect reference to good practice

Some attempts to justify departure from relevant good practice refer to inappropriate guidance (e.g. standards written to address fire risk in premises with less significant fire hazards than those in question). For example, it may be the case that a duty holder in a hotel refers to guidance on offices, instead of guidance that addresses the risks commonly encountered in hotels (e.g. in offices occupants are usually awake and both familiar with and aware of their surroundings; in the case of hotels, occupants may be asleep, sensory impaired and/or unfamiliar with their surroundings). It is important that those assessing risk are mindful that the guidance they use, either directly or as a ‘benchmark’, is appropriate to the environment that they are considering. Another example might be to make reference to design solutions used elsewhere, but where the context is different in crucial ways. An example might be a railway rolling stock manufacturer who wishes to offer vehicles to the operator of an underground railway system. That rail system has been in operation for many years and the infrastructure is built to standards which are long superseded. While the vehicles might be entirely satisfactory when used on modern infrastructure, compliant with current standards, it may be necessary to compensate for the higher risk inherent in operating on much older infrastructure by reducing the fire risk associated with the rolling stock. In this case, comparison of the risk posed by a part of the system, rather than the whole system itself, is of questionable validity.

5.7.8

Not considering risk to particularly vulnerable occupants

When assessing fire risk, those undertaking the analysis should be fully aware of the occupancy profile of the premises. They should ensure that the assessment considers whether any occupants are likely to be present whose response to a fire emergency in the premises might be delayed, or whose ability to make good their escape might be impaired, by a sensory or physical impairment (whether permanent or temporary). Examples might include:

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This is not good practice and should be avoided. When using cba either qualitatively or quantitatively, the judgment should be made against the cost of the relevant works when they have been competently and correctly designed, supplied and installed, not against the cost of correcting works designed, supplied or installed incorrectly. To put it simply, one cannot use the consequences of a mistake or deliberate failure to observe good industry practice as input to a cba.

5-9

5-10 young children

——

the elderly

——

persons with a sight and/or hearing impairment

——

persons with restricted mobility (e.g. wheelchair users)

——

persons who are bed-ridden.

In all cases, it will be important for the risk assessment to consider the risk to each individual type of occupant and to conclude whether the existing or proposed risk reduction measures adequately control risk to an acceptable level. It is normally very important to consider whether relevant good practice exists and it would be appropriate to apply that good practice wherever it is reasonable to do so. If variation from that guidance is being considered, it is strongly recommended that those undertaking the risk assessment are able to construct a robust case for the proposed risk reduction measures being equivalent to that good practice. It is recommended that the assessors do not base the assessment only on the current occupants of the premises; one should also consider whether it is foreseeable that vulnerable occupants might be in the premises, even if they are not currently present. For example, if a building has step-free access to all or part of it, then it should be considered that wheelchair users might be found in all accessible parts of those premises, even if it is not intended (or evident) that they are, or if there is no particular reason for them to be in that part of the premises, or even if there is a claim that management procedures will prevent them from being present in those locations. Accessibility is growing in prominence as a key design consideration, and where accessibility is provided it should be assumed that it will be utilised. The risk assessment should therefore take into account the potential presence of persons with restricted mobility (including wheelchair users) and appropriate procedures and/or physical protection measures should be provided to ensure that they can be safely evacuated. It is unlikely to be acceptable to argue that, because few vulnerable people are likely to be in the premises, the probability of simultaneously: ——

having a fire of significant size and

——

having a vulnerable person in the premises

is so small as to render the cost of any fire risk reduction measure aimed solely at that group grossly disproportionate to the risk reduction achieved. This is not viewed as good practice, because it may place a vulnerable group at a significantly higher individual risk than other building occupants, and it fails to maintain risk at levels equal to or better than relevant good practice. Whether it can be

claimed that individual risk is low or not, this approach is unlikely to satisfy the test of societal concern, which makes its acceptability highly questionable. By making their premises accessible to those vulnerable groups, it is expected that the duty holder will take steps to reduce their risk from fire to a level comparable to that of the other occupants of the premises.

References BSI (2001) BS 7974: 2001 Application of fire safety engineering principles to the design of buildings. Code of practice (London: British Standards Institution) (Note: BS 7974: 2012 has been replaced by BS 7974: 2019) BSI (2003) PD 7974-7: 2003 Application of fire safety engineering principles to the design of buildings. Probabilistic risk assessment (London: British Standards Institution) (Note: PD 7974-7: 2003 has been replaced by PD 7974-7: 2019) BSI (2017a) BS 4971: 2017 Conservation and care of archive and library collections (London: British Standards Institution) BSI (2017b) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) BSI (2018) BS EN 16893: 2018 Conservation of cultural heritage. Specifications for location, construction and modification of buildings or rooms intended for the storage or use of heritage collections (London: British Standards Institution) DfT (2007) Highways Economics Note No. 1: 2005 Valuation of the Benefits of Prevention of Road Accidents and Casualties (London: Department for Transport) FM Global (2015) Property Loss Prevention data sheet 1-22: Maximum foreseeable loss (Johnston, RI) FSEG (2017a) EXODUS introduction. Available at http://fseg.gre.ac.uk/ exodus/index.html FSEG (2017b) SMARTFIRE introduction. Available at http://fseg.gre. ac.uk/smartfire/index.html Gadd S, Keeley D and Balmforth H (2003) Good Practice and Pitfalls in Risk Assessment Health & Safety Laboratory Research Report 151 (Sudbury: HSE Books) HSE (2001) Reducing Risks, Protecting People: HSE’s decision-making process (Sudbury: HSE Books) LPC (2000) LPC Design Guide for the Fire Protection of Buildings (Borehamwood: Loss Prevention Council) Tavares RM and Galea ER (2009) ‘Evacuation modelling analysis within the operational research context: A combined approach for improving enclosure designs Building and Environment 44 (5) 1005–1016 Tavares RM, Tavares JML and Parry-Jones SL (2008) ‘The use of a mathematical multicriteria decision-making model for selecting the fire origin’ Building and Environment 43 (12) 2090–2100

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——

Fire safety engineering

6-1

6

Fire dynamics

Fire dynamics describes the complex subject of fire behaviour and encompasses chemistry, physics, heat transfer and fluid dynamics. With knowledge of fire dynamics, a more fundamental approach to fire safety engineering can be applied at the design stage. It can also be used in response to an incident that has highlighted a fire hazard with a view to investigation and research. Fire is a chemical reaction between combustible species and oxygen from the air, which produces heat, the mode of burning depending more upon the physical state and distribution of the fuel and its environment than on the chemistry. An example often quoted is that a wooden log is difficult to ignite but thin sticks can be ignited easily and will burn fiercely when piled together. This section aims to present a basic understanding of the processes which govern fire and smoke development and to guide the reader in the available techniques for calculating the important parameters. It is not exhaustive and much use will be made of references to more detailed publications, which should be consulted for further information. Important references include Drysdale’s An Introduction to Fire Dynamics (2011) and Karlson and Quintiere’s Enclosure Fire Dynamics (2000). It should be noted that most fire safety engineering calculations are based upon experiment and testing. Therefore, the validity of such calculations will be limited and extrapolation beyond these limits may not be appropriate. It may be prudent to carry out further testing or modelling to validate the design parameters used, if considered necessary by designers or approvers. This can be in the form of physical testing or computational simulation.

6.2 Ignition Ignition is the process whereby a material passes from a relatively inert state to one where a reaction takes place that can produce temperatures significantly in excess of ambient. Ignition of most materials requires the application of an external source of heat, the incident heat flux causing the surface temperature of the fuel to rise. In the case of flammable liquids, this liberates vapour; solid materials decompose to release flammable volatiles. Combustion takes place in the gas phase above the fuel surface. Whether or not ignition occurs, and whether the reaction then becomes self-propagating, depends on a complex heat balance between the incident heat flux, the convective and radiative heat gains by the fuel, and the heat losses to the surroundings. For the types of materials commonly found

in the construction/building environment, it has been found by experiment that the critical radiant heat flux for ignition where there is already a flame present (i.e. pilot ignition) is in the range 10–30 kW · m–2. For spontaneous ignition, where there is no flame present, critical heat fluxes are higher, at about 40 kW · m–2. In both cases the actual values depend on the fuel.

6.3

Fire growth

For sustained combustion to occur, oxygen, heat and a fuel source must all be present. The removal of any one of these will terminate the reaction. The burning process in fires involves pyrolysis (i.e. thermal decomposition) of fresh fuel. This pyrolysis will produce volatiles from the surface of the fuel and these gases will oxidise in the flaming region, generating combustion products and releasing heat. If there are no control measures present, and both air and fuel are available, it must be assumed that the fire will continue to grow in a manner that may be predictable, based on experimental or other evidence. However, the calculation of flame spread or fire growth rates from first principles is not easy. Characteristic fire growth rates are given in section 6.5.3.1.

6.4

Compartment fires

6.4.1 General A distinction may be made between fires arising in the open, where radiated heat is lost to the surroundings, and fires which occur in confined spaces or compartments. In the latter, heat is transferred to the compartment walls by radiation from the fire and also by convection from the hot gases that accumulate within the compartment. Reradiation from these hot boundaries can significantly increase the heating of combustibles in the room. If there are openings to the compartment to permit the inflow of air, and if there is sufficient fuel, the fire will continue to grow and the temperature of the hot gas layer at ceiling level will rise. Ultimately, the point may be reached where the downward radiation from this layer is so intense that all of the remaining fuel in the compartment becomes involved. This occurs at layer temperatures of 500–600 °C (see section 6.8.4). The transition from growing to fully developed fire happens very rapidly, and the event is often referred to as ‘flashover’. Following flashover, the rate of heat release of the fire increases rapidly and the oxygen content decreases.

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6.1 Introduction

Fire safety engineering Flashover is unlikely to occur in large or tall compartments with small fire loads, such as airport concourses, multistorey malls and atria protected from fire in an adjacent enclosure. There is the potential for fire spread beyond the initial fire source by radiative heat transfer, and therefore the risk of fire spread within large or tall compartments cannot be discounted. Therefore, the siting of combustibles in such spaces should be considered as part of the design process, and further guidance on this issue is given in Annex B of BS 9999: 2017 (BSI, 2017). However, given sufficiently high fire loads, such as in high bay warehouses, fire development may reach flashover conditions.

Flashover

Initiation

Growth

Steady-state

Decay

Time

Fuel bed-controlled fires have excess air available and their combustion rate, heat output and growth are limited by the fuel being burnt. All the burning takes place within the fire compartment.

Figure 6.1  Stages of development of a fire

Anyone remaining in a compartment which has undergone flashover is unlikely to survive. The risk of fire spread from the compartment to adjacent areas increases greatly and the structure becomes heated.

6.5

Because radiation from the smoke layer is the driving force in initiating flashover, any factors that promote loss of heat from the layer will tend to reduce the risk of its occurrence. In particular, in compartments that are high or wide and where there is limited material to burn, the smoke will be unlikely to reach temperatures that would result in flashover. Flashover is unlikely to occur where sprinklers are operating.

6.5.1 General

A useful way of showing the development of a compartment fire is illustrated in Figure 6.1. The stages are: ——

Initiation: the fire will grow only slowly as a result of flame spread over the item first ignited.

——

Growth: the fire will grow more quickly and begin to spread to other items, but remain effectively local.

——

Fully developed steady-state or post-flashover: all the combustibles are involved and flames appear to fill the entire volume; the average temperature is very high.

——

Decay: at this stage, the average temperature of the fire has fallen considerably from its peak value.

6.4.2

Limiting fire development

Once flashover has occurred, the development of the fire in a compartment will be limited by the in-flow rate of air (i.e. ventilation-controlled fires) or combustible material (i.e. fuel bed-controlled fires), or by firefighting. Ventilation-controlled fires have their combustion and heat output controlled by the amount of air reaching the fire, which is governed by the openings to the fire compartment. A ventilation-controlled fire usually means that the whole compartment is involved and flashover has occurred. Flames may project from the openings of the compartment, and significant combustion of heated fuel gases may take place outside, where they first come into contact with sufficient oxygen.

Calculation of fire parameters

The expressions given in the following sections have previously been published in the technical literature of the fire safety industry. They are the result of experiment and observation and therefore each has its limitations.

6.5.2

Design fires

The design fire is characterised by the variation of heat output with time. In the initial stages of fire growth it is assumed that the fire is well ventilated, its rate of burning being characterised by the type, amount and configuration of the fuel. The fire is assumed to be confined initially to a single object or group of objects. If unchecked, the fire may spread to adjacent objects and, once flames reach the ceiling, flashover may occur and the whole room or compartment becomes involved in a fully developed fire. After flashover, the rate of smoke production can be so great that smoke control becomes impracticable. However, if there is a post-flashover fire in a small room, it may be possible to design a smoke control system that protects an adjacent large-volume space, such as an atrium, when smoke emerges from a window or doorway of the room. Types of smoke control system and their practical application are considered in chapter 10: Smoke ventilation. The parameter that governs most strongly the way in which a fire and its products behave is its rate of heat release, commonly termed ‘fire size’. In order to carry out a fire engineering design, it is essential to define at the outset a series of design fires that represent the worst fire situations likely to arise in the building under consideration. Information is available, both experimental and theoretical, that may be used by the designer in selecting suitable design fires. Pre-flashover fires are considered in section 6.5.3; post-flashover fires are dealt with in section 6.5.4.

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Temperature

6-2

Fire dynamics

6.5.3

6-3

Pre-flashover fires

The design fire size will depend on the characteristics of the type and arrangement of the fuel and may be categorised for design purposes as one of the following: ——

a growing fire

As a result of measurements, it has been found possible to characterise fire growth rates in different ways:

——

a fire having a fixed size for a finite time

——

t-squared fires (UK and USA)

——

a steady-state fire.

——

t-cubed fires

Fixed size or steady-state fires will usually have grown to some limit, further extension being restricted by one or more of the following:

——

standard fires, types 1, 2 and 3 (Japan)

——

growing fires (Australia).

——

fire control activities, such as automatic (or manual) fire suppression

——

sufficient space separation to neighbouring combustibles

This Guide concentrates on the method of determining fire growth rates used in the UK and USA. Fire growth rates for various types of fire have been compared by Bukowski (1993) (see Figure 6.2).

——

for hydrocarbon pool fires, the leakage versus burning rate or, if bunded, the extent of the bund.

6.5.3.1

Fire growth rate

Much experimental work has been carried out in the USA on heat release rates in fires as a function of time. Some of the results are summarised in NFPA 92 (NFPA, 2015). Additional data on real fires are available from the National Institute for Standards and Technology (NIST) (www.nist. gov) and BRE (www.bre.co.uk).

A fixed design fire size applicable to all situations is not feasible, especially when designing for means of escape or estimating the activation time of automatic detectors. It is more realistic to design based on a growing fire, using the widely accepted t-squared growth rates, and a maximum heat release rate. It is not possible to predict the length of the incubation period (see Figure 6.3), and therefore it is recommended that this period is ignored in this approach. This provides inherent conservatism to the design calculation.

These large-scale tests show fire growth and decay for a series of objects and groups of objects. These data show that fire curves are closer to spikes, with rapid growth and rapid decay. The fact that heat release rate peaks may be very high but last for a limited time should be taken into account when designing fire systems and allowing for appropriate safety factors.

A great deal of experimental work has been carried out on rates of heat release from different materials when burned in fire tests. Much of this information is summarised in the SFPE Handbook of Fire Protection Engineering (SFPE,

In many instances, building fires go through an initial incubation period, when the growth rate is significantly

30

US slow US medium

★ 25



Heat release rate / MW







✻

US fast

★

US ultra-fast

★



15



★



20



Australia <1140 MJ·m–2

★



Australia 1140 – 2280 MJ·m–2

★

Australia 1140 – 4560 MJ·m–2



10

✻

★

Japan (t2)

✻ 

★

5

 ★

★  ✻ 0★ 0

✻

★

 ★ ✻

★  ✻ 50

★  ✻  ✻ 100

✻ 150

✻

✻

✻

200 250 Time / s

✻

✻

300

✻

✻

✻

Japan (No. 1) 

350

Figure 6.2  Bukowski’s comparison of idealised fire growth curves (Bukowski, 1993)

400

450

Japan (No. 2)

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2016). Many of the measurements relate to heat release rates from goods such as those which might be stored in warehouses. There is also a significant body of data on foam-filled furniture (Babrauskas, 1986).

6-4

Fire safety engineering Table 6.1  Characteristic growth time for various classes of fire

It has been found that, after this incubation period, the heat release rate grows approximately as the square of the time (NFPA, 2015), i.e. Qt = at2



(6.1)

Fire class

Characteristic growth time, tg / s

Constant a / kW · s–2

Ultra-fast

 75

0.1876

Fast

150

0.0469

Medium

300

0.0117

Slow

600

0.0029

Table 6.2  Growth rates for growing fires

where Qt is the total heat release rate of the fire (kW), a is a constant (kW · s–2) and t is time (s).

Building area providing fuel

Growth rate

Dwelling

Medium

Figure 6.3 illustrates t-squared fire growth. The growth parameter for a t-squared fire is defined by the time taken for the heat output to reach 1055 kW (i.e. approximately 1 MW). This is known as the characteristic growth time. It has been suggested that fires may be conveniently classified as ‘slow’, ‘medium’, ‘fast’ and ‘ultra-fast’, depending on the characteristic growth time.

Office

Medium

Shop

Fast

Warehouse

Ultra-fast*

Hotel bedroom

Medium

Hotel reception

Medium

Assembly hall seating

Medium–fast

Table 6.1 gives the characteristic growth time, tg, and the corresponding values of constant a for the various classes of fire. The fastest burning upholstered sofas and plastic goods stacked to a height of about 4.5 m give ‘ultra-fast’ growth rates, while other upholstered furniture and lower piles of plastic goods give ‘fast’ rates. Tightly rolled paper produces a ‘slow’ growth rate. Experiments on burning computer workstations suggest ‘medium’ to ‘fast’ growth rates.

Picture gallery

Slow

Display area

Slow–medium

*  Depends on fire load

Fire growth depends on the type of fuel and its arrangement, but some growth rates are suggested in Table 6.2, based on the experimental evidence available.

3

Heat release rate / MW

Continuously growing fire 2

1

Incubation period

0 Time

Growth time Effective ignition time

Figure 6.3  Illustration of t-squared fire growth. (Reprinted with permission from NFPA 92-2018 Standard for smoke control systems, Copyright © 2017, National Fire Protection, Quincy, MA. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.) (Original in Imperial units.)

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slower than the t-squared rates, such as the initial period in small or smouldering fires. This period (see Figure 6.3) is of indeterminate length and is ignored for design purposes, although the fire may be detected during this period by the occupants or by an automatic detector, if adjacent to the source.

Fire dynamics

6-5

Research suggests that for a high rack warehouse (fire in the flue) the growth rate can be modelled as a ‘t-cubed’ fire, given by (Ingason, 1993) as Qt = 0.045 t3 (6.2)

For this rapid fire growth, the incipient stage is significant and the curve is valid up to 10 MW for a 10 m high rack (there are no data for fires greater than 10 MW). For a fire in the racking flue, the amount of entrainment of fresh air in the rack plume is restricted, compared to that for a fire on the face of the rack. For a typical cellulosic fire, racking flue entrainment can be estimated as

mflue = Q1.08 # 10-4V t3

(6.3)

where mflue is the mass of smoke produced prior to sprinkler operation for a fire in a racking flue (kg · s–1) and t is time (s) (CIBSE, 2010: appendix 6.A1). Equations 6.2 and 6.3 are to be used together. 6.5.3.2

Unit heat release rate

Estimates of heat release rates per unit floor area or per unit fuel area for various commodities and materials can be gained from the SFPE Handbook (SFPE, 2016) and NFPA 92 (NFPA, 2015). Survey data from actual occupancies in use have also been published (BSI, 2002a). Measured survey loads, q, are given in MJ per square metre of floor area. By assuming a conservative burn-out time of 20 minutes (i.e. 1200 s), the unit heat release rate can be estimated for well-ventilated compartment fires:

Qu = q 1200 (6.4)

where QU is the unit heat release rate (kW · m–2) and q is the measured survey load (kJ · m–2). Note that the measured survey load is usually given in MJ · m–2 and must be converted to kJ · m–2 for use with equation 6.4. Some commonly used values of heat release rate are shown in Table 6.3. 6.5.3.3

Steady-state fires: not sprinklered

Once the fire has spread from item to item until all the available fuel is burning, the heat output will reach a steady value, eventually declining as the fuel decays. The estimation of the steady value is given in section 6.5.4. 6.5.3.4

Steady-state fires: sprinklered

For design purposes, the value of Q may be assumed as steady after operation of the first sprinkler (see section 6.6.3 regarding sprinkler response and activation). Table 6.3  Commonly used values of heat release rate (NFPA, 2015) Occupancy

Unit heat release rate, QU  / kW · m–2

Offices

290

Shops

550

Industrial

260

Hotel rooms

249

6.5.3.5

Transient fires

To simplify calculations of smoke filling during the transient phase (see section 6.8), an average value of Q may be used:

Qt, ave =

#0 t Qt dt t

(6.5)

where Qt, ave is the average total heat output of the fire (kW) and t is time (s). For t-squared fires:

Qave = 333 Qt tgV2 (6.6)

where tg is the characteristic growth time (s). Values of tg are given in Table 6.1.

6.5.4

Post-flashover fires

6.5.4.1

Condition for flashover

For design purposes, it may be assumed that flashover does not occur if the smoke layer at ceiling level is at a temperature of less than 600 °C (McCaffrey et al., 1981). A method for calculating this temperature is given in section 6.7.5. Note that in the plume above a fire the temperature at the tip of intermittent flames is about 350 °C and at the tip of sustained flames is about 550 °C. If a correctly designed and maintained sprinkler system (or other approved fire suppression system designed to achieve fire control) operates, it may be assumed that flashover will not occur, since sprinklers are designed to operate while the smoke layer is at a temperature much lower than the generally accepted flashover temperature of 600 °C. Because flashover is such a serious event, a great deal of research effort has been invested in methods to predict the conditions which give rise to it. A presentation and comparison of the different correlations which are available are given in the SFPE Handbook (SFPE, 2016). The simplest of these relates the heat release rate required for flashover, Qf (kW), to — what has become known as the ventilation factor (Avo √ ho), such that

Qf = 600 Avo ho (6.7)

where Qf is the heat release rate required for flashover (kW), Avo is the area of the opening to the compartment (m2) and ho is the height of the opening (m).

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However, it should be noted that the validity of this assumption is the subject of some considerable debate in fire engineering circles and may be potentially open to some criticism. From the agreed value, it is assumed that no further items of fuel ignite, and the value of mass flow in the plume is calculated accordingly. After operation, it may be assumed that the sprinklers cool most of the smoke layer to a temperature less than the operating temperature of the sprinklers. For calculation purposes, an average smoke layer temperature of 100 °C may be assumed with conventional sprinkler heads, while the sprinklers are operating.

6-6

Fire safety engineering

6.6

The total heat release rate is given by

Qt = Hc # R (6.8)

6.5.4.2

Ventilation-controlled fires

The mass rate of burning is given by

R = 0.02 !Ao ho1/2 QAt - AoVQw / dV$ (6.9) 1/2

where R is the mass rate of burning (kg · s–1), Ao is the area of ventilation opening (door, window etc.) (m2), ho is the height of ventilation opening (m), At is the area of room surface (wall, floor, ceiling) (m2), w is the width of wall containing the opening (m) and d is the depth of room behind the opening (m) (Thomas et al., 1963). Effective values for these parameters for rooms with more than one opening are beyond the scope of this document but can be derived using the procedures given in the Appendix to this chapter. Equation 6.9 has been derived from experiments with wood cribs and can be used for most types of fire load found in houses, offices and shops. Conventionally, fire load may be expressed in terms of the equivalent weight of wood. If expressed in MJ or MJ · m–2, the fire load may be converted to kg or kg · m–2 of wood by dividing by 18  MJ · kg–1; for example, 360 MJ · m–2 is equivalent to 20  kg · m–2 of wood. 6.5.4.3

Fuel bed-controlled fires

With low values of fire load, equation 6.9 overestimates the mass rate of burning by a factor of 2 or 3. An effective fire duration of 20 minutes may be assumed, with R then being given by

R = L 1200 (6.10)

where R is the mass rate of burning (kg · s–1) and L is the total fire load (kg), or

L = QL AfV Af (6.11)

where Af is the floor area (m2) (Law, 1978). Values of L / Af (kg · m–2) are derived from surveys or design data. Where such data are expressed in MJ · m–2, they may be converted by dividing by 18 (see section 6.5.4.2). For design purposes, R should be calculated from equations 6.9 and 6.10 and the lower value adopted. If the heat release rate is needed for the approving authority, this can easily be calculated by multiplying R by the heat of combustion of the fuel.

The following paragraphs deal with the effect of sprinklers on fire growth. Sprinkler design is considered in detail in chapter 11: Fire suppression.

6.6.1

General principles

The plume of hot smoky gases from a fire rises as a result of its buoyancy. When it hits the ceiling the plume turns and spreads laterally, where it may interact with sprinklers, eventually causing them to operate. The time to sprinkler operation depends on: ——

fire growth rate

——

sprinkler location

——

sprinkler sensitivity.

6.6.2

Sprinkler location

As the smoke plume rises from a fire, it draws in air from the surroundings, which causes it to cool. Therefore, the higher the ceiling, the lower will be the temperature of the smoke that reaches the sprinklers. Additional cooling then occurs as the smoke spreads laterally. Clearly, the hotter the smoke, the more rapidly the sprinkler will operate.

6.6.3

Sprinkler and smoke detector sensitivity

In order to operate and release water onto a fire, a sprinkler must be heated to its operating temperature, usually about 70 °C, at which point a temperature-sensitive element is designed to fail, e.g. a solder link melts or a glass bulb breaks. The rate at which the element heats up when exposed to hot smoke depends on its shape and mass. A heavy, short bulb will take longer to reach a given temperature than a light, slim bulb. The parameter used to describe sprinkler sensitivity is known as the response time index (RTI), see chapter 11: Fire suppression. Sprinklers with RTI values below 50 m1/2 · s1/2 are described as having a quick response, while those with values up to 350 m1/2 · s1/2 are regarded as having a standard response (BSI, 1999). Concealed sprinkler heads are not designated a thermal sensitivity response rating by manufacturers due to the nature of the sprinkler assembly. However, work by Annable (2006) determined rti values for the overall assembly arrangement for a limited number of concealed sprinkler head types. This work demonstrated that for a concealed sprinkler with a temperature-sensing element with a quick response, the rti of the overall arrangement was not quick response, but was within the expected range of a standard response head. Common practice assumed in design is that the rti of the concealed sprinkler head temperaturesensing element should be quick response, but with the overall assembly arrangement assumed to be a standard response head, and the value of rti used for any concealed sprinkler activation calculation should be discussed and agreed with the approving authorities.

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where Hc is the heat of combustion (kJ · kg–1) and R is the mass rate of burning (kg · s–1). (The heat of combustion, Hc, is discussed in chapter 10: Smoke ventilation, and values for various materials are given in PD 7974-1: 2003 (BSI, 2003a) or the SFPE Handbook (SFPE, 2016). The rate of burning, R, is considered in sections 6.5.4.2 and 6.5.4.3.)

Effect of sprinklers

Fire dynamics

6-7

Note that a smoke detector can be considered as an equivalent heat detector having an RTI of 0.5 m1/2 · s1/2 and a fixed temperature rise of 13 °C (Evans and Stroup, 1985).

6.6.4

6.7

Smoke plumes

6.7.1

Introduction to smoke ventilation calculations

For most smoke ventilation calculations (see chapter 10: Smoke ventilation), it is essential to know: (a)

the plume type; for example, an axisymmetric plume (see section 6.7.3) or a plume flow from an opening (see section 6.7.4) — the entrainment equations associated with different plume types calculate the mass flow rate of smoke produced (msmoke)

(b)

the temperature of the hot gases (see section 6.7.5) and

(c)

the volume flow rate of smoke (see section 6.7.6).

Effect on fire size

Real fire tests are rarely performed. However, should a series of tests be carried out on the intended typical layout (i.e. room dimensions, fuel type etc.) and if these tests show that a fire will be quickly suppressed with the installed sprinkler system, then it seems reasonable to assume that combustion effectively ceases when the sprinklers operate. In a room equipped with sprinklers, a fire may grow until the heat in the plume sets off the first sprinkler heads. The effect of the sprinklers on the design fire size can be taken into account by assuming that the fire stops growing when the sprinklers are activated. The design fire is then estimated as the size the fire has grown to at the moment of sprinkler actuation unless there is reason to suspect that the fire will continue to spread after the sprinklers have been actuated. Since the sprinklers will cool most of the smoke layer to below 100 °C, flashover is not likely to occur where they are installed. It can then be assumed conservatively that the fire will have a constant rate of heat release (see Figure 6.4). Alternatively, it could be assumed that, after sprinkler activation, the heat output will slowly decrease. Experiments in small compartments have suggested that fire heat release rates will fall by 50% over a period of a few minutes (Madrzykowski and Vettori, 1991). In some circumstances, it may be assumed that the fire continues

By using this methodology, the effectiveness or performance of a smoke ventilation system can be determined. Section 6.7.7 provides information on the flowing layer depth, which can be used in conjunction with the guidance given in chapter 10: Smoke ventilation to calculate the depth of channelling screens etc. The proportion of the total heat release rate in the plume varies with the type of combustible material and the characteristics of the compartment (for flow out of an opening). For the purposes of design, the convective portion (Qp) can be assumed to be 66% of the total heat output of the fire (Qt) (SFPE, 2016).

6.7.2 Entrainment It is assumed that the volume of smoke produced is equal to the amount of air entrained into the plume. The concentration of smoke particles and toxic products depends on the type of fuel and ventilation rate. Figure 6.4  Typical fire model Steady-state fire

Fire growth

t2 growth period

Decay period

Design fire Natural fire It may be assumed that decay occurs after sprinkler activation or after a period of steady-state burning; conservatively, it may be assumed that there is no decay Time

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It is possible to use computer software to assess the effect of fire growth, sprinkler location and sprinkler sensitivity on sprinkler activation as an alternative to hand calculation. One such computer zone model is B-RISK (Wade et al., 2013), which can be used to predict sprinkler activation times and corresponding fire sizes at sprinkler activation. B-RISK utilises the differential equation describing the temperature of the sprinkler sensing element based on the rti concept of Heskestad and Bill (1988), incorporating the gas temperature and velocity in the vicinity of the sprinkler sensing element, using the unconfined ceiling jet correlation by Alpert in chapter 14 of the SFPE Handbook (SFPE, 2016).

to grow but at a slower rate. Whether or not such an assumption is made, the fire may continue to burn until all the fuel is consumed.

6-8

Fire safety engineering

For the purposes of smoke ventilation design, the zone of interest is above the flame tip height.

6.7.3

Axisymmetric plume

An axisymmetric plume is expected for a fire originating on the floor away from the walls. It has a virtual point source. Air is entrained from all sides and along the entire height of the plume until the plume becomes submerged in the smoke layer beneath the ceiling. The choice of calculation depends on the height of the plume above the fuel surface (z) and the linear dimension of the source (Ds) (BSI, 2002b). Typically, the fuel surface is taken as the finished floor level and the linear dimension is taken as the diameter of the fire, unless otherwise specified by the designer. The interface between the ‘far field’ and the ‘near field’ is often assumed to be at the flame tip height, with the ‘far field’ above the flame height and the ‘near field’ below it. See section 6.9.3 for further guidance on calculating the flame height of the plume.

In the ‘far field’,

msmoke = 0.071 Q1p/3 Qz - z0V5/3 (6.12)

where msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of the fire (kW), z is the height of the plume above the fuel surface (m) (see Figure 6.8) and z0 is the height of the virtual source above the fuel surface (m),

z0 =- 1.02 Ds + 1.38 Q* 5/3 D s

(6.13)

where Ds is the linear dimension of the source (typically diameter) (m), and

Q* =

Qt Qt = t0 T0 cp g1/2 D 5s /2 1110 D 5s /2

(6.14)

where Q* is a dimensionless heat release rate, Q is the total heat output of the fire (kW), g is acceleration due to gravity (typically 9.81) (m · s–2), t0 is the ambient air density (typically 1.204 at 20 °C) (kg · m–3), T0 is the ambient air temperature (K) and cp is the specific heat of air at constant pressure (typically 1.006) (kJ · kg–1 · K–1) (Zukoski et al., 1981). 6.7.3.2

Near field

In the ‘near field’,

6.7.4

Flow from an opening

This Guide recommends that the following equations be used to calculate flow from an opening. It is, however, acknowledged that there are alternative calculation methods (Morgan et al., 1999; Kumar et al., 2008; NFPA, 2015). Spill plumes occur when the flow of gases leaving a fire compartment opening rotate around and vertically rise from the opening or balcony edge into the adjacent space. The ascending spill plume entrains air as it rises. The total flow in the spill plume depends on the size of the opening, the convective enthalpy of the gases flowing through the opening, the presence of a balcony, downstand or other construction element that affects either the flow through the opening or the subsequent entrainment into the rising spill plume, and the vertical height between the spill edge and the smoke layer interface in the adjacent space. 6.7.4.1

Flow from an opening of a room

The horizontal mass flow from an opening of a room containing a fire (see Figure 6.5) is given by

mo = 0.09 Qp1/3 Wo2/3 ho (6.16)

where mo is the horizontal mass flow of smoke from the room opening (kg · s–1), Qp is the convective heat output of fire (kW), Wo is the width of the opening (m) and ho is the height of the room opening (m).

Far field

6.7.3.1

where msmoke is the mass flow of smoke in the plume (kg · s–1), p is the perimeter of the source (m) and z is the height of the plume above the fuel surface (m) (Thomas et al., 1963).

msmoke = 0.19 p z3/2 (6.15)

The smoke layer depth below the compartment opening, do (m) (see Figure 6.5), is given by

do =

1 mo 2/3 & (6.17) # Cd 2Wo

where mo is the horizontal mass flow of smoke from the room opening (kg · s–1), Wo is the width of the room opening (m) and Cd is 1.0 for a flat ceiling below the spill edge or 0.6 for a downstand below the spill edge (BSI, 2003b). 6.7.4.2

The adhered spill plume

Adhered spill plumes are applicable where there is a wall or solid construction directly above the spill edge, preventing entrainment from one side and leading to the plume adhering to the wall. Adhered plumes are also known as single-sided plumes, since entrainment occurring above the spill edge occurs only on one face (see Figure 6.6). Calculating total flow (Ws / ds ≤ 13) Where Ws / ds ≤ 13, the entrainment for the adhered plume is given by

msmoke = 0.3 Q1p/3 Ws1/6 d1s /2 zs + 1.34 ms (6.18)

where msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of fire (kW), Ws is the width of the flow at the spill edge (m), ds is the

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At a given height, entrainment depends on the heat output and, at small plume heights, on the geometry of the source. At large plume heights, entrainment is equivalent to that above a point source. The plume itself may be in the room of fire origin (e.g. axisymmetric plume directly above the source) or it may be outside the room, having emerged from an open door or window (e.g. a spill plume).

Fire dynamics

6-9

mo, do

Wo

Qp

Compartment opening

Fire compartment tment Front view

ho

Figure 6.5  Plume from a room opening

Section

msmoke Adhered spill plume zs Rising gp plume Wall

ms, ds, hs

Spill edge

Ws

Qp

Fire compartment parrtment Figure 6.6  Adhered spill plume Front view

smoke layer depth below the spill edge (see equation 6.19) (m), zs is the height of rise from the spill edge to the underside of the smoke layer over which entrainment can occur (m) and ms is the mass flow of smoke in the smoke layer below the spill edge (see equation 6.20) (kg · s–1),

1 ms 2/3 ds = & (6.19) # Cd 2Ws

where Cd is 1.0 for a flat ceiling below the spill edge or 0.6 for a downstand below the spill edge, and

ms = 0.09 Q1p/3 Ws2/3 hs (6.20)

where hs is the height of the spill edge above the level of the fire (m) (Harrison and Spearpoint, 2010a). Calculating total flow (Ws / ds > 13) Where Ws / ds > 13, the entrainment for the adhered plume is given by

msmoke = 0.08 Qp1/3 Ws2/3 zs + 1.34 ms (6.21)

where msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of fire (kW), Ws is the width of the flow at the spill edge (m), zs is the height of rise from the spill edge to the underside of the smoke layer over which entrainment can occur (m) and ms is the mass flow of smoke in the smoke layer below the

Section

spill edge (see equation 6.20) (kg · s–1) (Harrison and Spearpoint, 2010a). Large entrainment heights For large entrainment heights, where zs > ztrans, the plume flow becomes axisymmetric in nature, and the total mass flow in the adhered spill plume is given by equation 6.12, with z0 taken to be zero. The transition height ztrans is calculated as (Harrison and Spearpoint, 2010b) 6.7.4.3

ztrans = 3.4 QWs2/3 + 1.56 ds2/3V (6.22) 3/2

The balcony spill plume

Balcony spill plumes are applicable where a balcony projects beyond the compartment opening and there is no wall or solid construction directly above the spill edge, therefore allowing entrainment to occur from both sides of the rising plume. Balcony plumes are also known as double-sided plumes, as entrainment occurring above the spill edge occurs on both faces (see Figure 6.7). Channelling screens (or side walls) below the level of the spill edge and extending from the compartment opening can be used to reduce the lateral spread of the spill plume, thereby reducing the amount of entrainment above the spill edge.

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Rising plume

6-10

Fire safety engineering

msmoke

Balcony spill plume

Rising plu plume me

zs

Balcony

Balcony

Channelling screen

Ws

Room opening

ms, ds, hs

Spill edge

Qp

Channelling elling screen en

Front view

Figure 6.7 Channelled balcony spill plume

Section

Channelled balcony spill plume

6.7.5

The total flow in a channelled balcony spill plume is given by

The excess average temperature of the hot gases can be calculated using the following equation:



msmoke = 0.16 Q1p/3 QWs2/3 + 1.56 d2s /3V zs + 1.34 ms (6.23)

where msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of the fire (kW), Ws is the width of the flow at the spill edge (i.e. separation between channelling screens) (m), ds is the smoke layer depth below the spill edge (see equation 6.19) (m), zs is the height of rise from the spill edge to the underside of the smoke layer over which entrainment can occur (m) and ms is the mass flow of smoke in the smoke layer below the spill edge (see equation 6.20) (kg · s–1) (Harrison and Spearpoint, 2008). Note that for large entrainment heights, where zs> ztrans, (see equation 6.22) the plume flow becomes axisymmetric in nature and the total mass flow in the adhered spill plume is given by equation 6.12, with zo taken to be zero.



Smoke temperature

i=

Qp msmoke cp (6.25)

where msmoke is the mass flow of the smoke (kg · s–1), Qp is the convective heat output of the fire (kW), cp is the specific heat of air at constant pressure (kJ · kg–1 · K–1) and i is the excess average temperature (°C). Smoke temperature can be found by adding the ambient temperature of the air to the excess temperature (i). The axial plume temperature is given by

Tc = 2i + T0 (6.26)

where Tc is (absolute) axial temperature (K) and T0 is ambient air temperature (K).

No channelling screens below balcony Where there are no channelling screens below the balcony, the entrainment in the vertical plume is given by   msmoke = 0.16 Q1p/3 Q!Wo + b$2/3 + 1.56 d2o/3V zs + 1.34 mo (6.24) where msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of fire (kW), Wo is the width of the flow at the compartment opening (m), b is the breadth of the balcony (m), do is the smoke layer depth below the compartment opening (see equation 6.17) (m), zs is the height of rise from the spill edge to the underside of the smoke layer over which entrainment can occur (m) and mo is the mass flow of smoke in the smoke layer below the compartment opening (see equation 6.16) (kg · s–1) (Harrison and Spearpoint, 2010c). This equation is limited to cases where Wo ≥ 2b. It has not been verified for cases where a downstand exists prior to the spill edge, so should not be applied in that situation.

6.7.6

Volume flow rate of smoke

The volume flow rate of smoke is



V = msmoke

T t0 T0 (6.27)

where msmoke is the mass flow of smoke (kg · s–1), t0 is the ambient air density (typically 1.204 at 20 °C) (kg · m–3), T0 is ambient air temperature (K) and T is smoke temperature (K).

6.7.7

Ceiling flow

Smoke will flow along the ceiling towards the vents or fans. This flow is driven by the buoyancy of the smoke. Irrespective of the reservoir or ventilation area, this flowing layer would still have a depth related to:

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b

Fire dynamics

6-11

the width of the reservoir

——

the temperature of the smoke, and

——

the mass flow rate of smoke.

h

z

This depth (dl) can be calculated as dl = T



Ml Tl 2/3 Y (6.28) ci l0.5 Wl

where dl is the depth of the flowing layer (m), Ml is the mass flow of smoke entering the layer (kg · s–1), Tl is the smoke layer temperature, c is the downstand factor, i is the excess temperature (e.g. rise of the smoke layer above ambient) (°C) and Wl is the width of the reservoir or the distance between channelling screens etc. (m) (BSI, 2003b). The downstand factor (c) is equal to 36 if a deep downstand is present at right angles to the flow, or 78 if no downstand is present at right angles to the flow. Ml would usually be taken to be the mass of smoke (msmoke), while Tl is taken to be the average temperature of the smoke plume as it enters the layer.

6.8

Accumulated ceiling layer

6.8.1 General The simplest zone model postulates that smoke rises to form a smoke layer of uniform depth and temperature with a substantially smoke-free layer below it. Smoke control systems are frequently required to maintain a minimum height for the smoke-free layer for a specified time (see chapter 10: Smoke ventilation).

6.8.2

Smoke filling times

For steady-state smoke control design, the entrainment equations may be used to calculate the smoke exhaust required.

zf Figure 6.8  Axisymmetric smoke filling a room with a low-level opening

Calculation routines for simple smoke filling can easily be written. A specified growth curve (e.g. fast, medium or slow) is subdivided into time elements and the entrainment equations are applied to each successive element. The layer depth in the reservoir at the end of each time element can then be taken as the starting point for the next element. The smoke layer will therefore consist of a number of elemental thin layers. In addition to adding elemental layers, elemental smoke extract may be subtracted, depending on what type of smoke control (if any) is applied. The output of the program can show, as a function of time, the following: ——

clear layer position

——

average temperatures

——

average visibilities.

6.8.3

Smoke filling: rooms with low-level ventilation openings

In such rooms, there is no smoke flow out of the low-level opening in the wall (see Figure 6.8). Heat loss to the room surfaces, which would result in slightly smaller fire development, is neglected. 6.8.3.1

Axisymmetric plume

The elapsed time at which the smoke-free layer is at a height z (m) is obtained by solving the differential equation

t0 Af

Qp dz + msmoke + = 0 (6.29) dt T0 cp

However, in some large spaces the volume of the smoke reservoir is so large that the size itself is a form of smoke control, since any smoke reservoir will take a finite time to become full. This time may be calculated by a number of methods, as follows:

where Af is the floor area of the room (m2), msmoke is the mass flow of smoke (kg · s–1), Qp is the convective heat output of the fire (kW), cp is the specific heat of air at constant pressure (kJ · kg–1 · K–1), t0 is the ambient air density (typically 1.204 at 20 °C) (kg · m–3), T0 is the ambient air temperature (K), z is the height of the plume above the fuel surface (m) and t is time (s).

——

The variation of msmoke with z is described in section 6.7.

——

by using a computer program to integrate calculated smoke volumes produced at small time intervals (e.g. the ‘available safe egress time’ (aset) model) by integrating various relationships mathematically, using simplifying assumptions, to derive a formula (see below).

The latter method, being more approximate in nature, will usually produce a conservative figure.

Solutions to equation 6.29 are given in Figure 6.9 for an axisymmetric plume (equation 6.12) and constant Qp, using dimensionless parameters as follows: Z=z h Q* = Qp "t0 T0 cp QghV1/2 h2% = Qp Q1100h5/2V

x = t Qg hV1/2 Qh2 AfV = Q3.13th3/2V Af

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——

6-12

Fire safety engineering

Figure 6.9 solves the following integral: x=



#z

1

6.8.3.2

dZ

(6.30) 0.195 QQ*V1/3 Z 5/3 + Q*

For a spill plume, such as given by equation 6.18, 6.21, 6.23 or 6.24, i.e.

Where the ceiling area and the smoke base area are both equal to Af , the average density of the smoke layer (ts) is given by

where a is a numerical factor, Ws is the width of the flow at the spill edge (m), msmoke is the mass flow of smoke in the plume (kg · s–1), Qp is the convective heat output of the fire (kW), zs is the height of the rise from the spill edge to the underside of the smoke layer over which entrainment can occur (m), the differential equation is

The average temperature of the smoke layer Ts (K) is given by

QTs - T0V T0 = 1 !1 - Q* x Q1 - ZV$ (6.32)



mCO = C QQp cp T0V (6.33)

Qp dzs + aQ1p/3 Ws2/3 zs + = 0 (6.37) dt T0 cp

where Af is the floor area of the room (m2), cp is the specific heat of air at constant pressure (kJ · kg–1 · K–1), t0 is the ambient air density (typically 1.204 at 20 °C) (kg · m–3), T0 is ambient air temperature (K) and t is time (s).

where mCO is the mass rate of generation of carbon monoxide (kg · s–1), the mass fraction in the ceiling layer (fm) is given by

fm = CQ* x Q1 - ZV (6.34)



t0 Af



Where an impurity such as carbon monoxide can be related to Qp by the expression

msmoke = aQp1/3 Ws2/3 zs (6.36)



ts t0 = 1 - Q* x Q1 - ZV (6.31)



Spill plume

The solution to this equation, with constant Qp, is

QQ*V1/3 x =



where C is given by equation 6.35b below. Note that

mCO = YCO R = YCO Qt Hc (6.35a)

where



C = YCO cp T0 Hc (6.35b)



a + QQ*V2/3 1 ln U 2 Z (6.38) a2 a2 Z + QQ*V2/3

Q* = Qp "t0 T0 cp QghV1/2 QhWsV% = Q Q1100 h3/2 WsV

1.0

Figure 6.9  Solutions of equation 6.29 for an axisymmetric plume

0.8

Value of Z

0.6

0.4

0.2 0.002 Q* = 0.5

0.2

0.1

0.05

0.02

0.01

0.0 0

2

4

6 Value of

[(Q*)1/3 τ

8 ]

10

12

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where Hc is the heat of combustion (kJ · kg–1), YCO is the mass yield of carbon monoxide per unit mass of fuel decomposed (kg · kg–1), R is the rate of burning (kg · s–1) and Q is the total heat output of the fire (kW).

where h is the floor-to-ceiling height of the room or the height of the ceiling above the base of the fire (m) (see Figure 6.8) and g is acceleration due to gravity (m · s–2).

Fire dynamics

6-13

x = t Qg hV1/2 QhWs AfV = 3.13 th1/2 Ws Af

a2 = a QT0 cp t20V / = 2.72 a 13

Z = zs h



QQ*V1/3 x = 0.303 QQWs2V1/3 t Af



where h is the floor-to-ceiling height of the room or the height of the ceiling above the base of the fire (m) and g is acceleration due to gravity (m · s–2). Equations 6.31, 6.32 and 6.34 can be used to calculate the average temperature, density and mass fraction by inserting the above values. This solution can be used where smoke flows from a communicating space into a large volume space, such as a shopping mall or atrium, by entering equation 6.18, 6.21, 6.23 or 6.24 and the dimensions Af and h of the large volume. Room filling with smoke extract from layer

6.8.3.3

A critical height of the smoke layer may be dictated by the need to keep it above eye level, inside a reservoir or, if otherwise too hot, well above head level. This is covered in further detail in chapter 10: Smoke ventilation. If the critical ‘clear layer’ height zc (m) would be reached before the occupants have escaped, then extract from the smoke layer can be provided, under steady-state conditions, as follows:

Mout = Mc (6.39)

where Mout is the mass flow rate of the vented smoke (kg · s–1) and Mc is the mass flow rate in the plume (kg · s–1) at height zc (m). The temperature of the vented smoke, Ts (K), under steady-state conditions will be given by

Ts - T0 = Qp QMout cpV (6.40)

and the volume flow rate, v (m3 · s–1), by

v = QMout t0V + Qp Qt0 T0 cpV (6.41)

With natural ventilation, the mass flow rate of the vented smoke is given by

Mout =

Cd Avo t0 !2gQh - zVQTs - T0V T0$1/2 Ts1/2 "Ts + QAvo AviV T0% 2

1/2

(6.42)

h1 A2 T = 22 1 (6.43) h2 A1 T0

where A1 and A2 are the areas of the lower and upper openings, respectively, and T0 and T1 are the lower and upper temperatures, respectively (Thomas et al., 1963). The sum of h1 and h2 must always equal the total distance between the upper and lower openings, and therefore the location of the neutral plane can be determined.

6.8.4

Smoke filling: open rooms approaching flashover

The calculations given in section 6.8.3 are not suitable where flames are approaching ceiling height or where smoke flows out of the wall opening. Under these circumstances, the following equation may be used:

Ts - T0 = 9.15 !QQ2p QAo h1o/2 ak AtVV$ (6.44) 1/3

where Qp is the convective heat output of the fire (kW), Ao is the area of ventilation opening (door, window etc.) (m2), ho is the height of the ventilation opening (m), ak is the effective heat transfer coefficient (kW · m–2 · K–1) and At is the area of the room surface (wall, floor, ceiling) (m2) (McCaffrey et al., 1981). Equation 6.44 was derived for At / (Ao ho1/2) values between 16 and 530 m–1/2. By substituting (Ts – T0) = 580 K in equation 6.44, the value of Q at flashover is given by

1/2 Qf = 505 QAo h1o/2 ak AtV (6.45)

where Qf is the convective heat output of the fire at flashover (kW). For [Anet / (Avo ho1/2)] < 10  m–1/2, the following value for Qf is recommended (Thomas, 1981):

Qf = 5.2 Anet + 252 Ao h1o/2 (6.46)

where

Anet = At + Ao (6.47)

The effective heat transfer coefficient is derived from

ak = Qmw tw cw tcV1/2 (6.48)

where Avo is the outlet ventilation area (m2), Avi is the ventilation inlet area (m2) and Cd is the discharge coefficient (BSI, 2002b). Values for discharge coefficients (between 0.6 and 0.9) are provided by the vent manufacturer.

where mw is the thermal conductivity of the wall material (kW · m–1 · K–1), tw is the density of the wall material (kg · m–3), cw is the specific heat capacity of the wall material (kJ · kg–1 · K–1) and tc is the characteristic burn time (s) (Drysdale, 2011).

The location of the extract points is determined by the location of the neutral plane, so that inlet air enters within

Table 6.4 gives values of ak for a characteristic burn time of 900 s.

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the negative pressure zone, and the extract air is taken from the positive pressure zone. The height of the neutral plane, therefore, must be known. If h1 and h2 are the distances from the neutral plane to the lower and upper openings, respectively, then

6-14

Fire safety engineering

6.8.7 Stratification

Material of surface

ak / kW · m–2 · K–1

Concrete

55 × 10–3

Brick

36 × 10–3

When the ambient temperature at ceiling level is significantly higher than at the level where the fire starts, the upward movement of the smoke plume may cease, due to lack of buoyancy, and stratification may occur.

Plaster

21 × 10–3

The maximum height of rise of an axisymmetric plume is given by

10–3

Plasterboard

13 ×

Fibre insulating board

5.2 × 10–3



Flashover is not expected until there are sustained flames at ceiling level. For axisymmetric sources of base dimension less than the ceiling height, the minimum condition for flashover is given by

hf 1 0.094 Q2p/5 (6.49)

zm = 5.54 Q1p/4 QdT/dzV-3/8 (6.53)

where zm is the maximum height of smoke rise above the base of the fire (m), Qp is the convective heat release rate (kW) and dT / dz is the rate of change of ambient temperature with respect to height (assumed to be linear) (K · m–1) (NFPA, 2015).

where hf is the height of the ceiling above the base of fire for flashover (m) (Cox and Chitty, 1980).

6.9

For extended area sources, the minimum condition for flashover is given by

6.9.1 General



hf 1 0.035 Q2p/3 Qd1 + 0.074 Q2p/5V (6.50) 2/3

where dl is the longer dimension of the source (m).

6.8.5

Heat transfer to building surfaces

In the simple room filling model considered in 6.8.3, heat transfer to the ceiling and wall surfaces is neglected. This is a conservative assumption in that the volume of smoke is overestimated. However, if low-temperature smoke is filling a large reservoir, then cooling may lead to loss of buoyancy, which should be taken into account. In the absence of experimental data, it is suggested that cooling effects should be allowed for where the area of the reservoir is greater than 2000 m2, and/or the average layer temperature is less than 10 K above ambient when calculated by neglecting cooling. Further guidance is given in chapter 10: Smoke ventilation.

6.8.6

Heat transfer from smoke layer by radiation

The radiation emitted from a hot smoke layer is given by

Ir = fs v Ts4 (6.51)

Flame calculations

Various methods are available to calculate flame heights for both hydrocarbon and cellulosic fires, and for post-flashover fires. These are mainly used to estimate radiant heating or radiant and convective heating of combustible materials and elements of the structure, although it may be necessary to assess radiant effects on personnel, such as firefighters. Calculating flame height can show where flame impingement is likely to occur. For example, if it can be shown that a steel member is not engulfed in flame, it may be possible to use materials which that shorter fire resistance periods.

6.9.2

Heat flux calculation

By assuming flame heights and areas of burning, it is possible to calculate the radiation due to a fire which impinges on a separate fuel package. In areas not equipped with sprinklers, fires will tend to grow until limited by lack of fuel or air. In compartments where items of fuel are very widely spaced, it is possible to predict whether fire spread will occur from item to item. This is done by calculating the radiative heat flux originating from the fire and which falls on the target item:

Ir = zff v Tf4 (6.54)

where Ir is the intensity of the emitted radiation (kW · m–2), fs is the emissivity of the smoke layer, v is the Stefan– Boltzmann constant (5.67 × 10–11) (kW · m–2 · K–4) and Ts is the average (absolute) smoke layer temperature (K).

where Ir is the radiative heat flux (kW · m–2), z is a configuration factor (see below), ff is the flame emissivity, v is the Stefan–Boltzmann constant (5.67 × 10–11) (kW · m–2 · K–4) and Tf is the flame temperature (K) (SFPE, 2016).

As a conservative assumption, fs may be taken as unity. Alternatively, it may be estimated for a ceiling layer from

The configuration factor, z, represents the geometrical relationship between the source and target. The above is a very general method for calculating radiative heat flux. A more detailed analysis, including techniques for calculating z, is given in the SFPE Handbook (SFPE, 2016).



fs = 1 - exp !- Q0.33 + 470 mfVQh - zV$ (6.52)

where h is the height of the ceiling (m), z is the height of the layer interface (m) and mf is the mass concentration of smoke aerosol (kg · m–3) (SFPE, 2016).

The heat flux impinging on combustible material will cause it to heat up. Whether this heating results in

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Table 6.4  Effective heat transfer coefficient to the surfaces of a room or compartment

Fire dynamics

6-15 drawn to the SFPE Handbook (SFPE, 2016). Hydrocarbon fires in the open are likely to be influenced strongly by the wind, and this should be taken into account.

6.9.3



Calculation of flame height

The larger the flame or the surface that is radiating heat, the larger will be the total heat that is emitted. This implies that larger flames give larger values of z. Therefore, the estimation of flame heights is a crucial part of the calculation process. For most fires away from walls, the plume can be considered to be axisymmetric. The mean flame height of luminous flames for fires is given by

zf = 0.2 Q2t /5 (6.55)

where Qt is the total heat output of the fire (kW) and zf is the mean flame height of the luminous flame (m) (Cox and Chitty, 1980) (see Figure 6.8). As an alternative to equation 6.55, the mean flame height is also given by

zf = 0.235 Q2t /5 - 1.02 D f (6.56)

where Df is the fire diameter (m) (SFPE, 2016). If unknown, the fire diameter may be estimated from the heat output by assuming an average fire load density and then calculating the area of burning. As equations 6.55 and 6.56 do not perfectly agree, the more conservative choice should be made if there is any doubt. The above relationships do not apply to hydrocarbon fires. The calculation of such fires is complex and attention is

6.9.4

Flame projection (postflashover)

On occasions it may be necessary to calculate the flame projection from openings in a compartment that is involved in a fully developed fire (see Figure 6.10). Flame projection from the windows or doors in a compartment can be estimated from the work of Law and O’Brien, as contained in Eurocode 1 (BSI, 2002a: annex B). The height of the flame above the top of the opening, zfo , is given by zfo + ho = 12.8 QR wV 2/3

where zfo is the flame height above the top of the opening (m), ho is the height of the opening (m), R is the rate of fuel combustion (kg · s–1) and w is the width of compartment openings (m). For cellulosic fires, the ventilation-controlled rate of burning, R, may be calculated from Thomas’s correlation (Thomas, 1973) as follows:

R = 0.02 "QAt - AoVQAo ho VQw dV% 1/2

The heat output of the fire is given earlier by equation 6.8.

6.9.5

Fire resistance assessment

The fire resistance value is based, for example, on a furnace test specified in ISO 834-1: 1999 (ISO, 1999), BS 476-20: 1987 (BSI, 1987) or BS EN 1363-1: 2012 (BSI, 2012) (or from conditions for fire resistance testing for specific applications). A real fire may be shown to be less or more severe (see Figure 6.11), in which case the fire resistance period may be reduced (Butcher and Parnell, 1983) or may need to be increased. In Figure 6.11, curves 60(1/4) and 60(1/2) are typical of shop fires (60 kg · m–2), and curves 30(1/4) and 30(1/2) are typical of office fires (20–30 kg · m–2).

Flame projection d

zfo

Ao = ho w

ho

w

Front view

(6.58)

where R is the rate of fuel combustion (kg · s–1), At is the area of enclosing walls (m2), Ao is the area of the opening (m2), ho is the height of the opening (m), w is the width of the wall containing an opening (m) and d is the depth of the room behind an opening (m).

Flame projection Fla zfo

(6.57)

ho

Co Compartment op opening Compartment opening Section

Figure 6.10  Flame projection from an opening

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ignition depends on the intensity of the incident flux. Experimental work by Babrauskas (1981) suggests that for very thin materials, such as curtains, the heat flux required for ignition could be relatively low, at around 10 kW · m–2. For thick materials, the value may be higher, i.e. about 40  kW · m–2. BR187 (Chitty, 2014) gives a conservative value of 12.6  kW · m–2 to be used in design, based on the piloted ignition of unprotected dry wood; although, spontaneous ignition and the effects of paint and moisture can further increase the critical radiation intensity required to cause ignition. The Ignition Handbook (Babrauskas, 2003) provides ignition conditions for a range of materials. It is suggested that a value of 20 kW · m–2 be taken as appropriate for most materials. This figure is the same as that found by Thomas and Bullen (1979) as the critical heat flux for flashover in a room.

6-16

Fire safety engineering (a) Simple case

1200

Average temperature / °C

800

600

60(1/4) 60(1/2) 30(1/4)

400

30(1/2) 15(1/4)

200

0

15(1/2) 7.5(1/4) 7.5(1/2) 0

10

20

30 40 Time / minutes

Af = w1 w2

50

Ao = wo ho

Anet = 2 Af + 2 h Qw1 + w2V - Ao

60

d w = w2 w1

Note: 60(1/2) means fire load 60 kg·m–2 of floor area and ventilation 50% of one wall Figure 6.11  Effect on fire temperature of fire load and ventilation. (Reproduced from Designing for Fire Safety by EG Butcher and AC Parnell, by permission of David Fulton Publishers Ltd.)

(b) More than one window

Methods for calculating compartment temperatures are beyond the scope of this section. However, detailed calculation procedures are given by Law and O’Brien in Eurocode 1 (BSI, 2002a: annex B), in the SFPE Handbook (SFPE, 2016) and by Thomas (1986).

ho3 ho2 wo2

ho1 wo1

Appendix: Dimensions of a room or compartment The following calculated:

dimensions

and

areas

should

be

Ao1 = wo1 ho1

Ao2 = wo2 ho2 etc.

Ao = A1 + A2 + etc.

wo = wo1 + wo2 + etc.

h= Af

Floor area (m2)

Ao

Area of opening (window or doorway) of room (m2)

Anet

Internal surface area of room minus area of openings (m2)

c

Core dimension (m)

d

Depth of opening (m)

h

Floor-to-ceiling height of room or height above base of fire (m)

ho

Height of opening (window or doorway)

w

Width of wall containing an opening (m)

wo

Width of an opening or doorway (m)

Ao1 + Ao2 + etc. Ao

(c) Windows in more than one wall Wall 3

Wall 4

(Wall 1 contains the greatest window area)

wo3

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Furnace curve (BS 476)

1000

Fire dynamics

6-17

Aow1 = window area on wall 1 Aow2 = window area on wall 2 etc.

BSI (2003b) BS 7346-4: 2003 Components for smoke and heat control systems. Functional recommendations and calculation methods for smoke and heat exhaust ventilation systems, employing steady-state design fires. Code of practice (London: British Standards Institution) (2003) BSI (2012) BS EN 1363-1: 2012 Fire resistance tests. General requirements (London: British Standards Institution)

w2 Aow1 w1 Ao

BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution)

d w=

Bukowski RW (1993) ‘A review of international fire risk prediction methods’ Proceedings of the 6th International Fire Conference (Interflam ’93) (Oxford: Interscience Communications)

(d) Compartment with core

Butcher EG and Parnell AC (1983) Designing for Fire Safety (London: David Fulton Publishers) Chitty R (2014) External Fire Spread: Building separation and boundary distances BR 187 (2nd edition) (Garston, Watford: IHS BRE Press) CIBSE (2010) CIBSE Guide E (3rd edition) (London: Chartered Institution of Building Services Engineers) Cox G and Chitty R (1980) ‘A study of the deterministic properties of unbound fire plumes’ Combustion and Flame 39 191–209 c2

c1

Af = w1 w2 - c1 c2 Anet = 2 Af + 2 h Qw1 + w2 + c1 + c2V - Ao d w=

Qw2 - c2V Aow1 Qw1 - c1V Ao

References Annable K (2006) Effectiveness of Sprinklers in Residential Premises – An Evaluation of Concealed and Recessed Pattern Sprinkler Products. Section 5: Thermal sensitivity BRE Report 218113 (Watford: BRE Ltd) Babrauskas V (1981) Will the Second Item Ignite? Report NBSIR 81-2271 (Gaithersburg, MD: National Institute for Standards and Technology) Babrauskas V (1986) ‘Free burning fires’ Fire Safety Journal 11 33–51

Drysdale DD (2011) An Introduction to Fire Dynamics (2nd edition) (Chichester: Wiley) Evans DD and Stroup DW (1985) Methods to Calculate the Response of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings NBSIR 85-3167 (Washington, DC: National Bureau of Standards) Harrison R and Spearpoint M (2008) ‘Characterisation of balcony spill plume entrainment using physical scale modelling’ Proceedings of the 9th Symposium of the International Association for Fire Safety Science (London: IAFSS) 727–738 Harrison R and Spearpoint M (2010a) ‘Physical scale modelling of adhered spill plume entrainment’ Fire Safety Joural 45 (3) 149–158 Harrison R and Spearpoint M (2010b) ‘A simple approximation to predict the transition from a balcony spill plume to an axisymmetric plume’ Journal of Fire Protection Engineering 20 (4) 273–289 Harrison R and Spearpoint M (2010c) ‘A comparison of channelled and unchannelled balcony spill plumes’ Journal of Building Services Engineering Research and Technology 31 (3) 265–277 Heskestad G and Bill RG (1988) ‘Quantification of thermal responsiveness of automatic sprinklers including conduction effects’ Fire Safety Journal 14 113–125

Babrauskas V (2003) Ignition Handbook (Issaquah, WA: Fire Science Publishers/SFPE)

Ingason H (1993) Fire Experiments in a Two-dimensional Rack Storage (Brandforsk project 701-917) SP Report 1993:56 (Borås, Sweden: Swedish National Testing and Research Institute (SP))

BSI (1987) BS 476-20: 1987 Fire tests on building materials and structures. Method for determination of the fire resistance of elements of construction (general principles) (London: British Standards Institution)

ISO (1999) ISO 834-1:1999 Fire-resistance tests. Elements of building construction. Part 1: General requirements (Geneva: International Organization for Standardization)

BSI (1999) BS EN 12259-1: 1999 Fixed firefighting systems. Components for sprinkler and water spray systems. Sprinklers (London: British Standards Institution)

Karlson B and Quintiere JG (2000) Enclosure Fire Dynamics (Boca Raton, FL: CRC Press)

BSI (2002a) BS EN 1991-1-2: 2002 Eurocode 1: Actions on structures Part 1–2 General actions – Actions on structures exposed to fire (London: British Standards Institution) (2002) BSI (2002b) PD 7974-2: 2002 The application of fire safety engineering principles to fire safety design of buildings - Part 2: Spread of smoke and toxic gases within and beyond the enclosure of origin (Sub-system 2). (London: British Standards Institution) (Note: PD 7974-2: 2002 has been replaced by PD 7974-2: 2019) BSI (2003a) PD 7974-1: 2003 The application of fire safety engineering principles to fire safety design of buildings. Initiation and development of fire within the enclosure of origin (Sub-system 1) (London: British Standards Institution) (Note: PD 7974-1: 2003 has been replaced by PD 7974-1: 2019)

Kumar S, Thomas PH and Cox G (2008) ‘A novel analytical approach for characterising air entrainment into a balcony spill plume’ Proceedings of the 9th Symposium of the International Association for Fire Safety Science (London: IAFSS) 739–750 Law M (1978) ‘Fire safety of external building elements – the design approach’ Engineering Journal 15 59–74 McCaffrey BJ, Quintiere JG and Harkleroad MF (1981) ‘Estimating room temperatures and the likelihood of flashover using fire test data correlations’ Fire Technology 17 (2) 98–119 and 18 (1) 122 Madrzykowski D and Vettori RL (1991) A Sprinklered Fire Suppression Algorithm for the GSA Engineering Fire Assessment System (Gaithersburg, MD: National Institute for Standards and Technology)

This publication is supplied by CIBSE for the sole use of the person making the download. The content remains the copyright property of CIBSE

Ao = Aow1 + Aow2 + etc.

6-18 Morgan HP, Ghosh BK, Garrad G, Pamlitschka R, De Smedt J-C and Schoonbaert LR (1999) Design Methodologies for Smoke and Heat Exhaust Systems BRE Report 368 (Garston, Watford: BRE Press)

SFPE (2016) SFPE Handbook of Fire Protection Engineering (5th edition) (Boston, MA: SFPE; Quincy, MA: NFPA)

Thomas PH (1986) ‘Design guide – structural fire safety’ (CIB W14 Workshop) Fire Safety Journal 10 (2) 77–137 Thomas PH and Bullen ML (1979) ‘On the role of KtC of room limiting materials in the growth of room fires’ Fire and Materials 3 (2) 68–73 Thomas PH, Hinkley PL, Theobald CR and Simms DL (1963) Investigations into the Flow of Hot Gases in Roof Venting Fire Research Technical Paper No. 7 (London: The Stationery Office)

Thomas PH (1973) Behavior of Fires in Enclosures – Some recent progress (Pittsburgh, PA: Combustion Institute)

Wade C, Baker G, Frank K, Robbins A, Harrison R, Spearpoint M and Fleischmann C (2013) B-RISK User Guide and Technical Manual BRANZ Study Report 28 (Judgeford, Porirua City: BRANZ Ltd)

Thomas PH (1981) ‘Testing products and materials for their contribution to flashover in rooms’ Fire and Materials 5 (3) 103–111

Zukoski EE, Kubota T and Cetegen B (1981) ‘Entrainment in fire plumes’ Fire Safety Journal 3 (3) 107–121

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NFPA (2015) NFPA 92 Standard for smoke control systems (2015 edition) (Quincy, MA: National Fire Protection Association)

Fire safety engineering

7-1

7

Means of escape and human factors

7.1.1 General This section covers the basic principles of designing for escape by using the established fire safety design codes or an alternative fire safety engineering approach.

the primary objective of the document is to ‘ensure that an adequate standard of life safety can be achieved in the event of fire in the building’. NFPA 101 Life Safety Code (NFPA, 2018) sets the following goals in relation to fire: A goal of this Code is to provide an environment for the occupants that is reasonably safe from fire and similar emergencies by the following means:

This Guide is not intended to replace existing codes of practice, and reference to them will still be necessary. However, it is intended that this chapter will assist designers in applying best practice and provide an understanding of some of the underlying principles of means of escape design.

7.1.2

Requirements of building regulations

As described in Chapter 2, most countries have introduced legislation to ensure the safe design of buildings. These regulations are generally supported by guidance documents, which describe how adequate provision for escape can be achieved. These guidance documents often provide ‘deemed to satisfy’ solutions and set limits on maximum travel distances, prescribe exit widths, specify fire resistance requirements etc. However, increasingly, the regulations allow for other solutions, provided it can be demonstrated that the occupants of a building are ultimately able to reach a place of safety outside the building. This can be done by means of a fire engineering assessment, which should be entrusted to suitably qualified and experienced persons.

7.2

Objectives of escape design

7.2.1 General The objectives of any escape design are similar and are typified by the requirements of the Building Regulations 2010 for England and Wales, for example, which state: The building shall be designed and constructed so that there are appropriate provisions for the early warning of fire and appropriate means of escape in case of fire from the building to a place of safety outside the building capable of being safely and effectively used at all material times.

The guidance in support of these regulations – Approved Document B (HM Government, 2013) – provides recommendations to control or mitigate the effects of fire and

(1) Protection of occupants not intimate with the initial fire development (2) Improvement of the survivability of occupants intimate with the initial fire development.

The code then sets the following objectives: ——

Occupant protection: A structure shall be designed and constructed and maintained to protect occupants not intimate with the initial fire development for the time needed to evacuate, relocate or defend in place.

——

Structural integrity: Structural integrity shall be maintained for the time needed to evacuate, relocate, or defend in place occupants who are not intimate with the initial fire development.

——

Systems effectiveness: Systems utilised to achieve the goals set out by the Code shall be effective in mitigating the hazard or condition for which they are being used, shall be reliable, shall be maintained to the level at which they were designed to operate, and shall remain operational.

The objectives of these codes should be achieved without the need for outside assistance, e.g. from the fire service, whose arrival may be delayed. Both UK and international guidance assume a single fire source and therefore do not take account of the potential impact of an arson attack involving multiple ignition locations.

7.2.2

Evacuation strategies

The simplest escape strategy is to ensure that, as soon as a fire has been confirmed, all the occupants proceed to leave the building simultaneously. However, some situations require variations from this strategy of simultaneous evacuation, for example: ——

the provision of protected refuges where disabled people can await assistance in relative safety, i.e. protected from the effects of fire and smoke

——

apartment buildings where a defend-in-place strategy is adopted by providing a high degree of fire

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7.1 Introduction

7-2

Fire safety engineering

protection, such as fire-resisting between individual dwellings ——

separation

Identify the maximum number of occupants in each part of the building (occupant capacity) Determine the number and width of exits required to accommodate the occupants (usually after discounting the widest exit)

——

tall buildings where phased evacuation is adopted and only the fire floor (and sometimes the one above) is evacuated in the first instance

——

very high rise buildings where escape down stairs can be prolonged and tiring and protected refuge levels are provided where people can wait in safety before being evacuated using the lifts or stairs

Establish the degree of protection required to stairs, escape corridors and refuge areas (if any)

——

facilities where the immediate interruption of some function could cause major problems (e.g. air traffic control centres or hazardous process plants) and the evacuation of key personnel must be delayed

Ensure that the distance of travel to the nearest exit is acceptable (from all points)

——

prisons or mental health facilities where escape may be into adjoining secure areas or into a secure compound.

7.3

Specify other measures required to assist in the use of escapte routes: ● fire detection ● fire alarm ● emergency lighting ● signage ● release of security doors etc.

Design codes

The guidance document used for design of the means of escape will largely depend on the type of building involved. Guidance is provided in various documents, such as: ——

Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (Section B1: Means of warning and escape) (HM Government, 2013)

——

Technical Handbook — Non-Domestic (Scottish Govern­­ment, 2017)

——

BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (BSI, 2017)

——

BS 9991: 2015 Fire safety in the design, management and use of residential buildings. Code of practice (BSI, 2015)

——

Health Technical Memorandum 05-02: Firecode. Guidance in support of functional provisions (Fire safety in the design of healthcare premises) (DoH, 2015)

——

NFPA 101: Life Safety Code (NFPA, 2018)

——

Australian Building Code Board: National Construction Code (ABCB, 2016)

——

New Zealand Building Code.

The British and NFPA codes are internationally recognised and are widely used beyond their respective countries of origin. In certain parts of the world, designers will have the option of using NFPA or British Standards, perhaps in some instances supplemented by local codes. The key steps involved in escape design using traditional prescriptive codes are illustrated in Figure 7.1.

7.3.1

Occupant capacity

The occupant capacity of a room, storey or other part of a building is the maximum number of persons that it is designed or expected to hold. In theatres and cinema

Figure 7.1  Escape design: key steps

auditoria, where a fixed number of seats are provided, the maximum number of occupants can be readily and accurately established. However, in many situations it is necessary to estimate the likely maximum occupancy based on floor space factors. Floor space factors are given in terms of the likely minimum area occupied by each person (m2 per person) and are usually very conservative (i.e. they are likely to significantly overestimate the building population). The population can then be determined by dividing the area of the room or storey by the floor space factor. Some typical floor space factors given in various guidance documents are summarised in Table 7.1. The population of a room can be determined as follows:

occupant capacity =

area of room (7.1) floor space factor

In calculating the occupant capacity based on British codes, toilets, stair shafts, voids and fixed elements of structure (but not counters and display units etc. in retail premises) can generally be discounted from the floor area calculation. However, in most cases (except assembly use) NFPA codes utilise the gross floor area. Where specific data are available to demonstrate the actual maximum occupancies (e.g. a retailer’s own trading figures or number of covers in a restaurant), British codes recognise that these may be used instead of the standard floor space factors. A common example is the acceptance of a floor space factor of 10 m2 per person in office buildings, where guidance such as Approved Document B (ADB), Volume 2 suggests 6 m2 per person (BSI, 2013). However, if the use changes from a traditional office to a call centre with a

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hospitals where escape involves progressive horizontal evacuation from the fire-affected area into adjoining fire compartments

Means of escape and human factors

7-3

Table 7.1  Floor space factors recommended in British and US guidance documents Type of accommodation

Maximum number of persons

Floor space factor / m2 per person NFPA 101

Bars, standing spectator areas (concentrated use without fixed seating)

0.3

Amusement arcade, assembly hall, bingo hall (less concentrated use without fixed seating)

0.5

1.4

Exhibition hall

1.5

1.4

Restaurant, committee room, staffroom etc.

1.0

1.4

Shop sales area

2.0–7.0

Office

6.0

Library

7.0

Kitchen

7.0

9.3

Art gallery or museum

5.0

–

Industrial production

5.0

9.3

– – – –

9.3 1.4 1.9 27.9

Airport terminals: Concourse Waiting areas Baggage claim Baggage handling

0.65

2.8–5.6 9.3 4.6–9.3

more densely packed seating arrangement, the exit provision based on 10  m2 per person may prove to be inadequate. It is therefore important that any reduction in exit capacity that may restrict the future flexibility of use is agreed with the client and recorded in a fire safety management plan (see chapter 14: Fire safety management). However, it should be noted that the NFPA codes do not allow any relaxation of the specified floor space factors. In some escape designs, it may be necessary to hold people in a protected refuge area before they ultimately leave the building. When estimating the holding capacity of a protected refuge area, a figure of 2 persons per m2 is suggested as a reasonable maximum occupant density.

Exit widths

When the occupant capacity has been established, the required width of exits can be determined. The minimum recommended exit width can vary depending on the guidance fire safety code used. As an example, the clear exit width per person in BS 9999 can be as low as 2.4 mm per person, while in NFPA 101 it can be as high as 7.6 mm per person (subject to overall minimum width constraints). The route to any one exit may be blocked by fire and it is therefore usual practice in British codes to discount the largest exit from the calculations. Therefore, if three equally sized exits are available and these need to accommodate 500 people, the required width would be (500 × 5 mm) = 2500 mm. Since it is necessary to discount one exit, the required minimum clear width of each of the remaining two exits would be (2500 / 2) = 1250 mm. The third discounted exit should also be at least 1250 mm clear width. ADB Volume 2 assumes that an exit

60

Minimum clear width of exit / mm 750

110

850

220

1050

less than 1050 mm wide will have a proportionately lower capacity than a larger exit and the exit capacities given in Table 7.2 are widely adopted. A different approach is adopted in NFPA 101, where it is not necessary to discount an exit or to adopt reduced capacities for door openings between 810 and 1050 mm wide. In some fire safety codes, the main entrance/exit of the building must be larger than other exits. For example, in NFPA 101, the main entrance/exit of assembly occupancies must be able to accommodate at least one-half of the total occupant load. In dance halls, discotheques, nightclubs and assembly occupancies with festival seating, the main entrance/exit must be able to accommodate at least two-thirds of the total occupant load. BS 9999 outlines a risk-based approach to designing means of escape and can accommodate narrow exit widths based on the design of the building and level of building management. It is important that BS 9999 is used in its entirety and that the escape provisions are not cherry-picked.

7.3.3

Stair capacities

7.3.3.1

Simultaneous evacuation

A protected stair enclosure can be considered as a place of relative safety. The capacity of a stair is therefore dependent on the rate at which people can leave by the final exit and the number of people that can be accommodated (stacking capacity) in the enclosure. Following British codes, the capacity of a stair designed for simultaneous evacuation can be derived from the following equation (subject to minimum stair widths, which depend on the occupancy type):

P = 200 w + 50 Qw - 0.3VQn - 1V (7.2)

where P = the number of people that can be served by the stair, w = the width of the stair (m) and n = the number of storeys served. Equation 7.2 can be rewritten to give the required width (w) of the stair, as follows:

w=

P + 15 n - 15 150 + 50 n

(7.3)

NFPA 101 adopts a simpler approach, where multiple levels are evacuated simultaneously. The stair width is calculated by multiplying the total number of people needing to evacuate at one time by the required width per person.

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ADB Volume 2

7.3.2

Table 7.2  Capacities for narrow exits

7-4 7.3.3.2

Fire safety engineering Phased evacuation

Most British codes recommend a stair width of 5 mm per person (i.e. the same width criterion as for horizontal travel). However, to take account of the slower speed of travel down stairs, NFPA 101 typically recommends the provision of 7.6 mm per person (subject to minimum stair widths). It should be noted that in NFPA 101 the minimum stair width can increase to 18 mm per person, depending on the occupancy type. To ensure that a phased evacuation can be managed effectively, additional fire protection measures may be necessary, such as an increased level of compartmentation, a public address system, fire telephones and an automatic detection system.

7.3.4

Alternative exits

A basic principle of designing for escape is that escape routes should be available in at least two directions, unless the distance to be travelled is short (between 6 m and 30 m depending on building use, level of fire protection and jurisdiction) and the number of occupants is limited (typically to a maximum of 50 to 60 people in the deadend area). A choice of escape routes is of little value if they are all likely to be obstructed by fire at the same time. Therefore,

In British guidance, where the maximum occupancy of a room or storey exceeds 600 people, at least three adequately separated exits should be provided. NFPA 101 generally requires a minimum of three exits for 500 to 1000 occupants and a minimum of four exits where the occupant load is more than 1000 persons.

7.3.5

Travel distances

Traditional fire safety design codes place limitations on the maximum distance that can be travelled to an exit. The travel distances should be measured along the route which will be travelled and not the direct (straight line) distance. However, where the final layout of the building is not known, a good rule of thumb is to assume that the travel distance will be approximately 1.5 times the direct distance. The recommended maximum travel distances for a selection of different occupancies as given in British and US fire safety design codes are summarised in Tables 7.3 and 7.4. BS 9999 outlines a risk-based approach to designing means of escape and the document may permit longer travel distances (compared to ADB Volume 2) based on the geometry of the building and level of building management.

B Room or area

ag on

al

A

al

of ½ = in im M

A

um

di

st

an

ce

C

di

on

ag Di

≥ 45°

B

Figure 7.2  Separation of exit routes

C

Figure 7.3  Separation of exit routes. (Reprinted with permission from NFPA 101®-2018, Life Safety Code®, Copyright © 2017, National Fire Protection Association, Quincy, MA. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.)

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In high-rise buildings, it is common practice to design the stairways based on phased evacuation, i.e. a process in which the fire floor only (or the fire floor and the one above) is initially evacuated, the remaining floors being evacuated as and when necessary. This requires adequate fire compartmentation between levels to protect those levels that are not evacuated immediately.

British guidance recommends that alternative escape routes should be provided in directions which are at least 45° apart or be separated by fire-resisting construction (see Figure 7.2). US codes, such as NFPA 101, recommend that alternative exits should be separated by a distance equal to at least one-half the diagonal drawn across the room, or one-third in sprinklered buildings (see Figure 7.3).

Means of escape and human factors

7-5

Table 7.3  Maximum recommended travel distances where escape is available in one direction only

Table 7.4  Maximum recommended travel distances where escape is available in more than one direction

Building use

Building use

ADB Volume 2

Technical Handbook — Non-Domestic

Maximum travel distance where escape is available in more than one direction / m

NFPA 101*

ADB Volume 2

Technical Handbook — Non-Domestic

NFPA 101*

Office

18

18

23 (30)

Office

45

45

60 (91)

Shop and commercial

18

15

23 (30)

Shop and commercial

45

32

30 (60)

Assembly buildings

18

15

6.1 (6.1)

Assembly buildings

45

32

45 (60)

Assembly buildings with fixed seating in rows

15

15

6.1 (6.1)

Assembly buildings with fixed seating in rows

32

32

45 (60)

Industrial

25

18

15 (30)

Industrial

45

45

60 (75)

Plant rooms (within room)

9

18

15 (30)

High fire hazard

9

15

–

Plant rooms (within room)

35

45

60 (75)

High fire hazard

18

32

23 (23)

*  Figures in parentheses indicate the allowable travel distance where sprinklers are installed

*  Figures in parentheses indicate the allowable travel distance where sprinklers are installed

7.3.6

If lobby protection is not provided to all escape stairs, it is normally necessary to discount one whole stair from the exit calculations. However, if lobbies are provided it can be assumed that all protected stairways will be available for escape. (Note: it is still necessary to discount one storey exit on the fire floor.)

Fire protection to escape routes

7.3.6.1 General Escape stairs and, in certain cases, escape corridors need to be enclosed with fire-resisting construction to prevent the ingress of fire and smoke. For escape purposes, a minimum fire resistance of 30 minutes is normally recommended, although this may be increased if the stair also acts as a protected shaft providing separation between levels. It is important to prevent substantial smoke infiltration into protected escape routes and therefore all elements of the enclosing structure should be adequately sealed against smoke ingress and doors should be provided with smoke seals. 7.3.6.2

Protected lobbies

Additional protection against the ingress of smoke into a stairway can be achieved by the provision of a protected lobby (see Figure 7.4) and/or pressurisation of the stair enclosure.

7.3.7

Facilities for disabled people

To ensure the safe escape of disabled people from buildings it is essential to consider both management and design issues. The design of disabled egress routes should be coordinated with the access strategy for the building. Provisions should be made to ensure that disabled people can be evacuated from the building to a place of safety. It is not appropriate for the designer or management to rely on the fire service to facilitate their escape – the fire service should only be considered as a back-up. Where step-free access to a place of safety outside the building is not available, fire protected refuges should be provided. These are usually provided within a protected stair or lobby but can be a separate fire compartment with

British guidance normally recommends protected lobbies to stairs when: ——

only one escape stair is available

——

the escape capacity of one of the stairs is not to be discounted

——

the height of the top storey is greater than 18 m

——

the building is designed for phased evacuation

——

the stair is designated as a firefighting stair

——

the stair serves basement levels.

When following NFPA guidance, it is usual to provide smoke-proof enclosures to stairs in high-rise buildings (>23 m in height), which involves the provision of ventilated lobbies or pressurisation of the stairs. (Lobbies are not necessary under NFPA guidance if the stairs are pressurised.)

Landing Fire door

Protected lobby

Stair

Fire-resisting construction Figure 7.4  Protected lobby to staircase enclosure

Fire door

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Maximum single direction travel distance / m

7-6

Fire safety engineering

7.3.8 Lifts

Where provided, each refuge should be accessible to a wheelchair and provide an area of at least 900 mm ×  1400 mm in which a wheelchair user can await assistance. A suitable means of two-way voice communication should be provided within the refuge so that the occupants can indicate their need for assistance and be kept informed of forthcoming assistance.

However, in certain types of building (e.g. very high rise and deep basements) it will be advantageous to use suitably designed and constructed lifts in the evacuation of the less physically able members of the population.

It may be appropriate to utilise the lift(s) for the evacuation of disabled people. It is important that evacuation using protected lifts is only carried out under management or fire service control, in accordance with clearly defined procedures. Often the focus of provision for escape for disabled people is directed towards wheelchair users. However, there are many other groups of people who find it difficult to escape, and their needs should be considered in both the design and the management of a building. These groups and the facilities which can be used to assist them include the following: (a)

(b)

(c)

(d)

(e)

Mobility-impaired people and people able to manage only a few steps in an emergency: ——

suitable continuous handrails on steps

——

suitable goings and risers of stairs

——

suitable places to rest along the escape route

——

early warning

——

knowledge of the most appropriate direction to travel

——

evacuation lifts (under management/fire service control).

It has long been standard practice to recommend that lifts are not used for evacuation in a fire emergency. This is because of the potential dangers of smoke ingress into the lift, loss of power and the possibility of doors opening and discharging at the fire floor.

The use of lifts for evacuation should only be under building management or fire service control and it is essential that clear procedures are developed for their use. Guidance on the use of lifts for evacuation may be found in NFPA 101, BS 9999, HTM 05-03 Part E: Escape lifts in healthcare buildings (DoH, 2006) and CIBSE Guide D: Transportation systems in buildings 2015. Human factors in the use of lifts for egress are considered by Pauls et al. (1991). 7.3.8.1

Passenger lifts should be in fire-resisting shafts with enclosed fire-resisting lift lobbies. The lifts should be designed in accordance with code recommendations for evacuation lifts, for example, Annex G of BS 9999. Standby power to each designated evacuation lift should be provided. Other features, such as the protection of electrical equipment against the ingress of firefighting water, should be considered. Fixed emergency communications systems (fire/emergency telephones) in the lift cars and lift lobbies (and also at each floor level of exit stairs) should also be provided. Under emergency conditions, the lift should only be capable of being operated by designated persons (i.e. management or fire service personnel using an override key). 7.3.8.2

Blind and partially sighted people: ——

suitable continuous handrails on steps

——

tactile and visual markings

——

clear information

——

wide escape routes to facilitate assistance.

Hearing-impaired and deaf people: ——

visual indication that there is an emergency

——

clear written information.

People with mobility impairments resulting from asthma, heart disease, pregnancy etc.: ——

smoke-free protected routes

——

places to rest en route

——

wide escape routes to facilitate assistance.

People with learning difficulties and cognitive disabilities: ——

identification of escape routes

——

clear information.

Evacuation lifts

Lift lobbies enclosed in fire-resisting construction

The passenger lift lobbies should be enclosed in fireresisting construction. The doors forming the enclosed lobbies can be ‘held-open’ by automatic door release mechanisms so that they do not present an obstruction in normal operation and only close upon operation of the fire alarm system on the floor concerned. The lift lobbies should be large enough to accommodate the number of people likely to need to use the lifts to evacuate the fire floor (i.e. they should accommodate the anticipated number of disabled people and their helpers). 7.3.8.3

Closed circuit TV to lift lobbies

The provision of cctv to passenger lift lobbies will assist both building management and the fire service to determine the most appropriate floor(s) to which to dispatch the evacuation lifts. 7.3.8.4

Real-time signs in lift lobbies

Signs should be provided in evacuation lift lobbies to report system status in real time and provide an indication

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direct access to a stair. Refuges should be used in conjunction with a pre-prepared escape plan. Fire marshals should be designated to assist disabled people in their descent down the stairs. In sprinkler-protected buildings, NFPA codes do not generally recommend the provision of separate refuges, as a sprinkler-protected level is considered to provide a reasonably safe refuge.

Means of escape and human factors

7-7

7.3.11

7.3.8.5

When designing for means of escape, consideration should be given to the provision of other supporting measures that are described more fully in other sections of this Guide:

Refuge floors

In very high rise buildings it may be difficult for many of the occupants (who would not be classified as disabled) to descend the full height of the building using the stairs. The designation of selected refuge floors, where people can transfer to lift evacuation under building management/fire service control can be of benefit. As the refuge floors will need to accommodate occupants from a number of floors they could become crowded. Therefore, the maximum potential numbers using them will need to be established to determine how many refuge floors will be needed. Typically, refuge floors would be provided at every 20 floors. Appropriate signage should be provided within the stairs to direct people to the designated refuge floors.

——

fire alarms

——

exit and directional signage

——

emergency escape lighting

——

automatic fire detection

——

automatic suppression systems (e.g. sprinklers)

——

automatic release of security locks and door holdopen devices

——

wayfinding.

7.4

Fire safety engineering design approaches

7.3.9 Escalators For some facilities (e.g. underground stations), escalators provide the primary means of escape and there may be other situations where the use of escalators would be of assistance in the evacuation process. However, it is essential to ensure that escalators (or open stairways) used for means of escape will not discharge people into an area likely to be affected by fire, nor that they may be closed off, in the early stages of a fire, by a shutter operated by a fire alarm or smoke detector. Current UK codes, i.e. ADB Volume 2 or BS 9999, do not recognise the use of escalators as part of the means of escape, but if an escalator discharges to an area containing only a very limited fire load (e.g. a well-controlled entrance lobby), then it may be feasible to accept an escalator as an exit route. This is advantageous as people will, in any case, tend to use routes, such as these, with which they are familiar. In these circumstances, the escalators leading to the exit could be maintained in operation. When assessing the capacity of an escalator, it should be assumed that, unless a secure power supply is provided, the mechanism will be stationary. The riser and tread dimensions of escalators are not the same as for stairs, and movement is not as easy. However, they are often used in the stationary mode and, in these circumstances, the flow capacity may be taken as 56 persons per minute per metre width (measured between the innermost part of the handrails). (This figure is derived from NFPA 130 Standard for fixed guideway transit and passenger rail systems (NFPA, 2017).)

7.3.10

Mechanised walkways

Mechanised walkways are generally accepted for means of escape but their capacity is normally assessed on the assumption that they are stationary. It is not recommended that travellators with magnetic locking systems for trolleys (e.g. in supermarkets) are used for means of escape as the locked trolleys may impede escaping occupants.

Other measures

The recommendations presented previously in this chapter reflect the recommendations of guidance documents that have historically proved to be effective in ensuring the safety of building occupants. However, many of these recommendations do not have a firm scientific basis and do not necessarily provide the optimum solution. The guidance documents prescribe travel distances and exit widths etc. but make no mention of the time required to escape. However, the escape process is strongly time related. For an escape design to be successful, the time available before untenable conditions occur must be greater than the time required for escape. This can be written as:

aset

>

rset (7.4)

where aset is the available safe escape time (i.e. the time from ignition to the onset of untenable conditions) and rset is the required safe escape time (i.e. the time following ignition after which all the occupants can leave the fire-affected space and reach a place of safety). The evaluation of aset is covered in other sections of this guide. A method for estimating rset is described below. The basic equation used to describe the escape from a building or space is as follows:

tdet + ta + tpre + ttrav = tesc

(7.5)

where tdet is the time from ignition to detection by an automatic system or the first occupant, ta is the time from detection to a general alarm being given, tpre is the pre-movement time of the occupants (this may be expressed as a distribution of times for the population or may be represented by a single representative value) and ttrav is the travel time of the occupants (this may be represented by a distribution of individual times or a single value that is representative of the whole population).

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of the likely time before cars would be expected to arrive to evacuate a floor.

7-8

Fire safety engineering

Available safe escape time (ASET) Margin of safety

Evacuation time Pre-movement time (tpre) Recognition time

Travel time (ttrav)

Response time

Alarm time (ta) Detection time (tdet)

Figure 7.5  Factors involved in assessing the total escape time

This general approach is illustrated in Figure 7.5. The calculation of tdet and ta represents the delay (if any) between activation of a fire detector and the alarm being broadcast. The factors influencing, and the methods of estimating, tenability limits, pre-movement times (tpre) and travel times (ttrav) are described below.

7.4.1

Tenability limits for design

While escaping from a fire-affected building, the occupants should not be subjected to undue hazard because of smoke or heat. Escape routes can be protected from the effects of fire by passive measures (e.g. enclosure of corridors or stairs with fire-resisting construction) or active systems (e.g. smoke control) or a combination of passive and active systems. The following subsections give suggested design limits for short-term exposure (i.e. before the occupants can enter a protected route or escape to open air). Conditions within protected routes and refuge areas should not approach these values.

(a)

Maintain a layer of air that is relatively clear of smoke above eye level. Typical design values are 2–3.5 m above floor level, depending on building geometry and smoke modelling technique. (Note that the temperature of the smoke layer should not exceed 200 °C to limit the downward radiant heat flux to less than 2.5 kW · m–2, at which severe skin pain can occur (BSI, 2004).)

(b)

Ensure that the visibility through any smoke will be sufficient for exits to be identified and reached without undue hindrance. (Generally, people are reluctant to proceed through smoke if the visibility distance is less than 10 m (BSI, 2004).)

Where there is a clearly defined escape route, a visibility of 10 m (equivalent to an optical density of 0.1 dB · m–1) is normally considered reasonable. The visibility distance is roughly doubled if back-illuminated signs (i.e. integrally lit escape signage) are provided. In public buildings and large spaces where wayfinding may be difficult, greater visibility distances may be required to ensure that exit routes can be identified.

7.4.2 Smoke

7.4.3 Heat

The smoke produced from typical building contents will normally cause loss of adequate visibility before debilitating toxic conditions occur. It is therefore usual to design to ensure that adequate visibility is maintained and the toxic impact of smoke can be neglected for many typical building types. However, the impact of combustion products from any highly toxic materials should be checked (e.g. in buildings used for the storage or processing of toxic chemicals).

The maximum temperature of dry inhaled air that can be tolerated for a short period is 120 °C. Note that under the conditions of high humidity, that may result from firefighting activities (including sprinkler operation), the maximum survivable temperatures will be considerably lower (approximately 60 °C) and this temperature should be adopted as a maximum for design purposes.

While travelling within a fire-affected space and before reaching a protected escape route or other place of relative safety, the occupants should not be subject to conditions that will result in a loss of visibility. The following design limits are suggested:

Excessive levels of heat radiation can induce severe burns and skin pain. Prolonged exposure to a radiant heat flux exceeding 2.5  kW · m–2 can cause severe pain and this figure is the maximum recommended design value for short-term exposure (BSI, 2004). A black-body radiator at a temperature of 200 °C will emit a radiant heat flux of approximately 2.5  kW · m–2 and therefore people

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Required safe escape time (RSET) (tesc)

Means of escape and human factors should not be expected to escape below a smoke layer at a temperature greater than this.

Pre-movement times

7.5.1

Behaviour of people

Studies of behaviour in fires indicate that, generally, people do not panic nor do they act in an irrational way when judged from their perspective of the situation (Sime, 1994). Their actions are, however, not always what the designer had in mind and this may result in a significant delay (pre-movement time) between an alarm being broadcast and the commencement of movement towards an exit. The behavioural tendencies of people should be considered as part of the fire safety design, e.g. as indicated below. ——

Deaths in large-scale fires attributed to ‘panic’ are far more likely to have been caused by delays in people receiving information about a fire.

——

Traditional fire alarm sounders cannot always be relied upon to prompt people to move immediately to safety.

——

The pre-movement time (i.e. people’s response to an alarm) can be more important than the time it takes to physically reach an exit.

——

Much of the movement in the early stages of fires is characterised by activities such as investigation rather than escape.

——

If an exit is not seriously obstructed, people tend to move in a familiar direction, even if the route is longer, rather than use an unfamiliar fire escape route.

——

Individuals often move towards and with group members and maintain proximity as far as possible with individuals to whom they have emotional ties.

——

Fire exit signs are not always noticed (or recalled) and may not overcome difficulties in orientation and wayfinding in a complex architectural layout.

——

People are often prepared, if necessary, to try to move through smoke despite the dangers that this may present.

——

People’s ability to move towards exits may vary considerably (e.g. a young, fit adult as opposed to a person who is elderly or who has a disability).

——

Reversal of direction, e.g. after moving towards an initially unseen fire.

7.5.2

Occupancy types

The mobility of occupants, their familiarity with their surroundings and the ease of wayfinding allowed by the setting can influence the time required to evacuate a building. When considering the effect of different types of occupancy, the following characteristics can be significant:

(a)

occupants predominantly familiar with the building and awake (e.g. offices, schools and industrial premises etc.)

(b)

occupants possibly unfamiliar with the building but awake (e.g. shops, exhibition halls, museums, leisure centres and other assembly buildings)

(c)

occupants possibly sleeping but predominantly familiar with the building (e.g. dwellings)

(d)

occupants possibly sleeping and unfamiliar with the building (hotels etc.)

(e)

significant number of occupants requiring assistance (e.g. hospitals and nursing homes)

(f)

occupants held in custody (e.g. prisons).

Similar categorisation of occupancy characteristics is presented in the initial chapters of BS 9999 (BSI, 2017). Access to buildings for disabled people is now required in nearly all new buildings and, as far as reasonably practicable, in existing buildings. Therefore, when designing for escape, an appropriate proportion of disabled people should be assumed to be present in all the above-listed categories. In multiple-use buildings, the effect of one use on another must be considered to ensure that means of escape from one use will not be prejudiced by another, e.g. where one use will be closed outside trading hours, independent means of escape may have to be provided for another, more continuous use. Similarly, where security requirements might compromise the availability of exits, suitable measures must be taken to ensure that exits are available to all occupants under emergency conditions.

7.6

Evaluation of total pre-movement time

Pre-movement time can be at least as important as the time that it takes to travel to and through an exit. For each occupant, the time taken from the first cue indicating the presence of fire to the start of movement towards an exit represents the total pre-movement time for the occupant and will be influenced by factors such as: ——

the spatial location of the occupant

——

the location of the fire and the pattern of fire growth

——

the visibility of the fire by the occupant (i.e. those nearest to the fire with clear visual access are more likely to respond quickly)

——

the type of cue or warning received (voice alarm, bells, smell of smoke etc.).

This pre-movement time can be subdivided into two parts: recognition time and response time (see also Figure 7.5).

7.6.1

Recognition time

The recognition time is the period after an alarm or other cue is evident but before the occupants begin to respond.

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7.5

7-9

7-10

Fire safety engineering

The recognition time ends when the occupants accept that there is a need to respond and take some action (e.g. putting on a coat before leaving).

7.6.2

Response time

The response time is the period after the occupants recognise the alarms or cues and begin to respond to them, but before they begin to move towards an exit. As with the recognition period, the response time may range from a few seconds to many minutes, depending on the circumstances. During the response period, the occupants cease their normal activities and may engage in a variety of activities in response to the potential emergency. Examples of activities undertaken during the response period include: ——

investigation to determine the source, reality or importance of a fire alarm

——

stopping machinery/production

——

securing money

——

searching for children and other family members

——

putting on coats

——

collecting ‘essential’ belongings (personal effects and keys etc.)

——

first-aid firefighting etc.

7.6.3

Design approach

It is feasible to introduce both recognition time and response behaviour into an evacuation model to estimate the total pre-movement time, but there is a lack of available data on recognition time and the range of possible behaviours are difficult to quantify. The most practical approach is therefore to derive distributions for total pre-movement time from staged evacuations or the investigation of real incidents. Pre-movement times may vary considerably for different individuals or groups of individuals. An important factor is the degree of visual access afforded. For example, in an open-plan setting such as a theatre auditorium, the distribution of pre-movement times is likely to be narrow and everyone will start to move at about the same time, particularly if instructions are given from the stage. In a multiple enclosure setting, such as a hotel, there is likely to be a wide distribution of pre-movement times characterised by a ‘head’ of early and a ‘tail’ of late starters. Those in the enclosure containing the fire may complete the evacuation process before those in other enclosures even recognise the need for action.

7.6.4

Pre-movement time of the first few occupants

The time at which the first few occupants start to move towards an exit is particularly important because the evacuation process does not begin until this time is reached. The duration of the pre-movement stage will be highly dependent on the occupancy type, the nature of the warning system and the implementation of the emergency management procedures. In situations where occupants are awake and familiar with a building, and well trained in the emergency procedures (e.g. a well-managed office), then the pre-movement time of the first occupants to respond should be very short (less than 20 seconds). In occupancies such as shops or assembly buildings (where the occupants are awake but unfamiliar with their surroundings) this phase of pre-movement time can also be very short, provided that staff are well trained and take action to direct customers to the exits. A voice alarm can significantly reduce the pre-movement time in settings where the occupants are unfamiliar with the emergency procedures and may be unsure as to the meaning of a bell or klaxon. The reduction in pre-movement time provided by a voice alarm is recognised in the design approach used in BS 9999 (BSI, 2017). Very short times to first response are typical of evacuations observed in a range of occupancies in these categories. Where fire safety management is not of a high standard, then the pre-movement time can be much longer and is unpredictable. Good fire safety management is therefore an essential requirement whether the escape provisions have been designed based on fire safety design codes or fire safety engineering principles. In Great Britain, the implementation of adequate evacuation procedures is a requirement of the Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541) (for England and Wales) and the Fire (Scotland) Act 2005. In situations where occupants may be asleep, the premovement time is likely to be much longer, irrespective of the warning and fire safety management system used. Even for very well-designed and well-managed hotels, pre-movement times for some individuals may extend towards 30 minutes (for example, guests who may have taken sleeping pills or be under the influence of alcohol).

7.6.5

Pre-movement time distribution

Once the first few occupants have begun to move, the pre-movement times for the remainder of the occupants in an enclosure tend to follow a log-normal frequency–time distribution (BSI, 2004). Figure 7.6 illustrates typical pre-movement time distributions in well-managed open-plan occupancies. The delay period before the first few occupants begin to move is typically followed by a rapid increase in the proportion of the population entering their travel phase. There is then typically an extended ‘tail’, during which the last few occupants begin to travel. Pre-movement time distributions are likely to be much wider in multiple enclosure buildings than in single enclosures and will be influenced by the type of warning and

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During the recognition period, the occupants continue with their current activities. The length of the recognition period can be extremely variable, depending on factors such as the type of building, the nature of the occupants, their familiarity with the alarm system (training), the type of alarm and fire safety management procedures.

Means of escape and human factors

7-11

0.25

(a) High occupancy (e.g. shop)

Pre-movement phase

0.15

Approach phase

0.1

Exit flow phase

0.05 0

Time 0

20

40

60 80 100 Time / seconds

120

140 (b) Low occupancy (e.g. warehouse)

Figure 7.6  Pre-movement distributions from a number of studies (BSI, 2004) Pre-movement phase

management system in place. Generally, short and narrow pre-movement time distributions occur where the occupants are awake and familiar with their surroundings. In well-managed single enclosures, the pre-movement time should be less than one minute. In multiple occupancy sleeping scenarios, the pre-movement time distribution is likely to be much wider (e.g. 10 to 30 minutes). It is important to recognise that, while the total premovement time can constitute a large proportion of the total evacuation time, it is not appropriate to simply add total pre-movement and total travel times as this will overestimate the total evacuation time. For spaces with a high occupant density, the initial period before the first individuals start to move is the important pre-movement factor as after this period the travel time is likely to dominate. Where occupant densities are low, the total evacuation time will be equivalent to the sum of the total pre-movement time and the travel time. This overlap between pre-movement and travel times is illustrated by the timelines in Figure 7.7. Table 7.5 provides guide values for pre-movement times where a good standard of fire safety management is implemented.

Approach phase Exit flow phase Time Figure 7.7  Overlap between phases of the evacuation process

Table 7.5  Suggested guide values of pre-movement times (wellmanaged environment) Building type

Occupancy type

Residential

Dwellings

Pre-movement time / minutes 5

Hotel bedrooms

20

University hall of residence

20

Institutional and health

Day centre, surgery, clinic

2

Education

School, college, university

1

Offices

Office

1

Bank

2

Shop or department store

3

Shopping complex

3

Retail

Further information on pre-movement times is given in PD 7974-6 (BSI, 2004).

7.7

Travel time

The travel time is the time (after commencement of movement) required to reach and pass through an exit into a place of safety. Once the population of a space have begun to move towards the exits, the travel time can be estimated, taking account of the following parameters: ——

number and distribution of occupants

——

speed of travel towards exit

——

rate of flow through restrictions (doorways, stairs etc.).

An analysis of these factors can provide an indication of the minimum time in which a room, floor or building could be evacuated if the occupants were to react immediately and appropriately in response to a warning of fire. Calculations will indicate whether it is the distance to be travelled or the width of the escape route that is the limiting factor in determining the travel time. The number and distribution of occupants will usually be evaluated in a similar manner, whether adopting fire safety design codes or a fire safety engineering approach to escape route design. Typically, in sparsely occupancy buildings (e.g. warehouses) the distance to be traversed will dominate the travel time, whereas in buildings with a high occupant density (e.g. shops) queuing at exits is likely to dominate the travel time.

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Frequency

0.2

7-12

7.7.1

Fire safety engineering

Time of travel to an exit

When descending stairways, the typical free movement speed is reduced to 1.1 m · s–1, giving a vertical component of velocity of the order of 0.75 m · s–1. On the flat, provided adequate space and accessible doors are provided, wheelchair users can evacuate quickly without causing obstruction (Shields, 1993). However, persons using walking aids require much more time. This varies widely, but for design purposes it is reasonable to assume that they can move at about half the speed of the average person, say 0.6 m · s–1. Once people start to evacuate, the time taken for them to reach a place of safety will usually be dominated by the time taken to pass through restrictions such as doorways, which are traditionally designed to accommodate all the occupants in a nominal period of 2½ minutes. As it will rarely take as long as 2½ minutes to travel to an exit, the rate of arrival is likely to be greater than the doorway can accommodate and a queue will form (except in cases where the occupancy numbers are very low). This is implicit in the established fire safety design codes. In most buildings with a high occupant density, the occupants will be distributed throughout the accommodation and those people located nearest to an exit will have a very short travel time of only a few seconds. Individuals who are located some distance from an exit will clearly take longer. However, unless the time taken to move to the exit exceeds the notional evacuation time (typically 2½ minutes), the individuals may still have to queue on arrival at the exit doorway. Therefore, in many cases, unless the distance to be travelled exceeds 150 m, travel distance is unlikely to have a dominant effect on the overall evacuation time, i.e. 150 m can be travelled in about 2 minutes at a speed of 1.2 m · s–1. Even at 0.6 m · s–1, over 70 m can be traversed in 2 minutes. For buildings with very low occupant density, there will be no queuing at storey exits and the total evacuation time will largely be determined by the longest travel distance. However, it may be desirable to restrict travel distances so that the location of exits can be readily identified and so that those who are only able to walk slowly are not put at risk.

Where stairs must be negotiated prior to reaching a storey exit, allowance should be made for the slower speed of travel on stairs and the effect on any disabled people, e.g. wheelchair users. As a fire could occur adjacent to an exit, when estimating the time required to reach a storey exit, one of the exit routes should be assumed to be unavailable. This means that distances to be travelled (and hence estimates of travel times) need to be measured using a different method to that stipulated in fire safety design codes, which always measure travel distance to the nearest exit. Figure 7.8 illustrates the traditional method of measuring travel distances (route 1) and the method that should be used in a fire engineering assessment of travel time (route 2). When designing in accordance with the traditional fire safety design codes, the travel distance is measured along the shortest route of travel to the nearest exit (taking account of any obstructions). From point C, the shortest route to exit B is route 1. With the exception of hospitals, fire safety design codes usually place no limit on the distance of travel to an alternative exit (exit A in this instance). When carrying out a fire safety engineering assessment, it is necessary to establish the time required to travel to an exit. In a sparsely occupied warehouse, where the fire location is obscured (e.g. by high racking or shelving), some of the occupants may move towards the nearest exit, which may prove to be blocked by the fire. In these circumstances, the calculation of travel time should take account of the actual route that may be taken before the fire becomes visible. Route 2 illustrates this concept, where an occupant initially moves towards the nearest exit (exit B) but, on reaching point D, realises that the exit is blocked by fire. It is then necessary to retrace part of the route before leaving through exit A. The measurement of travel distances or calculation of travel times should either be based on the worst-case condition or take account of all the possible occupant locations. Route 2 (used to calculate travel time) D Exit A

In the case of buildings over a certain height and floor area, provision for access and facilities for firefighting may dictate the maximum distance between stairs. In large open areas, travel distances substantially in excess of those specified in fire safety design codes may be acceptable, provided that the exits are clearly visible and accessible. In areas where the route to an exit is unavoidably tortuous, a good wayfinding system should be provided. It may

C

Exit B

Route 1 (travel distance as used in prescriptive codes) Figure 7.8  Measurement of travel distance

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The speed of travel and the crowd density are related – at high crowd densities the ability to walk freely is restricted and hence the speed of travel will be reduced. At densities of approximately 4 persons per m2, movement can become very slow, leading to anxiety and discomfort. Where occupant density is relatively low (i.e. 2 m2 per person or more), 1.2 m · s–1 can be taken as an average walking speed for design purposes.

also be necessary to provide exits more frequently than in large open areas to ensure that the occupants can readily locate the exit route. The use of wayfinding systems incorporating illuminated floor tracks may be of considerable assistance in guiding people to the nearest exit.

Means of escape and human factors

7.7.2

Exit widths

7.7.2.1 General

While fire safety design guidance on exit widths has historically proved to be adequate, there is no scientific basis for the original choice of 2½ minutes. In many cases, where smoke filling times are prolonged (due to a high ceiling or the provision of smoke ventilation etc.), exit widths based on longer evacuation times may be acceptable. For example, the maximum notional exit time adopted by British Standards for shopping centres is 5 minutes, which is justified in terms of the smoke control and sprinkler protection provision in large shopping centres. However, it is essential to realise that, due to the characteristic delay before people start to move and deviations in movement from the optimum escape route, the notional exit time can be much less than the actual time required to evacuate a space. 7.7.2.2

Exit flows

Once evacuation has started towards the exits, the main physical constraint on the time taken to evacuate will usually be the width of doorway openings, corridors and stairs. For design purposes, it may be assumed that the maximum flow rate of persons through a doorway or level corridor is given by equation 7.6. For openings and corridors of width 1.1 m and greater:

Fp = 1.333 w (7.6)

where Fp is the number of persons passing through the opening in 1 second (person · s–1) and w is the width of the opening or corridor in metres, after allowing for any obstructions. Assuming a notional exit time of 2½ minutes, equation 7.6 is equivalent to the method of determining exit widths given in British codes and NFPA guidance, i.e. that the capacity of an exit is 1 person per 5 mm of exit width (subject to minimum width criteria). It should be noted that the flow rate through an exit may be reduced if there is downstream congestion (i.e. if the occupant density significantly exceeds 2 person · m–2). 7.7.2.3

Stairway capacity

It is generally assumed that a protected exit stair provides a place of relative safety where people may remain for the duration of the evacuation process. However, in very tall buildings it may take over an hour for all of the occupants to descend the stairway and reach open air.

Despite the considerable time that the complete evacuation may take, a stair must have sufficient capacity to enable all of the occupants of a fire-affected floor to enter within a relatively short period of time. The maximum number of people who can be physically accommodated by an escape stair in a given time depends on three main factors: (a)

the width of the storey exits at each level

(b)

the width of the stair and its final exit

(c)

the number of persons who may be accommodated within the stair enclosure (stacking capacity).

The doors opening into the stair (see (a) above) should be sized to accommodate the anticipated number of people at each level. However, if the stair is congested with large numbers of people descending from the floors above, it may not be possible to enter the stair, even if the individual storey exits are of adequate width. During the evacuation process, people will be entering the stair at a number of different levels and some will be leaving through the final exit. Therefore, the stair must have sufficient floor space to accommodate those persons who are remaining within the stair enclosure (i.e. the difference between the number who have entered and the number who have left the stair). The maximum number of people that can be accommodated within a stairway at any one time is given by:

Nc(max) = pAS (7.7)

where Nc(max) is the maximum number of people that can be accommodated within a stairway at any one time, p is the maximum occupant density of the stair (person · m–2), A is the horizontal area of the stair and landings per storey (m2) and S is the number of storeys. The maximum density of people who can be accommodated on stairs and landings without suffering extreme discomfort is approximately 3.5 person · m–2. The number of persons leaving the stair is limited primarily by the width of the final exit and can be obtained using the calculation described in equation 7.6. The exit capacity of a stairway can therefore be estimated as follows:

Nin (max) = 1.333Ws t + 3.5A QS - 1V (7.8)

where Nin(max) is the maximum number of people able to enter the stair within a specified period, Ws is the width of the stair (m), t is the time available for escape (s), A is the horizontal area of stair and landings per storey (m2) and S is the number of storeys served. Equation 7.8 gives similar (but not necessarily identical) results to those given in Table 7 of Approved Document B, Volume 2 (HM Government, 2013). This table gives stairway capacities that are based on the same general principle but using a simplified calculation procedure (see equations 7.2 and 7.3 in section 7.3.3.1). It is important to have an accurate assessment of the total number of persons that a stairway can accommodate in a

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Traditional fire safety design codes set exit width requirements based on the anticipated population of the building. The time required to pass through the exits is not explicitly stated but is normally based on a notional evacuation time. This notional time does not take account of the delays that are likely to occur before people respond to an alarm (pre-movement time). The notional time implicit in most guidance is 2½ minutes, although this may be extended to up to 8 minutes for the design of open-air sports stadia.

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Fire safety engineering

specified period. A simple approach, like the one given in equation 7.9, may be used to calculate this, assuming the following conditions: an occupant density (p) in the stair of 2 person · m–2

——

a flow of 1.2 person · s–1 · m–1 of effective stair width (where the effective stair width, We, is 0.3 metres narrower than the actual width due to the natural tendency of people to keep a distance from walls and handrails).

The acceptance capacity of the stair may then be given by the following equation: Nin (max) = 1.2 tWe + pA QS - 1V (7.9)



where A is the horizontal area of stair and landings per storey (m2), S is the number of storeys served, t is the available exiting time (s) and We is the effective stairway width (m). Note that equation 7.9 gives the maximum acceptance capacity of the stair. The actual flow into the stair may be constrained if the storey exits are too narrow. Note that stairs which extend vertically more than 30 m should not exceed a width of 1.4 m unless they are provided with a central handrail, in which case they should be at least 1.8 m wide. This is because, in very tall buildings, people prefer to stay within reach of a handrail when making prolonged descent, hence the central part of a wide stair is little used and could be hazardous.

7.7.3

Evacuation simulation models

It is also important to recognise that many computational evacuation models incorporate numerous user-adjustable parameters, which can significantly influence the results of a simulation in ways which may not always be apparent to the viewer. The default parameters supplied with a given model do not necessarily represent the developer’s recommendations and will almost certainly not be suitable for all evacuation scenarios. Careful consideration should be given to the appropriateness of the parameters chosen for any given simulation. When the above points are taken into account, computational evacuation modelling can be an effective design tool if used with care. The facilities for graphical presentation included in most models can allow users to improve many aspects of a design using the visual outputs. The types of output available from different evacuation models are illustrated in Figures 7.9 to 7.11.

Computational evacuation modelling can enable the psychological response and movement of people under emergency conditions to be explored, as well as providing a dynamic assessment of people flows and crowd movement.

7.7.4

There are many models commercially available, with differing methodologies, capabilities and aims. The most prominent inputs can be broken down into the following common elements:

Calculation procedures and design assumptions should be chosen on a conservative basis (worst credible case) and, if this is done, an additional safety margin should not be necessary.

——

a representation of the building geometry

——

occupants’ physical characteristics (e.g. size, walking speed etc., which may vary across the population)

——

occupant behaviour (e.g. exit selection and response times)

——

occupant dynamics (i.e. occupants’ movements and interactions with one another).

7.8

Design safety margin

Information and wayfinding systems

7.8.1 General

The consequent outputs will vary from model to model, but typically include a visualisation of people movement within the building spaces. Time histories for variables such as occupant density, walking speed, door flow rates, door usage etc. are also usually available. Some evacuation models are also able to incorporate the effects of fire and smoke on the occupants by importing data from separate computational fluid dynamics software packages.

It is important to emphasise the role played by effective information, warning and wayfinding systems, including the architectural design of a setting, in achieving an adequate level of life safety.

To date, there is no formal standard by which building fire evacuation models (or their application in fire engineering

Informative fire warning (ifw) systems have electronic visual displays to supplement other forms of alarm, and such

7.8.2

Informative fire warning systems

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——

design) may be assessed – although work is being undertaken towards achieving this aim (for example, NIST Technical Note 1822 (Ronchi et al., 2013)). Each model therefore represents only its developer’s validation/verification efforts and consequent assumptions regarding human behaviour. It is therefore important that the approach that has been taken towards validating/verifying an evacuation model is clearly set out by the developer, along with any subsequent limitations of its application. However, as with any engineering tool, it is ultimately incumbent upon the user to make every effort to understand such limitations, and take steps to ensure that their chosen model is appropriate for a particular use. In order to achieve this, further validation specific to the proposed application may be necessary. Indeed, where practicable, and particularly for existing buildings, it is often desirable to calibrate the computational model against people movement data gathered by observations on site.

Means of escape and human factors

7-15

Figure 7.10  FDS+Evac (National Institute of Standards and Technology (NIST), VTT Technical Research Centre of Finland): simulation of a supermarket

Figure 7.11  buildingEXODUS (University of Greenwich): simulation of an office

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Figure 7.9  Pathfinder (Thunderhead Engineering Consultants Inc): simulation of a football stadium

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Fire safety engineering

7.8.4

Emergency wayfinding systems

Emergency wayfinding lighting systems consist of low-mounted tracks of light and marking of doorways on exit routes in conjunction with standard exit and directional signs (see Figure 7.12). The systems come into operation when power to the normal lighting fails or when the alarm system is activated. Systems can be powered or photoluminescent. In corridors, a lighting system mounted on the walls on each side of the corridor at 250 mm or less above the floor level provides direct illumination of the floor and highlights the path to be followed. The lighting should be as continuous as possible and recommended colours are white or green. Floor marking systems can be effective in highlighting a route through wide areas, such as plant rooms where wall mounting is not feasible.

Figure 7.12  Emergency wayfinding system (Reproduced by permission of LumAware, http://www.lumawaresafety.com.)

References ABCB (2016) National Construction Code 2016 (Canberra: Australian Building Code Board)

systems can significantly reduce pre-movement time. A Technical Note produced by Ramachandran (1991) presents basic features desirable in such fire warning systems.

7.8.3

Marking of means of egress

BSI (2004) PD 7974-6: 2004 The application of fire safety engineering principles to fire safety design of buildings. Human factors. Life safety strategies. Occupant evacuation, behaviour and condition (Sub-system 6) (London: British Standards Institution) (Note: PD 7974-6: 2004 has been replaced by PD 7974-6: 2019) BSI (2011a) BS ISO 3864-1: 2011 Graphical symbols. Safety colours and safety signs. Design principles for safety signs and safety markings (London: British Standards Institution)

British fire safety design codes recommend that exits are marked with pictographic exit signs depicting a running person. The design and construction of fire safety signs are detailed in the current British Standards (BSI, 2011a–c, 2013, 2014) and in section 7.10 of NFPA 101 (NFPA, 2018).

BSI (2011b) BS EN ISO 7010: 2012+A7: 2017 Graphical symbols. Safety colours and safety signs. Registered safety signs (London: British Standards Institution)

In certain circumstances, for example where direct line of sight of an exit is not possible and doubt may exist as to its position, a direction sign (or series of signs) should be provided. There are also requirements for other notices, e.g. ‘FIRE DOOR— KEEP SHUT’ on doors.

BSI (2013) BS 5499-4: 2013 Safety signs. Code of practice for escape route signing (London: British Standards Institution)

Where escape lighting is required, all exit and exit routes signs should be illuminated in the event of failure of the normal lighting. This may be achieved by one of the following: ——

externally illuminated signs

——

internally illuminated signs

——

self-luminous signs.

BSI (2011c) BS ISO 20712-1: 2008 Water safety signs and beach safety flags. Specifications for water safety signs used in workplaces and public areas (London: British Standards Institution)

BSI (2014) BS 5499-10: 2014 Guidance for the selection and use of safety signs and fire safety notices (London: British Standards Institution) BSI (2015) BS 9991: 2015 Fire safety in the design, management and use of residential buildings. Code of practice (London: British Standards Institution) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) CIBSE (2015) GVD/15 CIBSE Guide D Transportation systems in buildings (London: Chartered Institution of Building Services Engineers) DoH (2006) Health Technical Memorandum 05-03: Firecode. Fire safety in the NHS. Part E: Escape lifts in healthcase premises (London: Department of Health)

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In situations where wayfinding could be difficult, serious consideration should be given to the advantages offered by continuous luminous wayfinding systems and directional markers instead of conventional high-level emergency lighting (Webber and Aizelwood, 1993, 1994).

Means of escape and human factors DoH (2015) Health Technical Memorandum 05-02: Firecode. Guidance in support of functional provisions (Fire safety design in the design of healthcare premises) (London: Department of Health)

NFPA (2017) NFPA 130 Standard for fixed guideway transit and passenger rail systems (Quincy, MA: National Fire Protection Association) NFPA (2018) NFPA 101 Life Safety Code (Quincy, MA: National Fire Protection Association) Pauls J, Gatfield A and Juillet E (1991) ‘Elevator use for egress: The human-factors problems and prospects’ Proc. Symp. Elevators and Fire, New York, February 1991 (American Society of Mechanical Engineers) Ramachandran G (1991) ‘Informative fire warning systems’ Fire Technology 27 (1) 66–68

Ronchi R, Kuligowski ED, Reneke PA, Peacock RD and Nilsson D (2013) NIST Technical Note 1822 The process of verification and validation of building fire evacuation models (Gaithersburg, MD: National Institute of Standards and Technology) Scottish Government (2017) Technical Handbook – Non-Domestic (Livingston: Building Standards Division) Shields TJ (1993) Fire and Disabled People in Buildings BRE Report BR 231 (Garston: Building Research Establishment) Sime JD (1994) ‘Escape behaviour in fires and evacuations’ in Stollard P and Johnson L (eds) Design Against Fire – An Introduction to Fire Safety Engineering Design (London: Chapman and Hall) Webber GMB and Aizelwood CE (1993) Emergency Wayfinding Lighting Systems BRE Information Paper 1/93 (Garston: Building Research Establishment) Webber GMB and Aizelwood CE (1994) Emergency Wayfinding Lighting Systems in Smoke BRE Information Paper 17/94 (Garston: Building Research Establishment)

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HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019)

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8

Fire detection and alarm

Fire alarm systems were once considered to be a standalone requirement for early warning of a fire situation, but increasingly they are being used as part of a fire engineered solution for a given building. In addition to local planning or building regulation requirements, fire alarm design is usually undertaken in accordance with one of two principal standards, depending on where in the world the building is located. ——

The British Standards Institution (BSI) publishes a number of documents that are commonly used standards within the Commonwealth as well as the Middle and Far East.

——

The alternative standard commonly used throughout the world is the National Fire Protection Association (NFPA) standard.

This Guide explains the application of fire alarm design in countries that adopt both BSI and NFPA standards, as well as seeking to highlight the differences between the two approaches. The first thing to establish is the actual need for a fire alarm system. Initially, this need can be determined through reference to local regulations and associated guidance documents, consultation with the approving authorities, consultation with the client and insurer (e.g. for business continuity and property protection) and, where necessary, with reference to any fire safety risk assessment for the building. However, buildings that adopt a fire engineered strategy may have different requirements. This could require more comprehensive protection than the minimum ‘code’ requirements, but may, on occasion, require a lower level of protection based on a lower risk. Each country will have its own specific recommendations or requirements. While either BSI or NFPA standards may apply, a good understanding of local recommendations or requirements is essential. As an example, within England and Wales, Part B of Schedule 1 to the Building Regulations 2010 (SI 2010/2214) requires that strategies be put in place within all new buildings to notify occupants of a fire. This requirement can be satisfied in small commercial premises simply by someone shouting ‘Fire!’. However, in larger premises, it may be necessary to provide an electrically operated fire alarm system. In residential buildings, it will be necessary to provide a system of automatic fire detection (e.g. via smoke detection), and in non-residential buildings a system consisting of manual call points may be adequate. Larger multi-tenanted non-residential buildings may require a sophisticated analogue addressable fire alarm system. So, for example, within England and Wales, it is not necessarily the default

position that non-residential buildings require an automatic fire detection system including smoke detectors, although these are often provided as their life safety benefit is universally recognised, and they can also be used as a compensatory feature from some other variation from general fire safety guidance. To ensure that an adequate and appropriate system is considered from a project’s inception, some initial considerations must be borne in mind.

8.1.1

Identifying the need and level of coverage for a fire alarm system

First, it is necessary to determine if a fire alarm system is required at all. If one is, it will then be necessary to determine the level of coverage/protection that will need to be provided. This will depend upon the size, complexity and use of the building, in addition to any local code, fire strategy, insurance or client requirements. Relevant considerations include the following: ——

Are there any local codes or standards that define minimum life safety requirements?

——

Does the size or complexity of the building warrant a fire alarm system?

——

Are any unusual hazards present?

——

Does a sleeping risk exist?

——

Is the building mixed-use or multi-tenancy?

——

Is the protection for life or property?

——

If provided for property protection/business continuity, are there any specific client or insurance requirements?

——

Has a fire strategy (or fire engineering strategy) been prepared for the building that defines fire alarm requirements?

——

Does any automatic fire safety system require detection to operate effectively?

Local codes and standards may explicitly describe the requirement (or otherwise) for a fire alarm system. However, it should always be borne in mind that these should generally be considered as minimum requirements, and will normally only be required to achieve a minimum level of life safety in an otherwise ‘compliant’ building design. Other factors may require an increase (or variation) from the minimum requirements of local codes and standards. Some regulatory systems may also require that consideration be given to an automatic fire detection and alarm system as part of an overall risk assessment of a

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8.1 Introduction

8-2 building (e.g. the Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541) in England).

——

Building Regulations 2010 Approved Document B: Fire Safety (England) (HM Government, 2013)

——

Building (Scotland) Regulations 2004 — Technical Handbook – Non-Domestic, Section 2: Fire (Scottish Government, 2017)

——

Building Regulations (Northern Ireland) 2012: Technical Booklet E: Fire Safety (DFPNI, 2012)

——

Building Regulations 2010 Approved Document B: Fire Safety (Wales) (Welsh Government, 2015)

——

BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (BSI, 2017a)

——

BS 9991: 2015 Fire safety in the design, management and use of residential buildings. Code of practice (BSI, 2015a)

——

various risk assessment guides provided in support of the Regulatory Reform (Fire Safety) Order 2005 (however, these are not normally used for fire alarm selection in new buildings).

There may be particular aspects of the building design (such as size, complexity, mixed uses, sleeping risks, multiple tenancies or areas of high fire risk) that may warrant a fire detection system. If, for example, the building under consideration is a single-storey workshop with a handful of small rooms and no public access, then there may be no need to provide a fire alarm system. However, a large shopping centre or hotel may require comprehensive automatic fire detection coverage. Local codes and standards are generally developed to address life safety needs within a building. However, there can be a need for a fire alarm system for property protection or business continuity. This may be to protect unoccupied areas, high-value assets or business-critical infrastructure. Any such requirements may be explicitly defined directly by the client, owner or occupier, or by their insurers. The building design may have included input from a life safety code consultant or a fire engineer. It is important to ensure that any fire detection and alarm system design aligns with their requirements. This can be particularly important in countries where fire engineered or performancebased design solutions are commonplace. Such solutions can routinely require a specific level of fire detection and alarm to achieve the required level of fire safety performance. It is also important to remember that a particular level of fire alarm/fire detection may be necessary to ensure other fire safety systems can perform as required. For example, while certain countries may not require automatic fire detection in enclosed car parks to provide early warning to occupants, such detection may be required in any event to operate a mechanical smoke ventilation system. Similar

considerations may apply to many fire-safety-related building services provisions, such as automatic fire and smoke dampers, pre-action sprinkler systems, automatic fire and smoke curtains, and devices to release fire doors that are otherwise held open by electromagnets. BS 5839: Parts 1, 6 and 8 (BSI, 2013a, 2013b, 2013c) and BS 9999 (BSI, 2017a) recognise the use of fire alarm systems to provide signals to initiate other fire protection systems, such as smoke control or sprinkler systems. The standards do not, however, apply to such systems or the ancillary circuits that interface with them. NFPA 72 (NFPA, 2016) makes reference to fire safety function control. This is covered by section 6.15 of NFPA 72 and is more specific about the control of other life safety systems by the fire alarm control panel. Should it be decided that a fire alarm system is required, then the following types need to be considered: ——

manual fire systems

——

automatic fire detection systems.

Manual alarm systems, which consist of fire alarm boxes (either manual break-glass, call-point or pull-station type) and alarm sounders connected to a control panel, can only be operated and the alarm raised when activated by an individual having detected a fire incident. Automatic systems, which typically consist of smoke and heat detectors (although other types of detection are available), in addition to fire alarm boxes and alarm sounders connected to a control panel, are designed to raise the alarm whether or not personnel are present at the time, thus giving early warning of a fire incident. Hence, where the term ‘automatic fire detection’ (afd) is used, this generally refers to systems that include an automatic detector, rather than simply manual call points. BS 5839 categorises automatic fire alarm systems as being either ‘P’ systems, which are designed to protect property, or ‘L’ systems, which are primarily designed for the protection of life. A category P system may be used where a building has valuable contents but is seldom occupied by people. A category L system may be used in a highly populated building, such as a hotel. Further subdivision is identified in BS 5839 by classifying category P and L systems as either P1 or P2, and L1, L2, L3, L4 or L5. These types of system are described in further detail in section 8.2. The type of system required should be identified at the outset. Codes of practice for fire alarm and detection systems for buildings are given in BS 5839. Part 1 (BSI, 2013a) deals with system design, installation and servicing, and Part 6 (BSI, 2013b) provides a code of practice for detection and alarm systems in domestic buildings. BS EN 54 (BSI, 1997, 1998, 2001, 2006, 2015b, 2015c, 2017b) covers the design of control and indicating equipment, detection devices, sounders and power supplies. In addition to the recommendations applicable to British Standards, this Guide also provides information on the recommendations of NFPA 72: National Fire Alarm and Signaling Code (NFPA, 2016).

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The principal guidance documents (provided in support of the functional objectives of the relevant fire safety legislation) covering the need for fire protection in various types of premises within the United Kingdom are as follows:

Fire safety engineering

Fire detection and alarm

8.1.2

Need for consultation

The fire detection and alarm requirements for most building types are covered by national and local legislation and its supporting guidance and codes. It is always advisable to consult the approving authority or authority having jurisdiction regarding the applicable legislation covering particular premises and for guidance on the type of system that may be required. To ensure that the requirements of all stakeholders are adequately captured, during the initial stages of the design of a fire alarm system it is important to consult with all interested parties, which may include: ——

building owner

——

building occupier/tenant

——

authority having jurisdiction (e.g. building control, fire service etc.)

——

architectural and engineering consultants

——

building insurers (where possible)

——

system installers

——

government health and safety departments

——

government heritage departments (where buildings are protected from alteration due to their historic value).

8.1.3

Cause and effect

Fire alarm design, especially when integrated into a fire engineered solution, can become complex. The interrelationship with other systems can become critical, and a method of checking the operation in all known conditions is an important design tool for describing the operation of a fire alarm system. The development of a table or chart that cross-references a set of known events with the outcome (or consequences) of each event can be an important part of the design process, not only during design, to ensure that nothing is missed, but also as a commissioning tool and, ultimately, as a prediction tool for building managers. This cause and effect schedule should include fault events that are reasonably likely over the life of the system, and should cover all foreseeable eventualities, single points of failure and linked operations. This will draw the designer’s attention to any situations that might not immediately be apparent, but which could occur on the failure of seemingly unconnected events.

8.1.4

Managing false alarms

Unacceptable rates of false alarm can result in significant difficulty in managing fire safety in buildings effectively. Frequent false alarms can result in alarms being ignored

or alarm systems being deactivated. False alarms can also have a significant impact on business continuity, for example if a stadium or airport terminal needs to be partially (or even completely) evacuated, or if a production line needs to be shut down. It is therefore critical that careful consideration is given to means by which the rate of false alarms can be reduced. A simple cause of false alarm is the incorrect specification of detector head for the given environment. The use of smoke detection in kitchens, which may be regularly subject to burning toast, for example, is a classic example. Similarly, the use of beam detectors in areas where the beam may be obscured by forklift trucks or affected by building movement can result in false alarms. Similar issues can arise due to the incorrect specification and location of manual call points. Manual call points can be subject to accidental or malicious activation in certain circumstances. Hence, call points may need to be located away from areas where they may be accidentally knocked or hit and/or provided with a cover. In some instances, it may even be appropriate to completely omit manual call points where the risk of false activation is unacceptably high. A simple form of fire engineered solution that has been used for many years is ‘alarm filtering’, with protocols such as ‘alarm verification’. In situations where false alarms would cause significant disruption, it is common practice to commission the fire detection system such that two detectors must operate independently to identify the presence of a fire before the system activates an audible alarm. This is often referred to as ‘coincidence detection’. Such systems usually provide a local warning to the building manager as soon as the first detector identifies a fire. This gives prior warning of an alarm, allows an investigation of the alarm to be carried out, reduces the risk of a faulty detector causing the unnecessary evacuation of a building and, if the alarm is genuine, gives warning of an imminent building evacuation. Typical examples where alarm filtering may be beneficial are hospitals, theatres, shopping malls, cinemas and stadia. Where coincidence detection is used, it is common practice to provide an upper time limit to the investigation period. Hence, if building management has not cancelled the alarm within a set time frame after the first detector head has activated, the fire alarm system would typically progress to full evacuation. Another example of alarm filtering is cross-zoning. This uses multiple detection loops with redundant detectors, and typically is used in systems with automatic discharge (such as deluge or clean agent). In this case, alarm filtering is used to manage the financial risk of an accidental discharge. Temporary building works can also result in false alarms — this is particularly true in the case of dusty or ‘hot’ works. It may be necessary for temporary measures to be taken to minimise the risks associated with these activities. False alarms can also result from inadequate maintenance of a system. This is an important reason for ensuring that all fire detection and alarm systems are provided with adequate maintenance and servicing regimes.

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This chapter provides some basic recommendations for the design, installation and application of fire alarm systems and equipment, and it is not intended as an alternative to any parts of standards such as BS 5839 or NFPA 72.

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8-4

8.2

Fire safety engineering

Classification of alarm systems

8.2.1

Household systems

NFPA 72 identifies systems for household protection as one of three main types, whereas under British Standards, domestic systems and non-domestic systems are covered by separate standards.

8.2.2

Systems for property protection

Fire alarm systems intended for the protection of property (referred to as category P systems under British Standards) will automatically detect a fire at an early stage, indicate its location and raise an effective alarm in time to summon the firefighting forces (i.e. both the ‘in house’ firefighting team and the fire brigade). A key difference between a category P system and one that is provided for life safety only (category L) is the requirement for the alarm to be transmitted to a receiving centre, to allow the fire service and any additional relevant persons to be alerted. However, because category P systems are not necessarily provided for life safety, there may be a reduced requirement for audible alarms to instigate evacuation throughout the premises. NFPA 72 does not differentiate between systems designed for the protection of property or life and covers all aspects under the protected premises system type. 8.2.2.1

BS 5839: Part 1 classification

British Standard BS 5839-1: 2013 (BSI, 2013a) subdivides category P systems as follows: P1 systems All areas should be covered by detectors, with a few exceptions. Such exceptions may include certain voids (typically less than 800 mm in height, unless the spread of fire between rooms can take place through such voids, also noting that floor voids in data processing rooms are conventionally protected irrespective of depth), small (<1 m2) cupboards, toilets and bathrooms and some small lobbies. P2 systems Detectors are required in defined areas in a building which have a high fire risk, e.g. areas containing the presence of ignition sources and easily ignitable materials, or areas with a high consequence of fire. Areas

BS 5839-1 requires that voids with depths greater than 1.5 m should be treated as rooms. This requirement will apply regardless of which type of system is selected. 8.2.2.2

NFPA 72 classification

The NFPA does not identify such system types. Designers are required to use their judgment and experience to determine the level of coverage required. However, once this decision has been made, guidance is provided. The following gives an overview of the areas to be covered. NFPA 72 should be consulted for specific details. Total (complete) coverage Total coverage refers to all rooms, storage areas, lofts, attics, ceiling voids and other subdivisions and accessible spaces with the following exceptions: ——

where inaccessible areas do not contain combustible materials

——

where there are small concealed spaces over rooms, provided they do not exceed 4.6 m2 (50 ft2) in area

——

detectors shall not be required below an open grid ceiling subject to specific recommendations

——

detectors shall not be required in concealed accessible spaces above suspended ceilings that are used as a return air plenum meeting the recommendations of NFPA 90A (NFPA, 2015)

——

detectors shall not be required beneath open loading docks or platforms subject to specific recommendations.

Partial coverage Detection shall be provided in all common areas and work spaces such as corridors, lobbies, storage rooms and other tenantless spaces. Selective coverage Where local codes, standards or legislation require the protection of selected areas. No required coverage Where detection is not required by code, law or standard, yet is a specific requirement of the client.

8.2.3

Systems for life protection

BS 5839-1 gives clear guidance on systems designed for life protection and this is detailed below. As stated in section 8.2.2.2, the NFPA does not identify such system types. Designers are required to use their judgment and experience to determine the level of coverage required. Under BS 5839-1, fire alarm systems for the protection of life (category L) can be relied upon to sound a fire alarm to ensure that occupants are alerted to a fire and can commence escape at an early stage.

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The approaches taken by BSI and NFPA differ in their classification of systems. While British Standards classify systems as being for the protection of property or of life, and there is a separate standard for dwellings, BS 5839-6: 2013 (BSI, 2013b), NFPA 72 (NFPA, 2016) splits system classification into those designed for households, those designed for protected premises and those requiring supervising station cover. The following paragraphs explain the type of categories identified in each standard.

without detection should be separated by a fire-resisting construction.

Fire detection and alarm

8-5

8.2.4

L1 systems Detection coverage is as for P1 systems (see above) (i.e. essentially comprehensive coverage with a limited number of permitted exceptions).

This type of system is identified by NFPA 72 and is not mentioned specifically in BS 5839. Supervising station fire alarms are networked systems where one building is used as the main control point for a fire alarm system covering a number of buildings. An example would be a college campus, where a central control building holds the main control panel under the supervision of a site management team. The other buildings then have individual systems that are networked to the main control system.

L2 systems Essentially for the protection of escape routes and rooms that directly open onto escape routes (which is an L3 level of coverage, see below), and also for specified areas where a fire could lead to a high risk to life safety (this could include areas where the probability of fire is high, the combustible inventory is high or the risk to life is high). The onus on defining these ‘additional’ high-risk areas remains with the designer, therefore L2 systems are those that include all L3 areas and additional (designer defined) areas of risk. L3 systems For the protection of escape routes and rooms opening on to escape routes. This includes stairways, corridors and other areas that form parts of a common escape route, and also all of the room spaces that open onto these defined escape routes. Again, there is a limited number of areas where detection coverage may not be required for escape routes or rooms that open onto escape routes. Areas covered by L3 systems should always include those appropriate to L4. L4 systems For the protection of escape routes, including stairways, corridors and other parts that form part of a common escape route. L5 systems For the protection of selected rooms and areas only. This type of system is normally provided to achieve a specific fire safety goal.

Supervising station fire alarms

Such systems can also aid the fire brigade by allowing them to establish an information point at a safe distance from the location of the fire.

8.2.5

Manual fire alarm systems

BS 5839-1 defines systems that include manual call points only, with no additional automatic fire detection systems, as category M systems. These manual call points are distributed at strategic locations within the building. As discussed above, it is normally necessary for category L systems to fulfil the requirements for category M systems. Again, as stated in section 8.2.2.2, the NFPA does not identify such system types. Designers are required to use their judgment and experience to determine the level of cover required.

8.2.6

Systems for domestic dwellings

BS 5839-6 covers the recommendations for fire detection within dwellings. The recommendations are quite complex and have been broken down into six grades: Grade A

A fire alarm system that conforms to certain specific recommendations of BS EN 54-2: 1997 (BSI, 1997) (for control and indicating equipment) and BS EN 54-4: 1998 (BSI, 1998) (for power supply) and having been designed and installed in accordance with specific sections of BS 5839-1.

Grade B

A fire alarm system that conforms to certain specific recommendations of BS EN 54 (fire detectors, fire alarm sounders and control and indicating equipment, power supply).

Grade C

A system of fire detectors and sounders connected to a central control panel with mains power supply and battery back-up.

Grade D

A system of mains-powered smoke alarms with battery back-up.

Grade E

A system of mains-powered smoke alarms without battery back-up.

Where it can be identified that only certain areas of a building present an unacceptable risk from fire, then it may be appropriate to install automatic detection in these rooms only (which could result in an L5 or P2 standard of coverage).

Grade F

A system of battery-powered smoke alarms.

BS 5839-1 gives further details on the system categories and requirements for coverage.

Once the appropriate grade for a system has been determined, a category needs to be established. Categories largely

Category L5 systems could include one or two detectors only, but they might also include detection to an L2, L3 or L4 standard. For example, as part of a fire engineering strategy, an airport terminal may be provided with comprehensive fire detection coverage (essentially to an L1 standard) in many areas of the building, but detection could be omitted in very large and sterile concourses, where it would not be appropriate. Some variation in manual call point locations could also form part of the strategy. While reasonably comprehensive, the overall system would not satisfy L1, L2, L3 or L4, so the system would be classified as L5. Category L systems would typically also be required to provide manual call points, in accordance with the requirement for a category M system (see below). However, such manual call point coverage might not be required in certain circumstances, or where it is not considered necessary as part of the fire safety goals of a category L5 system.

Where systems to grades D, E or F are installed with more than one smoke detector, these should be interlinked within the same dwelling.

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Category L systems are subdivided as follows:

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Fire safety engineering

follow the convention in BS 5839-1 and are summarised below (noting that ‘D’ is included in the ‘L’ and ‘P’ designation to reflect domestic application):

LD2 A system installed in escape routes and areas that may present a high fire risk or where the risk to life safety is high. LD3 A system installed in the escape routes (e.g. internal entrance hallways or stairs). PD1 A system installed throughout the dwelling, other than toilets and bathrooms. PD2 A system installed in defined rooms or areas of the dwelling. The choice of grade and category of system will again depend on the relevant codes and standards, local regulations, the use and size of the building and the nature of the occupants (e.g. owner-occupiers, students in halls of residence or short-let temporary tenants) and should be confirmed with all relevant stakeholders. NFPA 72 also addresses the use of fire alarm systems in private dwellings. The recommendations are given in chapter 11 of the code, and while similar levels of detection to those given in BS 5839-6 are covered, they are more prescriptive and categorised into building types rather than into grades and categories. This makes selection of appropriate systems easier. Power supply requirements to detectors are also similar to those in BS 5839-6.

8.3

Types of fire detection systems

All fire detection systems use the same principle to detect a fire situation — a fire or combustion product causes a disturbance in the steady-state signal within the detection device. The differences between types of systems relate to what products the devices are designed to detect and the way that the disturbance signal is processed by the fire alarm control panel. Most fire detection systems fall into one of two main categories: ——

conventional monitored systems

——

addressable systems (including analogue addressable).

8.3.1

Conventional monitored systems

Conventional monitored systems use a basic method of detecting a fire. The detection points (either smoke or heat) are wired in radial circuits from the control panel. At the end of each circuit, a resistor or semiconductor device is used to create a known resistance across the circuit and hence provide a steady-state reference. Because

Sounders on this type of system are wired on separate circuits in fire-resisting cable, as they are not monitored and must continue to operate in the event of a fire.

8.3.2

Addressable systems (including analogue addressable)

While detectors connected to addressable systems operate in the same basic way as for conventional monitored systems, they are connected to ‘loops’ rather than radial circuits. Each detector is allocated a unique identification or ‘address’ during the commissioning process. This allows the control panel to recognise the change in the steady state of individual detectors, as opposed to changes in circuit steady state with conventional monitored systems. The benefit of connecting to loop rather than radial circuits is that damage to part of the circuit can be isolated, allowing the system to continue in operation. In order to achieve this, zone isolator units are placed in the loop between zones. Analogue addressable systems are the most common type of system being installed at present. They use detectors that constantly relay information on their operating condition to the control panel. This type of information will allow the control panel to determine if a particular detector is being subjected to an abnormally high ambient level of smoke in normal use, and hence compensation can be made. In addition, the control panel can monitor the contamination levels on each of the system’s detectors and report when maintenance is required. In some buildings it may be desirable for the detectors to be less sensitive during the daytime, when the building is occupied, than at night, when the building is unoccupied. Analogue addressable systems can be programmed to operate in this way. Zones of conventional detectors and call points may be connected to an analogue system by means of suitable interfacing devices.

8.4

Detection zoning

To ensure rapid and unambiguous identification of the fire source, the protected area should be divided into detection

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LD1 A system installed throughout the dwelling, other than toilets and bathrooms.

the circuits are constantly monitored, wiring does not technically need to be fire rated, as a circuit break will immediately be notified to the panel as a change in the steady state. If a detector is activated by a fire, then its operation will also alter the steady-state resistance of the circuit to which it is connected and the fire alarm panel will raise the alarm. As each radial circuit from the control panel will have a number of detectors connected to it, identification of the location of a fire is limited to the knowledge of the affected circuit. It is common practice to allocate one radial circuit to one fire zone, and therefore activation of a detector will be registered at the control panel as being within the zone covered by that circuit. Figure 8.1 shows a diagram of this type of system. Following activation of a device, the zone in which the device is located must be searched to identify the precise location of the alarm. No other information about the zone can be obtained at the control panel.

Fire detection and alarm

Zone 1

8-7

Zone 2 EOL

Zone 3 EOL

Detector

Zone 4 EOL

EOL

EOL End of line resistor

+ – Detection zone 1

+ – Detection zone 2

+ – Detection zone 3

+ – Detection zone 4

Fire alarm control panel Note: a wiring fault in one detection zone will not cause a fault in another detection zone Figure 8.1  Wiring of detectors and call points within a detection zone

zones. When determining the area to be covered by a zone, consideration should be given to accessibility, size, the fire management strategy determined for the premises and, particularly in occupied premises, to the need for each detection zone to be accessible from the main circulation routes leading from where the control panel is situated. Addressable systems are able to give far more accurate information on the location of a fire source.

——

The zoning arrangements should complement the fire strategy. This is particularly important for large buildings with complex fire strategies (e.g. which include phased evacuation).

——

Detection zone limits can be relaxed only for certain category M systems.

——

Following a fire incident, a person escaping from the source of the fire may activate a manual call point on the escape route but in a different zone to that in which the fire is located. Therefore, it may be an advantage to have manual call points within separate zones to those of the detectors. This will avoid misleading information regarding the position of fire, particularly on staircase landings.

——

The wiring of the detectors should be arranged such that a fault on one detection zone does not prevent the operation of detectors in another zone; for compliance, detectors are normally wired on a conventional panel as shown in Figure 8.1.

NFPA 72 (NFPA, 2016) does not give formal recommendations for zoning, except for wireless systems. In such systems, each detector position has to be individually identifiable. The recommendations of BS 5839-1 (BSI, 2013a), however, are quite specific. In general, the following BS 5839 recommendations relating to the size of a zone should be observed: ——

If the total floor area (i.e. the total of the floor areas for all storeys) of the building is not greater than 300 m2, then the building may be treated as a single zone, no matter how many storeys it may have. Otherwise, each zone should not extend over more than one storey.

Where fire alarm systems are being designed for buildings outside British Standards recommendations, care should be taken to ensure the system is zoned with a view to satisfying the following points:

——

The total floor area for a zone should not exceed 2000 m2 (where non-addressable detection is used).

——

The search distance (i.e. the distance that has to be travelled by a searcher inside a zone to determine visually the position of a fire) should not exceed 60 m (unless addressable detection is used). The use of remote indicator lamps outside doors may reduce the number of zones required.

——

Search areas within a zone should be minimised by limiting their geographic area.

——

Fire zones that pass through building features, such as staircases, should be individual zones.

——

Areas of high risk should be individually zoned.

Where stairwells or similar structures extend beyond one floor but are in one fire compartment, this should be treated as a separate fire zone (unless addressable detection is used).

——

There should be a logical sequence to the layout and numbering of zones.

——

When planning zones, the following points should also be considered:

With addressable or analogue addressable systems, each device (e.g. detector or call point) is given a numerical address code. Devices are wired in a loop arrangement. The manufacturer should be consulted as to the maximum

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Call point

8-8

Fire safety engineering Zone 1

Zone 2

Zone 3

Zone 4

Detector Call point

+ – Detection loop 1 OUT

+ – Detection loop 1 IN Fire alarm control panel

Note 1: short-circuit isolators are fitted between each zone so that a wiring fault in one detection zone will not cause a fault in another detection zone. Note 2: short-circuit isolators are also fitted between loop OUT and the first detection device, and loop IN and the last detection device; in many cases these are built into the control panel circuitry. Figure 8.2  Wiring of detectors and call points on a detection loop

number of devices that can be accommodated on a loop, and the length of one loop. One loop can cover several detection zones. Short-circuit isolators are placed between zones, as shown in Figure 8.2, so that a fault in one zone does not affect devices in another zone. With addressable systems, devices can be assigned into separate zones by programming of the panel software. With addressable or analogue addressable systems, the detector or manual call point in alarm can be shown by the use of an alphanumeric display. However, this on its own will not be acceptable and the zone in which the detector or manual call point has operated should also be displayed, e.g. by means of an led indicator. The zonal identification diagram or chart may be mounted adjacent to the control panel and, as BS 5839-1 also requires a plan of the building to be displayed, the use of a mimic diagram provides a suitable means for zone identification.

8.5

Manual call points

The manual call point (often referred to as a manual break-glass unit) is a device to enable personnel to raise the alarm, in the event of a fire, by simply breaking a frangible element and thus activating the alarm system. BS 5838-1 provides guidance for the correct siting and positioning of manual call points. This includes the following: ——

Manual call points should be located on all storey exits (e.g. exits into stairs) and all exits to the open air.

——

Manual call points should be located so that no person needs to travel more than 45 m from any position within the premises in order to operate one. This distance may need to be reduced in certain circumstances (e.g. where there is a risk of rapid fire spread, a high number of mobility impaired occupants etc.).

——

Generally, call points should be located at a height of 1.4 m above the floor at easily accessible, wellilluminated and conspicuous positions, free from obstructions.

——

The method of operation of all call points in an installation should be identical, unless there is a particular reason for differentiation.

Where manual call points are located on the landing of an enclosed staircase (except the final exit call point), they shall be included within the zone that serves adjacent accommodation on that level. Manual and automatic devices may be installed on the same system. However, it may be advisable to install the manual call points on separate zones for speed of identification (see section 8.4).

8.6

Types of fire detection devices

8.6.1 General Detectors are designed to identify the presence of byproducts of a fire. These are primarily smoke or heat, but

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Short circuit isolator

Fire detection and alarm can also include other combustion products (e.g. carbon monoxide) or radiation. For each of these fire by-products, a number of types of detector are available:

8-9

8.6.4

Combined or multi-sensor heat and smoke detectors

Smoke detection: types of detector include point ionisation smoke detectors, point optical smoke detectors, optical beam detectors and aspirating systems. Video detection can also be used to identify the presence of smoke.

In combined detectors, the benefits of both heat and smoke detection are gained. This type of detector generally uses the optical method of smoke detection along with a flat-response heat detector. Modern multi-sensor units can use a number of inputs, including heat, smoke and combustion gases, to determine the alarm state.

——

Heat detection: detector types include point fixed heat detectors, point rate of heat rise detectors and linear heat detectors.

8.6.5

——

Flame detection: detector types include ultraviolet and infrared flame detectors.

It is common for detector units to analyse for multiple phenomena, for example combined heat and smoke detection. When choosing the type of detector to be used in a particular area, it is important to remember that the detector must be able to discriminate between fire and the normal environment within the building, e.g. smoking in hotel bedrooms, fumes from forklift trucks in warehouses, steam from bathrooms, smoky cooking in kitchens etc. Many common methods of detection use ‘point-type’ detectors, where each detector serves a specific point in the protected space. Most traditional types of smoke and heat detector are point detectors. Detectors may alternatively be ‘line-type’, or ‘linear’, where the detector analyses for a phenomenon occurring at some point along its length. This includes linear heat detection and optical beam detection.

8.6.2

Ionisation chamber smoke detectors

In ionisation chamber detectors, an electrical current flows between two electrodes. The current is reduced by the presence of smoke. Ionisation detectors are particularly sensitive to small-particle smoke, such as that produced by rapidly burning fires, but are relatively insensitive to large smoke particles in dense smoke or smouldering fires, such that those produced by overheated pvc or smouldering polyurethane foam. When used in an incorrect location, ionisation detectors can be responsible for a higher frequency of false alarms than optical types. Care should be taken when disposing of ionisation detectors due to their radioactive content. Local restrictions on disposal need to be observed.

8.6.3

Optical chamber smoke detectors

In optical chamber detectors, light is scattered or, in some cases, absorbed by smoke particles. They are sensitive to large particles found in optically dense smoke, but are less sensitive to smaller smoke particles. Optical detectors are the most common type in use due to their better performance in terms of lower frequency of false alarms and their ability to detect smouldering fires.

Point-type heat detectors

Point-type heat detectors respond to temperatures surrounding a particular spot. All point-type heat detectors should include a fixed temperature element operating at a predetermined temperature. Some may also include a rate of rise element designed to operate in response to a rapid rise in temperature. In general, heat detectors are less sensitive than other types of detector, and therefore they should be used where background smoke or particulate matter would render smoke detectors unsuitable.

8.6.6

Linear heat detectors

A linear heat detector consists of a special cable that is able to detect changes in temperature along its length. Two types are available. The simple metallic cable type utilises two steel cores twisted together, each insulated with a temperature-sensitive polymer. If any section of the cable is heated to above the preset alarm value, the polymer insulation melts and the two wires are allowed to touch, generating an alarm condition. Fibre optic linear heat detection is more sophisticated, in that it continuously monitors the temperature along its length, typically at 1 m intervals. This allows the controlling system some degree of self-learning and permits the analysis of unusual temperature events.

8.6.7

Beam detectors

In many installations, point-type heat detectors or smoke detectors will be satisfactory. However, in buildings with very high ceilings, these types of detectors are difficult to access and detection might not occur until the fire is well established (especially in the case of heat detectors). In these situations, dedicated optical beam detectors are more suitable. Optical beam detection may also be suited to the protection of very large and open spaces. Figure 8.3 shows the general arrangement of a beam detector. The transmitter propagates an infrared beam, which travels across the protected area to the receiver. In the event of a fire, the amount of infrared light that will be received by the receiver is reduced due to the presence of smoke. The receiver can be located at the opposite side of the protected space from the transmitter. Alternatively, the transmitter and receiver may be located together, with a mirror located at the opposite side of the space, designed to reflect the transmitter signal back to the combined unit.

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——

8-10

Fire safety engineering

Transmitter

Smoke

one or more pipes, drilled at regular intervals, installed throughout the area to be protected and connected to the detector (the holes serve as individual smoke detectors)

——

a pump that draws air through the pipes to the detector, where it is analysed for the presence of smoke

——

an optional filter to remove dust particles etc., which may have been drawn into the pipes

——

appropriate electronic equipment to indicate the presence of smoke and control the operation of output relays etc.

Fire Figure 8.3  Operation of a beam detector

Beam detectors are normally sited just below the ceiling, and can be used in areas with high ceilings and areas where the installation and/or maintenance of point detectors may prove difficult (such as in warehouses), may be too expensive or may interfere with the decor of the building. They are particularly suited to warehouses, aircraft hangers, historic buildings, art galleries, atria, shopping centres and loft spaces. However, care must be taken to ensure that any possible flexing of the building is taken into account when choosing the locations of the units. Care should also be taken with unusually high spaces, where a smoke layer is likely to form below the ceiling (e.g. due to stratification of smoke). In such a situation, the detectors need to be placed below this level.

Aspirating systems have an advantage over other types of fire detection systems in that the pipework can be hidden in the ceiling or behind walls. In addition, they are unaffected by high air flows. Unlike point detectors, which wait for smoke to reach them, air is drawn to the detector. Therefore, they can be used in areas where smoke detection would otherwise prove difficult, such as in atria, stadia, gymnasia and large function rooms with high ceilings. They are also suitable for use in dusty environments, such as car parks. As with beam detectors, care should also be taken with unusually high spaces, where a smoke layer is likely to form below the ceiling (stratify). In such a situation, the aspirating system pipework needs to be placed below this level. Detection equipment of this type may be marginally more costly than a conventional fire detection system and control system. However, the benefits in terms of reduced maintenance costs cannot be dismissed.

See chapter 6 for fire size and temperature gradients for smoke behaviour.

Normally, the control panels can be configured to give three levels of response, depending on the level of smoke detected, for example:

8.6.8

Level 1

Notify responsible personnel that smoke has been detected.

Level 2

Switch off air vents and/or switch off power supplies to certain areas to prevent the fire from igniting.

Level 3

Indicate a general fire alarm condition and signal that a fire has been detected to other systems and communication centres.

Aspirating systems

In some premises where expensive equipment is housed, such as computer rooms and telephone exchanges, it is important to detect smoke before the outbreak of flaming combustion. In such situations, an aspirating system should be considered. In addition to this, it is becoming more popular to use aspirating systems in areas where access for maintenance would be difficult to arrange, such as enclosed public areas. In some heritage buildings, the ability to conceal the detection pipework is a consideration for the use of this type of device. The ability to locate the sensing unit away from the area being protected is also leading to new applications being found for these systems, such as in cold stores. The accuracy of aspirating systems has increased over the past few years, and they are now more resilient to false alarm. Their cost has also been falling. As a result, these systems can now offer alternatives to traditional systems in general use. Aspirating systems generally consist of the following component parts: ——

an extremely sensitive detector (approximately 10–200 times more sensitive than a typical point detector) housed in a control unit

Recommendations for the design and installation of aspirating systems are given in BS 5839-1 (BSI, 2013a).

8.6.9

Flame detectors

Flame detection is now mostly limited to specialist applications requiring very quick detection of flames and where high-value assets are being protected, such as aircraft hangars. They can generally be used in areas that contain materials that are likely to produce rapidly spreading flaming fires, such as flammable liquids. There are two main types of flame detector: ——

ultraviolet flame detectors, which detect the ultraviolet radiation within a flame

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—— Receiver

Fire detection and alarm ——

infrared detectors, which respond to the flickering component of the infrared radiation from a fire.

8.6.10

Gas combustion detectors

This type of device is capable of detecting some of the gaseous products of combustion rather than the smoke or heat that is generated. The most common type is the carbon monoxide detector, which are particularly good at detecting a fire where the oxygen supply to that fire is restricted. This makes them very effective at detecting smouldering fires where the lack of heat or oxygen can hinder fire development. It also makes them suitable for use in residential properties as monitoring devices where gas-fired heating equipment is present and there is a risk of the air supply to that equipment being restricted or the flue being blocked. They can also be less affected by other common causes of false alarms, such as dust and steam. Although carbon monoxide detectors have advantages over other types, there are some disadvantages that should be borne in mind. These include the following: ——

Carbon monoxide will diffuse within the atmosphere. If it is contained within a building, it can travel a significant distance from the source of the fire. This means that a detector responding to the gas may not be the nearest to the source of the fire, and may not even be in the same zone or floor level.

——

Because they are designed to detect gases rather than particles of smoke or rises in temperature, carbon monoxide detectors might not respond to a fire that generates a high level of smoke and has a good oxygen supply.

——

The sensing element within commonplace carbon monoxide detectors has a finite life, and so replacement must become part of the maintenance regime for the system in which they are installed. Longer life alternatives are available which use infrared detection methods. However, these are not widely used in the construction industry, being prohibitively expensive.

Careful thought should be given to the placing and spacing of these detectors, and their use alongside smoke and heat detectors rather than instead of them.

8.6.11

water vapour. One advantage of using the cctv system is that cost can be shared and, as most vsds can monitor a number of cameras at once, processing equipment costs can be minimised. vsd is particularly useful in large open areas, where smoke paths cannot be predicted. The systems do not rely on smoke reaching particular detection heads and therefore give a much wider coverage per detector. Typical applications would be areas where the installation of traditional detection would be unsightly or where valuable equipment is stored over a large area and a fire situation needs to be detected quickly.

As with most software-based systems, the trigger thresholds can be set to work at varying levels in order to minimise false alarms. It should be noted that cabling systems will have to be carefully considered if they need to operate during a fire situation. It should also be noted that vsd requires the cameras to be able to ‘see’, which will require lighting to be maintained at all times. Some cameras are designed to work in infrared lighting and, again, this will need to be maintained at all times. Building maintainers will need to understand the relationship between the vsd and the lighting installation so that future development within a building does not compromise the vsd.

8.7

The recommendations of BS 5839-1 (BSI, 2013a) and NFPA 72 (NFPA, 2016) differ significantly in this area. While very specific guidance is provided in BS 5839-1, based on permissible distances, the NFPA 72 guidance is based on statements as to where detectors should or should not be placed, along with general spacing information (to be confirmed by the equipment manufacturer).

8.7.1

Heat and smoke detectors

In a building, the greatest concentration of smoke and heat will generally occur at the highest parts of enclosed areas, and therefore detectors should normally be sited at these locations. BS 5839-1 includes the following recommendations: (a)

Heat detectors should be sited so that the heatsensitive element is not less than 25 mm nor more than 150 mm below the ceiling or roof. This increases to 600 mm for smoke detectors. If a protected space has a pitched or north-light roof, detectors should be installed in each apex.

(b)

The maximum horizontal distance between any point in the area and the nearest detector is as follows for point type heat and smoke detectors:

Video smoke detection

Video smoke detection (vsd) is a system based on the use of conventional closed-circuit television (cctv). A processing unit is connected to the cctv system, which is preprogrammed with known smoke characteristics (algorithms). By monitoring the live images offered by the cctv system, smoke patterns can be identified early and the alarm raised. These systems are sophisticated to the level of being able to distinguish between smoke and

Siting and spacing of detectors

——

under flat horizontal ceilings and in corridors more than 2 m wide (Figure 8.4(a)), 5.3 m for point-type heat detectors and 7.5 m for point-type smoke detectors

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Flame detectors are unable to detect smoke from smouldering fires and are therefore used in specialised applications or to supplement heat or smoke detectors. They are not used as general-purpose detectors and in many applications have been superseded by video detection.

8-11

8-12 for square-type arrays (Figure 8.4(b)), maximum spacing between smoke detectors is typically 10 m, and for heat detectors the maximum distance is typically 7 m

——

in corridors of width not exceeding 2 m, detectors only need to be installed on the centre line. Smoke detectors may be mounted at intervals of 15 m and heat detectors at intervals of 10.6 m, provided that the maximum dimension from end walls is 7.5 m and 5.3 m for smoke and heat detectors, respectively in the apex of a pitched or north-light roof, add to the maximum horizontal distance 1% for each degree of slope to a maximum increase of 25% (Figure 8.4(c)). For example, for a point smoke detector at the apex of a 20° slope, 20% of 7.5 m is 1.5 m. Therefore, the maximum distance of travel is 9 m; the maximum area of coverage may also be increased proportionally.

Where the passage of smoke or hot gases towards a detector is likely to be disturbed by a ceiling obstruction (such as a beam), further allowances should be made, as follows: ——

for an obstruction having a depth greater than 10% of the height of the ceiling (e.g. beams), the obstruction should be considered as a wall

——

detectors should generally be avoided within 500 mm of a wall or obstruction.

(d)

Detection above a perforated ceiling may be used to protect the space below, provided that at least 40% of the ceiling is ‘open’, perforations are uniformly distributed, with a minimum dimension of 10 mm, and the ceiling thickness is not more than three times the perforation diameter.

(e)

Detectors should not be located within 1000 mm of a ventilation supply point.

The guidance in NFPA 72 differs, as follows: (a)

Point-type smoke detectors should not be installed closer than 100 mm (4 inches) from the edge of the ceiling and, if mounted on a side wall, should be in a band between 100 mm (4 inches) and 300 mm (12 inches) from the ceiling.

(b)

A spacing of 9.1 m (30 feet) can be used as a guideline for detector spacing. However, this needs to be confirmed with the specific detector manufacturer.

The spacing for heat detection is not so specific, referring the engineer to manufacturers for information. However, certain provisos are made. Detectors should be no more than half the manufacturer’s listed spacing from walls or partitions, and all points of the ceiling should have a detector with 0.7 times the listed spacing. BS 5839-1 is easier to understand in its guidance on this issue, giving diagrammatic assistance to convey the point. Depending on the type of ceiling, NFPA 72 gives different spacing recommendations based on multipliers of the listed spacing.

10 m

7.5 m 10 m

(a)

(b)

Apex of pitched roof

North-light roof

7.5 m

(c)

Figure 8.4  Siting and spacing of heat and smoke detectors: (a) maximum distance between any point and a smoke detector under a flat ceiling (5.3 m for heat detectors); (b) maximum spacing for smoke detectors in a square array (7 m for heat detectors); and (c) under apex of a pitched or north-light roof

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——

——

(c)

Fire safety engineering

Fire detection and alarm

8.7.2

Beam detectors

A number of specific requirements for point detector coverage, including proximity to ceilings and obstructions, apply equally to beam detector coverage. NFPA guidance refers the engineer to manufacturers’ instructions with regard to beam detectors.

8.7.3

Flame detectors

Flame detectors operate by monitoring the frequency of light in the protected area. Types are available to monitor infrared and ultraviolet light. If a flame detector ‘sees’ the particular frequencies of light that correspond to a fire, then the alarm is raised. Flame detectors do not depend on smoke or heat being transported to them. Therefore, they do not need to be ceiling mounted. They should be installed strictly in accordance with the manufacturer’s recommendations. More than one flame detector can be used to cover a single area to ensure that the flame is detected in the shortest possible time.

8.7.4

Ceiling height limits

BS 5839-1 provides guidance regarding the maximum ceiling height that may be protected for a given detector type. The general maximum heights applicable are summarised as follows: ——

heat detection (to BS EN 54-5: 2017) (BSI, 2017b): 7.5 m to 9.0 m (depending on the classification)

——

point smoke detection (to BS EN 54-7: 2001) (BSI, 2001): 10.5 m

——

carbon monoxide detection (to BS EN 54-26: 2015) (BSI, 2015c): 10.5 m

——

optical beam detection (to BS EN 54-12: 2015) (BSI, 2015b): 25 m to 40 m (depending on sensitivity and risk of stratification)

——

aspirating detectors (to BS EN 54-20: 2006) (BSI, 2006): 10.5 m to 40 m (depending on class and risk of stratification).

8.8

Control equipment

8.8.1

Siting of control panel

The control and indicating panel — which identifies the location of a fire, indicates faults and controls the operation of alarm sounders and other signalling devices — should comply with the recommendations of BS EN 54-2 (BSI, 1997) or the applicable recommendations in countries applying other standards.

In deciding where the control panel is to be sited, two factors should be considered: ——

Availability of staff: the control panel needs to be located in a position where staff on duty can easily see the indications being given by the panel.

——

Accessibility by the fire brigade: the control panel should preferably be located on the ground floor and in the immediate vicinity of the entrance to the building likely to be used by the fire brigade.

Adjacent to the control unit should be a zone designation chart or, better still, a diagrammatic plan showing zone locations.

8.8.2

Audible and visual alarm

An important component of any fire alarm system is the alarm sounder, normally a bell or electronic sounder, which should be audible throughout the building in order to alert the occupants of the building. Where the fire alarm system forms part of a fire engineered strategy, a voice alarm (va) may be used in place of traditional sounders. BS 5839-1 (BSI, 2013a) and NFPA 72 (NFPA, 2016) have different recommendations on the subject of alarm sounders. 8.8.2.1

BS 5839: Part 1 recommendations

For the UK and where BS 5839-1 is the prevalent standard, the following notes provide guidance on the correct use of alarm sounders. ——

A sounder should produce a minimum sound level of either 65 dBA or 5 dBA above any background noise likely to persist for a period longer than 30 seconds, whichever is greater, at any occupiable point in the building. Note that single doors could reduce the sound level by 20 dBA, or 30 dBA in the case of fire doors. During commissioning of the system, it is common to find areas of the building in which the sound level falls slightly below 65 dBA due to the furnishings and fit-out items absorbing and attenuating the sound. This generally results in the subsequent installation of additional sounders. If the area in question is a small confined area or small room, then a measured level 2 or 3 dBA below that set out in BS 5839 may be acceptable, as this difference would be imperceptible to the human ear.

——

If the alarm system is to be used in premises such as hotels, boarding houses etc., where it is required to wake sleeping persons, then the sound level should be 75 dBA minimum at the bed-head. This may require the installation of a sounder in each bedroom.

——

If the alarm system is to be used in premises such as a nightclub, where the background sound can be at such a high level as to limit the effectiveness of the sounders, provision should be made to disconnect the music equipment on activation of the fire alarm system.

——

In cases where one or more of the occupants are deaf, there are a number of ways of alerting the person(s) of a fire. In many instances, there will

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Generally, the beam should not pass closer than within 500 mm of a wall, partition or duct (excluding within 500 mm of the transmitter and receiver or reflector(s)). If there is a possibility of people walking in the area of the beam, then the beam detector should be installed at least 2.7 m above the floor. Additional consideration should be given to any interaction with frequently moving objects that may affect the beam, such as vehicles and forklift trucks.

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Fire safety engineering

——

In cases where persons who need to be alerted of a fire alarm include people who are deaf, then flashing beacons can be wired into the sounder circuits. In situations such as nursing homes, a vibrating disc may be used, placed under a mattress or pillow. In the UK, the Equality Act 2010 and Building Regulations Approved Document M (HM Government, 2015) should be consulted with regard to provision in this area.

When using a voice alarm system (typically designed to BS 5839-8: 2013) (BSI, 2013c), care will be required to ensure the message is clearly audible at the elevated volume levels needed to ensure the alarm can be heard throughout the building. In addition, the zoning of audible warnings when using voice alarm systems will need to be matched to the evacuation zones. Visual signal devices should be red or white (unless conflicting with other warning devices), with flash rates suitable to avoid triggering seizures in those with photosensitive epilepsy. All audible warning devices used in the same system should have a similar sound and should be distinct from any alarm sounder that is used for other purposes. Ideally, the frequency should lie in the range 500–1000 Hz for fire alarm sounders. Modern electronic sounders offer a choice of sound tones (fluctuating or constant). While the sound power level (spl) will not change within a particular sounder, experimentation with different tones can result in a more distinctive sound against the background noise. A large number of quieter sounders, rather than a small number of very loud sounders, may be preferable to prevent noise levels in some areas from becoming too loud. At least one sounder per fire compartment will be necessary. It is unlikely that sounder noise levels in a room will be satisfactory if more than one dividing wall or door separates it from the nearest sounder. The level of sound provided should not be so high as to cause damage to hearing. The number of fire alarm sounders used inside a building should be sufficient to produce the sound level recommended, but should in any case be at least two. For category P systems, an external sounder or visual warning device may be required, coloured red and marked ‘FIRE ALARM’. Where mains-powered sounders are used to supplement 24 V dc sounders then the 240 V ac supply should be monitored. 8.8.2.2

NFPA 72 recommendations

Where NFPA 72 is the relevant standard, the requirements are different. NFPA 72 identifies different areas as

requiring different levels or ‘modes’. These modes are broken down as follows: ——

Public mode: sounders should produce a level of 75 dBA at 10 ft, 15 dBA above average ambient sound or 5 dBA above the maximum sound level, with duration of at least 60 seconds.

——

Private mode: sounders should produce a level of 45 dBA at 10 ft, 10 dBA above average ambient sound or 5 dBA above the maximum sound level, with duration of at least 60 seconds.

——

Sleeping mode: sounders should produce a level of 70 dBA at 10 ft, 15 dBA above average ambient sound or 5 dBA above the maximum sound level, with duration of at least 60 seconds.

The maximum sound levels should not exceed 120 dBA for any type of system. In addition to the above, mechanical equipment rooms should be designed with a level of 85 dBA. NFPA 72 requires the use of temporal audible signals so there is a clear definition of the fire alarm signal across installations. The level of visual alarm (or alternatives) should be determined locally where NFPA 72 is applied. In the USA, this aspect is governed by the Americans with Disabilities Act 1990, which gives stringent guidelines depending on the type and use of the building.

8.8.3

Activating other safety measures

In addition to controlling alarm sounders, fire alarm panels may also be used to activate other safety measures. These include disabling lifts, providing fire signals to fire suppression control panels, activating public address announcements, closing smoke and fire doors, shutting down plant, activating smoke control systems etc. In some circumstances, it may prove economical to have more than one fire alarm panel in a building to avoid having to bring the cabling required for smoke detectors, call points, sounders etc., back to one central point. In such cases, it may be necessary for one fire alarm panel to send signals to other alarm panels. Fire alarm panels may also be used to send signals to building management systems, radio paging systems, communications monitoring systems or to an off-site monitoring station. Many systems have the capability to communicate with computer systems whereby graphical and textual information may be displayed on a computer screen. Events such as device activations, silencing of alarm sounders etc., may be stored by the computer and in the control panel’s event log and a print-out obtained.

8.8.4 Cables The type of cable used in fire alarm systems can be divided into two main types: those that need to continue to function during a fire condition, and those that can fail, having already served their purpose.

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be enough people about to ensure that any deaf occupants are made aware of the fire alarm sounding. In situations where a deaf occupant is working alone or undertakes an activity that results in their location being difficult to pinpoint, then radio paging may be an option to consider.

Fire detection and alarm

Suitable cables can include mineral-insulated coppersheathed cable (MICC) complying with BS EN 60702-2: 2015 (BSI, 2015d) and ‘soft skin’ types complying with BS 7629-1 (BSI, 2015e) with respect to their construction. However, the performance of the latter types when subjected to fire should be verified with the cable manufacturer prior to their use. Other types of cable can be used and the standards to which they should comply are given in section 26 of BS 5839-1 (BSI, 2013a). Cables are normally required to be ‘standard’ fire resistant for general use, or ‘enhanced’ fire resistant for situations where they are expected to continue to perform for extended periods in a fire (e.g. longer than an initial evacuation period). Standard cables typically need to meet a PH30 classification to BS EN 50400: 2015 (BSI, 2015f), and additionally meet a 30-minute survival time. These tests include the requirement that the cable continues to maintain signal integrity if subjected to a propane burner at 850 °C and subjected to impact tests for a period of 30 minutes, in addition to a test that includes the application of water spray. Enhanced cables may be necessary, for example, in certain multi-phased evacuation, unsprinklered buildings, in unsprinklered buildings greater than 30 m in height, or where a fire in one area does not instigate evacuation of other areas (e.g. hospitals). Enhanced cables typically need to meet a PH120 classification to BS EN 50400, and additionally meet a 120-minute survival time to BS 8434-2: 2003 (BSI, 2003). The BS 8434-2 test is particularly onerous in that the test temperature increases to 950 °C and the water spray time increases to 60 minutes. Cables must be provided with appropriate fixings or support in order that they remain in place and operating correctly if subjected to changing conditions during a fire. This is particularly important when ‘soft skin’ cables are specified, and the practice of using plastic cable ties as fixings should be avoided.

8.8.5

Radio-based systems

Fire alarm systems are available in which communication between the detectors and the control panel is made by means of radio signals. The advantages and disadvantages that need to be considered before designing a radio-based system are listed below. The advantages of radio-based systems are as follows: ——

In general, the absence of wiring between system components, e.g. detectors and control panel, means that radio-based systems are generally cheaper and quicker to install than hard-wired systems. Disruption is kept to a minimum, since installation can normally take place while the building is occupied. Systems can extend beyond a single building without the need for inter-building wiring.

——

Since only a minimal amount of wiring is involved during installation, damage to existing surfaces is kept to a minimum.

——

Individual detectors can be identified.

——

Radio-based systems can continue to operate during a fire condition. Hence the need for fireresistant cable is reduced.

——

Temporary fire cover for special risks, e.g. a marquee or an exhibition, can be easily arranged.

The disadvantages of radio-based systems include the following: ——

Each detector, call point or other device that is not wired to the control panel will require a local power source.

——

There is a possibility that the receiver may be affected by interference signals from other sources or that the transmission path could be temporarily or permanently blocked.

——

There are limitations on the allowed frequency spectrum, which could lead to interference between simultaneous signals. Therefore, it is considered unwise to send monitoring signals at frequent intervals. Hence for some (but not all) faults there may be a significant delay (possibly hours) before the occurrence of a fault is registered on the control panel.

The installation of a radio-based system should, as with other fire alarms systems, comply with the recommendations of BS 5839-1, section 27 of which deals with radio-based systems.

8.8.6

Power supplies

In general, the fire alarm control panel and associated devices operate at extra low voltage (elv), typically 24 V dc, and receive this supply either from a built-in charger/ rectifier circuit (powered from the local mains ac supply) or from a dedicated elv dc power supply. In the event of failure of the mains supply, a standby elv dc supply is automatically provided by batteries, or in some cases a generator. The power supply to fire alarm equipment should be used for the fire alarm only. Connection to the mains supply should be from a dedicated circuit that derives its supply from a point as close as possible to the origin of the supply within a building. This will typically be a spare fuse-way in a main switch panel rather than a downstream distribution board. The advantage of this is a reduction in the risk of loss of supply due to circuit failure. The protective device, be it fuse, miniature circuit breaker (mcb) or moulded case circuit breaker (mccb), should be clearly marked in red, carry some means of preventing accidental operation and bear a notice stating ‘FIRE ALARM – DO NOT SWITCH OFF’. Care should be taken in the design of the power supply to ensure that the transition from mains to standby batteries does not cause momentary interruptions in the supply to the equipment. Operation of a single protective device should not interrupt supplies or cause the system to fail.

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Cables which need to continue operating during a fire condition include power supply cables and links to sounders and remote communication centres. Those which do not need to continue to operate, having served their purpose, include cables to detectors and failsafe cables to auxiliary devices such as door release devices.

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Fire safety engineering

The duration and power required for the standby power supply will depend on the purpose of the system. For category L systems, a standby duration of 24 hours is required, with sufficient capacity to maintain the evacuate signal in all zones for 30 minutes. If the premises are likely to be unoccupied and not supervised for a period exceeding 24 hours, then consideration should be given to engaging a remote monitoring centre for monitoring of power supply faults or to increasing the standby duration. In buildings with a category P system, and if the building may be unattended and has no power supply monitoring link, then the required duration is 24 hours longer than the period for which the building may remain unoccupied (or 72 hours, whichever is less), after which there should be sufficient capacity to operate all fire alarm devices for 30 minutes. Again, where the building could be unattended for longer periods, remote monitoring of the power supply should be considered. Methodologies for determining standby battery capacity are provided in BS 5839-1. Nevertheless, fire alarm equipment manufacturers will ensure that batteries supplied with their equipment are adequate for the standby period required by the design. Once again, early consultation is essential to ensure that the requirements of the system are fully understood by all parties.

8.9

Hazardous areas

There are potentially explosive areas in which fire detection equipment needs to be installed. Such premises may be protected in one of the following ways.

Safe area Fire alarm control panel

+ Detection zone –

8.9.1

Flameproof equipment

Detection equipment is housed within a flameproof enclosure. If a fault should occur that produces an electrical spark, the spark is contained within the housing and not released into the potentially explosive environment.

8.9.2

Intrinsically safe equipment

Detection equipment installed in the potentially explosive area is fed through suitable barriers or isolators that limit the amount of electrical energy entering into the hazardous area (see Figure 8.5). If a fault occurs on electrical equipment installed within the hazardous area, causing a spark to be produced, the amount of energy released will be insufficient to cause an explosion. The Zener barrier is an electronic device that limits the current that may enter the hazardous area. The end-ofline resistor is used to monitor the supply from the control panel to the detection devices.

8.10

Construction sites

The reader should also refer to chapter 15: Fire safety on construction sites in this Guide.

8.10.1

Temporary fire alarm systems

Construction sites need to be provided with a suitable warning system to alert all persons on the site in the event of a fire. On small sites, this can be a simple management procedure. However, more complex sites will need a different approach. Issues to consider include complexity of the escape routes, the need to keep escape routes clear and protected, the changing personnel who may not be familiar with the site and, in some instances, the value of the site, particularly as it approaches completion.

Hazardous area

Zener barrier +

+

In

Out

–

–

End of line resistor

Detectors/call points etc

Note 1: the control panel and Zener barrier are wired in the safe area. Note 2: current entering the hazardous (e.g. potentially explosive) area is limited by the use of a Zener barrier.

Figure 8.5  Wiring of detectors within a hazardous area

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The construction of the power supply should comply with the recommendations of BS 5839-1, NFPA 70: National Electrical Code (NFPA, 2017) or local standards as appropriate.

Fire detection and alarm

Construction continues to be a multi-nationality industry and it is common to have 20-plus nationalities on a site at any one time. The need for clear, unambiguous signage and warning signals is of utmost importance to ensure safety is maintained.

8.10.2

Fire alarm systems in buildings with phased handover

Where buildings are designed and constructed for mixed use, such as retail complexes and high-rise office/residential accommodation, construction works may still be under way while parts of the complex are occupied. The fire alarm system may well be completed in the occupied part of the building or complex. However, the system cannot give full protection and will need to be supplemented by a temporary system in the construction area. This arrangement brings added complexity over a continually changing temporary system installed on a straightforward construction site. Evacuation procedures will need to be agreed between parties who would normally be unconnected. The risks involved in false alarm should be assessed, as this may have increased commercial or nuisance implications over a straightforward construction site. Escape routes will have to be carefully planned to ensure sufficient segregation is in place to avoid overcrowding of escape routes. Access for fire brigade vehicles and firefighters will have to be considered on a frequent basis and may involve the cooperation of a number of different bodies.

8.11

Tall buildings

Over the past few years, there has been an increase in the number of tall buildings being erected around the world. This type of construction brings with it particular problems for fire alarm design, as traditional alarm systems do not lend themselves to this type of building. Considering the advances in construction methods and the desire to reduce the size of access cores, the fire alarm design will generally become part of the overall fire engineering strategy for the protection for the building. It may therefore be necessary to provide widely varying levels of detection in different parts of the building, as well as different types of audible warning, depending on the building’s use. As an example, a predominantly residential building may have smoke detection and sounders individual to each apartment that do not generate a general alarm, while other

floors of the same building may contain office accommodation that has a category L1 (or total coverage) system. Such system design and its intended operation would benefit from the early completion of a cause and effect table. Care should also be taken with regard to cabling types and control panel positions within tall buildings.

References BSI (1997) BS EN 54-2: 1997+A1:2006 Fire detection and fire alarm systems. Control and indicating equipment (London: British Standards Institution) BSI (1998) BS EN 54-4: 1998 Fire detection and fire alarm systems. Power supply equipment (London: British Standards Institution) BSI (2001) BS EN 54-7: 2001 Fire detection and fire alarm systems. Smoke detectors. Point detectors using scattered light, transmitted light or ionization (London: British Standards Institution) BSI (2003) BS 8434-2: 2003 + A2: 2009 Methods of test for assessment of the fire integrity of electric cables. Test for unprotected small cables for use in emergency circuits. BS EN 50200 with a 930° flame and with water spray (London: British Standards Institution) BSI (2006) BS EN 54-20: 2006 Fire detection and fire alarm systems. Aspirating smoke detectors (London: British Standards Institution) BSI (2013a) BS 5839-1: 2013 Fire detection and fire alarm systems for buildings. Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises (London: British Standards Institution) BSI (2013b) BS 5839-6: 2013 Fire detection and fire alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises (London: British Standards Institution) BSI (2013c) BS 5839-8: 2013 Fire detection and fire alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of voice alarm systems (London: British Standards Institution) BSI (2015a) BS 9991: 2015 Fire safety in the design, management and use of residential buildings. Code of practice (London: British Standards Institution) BSI (2015b) BS EN 54-12: 2015 Fire detection and fire alarm systems. Smoke detectors. Line detectors using an optical beam (London: British Standards Institution) BSI (2015c) BS EN 54-26: 2015 Fire detection and fire alarm systems. Carbon monoxide detectors. Point detectors (London: British Standards Institution) BSI (2015d) BS EN 60702-2: 2002+A1:2015 Mineral insulated cables and their terminations with a rated voltage not exceeding 750 V. Terminations (London: British Standards Institution) BSI (2015e) BS 7629-1: 2015 Electric cables. Specification for 300/500 V fire resistant, screened, fixed installation cables having low emission of smoke and corrosive gases when affected by fire. Multicore cables (London: British Standards Institution) BSI (2015f) BS EN 50400: 2015 Method of test for resistance to fire of unprotected small cables for use in emergency circuits (London: British Standards Institution) BSI (2017a) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) BSI (2017b) BS EN 54-5: 2017 Fire detection and fire alarm systems. Heat detectors. Point heat detectors (London: British Standards Institution) DFPNI (2012) Technical Booklet E: Fire Safety. Building Regulations (Northern Ireland) (Belfast: Department of Finance and Personnel) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019)

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Because of the changing nature of buildings during construction, temporary fire alarm systems have to be dynamic. It may be appropriate to review the installation daily as construction progresses, as escape routes may get longer, change direction or simply cease to exist. Signage and education of persons on site need to reflect this. Attention will also need to be paid to sound levels and visual warning devices, as these can quickly become ineffective by the introduction of only a few additional building elements. Regular maintenance needs to be carried out to ensure detectors are not contaminated by construction-generated dust.

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8-18

Fire safety engineering NFPA (2017) NFPA 70 National Electric Code (Quincy, MA: National Fire Protection Association)

NFPA (2015) NFPA 90A Standard for the installation of air-conditioning and ventilating systems (Quincy, MA: National Fire Protection Association)

Scottish Government (2017) Technical Handbook – Non-Domestic (Livingston: Building Standards Division)

NFPA (2016) NFPA 72 National Fire Alarm and Signaling Code (Quincy, MA: National Fire Protection Association)

Welsh Government (2015) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating 2010, 2013 and 2016 amendments) (Cardiff)

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HM Government (2015) The Building Regulations 2010 Approved Document M: Access to and use of buildings (Newcastle upon Tyne: NBS)

9-1

9

Emergency lighting

This chapter provides guidance on emergency lighting with regard to fire engineering. More detailed guidance on the general principles of emergency lighting is given in the Society of Light and Lighting (SLL) Code for Lighting (SLL, 2012) and SLL Lighting Guide 12: Emergency Lighting (SLL, 2015). To be effective in facilitating the safe evacuation of a building in the event of a fire, all escape routes must be adequately illuminated. Any routes that are part of the normal circulation routes within the building necessarily need, in any case, to be properly illuminated at all material times. Emergency lighting (also referred to as escape lighting, safety lighting and standby lighting, depending on its purpose) is provided to ensure that, in the event of failure of a building’s main lighting system, there remains a level of artificial illumination which will either allow safe egress from the building or allow people to stay in place until the main lighting returns. Emergency lighting should be viewed in a different way to fire alarm systems. While both are important in maintaining people’s safety, the differing approach is taken for a very good reason. While a fire alarm system provides early notification of a potentially catastrophic event, the building owner/occupier will be happy if the system is never called into action. In contrast, loss of power to the workplace is not uncommon. It is, in fact, common enough for building occupants to often view it with bemusement rather than panic. But the sudden loss of lighting can put people in grave danger if they happen to be working on moving equipment or attempting to move about. Therefore, the need for emergency lighting is very important as it is more likely to be put to use during its lifetime than is a fire alarm system. Loss of power, and hence loss of lighting, may occur during a fire as a result of the fire, but can occur at other times for a variety of reasons. Where the loss of lighting could result in a life threatening or unexpected situation arising, then an assessment should be made of the overall risk and appropriate action to be taken. This could include a behavioural assessment of the building occupiers, which considers how they are likely to respond naturally to a lighting failure as well as to any management procedure imposed on them. Early discussion with the building owner and other designers is important to understand how occupants will be managed during a lighting failure and if any unusual hazards are present. It is often assumed that the emergency lighting system and fire alarm system should be interconnected so that on

activation of the fire alarm system, the emergency lighting is also activated. This may be the case in premises such as theatres and cinemas, where lighting may be dimmed. Where a fire causes the failure of mains power, the emergency lighting should operate on detecting that loss, independently of the fire alarm system. If the emergency lighting comes on during a fire alarm test or if an error occurs, then by the time the staff are able to return to the building the battery capacity may have fallen too low to provide the required period of coverage: time will be needed to recharge the batteries before staff would be allowed to reoccupy the building. In a situation where the fire and rescue service choose to isolate power within a building, the emergency lighting should respond to that action by detecting the loss of mains power. This chapter should also be read in conjunction with chapter 7: Means of escape and human factors, which looks at the use of wayfinding signage.

9.2

Siting of essential escape lighting

9.2.1

Initial design

It is important to identify specific escape routes before commencing on the design of an emergency lighting system. This should be done in consultation with the architect (if appointed), building owner, fire officer and building control officer. At this stage it would also be advisable to identify any specific requirements that the building’s insurers may wish to impose. Following consultation with these parties, the initial design commences with the siting of luminaires to cover specific hazards and to highlight safety equipment and safety signs (see Figure 9.1). Typical locations where such lighting should be sited include the following: ——

on or in designated stairs, corridors, aisles, ramps, escalators and passageways

——

at each exit door

——

near intersections of corridors

——

near each stairway so that each flight of stairs receives direct light

——

near each change in direction

——

near any change in floor level

——

near firefighting equipment

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9.1 Introduction

9-2

Fire safety engineering

(c) Near each staircase

(b) Near intersections of corridors

Fire extinguisher (d) Near each change in direction

(e) Near any changes in floor level

(f) Near firefighting equipment

Break-glass unit

(g) Near each fire alarm break-glass unit

(h) To illuminate exit and safety signs

Figure 9.1  Locations where emergency luminaires must be sited

——

near each fire alarm call point

——

near first-aid equipment

——

at non-illuminated exit and safety signs, as required by the enforcing authority.

There may be instances where other measures, behaviours or management policies either increase or reduce the need for emergency lighting. An early meeting with the interested parties should be used to identify such instances and allow the design to reflect them. A policy such as allowing the occupants to stay in place during a lighting failure may increase the need for emergency lighting, whereas the use of, for example, vision panels in doors opening onto escape routes may provide the recommended levels of emergency illumination within the adjacent room and reduce the need in that particular room. The principal documents covering the need for emergency lighting in various types of premises within the UK are as follows: ——

Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541) (England and Wales)

——

Fire (Scotland) Act 2005

——

BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (BSI, 2017)

——

BS 5266-1: 2016 Emergency lighting. Code of practice for the emergency lighting of premises (BSI, 2016)

——

Building Regulations 2010 Approved Document B: Fire Safety (England) (HM Government, 2013)

——

Building Regulations 2010 Approved Document B: Fire Safety (Wales) (Welsh Government, 2015)

——

Technical Handbooks (Scotland) Section 2: Fire (Scottish Government, 2017a, 2017b)

——

Building Regulations (Northern Ireland) 2012, Part E: Fire safety.

In addition to the recommendations applicable to the UK, this guide also considers fire alarm and detection installations across the world and the recommendations of NFPA 101: Life Safety Code are also considered (NFPA, 2018a).

9.2.2

Additional escape lighting

After siting luminaires at the locations listed in section 9.2.1, consideration should be given to installing luminaires at other locations, including the following: ——

lift cars; although not considered as part of the escape route, emergency lighting is required since failure of the normal lighting could result in persons being confined in a small dark space for an indefinite period

——

moving stairs and walkways

——

toilets with areas exceeding 8 m2 and any toilet for disabled people or with baby-changing facilities

——

external areas in the immediate vicinity of exits; if the identified place of safety is distant from the building, the route to it should be treated as part of the escape route for emergency lighting purposes.

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(a) At each door exit

Emergency lighting

9.2.3

High-risk task areas

9.2.4

Open-plan and undefined areas

Open and undefined spaces, referred to in BS EN 1838: 2013 (BSI, 2013) as ‘anti panic’ areas, are spaces where no defined escape route exists. In this situation, the office furniture may hinder the safe escape of occupants if the lighting system fails. BS 5266-1 (BSI, 2016) gives examples of open-plan areas that may need emergency lighting following a risk assessment. In England, the Building Regulations 2010 recommend that areas over 60 m2 be provided with emergency lighting. Due to the size and nature of such large spaces, they will also include areas previously referred to as undefined escape routes. In such situations, occupants of a space may take several different routes to the nearest exit. The minimum illumination level for such situations recommended by BS 5266-1 is 0.5 lux in the core area. This recommendation is a minimum level, and designers are asked to consult with building owners to assess the way in which the building will be used and how that might affect the level of illumination to be provided. The National Fire Prevention Association (NFPA) and International Building Code (IBC) take a different approach to open-plan areas. There is no requirement for open-plan areas to have illumination throughout; however, parts of open-plan areas should be classified as escape routes and illuminated in accordance with the recommendations in section 9.2.6 below. Some judgment is required to assess which parts of open-plan areas should be treated as ‘escape routes’, but they are generally dictated by the furniture layout and are the areas likely to be used as egress routes by a number of people.

9.2.5

Illumination of exit signs

Exit signs can be either illuminated internally or externally from a remote source. The specific requirements for exit signs under UK legislation are given in the Health and Safety (Safety Signs and Signals) Regulations 1996 (SI 1996/341). For countries applying other codes, the requirements can be found in NFPA 5000 (NFPA, 2018b), the International Building Code (IBC) 2015 (ICC, 2015) or NFPA 170 (NFPA, 2018c). If applying international codes, it should be noted that NFPA 101 and the International Building Code 2015 require exits signs, whether located internally or externally, to be illuminated at all times. However, NFPA 101 does qualify this by stating that this condition applies when the building has normal power and is occupied. All emergency exit signs within a particular building should be uniform in colour and format as well as being located within a sufficiently close proximity to the

relevant door to ensure that its association is unambiguous. Signs should be sited to ensure that a clear contrast is apparent between the sign and its surroundings. Signs which only show text should no longer be installed. Signs complying with BS 5499-1: 2002 (BSI, 2002) may still be used in the UK if they are to be installed in a building which currently has this type of sign. This is only due to the citing of BS 5499-1 in the Building Regulations 2010 Approved Document B: Fire Safety (HM Government, 2013) as BS 5499-1 has now been withdrawn and replaced by BS ISO 3864-1: 2011 (BSI, 2011). Self-luminous signs may also be used as exit signs. If used, however, these must also comply with the appropriate legislation or code.

9.2.6

Lighting levels for escape routes

Escape routes have specific recommendations in terms of minimum levels of illumination. It is essential that a minimum level of illumination is maintained along escape routes, including during a main lighting failure. BS 5266-1 recommends a minimum illumination of 1 lux at floor level along the centre line of an escape corridor up to 2 m wide (BSI, 2016). NFPA 101 (NFPA, 2018a) and the International Building Code (ICC, 2015) both recommend that a much higher average of 1 foot candle (11 lux) is achieved, with a minimum of 0.1 foot candle (1.1 lux) at any point along the path of egress.

9.2.7

Emergency safety (stay-inplace) lighting

In 2016, BS 5266-1 introduced the concept of safety lighting (BSI, 2016). Where building owners or tenant organisations prefer or expect occupants to stay in place during a lighting failure, then provision should be made to ensure the safety of those occupants until the normal lighting returns. Decisions regarding emergency safety lighting should be subject to a risk assessment and may include, for example, the introduction of emergency lighting into areas where it would otherwise not be required.

References BSI (2002) BS 5499-1: 2002 Graphical symbols and signs. Safety signs, including fire safety signs. Specification for geometric shapes, colours and layout (London: British Standards Institution) BSI (2011) BS ISO 3864-1: 2011 Graphical symbols. Safety colours and safety signs. Design principles for safety signs and safety markings (London: British Standards Institution) BSI (2013) BS EN 1838: 2013 Lighting applications. Emergency lighting (London: British Standards Institution) BSI (2016) BS 5266-1: 2016 Emergency lighting. Code of practice for the emergency lighting of premises (London: British Standards Institution) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution)

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In addition to the above, emergency lighting should also be provided for areas in which high-risk tasks are undertaken. These include areas such as plant rooms, lift motor rooms, electrical switch rooms and any area where a safety hazard is present, which may become a danger to people moving about in darkness.

9-3

9-4 HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volumes 1 and 2 (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019)

NFPA (2018a) NFPA 101 Life Safety Code (Quincy, MA: National Fire Protection Association) NFPA (2018b) NFPA 5000 Building Construction and Safety Code (Quincy, MA: National Fire Protection Association) NFPA (2018c) NFPA 170 Standard for fire safety and emergency symbols (Quincy, MA: National Fire Protection Association)

Scottish Government (2017a) Technical Handbook – Domestic (Livingston: Building Standards Division) Scottish Government (2017b) Technical Handbook – Non-Domestic (Livingston: Building Standards Division) SLL (2012) SLL Code for Lighting (London: Chartered Institution of Building Services Engineers) SLL (2015) SLL Lighting Guide 12 Emergency Lighting (London: Chartered Institution of Building Services Engineers) Welsh Government (2015) The Building Regulations 2010 Approved Document B: Fire Safety. Volumes 1 and 2 (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Cardiff)

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ICC (2015) International Building Code 2015 (Washington, DC: International Code Council)

Fire safety engineering

10-1

10

Smoke ventilation

These objectives may have different timelines and identification of the timeline required for the design is a critical part of system design.

10.1.1 General The spread of smoke and other products of combustion throughout enclosed spaces can present a significant hazard to the safe evacuation of occupants and the ability of firefighters to operate and can cause substantial damage to properties and business. Smoke can spread a significant distance from the source of the fire unless controlled. To prevent or minimise the risks, there is a wide range of means by which the movement of smoke can be minimised and controlled. These generally form part of a package of fire protection measures, which may include the provision of smoke barriers, fire-resisting construction and smoke ventilation systems, often in combination with other active systems, such as sprinklers and smoke detection.

10.1.3

Smoke ventilation systems tend to operate on one (or a combination) of the following principles and can be mechanical and/or natural: (a)

Smoke management or control systems: These systems are based on ensuring sufficient ventilation and containment of smoke to maintain a smoke-free, clear layer above finished floor level. The purpose of the clear layer can be to minimise smoke damage to property (e.g. stored goods) or to provide suitable conditions for occupants to escape.

(b)

Diluting the smoke within the space with fresh air or smoke clearance: These systems are based on providing sufficient ventilation to dilute the smoke to an extent where tenable conditions are achieved. This approach is particularly useful in circumstances where the normal internal conditions or wind pressures adversely affect the formation of a stable smoke layer. A form of these systems can be used to remove heat and smoke to assist fire service operations in spaces such as basements and some atria (commonly referred to as ‘air change’ systems).

(c)

Opposed air flow: The flow of air prevents the flow of smoke into adjoining spaces. These systems tend to be used in small enclosed areas (e.g. stairs, corridors etc.)

(d)

Pressure differential systems: These systems typically work on either pressurisation or depressurisation of a space or an adjoining space.

However, it is essential that the design of the smoke control systems is consistent with both the planning of the spaces within the building and the objectives of the fire strategy. At the outset of the design, it should be clear why a smoke control system is required. The system should be as simple and reliable as possible, since the provision of an overly complex design can lead to a lower level of reliability. It is likely that the smoke control system design will involve several parties (for example, the architect, fire engineer, building services engineer and the contractor). Therefore, particular care should be taken to agree and define the respective responsibilities at an early stage in the design process. One framework option, to assist in the definition and documentation of responsibility, is provided in BS 7346-8: 2013 (BSI, 2013a).

10.1.2

Objectives of a smoke control system

Principles of smoke ventilation systems

10.2

System considerations

The objectives of the smoke control systems should be set by the designers. Typically, systems have several objectives, which may have identical or different priorities. Typical objectives can include:

10.2.1 General

(a)

maintaining tenable conditions in the area of fire origin or areas adjoining the fire

10.2.2

Key considerations

(b)

minimising smoke spread to adjoining parts of the building

10.2.2.1

Maintaining a smoke-free layer

(c)

removing smoke from the building during or post firefighting operations.

Where the aim of the system is to maintain a smoke-free layer, consideration must be given to the layer height

Designers of smoke control systems should consider the following aspects as part of the design.

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10.1 Introduction

10-2

Fire safety engineering

To determine the required clear layer height for means of escape or the protection of property, the temperature of the smoke and the depth of the smoke layer are important to limit radiation received beneath (see section 10.3 below on tenability criteria). To ensure that smoke is maintained a safe distance above head height, and also to ensure that radiation from the smoke layer is not excessive (assuming a maximum smoke layer temperature of 200 °C as described in section 10.3), recommended minimum values for the clear layer height in BS 7346-4: 2003 (BSI, 2003a) are 3 m for public buildings (e.g. malls and exhibition halls) and 2.5 m for non-public buildings (e.g. offices). BS 7346-4 also recommends that, where the predicted layer temperature is less than 50 °C above ambient, 0.5 m should be added to any recommended minimum value to take into account smoke cooling. Where smoke control is provided for property protection reasons, BS 7346-4 also recommends that a similar value of 0.5 m be applied above the top of any stacked goods. 10.2.2.2

Area of reservoir

Historically, an area of 2000 to 3000 m2 has been adopted as the maximum reservoir size to prevent excessive cooling and downward mixing of smoke (Morgan et al., 1999). However, this is an arbitrary limit and larger reservoirs may be acceptable, provided appropriate consideration has been given to heat loss to the surrounding structure. This may necessitate a more complex numerical fire engineering analysis or the use of computational fluid dynamics modelling. 10.2.2.3

Reservoir screens and curtains

The screens or curtains enclosing the edges of a reservoir must be constructed from materials that can withstand the calculated smoke temperature for the required period. These screens should be impermeable, but some leakage, e.g. at the junction of screens, is not likely to be critical for most applications. Where these are fixed screens, the depth or drop of the screens or curtains should be at least to the level of the base of the smoke layer. However, consideration should be given to increasing this depth to add a margin of safety. For example, BS 7346-4 suggests an additional 0.1 m. Retracting screens or curtains may, in certain circumstances, deflect from the normal vertically hanging position due to the pressure of gases acting on the smoke curtain. That horizontal deflection of the curtain causes the bottom of the curtain to rise, which could lead to leakage of smoke underneath the curtain if the rise takes the bottom of the curtain above the base of the smoke layer. This should be considered when calculating the depth of the curtains and some margin of safety may be required. Further guidance can be found in BR 368 (Morgan et al., 1999).

10.2.2.4

Replacement air

For any smoke removal system to work effectively, it requires a source of replacement air. The replacement air can be supplied either by natural means or mechanically. It is important that the sources of inlet air are located such that the inlet air does not allow the hot smoke layer to become excessively turbulent or cool to the detriment of the smoke ventilation system. It may be necessary to consider locating the inlet air at low level or remote from the smoke layer base. Designers should consider the velocity of incoming air. Excessive velocities through openings used for means of escape can impede the evacuation of occupants, while excessive velocity close to the base of the smoke layer can increase the turbulence of the layer (and therefore the quantity of the smoke). In the UK, a maximum velocity of 5 m · s–1 across doorways or other openings used for escape is commonly used (BSI, 2003a). BS 7346-4 also recommends that, to avoid the incoming air disturbing the smoke layer or pulling down smoke from the layer (Venturi effect), the upper edge of an inlet opening should be 1 m or more below the smoke layer base or the inlet air speed beneath the layer should be less than 1 m · s–1. NFPA 92 makes a similar recommendation in stating that the make-up air velocity should not exceed 1.02 m · s–1 where the make-up air could come into contact with the plume unless a higher air velocity is supported by engineering analysis (NFPA, 2015a). In practice, replacement air will come via the flow paths of least resistance, which may include leakage from the facade and other openings. However, care needs to be taken when using these paths as a source of replacement air as the air-tightness of buildings increases under the environmental requirements of national building regulations. NFPA 92 also recommends that make-up air be designed at 85%–95% of the exhaust (not including leakage through small leakage paths). When designing mechanical smoke removal systems, the replacement air requirement should be based on volume balance, not mass balance. When designing natural smoke removal systems, replacement air should be based on mass balance. Where a powered inlet is used in combination with a powered exhaust, consideration should be given to the impact of changing pressures generated by the fire as it develops and the potential impact on the forces acting on the fire escape doors etc. 10.2.2.5

Number of extract points

When the smoke layer is relatively shallow, a high extract velocity at any single point may lead to plug-holing, whereby air is extracted from below the smoke layer, as opposed to the smoke itself. This leads to a significant loss in the ability of the system to remove smoke efficiently and, accordingly, several extract points may be needed at a lower velocity.

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required. It should be noted that clear layer heights are difficult to achieve where there are low ceiling heights, such as in residential corridors, and instead smoke dilution or smoke clearance systems may be more appropriate.

Smoke ventilation

10-3

The maximum volumetric flow rate that can be exhausted by a single exhaust vent can be calculated (NFPA, 2015a) as Vmax = 4.16cd 5/2 T

Ts - T0 1/2 Y (10.1) T0

where Vmax is the maximum volumetric flow rate without plug-holing at Ts (m3 · s–1), c is the exhaust location factor (dimensionless), d is the depth of smoke layer below the lowest point of exhaust (m), Ts is the absolute temperature of the smoke layer (K) and T0 is the absolute ambient temperature (K). Note: c = 1 (for exhaust vents centred no closer than twice the diameter from the nearest wall) or 0.5 (for vents centred closer than this or located on a wall). Where multiple exhaust vents are needed to prevent plug-holing, the minimum separation distance can be determined (NFPA, 2015a) by

Smin = 0.9Ve1/2 (10.2)

where Smin is the minimum edge-to-edge separation between vents (m) and Ve is the volumetric flow rate of one exhaust vent (m3 · s–1). The volumetric flow rate of a smoke exhaust can be determined (BSI, 2003a) using

V=

mTs (10.3) t0 T0

where V is the volumetric flow rate of smoke exhaust (m3 · s–1), m is the mass flow rate of smoke exhaust (kg · s–1), Ts is the absolute temperature of the smoke layer (K), T0 is the absolute ambient temperature (K) and t0 is the density of air at ambient temperature (kg · m–3). 10.2.2.6

10.2.2.8

Pressure differentials

It is important that excessive pressure differentials are not created by the design of the system. Pressure differences between the pressurised/depressurised space and adjoining accommodation should be designed so that the force required to open the door, typically measured at the door handle, shall not exceed regulatory or manufacturer’s requirements. This is typically 100 N in Europe (BSI, 2005) or 67 N under the guidance of NFPA 101 (NFPA, 2015b). Where it is not possible to calculate door opening forces, such as during the early design stages, the pressure difference across a closed door between the pressurised area and adjoining space should be not greater than 60  Pa in Europe (BSI, 2005). Additional considerations relating to the impact of the pressure difference between the area of fire origin and the adjoining accommodation include the risk of closed doors being pushed/pulled open, or adverse or undesired movement of smoke into adjoining spaces. For example, unlatched doors may be pulled open due to the pressure difference between two adjoining spaces. This can occur where the pressure difference is between 25 and 30 Pa. However, these circumstances are dependent on the doorset and ironmongery, including self-closing mechanisms.

Smoke layer depths

It is not recommended that a smoke extract system be designed with a height from base of fire (usually floor) to base of smoke layer of less than 10% of the height from fire to ceiling (BSI, 2003a). Likewise, no smoke extract system should be designed with a height from base of fire to the base of the smoke layer of more than 90% of the height from base of fire to ceiling (BSI, 2003a). However, guidance given in NFPA 92 suggests that smoke layer depth should be a minimum of 20% of the floor-to-ceiling height, unless based on an engineering analysis (NFPA, 2015a). 10.2.2.7

The space above a partially open suspended ceiling which has less than 25% of its geometrical free area open should be treated as a plenum chamber.

Suspended ceilings

Imperforate suspended ceilings should be treated as the top of the smoke layer. Provided the suspended ceiling is designed in such a way that it would not prematurely fail on being exposed to the predicted design temperatures of the smoke layer, channelling screens and smoke barriers need not be continued above a closed suspended ceiling. Partially open suspended ceilings with more than 25% of evenly distributed geometrical free area need not be taken

10.3

Tenability criteria for smoke ventilation system design

10.3.1

Hazards of smoke

The toxic products of fire include irritant and narcotic components, which can cause disorientation, incapacitation or death, with effects dependent on the concentration and length of exposure. The predominant irritant components are organic smoke products and acid gases, such as hydrogen chloride (HCl). The immediate effects of irritants are related to the concentration, but may include pain in the eyes and lungs, accompanied by difficulty in breathing. The predominant narcotic component is carbon monoxide, with hydrogen cyanide also being important in pre-flashover fires. Narcotic effects, disorientation and collapse occur only when a certain dose (i.e. the product of exposure concentration and exposure time) has been inhaled over a period.

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into account when considering smoke movement (BSI, 2003a). Channelling screens and smoke barriers should be continued above the suspended ceilings (to structural soffit) where necessary.

10-4

Smoke particles and irritant products can, in sufficient concentrations, reduce visibility. While loss of visibility is not directly life threatening, it can prevent or delay escape and thus expose people to the risk of being overcome by smoke.

10.3.2 Temperature The human body cannot tolerate elevated temperatures for any extended period of time, as pain and skin damage will begin to occur when the temperature at the basal layer of the skin exceeds 44 °C. The amount of damage is a function of both the skin temperature and the duration of time for which the temperature is elevated above the 44 °C threshold. Chapter 68 of the SFPE Handbook allows an interested reader to predict skin burns (SFPE, 2016). Heat exposure occurs when a person comes into contact with hot gases. A recommended value for demarcation between skin burns and hyperthermia (heat stroke) is 120 °C (Klote et al., 2012).

10.3.4

Visibility in smoke

Familiarity with your surroundings has a major impact on visibility distances, as a person in a familiar environment only needs to see enough of their surroundings to be able to maintain their orientation, while a person in unfamiliar surroundings needs to be able to see exits or escape signage. A person’s level of familiarity with their environment may also decrease significantly when that environment is filled with smoke. Typically, a tenability limit for visibility for escape purposes is a visibility distance of 8–10 m (BSI, 2017). For most fire types, it is likely that smoke at this concentration will cause some eye irritation but it is unlikely to contain irritants at concentrations high enough to seriously inhibit escape or cause collapse. It is expected that a person in their own dwelling would be familiar with their surroundings even if they could only see for 3–4 m (Klote et al., 2012). For a static, homogenous smoke layer, optical smoke density per m (D) can be calculated (BSI, 2002):

D=

Dm fb (10.5) Vt

Exposure of naked skin to temperatures above 120 °C can result in incapacitation due to skin pain and burns, so this temperature can be used as the upper tenability limit for direct exposure to (or immersion in) hot combustion gases.

where Vt is the total volume of smoke (m3), fb is the total mass of fuel burnt (kg) and Dm is the mass optical density for the fuel concerned (m2 · kg–1). Vt can be calculated from the volume of the smoke layer, and mass optical densities for generic products are shown in Table 10.1.

Humidity does not have a great impact at this intensity, but permitted exposure temperatures can drop to approximately 55 °C (wet smoke) and 75 °C (dry smoke) for increased exposure times of up to 30 minutes (Klote et al., 2012).

Total mass of fuel burnt (fb) is calculated by multiplying the mass burning rate of the fuel (mfuel) by the time (s). This can be found from the heat release rate at steady state (BSI, 2003b):

Other sources note that thermal burns to the respiratory tract can occur upon inhalation of air above 60 °C that is saturated with water vapour (NFPA, 2017). NFPA 130 suggests that this is the tenable limit applied, at head height, where high levels of water vapour may be present (e.g. where sprinklers have activated or during firefighting operations).

10.3.3 Radiation The level of radiant heat received from the smoke plume or layer can affect the ability of the occupants to evacuate by causing pain at far lower levels than those required for piloted ignition. For prolonged exposure, the tenability limit for exposure of skin to radiant heat is approximately 1.7 kW  ·  m–2 (NFPA, 2017). Below this value, exposure can be tolerated almost indefinitely without significantly affecting escape. Above this threshold value, the time to burning of skin due to radiant heat decreases rapidly according to the equation

tirad = 1.33 q-1.35 (10.4)

where tirad is the time (min) and q is the radiant heat flux (kW · m–2).



Qsteady = mfuel HC (10.6)

where Qsteady is the rate of heat release at steady state (kW), mfuel is the mass burning rate of fuel (kg · s–1) and HC is the effective calorific value of fire load (kJ · kg–1). Calorific values for different materials can be researched in PD 7974-1: 2003 (BSI, 2003b) or the SFPE Handbook (SFPE, 2016) but wood is typically 18 MJ · kg–1 and polyurethane 23  MJ · kg–1. Visibility in smoke is defined in terms of the furthest distance at which an object can be perceived, S (m), the optical density per unit length (m–1), D, and a visibility Table 10.1  Mass optical density for given materials (BSI, 2002) Material

Mass optical density, Dm / m2 · kg–1

Cellulosics Plywood Douglas fir

400 290 280

Plastics PMMS PVC Polyurethane Polystyrene

240–1000 150 640 220–330 790–1400

Generic building contents

300

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The temperature of smoke is significant, since it can cause burns both by convection (to exposed skin and lungs) and by radiation. With long exposure times there is also the risk of hyperthermia.

Fire safety engineering

Smoke ventilation

10-5

coefficient, K (m–1). This can be determined from (Klote et al., 2012) S=

K (10.7) 2.303D

Light-emitting objects, such as electric lights, are more easily perceived than objects which receive ambient illumination. These differences are reflected in the typical visibility coefficients given below for wood- and plasticbased fires: ——

for light-emitting signs: K = 8

——

for light-reflecting signs: K = 3

——

for building components in reflected light: K = 3.

10.3.5 Toxicity

A simple approach is to provide a tenability limit for 5-minute and 30-minute exposure durations based on the concentrations of carbon monoxide, carbon dioxide, oxygen and hydrogen cyanide in the fire effluent. Table 10.2 shows some proposed limiting exposure times for asphyxiants based on a 0.3 fed tenability limit for conditions considered typical for fires in buildings (BSI, 2004). Fires likely to involve fuels containing significant quantities of nitrogen-containing materials (>2% nitrogen by mass of fuel) are those involving furniture or clothing, such as fires in residences or retail premises, while fires involving mainly cellulosic or other materials low in nitrogen (<2% by mass of fuel) are more likely in offices. An alternative method is to compare the concentrations against the concentration that is lethal to 50% of animal subjects (lc50) for a given period of time (usually 30 minutes) (see Table 10.3).



FED =

mf t LC50

fed

(10.8)

where fed is the fractional effective dose, mf is the mass concentration of fuel burned (g · m–3), t is the exposure time (min) and lc50 is the lethal exposure dose from the test subject (g · m–3 · min–1). An fed of 1 (unity) is considered to be fatal and various values from 0.5 (Klote et al., 2012) to 0.3 (NFPA, 2009) may represent levels reflective of incapacitation.

10.3.6

Maximum asphyxiate concentration as CO / ppm 5-minute exposure

Noise levels: design values

High noise levels created by the extraction system should be avoided. Noise levels should be limited to 115 dBa for

30-minute exposure

Retail/residential (>2% nitrogen by mass of fuel)

800

125

Offices (<2% nitrogen by mass of fuel)

1200

275

Table 10.3  Approximate lethal exposure dose lc50 for common materials (Reprinted from Handbook of Smoke Control Engineering by Klote et al. © 2012. ASHRAE.) Approximate lc50 dose / g · m–3 · min–1

Material

Carbon monoxide (CO) exposure accounts for the majority of fire fatalities, although smoke often includes other toxic gases and factors such as hyperventilation due to high levels of carbon dioxide (CO2) or hypoxia caused by oxygen (O2) deprivation will also have an impact. As such, toxicity is often expressed as a fractional effective dose (fed).

For an exposure at a constant concentration, the (Klote et al., 2012) is

Fuel type

Non-flaming Fuel-controlled Fully developed fire fire fire Cellulosic (e.g. wood)

730

3120

750

C, H, O plastics

500

1200

530

PVC

500

300

200

Wool/nylon

500

920

70

Flexible polyurethane

680

1390

200

63

100

54

Rigid polyurethane

a few seconds of exposure and 92 dBa for the remainder of the exposure time (NFPA, 2009). Consideration should also be given to the impact of excessive extraction system noise levels on the ability of occupants to hear and understand any fire alarm systems, particularly those including voice alarms.

10.4

Design of systems

10.4.1

Smoke dilution systems

A smoke dilution system or purging system is based on diluting the smoke within a space such that the design criteria within that space, e.g. tenability or containment temperature limits, are not exceeded. While smoke dilution could be based on simple dilution using only the volume of the space, this approach is unlikely to be effective in any but the largest spaces with relatively small fires. It is unlikely that sufficient dilution can be achieved to maintain tenable conditions for a substantial period without ventilation of the smoke. Therefore, the majority of smoke dilution systems work on the basis of smoke extract and air inlet points being provided. Prior to the design of a smoke dilution system, the designer should consult all appropriate local codes and regulations to ensure that such systems are acceptable to the authority having jurisdiction.

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Table 10.2  Design tenability limit exposure concentrations for asphyxiant gases expressed as carbon monoxide for 5-minute and 30-minute exposures (BSI, 2004)

10-6

Fire safety engineering

10.4.1.1

Smoke clearance or purging systems

Since there is no need to maintain a clear layer, replacement air for dilution systems may be from both high and low levels. Caution should be exercised in the location of the supply and exhaust points to prevent the supply air from being extracted by the exhaust and thus shortcircuiting the system. Dilution systems are often based on nominally prescribed air change rates, but can be calculated based on times to improve visibility or temperatures within the space, using calculations or computational modelling. An extract rate of six (or 10) air changes per hour has been widely adopted as a prescriptive standard for the purpose of smoke clearance, although in atria a decrease to four air changes per hour where sprinklers are provided is used in England and Wales, where fire loading at the base of the atrium is controlled (BSI, 2017). The time to improve the visibility within a space to a predetermined level can be calculated from the following equation (SFPE, 2002):

c = e-at (10.9) c0

where c is the concentration at time t, c0 is the initial concentration, a is the air changes per minute (or purging rate) and t is the dilution time (min). The concentrations c0 and c must both be in the same units, and they can be any units appropriate for the particular contaminant (e.g. mass of smoke) being considered. Further reference should be made to chapter 6 of this Guide. An area can be considered to be ‘reasonably safe’ with respect to smoke obscuration if the concentration is not greater than 1% of the concentration at the fire (SFPE, 2002). 10.4.1.2

Cross-ventilation systems

Cross-ventilation has historically been widely used as a means of smoke dilution and/or dispersal, particularly for firefighting operations, and is based on the flow of air between (typically) opposing vents on the same floor level to provide dilution. Cross-ventilation can be provided naturally or using mechanical systems. Natural cross-ventilation In the case of natural cross-ventilation, in the UK, this has traditionally been based on providing nominally prescribed vent areas based on a percentage of the floor

As the required ventilation areas are prescriptive, the designer should make reference to the required codes of practice and standards for the appropriate jurisdiction. For UK car parks, for example, it is recommended that sufficient smoke ventilation equal to an aggregate of 2.5% of the floor area is provided at each level (BSI, 2013b). The distribution should be such that a minimum aggregate area of 1.25% of the total floor area is provided equally between two opposing walls (e.g. a minimum of 0.625% per opposing wall). As long as the minimum ventilation area is equal to 1.25% of the floor area provided on two opposing walls, the remaining vents can be provided in any location. It should be noted that requirements for car fume ventilation may exceed those for smoke. Smoke vents in the wall or ceiling can be used to form any part of the ventilation strategy, provided a through draft is created. Where openings have louvres etc., the effective free area provided should take into account the restriction. Mechanical cross-ventilation Mechanical cross-ventilation systems can comprise either entirely mechanical systems, with mechanical extract and mechanically provided inlet, or, more commonly, natural inlet and mechanical extract to provide cross flow. Mechanical cross-ventilation systems are typically found in car parks and designed, in the UK, to operate at 10 air changes per hour. For a typical UK car park provided with a ducted smoke ventilation system, it is recommended that the extract system should be designed to run in at least two parts, such that the total exhaust capacity of each part does not fall below 50% of the total extract rate (BSI, 2013b). As an example, if 10 m3 · s–1 is required to provide 10 air changes per hour in a car park, then the system should be designed such that it is provided in at least two parts, each part capable of ventilating at 5 m3 · s–1. For all other system types, the system should be designed such that the extract system takes into account fan or component failure in the design without reduction in performance. In addition, for car parks, extract points should be arranged so that 50% of the exhaust capacity is at high level and 50% is at low level and the extract points are evenly distributed. For all other purpose groups, the extract should typically be at high level and does not require high/low level extraction. The system should be designed such that failure of one part of the system will not jeopardise the other; this

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Dilution as a means of smoke clearance is often used for removal of cold smoke from a large space after the fire has been extinguished. Smoke clearance ventilation is typically undertaken using natural ventilation but a lack of buoyancy at high levels means that at heights in excess of 18 m the use of mechanical ventilation should be considered.

area of the building, at least half of the total of which should be equally distributed on two opposing sides of a space. No theoretical justification has been offered for the percentages given in the various codes of practice used in the UK, although it is reasonable to suppose that the vent areas that can result for large floor plates are such that, in most instances, they would provide an effective means of removal of heat and smoke.

Smoke ventilation

10-7

The discharge points for the smoke exhaust system should be located such that they do not cause smoke to be recirculated into the building or spread to adjoining buildings, or adversely affect the means of escape. The design of such systems should also ensure that there are no stagnant areas. While subject to local code requirements, in the absence of any detailed guidance it is recommended that all fans intended to exhaust hot gases should be appropriately tested to verify their suitability for operating at a minimum of 300 °C for a period of not less than 60 minutes. Impulse jet ventilation Impulse jet ventilation works by controlling the movement of air around the car park using locally mounted impulse jet fans. The permitted use and required performance of impulse fan systems is subject to local code requirements. Typically, the system should be designed such that the air change rate within the car park is a minimum of 10 air changes per hour. Impulse jet ventilation can also be designed to control the smoke to enhance means of escape or firefighting access provisions to the car park. Care should be taken to ensure that the number of impulse fans activated does not induce the movement of a volume of air greater than that which the extract fans are capable of extracting. No stagnant areas within the car park are permitted. Impulse fans should be carefully located to avoid exposing the doors to dynamic pressure effects, which might cause smoke to enter lobbies, staircases etc. used as means of escape. While subject to local code requirements, in the absence of any detailed guidance, it is recommended that all fans

Mechanical extract required to ensure that smoke is removed at a rate sufficient to create opposed airflow

intended to exhaust hot gases should be appropriately tested to verify their suitability for operating at a minimum of 300 °C for a period of not less than 60 minutes.

10.4.2

Opposed air flow systems

Air flow can be used to stop smoke movement through any space. Opposed air flow systems are based on inducing an air flow towards the area of the building containing the fire, such that the air velocity is sufficient to prevent the outflow of smoke (see Figure 10.1). Where opposed air flow is used to prevent smoke spread from the room of fire origin propagating into an adjoining large volume space (e.g. an atrium or shopping mall), the room of fire origin shall be ventilated at a sufficient rate to cause the ‘average air velocity’ (m · s–1) at the opening to exceed the ‘limiting average air velocity’ calculated as detailed below (NFPA, 2015a). The ‘average air velocity’ is found by dividing the extract rate by the area of all the openings, including those which do not open into the communicating space. An allowance should be made for any unknown leakage paths and a typical allowance of 15% is usually sufficient where these are not known. The ‘limiting average air velocity’ (m · s–1) can be found using

ve = 0.64 T gH

Tf - T0 0.5 Y (10.10) Tf

where ve is the limiting average air velocity (m · s–1), g is the acceleration due to gravity (9.81 m · s–2), H is the height of the opening as measured from the bottom of the opening (m), Tf is the temperature of the heated smoke (K) and T0 is the temperature of the ambient air (K). The temperature of the heated smoke Tf can be calculated using chapter 6. Smoke can be prevented from flowing from a large space to a small communicating space, where the small communicating space is located within the smoke layer, by supplying air to the small space. This can also be determined using equation 10.10 above.

Figure 10.1 Opposed air flow

Non-fire spaces may be pressurised if desired to enhance performance Shaft, stair or linking space

Opposed air flow

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includes the provision of power supplies. The designer should check the appropriate local codes of practice and regulations with regard to the need to provide sprinklers or other automatic water fire suppression systems to ensure that smoke temperatures are kept low in order to reduce the risks of fan failure.

10-8

Fire safety engineering



ve = 0.057 T

Q 1/3 Y (10.11) z

where ve is the limiting average air velocity (m · s–1), Q is the heat release rate of the fire (kW) and z is the distance above the base of the fire to the bottom of the opening (m). This equation is only valid where the limiting average air velocity is not greater than 1.02 m · s–1, or where z is less than 3 m. The above equation does not apply to corridor fires or where smoke enters a corridor via an open door from an adjoining room etc., where it is proposed to prevent further spread into the corridor by providing inlet air into the corridor. Instead, the following equation (SFPE, 2002) should be used, although it is noted that this equation is not applicable for sprinkler-controlled fires as the minimum velocity calculated would be too small.

vk = KT

g Q 1/3 Y (10.12) wt cT

where vk is the limiting average air velocity to prevent smoke flowing upstream (m · s–1), Q is the heat release rate of the fire (kW), w is the corridor width (m), t is the density of upstream air (kg · m–3), c is the specific heat of downstream gases, T is the temperature of the downstream mixture of air and smoke (K), K = 1 (constant) and g is the acceleration due to gravity (9.81 m · s–2). Temperature (T) can be calculated from chapter 6 and is considered to be the temperature of the smoke layer within the room. Where the adjoining space is located with openings above the smoke layer, air should be supplied from the adjoining space into the room of fire origin at the limiting average velocity, calculated as follows:

ve = 0.64 T gH

Tf - T0 0.5 Y (10.13) Tf

where ve is the limiting average air velocity (m · s–1), g is the acceleration due to gravity (9.81 m · s–2), H is the height of the opening, as measured from the bottom of the opening, Tf is the temperature of the heated smoke (K) and T0 is the temperature of the ambient air (K).

10.4.3

Pressure differential systems

10.4.3.1

Depressurisation systems

This method of smoke control is based on the extraction of air and/or smoke from the fire-affected part of the building to reduce the pressure in the space to less than that in the adjacent parts of the building. The induced pressure differential then inhibits the spread of smoke.

This system can also be referred to as a zoned smoke control system in the USA. This approach can be assisted by pressurising the adjoining spaces not affected by fire, for example the staircases or the zones immediately adjacent to the fire, such as the floor above and below the floor of fire origin. The minimum design pressure differences are dependent on local codes of practice, but a design pressure difference of 25 Pa between the depressurised and pressurised space may be sufficient for an unsprinklered room with a maximum ceiling height of 2.7 m (NFPA, 2015b). This could be halved to 12.5 Pa for a sprinklered room of any ceiling height. It is noted that BS EN 12101-6 recommends a minimum pressure difference of 50 Pa, irrespective of sprinkler provision or room height, when all the doors and openings are closed, a 0.75 m · s–1 velocity between pressurised and depressurised spaces when doors etc. are opened for means of escape and 2 m · s–1 for firefighting (BSI, 2005). The required extract rate can be calculated from the required pressure difference and the assumed leakage area using the following equation (BSI, 2005):

Q = 0.83 # Al # P 1/R (10.14)

where Q is the air flow into or out of a pressurised space (m3 · s–1), Al is the inherent leakage area from openings and building construction (m2), R = 2 (constant) and P is the pressure (Pa). So, the required air flow between a depressurised space and an adjoining one (at 0 Pa) with leakage area being only a single 2 m2 door, would be 8.3 m3 · s–1 to maintain a pressure difference of –25 Pa in the room of fire origin. Note: To ensure that the adjoining space is maintained at 0 Pa, inlet vents are needed from the adjoining room. This ventilation could be provided naturally or mechanically but must be sufficient to ensure that the pressure in the adjoining room does not decrease such that the pressure difference is below that required by the appropriate codes. For mechanical systems, this can be achieved by using the Q (m3 · s–1) value to calculate the ‘make-up’ air needed to be admitted into the space which is not depressurised. Temperature of extraction fans The exhaust fan temperature can be calculated, based on the gas temperatures calculated using zone models or hand calculations using the following equation (Klote et al., 2012):

! nj = 1 tj Vj Tj (10.15) Tfan = ! nj = 1 tj Vj

where Tfan is the temperature of the gases in the exhaust fan (°C), tj is the density of gases in space j (kg · m–3), Vj is the volumetric flow rate of exhaust from space j (m3 · s–1), Tj is the temperature of gases in space j (°C) and n is the number of spaces.

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Where opposed air flow is used to prevent smoke spread from a large space (e.g. atrium) to an adjoining small communicating space below the smoke layer interface, this can be achieved by providing air into the space the designer wishes to remain smoke free. The air shall be supplied into the space at the ‘limiting average velocity’ (NFPA, 2015a) calculated as follows:

Smoke ventilation

Use of the HVAC system It is possible to use the building’s hvac system, depending on the type of system, the kind of depressurisation system and the arrangement of the hvac zones. The use of hvac is subject to local codes of practice and regulations as well as the availability of a fully coordinated system to ensure that both smoke control and day-to-day functions can be achieved. The provision of further information on this subject is outside of the remit of this Guide but further guidance can be found in ASHRAE’s Handbook of Smoke Control Engineering (Klote et al., 2012). Use of computer modelling For complex designs, computer software can be used to undertake the calculations. While many different software packages are available, one of the more common is contam (Dols and Polidoro, 2015). This is a multizone indoor air quality and ventilation analysis computer program produced by the National Institute of Science and Technology (NIST) and available as a free download. 10.4.3.2

Pressurisation systems

An alternative to depressurisation the fire-affected area by extraction is to pressurise the surrounding areas, thus preventing the leakage of smoke from the fire-affected area into the adjoining spaces. Full reference should be made to local codes and regulations regarding system performance criteria, especially with regard to pressure differences. However, typically, US-based codes require a pressure difference of 12.5 Pa (sprinklered) and 25 Pa (unsprinklered and 2.7 m ceiling height) as per a depressurisation system (NFPA, 2015b). Conversely, European systems are typically based on a 50 Pa pressure difference (BSI, 2005). Due to the requirements for high air flows, pressurisation is usually reserved for critical parts of the escape and fire service access routes, such as staircases and lift lobbies. A typical example of a pressurised staircase and lobby is shown in Figure 10.2. The pressure differences provided are from BS EN 12101-6 (BSI, 2005).

a pressurisation system which compensates itself when doors are opened and closed. A compensated system is, therefore, one that adjusts for changing conditions by either modulating supply air flow or by relieving excess pressure. Compensated systems may have two or more different scenarios that require assessment and which will have different air flow requirements subject to the amount of leakage created by opening additional doors. An example may be a closed door scenario with minimal leakage and an open final exit scenario with substantial air flow to the outside via the open door. The air flow may need to be calculated as a leakage, using equation 10.14 above, or calculated as that required to maintain a given air speed (m · s–1) through the opening. Modulating the supply air flow is usually undertaken by providing a pressure sensor within the space linked to an inverter controlling the fan. Where this is provided, the engineer should be careful to ensure that the highest and lowest air flow requirements do not go outside the manufacturer’s recommended ranges for inverter-controlled fans. Typically, the lowest air flow rate is limited to 40% of the total air flow provided (e.g. a 10 m3 · s–1 fan could only be inverted down to 4 m3 · s–1). If natural overpressure relief is provided, then the calculation given in equation 10.16 can be used to calculate the area. The value of Q used in this case should be calculated based on (BSI, 2005)

Qc = Qfr - Qp (10.16)

where Qc is the air supply used to calculate overpressure relief vent (m3 · s–1), Qfr is the air supply needed to provide the required air flow through the open door into the fire room (m3 · s–1) and Qp is the air supply to the stair or lobby needed to satisfy the pressure differential requirement (m3 · s–1). Where overpressure relief is provided by natural ventilation, equation 10.17 should be used (BSI, 2005):

Apv =

Qc (10.17) 0.83 # P 0.5

Supply air

Supply air

Air relief

50 Pa

45 Pa

0 Pa

Supply air requirements can be determined using equation 10.14 above. As well as providing supply air, it is also necessary to ensure that the adjoining spaces do not pressurise by providing an air release path as well as ensuring that the pressurised space itself does not overpressurise where such systems are provided as ‘compensated’ systems.

Lift

Supply air

Compensated systems It may be necessary, either to comply with the fire engineering strategy or to comply with local codes, to provide

Figure 10.2  Pressurisation of protected area

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Alternatively, the extraction fan from the depressurisation zone shall be specified to be capable of handling smoke at a temperature of 1000 °C for unsprinklered buildings, or 300 °C for sprinklered buildings (BSI, 2005).

10-9

10-10

Fire safety engineering Table 10.4  Air leakage data from doors (BSI, 2005) Type of door

Leakage area / m2

Pressure differential / Pa

Air leakage / m3 · s–1

Air release path

Single-leaf opening into a pressurised space

0.01

8 15 20 25 50

0.02 0.03 0.04 0.04 0.06

Single-leaf opening outwards from a pressurised space

0.02

Where the adjoining space is the room of fire origin, it is likely that ventilation will be formed due to window breakage; however, this cannot be relied upon. It is also possible that the adjoining space may be a corridor etc. without ventilation but which is otherwise smoke logged.

8 15 20 25 50

0.05 0.06 0.07 0.08 0.12

Double-leaf

0.03

Where air relief is provided by mechanical extraction, the calculated Q value for the pressurised space can be used to calculate the required extract rate.

8 15 20 25 50

0.07 0.10 0.11 0.12 0.18

Lift landing door

0.06

8 15 20 25 50

0.14 0.19 0.22 0.25 0.35

If an insufficient air release path is provided to the adjoining space, adjacent to a pressurised one, then over time the adjoining space will reach the same pressure. Smoke and other combustion gases could flow from the adjoining space into the pressurised one as a result.

Where an air release path is provided by natural ventilation, equation 10.18 should be used (BSI, 2005):

Q AVA = 2.5 (10.18)

where Q is the air flow into a pressurised space and AVA is the area of air/smoke relief vent (m2).

(m3 · s–1)

Note: The value of Q will be the higher of the values calculated when the doors are closed or when the doors are open depending on the design of the system and code requirements for the adjoining space. Leakage Aside from any open doors or windows, leakage may also occur from the building structure itself. Such leakage should be added to any leakage assumed for open doors etc. especially when assessing the ‘door closed’ scenarios. Tables 10.4 and 10.5 provide air leakage data for doors and wall construction. It is recommended that any calculated leakages are increased by 50% to reflect any potential increases in leakage found during the commissioning process. Number of injection points Pressurisation systems can consist of single or multiple injection points. The provision of injection points is usually determined by compliance with local codes. For example, NFPA 92 recommends that single injection point systems are not provided for staircases in excess of 30 m in height (NFPA, 2015a), while BS EN 12101-6 recommends that single injection is limited to buildings of less than 11 m in height and that, above this height, injection points should be provided with no more than three storeys between points (BSI, 2005).

10.4.4

Natural ventilation systems

There are a number of forms of natural ventilation provided within buildings, which can be broadly split into the following:

Table 10.5  Air leakage data for walls (BSI, 2005) Construction element

Wall tightness

Leakage area ratio, ALW/AWall* × × × ×

10–4 10–3 10–3 10–2

Exterior building walls (including Tight construction cracks, cracks Average around windows and doors) Loose Very loose

0.7 0.21 0.42 0.13

Internal and stair walls (including construction cracks, but not cracks around windows and doors)

Tight Average Loose

0.14 × 10–4 0.11 × 10–3 0.35 × 10–3

Lift well walls (including construction cracks, but not cracks around windows and doors)

Tight Average Loose

0.18 × 10–3 0.84 × 10–3 0.18 × 10–2

*ALW is total leakage area through the walls, AWall is the area of the walls

(a)

Smoke clearance systems: these are generally either dilution or cross-flow systems and are detailed in section 10.4.1.

(b)

Smoke control systems: these consist of high-level vents with low-level inlet and are provided to maintain conditions as determined by the designer, e.g. to keep a smoke layer at a predetermined height or maintain a tenable condition.

(c)

Smoke shafts: these systems are provided to protect adjoining spaces, such as firefighting lobbies and residential corridors.

10.4.4.1

Smoke control systems

Designers should use chapter 6 of this Guide to determine the relevant fire size and factors such as mass flow rate, volume flow rate and temperature of smoke. Section 6.8.3.3 in chapter 6 details the calculation methodology for estimating the mass flow rate of smoke through horizontal natural vents.

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where Qc is the air flow into a pressurised space (m3 · s–1), P is the pressure (Pa) and Apv is the area of air/pressure relief (m2).

Smoke ventilation

10-11

Where the size of the vents is unknown, these can be calculated (BSI, 2002) based on msmoke T T T0 m2smoke 1/2 (10.19) Cv T 2 g dt20 iT0 - # &Y A2i C2i

This can also be arranged to allow vent area to be determined in terms of Q, although this is recommended only for very large inlet areas:

Av =

m T C Qp 1 # & (10.20) #1 + msmoke Cp T0 t0 Cv Q2 g dV0.5 Qp1/2 3/2 smoke

1/2 0

1/2 p

where Av is the throat area of the ventilator (m2), msmoke is the mass flow rate of smoke (kg · s–1), T is the smoke temperature (K), Cv is the coefficient of discharge (dimensionless), g = 9.81 (m · s–2), d is the smoke layer depth (m), t0 is the ambient air density (kg · m–3), i is the excess temperature (°C), T0 is the ambient air temperature (K), Ai is the total area of all inlets (m2) and Ci is the entry coefficient for inlets (dimensionless). The coefficient of discharge (Cv) is provided by the manufacturer but typically taken as 0.6. If inlet air is provided by smoke ventilators in adjacent smoke reservoirs, then Ci would be the same as Cv. Ambient air density is typically taken as 1.2  kg · m–3. Excess temperature (i) is simply the smoke layer temperature (°C) minus the ambient temperature (°C). 10.4.4.2

Natural smoke shafts

Natural smoke shafts are commonly used to ventilate staircases and lobbies, either for firefighting shafts or residential common corridors. The main objective of these systems is to protect the adjoining staircase by ventilating the corridor or lobby giving access to the stair. The systems work by the provision of a natural ventilator from the lobby/corridor into a vertical smoke shaft, which is naturally ventilated directly to the outside at the head of the shaft. Replacement air for the system comes from a vent at the head of the adjoining staircase. The provision of a door between the stair and the lobby/corridor means that the system is only fully effective when the stair door is open. These systems work because of a net flow of air between the stair and lobby, and so generally ensure that the staircase is kept clear of smoke, but they may not only have limited success in maintaining tenable conditions in the lobby when the stair door is closed (when no inlet air is available), but also when the stair door is open. The design requirements for smoke shafts tend to be prescriptive and therefore the designer should make full reference to local codes prior to designing smoke shaft systems. Residential buildings In England, smoke shafts for residential buildings should be a minimum of 1.5 m2 in area and have a minimum dimension of 0.85 m in any direction (e.g. width) (HM Government, 2013).

The shaft should extend at least 2.5 m above the ceiling of the highest storey served by the shaft. This generally means that it is not always appropriate to vent the top floor level of the building via a smoke shaft, which should be vented in a different manner. The adjoining stair should be ventilated directly to the outside via a 1 m2 vent at the top storey level, which should open at the same time as the lobby vent. Additional guidance on the design of smoke ventilation systems for residential buildings using natural ventilation can be found in the SCA’s Guidance on Smoke Control to Common Escape Routes in Apartment Buildings (SCA, 2015). This guide is available from the SCA as a free download. Firefighting shafts Guidance on the use of natural smoke shafts in firefighting shafts in the UK is given in BS 9999 (BSI, 2017). Typically, the cross-sectional area (geometric free area) of the smoke shaft should be at least 3 m2. Historically, these smoke shafts have been provided with openings at the top and bottom; however, this design has now largely been superseded by the ‘closed-base’ smoke shaft approach, as described in the BRE project report 79204 (Harrison and Miles, 2002). The lobby ventilator should have a geometric free area of at least 1.5 m2. Both the width and the height of the lobby ventilator should be not less than 1 m. This ventilator should open on detection of smoke within the lobby. The adjoining stair should be ventilated via a 1 m2 vent at the head of the stair direct to the outside, which should open at the same time as the lobby vent. 10.4.4.3

Consideration of wind overpressures

Where natural ventilators are used for smoke extraction, it is important that they be positioned where they will not be adversely affected by external wind conditions. A positive wind pressure can be much greater than the pressures developed by a smoke layer. If this occurs at a smoke exhaust opening, the ventilator may act as an inlet rather than an extract. However, if the ventilator is sited in an area of negative wind pressure, the resulting suction force may assist smoke extraction. The effects of wind pressures on a ventilation system are not isolated to localised wind pressure effects. The wind pressures around the entire building envelope (i.e. global pressures) will dictate the smoke flow patterns within the building and the effectiveness of the ventilation system design. Tall buildings, or taller areas of the same building (such as rooftop plant rooms), can create a positive wind pressure on the upstream section of the lower roof area. The designer should consider the need to undertake a wind analysis and determine the external pressures at high-level vents and low-level openings, and also to estimate the internal pressure. In some instances, adverse effects may be overcome by positioning the ventilators in regions of the roof that are

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Av =

The shaft should terminate at roof level, at least 0.5 m above any surrounding structures within a horizontal distance of 2.0 m.

10-12

Fire safety engineering systems can be provided as an alternative to natural or pressurisation systems.

10.4.5

Comprehensive guidance on the design of mechanical smoke ventilation systems for residential buildings can be found in the SCA Guide on smoke control to common escape routes (SCA, 2015).

Mechanical ventilation

Mechanical smoke ventilation consists of fan systems to extract smoke. These systems may or may not be ducted, depending on the proposed design of the system. Designers should use the equations given in chapter 6 of this Guide to calculate the relevant fire size, type of smoke plume or flow and resulting mass flow rate for the proposed fire, in relation to the geometry under assessment. This information can then be used in conjunction with section 6.7.5 to calculate average plume temperature and section 6.7.6 to calculate the volume flow rate of the smoke. The volume flow rate of the smoke (m3 · s–1) calculated should be less than or equal to the rate of extract proposed. The risk of plug-holing can be minimised using the guidance provided in section 10.2.2.5. 10.4.5.1

Slot or slit extract

Slot extract systems can be employed to prevent the flow of smoke across the openings in a room and into adjoining spaces. They can also be used to supplement an exhaust system and remove the need for a downstand or channelling screen where employed over the length of the flow path. While a slot extract system is designed to prevent smoke entering an adjoining space, it will not necessarily maintain a clear layer within the room itself. It may be necessary to supplement the slot extract with additional mechanical ventilation from the room of fire origin. The extraction should be provided very close to the opening from a continuous slot, which may be situated in the plane of the ceiling or at very high level. It is considered that powered exhaust from a slot at right angles to a layer flow can completely prevent smoke passing that slot, provided that the extraction rate at the slot is at least 5/3 times the flow in the horizontal layer flowing towards the slit (Morgan et al., 1999). This allows a useful general method for sizing such extracts: (1)

Calculate the flow rate of gases approaching the opening or gap.

(2)

Multiply the mass flow by 1.667 (i.e.

(3)

Use the convective heat flux of the smoke layer (allowing for sprinkler cooling if applicable) to calculate the volume extract rate required.

10.4.5.2

5/3).

Residential smoke ventilation

Mechanical smoke ventilation systems can be used to prevent smoke entering the staircases and to maintain tenable conditions within the common areas. These

Prior to design of these systems, designers should take into account any local code requirements and recommendations.

10.4.6

Interaction between sprinklers and smoke vents

There has been much debate over whether sprinklers affect smoke ventilation, or vice versa. Experiments have demonstrated that there are no issues raised where both systems are used in the same building (McGrattan et al., 1998). The provision of smoke vents reduces the spread of fire products through the building due to the release of hot gases and fire material from the building. This improves the visibility and conditions in the building to enable occupants to escape and firefighters to undertake firefighting operations. Experimental studies have shown that early vent operation does not have a negative effect on sprinkler performance (Beyler and Cooper, 2001). Where sprinklers successfully contain a fire, vents may not be needed, except for post-fire smoke clearance. However, sufficient smoke may still be produced, even when the fire is suppressed, that there may be a benefit from smoke ventilation and the impact of this should be considered by the system designer.

References Beyler CL and Cooper LY (2001) ‘Interaction of sprinklers with smoke and heat vents’ Fire Technology 37 (1) 9–35 BSI (2002) PD 7974-2: 2002 Application of fire safety engineering principles to the design of buildings. Spread of smoke and toxic gases within and beyond the enclosure of origin (Sub-system 2) (London: British Standards Institution) (Note: PD 7974-2: 2002 has been replaced by PD 7974-2: 2019) BSI (2003a) BS 7346-4: 2003 Components for smoke control systems. Functional recommendations and calculation methods for smoke and heat exhaust ventilation systems, employing steady-state design fires. Code of practice (London: British Standards Institution) BSI (2003b) PD 7974-1: 2003 Application of fire safety engineering principles to the design of buildings. Initiation and development of fire within the enclosure of origin (Sub-system 1) (London: British Standards Institution) (Note: PD 7974-1: 2003 has been replaced by PD 7974-1: 2019) BSI (2004) PD 7974-6: 2004 The application of fire safety engineering principles to fire safety design of buildings. Human factors. Life safety strategies. Occupant evacuation, behaviour and condition (Sub-system 6). (London: British Standards Institution) (Note: PD 7974-6: 2004 has been replaced by PD 7974-6: 2019) BSI (2005) BS EN 12101-6: 2005 Smoke and heat control systems. Specification for pressure differential systems. Kits (London: British Standards Institution)

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sheltered from wind action or that will always produce suction. In other cases, the positioning of suitably designed wind baffles can overcome wind interference or even convert a positive pressure into suction. Locating the low-level openings in regions of a positive pressure can also help to improve venting.

Smoke ventilation BSI (2013a) BS 7346-8: 2013 Components for smoke control systems. Code of practice for planning, design, installation, commissioning and maintenance (London: British Standards Institution)

BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) Dols WS and Polidoro BJ (2015) NIST Technical Note 1887: CONTAM User Guide and Program Documentation Version 3.2. (Gaithersburg, MD: National Institute of Science and Technology) Harrison R and Miles S (2002) Smoke Shafts Protecting Firefighting Shafts: Their performance and design BRE Project Report 79204 (Garston: Building Research Establishment FRS) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) Klote JH, Milke JA, Turnbull, PG, Kashef, A and Ferreira, MJ (2012) Handbook of Smoke Control Engineering (Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers)

McGrattan KB, Hamins A and Stroup DW (1998) Sprinkler, Smoke and Heat Vent. Draft Curtain Interaction: Large scale experiments and model development. International fire sprinkler smoke and heat vent draft curtain fire test project NISTIR 6196-1 (Gaithersburg, MD: National Institute of Standards and Technology) Morgan HP et al. (1999) Design Methodologies for Smoke and Heat Exhaust Ventilation BRE Report BRE 368 (Garston: Building Research Establishment) NFPA (2015a) NFPA 92 Standard for smoke control systems (2015 edition) (Quincy, MA: National Fire Protection Association) NFPA (2015b) NFPA 101 Life Safety Code (2015 edition) (Quincy, MA: National Fire Protection Association) NFPA (2017) NFPA 130 Standard for fixed guideway transit and passenger rail systems (Quincy, MA: National Fire Protection Association) SCA (2015) Guidance on Smoke Control to Common Escape Routes in Apartment Buildings (Flats and Maisonettes) Revision 2 (London: Smoke Control Association) SFPE (2002) SFPE Handbook of Fire Protection Engineering (3rd edition) (Boston, MA: Society of Fire Protection Engineers; Quincy, MA: National Fire Protection Association) SFPE (2016) SFPE Handbook of Fire Protection Engineering (5th edition) (Boston, MA: Society of Fire Protection Engineers; Quincy, MA: National Fire Protection Association)

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BSI (2013b) BS 7346-7: 2013 Components for smoke and heat control systems. Code of practice on functional recommendations and calculation methods for smoke and heat control systems for covered car parks (London: British Standards Institution)

10-13

11-1

11

Fire suppression

This chapter covers the wide range of active firefighting systems and devices which are available to specifiers. When calling for the use of any particular system it is most important to understand the purpose that the system is to serve. Even the term ‘suppression’ can lead to confusion, since this may imply that fire extinction may be the expectation whereas, in some instances, this is not the case. It is vital that, in calling for the use of a specific system, the anticipated outcome and potential reliability are understood. For example, a gaseous fire protection system would normally be designed to ‘extinguish’ a fire but its ability may be severely compromised if the room integrity is breached by something like an open door. On the other hand, a sprinkler system would normally only be expected to ‘control’ a class A fire, so as to limit the release of heat and combustion products, and external intervention by the fire brigade may be necessary to complete the extinguishment process. The objectives of the end user may be simply to meet the obligations imposed on them by the authority having jurisdiction (ahj), which may be the local authority, the building fire insurers or the fire and rescue service. In this case, ‘compliance’ would be the objective and the exact nature of the suppression systems is likely to be clearly spelled out by the ahj. It is probable that any requirement imposed under the Building Regulations 2010, as amended, will be aimed at ‘life safety’ whereas the fire insurers are more likely to be aiming for ‘property protection’. In practice, a system designed to protect life will have a beneficial effect on the protection of property and vice versa. The two are very much entwined and often an identical system will fulfil both objectives. In cases when ‘compliance’ is not the only objective, it may be necessary to carry out a thorough review of the client’s objectives to establish which active systems may be necessary. In these cases, a clear understanding of the expectations in terms of acceptable levels of property and contents damage will be necessary. In some circumstances, where the building or contents are particularly valuable or business critical, a comprehensive scheme of protection may be appropriate. This could include passive protection (compartmentation), alarm and detection systems, active systems and even smoke ventilation and firefighting access to give the required resilience that is necessary to meet the needs of the project. An example of how this might work in practice is demonstrated in a recent, prestigious project in the UK where, in a particular area of the site, the risk was considered to be of such significance to the business that it was decided that ‘zero damage’ was the real objective. The decision was

made to try to deal with any fire incident at the earliest possible stage but to recognise that any of the measures could be subject to potential failure. The following is a summary of the measures adopted. (a)

Enhanced awareness of the potential for fire and the consequent risk to the business and management of the risk: ——

strict security control of access by personnel, and escorting of all visitors

——

detailed induction to include fire risk management, with regular refresher inductions

——

strict control of all works in the area, to include risk assessments and method statements

——

limitation of any storage and limited local combustible consumables.

(b)

Installation of an aspirating smoke detection system to give the earliest possible warning of fire. This system was intended to initiate investigation and action by security staff and not evacuation or activation of any suppression systems.

(c)

Installation of a ‘standalone’ point fire detection and alarm system (the ‘house’ system) to initiate evacuation of the area, provide warning to adjacent areas and summon the fire and rescue services.

(d)

Installation of an automatic inert gaseous firefighting system armed by a coincident smoke detection system in which two smoke detectors are required to initiate release of the gaseous agent.

(e)

Automatic sprinkler protection of the ‘wet’ type, with sprinkler heads protected from mechanical damage.

(f)

Compartmentation of the risk areas from adjacent areas on the same floor and from adjacent floors by construction which offers at least two hours’ fire resistance.

By providing these multiple methods of potential control, the building owner was able to put in place the maximum number of opportunities to stop the progress of the fire incident. The owner acknowledged that every stage has the potential for failure to control the fire and was willing to invest in many ‘layers’ of protection in the attempt to offset any weaknesses in the earlier stages. This is an exceptional project and it is not intended that this should be considered as a ‘model’ but it does serve to demonstrate that the ‘suppression’ tools in the box can be used in combination as well as in isolation to provide the potential to engineer for almost any objective. It is always important to consider the end needs of the building

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11.1 Introduction

11-2

Fire safety engineering

11.2

Sprinkler protection

11.2.1 General The use of a fixed system of water sprayers to fight fires in buildings can be traced back to the nineteenth century. The earliest systems consisted of simple, manually controlled arrangements of sparge pipes in vital areas, but these soon led to individually operated devices attached to a pressurised pipework system. The earliest fixed system in the UK is believed to have been installed in the Drury Lane Theatre, London in 1812. Other than the refinements in terms of aesthetics and thermal response brought about by improvements in engineering techniques and materials, little has changed in the design principles of sprinkler heads. The original idea of sealing a waterway in a fixture with an element that responds to local thermal conditions is both simple and reliable. Unnecessary complexity should be avoided and the introduction of any additional steps between fire detection and the discharge of water must be carefully considered to ensure that real benefits are not outweighed by reduced reliability. A sprinkler system is a very simple solution and it is that simplicity and well-documented reliability that makes the use of sprinklers an effective fire protection measure. Water is a very good firefighting medium for class A materials and most sprinkler systems are therefore most effective on a risk of this nature. The use of sprinklers on class B, C, D and E risks would need to be carefully considered. In simple terms, a conventional automatic sprinkler system consists of pipes and heat-sensitive valves (sprinkler heads) connected to a water supply. Fire is detected by individual sprinkler heads, which open to release water, in the form of spray, to the seat of the fire. The idea that the operation of a single sprinkler head results in all sprinkler heads discharging water is not true; this is a misconception generated by the film and television industry. The alarm is raised at the same time and the fire is kept under control until the arrival of the fire brigade. The principle objective is to control the fire for subsequent extinguishment by the fire brigade, but often the sprinklers will have accomplished extinguishment prior to their arrival. Common factors in large fires are delays in the discovery of the outbreak and a subsequent delay in the commencement of firefighting operations. Automatic sprinkler systems first detect and then immediately attack the fire, thereby restricting the growth of the fire and confining

damage. Automatic sprinklers have a good performance record, and it is reasonable to expect that the majority of fires in sprinkler-protected premises are controlled by the operation of four sprinklers or fewer. Real fire data collected by the National Fire Protection Association (NFPA) for the period 2007–2011 showed that, across all types of premises protected by a sprinkler system: ——

for wet-pipe sprinkler systems, 88% of reported fires were controlled by only one or two sprinklers

——

for dry-pipe sprinkler systems, 73% were controlled by only one or two sprinklers.

A report published in 2005 by the NFPA (Rohr and Hall, 2005) concluded that when sprinklers are present, the chances of an occupant dying in a fire are reduced by 50% to 75%, and the average property loss per fire is cut by 50% to 67%, compared to fires where sprinklers are not present. These figures are considered to understate the potential value of sprinklers as they exclude unreported fires but do include all types of sprinkler system, regardless of age or operational status. As even more emphasis is placed on proper operation of sprinkler systems, the need for increased reliability and availability is being met by established independent third-party certification of components, systems and companies. The merit of such schemes is referenced within current UK fire safety guidance, such as Approved Document B (HM Government, 2013), BS 9999: 2017 (BSI, 2017), BS EN 12845: 2015 (BSI, 2015a) and the Technical Bulletins of the Loss Prevention Council (LPC), which also directly address the issue of availability and reliability. Although sprinkler systems are reliable, there are occasions where sprinklers fail to control a fire. Recent data from the NFPA for fires in the USA in 2007–2011 concluded that sprinklers failed to operate in only 9% of building fires (Hall, 2013). However, the majority of these failures were due to human intervention (64% of the cases where sprinklers failed were because the system had been shut off before the fire started). For this reason, sprinklers cannot claim to be 100% effective and so it is occasionally suggested that they should not be used in trade-offs with other fire protection measures. This argument, however, is considered to be flawed in that it assumes that all other fire protection measures are 100% effective, which is clearly not the case. For example, fire doors may fail to prevent fire spread either due to being left open or because they are poorly fitting. In the design of buildings, a balance should be found between passive and active fire safety measures that address the needs of the building in the most rational and economical way. A comparison of the reliability of sprinklers compared to passive fire protection can be found in PD 7974-7: 2003 Application of fire engineering principles to the design of buildings (BSI, 2003a). The document gives probability figures for successful sprinkler activation between 0.75 and 0.95 (the latest US data suggest a probability of 0.93). These figures compare favourably with passive fire system figures from the British Automatic Fire Sprinkler Association’s Sprinklers for Safety (BAFSA, 1995), which include the following: ——

probability of fire doors being wedged open = 0.3

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occupier and/or owner in engineering the systems. Although the life safety risks will almost certainly be mitigated by meeting the obligations of the building codes or even the fire insurers, it may not always be the case that these systems will offer the levels of protection that the business needs. The early involvement of a qualified professional in any project is always recommended, see chapter 5: Application of risk assessment to fire engineering designs.

Fire suppression

11-3

probability of self-closing doors failing to close correctly on demand = 0.2

——

probability that fire-resisting structures will achieve at least 75% of the designated fire resistance standard = 0.25 for suspended ceilings

(e)

probability that fire-resisting structures will achieve at least 75% of the designated fire resistance standard = 0.65 for partition walls.

As the sprinklers will effectively be combating the fire, the number of firefighting shafts can potentially be reduced.

(f)

As the sprinklers will be controlling the fire size, the level of radiated heat flux will also be controlled. The result of this is that the separating distance between buildings may be reduced. Under the Building Regulations 2010, as amended, the distance is reduced by one-half.

——

This section of Guide E considers the principles of sprinkler system design and identifies the relevant design codes. It is not intended to act as a design manual and specialist advice should always be sought when a system needs to be designed.

11.2.2

Benefits of sprinklers

In its document Use and Benefits of Incorporating Sprinklers in Buildings and Structures, the British Automatic Fire Sprinkler Association (BAFSA) has listed the potential for using sprinklers to work in conjunction with other fire safety systems to attain coherent fire safety designs (BASFA, 2006). This approach permits reductions in some levels of fire resistance to support structure or the increase in fire compartment sizes. The document was prepared with the UK Building Regulations as the guide document but the data are applicable on an international scale. The following list details some of the potential concessions that may be considered due to the presence of sprinklers. (a)

(b)

(c)

(d)

Means of escape: As the action of the sprinklers is likely to reduce the rate of burning of a fire and, in consequence, the mass smoke flow, the time available for people to escape may be increased. The result of this is that the distance required to travel to an exit can potentially be increased without reducing the level of people’s safety. It is, of course, true that if smoke detection is present, evacuation would be well advanced prior to sprinkler activation. The argument would be valid only if sprinklers were being used as the means of detection. Compartmentation: As the action of the sprinklers will be reducing the intensity of a fire, the chance of it becoming large is reduced. This reduces the number of people being immediately threatened by a fire and offers a level of protection to people expected to remain in or enter the building during the fire. As the fire is likely to be controlled, the risk of fire spread to adjacent buildings is reduced. The result of this is that building compartment areas/volumes may be increased over those for a similar non-sprinklered building. Fire-resistance levels: The severity of a fire and its duration are likely to be reduced by the action of the sprinklers. The results of this are that a structural element is liable to maintain its load-bearing capacity and that a separating element will maintain both its integrity and its ability to resist the transfer of heat. The fire-resistance levels may therefore be reduced if sprinklers are fitted. Mechanical smoke extract: As a replacement for natural smoke exhaust, the presence of sprinklers permits the use of mechanical fans. The fans are

There are further ways in which sprinklers can be used in buildings with atria, in healthcare buildings, shopping complexes and other places of assembly. Reference to the BAFSA document is recommended if further guidance is required. Other uses that sprinklers offer are covered in the sections that follow.

11.2.3

Fire engineering using sprinklers

The use of a sprinkler system to automatically detect and fight a fire may be exploited as part of an engineered solution. The size of fire and the rate of release of combustion products may be reasonably predicted where a specific standard is used. The prescriptive guidance of compartment size, fire resistance values etc. where sprinklers are used will depend on the control of the release of heat from the fire given by sprinkler activation. This is discussed in some detail in chapter 6: Fire dynamics. It is generally accepted that a fire will stop growing at the time of sprinkler activation or shortly thereafter. The time that a sprinkler takes to operate in a fire can be predicted but is dependent on a wide range of variables, namely: ——

fire growth rate

——

ambient temperature

——

temperature rating of the sprinkler

——

response time index (rti) of the sprinkler

——

conduction factor of the sprinkler components

——

radial distance of the sprinkler from the fire

——

height of the sprinkler above the fire

——

distance of the sprinkler below the ceiling.

Factors such as the type of risk, type of fuel and expected heat release rate are also very important as they will directly influence the speed of sprinkler activation. These factors are fundamental to the way in which a sprinkler system needs to work. Understanding the fuel load (or ‘hazard’, as it is termed in the design codes or ‘rules’) is vital. A system designed to control a fire of 8.5 MW total heat output is unlikely to contain a fire expected to rapidly grow to 15 MW. The expected fire size or design size fire

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protected from the effects of extremely hot smoke by the action of the sprinklers on the fire. This is particularly useful in basement conditions when access to outside air is not possible.

——

11-4

The use of a more performance-based approach will not be suitable for many building designs. For simple buildings, where a large level of flexibility in either its current or its future use is envisaged, the prescriptive guidance of system engineering given in the various rules and codes should be used wherever possible and practicable. If bespoke or non-standard sprinkler designs are used, or some of the system features do not meet the objectives laid down in the adopted design code, their full impact on the performance of the system’s speed of reaction to fire and its ability to restrain fire growth will need to be taken into account. This section of Guide E attempts to strike a balance between the recommendations of the current standards and the principles upon which they are based and the fire engineered approach relying on first principles. Where the nature of the risk falls outside the scope of the guidance in the rules, or novel designs or techniques are employed, the objectives of the standard system in terms of response time and water spray performance should be replicated if similar levels of control are to be expected. There are further uses for sprinklers not adequately covered by a number of international design codes. One of these would be the use of water to provide protection against fire spread or by enhancing the fire-resisting properties of materials such as glass. Sprinkler protection has the potential to increase the performance of glazing in fire situations and external drencher systems have been used to protect buildings from the effects of fire in adjacent buildings. Although not covered by many codes, there is no reason why this practice should not be extended to provide protection for internal elements of buildings as part of a fire engineered design. The location and spacing of the sprinklers would need to be determined for the particular situation, but locating sprinklers within 600 mm of glazing should provide a good spray distribution over the glazing. The use of sprinklers to protect glazing and external walls, although not common in the UK, is adopted in Australasia and Hong Kong. A sprinkler designed specifically to discharge water onto glazed assemblies and also for outside protection against exposure fires is available in the USA and is covered by NFPA guidance (NFPA, 2016a). Australian Standard AS2118.2: 1995 Wall wetting sprinklers (drenchers) covers the requirements of providing protection to external walls, windows and doors from exposure to fire (SA, 1995). The system is required to be automatic in operation and therefore uses either sealed sprinklers or open sprinklers with water being released via a detection system. The use of a film of water providing glazing with a recognised period of fire resistance is an accepted method

following testing by Kim and Lougheed (1997). Their work resulted in the development of a specific window sprinkler. This sprinkler, if used in accordance with the manufacturer’s recommendations, can provide a fire resistance level of 60 to 120 minutes. There are aspects to be aware of when proposing this type of active system to provide fire separation. A fire immediately next to the glazing is likely to cause the glass to fail. To mitigate this, it is recommended that a 900 mm high spandrel panel is adopted. This provides a level of protection during the fire’s initial growth phase, allowing the sprinkler to react prior to the glazing failure temperature being reached. The glass needs to be heat strengthened or tempered. The glazing should be vertically unobstructed as the presence of a horizontal mullion negates the sprinkler’s ability to cover the glass effectively. If a joint in the glass is required, it would need to be butt jointed for the sprinkler to be effective. It should also be noted that this sprinkler is for use on fixed glazing, and it is not suitable for operable windows.

11.2.4

Extinguishing mechanism

One of the key mechanisms of sprinkler effectiveness is the pre-wetting of unburnt combustible materials. This is of great importance at the design/installation stage, as the layout/arrangement needs to consider avoiding obstruction to the sprinkler spray pattern and discharge. There are two other main mechanisms involved in the way that water suppresses fire: cooling and ‘inerting’. Cooling of the item on fire will reduce the rate of heat release. Cooling also occurs in the flame, which reduces the concentration of free radicals. A proportion of the fire’s energy is dissipated in heating the water droplets. The inerting aspect, while fairly minor with the large water droplets formed by standard sprinklers, does play a part. The production of steam helps to displace oxygen from the flame zone. Water has a theoretical cooling capability of 2.6 MW· litre–1 per second (Grimwood, 2005) and this could be used, adopting a safety factor, to determine appropriate discharge densities when the heat release rate of the design fire to be addressed has been assessed. Babrauskas and Grayson (1992) compiled various fire load surveys from 1966 to 1975 and estimated an 80 percentile range for fire load for offices in the following countries, demonstrating a wide variation in the fire load: ——

USA: 835  MJ · m–2

——

Germany: 1002  MJ · m–2

——

Sweden: 635  MJ · m–2

——

Holland: 401  MJ · m–2

——

England: 535  MJ · m–2.

The 20th edition of the NFPA’s Fire Protection Handbook (NFPA, 2008) has values for offices which are quoted as 590 and 1075 MJ · m–2 for general offices and file storage. A comprehensive collection of surveys was presented by Yii (2000), whose report builds on work carried out by the

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needs to be determined to ensure that the sprinkler system water discharge rates are suitable. This is prescriptively done in the design codes, where a large range of hazard areas are listed along with the required water discharge rates and expected areas of operation. It can also be done by determining the fuel load and rate of heat release of the contents and the construction material of the building. This should be undertaken by experienced fire engineers.

Fire safety engineering

Fire suppression University of Canterbury, New Zealand, since 1994, with 11 surveys collated to produce a range of fire loads of between 224 and 800 MJ · m–2.

11.2.5

Rules and standards

There are many sets of internationally recognised design codes against which a sprinkler system can be designed. The principal rules applicable to sprinkler installations in the UK and other parts of the world are contained in the European Standard BS EN 12845: 2015, which is a harmonised document covering the European nations (BSI, 2015a). British Standard BS 5306-2: 1990 is now superseded by this standard. To include the UK’s specific requirements, a number of detailed bulletins (Technical Bulletins) are incorporated into the standard, forming the Loss Prevention Council’s Rules for Automatic Sprinkler Installations (LPC, 2016). There are a number of other internationally accepted design codes, chief among them being the National Fire Protection Association’s (NFPA) suite of codes. The NFPA codes tend to be the most widely adopted code throughout the world. Other popular standards include: ——

NFPA 13: Standard for the installation of sprinkler systems (USA) (NFPA, 2016a)

——

FM Data Sheet 2-0: Installation guidelines for automatic sprinklers (USA) (FM Global, 2014)

——

CEA 4001: Sprinkler systems planning and installation (Europe) (CEA, 2006).

Although this section of the Guide concentrates on the provisions of the UK codes, applicable comparisons have been made with NFPA 13. 

The majority of design codes advise that protection should be provided throughout the building under consideration, any building which communicates with it, and any neighbouring building that represents an exposure hazard to the protected building. If a communicating building or other exposure risk is not to be protected, then the protected building must be separated from the risk posed by the unprotected building. This is usually accomplished by the nature of the structure between the risk areas, but this may be supplemented by, for instance, an external drencher system. An engineered approach would involve an assessment of fire load, level of fire-resisting construction and the associated risks of fire spread potential. On this basis, it is possible to sprinkler-protect the risk areas only. The provision of a suitable level of fire compartmentation between sprinklered and non-sprinklered areas would be recommended, or virtual compartmentation utilising non-fire load areas, for example railway platforms, airport terminal buildings etc. Within any protected building there are sometimes areas where sprinkler protection would be hazardous, such as metal melt pans or frying ranges, and sprinklers should not be fitted in these situations. The impact of the absence of sprinklers should be fully considered and steps taken to mitigate the risk. Measures could take the form of alternative active fire protection systems, such as gaseous or water mist, or separation by means of a fire-resisting construction. There will be areas where sprinklers may not be essential due to the absence of an appreciable fire load, such as stairs, lifts, toilets etc. These can be considered as ‘permitted exceptions’, and usually a grade of fire-resisting construction is stipulated between the protected and non-protected areas. It should be noted that these permitted exceptions may not be applicable to sprinkler systems designed to NFPA 13. Cut-off sprinklers (sprinklers fitted on the non-protected side immediately above a window, doorway or other penetration of the compartment wall) can sometimes be used to improve the efficiency of the separation. Their use should be carefully considered as the benefit accrued by their installation may not be warranted if, for instance, there is no fire load on the non-sprinklered side. There are circumstances in both the LPC and NFPA rules whereby water curtains may be used for the protection of floor openings for escalators and open stairways.

11.2.7 11.2.6

Extent of sprinkler protection

Where a building is to be fitted with a sprinkler system that is compliant with the rules and standards noted above, the intent is that it will serve the entire building, although most codes do have exceptions. This is on the basis that sprinkler systems are designed to control a fire in the very early stage of its development and not necessarily to halt the advance of an already established fire. Where it is appropriate to leave an area unprotected by sprinklers, it is important to make other provisions, such as fire-resisting construction, automatic fire detection and, if necessary, other automatic firefighting systems.

Hazard classification

In order to match the capability of the sprinkler system with the type of risk with which it will have to cope, risks are grouped into hazard classifications. There are three main divisions, each based on the expected fuel load of the occupancy and the rate of fire growth expected from the contents or processes: ——

light hazard (low combustible loading with a slow rate of fire growth)

——

ordinary hazard (low to moderate combustible loading with moderate to fast rate of fire growth)

——

high hazard (high combustible content with fast to ultra-fast rate of fire growth).

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It is obvious from the data presented above that a great deal of consideration needs to be given to the density of water discharge required to control a fire outbreak if an engineered solution is to be adopted. The simplistic but safe approach would be to design to the highest figures. This offers a high level of protection and permits flexibility in the use of the protected facility. A more considered approach could be more restrictive, but might represent a better use of capital funds. It should also be noted that an engineered solution may attract increased insurance premiums, as the insurer could regard the system as a departure from the codes.

11-5

11-6

Fire safety engineering

Table 11.1  Minimum design densities and assumed maximum areas of sprinkler operation Minimum design density / litre · m–2 · min–1

Assumed maximum area of operation / m²

Equivalent number of operating sprinklers

Light

2.25

84

4

Ordinary, group 1

5

72

6

Ordinary, group 2

5

144

12

Ordinary, group 3

5

216

18

Ordinary, group 4

5

360

30

High

7.5–30

260–375

29–42

Notes: Care is required when adopting the equivalent number of operating heads, especially in high hazard areas. The equivalent number of operating sprinklers is the maximum number of sprinkler heads expected to operate before control of a fire is achieved. Table 11.2  Typical fire load densities Occupancies

Fire load density / MJ · m–2

Hazard class

Hospital

350

Light

Hotel

400

Ordinary 1

Industrial (non-flammables)

470

Ordinary 1

Office

570

Ordinary 2

Residential (institutional)

750

Ordinary 3

Place of assembly

750

Ordinary 3

Residential (flats)

870

Ordinary 3

900

Ordinary 3

Retail Industrial (high risk)

1800

NFPA 13 takes a different approach and provides a selection of values from curves for the design density and area of operation (Figure 11.1), as listed below: ——

for light hazard occupancy, the design density and area of operation may be selected from 4.1  litre · min–1 · m–2 over 139  m2 to 2.8  litre · min–1 · m–2 over 279 m2

——

for ordinary hazard, group 1, occupancy, the design density and design area of operation may be selected from 6.1  litre · min–1 · m–2 over 139 m2 to 4.1  litre · min–1 · m–2 over 372 m2

——

for ordinary hazard, group 2, occupancy, the design density and design area of operation may be selected from 8.1 litre· min–1 · m–2 over 139 m2 to 6.1  litre · min–1 · m–2 over 372 m2

——

for extra hazard, group 1, occupancy, the design density and design area of operation may be selected from 12.2  litre · min–1 · m–2 over 232 m2 to 8.1  litre · min–1 · m–2 over 465 m2

——

for extra hazard, group 2, occupancy, the design density and design area of operation may be selected from 16.3 litre· min–1 · m–2 over 232 m2 to 12.2  litre · min–1 · m–2 over 465 m2.

High

The ordinary and high hazard classes are sub-divided to further qualify the type of risk. The classifications principally depend on the quantity and type of combustible materials contained in the risk, the speed at which a fire is likely to develop and any processes which will produce particularly severe circumstances for fire propagation. Premises may often contain a combination of different risk classifications. The allocation of the appropriate classifications can be complex and will almost certainly require qualified judgment. The final decision will often rest with the fire insurer or other ahj. There are certain risks, such as oil and flammable liquids and gas hazards, for which standard sprinklers may not be suitable. Special requirements apply in these circumstances and special water spray systems are used, often with the firefighting performance enhanced by foam solution. The NFPA codes offer sound and detailed guidance for these types of risks. The hazard classification will dictate the minimum amount of water which must be provided at the fire in the form of spray and this is normally expressed as the ‘design density’ (in mm per minute or litre · m–² per minute). The expected maximum area of the sprinkler system which will be activated by the fire is also dictated and this ‘assumed maximum area of operation’ (amao) is expressed in square metres. It must be noted that there are substantial differences in the design approach between UK codes and NFPA 13. Typical UK code design densities and areas of operation are indicated in Table 11.1

The equivalent number of operating sprinklers will naturally vary with the selected design area of operation. The hazard classes detailed in Table 11.2 are typical occupancies and these can be equated to a typical fuel loading for these types of premises, taken from this Guide or PD 7974-4: 2003 (BSI, 2003b). Many of these occupancies would be classified as different hazard classes in NFPA 13. 11.2.7.1

Light hazard

Light hazard risks will be non-industrial, where the amount and combustibility of contents are low. This includes risks such as hospitals, hostels, schools etc. A maximum fire loading for this type of risk would be 400 MJ · m–². 11.2.7.2

Ordinary hazard

Ordinary hazard risks will be commercial and industrial occupancies involving the handling, processing and storage of mainly ordinary combustible materials, which are unlikely to develop intensely burning fires in the initial

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Hazard classification

Fire suppression

11-7 Density / mm∙min–1 4.1

6.1

8.1

10.2

12.2

14.3

16.3

z ha ar

z ha

372

d

d

Gr

ar

p ou

Gr

2

p ou 1

279

ry 2 i na

232

2000 1500 0.05

186

0.10

0.15

0.20

0.25

0.30

0.35

Figure 11.1  NFPA 13 area/ density curves. (Reprinted with permission from NFPA 13-2016 Standard for the installation of fire sprinkler systems, Copyright © 2015, National Fire Protection, Quincy, MA. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.)

139 0.40

Density / gpm∙ft–2

stages. A maximum fire loading for this type of risk would be 1000  MJ · m–². The ordinary hazard classification tends to be further subdivided, so a broad band of fuel loading can be expected, ranging from 400  MJ · m–² through 600, 800 and up to the 1000  MJ · m–² figure. These are not firm figures, but they can be used to determine the likely hazard rating required. Again, care is required, as storage risks can produce fires with a strong upward fire plume velocity. If the sprinkler system design does not take this into consideration, the sprinklers may underperform. Storage of goods is permitted under this classification but for the reason stated it is likely to be restricted in height and quantity. Included in the ordinary hazard classification are restaurants and cafes as well as hotels and industrial buildings. These are likely to incorporate large commercial kitchens. Most kitchen risks can be handled with standard sprinklers, but positioning the proposed fire extinguishing system over deep fat fryers presents a potential danger. Water entering hot oil at low velocity is likely to sink below the oil and quickly turn to steam. The volumetric expansion rate of water to steam is approximately 1 to 1620. This rate of expansion is equivalent to a small explosion and hot, burning oil is likely to be spread far from the source of fire origin. Special sprinklers are available for this type of risk, which operate at higher pressures, ensuring that the water droplets are not encapsulated by the hot oil and thus preventing the risk detailed above. More common for this type of risk, however, are dry powders, foam, CO2 or water mist (refer to sections 11.3, 11.4 and 11.5). 11.2.7.3

High hazard

High hazard risks will be commercial and industrial occupancies which have abnormal fire loads due to: ——

the process taking place

——

the presence of stored goods

——

the method of storage and the height to which goods are stored.

The risks are further subdivided as follows: ——

high hazard process risks

——

high hazard storage risks

——

other special hazards, as defined in LPC Rules Technical Bulletin 217: Categorization of goods in storage (LPC, 2016: Part 20).

Due to the factors mentioned above, a fire is likely to follow a fast to ultra-fast fire growth curve. Unchecked it is likely to grow to an extremely high output fire. The fuel load is likely to be above 1000 MJ · m–². The fire size would, in consequence, be such that the fire brigade is unlikely to achieve control easily. Even with sprinkler intervention, achieving fire control is likely to be difficult. For this reason, sprinkler spacing is reduced, discharge densities are increased and water supply duration periods increased. For storage risks, there are a number of variables to be considered, ranging from the method of storage (free standing, palletised racks etc.), the goods being stored, the packing materials and the height to which goods are stored. Sprinkler protection needs to be tailor-made to suit the risk, with sprinklers located at roof level only or a combination of roof sprinklers and sprinklers located within the racks. Other, more recent, methods of protecting high piled storage risks are early suppression fast response (esfr) and control mode specific application (cmsa) sprinkler systems. See sections 11.2.8.5 and 11.2.8.6 below. Special hazards, as defined in the LPC Rules Technical Bulletin 217, consist of: ——

aerosols with flammable content

——

clothes in multiple garment hanging stores

——

flammable liquid storage

——

idle pallets

——

non-woven synthetic fabric

——

polypropylene or polyethylene storage bins.

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ra

ra

Ord

t

ry 1 i na

2500

Ord

3000

465

t Ex

t Ex

4000

Ligh

Area of sprinkler operation / ft2

5000

Area of sprinkler operation / m2

2.0

11-8

11.2.8

Fire safety engineering

Sprinkler heads

11.2.8.1 General

Table 11.3  Colour code for sprinklers (BS EN 12845: BSI, 2015a) Glass bulb sprinklers Nominal operating temperature / °C

Liquid colour code

Fusible link sprinklers Nominal operating temperature within range / °C

Yoke arms colour code

57

Orange

57–77

Uncoloured

68

Red

80–107

White

79

Yellow

121–149

Blue

93

Green

163–191

Red

100

Green

204–246

Green

121

Blue

260–302

Orange

141

Blue

320–343

Black

163

Mauve

182

Mauve

204

Black

227

Black

260

Black

286

Black

343

Black

Three sizes of sprinkler are generally available to suit the various applications, i.e. nominal orifice sizes of 10, 15 and 20 mm. Generally, 10 mm sprinklers would be expected on light hazard installations, 15 mm on ordinary hazard installations and 20 mm on high hazard installations. esfr sprinklers can have sizes of 20 mm or more; however, the key is the K-factor (coefficient of discharge) and, for storage protection, larger is better/more effective. In fact, research has concluded that there are five key attributes of a sprinkler head that are important in sprinkler design, particularly for storage protection, to ensure that the correct amount of water is delivered to the fire area (the concept of actual delivered density): ——

rti

——

K-factor

——

temperature rating

——

orientation

——

spacing.

For these reasons there has been a move away from the traditional area/density design specification for storage sprinklers towards design criteria based on number of operating sprinkler heads at a given minimum operating pressure. The relationship between sprinkler orifice and droplet size is proportional, with larger droplets being formed from the larger orifices. This supports the use of the 10 mm sprinkler on low-output fire risks and the use of the 20 mm orifice on the high challenge fires. There are a number of different sprinkler types, ranging from the more functional conventional and spray pattern sprinklers to the more decorative recessed or concealed pattern sprinkler. The more decorative types of sprinkler are suitable for use on suspended ceilings and are either colour-matched to the ceiling or have the body of the sprinkler concealed

Table 11.4  Temperature ratings, classifications and colour codes. (Reprinted with permission from NFPA 13-2016 Standard for the installation of fire sprinkler systems, Copyright © 2015, National Fire Protection, Quincy, MA. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.) Maximum ceiling temperature

Temperature rating

°F

°F

°C

°C

Temperature classification

Colour code

Glass bulb colours

100

38

135–170

57–77

Ordinary

Uncoloured or black

Orange or red

150

66

175–225

79–107

Intermediate

White

Yellow or green

225

107

250–300

121–149

High

Blue

Blue

300

149

325–375

163–191

Extra high

Red

Purple

375

191

400–475

204–246

Very extra high

Green

Black

475

246

500–575

260–302

Ultra high

Orange

Black

625

329

650

343

Ultra high

Orange

Black

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Sprinkler heads are a crucial element in any sprinkler system. In most cases, they will act to both detect a fire and release water, in the form of spray, in the appropriate quantities and spray characteristics to fight the fire effectively. Normally, the sprinkler has a heat-sensitive element – a glass bulb or a fusible metallic link or a combination of both – which, in combination with other elements of the sprinkler, seals the head until activated by the fire. However, sometimes it is desirable for fire detection and the consequent release of water to be activated by other means. In these circumstances, the heat-sensitive element and sealing mechanism are removed from the sprinkler and such units are termed ‘open’ sprinklers. The control of the water supply is by other means, such as a ‘deluge’ valve, which can be activated electrically or pneumatically.

The operating temperature of sprinkler heads will normally be not less than 30 °C above the highest expected ambient temperature. In most conditions this will result in a sprinkler head rating of 68 °C, indicated by the familiar red bulb. See Tables 11.3 and 11.4 for the range of sprinkler bulb colours and temperature ratings.

Fire suppression

11-9 11.2.8.5

Recessed pattern sprinklers have the sprinkler body and all or part of the heat-sensitive element above the plane of the ceiling.

These use specially developed large capacity sprinkler heads fitted with quick response elements, which are designed to operate very early in the development of the fire. They deliver very large quantities of water over relatively small areas of operation to effect extinguishment of the fire.

Sprinkler heads and their components must not be painted. 11.2.8.2

Conventional and spray types

These are the most common types of modern sprinklers and are designed for use in most situations, either mounted directly onto the pipes or below a suspended ceiling. They are usually of the miniature type, designed to be as neat as possible to minimise the aesthetic impact. The only difference between a conventional and a spray type sprinkler is the type of spray produced and the direction in which it travels. A conventional sprinkler is designed to direct the spray both upwards and downwards from the deflector in roughly equal proportions. This will produce a significant degree of ceiling wetting, as well as direct distribution below. The spray sprinkler is designed to direct the majority of its spray downwards. These sprinklers are designed for either pendent or upright orientation, although some are designed so that they can be fitted in either way. These are called universal type. 11.2.8.3

Quick response sprinkler

Quick response sprinklers are defined as having an rti of 50 (metre-seconds)1/2 or less. The term ‘quick response’ refers to the listing of the entire sprinkler (including spacing, density and location) not just the fast-responding releasing element. The most common difference between a quick response sprinkler head and a standard response sprinkler head is known as thermal sensitivity. Quick response sprinkler heads activate slightly faster in a fire than a standard response head. Physically, the only difference between a standard response fire sprinkler and a quick response fire sprinkler is the size of the bulb. Standard response sprinklers have a 5 mm glass bulb, while quick response fire sprinklers have a 3 mm glass bulb. 11.2.8.4

Sidewall sprinkler

These are primarily used to keep ceilings clear of pipework for aesthetic reasons or to avoid having to disturb existing ceilings when installing pipework. Each sprinkler protects up to 17 m² in light hazard occupancies and 9 m² in ordinary hazard occupancies. There is a ‘quick response’ extended coverage model available, which is commonly used for the protection of hotel bedrooms to overcome the need for sprinklers and exposed pipework in the centre of the room. They are specifically designed to give an extended coverage of water of up to 21 m² and are designed to inhibit fire growth by extensive wall wetting. These sprinklers must be used in accordance with the installation standards and manufacturer’s guidelines; however, they are often specified in inappropriate locations.

Early suppression fast response (ESFR) sprinkler

The objective of extinguishing, rather than controlling, the fire is one of the major features of this type of system and, although the water volumes are large, the designed duration tends to be shorter, so they can be a very effective alternative to systems involving roof plus in-rack sprinklers.  11.2.8.6

Control mode specific application (CMSA) sprinkler

The cmsa approach to sprinkler protection employs special designs of sprinkler heads which have been successfully tested to protect risks in very specific configurations. The approach provides potential sprinkler solutions to scenarios which are challenging to design, in terms of the specific fire hazard and the guidance within the LPC rules. sprinklers are mainly used to control fires within storage risks.

cmsa

There is little room for error in the design and installation of these systems and the successful outcome of this system type is highly dependent on the correct application. It is essential that the requirements of Annex N and Technical Bulletin 235: Control mode specific application (CMSA) sprinklers of BS EN 12845 (LPC, 2016) are met. 11.2.8.7

Concealed pattern sprinkler

Concealed pattern sprinklers are fully recessed into the ceiling with an additional cover plate at ceiling level. The cover plate is attached to the sprinkler body with fusible elements so that the cover plate reacts to the fire first and drops away to allow the sprinkler itself to react to the thermal conditions. All ceiling-style sprinklers are likely to react more slowly to fire conditions than more traditional designs, principally because the heat-sensitive element is not located in the zone where the gases are hottest. The hottest gas layer is considered to be located 75–100 mm below a flat ceiling and the location of the sprinkler relative to this layer will have a bearing on the likely response time. There is a level of debate in the UK regarding the use of the concealed pattern sprinkler on risks that could be defined as having a ‘life safety’ implication. The term ‘life safety’ in relation to a sprinkler system is somewhat vague. The way that a building is designed in terms of people’s safety in case of fire is driven by the Building Regulations. The Building Regulations cover aspects of building design relating to fire safety ranging from means of warning, fire spread and access and facilities for the fire service. The aim of the Building Regulations is to ensure that a reasonable standard of life safety is achieved. The use of concealed pattern sprinklers on designated life safety risks is seen by some as not permissible. This is due

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within the ceiling, with the heat-sensitive element protruding below the ceiling.

11-10

Fire safety engineering ——

Dry pendent sprinklers: These take the form of special pipes with a valve at one end and a sprinkler head at the other. Operation of the sprinkler head at the bottom of the drop pipe opens the valve at the top end and allows water to pass down the pipe to the sprinkler outlet. They are used in situations where a pendent sprinkler is required on a system that is not normally charged with water, e.g. dry, alternate wet and dry or pre-action systems, and where the water that would normally be trapped in the drop pipe to the sprinkler head cannot be tolerated, e.g. where the water might freeze.

——

Dry upright sprinklers: These operate on similar principles to dry pendent sprinklers but are less commonly encountered.

——

Window drenchers: These drenchers spray water onto glazing (windows or fixed glazed sections) achieving a level of fire resistance.

Concerns that have been expressed relating to the concealed pattern sprinkler are its slower reaction time to a fire condition and the fact that it requires the twin actions involving the cover plate and then the sprinkler, which could potentially lead to non-sequential operation. Other concerns raised are that: ——

obstruction of the sprinkler casing vents will be detrimental to sprinkler operation, making monitoring of the ceiling void space usage important

——

the air gap between the cover plate and the ceiling is crucial in sprinkler operation terms, but a shadow effect results that often leads to these being sealed with paint or plaster

——

the installation of the sprinkler needs to be carefully undertaken to avoid misalignment, which makes the shadow effect more pronounced

——

the position of the sprinkler deflector in relation to the ceiling is important, i.e. if not carefully installed the casing can be too high, resulting in the deflector being above the bottom of the ceiling

——

the use of the ceiling void needs to be considered, as use as a supply plenum may result in air movement away from the sprinklers

——

when redecoration occurs, the cover plate is liable to be painted along with the ceiling, or papered over, which will further delay sprinkler actuation or cause the sprinkler element to react first to the fire condition

——

the sprinklers were initially restricted to cover risks in the UK up to ordinary hazard group 2, as it was felt that they would not be able to deal effectively with a faster growing fire.

The majority of the above concerns are covered in the installation instructions issued by the sprinkler manufacturers or listed in the sprinklers’ conditions of approval. 11.2.8.8

Other devices

Other devices which may be encountered include the following: ——

——

——

Multiple controls: These consist of valves held in the closed position with a heat-sensitive device and are used to feed one or more open sprinkler heads or sprayers. Medium-velocity sprayers: These produce a directional spray of fine droplets for controlling fires involving combustible liquids and gases with low flashpoints and to cool the surfaces of vessels. High-velocity sprayers: Such sprayers have open nozzles that produce a directional spray of larger droplets for extinguishing fires in combustible liquids with higher flashpoints.

11.2.8.9

Thermal sensitivity of sprinkler heads

The speed at which the heat-sensitive element of a sprinkler head will react to the local thermal conditions will depend on many factors, including the size and structure of the bulb or link, the material, shape and size of the sprinkler body and the type of fitting into which the sprinkler is inserted. The speed at which they react can be measured and compared using standard apparatus and this is normally carried out during the approval procedure for any particular sprinkler head. The rti is a measure of sprinkler thermal sensitivity and sprinklers are graded according to the sensitivity range into which they fall. Three response classes are recognised: ——

standard response A: corresponding to between 80 and 200 (m1/2 · s1/2)

——

special response: corresponding to between 50 and 80 (m1/2 · s1/2)

——

quick response: corresponding to (m1/2 · s1/2) or less.

rti

rti rti

values values

values of 50

The following can be used to determine sprinkler reaction time: (a)

Ceiling jet velocity and temperature:



i=

5.38 (Q / r) 2/3 for r / h > 0.18 h

(11.1)



i=

16.9 (Q) 2/3 for r / h ≤ 0.18 h5/3

(11.2)



U=

0.195Q1/3 h1/2 for r / h > 0.15 r5/6

(11.3)



U=

0.96Q for r / h ≤ 0.15 h1/3

(11.4)

where i is the maximum temperature of gases above ambient temperature (°C), Q is the rate of heat release from the fire (kW), r is the radial distance from the centre of the fire plume impingement (m),

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to the slower reaction time and the possibility that a component could fail due to either incorrect installation or post-installation interference. However, this is an issue that is not confined to life safety systems and is just as pertinent to systems installed to provide protection to property.

Fire suppression

11-11

h is the vertical distance between the fire source and the ceiling (m) and U is the gas velocity (m · s–1). (b)

1/2 dTd U QTg - TdV = RTI dT

(11.5)

where Td is the detector temperature, U is the instantaneous velocity of fire gases (m · s–1), Tg is the temperature of fire gases (K) and rti is the response time index (m1/2 · s1/2). Recessed, concealed and horizontal sidewall sprinklers are not classified and are referred to as ‘unrated’. It should be borne in mind that if sprinklers are to be used in a fire engineered solution and their speed of operation must be predicted, then the rti of the head must be used in the calculation. Use of these sprinklers therefore requires more information to be obtained from the sprinkler manufacturers. It does not necessarily mean that they cannot be used. Ad hoc testing of concealed pattern sprinklers fitted with a sprinkler with a ‘fast response’ element have indicated that the reaction times of these units are similar to that of a sprinkler classified as a standard response unit. As quick response sprinklers are likely to operate earlier in the development of a fire than would standard response sprinklers, it follows that the control effect of the sprinklers is likely to take place when the fire size is smaller. A smaller fire size places less demand on the water supply and the hydraulic demand on the system should also be reduced. Similarly, the smoke management system may be subject to a reduced demand if the fire size is restricted, see chapter 10: Smoke ventilation. These factors can reduce the impact made by a fire incident on the building and, consequently, on the resulting costs. Although the design codes have not been changed to date to take account of these effects, the benefits of quick response sprinklers may be exploited in fire engineered solutions for appropriate projects.

11.2.9

Types of sprinkler system

The method of feeding the water supply to the sprinkler heads, the control of that supply and the method of raising the alarm must be suitable for the type of risk, its location and its environment. Various types of system have been devised to meet the differing requirements and these are described below. A common element for all system types is a means to isolate the system from the water supply. One or more valves are placed in the supply line such that the supply of water may be isolated by the fire brigade following a fire, once they are satisfied that the fire is under control or extinguished. The same control valve is used to shut the system down for maintenance, alteration or extension.

11.2.9.1

Wet installations

This is the simplest and, consequently, the most reliable system, by far. It is also the most common. The entire system pipework is charged with water under its operational pressure. In the event of sprinkler head operation, the water is discharged immediately. Installations of this type are suitable for most risks but not where there is a danger that the water in the pipework may freeze or where the temperature may exceed 70 °C. 11.2.9.2

Alternate wet and dry installations

These systems are designed for areas which are subject to winter frosts. During the warmer months, the system is operated as a wet installation but, prior to the onset of frosts, the system is thoroughly drained and the control valves set to ‘winter’ operation. In this mode, the system pipework is charged with air under modest pressure. When a sprinkler head operates, the air pressure is reduced, which actuates the control valve, allowing water into the system to the operating sprinkler head(s). As soon as there is no longer any danger of freezing, the system should be returned to wet operation. The disadvantage of this type of system, when in the dry mode, is the potential delay between sprinkler operation and the arrival of water at the fire area. Therefore, the number of sprinkler heads which may be fed from this type of installation is restricted to a smaller number than for wet systems. A slight relaxation in this restriction is allowed when an ‘exhauster’ or ‘accelerator’ is fitted to the valve set. Such devices detect the drop in air pressure resulting from sprinkler operation and operate to charge the system with water more rapidly than would otherwise be possible. Alternate wet and dry installations are not suitable for high hazard storage risks nor are they to be used where the temperature may exceed 70 °C. These systems are no longer permitted under the LPC Rules. 11.2.9.3

Dry installations

The size of an installation should be limited so that the area isolated during shutdown is not too extensive. This can be engineered to reduce the number of installations by adopting zone or sectional valves.

These should only be considered for areas where a wet or alternate wet and dry installation cannot be used. Installations of this type are permanently charged with air under pressure and the action of the system is identical to that described for winter operation of alternate wet and dry systems.

In the case of systems which are in a ‘dry’ mode, the speed of delivery of water in the event of fire should be carefully

As well as being suitable for areas subject to permanent frost conditions, such as cold stores, they are appropriate

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Temperature rise:

considered. A maximum pipe volume of 2.5 m³ may be considered appropriate, or delivery of water to the most remote single sprinkler within 60 seconds. In the case of an engineered solution, the delay in delivery of water from a sprinkler once it has operated must be fully taken into account. The limitation of fire size will not begin until water is delivered and the effectiveness of the sprinkler operation could be prejudiced if this delay is excessive.

11-12

Fire safety engineering

for areas where the temperature is likely to exceed 70 °C, such as drying ovens. Tail-end alternate or tail-end dry systems

If limited areas of a wet installation are subject to frost, either periodically or permanently, then it is possible to install a small alternate or dry system as an extension to the wet system. These are termed tail-end alternate or tailend dry systems. The provisions and restrictions noted above for the appropriate full systems apply equally to these extensions. 11.2.9.5

Pre-action installations

This is a special type of dry installation that incorporates additional measures to pre-arm the system in the event of detection of the fire by another system. There are two different types of system, but in both cases an electronic fire detection system must be installed in the same area as the sprinkler system. The detection system and its integration with the control system should comply with an appropriate standard to ensure that it will operate when required. Type A systems The pipework is fed through a special ‘pre-action’ valve and water is only released into the system pipework on the actuation of the fire detection system, usually on the coincident operation of two fire detectors. When the system is in its normal operating mode, the system pipework is charged with low-pressure compressed air, which will escape in the event of damage to a sprinkler head or to the system pipework. This will raise the alarm but not allow water into the system. Simultaneous operation of the fire detection system and a sprinkler head is required before water can discharge from the system.

Such systems offer the obvious attraction of reduced water damage, but there are also drawbacks and installations of this type should only be considered after full consultation with the ahj. 11.2.9.7

Deluge installations

These are systems in which it is desired to operate all of the sprinklers heads, or spray nozzles, simultaneously. The sprinklers, sprayers or nozzles are of the unsealed, or ‘open’, type and are attached to a system of pipework connected to a deluge valve or, for smaller systems, a multiple control. Sensing of the fire can be by electronic fire detection or by a ‘dry pilot’ system in the risk area in which sprinkler heads are fitted to pneumatic pipework. Normally it is possible to release the system manually at the control valve station or some other location. Installations of this type are normally used for oil or flammable liquid risks, gaseous risks, cooling from exposure risks and high hazard group 4 process risks, as detailed in Annex A of BS EN 12845. A UK standard for the design of deluge systems is not available. Most deluge systems are designed to NFPA 15 (NFPA, 2017a).

11.2.10

System components

Many of the components necessary in a sprinkler system are tested and approved by a recognised third-party testing facility. These components include items such as: ——

alarm valves

——

accelerators and exhausters

Such systems are particularly suited to situations where the inadvertent operation of a sprinkler head, or a damaged pipe, would have exceptionally expensive or disruptive consequences. However, the added complication, in conjunction with reliance on a fire detection system, reduces reliability. Consequently, these systems should be considered only where there is no alternative. They should not be considered for high hazard risks.

——

deluge valves

——

adjustable drop pipes

——

direct-reading flow meters

——

multiple controls

——

pipe couplings and fittings

——

pre-action systems

Type B systems

——

electrical alarm pressure switches

These are alternate wet and dry or dry installations in which the detection system is used to charge the system with water at an early stage during fire development and prior to operation of the sprinkler heads. This is appropriate on large systems with a high volume and also where high hazards are involved and rapidly growing fires are likely to occur. In the event of failure of the detection system, the installation will operate as a conventional alternate or dry installation.

——

sprinkler heads

——

suction tanks

——

vortex inhibitors

——

water flow alarm switches

——

water sprayers and systems

——

fire pumps.

11.2.9.6

Recycling installations

The flow of water into the installation is controlled by a system of heat detectors installed in the same area as the sprinklers. The flow control valve is designed to open and close in response to the heat detectors and, after a

Standard items, such as pipes, fittings, stop valves and the like, are usually referred to in the codes and rules by a recognised national or international standard. Components should be fit for purpose and of a quality that will not be detrimental to the longevity of the system or its potential to operate correctly in fire conditions.

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11.2.9.4

predetermined delay, can close down the water supply when the sprinklers have controlled the fire. The supply may be re-opened in the event of re-establishment of the fire.

Fire suppression

11-13 Design point

Sprinkler head

Riser Drop

Distribution pipe

Riser

Installation control valves and riser

Main distribution pipe

Figure 11.2  Principal components of a typical sprinkler system

The principal components of a typical sprinkler system are shown in Figure 11.2. The various components of a sprinkler system listed above and shown in Figure 11.2 are detailed in BS EN 12845. Reference to the Standard will assist in detailing aspects of design relating to pipe grades, pipe supports, pipe fittings etc.

of material cost and availability, ease of installation, flexibility to take up site variances, experience and tradition, and avoidance of future problems with maintenance. This tends to lead to a common approach within the industry and, for example, a typical wet installation in the UK would include:

The anticipated use and life expectancy of the building may influence the choice of materials. If the environment is corrosive, then clearly the wet system components must be adequately protected. Alternate wet and dry systems are prone to more rapid internal corrosion than systems which are perpetually charged with water, and the use of unprotected steel pipe may limit the life of the pipework to 20 years or less. The use of galvanised pipe may be considered as a means of extending the life of the pipework.

——

an underground feed main in high-performance polyethylene (hppe) pipework with fusion-welded joints and fittings

——

installation pipework downstream of the alarm valve in black medium-grade steel tube to BS EN 10255: 2004 (BSI, 2004a), shop prefabricated as far as practicable

——

mains over 50 mm diameter with welded branches and sockets, joined to adjacent pipework with mechanical grooved joints and to plant items with flanges

——

pipework of diameter 50 mm or less fabricated with screwed joints to BS EN 10226-1: 2004 (BSI, 2004b) and joined with screwed fittings to BS EN 10242: 1995 (BSI, 1995).

A more recent development has been the use of plastic (chlorinated polyvinyl chloride, cpvc) pipes and fittings in above-ground (i.e. fire-exposed) situations. There are usually specific qualifications regarding their use. This material has proven to be particularly good for domestic and residential applications and retro-fitting in premises such as hotels, where the light weight and ease of installation are particularly important. It is likely that this material will be used more extensively in the future. The use of welding is another area where consideration should be given to authority preferences. The practice of in situ welding should be restricted and should be avoided if possible. These restrictions are due to the difficulties of quality control and the increased risk of fire on site (see chapter 14: Fire safety management). A strict quality control system for welded prefabrication is essential and techniques such as set-in sockets and ‘cut and shut’ direction changes should not be permitted, as these impair the flow of water through the piping network. Many options for pipe materials and jointing methods are available, but usually the choice will be based on a balance

Flexible pipe connectors have become very popular and commonplace over the past 10 years. Although the introduction of flexible connections to sprinkler heads has offered a number of benefits to assist in the installation of sprinkler systems at the second fix stage of a project, their use is also accompanied by a number of shortfalls that can prove detrimental to the operation of a sprinkler system in a fire condition. The flexible connection typically used by sprinkler contractors is often poorly fitted and will require adjustment. They cannot be installed over large plasterboard areas without a suitable number of access hatches for maintenance and visual inspection. Some insurers do not permit their use, and this opinion may increase with time.

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Arm pipe (horizontal)

Range pipes

11-14

11.2.11

Fire safety engineering

Installation planning ——

potential locations of any main risers through the building and subsidiary control valve locations, where planned

(a)

the system fully meets the needs of the risk and is capable of controlling an outbreak of fire

——

(b)

as many of the potential future uses of the building as possible are taken into account within the original design

potential locations of storage tanks and pump house, where these are proposed

——

(c)

the specific requirements of the owner/occupier, local authority, fire insurers and other ahjs are met

details of the planned electrical supply to the project, where an electric pump is necessary, to establish if this is of sufficient capacity and reliability

——

(d)

the local and national water byelaws are observed

an outline of the principal routes of main distribution pipes such that any structural or architectural impacts may be taken into account early in the design process.

(e)

the sprinkler system forms an integrated part of the overall construction, fire detection and fighting and means of escape strategies for the premises

(f)

the system is coordinated with the fabric of the building and other building services so as to minimise the aesthetic impact on the project.

Consultation with all interested parties should take place at the earliest possible time and the fire protection engineer should be involved as soon as possible when aspects such as building construction, space planning and services spaces may be influenced. The consequences of the system operation in fire and non-fire conditions should also be considered, and such matters as drainage of water resulting from sprinkler operation should be taken into account. The possibility of damage or interference to the system, both accidental and deliberate, should be ‘designed out’ wherever possible and contingency plans drawn up to deal with all eventualities should such damage arise. In terms of the building itself, as many aspects as possible should be taken into account at the earliest possible stage in the building design process. These include, but are not limited to, the following: ——

the occupancy and any processes that are to take place in the premises (information that will be used to determine the hazard classifications that will apply to the risk. It is not unusual for several different classifications to apply to various parts of the premises)

The effects of water run-off, resulting from the operation of the sprinkler system and any other firefighting operations, should be fully considered in the emergency planning. This will be especially crucial where soluble materials or chemicals are at risk or where synthetic foams are used in the firefighting system, due to the pollution risk. Fires on construction sites often happen when the sprinkler system, although partially installed, has not been put on line. It is important during the planning process that consideration is given to bringing the system on line as the building works progress. If early sprinkler protection is desired, a water supply ready for use is essential and this may mean having a temporary connection made to the town main or a temporary power supply available (diesel generator) if electric pumps are being used. The use of diesel rather than electric fire pumps may be a better option. If neither solution is possible or practicable then, as a minimum, a fire brigade breeching inlet should be in place to permit the fire brigade to utilise the system. This will require ensuring that sectional completion is implemented to avoid open pipe ends or blanked-off sections of piping.

11.2.12

Installation design

11.2.12.1

Sprinkler spacing and location

——

the details of any goods on the premises and the heights and storage methods planned, each type of goods being given a category and the combination of category of goods, storage method and height of storage further determining the type and classification of protection

——

details of town or local main water sources, including full flow testing of the mains to establish their suitability to supply water for the installation, either directly or as infill to a water storage tank

——

details of any existing water storage tanks, reservoirs, lakes, rivers etc. which may have potential to serve as feeds to the sprinkler system

The spacing and location of sprinklers is a vital element of the design of the system. It dictates the speed of response and the effectiveness of the sprinkler protection, and ultimately will have a major influence on the severity of a fire incident and its impact on the building. The two key factors affecting sprinkler system performance are prompt sprinkler operation and sufficient, unobstructed water discharge into the fire area. Therefore, the building’s construction features, height, layout and mechanical and electrical (m&e) services all have a significant impact on these two factors. Avoiding obstructions is of paramount importance for the sprinkler design and installation, which requires considerable coordination with all aspects of building design, infrastructure and services.

——

potential locations of the installation control valves, including consideration of fire brigade

The principles of design are relatively simple and are based on common sense, but the most important factor

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It is essential that the provision of sprinkler protection is properly planned in order that:

access in fire conditions and the need for disposal of test and system drain water

Fire suppression

11-15 Table 11.5  Sprinkler head spacing by risk

A series of maximum values is given in Table 11.5 as a guide to the designer but these should not be taken as target values. For instance, in a high hazard risk, the spacing of sprinkler heads may be reduced to a value significantly below the maximum to reduce the hydraulic demands on the system. Similarly, the spacing in certain areas may be reduced to enhance performance in that area of the risk. The approach must be balanced and based on sound engineering skills and experience. Where sprinklers are being used as part of an integrated fire engineering strategy, the speed of sprinkler operation may be crucial to the strategy objectives. The spacing and location of sprinkler heads relative to the ceiling or roof must be carefully considered. Spacing of sprinklers The maximum values given in Table 11.5 for sprinkler head spacing of normal (i.e. non-sidewall) sprinklers according to classification of risk are common to most codes. The area per sprinkler is calculated as the area located between four adjacent sprinkler heads, regardless of the spacing method used for the sprinklers (i.e. standard or staggered) for ordinary hazard risks. The maximum allowable distance between sprinkler heads for ‘standard’ sprinkler spacing in most countries is shown in Table 11.6. Using the maximum spacing for sprinklers (under BS EN 12845) in each hazard category would be: ——

light hazard 4.6 m × 4.6 m (approximate)

——

ordinary hazard 4 m × 3 m

——

high hazard 3.7 m × 2.4 m (approximate).

The NFPA code does allow some latitude when protecting small rooms. As the heat will build up more rapidly and the sprinkler activate more quickly than in a larger room, wider spacing can be adopted. The NFPA and Australian codes also permit special sprinklers to be used if the manufacturer’s guidance on their use is followed. Location of sprinklers Sprinkler location is again a matter of common sense. They should be close to the ceiling and not obstructed by ceiling features or other services. They need to be at a height above the risk where the sprinkler discharge will be effective. The British Standard covering the design of atria within buildings recommends heights of 7.5 m and 10 m depending on the response time of the sprinkler if control of a design size fire of 2.5 MW is to be achieved. The provision of atria in buildings therefore presents special problems. Often these are too lofty for effective

BS EN 12845: area per sprinker /  m2

NFPA 13: area per sprinker /  m2

Light hazard

21

11.1–20.9

Ordinary hazard

12

12.1

9

8.4–12.1

High hazard

Table 11.6  Maximum allowable distance between sprinkler heads BS EN 12845 / m

NFPA 13 / m

Light hazard

4.6

4.6

Ordinary hazard

4.0

4.6

High hazard

3.7

3.7

protection by sprinklers at ceiling level and the location of sprinklers at the edges of adjacent floors may require special consideration to enhance their ability to ‘cut-off ’ the atrium from the protected floor. It has been recognised for many years that sprinkler protection increases the life of glazing in fire situations and external drencher systems have been used to protect buildings from the effects of fire in adjacent buildings. Although not covered by existing UK codes, there is no reason why this practice should not be extended to provide protection for internal elements of buildings as part of a fire engineered design. The location and spacing of the sprinklers would need to be determined for the particular situation, but locating sprinklers within 600 mm of glazing should provide a good spray distribution over the glazing. The use of sprinklers to protect glazing and external walls, although not common in the UK, is adopted in NFPA 13. Systems for protecting atria have been designed that combine electronic flame detectors with open sprinklers or sprayers, fed on a zoned deluge system. Such systems are not covered by present codes. Therefore, each system must be tailored to suit the particular objectives and circumstances of the project, with the agreement of the appropriate authorities. The objectives would be to replicate the speed of sprinkler response and design density given by a ‘standard’ system for the risk involved. This has been achieved in some systems by using analogue infrared flame detection linked to a microprocessor programmed to activate various stages of alarm from first detection of any fire through to activation of the deluge system when a fire of, say, 0.75 MW heat release rate has been detected. Where sloping soffits or roofs are encountered, the hot gases produced from a fire will tend to collect first at the highest point of the roof. Therefore, in general, sprinklers should be located within a reasonable distance from the ridge when the roof slope is steep (exceeds 1 in 3, i.e. 18.5°). The positioning of sprinklers in relation to the ceiling or soffit is also important since this will affect the operating speed of individual sprinklers. The gas strata immediately adjacent to the soffit will be cooled by the fabric of the ceiling and therefore the sprinklers should be located

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concerning sprinkler performance is having a thorough understanding of the fundamentals of fire dynamics (see chapter 6: Fire dynamics).

11-16

Fire safety engineering water flowing through them simultaneously, even though the fire may only involve the sprinklers on one tie pipe.

between 75 mm and 150 mm below the soffit in order to place the sprinkler within the zone of the hottest gases. Suspended ceilings

Where suspended ceilings are fitted, the void formed between floors and the ceiling below should be protected if it is in excess of 0.8 m deep. This depth is considered by many in the insurance industry as usable space and could be used for ad hoc storage of materials (files, Christmas decorations and similar items). A void of less than this depth may require protection if combustible construction or contents are present. An assessment should be undertaken to verify the level of fire risk involved and this will include the construction materials’ combustibility, the fire loading expected within the void (fan coil units, duct insulation, cables etc.) and the relationship between combustible items and ignition sources. 11.2.12.3

Pipework system arrangements

There are three principal styles of pipework design: ——

——

‘Tree’ or ‘terminal’ systems: The traditional method of feeding sprinkler systems involves the sprinkler heads being fed, singly or in groups, from deadend range pipes linked to distribution pipes, which are fed, in turn, from the water supply through main distribution pipes. This system is hydraulically very simple in that, in the event of system operation, only those range pipes that feed the operating sprinklers, and the distribution and main distribution pipes which feed those ranges, will contain flowing water. ‘Gridded’ systems: The sprinkler heads are fed from ‘tie’ pipes which are fed from more than one distribution main (often termed a ‘track’), which may or may not be directly linked to the water supply (see Figure 11.3). This type of system is hydraulically more complex than the tree system since generally each sprinkler is fed from more than one direction. Therefore, all of the pipes in a system may have

Sprinkler heads

——

‘Looped’ systems: A loop, or multiple loop, configuration consists of a pipe immediately downstream of the sprinkler installation control valves connecting into a single or multiple loop pipe configuration. Range pipes that feed the sprinkler heads are fed from the loop pipes.

The rules for the design of sprinkler systems do not provide a basis for pipe diameter sizing for loop or grid systems other than by full hydraulic calculations. Loop, multiple loop and grid pipe configurations must not be used for dry and alternate wet and dry pipe sprinkler installations. Gridded systems can prove to be an economical method of sprinkler feed in certain circumstances, since the hydraulic load may be spread over a greater number of pipes, which can then be smaller in diameter than those in a tree system. Certain types of buildings, such as large, high hazard risks with large bays and flat or slightly sloping roofs, are more suited to this system. 11.2.12.4

Pre-calculated pipe arrays

The use of pre-calculated pipe sizes is common in light and ordinary hazard class systems. Pipe tables are provided and pipe diameters are influenced by pipe configuration. System design using full hydraulic calculations is required for some forms of sprinkler system design but may be used on all system designs. 11.2.12.5

Fully hydraulically calculated pipe arrays

Fully hydraulically calculated pipe arrays are arrays in which a detailed hydraulic analysis of the system is carried out to determine the precise hydraulic characteristics of the system and to balance the capacity of the water supply. Back track

Front track Tie pipes Installation control valves and riser

Figure 11.3  Component parts of a gridded system

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11.2.12.2

Fire suppression

11-17

The demand for favourable areas is not considered for systems designed to NFPA 13. The process involves establishing the individual sprinklers that are in the amao, which will be as close as possible to rectangular in the case of the most unfavourable location, and square for the most favourable location. The number of sprinklers contained in the amao is calculated from the areas covered by individual sprinklers added together until the design area of operation is covered. The minimum rate of flow through each sprinkler is obtained by multiplying the design density (l · m–² · min–1) by the area covered by each sprinkler. Also, each sprinkler must operate at a minimum running pressure to ensure that the correct spray characteristic is established. These vary according to hazard and location, as follows:

where P is pressure loss (millibars), Q is flow rate (l · min–1), C is the roughness coefficient for the type of pipe (contained within design guides or codes) and d is the mean internal pipe diameter (contained within design guides or codes). Although the calculations may be performed manually, software is now available, which is the preferred option, particularly for gridded systems, where the flow/pressure logic through the matrix of pipes is very complex. Where software is employed, the input data must be checked, preferably by performing an independent calculation using quality-tested and calibrated software or by carrying out extensive manual cross-checks. The results of full hydraulic calculations must be plotted onto a water supply graph to ensure that the hydraulic demand of the system can be met fully by the water supply.

11.2.13

Water supplies

Adequate water supplies are one of the most important issues in connection with sprinklers, and a full treatment is beyond the scope of this Guide. However, the following section identifies some of the salient points.

(a)

light hazard, all types: 0.7 bar

(b)

ordinary hazard, all types: 0.35 bar

The concept of automatic fire protection collapses if water is not available in sufficient quantities and for an adequate duration when required. Consequently, great attention must be given to the three aspects of water supply:

(c)

high hazard, intermediate rack systems:

——

reliability

——

2.0 bar for K80 sprinkler head

——

flow rate

——

1.0 bar for K115 sprinkler head

——

capacity (i.e. duration).

(d)

high hazard, other types: 0.5 bar

(e)

and cmsa: varies according to the risk and type of sprinkler chosen.

In simple terms, the higher the hazard, the higher the required flow rate and capacity, and the greater the need for reliability.

The minimum running pressure of standard sprinklers in NFPA 13 is 0.5 bar.

Water supplies are designated as follows, in order of increasing reliability:

The calculations may have to include sprinklers below ducts or other obstructions. Where intermediate rack sprinklers are involved, the final calculations must include both roof and rack systems operating simultaneously, even if the most unfavourable rack location is not in the same area as the most unfavourable roof location. This allows the building owner flexibility in the layout of the racks.

——

single supply

——

superior supply

——

duplicate supply.

esfr

The principal formula for the establishment of friction loss within the calculation process is the Hazen–Williams formula (an empirical relationship which relates the flow of water in a pipe to the physical properties of the pipe and the pressure drop caused by friction). Losses or gains as a result of differences in elevation are accounted for using a simplified method in which 1.0 m head is taken as 0.1 bar. The balance tolerances to be achieved in the calculations are stipulated in the codes, which also schedule the information which must be provided to any approving authority for checking purposes. The Hazen– Williams formula may be expressed as follows:

P=

6.05 Q1.85 # 107 C 1.85 d 4.87



(11.6)

Any of the above may be suitable for light and ordinary hazard risks, but only superior or duplicate supplies would normally be considered for high hazard risks. Acceptable sources for sprinkler water supplies include the following: ——

town main

——

automatic booster pumps, drawing from town main (where permitted)

——

automatic suction pumps drawing from a suitable source

——

elevated private reservoirs

——

gravity tanks

——

pressure tanks.

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The basis of the calculation is to establish the demand of the hydraulically most unfavourable situation for the installation. The demand of the hydraulically most favourable situation must also be established where the water supply is limited and an overload on demand may be detrimental or could shorten the time during which the supply will be available (e.g. a storage tank and automatic pumped supply). This may involve multiple calculations, since the most and least demanding situations may not be obvious.

11-18

Fire safety engineering

A single supply would normally be one of the following: a town main fed from a single source

——

a single automatic suction pump drawing from a suitable source

——

a single automatic booster pump drawing from a town main fed from a single source.

Superior supplies include the following: ——

a town main fed from more than one source and from both ends and not dependent on a common trunk main

——

two automatic suction pumps drawing from a suitable source

——

two automatic booster pumps drawing from a town main fed from more than one source and from both ends and not dependent on a common trunk main

——

an elevated private reservoir

——

a gravity tank

——

a pressure tank (light and ordinary hazard risks only).

Duplicate supplies comprise a combination of the above but tend in the UK to comprise a full holding capacity water storage tank and duplicate fire pumps. Where duplicate pumps are required, each pump must be capable of satisfying the requirements on its own. If two electric pumps are provided, independent electric supplies are required for each pump. For duplicate pumps, it is common practice to provide one electric and one diesel unit. If the capacity is too large to be provided by a single pump, three pumps may be used, each of which is capable of providing one-half of the required capacity.

Each section must be fed from a separate set of pumps or from separate stages of a multi-stage pump, but these may draw from a common water storage facility sized to suit the highest demand. Where pipes have been sized by full hydraulic calculation, then the flow/pressure characteristics of the pumps and the size of the storage tanks are based on these calculations. The calculations for the hydraulically most favourable and unfavourable locations should be accurately plotted on a graph using a linear scale for pressure and a square-law scale for flow. The resulting system demand curves should appear as virtually straight lines on the graph. The design site performance curve for the pump under two separate conditions, with the tank full and with the tank at its lowest operational level, should be plotted onto the same graph. The installation demand points must be covered by the pump curve when the tank water is at its lowest level so that the design flow rate is available through to the end of the operational period. The circumstances of a full design size fire operating the sprinkler system in the most hydraulically favourable location must also be considered and the increased flow rate resulting from such circumstances must be catered for in terms of both pump driver power and tank capacity. The demand curves for this installation should be extended on the graph (Figure 11.4). The point at which the most favourable curve intercepts the pump curve at its highest point is known as Qmax and this value is used to calculate the tank size and pump duty.

70

Figure 11.4  Pump duty graph for a typical installation

1 60 2

Height / m

50 40 7

0.5 bar

30

3 20

4

6

10

5

0 0

1000

2000

3000

4000

5000

6000

Q / l·min

–1

1 2 3 4

Hydraulically most unfavourable area curve Hydraulically most favourable area curve Hydraulically most unfavourable area demand Hydraulically most favourable area demand

5 Pump site performance − low water level ‘X’ (at pump outlet) 6 Pump site performance − tank full (at pump outlet) 7 Maximum demand flow, Qmax

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——

Where the difference between the highest and lowest sprinklers exceeds 45 m, the system is classified as ‘highrise’ in the UK and the system must be subdivided into sections, each having a highest to lowest differential not exceeding 45 m.

Fire suppression

11-19

The tank capacity is determined by allowing for the flow of Qmax for the design duration of demand, which is directly related to the hazard classification, as follows: light hazard: 30 min

——

ordinary hazard: 60 min

——

high hazard: 90 min.

The provision of suction lift fire pumps with priming arrangements is not an acceptable option in NFPA Standards. Vertical turbine pumps would be used.

The tank capacities that the above procedure generates can be adjusted if a reliable infill source is available. The majority of the design codes will permit a reduction in tank capacity as long as the shortfall in stored capacity is made up by the rate of infill into the tank during the discharge period. Sprinkler pumps must be arranged to start automatically in response to a drop in trunk main pressure and, once started, must run until switched off manually. The conditions under which the pump is operating will be defined as either flooded suction or suction lift, depending on the relationship of the pump centre line and low water level. Flooded suction conditions apply when not more than 2.0 m depth or one-third of the effective capacity, whichever encompasses the smaller volume of water, is below the centre line of the pump. With natural unlimited supplies, such as rivers, canals, lakes etc., the pump centre line must be at least 0.85 m below the lowest known or expected water level. A more simplistic method is used for sprinkler system design to NFPA 13. The minimum required tank capacity is based on the density/area calculation multiplied by the duration. Often, an allowance for hose streams is added to this requirement. The duration of the water supply is 30 minutes for light hazard systems, 60 or 90 minutes for ordinary hazard systems and 90 or 120 minutes for extra hazard systems. The lower duration values may be used when the system is supervised and adequately monitored.

A typical arrangement of a single pump water supply is shown in Figure 11.5. Common water supplies are of particular importance where water is a valued commodity. If a site has a number of buildings, consideration should be given to providing a water supply common to all buildings. The supply should be capable of furnishing the flows and pressures required by the building with the highest risk. There may be issues regarding the responsibilities of ownership, service and maintenance.

11.2.14

Commissioning and testing

In common with all piped services, the control of installation standards and proper commissioning and testing of the completed installations are very important. However, unlike other piped services, the completed installation will not normally be tested in full operational mode, therefore even greater care should be exercised to ensure that the design objectives are met.

Key

10

1 2 3 4 5

9

To installation control valves

In addition to the main sprinkler pumps, it is usual to provide a smaller capacity ‘jockey’ pump to make up small losses in the trunk main to prevent the operation of the main pumps in such circumstances. Unlike the main pumps, the jockey pump is automatically switched off when the predetermined cut-out pressure is reached.

Water storage tank Vortex inhibitor Stop valve Duty pump Check valve

6 7 8 9 10

Float valves Jockey pump Pipe union Pump start pressure switch Pressure gauge

From town main connection

8 7

6

1 To drain

5

4

3

2 Figure 11.5  Typical arrangement of a single pump water supply

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——

When pumps are considered as suction lift, then full priming facilities, including priming tank and pipework, must be provided. Separate suction pipes must be provided for each pump and the size of these pipes may be larger as a result of the imposition of a decreased velocity limit.

11-20

Fire safety engineering

11.2.14.1

Pneumatic and hydrostatic testing of installation pipework

Dry pipework should be tested pneumatically to a pressure of 2.5 bar for not less than 24 hours. Wet pipework should be tested hydrostatically to a pressure of 15 bar or 1.5 times the working pressure, whichever is the greater, for a period of at least 1 hour. With wet pipework it is common practice to carry out a preliminary pneumatic test prior to the hydrostatic test to establish that there are no major leaks or open ends. The manufacturers of cpvc pipe and fittings recommend against pneumatic testing of their products and this should be borne in mind when choosing the most appropriate material, and specifying the testing regime, for a particular system. The manufacturer of the pipe and fitting should be consulted if there is any doubt in respect of the safety of pneumatic testing. With systems that are normally dry, it may be appropriate to prove the capability of the system to deliver water to the remote ends of an installation within a reasonable time in response to the operation of a sprinkler head. 11.2.14.2

Water supply testing

The capability of the water supply should be tested, through the complete range of its design requirements, to prove that it will perform as required. Flow measuring devices must be provided at the installation control valves and also adjacent to pumps such that water flow and pressure can be accurately measured. In the case of diesel pump sets, additional tests should be carried out to prove the automatic starting sequence of the unit. 11.2.14.3

Alarms and monitoring facilities

Sprinkler and deluge systems are most often connected to some form of fire alarm system, which monitors the various system appurtenances. All alarms and alarm connections associated with the installation should be tested and links to any remote locations proven. All valve monitoring functions should be proven. When all tests have been carried out to the satisfaction of all authorities, then a completion certificate should be issued by the installing contractor.

11.2.15

Maintenance of sprinkler systems

When the system is handed over to the user, a comprehensive operation and maintenance manual should be provided, which should contain:

——

full documentation for the entire system, its components and all associated plant, alarms, utility supplies etc., including record drawings

——

instructions for the day-to-day operation of the system and procedures to be adopted in fire conditions

——

a full schedule of all maintenance and testing procedures required to keep the system in full working order.

Requirements for the maintenance of sprinkler systems are detailed in Technical Bulletin 203: Care and maintenance of automatic sprinkler systems for BS EN 12845 (LPC, 2016). For sprinkler systems designed to NFPA 13, a comprehensive schedule is provided in NFPA 25: Standard for the inspection, testing and maintenance of water-based fire protection systems (NFPA, 2017b). It is often wise for the user to have the testing, maintenance and servicing carried out under a service agreement with the installer or an accredited servicing company. The LPS 1048 scheme lists contractors considered to be suitable for undertaking the maintenance of sprinkler systems and choosing a contractor from this list should justify an expectation of reliability and capability (LPCB/BRE Global Limited, 2015). Care should be taken to ensure that all appropriate personnel are aware of the actions which are necessary in the event of fire and in the event of mechanical damage to a part of the system. When a system is shut down following either of these incidents, the necessary repairs and replacement of sprinklers should be carried out and the system returned to an operational condition as quickly as possible. All interested authorities should be advised and the stock of replacement sprinkler heads held on site should be replenished as quickly as possible if any sprinklers have been used. Care should also be taken to ensure that following a fire incident all damaged components are replaced. A thorough inspection by suitably qualified personnel may be necessary to establish the extent of the damage to the system.

11.2.16

Property protection

References are often made to sprinkler systems being for ‘property protection’ or ‘life safety’. It is true to say that, whatever the ultimate purpose of a system, the bulk of the design will be identical. A property protection sprinkler system will almost certainly give some life safety benefits and a life safety system will also protect the property. The spacing of sprinklers, sizing of pipes and general arrangement of the systems is likely to be identical. The enhancements which are required to be included in a ‘life safety’ system are geared mainly towards improvements to potential reliability, to ensure that water is available at the sprinkler heads when it is required, as discussed below.

11.2.17

Life safety systems

Although the origins of a sprinkler installation relate to the protection of property, the consequent control of fire means that any sprinkler system may be regarded, in part,

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Notwithstanding the need to monitor the installation work during its progress, the commissioning and testing normally carried out is likely to consist of the following elements.

Fire suppression

The term ‘life safety’ was introduced into the sprinkler standards in 1990, with the change from the Rules of the Fire Offices’ Committee, 29th edition (FOC, 1973) to BS 5306-2: 1990 (BSI, 1990). However, this term is also widely used in the world of fire safety engineering, and beyond, with a different meaning. As such, Annex F ‘Special requirements for life safety systems’ has been retitled in the 2015 edition of BS EN 12845 as ‘Additional measures to improve system reliability and availability’. An example of an installation for life safety is an enclosed shopping centre, where sprinklers may be required within shop units to prevent the spread of fire and to limit the products of combustion, thereby assisting the safe escape of the occupants and making the fire brigade’s task less onerous. In such cases, the reliability and availability of the system becomes even more important than in situations where only commercial risks need to be considered. Additional measures considered necessary by the UK design codes to improve system reliability and availability are that: ——

they must be ‘wet’ pipe installations

——

they must be arranged into zones of not more than 2400 m2 which cover only one ownership and one floor level

——

water flow into each installation control valve and each zone must be monitored and the device connected to a fire alarm panel

——

the installation control valves must be arranged with either a valved bypass or with a parallel duplicate valve set such that the valves may be maintained without interrupting the supply of water to the sprinkler system

11.2.18

Domestic and residential sprinklers

There is an increasing move towards the more widespread use of domestic and residential sprinkler protection, as UK fire statistics show that the majority of fire deaths and injuries occur in dwellings (ODPM, 2004). The potential to save lives in fires is greater in this field than any other area of sprinkler protection. Automatic fire sprinkler systems are a well-established technology and have demonstrated their effectiveness in protecting life and property for industrial and commercial premises over many years. These systems also offer a potential means of saving lives, reducing injuries and reducing property damage in domestic and residential occupancies. With materials such as cpvc pipework and fittings becoming more readily available and a greater awareness of the potential benefits of sprinkler protection, the use of sprinklers is gradually increasing, especially in high-rise buildings. The principles of sprinkler location, pipe feed and water supply resilience for these systems is similar to those for commercial and industrial risks discussed earlier, but expected flow rates are fairly low, comparable with those in light hazard systems. Residential sprinklers are installed in a wide range of properties – new, existing, refurbished, historic, residential, domestic, single properties and whole estates. They are installed for a variety of reasons, some of which include: ——

life safety

——

property protection

——

Building Regulations requirements

——

fire service recommendation

——

decision of owner or developer

all stop valves that are located in the path between water source and sprinkler head must be electrically monitored and tamper-proof

——

following a fire incident

——

protection of people who are vulnerable or at high risk

——

permanent test and drain facilities are required for each zone

——

as a compensatory feature to meet Building Regulations requirements.

——

flushing valves are required in each zone

——

quick response sprinklers are required – there are restrictions on the type of sprinklers suitable for such systems

——

the water supply must be reliable and consist of two single water supplies or two stored water supplies

——

——

additional information is required on the block plan to indicate zone valve locations

——

there are restrictions on the extent of areas which may be shut down for maintenance, repair or alteration at any one time; and strict notification procedures prior to shutdown may be required.

A typical system will consist of a water supply, a control valve, a backflow prevention check valve, a priority demand valve, an alarm system and an array of pipework fitted with sprinkler heads (see Figure 11.6). The system is permanently charged with water. Further requirements for fire sprinkler systems for domestic and residential occupancies can be found in BS 9251: 2014 (BSI, 2014). The greatest resistance to the use of domestic and residential sprinklers is caused by perceptions of high cost and the risk of unwanted operation, although these are unsubstantiated myths.

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as a life safety system in that the safety of the building occupants, those of adjacent properties and the firefighters may be improved if a sprinkler system is fitted. There are also circumstances in which a sprinkler system is installed specifically for life safety purposes and may form part of an integrated life safety strategy, providing concessions with regard to other fire safety measures.

11-21

11-22

Fire safety engineering the use of ‘concealed’ type sprinklers, discussed above, is permitted in certain circumstances so that the presence of sprinklers can be less obvious.

2

11.2.20

9 3

1 5

6

10

11 8

7

1 Pressure gauge 2 To domestic drop off points 3 Priority demand valve (optional) 4 Drain valve 5 Back flow prevention device 6 Stop valve

7 Incoming cold water main 8 Lever operated fullway stop valve 9 Alarm device 10 To sprinklers 11 Combined drain and alarm test valve

Figure 11.6  Typical sprinkler installation control valve and water supply arrangement

11.2.19

Sprinkler protection in schools

Recognition of the ability of sprinkler systems to provide a reliable and resilient method of property protection for schools has led to the development of specialist guidance alongside the main guidance provided within the LPC rules. Technical Bulletins in both the BS and BS EN versions of the rules have been added and these focus on the classification of hazard, selection of sprinklers and provision of water supplies, the requirements for which have been adjusted in line with the specific needs of this specialist area. The guidance recognises the obvious concerns in respect of vandalism to sprinklers and, although it is never possible to have an effective automatic firefighting system which is not vulnerable to some degree,

Third-party certification and approved contractors

A voluntary scheme exists within the UK for the registration of sprinkler systems that are constructed to a recognised standard. This is administered by the Loss Prevention Certification Board (LPCB) and the scheme is termed LPS 1048 (LPCB/BRE Global Limited, 2015). Companies listed under this scheme will also have been assessed to ISO 9001: Quality management systems (BSI, 2015b). Contractors who work within the scheme are listed under four different approval levels, indicating the level of LPCB supervision required and the ability of the contractor to issue certificates. The scheme also identifies five different categories of work type. The contractor will have proved its competency to undertake the design, installation and maintenance of sprinkler/suppression systems. Other third-party certification schemes also exist, such as Exova Warrington and International Fire Consultants. These are illustrated in the comparison chart in Figure 11.7 for sprinkler systems designed and installed to both BS EN 12845 and BS 9251 (BASFA, 2017). The facility to recognise and schedule areas of a project which do not fully conform to the letter of the rules is an integral part of the service. A schedule of ‘nonconformities’ may be provided within the certification paperwork. The absence of a certificate of conformity should not necessarily be construed as condemnation of the sprinkler protection. The ahj should be in agreement with all of the features of the sprinkler protection. The use of third-party accreditation is not currently adopted throughout the world but is a desirable system.

LPC Rules Incorporating BS EN 12845 Commercial and industrial sprinkler systems BRE/LPCB LPS 1048 Level-1

Exova Warrington Certification Ltd FIRAS C&I

International Fire Consultants IFCC C&I

Approved

Approved

PC

Certificated Level-2

Approved

PC

PRE-CALCULATED

Certificated PCW

Certificated

Approved

PCW

Certificated

Level-3

Approved

FHC

Approved

FHC

Level-4

Certificated

FHC

Certificated

FHC

BS 9251 Residential and domestic sprinkler systems BRE/LPCB LPS 1301

Exova Warrington Certification Ltd FIRAS R&D

BS EN 12845 SYSTEM TYPE

International Fire Consultants IFCC R&D

FULL HYDRAULICALLY CALCULATED

BS 9251 SYSTEM TYPE FULL HYDRAULICALLY CALCULATED

PC – pre-calculated, PCW – pre-calculated with water supplies, FHC – fully hydraulically calculated

Figure 11.7  Third-party certification comparison chart for sprinkler contractors designing and installing systems to BS EN 12845 and BS 9251 (Courtesy of the British Automatic Fire Sprinkler Association, Information File BIF No. 20.)

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4

Fire suppression

11.3

Foam systems

11-23 Foam is not suitable for: live electrical hazards

11.3.1 Introduction

——

three-dimensional running fuel fires.

This section is intended to provide the user with outline design criteria and descriptions for the main types of foam system. It has been produced with reference to BS EN 13565-2: 2009 (BSI, 2009).

11.3.3

European standards also exist for foam concentrates (EN 1568 series; see e.g. BSI, 2008), and these are also referred to. There are also the internationally used National Fire Protection Association (USA) codes: ——

NFPA 11: Standard for low-, medium-, and highexpansion foam (NFPA, 2016b)

——

NFPA 16: Standard for the installation of foam-water sprinkler and foam-water spray systems (NFPA, 2015a).

Foam systems are most commonly used to protect flammable liquid pool fire hazards, or defined flammable liquid hazards, including those associated with flammable liquid storage tanks and containers. The choice of foam concentrate and foam proportioning system will vary according to the type of system, the water supply pressure and whether a central supply is used to serve a number of hazard areas. Foam systems may also be used as ‘wetting agents’ for class A materials (ordinary combustibles) in some applications.

11.3.2 General In a foam system, foam concentrate is ‘proportioned’ at a carefully controlled ratio – usually 3% concentrate to 97% water, or 1% to 99% to produce foam solution. This solution is then ‘aspirated’ with air to form foam bubbles, and applied to the surface of the flammable liquid. Foam extinguishes fires by: ——

smothering the fire by preventing air mixing with the flammable vapour

——

suppressing the release of flammable vapour from the fuel surface

——

separating the flames and heat from the fuel surface

——

cooling the fuel surface and the sources of ignition.

To be effective foams must: ——

flow freely

——

form a tough cohesive blanket

——

suppress flammable vapours

——

seal against hot surfaces

——

resist heat

——

resist fuel pick-up

——

retain water

——

offer good ‘burn-back resistance’.

Types of foam concentrate

Foam concentrates are grouped and defined as follows. The performance characteristics of some of these foam concentrates are shown in Table 11.7. 11.3.3.1

Fluoroprotein foam (FP)

This protein-based foam with fluorochemical additives is generally best used aspirated, is stable but flows freely and has good firefighting properties with relatively low fuel pick-up as long as it is applied gently. Standard fluoroprotein foam is not suitable for use on water-soluble risks. It generally produces a thick, stable foam with excellent burn-back resistance. 11.3.3.2

Aqueous film-forming foams (AFFFs)

afffs were developed specifically for crash fire situations where fast fire knockdown is vital to maximise chances of personnel rescue. They are a combination of fluorocarbon surfactants and synthetic foaming agents, which gives the foam solution surface tension characteristics capable of producing a thin vapour-sealing film on a hydrocarbon liquid surface. This film spreads rapidly over the surface of a fuel, resulting in fast flame knockdown. afffs are formulated to drain foam solution quickly from the foam bubble to produce optimum film formation for rapid fire knockdown. To achieve this, long-term sealability and burn-back resistance are sacrificed to some degree. Due to their film-forming ability and their low energy requirement to produce good quality foam, afffs can be used through non-aspirating equipment, such as conventional sprinkler heads. Thus, for example, existing water deluge systems can be easily converted to foam systems by merely adding the appropriate proportioning equipment.

11.3.3.3

Synthetic detergent (SD)

sd foam concentrates are based on a mixture of synthetic foaming agents with additional stabilisers. They are very versatile in that they can be used to produce low-, mediumor high-expansion foams. For this reason, they are often referred to as ‘high-expansion foam concentrates’. In addition, they can provide a certain amount of ‘wetting action’ for class A solid combustible material fires.

The foams produced from sd concentrates have good fluidity, will flow around obstructions and achieve rapid knockdown. However, they have low stability and relatively rapid drainage times and so provide little radiant heat resistance and tend to dissipate fairly quickly. Therefore, sd foams exhibit very little burn-back resistance and their fuel surface-sealing capabilities are limited. High-expansion foam can be used for various hazards, such as paper stores and vapour suppression of liquefied natural gas (lng). Standard ‘syndet’ foams are not suitable for use on water-soluble fuels. Not all types available

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——

11-24

Fire safety engineering

Table 11.7  Performance characteristics of some foam concentrates fp

afff

sd

fffp

mp

Cohesion

***

**

**

***

***

Vapour suppression

****

**

**

***

****

Stability/water retention

***

**

**

***

***

Flowability/flame knockdown

**

****

***

***

***

Heat resistance

****

**

*

***

***

Sealing capability

****

**

*

***

****

Burn-back resistance

****

**

*

***

****

Fuel tolerance hydrocarbons

***

***

*

***

***

Fuel tolerance polar solvents

0

0

0

0

***

**** = excellent, **** = good, ** = reasonable, * = poor, 0 = inadequate Note: This table is an attempt to show the properties attainable from each generic type of foam concentrate for firefighting of flammable liquids from a good quality foam of that type. It is important that a recognised high-quality standard relevant to the risk is applied. There can be considerable performance differences between foams of the same generic type across the commercial marketplace. Other factors, such as cost effectiveness, standardisation on site, storage conditions and corrosion, must be considered prior to final choice of agent.

exhibit good dry chemical compatibility. sd foams are available for use at various concentrations. The most common are used at 1.5–2%. Low-temperature grades are available. 11.3.3.4

Film-forming fluoroprotein (FFFP)

In order to combine the good stability and heat resistance of a protein-based foam and the fast knockdown of a film-forming one, some manufacturers have developed an fffp type. The result is usually foam that exhibits good all-round properties but may not achieve quite the same knockdown as an afff or quite the same burn-back resistance as an fp foam. This is understandable because, for fast knockdown, a rapidly draining fluid foam is better, whereas for burn-back resistance a slow draining stable foam is better. Thus, the two features being sought tend to require conflicting properties. Standard fffps are not suitable for use on water-soluble fuels. They are available in 3% and 6% grades with low temperature capability. fffps can be used through mediumexpansion foam-making equipment to achieve expansions up to approximately 50 : 1, but are generally used at low expansions up to 10 : 1. 11.3.3.5

Alcohol resistant

Polar solvents and water miscible fuels, such as alcohols and ketones, are destructive to standard hydrocarbon-type foams because they extract the water contained in them and rapidly destroy the foam blanket. These fuels require a special type of ‘multi-purpose’ concentrate, often known as ‘alcohol resistant’ (ar). Some of these have a synthetic afff base and some an fffp base. Both types can be used, with the right application techniques, on hydrocarbon and polar solvent fires. They contain special polymeric additives that remain in the foam until it comes into contact with the water-soluble fuel. As the fuel extracts the water in the foam bubbles, a tough polymeric membrane is formed on the fuel surface, preventing the further destruction of the foam blanket on top of it. This effect does not occur on a standard hydrocarbon liquid but instead the

foam behaves as a conventional afff or fffp, with additional stability and burn-back resistance caused by the polymer additives. Hence, modern multi-purpose (mp) foams can provide an effective agent for both types of flammable liquid. Earlier types of mp foams were designed for 3% use on hydrocarbons and 6% on polar solvents (i.e. they differed from most conventional foams in that they were used at different concentrations according to the fuel type). There are now grades available for use at 3% on both hydrocarbons and polar solvents. One very important aspect of mp foams, which can have a significant influence on system design, is that of concentrate viscosity. mp foam concentrates tend to be more viscous than other types of concentrate and therefore may require different proportioner characteristics, especially in systems where concentrate pumps are used. 11.3.3.6

Class A foam

Class A foams are primarily wetting agents, which reduce the surface tension of the water, giving greater penetration and effectiveness on ordinary combustibles. They can also be aspirated to enable them to be used as a surface fire barrier. 11.3.3.7

Fluorine-free foams

Due to increasing concerns about fluorinated compounds within the majority of foam concentrates that are available on the market, a number of manufacturers have produced ‘fluorine-free’ versions. They have been in development for several years and some end users have adopted them for environmental reasons. The performance of fluorinefree concentrates is usually reviewed and, if a large amount is to be purchased, a recognised fire test is conducted to ensure that it is suitable for the intended application and gives acceptable extinguishing, vapour suppression and burn-back performance. Such tests include those identified in EN 1568 and by LASTFIRE (Large Atmospheric Storage Tank Fires) — a consortium of international oil

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Property

Fire suppression

11.3.3.8

C6 foams

Recently, many manufacturers have started to produce so called ‘C6’ versions of fluorinated foams that have shorter fluorocarbon chain lengths than foams available in the past, which usually contained fluorinated chain lengths with at least eight carbons (‘C8’). Based on groundwater and soil monitoring studies, it is currently thought that potential breakdown products of C6 versions might be persistent in the environment but not necessarily bioaccumulative or toxic. In terms of performance, C6 foams are rapidly approaching the levels obtainable by ‘legacy’ C8-based foams but end users should perform fire testing to determine suitability.

11.3.4

Foam proportioning

and discharge outlet. High back pressure will stop the device picking up foam concentrate. A line proportioner is essentially a fixed flow device and it is very important to precisely match the flow/pressure characteristics of the proportioner with those of the foam discharge device. Failing to do so is probably the most common reason for system failure. 11.3.4.2

Bladder tank

A bladder tank proportioning system comprises a pressure vessel with a rubber bladder of foam concentrate inside it. Water is fed from the foam system inlet water supply, under pressure, into the shell of the vessel to pressurise the space between the vessel wall and the bladder. The water pressure thus squeezes the foam concentrate out of the bladder through a delivery pipe to a foam proportioner. The proportioner mounted in the pipework to the foam system mixes the water flowing through the proportioner and foam concentrate at the required ratio.

The purpose of the proportioner is to introduce foam concentrate into the water supply to form foam solution. As finished foam properties are highly dependent on using the foam concentrate at the correct percentage, the accuracy of foam proportioning equipment plays an important part in ensuring that good quality foam is produced by the overall system.

Bladder tanks are used extensively in fixed systems where variable flow is required, water pressure is limited and no power supplies are available to drive pumps. However, extreme caution is required when refilling the system in order not to break the diaphragm inside the foam tank. In addition, the routine maintenance and inspection procedure to ensure that they are ready for use can be more complicated than with other systems.

If the foam concentrate is proportioned at too low a percentage, the foam solution will be weak and may fail to form stable bubbles. If the concentration is too high, the foam will be too stiff and may fail to flow across the fuel surface to extinguish the fire completely.

Wide-range proportioners are available that typically operate from 80  l · min–1 of solution flow up to over 5000  l · min–1. These were specially developed for use in foam enhancement of sprinkler systems.

Foam concentrate is mixed with water at the required ratio (usually 3% or 1%, and although some foams can be proportioned at 6%, these are becoming less popular). There are many different types of proportioner available to the firefighter for mobile use and to the fire protection engineer for fixed systems. 11.3.4.1

Inductors (line proportioners)

The line proportioner induces foam concentrate into the water line by means of Venturi action. Water, at high pressure, is fed into the inductor inlet and passes through a nozzle into a small chamber built into the device. Water entering the device contains a certain amount of ‘energy’ as velocity and pressure. As it enters the nozzle, the velocity increases dramatically and, consequently, the pressure has to drop. A foam concentrate container is connected, via a pipe or tube, to the induction chamber and so the foam liquid is ‘driven’ into the device by atmospheric pressure. A pressure drop of approximately 35% has to occur over the unit for it to function properly. This may present a problem if water pressure is low, resulting in insufficient pressure at the final discharge outlet. Following on from this, the maximum allowable back pressure on the unit is approximately 65%. Back pressure is affected by elevation difference and friction losses between the proportioner

11.3.4.3

Balanced pressure proportioning

A balanced pressure proportioning system comprises a foam concentrate pump drawing from an atmospheric storage tank and pumping foam concentrate through a pressure balancing valve into a proportioner. The pressure balancing valve senses both the foam and water pressures entering the proportioner and regulates the foam pressure down to match the water pressure. Like a bladder tank system, it will operate over a wide range of flows and pressures depending upon the proportioner and the foam concentrate. 11.3.4.4

Water-driven foam metering pumps

These units have a water motor, within the water line to the foam system, which drives a foam pump drawing from an atmospheric foam storage tank. The flow of the foam pump is matched to the speed of, and thus flow through, the water motor to deliver the correct amount of foam concentrate into the water downstream of the water motor. These units will proportion accurately over a limited range of flows and pressures, and are available in various sizes and capacities, up to many thousands of litres per minute. They have become increasingly popular over the past few years because they can be used in either fixed or mobile foam systems and the proportioners are usually skid mounted or supplied so that they can be easily put onto vehicles.

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and storage companies which reviews the risks associated with fires in storage tanks and develops best industry practice, based on research, academic studies and experience, to mitigate those risks.

11-25

11-26 11.3.4.5

Fire safety engineering Premix foam units

11.3.5

Types of foam system

11.3.5.1

Low-expansion foam systems

Expansion is defined as the ratio between the volume of ‘finished’ foam produced and the foam solution required to make that foam. Methods for measuring foam expansion can be found in NFPA 11 (NFPA, 2016b) and EN 13565-2 (BSI, 2009). Low-expansion foam typically has an expansion of up to 20 : 1. Low-expansion foam systems are used for the protection of cone roof and floating roof flammable liquid storage tanks, tanker loading and off-loading bays, process areas, oil-fuelled machinery spaces and aircraft landing and servicing areas. They are also used for protection of dykes and bunds (secondary containment) around storage tanks. Compressed air foam systems (cafs) are available that aspirate the foam water solution within the foam delivery system so that pre-aspirated foam is discharged at the nozzles. Compressed air foam is usually very stable but its suitability for a given application should be checked. 11.3.5.2

Medium-expansion foam systems

Medium-expansion foam typically has an expansion of between 20 : 1 and 200 : 1, although most operate at around 50 : 1. These systems are often used for dyke/bund protection and for manual firefighting on minor spills where a thick, stable blanket of foam is required. Mediumexpansion foam is sometimes used as a means of suppression of flammable and/or toxic vapours from spills to protect personnel and prevent ignition of flammable vapours, although it will never be 100% effective at suppressing vapours – especially with high-vapour-pressure fuels and liquefied gases, so caution is always recommended. 11.3.5.3

High-expansion foam systems

High-expansion foam usually has an expansion of between 200 : 1 and 1000 : 1. It is used for limited vapour suppression and fire control of outdoor spills of lng at expansions up to 500 : 1. It is also used for protection of warehouses, tunnels, aircraft hangers and sometimes cable voids, where water damage and/or water availability could be a problem. To be effective, high-expansion foam must fill the hazard to above the height of the highest hazard. As a result, it poses problems of breathing, hearing and disorientation for anyone within it, and can make it difficult for firefighters to find the seat of the fire.

Foam system discharge devices

11.3.6.1

Foam chambers for fixed roof oil storage tanks

Fixed foam pourers are often used as the primary protection method for cone roof tanks. There are three components to a foam pourer assembly used for storage tank protection, including the foam generator, vapour seal box and discharge device (pourer). Normally, the pourer itself is of a type that forces foam back against the tank wall, so that it flows down relatively gently onto the fuel surface. The pourers are located immediately below the weak seam joining the roof to the tank shell. 11.3.6.2

Rimseal foam pourers for oil tanks with open top floating roofs

The main fire risk for open top floating roof tanks is the seal area between the tank shell and the floating roof, so rim seal foam pourers are often provided. The pourer system comprises a number of pourers positioned strategically around the top of the tank discharging foam into the seal area. In most cases, a foam dam is fixed on the tank roof to contain the foam in the seal area. With foam pourers, it is only possible to apply foam over any secondary seal or water shield in the rim seal area. Other types of system are available (catenary and coflexip) with which it is possible to inject foam directly into the space underneath, but these are not so common and introduce an additional maintenance burden. 11.3.6.3

Subsurface foam units for fixed roof oil storage tanks

With sub-surface application or ‘base injection’, the foam is forced directly into the fuel either via a product line or at a point near the bottom of the tank (but above any water base that may be present). The foam then travels through the fuel to form a vapour-tight blanket over the entire surface. 11.3.6.4

Foam water sprinklers

These are open nozzles mounted above process or fuel handling areas. They consist of an air induction body into which the foam solution discharges. The air is drawn in and mixes with and aspirates the foam, which is then spread evenly over a circular area by a deflector plate. 11.3.6.5

Water sprinkler and sprayers

Conventional sprinkler and water spray systems can deliver fluorosurfactant-based foams, which are effective with little or no aspiration, as afff, ar-afff and also fffp in some instances. 11.3.6.6

Foam branch pipes and monitors (foam ‘cannons’)

Foam branch pipes and monitor nozzles can project foam horizontally and vertically over long range, but the plunging of the foam into the fuel can reduce their effectiveness. Their use is discouraged for polar solvent fuels, including

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One way of proportioning is, of course, simply to mix the foam concentrate with water in a large container to form ‘premix’. This can then be stored ready for pumping to the foam discharge devices when required. Premix is used in foam extinguishers and in some relatively small systems where the storage tank is pressurised with nitrogen or air so that the automatic opening of a valve by a detection system gives immediate discharge to the foam application equipment. As these systems have limited capacity, they are used for protection of small hazard areas, such as remote boiler rooms or oil storage rooms in buildings.

11.3.6

Fire suppression

11.3.6.7

Foam inlet (‘semi-fixed’) systems

These consist of a fire brigade pumping-in connection on the outside of a building or hazard area, with ‘dry’ piping routed to foam discharge devices within a small hazard area, such as a basement fuel oil storage room. The fire service personnel pump foam solution into the system from outside and the foam is applied directly to the hazard area, without the need to enter the hazard area. 11.3.6.8

Medium-expansion foam generators

Medium-expansion foam generators consist of a body with a mesh screen on the outlet and a foam solution nozzle mounted axially in the (air) inlet. The solution is sprayed onto the mesh and the induced air flow blows the solution into bubbles. They are mounted above and beside the hazards they protect. The generators produce thick, stable foam but it cannot be ‘thrown’ as far as low-expansion foam from a standard branch pipe. Generators are available in a number of capacities to suit the total foam application rate required. They are often used in bund protection applications where foam is required to cover a large area quickly and maintain post-fire security – but they can be used for vehicle fires and in small equipment rooms where there is a possibility of a flammable liquid pool fire. 11.3.6.9

High-expansion foam generators

The basic process to be followed when designing a foam system is summarised below. (1)

Identify the flammable or combustible liquid.

(2)

Define a potential fire area.

(3)

Identify a suitable foam type (e.g. and proportioning rate.

ar-afff)

fp, afff,

(4)

Select and specify the foam solution application method/devices to be used.

(5)

Determine a foam solution application rate and required run time from published standards.

(6)

Establish the required number of foam application devices.

(7)

Determine foam concentrate requirement (using the calculation methods in EN 13565-2 or NFPA 11).

(8)

Determine the water delivery rate required.

(9)

Identify the available water supply and its quantity, rate and pressure.

(10)

Assess the best methods of providing the foam and water supplies (i.e. fixed or mobile foam supplies, proportioning system type etc.).

Foam-enhanced sprinkler systems use the assumed maximum area of operation (amao) (see section 11.2) as the design basis. The duration of foam discharge varies according to the type of system and the hazard. Sprinkler, deluge and other spill fire hazards generally require a minimum 10 minute supply of foam. Fuel in depth hazards, such as tanks, have longer discharge times of between 30 and 90 minutes depending on the volatility of the fuels.

11.3.8

Components and materials

High-expansion foam generators consist of a body with a mesh screen on the outlet and one or more spray nozzles in the (air) inlet. It is not possible to achieve expansions up to 1000 : 1 with straightforward drawing in of air to the foam solution by Venturi action; it is necessary to actually drive air in. This is normally done by use of a fan, which can be water driven or electric motor driven. Combustion products present in the air used to generate the foam can severely affect the expansion ratio achieved. It is always preferable to draw air from a clean, outside source. If this is not possible, a large factor to compensate for foam loss must be applied to the application rate of foam. For this reason, high-expansion generators should be mounted above the level that the foam is required to reach in order to draw fresh air in to produce the foam.

Foam concentrates and foam solutions may attack galvanised pipe, so piping is usually black steel, although some foam concentrates require stainless steel or copper alloy. Foam systems have operating pressures similar to those of sprinkler systems, so the same pipe, fitting and valve standards apply. All pipework must be adequately supported and be pressure tested to 1.5 times the maximum working pressure after installation. It is usually a good idea to ensure that pipework is designed to avoid foam concentrate being static in a line for extended periods, where it can deteriorate; viscosity of the concentrate and ease of pumping should also be taken into account when designing systems.

11.3.7

To verify that the foam system is functioning correctly, each system should be tested as part of the commissioning process and annually thereafter. Ideally, each system should be allowed to discharge foam to check the correct functioning and coverage of the discharge devices (cone roof tank foam chambers are available that can be turned to discharge away from the tank so as not to contaminate the product within). During the test, a sample of the foam should be taken to check expansion ratio, 25% drainage time and also that the foam proportioning system is mixing at the correct ratio. Such tests are specified in EN 13565-2 and NFPA 11.

Foam system design

Foam systems are required to deliver foam at or above a minimum application rate or density for a minimum length of time. These vary according to the type of hazard, the discharge device and the foam concentrate used. Both NFPA 11 and EN 13565-2 give these basic design criteria for most situations that the designer will encounter, but where information is not available it is prudent to check with the foam manufacturer (e.g. in the case of application of foam to polar solvent and alcohol hazards where recommended application rates can differ from the standards).

11.3.9 Testing

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alcohols, where much gentler application is required. Smaller capacity units are generally hand-held, while larger units, up to 60 000 l · min–1 and higher, are sometimes mounted on turrets or trailers that can rotate and elevate. They are used for storage tank and area protection, including bunds, process and handling areas, aircraft hangers and helicopter decks.

11-27

11-28 Any foam solution discharged should be contained, collected and disposed of by environmentally safe means.

Modern foam concentrates can be expected to have a shelf life of 10 to 20 years depending on the type of foam and the storage conditions. However, premix foams have a limited life and should be replaced every one to three years, depending on thorough testing of a sample. It is good practice for the end user and manufacturer to keep retained samples of concentrate as a ‘guarantee’ for foam systems containing large quantities of concentrate, or if bulk supplies are purchased, so that physical properties can be checked to establish the reason for any deterioration in foam concentrate if a dispute arises.

11.3.10 Documentation Part of any contract involving the supply of foam equipment should include a requirement for descriptions of the system, and detailed testing and inspection methods and schedules. At the very minimum, the documentation should include step-by-step instructions of how to measure the system parameters described in standards such as EN 13565-2 (e.g. application rate, time to achieve effective discharge, proportioning rate, expansion and drainage time). Each system should be provided with the following documentation: ——

scaled plan and section drawing of the hazard and the foam system, including foam supply proportioners and their location, piping and discharge devices, valves and pipe hanger spacings etc.

——

isometric view of the agent distribution piping system, showing the lengths, sizes and node references relating to the flow calculations

——

flow calculations, giving pipe and nozzle sizes

——

name of owner and occupant

——

location of area in which the hazard is located

——

location and construction of the protected hazards

——

foam concentrate information, including agent used, proportioning concentration and quantity provided

——

foam concentrate physical property data, including acceptable tolerances (minimum pH, specific gravity, sediment content, refractive index)

——

specification of the water and foam supplies used, including capacity, pressure and quantity

——

description of occupancy and hazards protected

——

description of discharge devices used, including orifice size/code (where applicable)

——

description of pipes, fittings and valves used, including material specification.

11.4

Water mist systems

11.4.1 Introduction It is useful to detail the applicable standards covering water mist systems prior to covering the technology. ——

NFPA 750 (2015) Standard on water mist fire protection systems

——

BS 8458: 2015 Fixed fire protection systems. Residential and domestic watermist systems. Code of practice for design and installation

——

BS 8489-1: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Code of practice for design and installation

——

BS 8489-4: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Tests and requirements for watermist systems for local applications involving flammable liquid fires

——

BS 8489-5: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Tests and requirements for watermist systems for the protection of combustion turbines and machinery spaces with volumes up to and including 80 m3

——

BS 8489-6: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Tests and requirements for watermist systems for the protection of industrial oil cookers

——

BS 8489-7: 2016 Fixed fire protection systems. Industrial and commercial watermist systems. Tests and requirements for watermist systems for the protection of low hazard occupancies.

Note: The British Standards BS 8458 and BS 8489 differ significantly from the Draft for Development documents that have been in circulation since 2011 and are now withdrawn. Note: There is a European Technical Specification, TS 14972, which is in committee stage to become a European Standard prEN 14972 Fixed firefighting systems. Watermist systems. Part 1: Design and installation. This standard also has a number of test requirement standards as part of the series. No date has been set for publication although the latest version (2017) is now at committee stage after public consultation. In addition to these standards are specific standards written by insurance-governed approvals bodies. The most important and globally recognised are detailed below. ——

Factory Mutual Global FM 5560 (2016) Approval standard for water mist systems (this standard covers fire testing for specific applications and component and system approval)

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In addition, a sample of foam concentrate should be analysed yearly to check that its physical properties (e.g. pH, specific gravity, sediment content, refractive index, viscosity etc.) are still within the manufacturer’s tolerances. While these properties do not directly affect fire performance, any major change throughout the lifetime of the foam might indicate deterioration, degradation or contamination that might ultimately affect fire performance if the foam solution made from the concentrate is applied to a fire.

Fire safety engineering

Fire suppression FM 4-2 (2013) Water mist systems

——

Underwriters Laboratory UL 2167 (2011) Water mist nozzles for fire protection service (this standard covers fire testing for specific applications and nozzle approval)

——

VdS 3188 (2015) VdS Guidelines for water mist sprinkler systems and water mist extinguishing systems (high pressure systems). Planning and installation (this document differentiates between technologies and is based on VdS fire testing for specific applications and component approval).

The UK Loss Prevention Council (LPC) adopts the use of the fire tests detailed in BS 8458 and BS 8489 Parts 4, 5, 6 and 7 but does not cover component approval. The BS 8489 parts are taken directly from the sections published in FM 5560. The above standards focus principally on land-based applications. Marine systems have different standards, coverage of which is outside of the scope of this Guide. In general, a water mist system that has been proven for marine use should not be assumed to be suitable to meet the test requirements of land applications. These standards cover the requirements to meet the intent of the application design, the installation, commissioning and maintenance of water mist systems. They do not allow the user to design the system. This will be dependent on the particular manufacturer of the system, the applicable design based on fire testing appropriate to the risk and the necessity for third-party approval of system components. The Fire Protection Association (FPA) has published questionnaires developed through the RISCAuthority in relation to providing assessment on the suitability of water mist and to ensure that all salient design and operational points are detailed and documented: ——

Water Mist Questionnaire: Building compartment protection – ‘Deluge’ open-head systems – IQ1 (Version 2, November 2015)

——

Water Mist Questionnaire: Building compartment protection – Local application protection – IQ2 (Version 2, November 2015)

——

Water Mist Questionnaire: Building compartment protection – Systems incorporating ‘thermally-actuated’ closed heads – IQ3 (Version 2, November 2015).

11.4.2

Properties of water mist

Water mist is defined in British and European Standards as a water spray in which 90% of the droplet diameters are less than 1 mm measured in a plane 1 m from the nozzle. (Note that this value is 99% in the NFPA 750 standard.) Water mist is used as a firefighting method for the protection of class A, class B and class F fires. Class A fires include wood, paper and plastics and are deep-seated fires. Class B fires are liquid or solid hydrocarbons, such as paraffin, petrol, diesel, kerosene, and alcohols including paints and solvents. Class F fires are cooking fats and oils — essentially an extension of class B fires but with much higher ignition temperatures. The purpose and operation

of water mist on each fire type differs and it is important to understand the effective mechanisms before applying to provide the necessary protection. A detailed risk assessment is therefore essential. The RISCAuthority questionnaires are a useful tool for this process. The small water droplet size increases the amount of surface area available to make contact and absorb heat from a fire. Heat is then extracted from the burning combustibles in one of two ways: through the energy loss in increasing the droplet temperature from ambient temperature to 100 °C (specific heat capacity); or through the energy required to change the phase into vapour (latent heat of vaporisation). The former mechanism contributes to 13% of the cooling effect and the latter, 87%. If the water droplets are vaporised then two additional mechanisms come into play. The first is the displacement of oxygen around the flame front, which results in the amount of oxygen available for combustion decreasing. The second is to provide a physical screen that attenuates the radiation, preventing radiative heat spread to adjacent areas. Smaller water droplets are effective in being carried into the base of the fire through thermal movement (entrainment), but are also subject to the influence of ventilation and thermal barriers from the fire itself, particularly when discharging from height. The performance of the system is critically dependent on fire type. Class B and class F fires are characterised by high heat release rates. This maximises the evaporation of the water mist droplets and full extinguishing of the fire can be achieved. It is interesting to note that the larger the fire in the smaller the volume, the more effective the system can become; and that, also, it requires a minimum fire size before extinguishment can take place. Conversely, for class A fires, in which we can include cable fires, the heat release rate is low, and only a small amount of water mist is vaporised, thus negating up to 87% of the cooling capacity and the corresponding effects of oxygen dilution/radiative attenuation. Water mist systems designed to protect class A hazards are designed for suppression/control not extinguishing and use a higher water density than for class B applications. For class A fires, systems using slightly larger droplet sizes use less water as the additional droplet mass helps with surface wetting and penetration in cooling deep-seated fires. The advantages of water mist systems include the consumption of less water than an equivalent sprinkler system, with consequent benefits in reduced water capacity, pipework size and collateral damage. For purposes of comparison, typical values for water usage are shown in Table 11.8, based on approved listings from a range of manufacturers. Table 11.8  Comparison of typical water use values for water mist and sprinkler systems Fire class

Water mist / l itre· min –1 · m–2

Sprinkler / litre · min–1 · m–2

Light/ordinary hazard (class A)

1.7–2.2

5

Class B

0.16–0.5

5–7.5

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——

11-29

11-30

11.4.3

Fire safety engineering

Fire test protocols

——

Class A fires: light hazard occupancies (roughly equivalent to BS EN 12845 ordinary hazard group 1): FM 5560 Appendix G; BS 8489-7: 2016.

——

Class B fires: machinery spaces (various volume limits): FM 5560 Appendices A, B, C, D, E, F; BS 8489-5: 2016; local application: FM 5560 Appendix I.

——

Class F fires: industrial oil cookers: FM 5560 Appendix J.

Note: The local application for a land-based fire test differs significantly from those for marine fires. Marine fire tests only cover exposed spray fires, whereas land tests cover concealed spray fires and both exposed and concealed pool fires. Marine approved systems have not been proven to work for land-based fire tests. Furthermore, there is a marine requirement for a secondary protection system to be provided in the event of the water mist system failing to extinguish a fire. As a minimum, this has to be adhered to, along with the limitations of fire scenarios, should a marine approved system be considered for land use. Other fire test protocols published in FM 5560 include the protection of wet benches, data processing equipment rooms/halls etc. UL 2167 includes similar tests as undertaken for marine applications (such as cabin spaces) and for higher hazards, including storage with limited heights (as defined in NFPA 13). VdS also has fire test protocols for ordinary hazards, concealed spaces (floor/ceiling voids), car parking, storage and cable tunnels. It is important to note that all fire test protocols have limitations. These limitations include ceiling height, volume, ventilation, openings, fire load etc. Thus, a system approval for light hazard to 5 m height is not valid for a room of greater height. Where a water mist solution is applied outside the boundaries of testing, either by virtue of limitations above, or an application not covered by, one of the published protocols, then the following approaches can be considered.

11.4.4

Types of water mist systems

11.4.4.1

Pressure and water supply

The type of water mist system is normally characterised by the amount of pressure used and the type of water supply. NFPA 750 introduced the categorisation of pressure, principally to differentiate between the various materials and engineering pertinent to each. However, the use of pressure terms, such as ‘high’, ‘intermediate’ and ‘low’, has led to confusion, and largely been driven by the marketing efforts of companies with a single technological offering. Indeed, many of the myths surrounding water mist, including the ‘black box’ design approach, have been driven by such companies. The important point is that, as long as the water droplet size meets the criteria of the definition of water mist, and the water mist system has been fire tested and approved, the pressure is irrelevant. For completeness, at a simple level there are two types of pressure system: one operating below 16 bar and one operating above 16 bar. In reality, most systems that are approved and listed operate at 12 bar or below, or at 70 bar or above. There are systems in between, but the key differentiators are the means of generating pressure and the pipework systems utilised. To complicate matters further, systems exist that are single fluid (using only water) and twin fluid (using water and a gas propellant, normally nitrogen). Additionally, the actual water supply can be from stored water tanks and pumps (similar configuration to sprinkler systems) or cylinder-based water supplies and a separate supply of propellant gas. The key difference between the two is that any system containing water or propellant gas cylinders has a finite supply of either water or propellant gas or both, thus limiting total available discharge time.

In the case of an established fire test at, say, an increased height, then the fire test could be repeated in exactly the same configuration at the required height. A pass within the criteria of the original certification, subject to thirdparty witness and review, could provide justification for use.

Single fluid systems operating at 16 bar or below, based on pumps, typically use similar hardware to sprinkler systems. Pumps are normally centrifugal. Often the basis for component approval is identical to that for sprinklers, alongside the required fire tests undertaken to provide system approval. Such ‘low’ pressure systems can also be used with water tanks and propellant cylinders, with the outlet pressure of the gas being regulated during discharge. Generation of the water mist is through engineered nozzle orifice and deflectors.

Where an application has no equivalent published fire test protocol, then full-scale fire testing is normally required. Details of specific requirements are given in NFPA 750 Annex C. The development of the fire test protocol and ‘pass/fail’ criteria, actual tests and report should be validated by a third party, ideally including the ahj, insurer and a third-party approval body, such as FM, LPCB, VdS, UL etc.

Single fluid systems operating at 70 bar or above, based on pumps, use positive displacement type pumps, stainless steel hydraulic pipe and specially fabricated valves. Water storage cylinders have a high pressure rating (normally 200 bar working pressure) with a special plastic lining to prevent corrosion. The water mist is created as high pressure loses its energy as it passes through finely drilled orifices.

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All standards for water mist state that it is imperative for the water mist system to be tested in accordance with third-party fire test protocols applicable to the hazard to be protected. The published fire test protocols include those detailed in FM 5560, UL 2167 and the VdS approvals programme, along with Parts 4, 5, 6 and 7 of BS 8489. Examples of fire test protocols are as follows:

A suitable risk assessment should be carried out and a detailed review undertaken of relevance to any proposed water mist system, supported by third-party fire test and component approval.

Fire suppression

11-31 within range, with a rapid drop-off as it approaches maximum flow. This type of pump uses a relief or unloader valve to allow the flow of water not used for system discharge to return back to the water supply tank. Positive displacement pumps operating at pressures above 50 bar require considerably more power at a given flow rate than the other type – centrifugal pumps. Centrifugal pumps, as often found in sprinkler systems, use a series of impellers of a given flow rate to increase the pressure. The pressure drops with increased flow. Selection of the pump is dependent on system flow and pressure requirements.

11.4.4.2

11.4.5.2 Nozzles

System configuration

There are two types of system configuration: deluge (using open nozzles) and automatic (using closed nozzles with alcohol-filled bulbs, as per sprinklers).

There are many different nozzle types, depending on the technology used and manufacturer approval. The most common types are:

Deluge systems are used for the protection of class B and class F risks. Deluge systems are applied in ‘total flood’ applications, in which the entire room is flooded, or local applications, in which the discharge is confined to a specific hazard area or object. The system is discharged after receiving a signal from a detection system. Sufficient water (and, in the case of a gas propellant system, gas as well) is required to maintain the water supply for the complete duration of discharge specified in the approval documentation. In the case of class F fires, the water mist often extinguishes the fire extremely rapidly but extended discharge is required to ensure that the fuel is cooled below its auto-ignition temperature/fire point. Protection of class A risks using deluge systems, e.g. cable tunnels, is normally addressed by configuring the risk in zones with design overlap to ensure that fire cannot spread between zones.

——

nozzles used for pressures of 50 bar and above, with small orifice outlets (available as automatic and deluge types)

——

nozzle design similar to sprinklers, with a smaller orifice and specially designed deflector plates, for pressures of 12 bar and below (available as automatic and deluge types)

——

twin fluid nozzles that mix propellant gas and water at the outlet orifice (available as deluge nozzles only).

Automatic water mist systems are more normally used in the protection of class A risks. The systems can be configured as wet or pre-action (as per sprinkler systems). Heat from a fire causes the alcohol to expand, which breaks the frangible bulb, and water discharges local to the risk. The design area is based on third-party approval and the relevant applicable standard. Typically, for light/ordinary hazard risks with water mist approval, the design area is between 72 m2 and 140 m2. The system must have sufficient flow and water supplies to meet the most hydraulically favourable and unfavourable demands. Design discharge times should be never less than 30 minutes and are more usually for 60 minutes. The British Standard BS 8489 has detailed appendices covering the calculation of design area, hydraulic gradients and water tank sizes. This is particularly relevant to ensure that the supplying installation company of the water mist system has the design knowledge to calculate these parameters correctly.

11.4.5

11.4.5.3 Valves Any valve installed in the system needs to be approved for use at the desired working pressures. The most common valves are detailed below. ——

Isolation valves: These are installed upstream (nearest the water supply) of zone (alarm) valves and deluge valves, to provide isolation in the event of maintenance. The valve should be monitored open and closed. Valves used for pressures above 70 bar tend to be of the ‘ball’ type; for pressures of 16 bar and below, butterfly, gate or ball valves can be used.

——

Zone (alarm) valves: These are incorporated into ‘wet systems’, i.e. automatic systems, and are used to section areas of a protected building. The valve is an assembly that should come complete with non-return valve, flow switch, drain/test valve and pressure gauges.

——

Deluge valves: These are used for deluge systems (ball-valve type for pressures of 50 bar and above; diaphragm or ball valve type for pressures below 16 bar). These valves can be activated electrically (via a solenoid) or pneumatically (via a separate air supply). Some types of valve have the functionality of remote resetting. Valves should be configured ‘latched’ (so that they remain open until closed). They can also be configured as a pre-action valve, with the necessary additional trim (including components associated with zone valves).

——

Pre-action valves: These are used on automatic systems where critical risks are being protected and unwanted water discharge needs to be minimised. Upstream is wet, but downstream is dry. The pipework downstream is filled with air, which

Water mist components

11.4.5.1 Pumps Pumps may be pneumatic, electric or diesel and either centrifugal or positive displacement. Positive displacement pumps work on ‘back pressure’ and have a ‘flat’ pump curve, with the flow constant at a given pressure

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Twin fluid systems (or hybrid systems) are third-party approved under a different scheme: FM 5580 Approval standard for hybrid (water and inert gas) fire extinguishing systems (2012). The water mist is formed as the two fluids mix at the nozzle. This type of technology can generate extremely small water mist droplets (~10 microns) at around 8 bar. This is interesting engineering proof that droplet size is independent of pressure used. These types of systems are only used for the protection of class B flammable liquid fires and must not be used for risks containing class A combustibles.

11-32

Configuration of valves should comply with the British Standard series BS 7273, in particular: ——

BS 7273-3: 2008 Code of practice for the operation of fire protection measures. Electrical actuation of preaction watermist and sprinkler systems

——

BS 7273-5: 2008 Code of practice for the operation of fire protection measures. Electrical actuation of watermist systems (except pre-action systems).

11.4.5.4 Pipe All pipe used in water mist systems must meet the requirements of the operating pressure of the system, be smooth walled to ensure efficient flow and be of a material such that no deposit of debris or clogging of nozzles can take place (particularly important where the nozzle outlets are very small). National standards also place restrictions on the use of certain types of pipe (e.g. upvc), with regard to strength and fire resistance, and where the pipe can be used. For all systems, stainless steel pipework is most often used, with minimum grade of 304, and more usually 316. Thin-walled crimp/press systems are suitable for operating pressures of 16 bar and below, while thicker walled tube is suitable for higher pressures. Ferrule connection methods for systems operating above 50  bar are not recommended due to the potential for pipework failure, particularly in cases of hammer effect (rapid increase in pressure or flow in a short period of time). For higher pressures, special fittings or deforming pipe at the fitting, so that no failure can occur, are preferred.

Certain insurance companies insist on the system meeting FM approval, and third-party approval is a requirement to comply with BS 8489. Third-party installation schemes are in preparation by Warrington Fire Research (FIRAS) and the LPCB.

11.4.7 Maintenance Maintenance requirements are given in the relevant standards — BS 8489 and NFPA 750. In general, pumpbased systems with a water supply tank have similar maintenance requirements to sprinkler systems. Cylinderbased systems are subject to the requirements of hydrostatic testing every 10 years, as is the case for gas extinguishing systems.

11.5

Gaseous fixed fire extinguishing systems

11.5.1 Introduction This section details the function and design of gaseous fixed fire extinguishing systems. These systems contain a fixed amount of extinguishing agent, in a gaseous or liquefied state, in containers installed in a fixed location. The containers or cylinders are connected to a pipe network and nozzles. They are deluge systems requiring electric activation from a fire extinguishing alarm panel, or a manual release. They are designed to extinguish class A and class B fires. The discharge agents used vary in applicability and characteristics but all are non-conducting, ‘clean’ agents that leave no residue upon discharge. This makes them ideal for the protection of electrical risks.

11.5.2

Type of application

Approvals bodies, such as FM, will not accept galvanised pipe, although a combination of approved galvanised pipe and nozzles with orifice size >4 mm in low-pressure systems may be deemed acceptable, subject to meeting certain minimum documentation requirements. However, care needs to be taken concerning the quality of galvanised pipe and acidity of the water, which could potentially cause a reaction that would corrode the pipe with the production of hydrogen gas as a by-product.

There are two main types of application of fixed extinguishing systems. The first, and by far the most common, is a ‘total flood’ system, whereby the entire enclosure is filled with agent. The second is a ‘local application’ system, whereby only an object within a much larger volume (e.g. transformer, cabinet, printing press) is protected. Discharge of the agent is local to that object. This method is preferred in cases where multiple hazards are located together (e.g. generators), so that only the hazard on fire receives discharged agent, leaving the remainder operational.

11.4.6 Approvals

11.5.3

The approval of water mist systems is vital to meet the fire protection requirements of the specification. This should include, as a minimum, certification of fire test and components pertinent to the risk being protected, thirdparty certification of the installing contractor and full document submittal, including the necessary hydraulic flow calculations. Unfortunately, due to the historical lack of standards, particularly in the UK, many systems have been installed that are either unsuitable for the protected risk and/or have no third-party approval for fire test or components, or correct design for discharge duration and coverage.

The extinguishing agents most frequently used are one of three types:

Extinguishing agents

——

synthetic (halocarbon)

——

inert

——

carbon dioxide.

Each agent has an extinguishing concentration which will vary depending on the type of fire. These can be categorised as class A (wood, paper etc.), higher class A (deep-seated fires, such as plastics and electrical cables)

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is monitored for any pressure loss to ensure integrity of the system. On detection of a fire by the fire detection system, a signal is sent to the valve to open. Water then enters the pipework but will remain there until there is sufficient heat to operate the thermal bulb(s) of the automatic system.

Fire safety engineering

Fire suppression

The Fire Industry Association (FIA) has produced a useful publication: Guidance document on the use of high and regular hazard concentrations for enclosures protected by gaseous fire fighting systems (2010) to advise on which category of class A is required. There are other technologies available, such as aerosols and permanent ‘hypoxic’ inerting systems that are covered in section 11.5.4. 11.5.3.1

Halocarbon and fluoroketone extinguishing agents

Halocarbon extinguishing agents are referred to as synthetic agents as they are chemically formulated specifically for their fire extinguishing characteristics. The main extinguishing agents in use and covered in this document are HFC-227ea, HFC-125, HFC-23 and the fluoroketone FK-5-1-12. HCFC Blend A, which was designed as an alternative to halon, is not covered as its use is now banned due to its ozone depletion potential. The agents are stored under pressure in liquid form and discharge as a gas. Other than HFC-23, the agents themselves have very low vapour pressures. In order to discharge the agents, a nitrogen pressurising medium is used. The most common fill pressure is 25 bar; however, 42 bar and even 70 bar systems are becoming more prevalent. Cylinder sizes vary between 5 litres and 343 litres and, dependent on fill ratio (which depends on agent type, storage temperature and factors which influence discharge time), allow a range of flexibility in cylinder selection. Discharge time has to be within 10 seconds and with 25 bar systems this often restricts the location of the cylinders to within or immediately adjacent to the risk. The higher pressure systems can extend the pipe distance and mitigate this restriction. Functional storage temperatures are between –20 °C and 50 °C. The lower the temperature, the more difficult it is to pressurise the pipework and achieve the required discharge time. Only HFC-23 will work below 0 °C and minimum temperatures for other gases are higher. Halocarbons and fluoroketones decompose at temperatures in excess of 500 °C and it is therefore important to avoid applications involving hazards where continuously hot surfaces are involved. Upon exposure to the flame, the agents will decompose to form halogen acids (HF). Their presence will be readily detected by a sharp, pungent odour before maximum hazardous exposure levels are reached. It has been concluded from fire toxicity studies that decomposition products from the fire itself, especially carbon monoxide, smoke, oxygen depletion and heat may create a hazard.

Table 11.9  Properties of halocarbon agents Property

alc

/%

Design concentration range / %

noael

/ % loael / %

FK-5-1-12

>10

5.3–5.9

10

>10

HFC-125

>70

11.2–11.5

7.5

10

HFC-227ea

>80

7.9–9

9

10.5

HFC-23

>65

16.3–16.4

50

>50

It is recommended that all systems are approved to either LPCB, FM, UL or VdS certification and that the installation is undertaken by an approved installer. In the UK, the certification scheme is the LPS 1204 (LPCB/BRE Global Limited, 2014). The safety levels for synthetic agents are normally limited by the toxicity level limits (see Table 11.9): ——

no observable adverse effect level (noael)

——

lowest observable adverse effect level (loael)

——

approximate lethal concentration (alc).

Maximum exposure limit is five minutes. HFC-227ea and HFC-125 HFC-227ea (heptofluoropropane) is a hydrofluorocarbon, sometimes known under the trade name FM-200. HFC-125 (pentofluoroethane) is a hydrofluorocarbon, sometimes known under the trade name Ecaro-25. The present understanding of the functioning of these hydrofluorocarbons is that 80% of their firefighting effectiveness is achieved through heat absorption and 20% through direct chemical means (action of the fluorine radical on the chain reaction of a flame). HFC-227ea and HFC-125 are classified as fluorinated gases (F-gases), which are controlled substances due to their high global warming potential. Discharge testing is not permitted and contents have to be monitored for leakage. Spain, as an example, applies an environmental levy tax which has effectively limited the sale of new systems. HFC-23 HFC-23 (trifluoromethane) is a hydrofluorocarbon, sometimes known under the trade name FE-13. The present understanding of the functioning of HFC-23 is that 80% of its firefighting effectiveness is achieved through heat absorption and 20% through direct chemical means (action of the fluorine radical on the chain reaction of a flame). HFC-23 has the highest vapour pressure of all the halocarbons and is normally stored under its own vapour pressure of 42 bar. Some systems are super-pressurised with nitrogen to enhance their flow characteristics or allow pressure monitoring without the need for weighing devices. Because HFC-23 is classified as an F-gas, discharge testing is not permitted and contents have to be monitored for leakage. Furthermore, since HFC-23 has the highest global warming potential of halocarbons commonly used

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and class B (liquid or solid hydrocarbons, such as paraffin, petrol, diesel, kerosene, and alcohols, including paints and solvents). All systems have a safety factor, depending on the design standard applied, of between 20% and 30% design concentration above the extinguishing concentration. Note that the US standard NFPA 2001 (NFPA, 2015b) has recommended design concentrations in general below those of the ISO and BS EN standards.

11-33

11-34

Fire safety engineering

in fire protection, first fill and refill after discharge will not now be permitted in Europe. As a result, no new systems of HFC-23 are being installed.

Table 11.10  Properties of inert agents Agent

Composition / % Argon

CO2

100

—

1.689

1.37

FK-5-1-12 FK-5-1-12, more commonly known under its trade name Novec 1230, is a fluoroketone. Under normal conditions Novec 1230 is a colourless and low odour fluid with a density around 11 times greater than air. The present understanding of Novec 1230 is that its firefighting effectiveness is through heat absorption and chemical means. FK-5-1-12 has almost zero global warming potential and a very short lifetime and therefore is not subject to the controls imposed by F-gas regulations. 11.5.3.2

Inert extinguishing agents

All inert extinguishing agents are naturally occurring gases or blends of naturally occurring gases that do not chemically react with combustibles. All agents have zero ozone depletion potential (odp = 0). The global warming potential (gwp) is not applicable since the agents consist of only naturally occurring gases. All agents are stored as a gas in steel containers with a storage pressure of 200 bar or 300 bar at 15 °C. The systems are designed and approved to operate in the temperature range of –20 °C to +50 °C, or as otherwise stated in separate component listings. Handling and installation of the system equipment should only be carried out by persons experienced in dealing with this type of equipment. All agents are colourless and odourless. The types and properties are detailed in Table 11.10. The agents extinguish fires by reducing the oxygen concentration below the combustion value of approximately 15%. A typical inert extinguishing system with 40% design concentration will reduce the oxygen concentration in the hazard to approximately 12.5%. The agents are effective and approved for class A and B fires. The carbon dioxide in IG-541 stimulates increased respiration. The safety levels for inert agents are limited by the acceptable minimum oxygen level reached. The two limits, noael and loael, with recommended maximum human exposure to each level in minutes are shown in Table 11.11. The footprint for inert gas systems is larger than that for equivalent designed halocarbon systems since the gas cannot be liquefied and higher design concentrations are required. Inert gas systems rely on the oxygen level being reduced, which is achieved by the addition of the inert gas, with the air being displaced to ensure no over-pressurisation occurs. This method requires more gas than the chemical cooling provided by halocarbon gas systems. However, their main advantages lie in the ability to install cylinders remotely from the risks (even at distances of hundreds of metres), their environmentally green credentials, the lower agent refilling costs post-discharge and the ability to configure multi-zone directional valve systems (see section 11.5.11). Discharge times are typically 60 seconds to deliver 95% of design concentration. However, it is recognised that for

IG-01 (argon)

—

IG-55

50

50

—

1.437

1.17

IG-100 (nitrogen) 100

—

—

1.185

0.97

IG-541

40

8

1.441

1.17

52

Table 11.11  Exposure duration at a given oxygen limit with the corresponding concentration of inert gas agent Toxicity level

Agent concentration / %

noael

43

12

≤5 minutes

loael

52

10

≤3 minutes

Below loael

Oxygen concentration / %

<10

Exposure limit

Unoccupied areas only

very large systems with long pipework runs, and restrictions on the pressure ratings of pipes, this is not always achievable. An update is included in the current ISO 14520 standards (ISO, 2015/2016) that permits an increase of the discharge time to 120 seconds. This extension has been adopted in the revisions of the BS EN 15004 standards published at the start of 2018 (see section 11.5.5). There are two main types of inert system. The first, found mainly in older systems, is known as orifice technology. Here, the agent is discharged at storage pressure (normally 200 bar or 300 bar), and the pressure reduced through an orifice plate to around 60 bar. The second, used in more modern systems, uses constant flow technology, where the flow is regulated at the valve, normally 40–60 bar. This removes the ‘peak’ flow upon initial release of agent and normally permits the use of pipe diameters one size down. Within both of these technologies, the specifics vary depending on the manufacturer. It is recommended that all systems are approved to either LPCB, FM, UL or VdS certification and that the installation is undertaken by an approved installer. In the UK, the certification scheme is the LPS 1204 (LPCB/BRE Global Limited, 2014). Liquid inert systems Technology has been developed using either argon or nitrogen to the exact design standards as above, but stored in a cryogenic state in low-pressure vacuum vessels, rather than high-pressure cylinders. These systems require evaporators to rapidly heat the liquid to the gas phase and usually rely on the longer (120 second) discharge times. The pipework must be stainless steel, but operating pressures are around 20 bar. Since it is possible that liquid at low temperature could enter the pipe, expansion (contraction) bellows need to be installed at regular intervals to prevent damage upon contraction. These systems have cost viability only for the larger installations but do have advantages due to ease of refilling, and no requirement for hydrostatic testing.

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Nitrogen

Density Relative @15 °C and density / 1013 mbar / air = 1 kg · m–3

Fire suppression 11.5.3.3

Carbon dioxide extinguishing agent

The discharge of carbon dioxide in fire-extinguishing concentration creates serious hazards to personnel, such as suffocation and reduced visibility during and after the discharge period. Consideration should be given to the possibility of carbon dioxide drifting and settling in adjacent areas outside the protected volume. Consideration should also be given to where the carbon dioxide can migrate or collect in the event of a discharge from a safety relief device of a storage container. Adequate safety measures will include physical isolation of discharge pipework and door interlock that cannot be opened prior to the network being isolated. The use of carbon dioxide has diminished over the years but it is still one of the best agents for local application in printing presses, and for total flooding of rotating machinery, for example. The design of carbon dioxide systems differs from halocarbon and inert gas agents, principally in the coverage of deep-seated class A fires where often an additional quantity of agent is discharged along a separate pipe network after the initial discharge. This extended discharge compensates for the lack of cooling provided by the agent and also any leakage within the enclosure. Discharge times varying between 30 seconds (local application class B fires) to 7 minutes (deep-seated class A fires), to 20 minutes or beyond for rotating machinery, such as turbines, so that discharge is maintained during the period of rotation shutdown. Its use in the protection of industrial deep fat fryers has been superseded by water mist technology since carbon dioxide lacks the cooling capacity required after extinguishment, and often re-ignition occurs once the blanket carbon dioxide has been dispersed.

11.5.4

11.5.4.1

Alternative fire extinguishing technologies Dry powder

Dry powder systems are the best protection method for class D reactive metal fires. The systems can be designed as total flood or local application. Dry powder is available in several forms, and careful selection is required, dependent on the fire class. The primary extinguishing mechanisms are chemical, inhibiting the flame reaction, and through inerting. Dry powder discharges obscure all visibility and their use is restricted to normally unoccupied areas. 11.5.4.2

Wet chemical

Wet chemical systems are used for the suppression of kitchen fires. They are designed for local application and

consist of a tank containing the wet chemical solution connected to a pressurising medium. Actuation of the system is by way of thermal links. The protected areas include the range, hood and ducts, which are installed with nozzles approved to the specific hazard or configuration. The system is automatic with manual override, standalone without the need for a separate fire detection system, and normally connected to a gas shut-off valve. 11.5.4.3 Aerosols Aerosols are small particles of dry powder used as an alternative to gas extinguishing systems. They are contained in small containers or cartridges of various sizes and can be used for local or total flood applications. The canisters are modular and one or more are located, evenly spaced, throughout the protected hazard. Actuation is electric via a signal from the releasing panel. The generation of the aerosol upon discharge is via an explosive charge and the aerosol is filtered through a coolant so that the temperatures are reduced. Care is required to ensure that the agent does not react with any compound within the protected hazard. Due to the reduction in visibility, their use is not permitted in areas that are normally occupied. 11.5.4.4

Oxygen-reduction systems

Oxygen-reduction systems are those that permanently inject either nitrogen or a nitrogen-enriched air mix into the protected enclosure to create a hypoxic atmosphere. At oxygen levels below 16%, most materials cannot combust and a fire cannot start. There are various methods used to create the mix, the most common being a membrane that filters out smaller oxygen molecules, allowing only the larger nitrogen molecules to pass. The air is supplied from a compressor and filtered before entering the membrane. Physiologically, the atmosphere created is similar to that found at altitude and, to most fit people, does not prevent a hazard to health. However, its use in permanently occupied areas is restricted by the Confined Spaces Regulations 1997, which refer to the reduced oxygen level presenting a danger due to the displacement of oxygen by toxic gases, rather than the reduction of actual oxygen concentration in itself. These systems are good at preserving materials that age through oxidation, such as paper and paintings, and are therefore a proactive method of protecting against fire and degradation in, for example, archives. The biggest drawback is that the building integrity has to be extremely high otherwise large systems are required, with high power consumption levels, necessary to maintain the air leakage rate with incoming hypoxic air. In many cases where positive pressurisation is present there can be significant challenges in achieving functionality in an economic manner. Properly designed systems normally take around 36 hours to reduce the ambient oxygen levels from 21% to 15%, and then have a duty on–off cycle of around 60%. The big advantage is that there is a large volume of hypoxic air and, even if a component fails, there is a long period of time before oxygen levels increase to the point where combustion can take place.

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Carbon dioxide (CO2) is stored either as a liquefied gas in high-pressure cylinders or in refrigerated low-pressure tanks. When the liquid discharges, it rapidly turns into its gas phase. When released directly into the atmosphere, liquid carbon dioxide forms solid dry ice (‘snow’). Carbon dioxide gas is 1.5 times heavier than air. It extinguishes fire by reducing the concentrations of oxygen to the point where combustion stops.

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Fire safety engineering

11.5.4.5

Cool gas generators

These are small canisters containing sodium azide, a coolant and a booster at zero pressure. Activation is via a small charge that starts the decomposition of the chemicals. The chemical decomposition generates nitrogen to discharge at around 10 bar, diluting the oxygen to a level below 15%. The residue remains within the generator and is not discharged. Applications are similar to aerosols and tube-operated systems and the applicability of standards is the same as per tube-operated systems.

11.5.5

International standards

Gaseous fixed fire extinguishing systems are detailed under several series within British Standards. The following provides an introduction to all types of systems and offers a general overview: ——

——

NFPA 2001 (2015): Standard on clean agent fire extinguishing systems

——

ISO 14520-1: 2015 Gaseous fire-extinguishing systems. Physical properties and system design. General requirements

——

ISO 14520-2: 2016 Gaseous fire-extinguishing systems. Physical properties and system design. CF3I extinguishant

——

ISO 14520-5: 2016 Gaseous fire-extinguishing systems. Physical properties and system design. FK-5-1-12 extinguishant

——

ISO 14520-8: 2016 Gaseous fire-extinguishing systems. Physical properties and system design. HFC 125 extinguishant

——

ISO 14520-9: 2016 Gaseous fire-extinguishing systems. Physical properties and system design. HFC 227ea extinguishant

——

ISO 14520-10: 2016 Gaseous fire-extinguishing systems. Physical properties and system design. HFC 23 extinguishant

——

ISO 14520-12: 2015 Gaseous fire-extinguishing systems. Physical properties and system design. IG-01 extinguishant

——

ISO 14520-13: 2015 Gaseous fire-extinguishing systems. Physical properties and system design. IG-100 extinguishant

——

ISO 14520-14: 2015 Gaseous fire-extinguishing systems. Physical properties and system design. IG-55 extinguishant

——

ISO 14520-15:2015 Gaseous fire-extinguishing systems. Physical properties and system design. IG-541 extinguishant.

Tube-operated systems

Modular cylinders or small canisters filled with an extinguishing agent with their own tube detection are available for the protection of objects (e.g. bus engines) and inside cabinets. The tube is pressurised and ruptures at a certain temperature. Depending on the configuration, the agent discharges either through the tube or through a separate outlet to a discharge nozzle(s). These systems are not covered by a specific design standard but the extinguishing agent design concentration and hold times (where applicable) should be the same as those for fixed systems. 11.5.4.6

design of gas extinguishing systems for IG-541 (ISO 14520-15: 2015 modified)

BS 5306-0: 2011 Fire protection installations and equipment on premises. Guide for selection of installed systems and other fire equipment.

Standards covering carbon dioxide systems include: ——

BS 5306-4: 2001 + A1: 2012 Fire extinguishing installations and equipment on premises. Specification for carbon dioxide systems

——

NFPA 12 (2015) Standard on carbon dioxide extinguishing systems

——

VdS 2093: 2017-08 VdS Guidelines for fire extinguishing systems. CO2 fire extinguishing systems. Planning and installation

——

ISO 6183: 2009 Fire protection equipment. Carbon dioxide extinguishing systems for use on premises. Design and installation

——

Comité Européen des Assurances CEA-4007 (2007) CO2 systems. Planning and installation.

Specific to halocarbons, fluoroketones and inert gases, the following BS EN, ISO and NFPA standards are available: ——

——

BS EN 15004-1: 2008 Fixed firefighting systems. Gas extinguishing systems. Design, installation and maintenance BS EN 15004-7: 2008 Fixed firefighting systems. Gas extinguishing systems. Physical properties and system design of gas extinguishing systems for IG-01 extinguishant

——

BS EN 15004-8: 2017 Fixed firefighting systems. Gas extinguishing systems. Physical properties and system design of gas extinguishing systems for IG-100 extinguishant (ISO 14520-13: 2015 modified)

——

BS EN 15004-9: 2017 Fixed firefighting systems. Gas extinguishing systems. Physical properties and system design of gas extinguishing systems for IG-55 extinguishant (ISO 14520-14: 2015 modified)

The standards relating to dry powder systems are: ——

NFPA 17 (2017) Standard for dry chemical extinguishing systems

BS EN 15004-10: 2017 Fixed firefighting systems. Gas extinguishing systems. Physical properties and system

——

BS EN 12416-2: 2001 Fixed firefighting systems. Powder systems. Design, construction and maintenance.

——

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Degradation of polymers that occurs through overheating (e.g. cables) does not form flaming combustion but damage will occur. To detect this effect, high-sensitivity air-aspirating systems are often used alongside oxygen-reduction systems.

Fire suppression Standards relating to wet chemical kitchen protection systems: UL 300 (2005) Standard for fire testing of fire extinguishing systems for protection of commercial cooking equipment

——

BS EN 16282-7: 2017 Equipment for commercial kitchens. Components for ventilation in commercial kitchens. Installation and use of fixed fire suppression systems.

Standards relating to aerosol fire extinguishing systems: ——

NFPA 2010 (2015) Standard for fixed aerosol fireextinguishing systems

——

ISO 15779: 2011 Condensed aerosol fire extinguishing systems. Requirements and test methods for components and system design, installation and maintenance. General requirements

——

UL 2775 (2014) Standard for fixed condensed aerosol extinguishing system units

——

PD CEN/TR 15276-1: 2009 Fixed firefighting systems. Condensed aerosol extinguishing systems. Requirements and test methods for components

——

PD CEN/TR 15276-2: 2009 Fixed firefighting systems. Condensed aerosol extinguishing systems. Design, installation and maintenance.

Standards relating to oxygen-reduction systems: ——

——

BS EN 16750: 2017 Fixed firefighting systems. Oxygen reduction systems. Design, installation, planning and maintenance PAS 95: 2011 Hypoxic air fire prevention systems. Specification.

11.5.6

Environmental considerations

The use of environmentally damaging chemical agents in fire extinguishing systems has come under scrutiny ever since the discovery that halon, one of the best fire extinguishing agents, damages the ozone layer. Bans and restrictions of its use in the Montreal Protocol led to the development of alternative chemical agents. Some of these, although having no ozone depleting compounds, have significant global warming potential, and legislation has followed to regulate their use. The two terms currently in use are global warming potential (gwp) and ozone depleting potential (odp). odp for all agents is now zero, and any agent with a gwp above 1 is subject to restrictions under the F-Gas Regulation (Regulation (EU) No. 517/2014 on fluorinated greenhouse gases). This imposes bans on the supply of perfluorocarbons and HFC-23 for fire protection, strict monitoring of contents, leakage, emissions and transport across borders. Inert gas agents and fluoroketones are unaffected. Quotas were introduced in 2018, which may affect the supply and costs of these agents used in fire protection systems. The FIA provides training and certification for engineers and companies that are authorised to undertake installation, commissioning and maintenance of F-gas systems.

The Department for Environment, Food and Rural Affairs (DEFRA) has a website offering guidance (www.defra.gov. uk/fgas), and F-Gas Support, a government-funded team, provides advice to organisations (PO Box 481, Salford, M50 3UD, [email protected]).

11.5.7

Safety considerations

The use of pressurised systems can be dangerous and requires adherence to a number of precautions. These relate to transportation, installation, maintenance and use. There have been serious accidents with both synthetic and inert gas cylinders that have discharged, either when not racked in or when in poorly installed systems, which have resulted in considerable damage to buildings and equipment, and even death. The FIA has published a useful guide: GN Safe handling of pressurised container assemblies used in fire extinguishing systems (2015). When discharged into an enclosed volume, the agent can create safety hazards to personnel in several ways: ——

reduction of available oxygen

——

products of combustion of the fire

——

products of decomposition of the agent itself (generally only halocarbons and fluoroketones)

——

toxicity of the agent

——

noise as the agent discharges through nozzles

——

dislodging of objects through turbulence

——

low temperature upon discharge in the vicinity of the nozzle that can cause frostbite and, in the case of humid atmospheres, water vapour.

Regarding the chemical effect, this is measured using the physiologically based pharmacokinetic (pbpk) model, which is used to determine maximum exposure time to halocarbons and fluoroketones. Specific limits are given in the sections relating to the agents above. Dry powder and aerosol systems should not be used in normally occupied areas due to the resulting reduction of visibility and the danger of inhaling the agent. Carbon dioxide should never be used in normally occupied areas due to its high toxicity at design concentrations which will result in death.

11.5.8

Pressure relief venting

When the extinguishing agent discharges into the protected volume, the displacement of residual air and the ingress of additional gas creates either an over-pressurisation or, in the case of certain agents, under- and over-pressurisation of the enclosure. The enclosure strength is measured according to the maximum differential pressure that can be withstood. This measurement is in pascals and can vary greatly, e.g. from plasterboard at ~250 Pa to blockwork at ~500 Pa. In most applications, to prevent structural damage, pressure relief devices are required. Types of pressure vent include counter-weight, pneumatic and electric.

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——

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Fire safety engineering operation of fire protection measures. Mechanical actuation of gaseous total flooding and local application extinguishing systems.

ISO/NP TS 21805 standard for vent guidance, based on the FIA document, was published in 2018 (ISO, 2018).

11.5.11

11.5.9

Hold time

The hold time, or retention time, is the period during which design concentration has to be maintained post-discharge, at a height relative to the risk or object being protected, as detailed in the standards. This time is calculated to take into account any additional cooling that may be required to ensure that the source of the fire has cooled below its ignition temperature and that no re-ignition will occur. The hold time can be measured by way of a door fan test. The ability of an enclosure to ‘hold’ an agent will be determined by the density of the agent, the integrity of the enclosure and actual configuration of ventilation. Often works are required to seal an enclosure in order to meet the required hold times (e.g. sealing cable holes etc). Note that hold times for synthetic and inert gases are 10 minutes and for carbon dioxide 20 minutes.

The actuation of multi-zone systems follows the same standards detailed above. However, the cause and effect configurations differ according to the system needs and are often quite complicated. Clear documentation, piping and instrumentation diagrams and thorough testing at commissioning and during maintenance are critical to avoid errors or dangers in operation (e.g. discharge into closed sections of pipe).

System configuration

The most common method of configuration for synthetic gas systems is for the extinguishing agent to be supplied in individual cylinders. Each cylinder will be of a suitable size with the appropriate fill density. If another risk has to be protected, e.g. a floor void within a room, then a separate cylinder can be added. Or, alternatively, if more than one cylinder is required for the room then further cylinders can be added. This configuration is known as a modular system, as the individual pipe runs from the cylinders are separate from each other. Where many cylinders are required, most typically seen in inert gas systems, the size and fill must be identical and the cylinders are connected by a pipe known as a manifold (see Figure 11.8). In high-pressure inert gas systems with orifice, this manifold is normally made of a higher grade of pipe, typically Sch 160. (Note: Sch = schedule number, with higher numbers referring to thicker walled pipe. Refer to the FIA Guidance Document: Pipework for gaseous fixed fire fighting systems, Version 1, May 2017.)

The FIA has published a guide: Application of hold time heights in enclosures protected by gaseous fire fighting systems (2010), which is useful in clarifying some of the requirements detailed in the standards. Note that there are changes in the later ISO 14520 standard and the upcoming BS EN 15004 standard that make the determination of acceptable hold times more realistic for actual risks.

11.5.10

System operation

Systems can be operated electrically, by manual means or pneumatically. An electrical signal is given by an automatic detection system that is configured in accordance with the requirements of BS 7273-1: 2006 Code of practice for the operation of fire protection measures. Electrical actuation of gaseous total flooding extinguishing systems. This should be consulted along with the BS EN 12094 series — Fixed firefighting systems. Components for gas extinguishing systems. Part 1 details the requirements and test methods for electrical automatic control and delay devices (such as extinguishing release panels). Mechanical operation that includes actuation via thermal links, pneumatic heat devices and manual release devices is covered in BS 7273-2: 1992 Code of practice for the

Manifold system (all cylinders hydraulically connected) All containers must be the same size and the same fill density

Modular systems (cylinders hydraulically separate) Different container sizes and different fill densities are acceptable Figure 11.8  Manifold and modular pipe system configuration

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Work by the US-based Fire Suppression Systems Association (FSSA) (Pressure relief vent area for applications using clean agent fire extinguishing systems, 3rd edition) looked specifically at the discharge pressures created when synthetic and inert agents are released. The FIA has written a guidance document on how to calculate the vent sizes based on agent amount, discharge rate and wall strength. It also covers specific arrangements to ensure that the egress path is determined correctly, including when the gas passes through more than one volume. Reference should be made to FIA’s Guidance on the pressure relief and post discharge venting of enclosures protected by gaseous fire-fighting systems (8th March 2012).

Fire suppression Downstream pipe in both types of system is between Sch 40 and Sch 80, dependent on diameter and required working pressure.

More complicated systems with multiple or uneven flow splits require hydraulic flow calculations to ensure that the correct amount of gas is discharged evenly and within the specified requirement (e.g. BS EN 15004 stipulates 95% of the extinguishing agent within the discharge time). Fixed extinguishing systems can be designed in a multitude of ways. In buildings where multiple risks are to be protected, there are two possible options. The first would be to put an extinguishing system in each risk. This can be costly and occupy a large amount of footprint that could otherwise be used for other equipment. The advantage is that a discharge in a single area will not affect other areas. The second approach would be to install a multizone system using directional valves. The cylinders are selected so that there is sufficient agent to protect the largest risk. The pipework is then configured with a valve per risk, known as a directional (or selector) valve, which is normally closed. In a fire event, a signal is sent to the correct valve and the correct number of cylinders required for that risk are discharged. This has the advantage that, with a large number of protected risks, the system install cost is cheaper than installing separate systems. The disadvantage is that once there has been a discharge, the amount of agent available is compromised for other risks (there would not be sufficient for the largest risks). Also, system configuration and actuation of valves can be complicated and thorough commissioning is crucial to ensure that system failure does not occur at a time of need. Often, a separate connected or unconnected reserve bank of cylinders is provided to keep downtime, while the discharge cylinders are being refilled, to a minimum.

11.5.12

Noise during discharge

As the extinguishing agent is released from the nozzles, it generates noise at a decibel level over a range of frequencies that has, in some instances, caused damage to hard disk drives. This is a relatively recent phenomenon that has been attributed to the increase in data density of hard disk drives, which results in them becoming much more sensitive to pressure and vibration. Other sound actions, such as clapping, can similarly cause read/write devices to malfunction. Reported incidences concern only inert gas systems, whether orifice or constant discharge type. There are several purported solutions on the market, based on ‘silent’ or ‘acoustic’ nozzles. However, the matter is more complicated than simply replacing an old (‘noisy’) nozzle with an acoustic one. Depending on the manufacturer, the nozzle coverage may be limited (resulting in larger numbers of nozzles being installed). In addition, sound power modelling is required, since other parameters can affect the output, such as the distance of the nozzle from the hard disk drive; the number of nozzles (as

sound has a cumulative effect); discharge time (which affects mass flow rate); the type of discharge system used (i.e. constant flow or orifice-type – which affects peak flow rate); and the construction of walls, floors and ceilings (which affects the reflection of the sound). Thorough evaluation should be undertaken using a proven modelled calculation method, based on the sound power output of the nozzle at a given flow rate, to estimate the maximum sound pressure level generated across a range of frequencies. The discharge noise for halocarbon and fluoroketone extinguishing agents is a result of the nitrogen propellant, not the extinguishing agent itself. There have not, to date, been reports of any damage occurring from the use of these types of systems, probably due to the fact that the sound pressure levels generated are generally much lower.

11.5.13

Maintenance requirements

Regulation (EU) No. 517/2014 on fluorinated greenhouse gases (which replaces Regulation (EC) No. 842/2006) requires that all systems containing halocarbon F-gases must be installed and maintained by competent individuals. Anyone who services F-gas systems must demonstrate their competence by having an independently awarded competence certificate. The UK statutory instrument is the Fluorinated Greenhouses Gases Regulations 2009 (SI 2009/261) and these regulations will be updated to accommodate the new EU Regulation. All hoses and operating valves should be inspected at regular intervals (detailed in the general standards in that section). Additionally, cylinder contents should be checked and refilled: ——

for liquefied agents (halocarbons and fluoroketones), if below 5% weight or 10% pressure (when adjusted for temperature)

——

for inert agents, if below 5% pressure (when adjusted for temperature).

For agents that are stored under their own vapour pressure, a gauge is not an accurate indicator of contents and these cylinders must be weighed, or be equipped with dynamic weight-monitoring devices. Enclosures should be tested for integrity and checks carried out to ensure that the hold time can be achieved at installation and thereafter every 12 months or immediately after any works that could affect the integrity have been carried out. Under the Pressure Equipment Directive (2014/38/EU), the Transportable Pressure Equipment Directive (2010/35/ EU) and the Carriage of Dangerous Goods Regulations (SI 2009/1348) hydrostatic testing is required every 10 years (applies in Europe but the requirement is lower in certain other countries). This will require physical removal of cylinders, decanting, testing and refilling. Normally, a service replacement cylinder is installed to minimise system downtime. The FIA has published a useful document Guidance on the periodic testing of transportable gas containers used in fire extinguishing systems (Version 2, November 2015).

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Simple systems with predetermined characteristics are known as pre-engineered systems, which permit design and installation within the bounds of testing documented in the supplier’s manual.

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References Babrauskas V and Grayson SJ (eds) (1992) Heat Release in Fires (London: Interscience Communications Ltd)

CEA (2006) CEA 4001 Sprinkler systems planning and installation (Paris: CEA Property Insurance Committee) FM Global (2014) FM Data Sheet 2-0 Installation guidelines for automatic sprinklers (West Glocester, RI) FOC (1973) Rules of the Fire Offices’ Committee for Automatic Sprinkler Installations (29th edition) (revised) (London: Fire Offices’ Committee) Grimwood P (2005) Firefighting flow rate: Barnett (NZ) – Grimwood (UK) formulae (available at https://firenotes.ca/download/Flow_Rates_for_ Firefighting.pdf) Hall, JR Jr. (2013) US Experience with Sprinklers (Quincy, MA: National Fire Protection Association) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) ISO (2015/2016) ISO 14520 Gaseous Fire Extinguishing Systems (Geneva: International Organization for Standardization) ISO (2018) ISO/NP TS 21805 Guidance on design, selection and installation of vents to safeguard the structural integrity of enclosures protected by fixed gaseous fire fighting systems (Geneva: International Organization for Standardization)

BAFSA (1995) Sprinklers for Safety (Ely: British Automatic Fire Sprinkler Association)

Kim AK and Lougheed GD (1997) Fire Protection of Windows Using Sprinklers (Ottawa: National Research Council of Canada)

BAFSA (2006) Use and Benefits of Incorporating Sprinklers in Buildings and Structures (Ely, Cambs: British Automatic Fire Sprinkler Association)

LPC (Loss Prevention Council) (2016) LPC Rules for Automatic Sprinkler Installations – incorporating BS EN 12845 (Moreton in Marsh: Fire Protection Association)

BAFSA (2017) Third party certification Information File BIF No. 20: March, Issue 2 (Aberfeldy, Scotland: British Automatic Fire Sprinkler Association) BSI (1990) BS 5306-2: 1990: Fire extinguishing installations and equipment on premises. Specification for sprinkler systems (London: British Standards Institution) BSI (1995) BS EN 10242: 1995 Threaded pipe fittings in malleable cast iron (London: British Standards Institution) BSI (2003a) PD 7974-7: 2003 Application of fire safety engineering principles to the design of buildings. Probabilistic risk assessment (London: British Standards Institution) (Note: PB 7974-7: 2003 has been replaced by PD 7974-7: 2019) BSI (2003b) PD 7974-4: 2003 Application of fire safety engineering principles to the design of buildings. Detection of fire and activation of fire protection systems. (Sub-system 4) (London: British Standards Institution) BSI (2004a) BS EN 10255: 2004 Non-alloy steel tubes suitable for welding and threading. Technical delivery conditions (London: British Standards Institution) BSI (2004b) BS EN 10226-1: 2004 Pipe threads where pressure tight joints are made on the threads. Taper external threads and parallel internal thread. Dimensions, tolerances and designation (London: British Standards Institution) BSI (2008) BS EN 1568: 2008 Fire extinguishing media. Foam concentrates (London: British Standards Institute) BSI (2009) BS EN 13565-2: 2009 Fixed firefighting systems. Foam systems. Design, construction and maintenance (London: British Standards Institute) BSI (2014) BS 9251: 2014 Sprinkler systems for domestic and residential occupancies. Code of practice (London: British Standards Institution) BSI (2015a) BS EN 12845: 2015 Fixed firefighting systems. Automatic sprinkler systems. Design, installation and maintenance (London: British Standards Institution) BSI (2015b) BS EN ISO 9001: 2015 Quality management systems. Requirements (London: British Standards Institution) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution)

LPCB/BRE Global Limited (2014) LPS 1204 Requirements for firms engaged in the design, installation, commissioning and servicing of gas extinguishing systems (Watford: BRE Global Ltd) LPCB/BRE Global Limited (2015) LPS 1048 Requirements for the approval of sprinkler system contractors in the UK and Ireland (Watford: BRE Global Ltd) NFPA (2008) Fire Protection Handbook (20th edition) (Quincy, MA: National Fire Protection Association) NFPA (2015a) NFPA 16 Standard for the installation of foam-water sprinkler and foam-water spray systems (Quincy, MA: National Fire Protection Association) NFPA (2015b) NFPA 2001 Standard on clean agent fire extinguishing systems (Quincy, MA: National Fire Protection Association) NFPA (2016a) NFPA 13 Standard for the installation of sprinkler systems (Quincy, MA: National Fire Protection Association) NFPA (2016b) NFPA 11 Standard for low-, medium-, and high-expansion foam systems (Quincy, MA: National Fire Protection Association) NFPA (2017a) NFPA 15 Standard for water spray fixed systems for fire protection (Quincy, MA: National Fire Protection Association) NFPA (2017b) NFPA 25 Standard for the inspection, testing, and maintenance of water-based fire protection systems (Quincy, MA: National Fire Protection Association) ODPM (2004) Fire Statistics – United Kingdom, 2002 (London: Office of the Deputy Prime Minister) Rohr KD and Hall, JR Jr. (2005) U.S. Experience with Sprinklers and Other Fire Extinguishing Equipment (Quincy, MA: Fire Analysis and Research Division, National Fire Protection Association) SA (1995) Australian Standard AS2118.2: 1995 Automatic fire sprinkler systems. Part 2: Wall wetting sprinklers (drenchers) (Sydney, NSW: Standards Australia) Yii HW (2000) Effects of surface area and thickness on fire loads Fire Engineering Report 00/13 (Canterbury, New Zealand: University of Canterbury)

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The standards relating to the requirements for testing are contained in BS EN 1968: 2002 Transportable gas cylinders. Periodic inspection and testing of seamless steel gas cylinders, applicable to seamless steel gas containers (inert and carbon dioxide cylinders and any halocarbon cylinder operating at 42 bar or above), and BS EN 1803: 2002 Transportable gas cylinders. Periodic inspection and testing of welded carbon steel gas cylinders, applicable to welded carbon steel gas (halocarbon cylinders at 25 bar and below). The manufacturers generally recommend that, at the time of testing, the valve be fully refurbished (for synthetic gases) or replaced at the time of testing. Recommendations are given in the 2015 FIA guidance document detailed above. It is also recommended that gas purity is checked to ensure that the decanted gases are properly filtered and cleaned before refilling. Certification by the original equipment manufacturer supplier of the gas is highly recommended.

Fire safety engineering

12-1

Fire resistance, structural robustness in fire and fire spread

12.1 Introduction Fire resistance is an integral component in the delivery of successful fire engineering input and design. The specification and integration of fire-resisting construction into design has benefits that extend beyond life safety. This chapter outlines some principles so the reader can ensure that fire-resistance design is: (a)

fully integrated into the conceptual and early stages of the building design process

(b)

implemented appropriately during specification and construction

(c)

manageable as the building moves into service.

12.2

Fire resistance

12.2.1

What is fire resistance?

Gas temperature / ºC

1200 1000 800 600 400 200 0

0

20

40

60 80 100 120 Time / minutes Figure 12.1  The standard (ISO 834) fire curve (ISO, 1999)

140

1999), ASTM E119-15 (ASTM, 2015) etc.) and, where appropriate, loading conditions (Hopkin et al., 2014).

Within the construction community, ‘fire resistance’ is conventionally referenced in the context of the performance (in a furnace test) of an isolated construction element, relative to specific performance criteria (integrity, insulation and load-bearing), under defined furnace heating (e.g. BS 476-20: 1987 (BSI, 1987), ISO 834-1 (ISO,

Performance (i.e. fire resistance) is typically measured in terms of time taken (in minutes) to breach any one or all of the given performance criteria (Table 12.1), depending on the nature of the construction element tested, when subject to the particular furnace time temperature curve (Figure 12.1). The specific heating curve and performance criteria vary subtly between different countries and are defined in a variety of standards permitted for use in differing jurisdictions. A summary of prominent standards is given in Table 12.2.

Table 12.1  Standard fire test performance criteria according to BS 476-20 Performance criteria

Performance expectation (a)

(b)

Integrity

Construction suffers collapse or sustained flaming on the unexposed face (side)

Construction is no longer considered impermeable, i.e. openings lead to either the ignition of a cotton pad on the unexposed side or gaps are sufficiently large for a gap gauge to penetrate

Insulation (Note: if an integrity failure has been deemed to occur, this also constitutes an insulation failure)

The mean of temperatures recorded on the unexposed face increases by more than 140 °C above its initial value

The temperature recorded at any single location on the unexposed face increases by more than 180 °C above the initial value

Load-bearing

Test specimen deflects by more than span / 20

The rate of increase of deflection, once deformation exceeds span / 30, is more than span2 / 9000d (where d is the depth of the structural specimen)

Table 12.2  Summary of primary international fire-resistance standards Primary nation/continent Standard

Title

Year

UK

BS 476-20 (BSI, 1987)

Fire tests on building materials and structures. Method for determination of the fire resistance of construction (general principles)

1987

USA

ASTM E119-15 (ASTM, 2015)

Standard test methods for fire tests of building construction and materials

2015

Europe

EN 1363-1 (BSI, 2012a)

Fire resistance tests. General requirements

2012

Canada

CAN/ULC-S101-14 (SCC, 2014)

Standard methods of fire endurance tests of building construction and materials

2014

Australasia

AS 1530 Part 4 (SA, 2014)

Fire-resistance tests for elements of construction

2014

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12

12-2

12.2.2 Context

Fire safety engineering ——

At the start of the twentieth century, the provision of ‘fire safe’ buildings became a social expectation when reviewing the impact of significant conflagrations (the great fires of Baltimore (1904) and San Francisco (1906) being two of the most prominent).

The severity of the thermal scenario (time–temperature curve) during the early iterations of the standard fire test is understood to stem from New York fire codes, developed towards the end of the nineteenth century (specifically, tests intended to appraise the fire performance of floors). These codes, informed by qualitative firefighter experience from that time, were predicated on a thermal scenario of peak temperature 1700  °F. At the time, this thermal scenario was intended to be more severe than any foreseen ‘real’ fire. Following criticism of the New York building structure fire testing concept, various construction material agencies sought change, with efforts led by the American Society for Testing Materials (ASTM). As a result, a new fire test standard was proposed in 1916, which is largely reflective of the standards adopted today. Most importantly, the thermal scenario adopted in today’s standards has significant synergy with that proposed at the turn of the nineteenth century (i.e. the peak gas temperature after 60 minutes of ISO 834 exposure (945 °C) broadly coincides with that of the nineteenth-century New York fire codes). Since the inception of the standard fire test in the early 1900s, the concept has been extended beyond testing inert materials to combustible materials, such as timber construction. For a fuller description of the development of structural fire testing see Gales et al. (2012).

12.2.3 Limitations In the context of the thermal scenario, the element arrangements tested in the fire-resistance procedure and the performance criteria against which ‘acceptable’ performance is quantified, fire resistance cannot represent the time to ‘failure’ of an element of construction in a real fire for a number of reasons (O’Loughlin and Hopkin, 2016): ——

——

The thermal condition, i.e. the standard fire curve, is not representative of real fire exposure as real fires can take many forms. It is also non-physical, as it neither cools nor acknowledges variability in peak temperature (or the time taken to achieve it). The structure boundary conditions (i.e. typically simply supported isolated elements) are not representative of whole structural frames, where structural elements interact (both positively and negatively).

The primary purpose of fire-resistance testing (and thus ratings) remains consistent with the time of the concept’s inception, i.e. a means of comparatively assessing the performance of elements, materials and products when subject to a standardised (fairly severe) heating condition.

12.3

Fire resistance in design: the fire-resistance period

It is typical of most jurisdictions that buildings are required to achieve certain levels of fire-resistance performance in meeting minimum life safety obligations. The aim of providing fire-resisting construction is normally to: (a)

ensure that the structure has an adequate likelihood of surviving burnout of a real fire, and/or

(b)

mitigate the spread of fire (within and beyond a building) and, by extension, manage the size of fire that the fire and rescue service may encounter.

The concept of the fire-resistance period, i.e. the dependence on time, was introduced by Simon Ingberg (Ingberg, 1928). Ingberg acknowledged that the standard time– temperature curve was not realistic and sought to make correlations between the severity of real fires and the equivalent durations in furnace conditions. These correlations were predicated crudely on energy consumption (Figure 12.2), where the fire load consumed from ignition to burnout in real fire experiments was observed, and related to corresponding periods of the standard time– temperature heating regime. Depending on the fire load density (or, in today’s terms, the purpose group), differing fire-resistance periods were proposed. These fire-resistance periods are, therefore, a crude proxy for the fire design requirements of isolated structural elements, to the extent Average occupancy curve determined on the basis of fire load and ventilation

1200

Area 1 1000 Temperature / °C

The fire-resistive principle developed momentum as proclaimed ‘fire proof ’ (largely inert) materials flooded the construction market-place in the wake of ‘great fires’ without any significant accompanying evidence regarding their actual performance in fire. The standard fire test emerged during this period as a means of assessing comparative performance of such materials and products in (what were considered to be) the most severe fires possible.

Standard time– temperature curve

800

Area 2

600 Critical temperature 400 200

Equivalent standard fire endurance time

Area 1 = area 2 0

1

2 Time / hours

3

4

Figure 12.2  Time equivalence – equal energy concept (Ingberg, 1928)

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The performance criteria are generalised and not typically representative of circumstances which reflect the failure of a building or component therein. Specifically, in the case of the load-bearing criteria, the deflection limit (span / 20) is adopted principally for the purpose of preventing damage to the furnaces used in the testing regime.

Fire resistance, structural robustness in fire and fire spread

12-3

Table 12.3  Fire-resistance rating requirements for building elements (hours) (Derived from the International Building Code (ICC, 2015).) Building element

Type I

Type II

Type III

Type IV

Type V

B

A

B

A

B

HT

A

B

Structural frame

3

2

1

0

1

0

HT

1

0

Building walls  Exterior  Interior

3 3

2 2

1 1

0 0

2 1

2 0

2 1/HT

1 1

0 0

Non-(load)bearing walls and partitions  Exterior

See Table 602 of the IBC

Non-(load)bearing walls and partitions  Interior

0

0

0

0

0

0

See Section 602.4 of the IBC

0

0

Floor construction   Including supporting beams and joists

2

2

1

0

1

0

HT

1

0

Roof construction   Including supporting beams and joists

1½

1

1

0

1

0

HT

1

0

HT = heavy timber. Further reference is made to dispensations within the IBC.

that they have an adequate likelihood of withstanding the burnout of an appropriately severe fire. The performance specification of materials, elements etc. that require fire resistance is most commonly informed by tabulated fire-resistance design guidance (typically in increments of 15 minutes) documented in prescriptive life safety guidance, e.g. Approved Document B (HM Government, 2013), NFPA 101 (NFPA, 2018a), NFPA 5000 (NFPA, 2018b), International Building Code (IBC) (ICC, 2015) etc. In the above mentioned guidance, the fire-resistance expectations for the more straightforward building situations are defined as a function of construction form, height, use and compartment size, depending on the guidance document referenced. An indicative extract from the IBC is provided in Table 12.3. The origins of fire-resistance periods, such as those shown in Table 12.3, should be a significant consideration in their adoption as: (a)

(b)

designing on the premise of fire-resistance periods would ensure an adequate likelihood of survival of a burnout of a structure and (non-combustible) enclosure similar to those observed by Ingberg, but would not necessarily be adequate for modern structures or, conversely, might be too onerous

(a)

the primary fire-resistance goal is the delivery of a building that satisfies the obligatory minimum level of performance necessary to achieve an adequate level of safety, and

(b)

the building to which the guidance is applied is simple/straightforward (or, specifically, in the case of Approved Document B, a ‘more common building situation’).

With regards to the first prerequisite, clients and developers may have a limited understanding of what strict adherence to life safety guidance delivers, which can often be detached from their goals and aspirations. For instance, such an approach may prove to be a barrier to the adoption of sustainable (and potentially combustible) materials, or it might not capture resilience ambitions, where a client wishes to protect assets or achieve a higher level of operational continuity. Regarding the second prerequisite, the prescriptive recommendations of life safety guidance inherently rely on the following precepts: (a)

The fire dynamics being adequately and conservatively represented by the standard fire curve (as introduced in section 12.2.2). The standard fire curve was developed to cater for post-flashover fire dynamics, which are typical of smaller enclosures and not necessarily applicable to large open-plan floor plates.

(b)

Limited, if any, structure and fire interaction. That is, the standard fire test was conceived to compare the ‘fire-proof ’ credentials of non-combustible materials. It was not intended, therefore, to assess the performance of combustible structural materials, such as timber. If there is the potential for the structure to form part of the fire’s fuel, e.g. due to exposed combustible elements, it would be prudent to consider the implications of this approach.

(c)

The response of the element of construction in fire being adequately and conservatively represented by the furnace conditions. In the case of structural fire resistance, this means that the structural

different types of structure designed to achieve a defined fire-resistance standard would achieve very different performances in reality.

12.4

Selecting the right solutions: prescriptive vs. performance-based design

The conventional means of specifying the required fire resistance of construction elements (i.e. tabulated prescriptive guidance) relies on two fundamental prerequisites, namely:

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A

12-4

Fire safety engineering

Ultimately, all projects seek to deliver a successful outcome, which means the delivery of solutions that are cognisant of the project obligations, goals and constraints. Achievement of this goal relies on the selection of the right engineering processes and tools necessary to yield the most appropriate solution for the given circumstances. This can only be achieved where there is an understanding of the scope and limitations of all structural fire design tools, whether that be the straightforward adoption of a prescriptive fire-resistance period or the implementation of a complex model. At the outset of a project, it is incumbent on the engineer to consider the project goals and determine whether a prescriptive solution is in keeping with these, or even relevant, given its origins and implicit limitations.

The factor of safety applied typically aims to broadly align performance-based assessments with the principles of prescriptive recommendations (i.e. it is quasi-comparative). (b)

Demonstration of performance relative to an explicit goal, typically expressed in terms of the frequency of return of the event that should be resisted or the design confidence limit (reliability) that should be achieved, e.g. the fire-resisting enclosure is designed to resist the full burnout of a fire corresponding with the 95th percentile confidence limit.

Form (a) is the basis of the process advocated when adopting the time equivalence methodology presented in BS EN 1991-1-2: 2002 (BSI, 2002a) and PD 6688-1-2: 2007 (BSI, 2007). In that guidance, design fires are assigned a factor of safety to ensure that the fire dynamics and severity are not considered without wider context, i.e. that the enclosure is part of a bigger building within which structural elements exist that are integral to the stability of the building.

12.5 Performance-based design

Form (b) is representative of the process utilised in the development of the ventilation-dependent fire-resistance period tables (tables 24 and 25) in BS 9999: 2017 (BSI, 2017). The development of these tables (Kirby et al., 2004) provides a useful example framework, relative to which other countries could develop similar concepts. The means of deriving the percentage of ‘severe’ fires (i.e. those that might lead to structural damage) that must be resisted by the building’s active and passive systems (termed ‘overall reliability’) is beyond the scope of this Guide; further guidance is available in the literature (Kirby et al., 2004; Hopkin, 2016; Hopkin et al., 2016a; Block and Kho, 2018).

12.5.1

12.5.2

In today’s environment, where buildings are increasingly complex and architecture ever more ambitious, performancebased fire-resistance assessments will be critical to the delivery of buildings that meet the functional requirements of life safety regulations.

Performance-based design in the context of fire resistance (design goals)

In offering an alternative performance-based design for elements that require fire resistance, it is first essential to consider the project goals and how they might be explicitly quantified in the form of tangible performance metrics. These goals will vary from project to project, and may constitute explicit employer requirements (likely in the context of resilience) or functional (life safety) exp­ectations. What constitutes an acceptable level of risk (and, thus, performance) varies from one jurisdiction to the next, as attitudes to the tolerable level of societal risk vary from country to country. With explicit consideration of fire resistance (specifically, the level of fire-resistance performance required of elements of construction), a performance-based assessment would typically take two forms: (a)

A deterministic quantification of the fire severity for a ‘reasonable worst case’ scenario (in terms of fire-resistance response), which is subsequently afforded a ‘safety margin’ commensurate with the consequence of failure, e.g. of magnitude governed by height, extent and occupancy characteristics.

Performance-based design in the context of fire resistance (fire conditions and benchmarking)

The key aspect of adequately quantifying the fire resistance required of elements of construction in a performance-based assessment (other than having a clear goal) is the definition of credible design fires on which product specification can be based. In the selection of the fire dynamics model(s) which will underpin the assessment, the designer must be cognisant of the limitations and inherent assumptions of the different options, as outlined below: ——

A post-flashover model, such as the parametric fire method outlined in EN 1991-1-2, is predicated on the assumption that: (a)

ventilation conditions exist, which are able to support the near simultaneous combustion of all fuel within the fire enclosure, and

(b)

a uniform/homogenous temperature can be expected throughout the full volume of the fire enclosure (this assumption, in particular, is unlikely to hold true in large modern open-plan buildings).

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response of a building subject to fire is adequately represented by the behaviour of isolated elements and that all failure modes of the system are captured within the limitations of the standard test. For more complex structural arrangements and/or unconventional materials, this may not be the case.

Fire resistance, structural robustness in fire and fire spread

12-5

Localised fire models, such as that proposed by Hasemi et al. (1995), are valid within certain heat release rate ranges. The inherent assumption is that the fire will not spread beyond the items first ignited. Therefore, this must be verified as part of the design process.

Standards and Technology (NIST) expert panels and Structural Engineering Institute (SEI) standards committees, is now available to designers via ASCE/SEI 7 (ASCE, 2017a). The ASCE approach seeks to bifurcate fire resistance and structural fire engineering as two discrete entities, allowing the designer to use two options:

——

A travelling fire method (tfm), such as those proposed by Stern-Gottfried and Rein (2012), Hopkin (2013) and Rackauskaite et al. (2015), relies on the quantification of key metrics regarding:

——

Option 1 is a standard fire-resistance design based on the building code; this is the traditional indexing system that refers to a single structural element in a furnace test and periods of fire resistance of between 1 hour and 4 hours.

(a)

the rate at which fires spread

——

(b)

the direction in which they travel

(c)

the time taken for fuel packages to be consumed

(d)

the temperature of the burning region (near field) relative to the far field.

Option 2 is a structural fire engineering approach that follows ASCE/SEI 7 Appendix E. It addresses performance objectives, thermal response and structural response. It proposes risk categories ranging from ‘global collapse permissible’ to ‘local or global collapse not permissible’, also referred to as ‘complete burnout’.

Regardless of the fire dynamics model adopted, it must be accepted that all inputs will invariably feature a degree of uncertainty and this must be addressed by some means. One approach would be by way of a sensitivity study or a broader sampling-based methodology, such as Monte Carlo analysis. The Institution of Fire Engineers (IFE) provides guidance on the application of modelling-based tools, via a process flowchart (Jowsey et al., 2013), which outlines the different types of sensitivity study that should be considered in different circumstances. The interaction of active suppression with enclosure fire dynamics is another important, albeit complex, consideration. Different approaches are advocated around the world, such as: ——

altering the design goal to reflect the probability of a severe fire developing being significantly reduced where sprinklers are installed (Law et al., 2015)

——

reducing the fire load density by a statistical factor, as is advocated in BS EN 1991-1-2 and PD 6688-1-2.

The fire resistance of products, systems and elements is defined according to the standard testing process. This has been the case for over a century and is likely to remain unchanged for many years to come. Therefore, it is often necessary to provide a direct link between performancebased (natural fire) assessments and fire-resistance ratings for the purpose of defining what materials or products are appropriate for achieving a given design solution. Commonly, the time equivalence concept is applied for this purpose, with specific guidance available in BS EN 19911-2 and PD 6688-1-2. This concept stems from the early principles proposed by Simon Ingberg, discussed previously (see Figure 12.2).

12.6

US approach to structural fire engineering

A new US approach to structural fire engineering, based on collaboration with the Society of Fire Protection Engineers (SFPE) standards committees, National Institute of

The ASCE/SEI Fire Protection Committee is currently developing a companion design guideline entitled ASCE/ SEI Guideline: Structural Fire Engineering (ASCE, 2017b). This guideline will provide recommendations and design examples. A summary article has been published by La Malva (2018).

12.7

Structural design for fire safety

A key element of successful fire engineering input is the development of solutions that ensure structures have an adequate likelihood of withstanding the burnout of a real fire. This typically means ensuring that principal load-bearing elements of structures are afforded fire resistance (or protection). In deriving what level of fire performance is acceptable, how it should be achieved and how protection/resistance provisions are apportioned, a logical process must be followed. Numerous design guides and textbooks focus on the topic of material behaviour in fire and structural fire engineering (or structural design for fire safety). It is not the intention of this chapter to reproduce this content. However, a logical structure is set out in Table 12.4, which may inform the design process and provides references where further guidance can be sought.

12.8 Compartmentation Compartmentation is the division of a building into fireresisting compartments, comprising one or more rooms, spaces or storeys, by elements of construction designed to contain a fire for a predetermined duration (FPA, 2008). It is a fire safety measure that can be used to gain time – the fire being contained while occupants have a chance to escape or take refuge until it can be extinguished (Stollard and Abrahams, 1999). Compartmentation also offers the chance of containing the fire to protect, at least, the rest of the property while the fire is extinguished. It can contribute to business continuity by limiting the extent of damage and benefiting post-fire recovery.

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——

12-6

Fire safety engineering

Table 12.4  Domain-based guidance – structural design for fire safety Component

Guidance / references

Goal-setting

Prescriptive

It is implicit that the building is simple and that the project goals pertain only to life safety. In such a case, the fire resistance recommendations of the prescriptive guidance are appropriate.

Performance based

The building is unusual or complex, or prescriptive design is sub-optimal. The level of appropriate life safety performance may be informed by PD 6688-1-2 (BSI, 2007), Kirby et al. (2004) or similar sources (Hopkin, 2016). The functional goals should be informed by the qualitative design review (qdr) process, following protocols set out in documents such as PD 7974-0: 2002 (BSI, 2002b) and PD 7974-8: 2012 (BSI, 2012b).

Design fires/fire dynamics

Localised fires

The fire may not spread beyond the items first ignited. Design fire guidance can be found in Mayfield and Hopkin (2011), PD 7974-1: 2003 (BSI, 2003), the SFPE Handbook (SFPE, 2016) or the wider literature.

Post-flashover fires

The enclosure is relatively small (<500 m2) and therefore flashover can be assumed to be possible. Hand calculation methods may be adopted, such as the Eurocode parametric fire (BSI, 2002a). Alternatively, single-zone models may be appropriate where ventilation conditions warrant further consideration. Commonly adopted tools include cfast (Peacock et al., 2016) and b-risk (Wade et al., 2013).

Travelling fires

Travelling fires are often considered appropriate where enclosures are of a scale such that a fully developed fire is likely, although flashover is unlikely. A typical application might be an open-plan office exceeding 500 m2 in floor area. Calculation methods are available in the literature, such as those proposed by Stern-Gottfried and Rein (2012), Hopkin (2013) and Rackauskaite et al. (2015).

Heat transfer to structural elements

General

Classical heat transfer, i.e. radiation, convection and conduction, is covered in many textbooks, including those that specifically target structural fire engineering (Drysdale, 2011; Buchanan, 2017; Quintiere, 2006). Finite element analysis (fea) is commonly adopted for complex heat transfer problems. Commercial tools are available that have been validated for structural fire engineering applications (Franssen and Gernay, 2016; Manie, 2016; Dassault Systèmes Simulia Corp., 2014; ANSYS Inc., 2013).

Steel

Steel has a very high conductivity. Therefore, lumped capacitance methods are often appropriate, whereby the structural element can be assumed to have a uniform temperature. Calculation methods can be found in BS EN 1993-1-2: 2005 (BSI, 2005) for unprotected and protected steel structures. Specialised guidance has been published by the Steel Construction Institute (SCI) (Law and O’Brien, 1981) for the purpose of appraising structures outside the compartment of fire origin. BS EN 1993-1-2 provides thermo-physical properties for application in finite element models (or other similar numerical models).

Concrete

Temperature profiles within standard-sized sections subject to ISO 834 (ISO, 1999) exposure are published in BS EN 1992-1-2: 2004 (BSI, 2004a). These are appropriate for simple element-based assessments. BS EN 1992-1-2 provides thermo-physical properties for application in finite element models (or other similar numerical models).

Timber

Under ISO 834 heating conditions, charring rates are utilised as a proxy for explicit heat transfer calculations. Typical one-dimensional values noted in BS EN 1995-1-2: 2004 (BSI, 2004b) are 0.5 and 0.65 mm/min for high-density hardwood and typical density softwood, respectively. BS EN 1995-1-2 provides thermo-physical properties for application in finite element models (or other similar numerical models). However, these are limited to ISO 834 exposure. Many challenges exist where wooden structures are either exposed by design or have the potential to become exposed during a real fire condition. A discussion is provided in Hopkin et al. (2016b).

Structural response and solutions

Structural analysis and performance criteria

Basic hand calculations are appropriate for verification purposes and the assessment of single elements or sub-frames. Guidance is available in textbooks (Buchanan, 2017; Cobb, 2014). The BRE/Bailey method (Newman et al., 2000) is a commonly adopted process for optimising passive fire protection to steel elements within composite assemblies.

Continued

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Domain

Fire resistance, structural robustness in fire and fire spread

12-7

Table 12.4  continued Domain

Component

Guidance / references

Concrete structures

Concrete structures typically achieve fire resistance inherently, through a combination of element sizing and cover to reinforcement. Tabulated solutions for ISO 834 exposure are offered in BS EN 1992-1-2 for beams, columns, floors and walls. In addition, layers of calculation methods exist for quantification of performance under different heating conditions (Buchanan, 2017; Wickström, 1986, 2016). The methods culminate in numerical modelling, where temperaturedependent material properties are provided.

Steel structures

Steel structures typically achieve fire resistance by way of applied fire protection. Commonly applied systems are referenced in the Association for Specialist Fire Protection (ASFP) ‘Yellow Book’ (ASFP, 2014). Depending on the element utilisation (i.e. how hard it is working relative to its capacity) different element temperatures are tolerable, with protection specified to ensure that these are not exceeded within the design fire-resistance period (or, where relevant, design fire). Calculation methods for beams and columns are provided in BS EN 1993-1-2. Temperature-dependent material properties are also provided for more advanced numerical simulations.

Timber structures

Commonly, timber structures are designed on an elemental basis. Charring rates are adopted to assess the residual cross-section at the end of the fire-resistance period. Where encapsulation is provided (e.g. plasterboard), its contribution can also be considered. The residual cross-section must be sufficient to support the applied loads in the fire condition. Calculation methods are provided in BS EN 1995-1-2. Since the publication of Eurocode 5 in 2004, a number of technological advances have emerged, such as cross-laminated timber. Therefore, more contemporary guidance exists, in the form of Fire Safety in Timber Buildings (SP Trätek, 2010).

Often, facilities are required within buildings to assist the fire and rescue service in carrying out their firefighting or rescue operations as efficiently as possible. In complex buildings, or high-rise buildings, fire service personnel should not only be provided with good access and water supplies, but also safe bridgeheads from which to work. Such bridgeheads might be linked to specially protected lifts and wet or dry rising water mains. This will enable fire and rescue service personnel to attack the fire earlier without the need to lay out hose. Such ‘vertical compartments’ provide many benefits to firefighting operations and these facilities should be considered as part of the fire compartmentation strategy. Refer to chapter 13 for more details regarding firefighting operations. For compartmentation to be effective, the enclosing boundaries, such as walls and floors, must be able to resist the spread of fire. This requires that: ——

all enclosing surfaces must have an appropriate level of fire resistance

——

all junctions of constructional elements are effectively sealed to maintain the fire resistance at the junction

——

the stability of the structure supporting the fireresisting boundary must be maintained for the required period.

Figure 12.3 details examples of penetrations (for services, etc.) through fire-separating elements, and example fire-stopping and sealing measures are described in the following section.

12.9

Concealed spaces and fire stopping

Guidance on fire stopping, fire-resisting walls and floors, and the protection of services passing through compartment boundaries is contained in national codes, such as Approved Document B (HM Government, 2013) in England. The alternative standards commonly used throughout the world are the National Fire Protection Association (NFPA) standards: NFPA 101 and 5000 (NFPA, 2018a and 2018b, respectively).

——

all holes are fire stopped

——

ducts penetrating fire-resisting boundary elements are provided with fire dampers or are also fire resisting, and other penetrations through which fire might spread (e.g. cables) are suitably protected

Fire dampers and fire-resisting shutters are usually actuated by fusible links. It should be noted that this method of actuation is effective at controlling fire spread only and not the spread of smoke. Large quantities of smoke can pass through an opening protected by a fire damper or shutter during the early stages of a fire before a fusible link-actuated mechanism will operate. To control such smoke transfer, smoke detector-operated smoke/fire dampers are used.

——

openings are protected by self-closing fire doors or fire-resisting shutters/curtains

Generic types of fire stopping and fire sealing systems include the following:

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Alternatively (and commonly) partial frame or full-frame finite element analyses are undertaken (Frassen and Gernay, 2016; Manie, 2016; Dassault Systèmes Simulia Corp., 2014; ANSYS Inc., 2013).

12-8

Fire safety engineering

Horizontal duct penetration

Horizontal multiple penetration

Sealing of blank opening

Horizontal cable tray penetration

Cable penetration

Vertical duct penetration

Multiple penetration (vertical and horizontal) Temporary multiple horizontal penetration

Vertical pipe penetration

Movement joint Figure 12.3  Typical applications for firestopping systems (adapted from ASFP, 2004)

——

——

Coated stone wool batts or boards: These can be used to fire stop penetrations through compartment walls and floors and allow additional services to be readily installed as required. In certain circumstances, a structural support for the seal will be required. Sealant/mastic coatings: Available as single or multipack systems comprising organic, inorganic or intumescent fillers, pre-dispersed in a suitable binder (i.e. acrylic, polysulphide, silicone etc.). The materials have a high viscosity and are dispensed by gun or trowelled into the opening and between penetrating services. They are suitable for penetration seals (coated batts/boards) in all forms of fire-resistant construction, particularly where openings are small, where penetrations are complex and where there is an imperfect fit between building elements or linear joints.

——

Mortars: Generally a gypsum- or cementitious-based powder blended with inorganic lightweight fillers, composite reinforcement and chemical modifiers. The compounds are designed to be mixed with water and placed around and between penetrating services, forming a rigid seal. The systems can be used to fire stop penetrations through concrete and masonry compartment wall and floor constructions.

——

Preformed elastomeric seals: These are made from elastomeric foam, sometimes with reinforcing sheets on either side. The foam and/or the reinforcing sheets may be intumescent. These products are

usually supplied in strip form and generally used to seal the gap at a movement joint between two building elements, such as between a floor and a wall. ——

Bags/pillows: Available in various sizes and shapes, these are specified for use in temporary or permanent fire stopping situations where services, such as cables, pass through walls and floors. Since they are easily removed, they are particularly suited to areas where services are frequently rerouted. They can also provide temporary protection during construction work. Bags or pillows are made from special fabrics and enclose a filling material which often incorporates an intumescent material.

——

Pipe closures: These are designed to preserve the integrity of a fire-rated compartment where various plastic pipes or plastic trunking pass through floors or walls. Unlike metal or cable service penetrations, plastic pipes and plastic trunking soften and collapse under raised temperature, therefore some means of preventing the passage of hot gases and smoke is required. This is achieved by strangling the cross-section of the pipe or trunking. There are variations in the design of pipe closures but the two principal methods are pipe collars and pipe wraps. Both systems confine an intumescent compound, which expands on exposure to fire, rapidly exerting pressure on the pipe. The plastic walls of the pipe, which will have softened due to the heat, collapse under this pressure, creating a constriction. Some pipe closures incorporate a mechanical device, which may or may not include

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Horizontal pipe penetration

Fire resistance, structural robustness in fire and fire spread

——

——

Plugs/blocks: These are available in a variety of shapes and sizes. They are generally supplied as rectangular blocks for rectangular penetrations or as cylindrical or conical blocks for circular penetrations. Pre-formed trapezoidal plugs/blocks are available for sealing openings below profiled metal decking. Plugs and blocks are formed from materials such as bonded vermiculite, mineral wool, gypsum or cementitious materials, polyurethane, modified rubber etc. They can be either rigid or flexible. Some fire-stopping plugs/blocks are inherently fire resistant, some rely on an intumescent coating and some are manufactured using intumescent materials. Cavity barriers: These are provided to close a concealed space against penetration of smoke or flame. In most applications they would be expected to have fire resistance of 30 minutes’ integrity and 15 minutes’ insulation. Small cavity barriers are used in small, narrow cavities between layers of construction. Products used in larger spaces above ceilings will require particular fixing systems and/ or support systems and are used to divide a large space into maximum dimensions, as specified by national regulations.

In order to ensure that the correct type of fire stopping is specified and/or installed, there are a number of key questions that still need to be answered before the final selection can be made. These key questions are listed below: (a)

Is the fire stopping to be used in a wall or a floor, or a junction between fire-separating elements, and what type of materials are used to form each element?

(b)

What fire resistance is required?

(c)

How big is the gap or opening?

(d)

Does the fire stopping have to cater for movement in the fire-separating element?

(e)

What type of services, if any, are penetrating the construction at the opening?

(f)

How many services are there?

(g)

What size is each service?

(h)

How close are the services to each other?

(i)

How close are the services to the edge of the opening?

(j)

Is the fire-stopping system suitable for use with the intended elements of construction?

In all cases, when a particular system is selected, the manufacturer of the fire-resisting system should be

contacted for specific advice and installation instructions for details of the permitted field of application of that fire-resisting system.

12.10 Dampers Despite many years of use, there is little recognised guidance for installing fire and smoke damper units when used for providing fire-resisting compartments and separation. The Association for Specialist Fire Protection publishes a guide to assist those involved in the manufacture, specification, installation, inspection and verification of fireresisting dampers installed in heating, ventilation and air conditioning (hvac) ductwork systems, known as the ‘Grey Book’ (ASFP, 2011). Types of fire dampers include the following: ——

Curtain fire dampers: These are constructed of a series of interlocking blades, which fold to the top of the assembly permitting the maximum free area in the airway. The blades are held open by means of a thermal release mechanism, normally rated at 72 °C ± 4 °C. The blades fall or are sprung to fill the airway to prevent the passage of the fire.

——

Intumescent fire dampers: These expand by intumescent activity under the action of heat to close the airway in order to prevent the passage of fire. The intumescent materials form the main component for fire integrity. In some instances this may be supported by a mechanical device to prevent cold smoke leakage. The type of intumescent material selected will influence activation temperatures and these temperatures typically range from 120 °C to 270 °C.

——

Multi-blade fire dampers: These are constructed with a number of linked pivoting blades contained within a frame. The blades are released from their open position by means of a thermal release mechanism, normally rated at 72 °C ± 4 °C. When the release mechanism is activated, the blades pivot and move to close the airway to prevent the passage of fire.

——

Single-blade fire dampers: These are constructed with a single pivoting blade within a frame. The blade is released from its open position by means of a thermal release mechanism, normally rated at 72 °C ± 4 °C. When the release mechanism is activated the blade pivots and moves to close the airway to prevent the passage of fire.

——

Multi-section dampers: Where the duct exceeds the maximum tested size of an individual damper (or single section), manufacturers may provide multi-section units. These will generally be supplied with some type of joining strip or mullion to allow the unit to be assembled on site.

——

Smoke control damper: These are single or multiblade dampers that generally have two positions: ‘open’ to allow smoke extraction or ‘closed’ to maintain the fire compartment. They do not have a thermal release mechanism, relying instead on a ‘powered’ control system to ensure that they achieve the correct position.

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an intumescent compound. Pipe collars incorporate a rigid outer casing, which acts as a restraint for the intumescent material, enabling the collar to be either surface fixed to the separating element or incorporated within it. Pipe collars may be incorporated into appropriately designed fire-resisting drainage gullies. Pipe wraps have no casing and must therefore be located within the separating element, which acts as a restraint for the intumescent material.

12-9

12-10

Fire safety engineering

Regardless of the type of fire-separating element in which the damper is to be mounted, there are only three main design criteria to be met, namely: that the damper should be fixed either within or directly adjacent to the fire barrier and be supported independently of the connecting ductwork, i.e. if the ductwork were to be removed from both sides of the damper it would continue to be an integral member of the barrier it protects

(b)

that the damper is installed in accordance with the manufacturer’s recommended tested method

(c)

that the installation meets or exceeds its design specification, especially with regard to its fire rating.

It is common for the UK industry to refer to ‘E’ classified products as ‘fire dampers’ and ‘ES’ classified products as ‘fire and smoke dampers’. ES classified dampers are fire dampers tested to BS EN 1366-2: 2015 (BSI, 2015) that meet the ‘ES’ classification requirements of BS EN 13501-3 (BSI, 2009), and achieve the same fire resistance in relation to integrity as the fire-separating element through which the duct/damper passes. Traditionally, ductwork passing through protected escape routes needed to be enclosed with imperforate fire-resisting construction to prevent the spread of smoke to the escape routes. Developments in damper technology and testing methods have enabled the use of ES leakage classified dampers, which are capable of reducing smoke leakage to a minimum. Typically, when protecting means of escape, there are two options in relation to damper provision: (a)

(b)

the ventilation ducting located within the protected escape routes is enclosed in 30-minute fire-resisting construction in terms of integrity and insulation, or ES classified fire dampers are provided to ventilation ducts where these penetrate the fire-resisting enclosure to the escape route, and, where fire dampers are used instead of a fire-resisting enclosure to ductwork, the fire damper should achieve an ES classification of 60 minutes, as described in BS EN 13501-3 and be successfully tested to BS EN 1366-2.

Fire dampers fitted only with fusible links are not suitable for protecting escape routes and the fire damper must close under the control of a smoke alarm.

12.11

Quality of specification, installation and maintenance

There is a very large range of products available for the provision of fire protection. Unless the chosen product is also third-party certified by a test body, it cannot necessarily be assumed that no changes to the basic product have occurred. Any changes in specification can affect the product’s performance under fire conditions. The certification process for a product involves rigorous testing, assessment and review of the design and specification of the product, coupled with regular audits of the quality procedures governing the factory production process and repeat testing, to ensure that they meet quality standards. By way of

It is important when a compartment wall or floor and separating wall are made up of a number of different elements (for example, partition-door glazing, penetration seals etc.) that a check is made to ensure that the fire resistance will be maintained. This may mean more testing, or that a detailed assessment needs to be carried out by a competent person. It is a common failing that the fire-separating elements are not properly installed or maintained, or even considered. Frequently encountered problems include large holes through fire-separating elements which are not fire stopped, the use of inappropriate materials for firestopping purposes, incorrectly installed fire-stopping systems such as collars or dampers, missing sections of wall between false ceilings and the structural soffit, and poorly maintained fire-resisting door sets. The problems broadly fall into four groups (Wilkinson, 2008): (a)

removal of substrate to allow passage of services, leaving excessive penetrations

(b)

fire stopping that is incorrectly installed

(c)

a lack of thought given to fire compartmentation at the time of construction

(d)

wear and tear rendering fire compartmentation provision ineffective.

It is critical that all elements of fire compartmentation, fire protection and fire separation are considered in the design, construction and in-use management of a building.

References ANSYS Inc. (2013) ANSYS Mechanical Users Guide Release 15.0 (Canonsburg, PA: ANSYS Inc.) ASCE (2017a) ASCE/SEI 7-16 Minimum design loads for buildings and other structures. Appendix E Performance-based design procedures for fire effects on structures (Reston, VA: American Society of Civil Engineers) ASCE (2017b) ASCE/SEI Guideline: Structural Fire Engineering (Reston, VA: American Society of Civil Engineers) ASFP (2004) ‘Red Book’ – Fire Stopping and Penetration Seals for the Construction Industry (Bordon, Hants: Association for Specialist Fire Protection) ASFP (2011) ‘Grey Book’ – Fire and Smoke Resisting Dampers (Bordon, Hants: Association for Specialist Fire Protection) ASFP (2014) ‘Yellow Book’ – Fire Protection for Structural Steel in Buildings (Bordon, Hants: Association for Specialist Fire Protection) ASTM (2015) ASTM E119-15 Standard test methods for fire tests of building construction and materials (West Conshohocken, PA: ASTM International)

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(a)

an example, in order to meet market demands for certification schemes on the fire performance of compartmentation products, BRE Global provides schemes such as LPS 1208: Fire resistance requirements for elements of construction used to provide compartmentation (LPCB, 2014). This scheme tests the performance requirements for walls, cavity barriers, floors and roofs, and defines the methods of test (based on the standard fire-resistance tests discussed above) necessary to satisfy the fire-resistance requirements for compartmentation given in loss prevention guidance, such as the Fire Protection Association’s publication, The LPC Design Guide for the Fire Protection of Buildings (FPA, 1999).

Fire resistance, structural robustness in fire and fire spread Block F and Kho TS (2018) ‘Determining the fire resistance rating of buildings using the probabilistic method – a state-of-the-art approach’ The Structural Engineer 96 (1)

BSI (2002a) BS EN 1991-1-2: 2002 Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire (London: British Standards Institution) BSI (2002b) PD 7974-0: 2002 Application of fire safety engineering principles to the design of buildings. Guide to design framework and fire safety engineering procedures (London: British Standards Institution) (Note: PD 7974-0: 2002 has been replaced by BS 7974: 2019) BSI (2003) PD 7974-1: 2003 Application of fire safety engineering principles to the design of buildings. Initiation and development of fire within the enclosure of origin (Sub-system 1) (London: British Standards Institution) (Note: PD 7974-1: 2003 has been replaced by PD 7974-1: 2019) BSI (2004a) BS EN 1992-1-2: 2004 Eurocode 2. Design of concrete structures. General rules. Structural fire design (London: British Standards Institution) BSI (2004b) BS EN 1995-1-2: 2004 Eurocode 5. Design of timber structures. General. Structural fire design (London: British Standards Institution) BSI (2005) BS EN 1993-1-2: 2005 Eurocode 3. Design of steel structures. General rules. Structural fire design (London: British Standards Institution) BSI (2007) PD 6688-1-2: 2007 Background paper to the UK National Annex to BS EN 1991-1-2 (London: British Standards Institution) BSI (2009) BS EN 13501-3: 2005+A1: 2009 Fire classification of construction products and building elements. Classification using data from fire resistance tests on products and elements used in building service installations. Fire resisting ducts and dampers (London: British Standards Institution) BSI (2012a) BS EN 1363-1: 2012 Fire resistance tests. General requirements (London: British Standards Institution) BSI (2012b) PD 7974-8: 2012 Application of fire safety engineering principles to the design of buildings. Property protection, business and mission continuity, and resilience (London: British Standards Institution) BSI (2015) BS EN 1366-2: 2015 Fire resistance tests for service installations. Fire dampers (London: British Standards Institution) BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution) Buchanan AH (2017) Structural Design for Fire Safety (2nd edition) (Chichester: Wiley) Cobb F (2014) Structural Engineer’s Pocket Book (Boca Raton, FL: CRC Press) Dassault Systèmes Simulia Corp. (2014) Abaqus Analysis Users Guide Version 6.14 (Providence, RI: Dassault Systèmes Simulia Corp.) Drysdale D (2011) An Introduction to Fire Dynamics (3rd edition) (Chichester, UK: Wiley) FPA (1999) The LPC Design Guide for the Fire Protection of Buildings (London: Fire Protection Association) FPA (2008) FPA Design Guide for the Fire Protection of Buildings: Compartmentation (Moreton in Marsh, Gloucestershire: Fire Protection Association) Franssen JM and Gernay T (2016) Users Manual for SAFIR 2016c: A computer program for analysis of structures subjected to fire (Liège: University of Liège) Gales J, Maluk C and Bisby L (2012) ‘Structural fire testing — Where are we, how did we get here, and where are we going’ in Proceedings of the 15th International Conference on Experimental Mechanics (ICEM) (Portugal: Faculty of Engineering, University of Porto)

Hasemi S, Yokobayashi T, Wakamatsu and Ptchelintsev A. (1995) ‘Fire safety of building components exposed to a localized fire’ AsiaFlam ’95 Proceedings of the First Asia-Flam Conference, Hong Kong (London: Interscience) HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) Hopkin DJ (2013) ‘Testing the single zone structural fire design hypothesis’ Interflam 2013 Proceedings of the 13th International Conference, Royal Holloway College, University of London Hopkin D (2016) ‘A review of fire resistance expectations for high-rise UK apartment buildings’ Fire Technology 53 (1) 87–106 Hopkin D, O’Loughlin E, Kotsovinos P and Bisby L (2014) ‘Fire resistance: Prescriptive guidance as a panacea?’ The Building Engineer (Dec) 20–22 Hopkin D, Ballantyne A, O’Loughlin E and McColl B (2016a) ‘Design goals – Fire resistance demands for tall residential buildings’ Interflam 2016 Proceedings of the 14th International Conference, Royal Holloway College, University of London Hopkin D, Schmid J and Friquin KL (2016b) ‘Timber structures subject to non-Standard fire exposure — Advances and challenges’ in World Conference on Timber Engineering 2016, Vienna. DOI 10.13140/ RG.2.2.22877.82406 ICC (2015) International Building Code 2015 (Washington, DC: International Code Council) Ingberg S (1928) ‘Tests of the severity of building fires’ NFPA Quarterly 22 43–61 ISO (1999) ISO 834-1 Fire-resistance tests. Elements of building construction. General requirements (Geneva: International Organization for Standardization) Jowsey A et al. (2013) ‘Interactive fire modelling process flowchart’ International Fire Professional 5 (July) 16–17 Kirby BR, Newman GM, Butterworth N, Pagan J and English C (2004) ‘A new approach to specifying fire resistance periods’ Structural Engineer 82 (19) 34–37 La Malva K (2018) ‘Developments in structural fire protection design – a US perspective’ The Structural Engineer 96 (1) Law M and O’Brien T (1981) Fire Safety of Bare External Structural Steel (London: Constructional Steel Research and Development Organization) Law A, Butterworth N and Stern-Gottfried J (2015) ‘A risk based framework for time equivalence and fire resistance’, Fire Technology 51 (4) 771–784 LPCB (Loss Prevention Certification Board) (2014) LPS 1208: Issue 2.2 LPCB fire resistance requirements for elements of construction used to provide compartmentation (Watford: BRE Global) Manie J (2016) DIANA Finite Element Analysis: User manual release 10.1 (Delft: DIANA FEA BV) Mayfield C and Hopkin D (2011) Design Fires for Use in Fire Safety Engineering (Garston, Watford: IHS BRE Press) Newman G, Robinson J and Bailey C (2000) SCI-P288: Fire Safe Design: A new approach to multi-storey steel framed buildings (Ascot: Steel Construction Institute) NFPA (2018a) NFPA 101 Life Safety Code (Quincy, MA: National Fire Protection Association) NFPA (2018b) NFPA 5000 Building Construction and Safety Code (Quincy, MA: National Fire Protection Association) O’Loughlin E and Hopkin D (2016) ‘Putting up resistance’ RICS Building Control Journal (Nov/Dec) 16–17

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BSI (1987) BS 476-20: 1987 Fire tests on building materials and structures. Method for determination of the fire resistance of elements of construction (general principles) (London: British Standards Institution)

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12-12 Peacock R, Jones W, Bukowski R and Forney G (2016) CFAST: Consolidated Fire and Transport (version 7): Technical reference guide (Gaithersburg, MD: National Institute of Standards and Technology)

Fire safety engineering Stern-Gottfried J and Rein G (2012) ‘Travelling fires for structural design — Part II: Design methodology’ Fire Safety Journal 54 96–112 Stollard P and Abrahams J (1999) Fire From First Principles: A design guide to building fire safety (3rd edition) (London: Spon)

Rackauskaite E, Hamel C, Law A and Rein G (2015) ‘Improved formulation of travelling fires and application to concrete and steel structures’ Structures 3 (Aug) 250–260

Wade C, Baker G, Frank K, Robbins A, Harrison R, Spearpoint M and Fleischmann C (2013) BRANZ Study Report No. 282: B-RISK User guide and technical manual (Porirua: BRANZ Ltd)

SA (2014) AS 1530 Part 4: 2014 Methods for fire tests on building materials, components and structures. Fire-resistance tests for elements of construction (Canberra: Standards Australia)

Wickström U (1986) ‘A very simple method for estimating temperature in fire exposed concrete structures’ in New Technology to Reduce Fire Losses and Costs (New York: Elsevier)

SCC (2014) CAN/ULC-S101-14 Standard methods of fire endurance tests of building construction and materials (Ottawa: Standards Council of Canada) SFPE (2016) SFPE Handbook of Fire Protection Engineering (5th edition) (Boston, MA: Society of Fire Protection Engineers; Quincy, MA: National Fire Protection Association)

Wickström U (2016) ‘Methods for predicting temperatures in fireexposed structures’ in SFPE (2016) SFPE Handbook of Fire Protection Engineering (5th edition) (Boston, MA: Society of Fire Protection Engineers; Quincy, MA: National Fire Protection Association), pp. 1102–1130

SP Trätek (Technical Research Institute of Sweden) (2010) SP Report 2010:19 Fire Safety in Timber Building: Technical guideline for Europe (Stockholm, Sweden: SP Trätek)

Wilkinson P (2008) ‘Fire safety in hospitals: Fire compartmentation’ Fire Safety, Technology & Management; incorporating the Journal of the Fire Service College 10 (1) 15–18

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Quintiere JG (2006) Fundamentals of Fire Phenomena (Chichester: Wiley)

13-1

13

Firefighting

While the risk and consequences of fire in the built environment can be reduced to as low as reasonably practicable through good design and management, it is nearly always impossible to fully remove the potential for a fire incident to occur. Therefore, regardless of whether a building has been designed to prescriptive codes or has adopted a performance-based fire engineering approach, it is always important to ensure that adequate measures for firefighting and to facilitate fire and rescue service access around and within a building are provided, appropriate to the use, size and occupancy of the building in question, to fulfil life safety objectives. Depending upon the project, firefighting facilities and access may also form a critical part of the property protection and/or environmental protection strategies. Although prescriptive design codes often provide a good benchmark for the design and implementation of firefighting measures, the origins and relevance of some of the criteria contained in such guidance can appear vague, and sometimes outdated in the context of modern building design and current fire and rescue service operational practices and technologies. Therefore, there is potential scope for fire engineering to be applied, where appropriate, to develop project-specific firefighting access strategies that take into account the bespoke nature of a scheme yet still deliver robust and safe access facilities for the fire and rescue service. However, it is important to remain aware that any application of fire engineering to fire and rescue service access must remain cognisant of the needs, requirements and potential limitations of the local fire and rescue service, both in terms of their equipment and their personnel. This chapter primarily aims to provide an overview of the relevant factors that fire and building services engineers (along with other relevant stakeholders) may need to consider when developing and implementing a firefighting access strategy. It will focus mainly on the operational firefighting tactics, procedures and equipment needs of the fire and rescue service, identifying key areas that may need to be considered when determining the level of provision for a particular design scheme. Additional commentary is also provided in relation to equipment provided for firefighting for use by occupiers of a building, such as fire extinguishers, but in reality the scope to use such measures to justify a fire engineered design is very limited. While this chapter has attempted to capture relevant themes and requirements for potential international application, references to firefighting procedures and expectations from the UK have been used to provide context.

13.2

The fire and rescue service as a stakeholder

As detailed in chapter 4 of this Guide, and in other recognised codes of practice, such as PD 7974-0: 2002 (BSI, 2002) or the International Fire Engineering Guidelines (NRC et al., 2005), the development of successful fire engineered design schemes often relies upon accounting for the needs of the various stakeholders involved (perhaps as part of a formal qualitative design review (qdr) process). With regard to incorporating firefighting provisions into a scheme, the local fire and rescue service are therefore a crucial stakeholder, both in terms of advising on their requirements during the design (and possibly construction) phases, as well as ongoing liaison with the management of the building or site once in use, to ensure that operational preplanning information is collected and that any fire safety legislative matters are addressed. The fire and rescue service are one of the only stakeholders present that potentially could be involved in a project across its lifetime, from inception all the way through to occupation and beyond. Although different fire and rescue services will often adopt similar approaches to firefighting, they can have different operational procedures, resources, equipment and requirements depending upon geographical location, both in the national and international contexts. If a building fire strategy refers to the design guidance contained in prescriptive codes of practice relevant to the geographical location in question, then in broad terms most local fire and rescue service requirements will be met. However, where fire engineering is being applied and has an impact on fire and rescue service access and operational firefighting, then more specific attention will need to be given by the fire engineer and wider design team to the needs of the local fire and rescue service; this will usually require early consultation with the fire and rescue service (i.e. as a stakeholder), potentially at different times during the design process, to make sure that adequate facilities and provisions can be included in the design scheme as soon as possible. It should be noted that such consultations may need to involve people at different organisational levels within the local fire and rescue service; usually initial discussions are had with personnel who are specialists in fire safety or fire engineering, but this could go on to include others who advise on water supplies, communications or operational fire crews. While this chapter identifies areas where there may be potential flexibility in approaches to firefighting and fire and rescue service access in certain scenarios, what is important for the fire engineer and project team to remember is that the fire strategy should not dictate to the local fire and rescue service assumed procedures or arrangements that are impractical for the local fire and rescue

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13.1 Introduction

13-2

Fire safety engineering

13.3

13.3.1

Firefighting by the fire and rescue service: general principles Key considerations

Firefighters face a huge range of potential hazards and risks as part of the work they do, and the modern built environment (and the pace at which it is evolving) poses many challenges. Fire and rescue services may be called upon to respond to a wide variety of operational incidents, which could include fire, explosions, flooding, road traffic collisions, structural collapse and chemical, radiation and biological hazards. This chapter focuses on the provision of measures that can be incorporated into a building’s design to assist with the emergency response to fire incidents, under typical fire safety-related legislation. There may be a need for some higher risk sites, buildings and facilities to consider other types of emergency incident and/or the provision of enhanced fire and rescue service access and firefighting provisions where additional legislative requirements exist (for example, additional measures may be required for a UK site where the Control of Major Accident Hazards Regulations 2015 (comah) are applicable). The activity of firefighting by fire and rescue service personnel is covered by legislative requirements, including those to ensure the health and safety of those undertaking the activity. This is a fundamental principle that needs to be acknowledged; firefighters and their equipment have limitations (see section 13.4). This has, in modern times, increased the need for firefighters to complete dynamic risk assessments when attending an incident to ensure that safe systems of work can be implemented. Those designing for fire and rescue service access and provisions outside prescriptive guidance need to remain cognisant of this to avoid proposing arrangements for a building that are impractical for use and/or place unreasonable and unrealistic demands on firefighters. When dealing with fires in buildings, there are four broad areas that can heavily influence the response and actions of firefighters based on hazard and risk assessment (DCLG and CFRA, 2011): ——

the construction and design of the building

——

the contents and use of the building (including occupancy type)

——

the nature of the fire and the operational tasks that need to be performed

——

working and environmental conditions.

While there can might many variables linked to the above that can impact upon the nature of fire and rescue service activities and intervention at the time of an incident, these four areas provide a good foundation from which fire and rescue service access strategies can be developed, and from which discussions with the local fire and rescue service can be had as part of this process. Detailed guidance relating to potential considerations and inputs that could be used to assess these four areas further can be found in PD 7974-5: 2014 (BSI, 2014a: clause 4.1 to 4.3). Although the fire and rescue service’s objectives may vary depending on the situation encountered on arrival at an incident and the available resources, for structure fires the general objectives of firefighting can be summarised as follows: ——

Assess the situation on arrival, including locating the fire, securing water supplies and identifying access and egress routes.

——

Perform rescues and ensure adequate medical support is summoned for casualties.

——

Prevent the fire from spreading (internally and externally to the structure, including stopping spread to exposure risks).

——

Surround and extinguish the fire.

——

Commence damage control operations (including salvage and environmental considerations), and commence post-fire ventilation and cutting away and, when possible, investigations.

It is the successful fulfilment of these general objectives that most prescriptive fire and rescue service access design guidance seeks to achieve through the provision of reasonable and practical measures. Therefore, any fire engineered strategy should also ensure that it can similarly deliver an adequate package of measures to do the same.

13.3.2

Tactical firefighting

The understanding of fire behaviour in the built environment is essential to the development and evolution of firefighting techniques and tactics. Continued industrial and academic research work – such as current studies being completed by the National Institute of Standards and Technology (NIST) and Underwriters Laboratories (UL) in North America (IAFC and NFPA, 2016) – along with the collection of evidence from the observations and experiences of firefighters is essential to improving the effectiveness and safety of firefighting procedures and equipment. Due to this, many fire and rescue services have now adopted the use of different tactical modes as part of their response to and management of fire incidents; the initiation of these different modes is dependent on the hazard and risk assessment (see section 13.3.1) completed by the Incident Commander, and may change at any time as an incident develops. For example, in the UK the following tactical modes could be declared during a fire incident (DCLG, 2008: section 4.4):

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service. The purpose for consulting the fire and rescue service at an early stage is hopefully to establish an understanding of and ‘buy in’ to the principles proposed by the fire strategy, thus de-risking the design approach to firefighting and fire and rescue service access. It needs to be demonstrated that the fire and rescue service access solution is equivalent to, if not better than, that which would be expected under prescriptive guidance; to achieve this (and where time and resources permit), it is encouraged that the fire and rescue service and the design team enter into active dialogue.

Firefighting

13-3

Offensive mode: where firefighting operations are being conducted within the hazard zone (e.g. committing firefighters to undertake firefighting and/or rescues within the fire compartment), where the potential benefits outweigh the identified risks present and there are adequate resources present.

——

Defensive mode: where firefighting operations are being conducted outside the hazard zone (e.g. firefighting using hose jets from outside the fire compartment, and not committing firefighters into the compartment), where the identified risks outweigh the benefits and there may be inadequate resources present.

——

Transitional mode: where both offensive and defensive tactics are being implemented at the same time; or where there is a shift from offensive to defensive.

By using these modes, firefighters can direct their resources most efficiently and safely, while at the same time monitoring (and, to a certain degree, predicting) the behaviour of the fire as an incident progresses. Although the fire and rescue service will aim to keep the management of an incident as simple as possible, it may be necessary for the Incident Commander to sectorise the building or incident area to ensure that appropriate command, control and safety can be maintained (DCLG, 2008: section 2.7). This involves breaking the building or area down into horizontal or vertical sectors, in which different tactical modes could be being implemented, with different firefighting or search and rescue activities being undertaken. This is important for fire engineers to note, as there is often a broad perception that firefighting by the fire and rescue service simply involves getting firefighters with charged hose lines to the fire compartment. In reality, fire incidents can be much more complicated than this, with different fire and rescue service personnel with different levels of equipment being tasked to undertake different activities in different sectors of an incident (note that this could potentially include firefighters undertaking activities and tasks above the floor of fire origin in multistorey buildings). It is therefore important where fire and rescue service access arrangements are proposed which deviate from prescriptive guidance that the fire engineer accounts for the potential working practices that may be implemented by the fire and rescue service for a reasonable set of worst case fire scenarios for the structure in question. This will need to be agreed with the local fire and rescue service.

13.4

Fire and rescue service equipment

13.4.1 Vehicles Fire and rescue services often have a diverse fleet of vehicles on which to call for different emergency situations. The two most common types of frontline appliance used to respond to incidents are pumping appliances and highreach appliances. Prescriptive design guidance typically requires access to buildings to be based on accommodating these two types of vehicle.

The standard vehicle of fire and rescue services is a pumping appliance. These may have a variety of titles, such as pump, water-tender, pump-ladder, engine company, pumper truck etc. But, whatever its title, for the purposes of planning for fire and rescue service attendance at a building, it is sufficient to refer to any such vehicle as a ‘pump’. A pumping appliance carries a large amount of equipment for firefighting use, including: built-in highand low-pressure pumps, a portable pump, high-pressure hose reels (booster hose), suction hose, a variety of branches and nozzles (nozzles and tips), breaking-in gear, ladders and breathing apparatus. Pumps usually also carry a quantity of water (typically between 1000 and 2000 litres) and foam compound (to produce firefighting foam). High-reach (or aerial) appliances are the second most common form of fire and rescue service vehicle. These are utilised at incidents where extended vertical reach is required. Appliances of this type can take several forms, such as aerial ladder platforms or turntable ladders, and typically have a capability to reach vertical heights of about 30 m. High-reach appliances are larger vehicles than pumping appliances (see section 13.6.1), being fitted with either a fixed telescopic ladder or essentially a crane with a caged platform that can be used to effect rescues from taller structures or to deliver high volumes of water from an elevated height. Fire and rescue services use many other types of specialist appliances (such as fire rescue units, command support units, hose layers, bulk foam units, foam tenders, and so on). For most typical built environment situations, no specific design requirements are imposed regarding facilitating access for these specialist appliances. However, there may be circumstances and specific site or building requirements where additional consideration needs to be given to planning for the attendance of specialist fire appliances that would be likely to attend in the event of an emergency (e.g. at an airport, access would potentially need to be planned for the use of foam tenders as well as pump and, possibly, high-reach appliances around the site).

13.4.2

Firefighting hose

Hose and associated branch and nozzle equipment is an essential tool for firefighting in that it ensures that firefighters can appropriately deliver water onto a fire to control and extinguish it. Fire and rescue services typically carry a variety of hose equipment on their appliances; this can include high-pressure hose reels, low-suction hose (layflat delivery hose), hard suction hose, and branches and nozzles that can deliver water at different flow rates and spray patterns. Hose is carried on fire appliances in individual pieces, known as lengths, which can be joined using couplings to create a hose line. In the UK, individual hose lengths are typically 20–25 m long, although for planning purposes it is reasonable to assume that each length of hose is 20 m in length. Therefore, if four lengths of hose were joined, these would form a single hose line of around 80 m in length. In other geographical areas, shorter hose lengths may need to be assumed, such as in the USA, where 15 m lengths are considered under NFPA guidance. Fire and rescue service planning and procedures assume that a single pumping appliance and crew can deploy and

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——

13-4

Fire safety engineering

——

distances from the perceived fire appliance arrival position to hydrants and dry fire main inlets

——

general hose coverage to the furthest point of the building (where required), and

——

other hose-related criteria that may be set out in prescriptive design guidance.

For example, under Approved Document B (HM Government, 2013) and BS 9999: 2017 (BSI, 2017a) guidance, pumping appliances should be afforded access to dry rising main inlets within 18 m, measured along a route suitable for laying hose; this distance enables the fire and rescue service to connect two separate lengths of hose (twinned) from the pumping appliance to the fire main inlet, with enough resilience in the design to account for differences in pumping appliance parking position or a shortened hose length. If a design proposes to increase the distance between the appliance and dry fire main inlet beyond 18 m, then the potential resulting implication is that the fire and rescue service may then have to use four lengths of hose to reach the fire main (along with the hose already required to connect to the hydrant) and charge it with water, which will increase both time and resource demand. When hose lines are charged (pressurised) with water for firefighting, the hose itself becomes relatively inflexible. A common misconception is that charged hose will be able to bend sharply around obstructions, when in fact it has to bend in a smooth curve. This is important to note when designing and installing fire main inlets and outlets. Firefighters should be able to connect hose to these face-on, with the inlet or outlet positioned so that there is enough clearance and working area for the hose to run out to or from it without obstruction or the need to bend around sharp angles. Similarly, when engineers and designers need to measure potential hose coverage distances (see section 13.9.1) from pumping appliances or fire mains, these should be measured conservatively, with the hose assumed to run through the mid-point of doorways or up or down the mid-point of stair flights and landings, rather than using unrealistic hose runs, such as tight up against walls or bending at right angles around door openings. Specific hose-bend radius data (e.g. sourced from the local fire and rescue service) may be used to inform the assessment of hose coverage distances in some circumstances.

13.4.3

Firefighter personal protective equipment (PPE), limitations and tenability

In order for firefighters to engage in firefighting, and search and rescue activities, they need to wear appropriate ppe, primarily to protect them from heat, smoke and toxic gases. Typical ppe includes helmet, tunic, leggings, gloves, flash hood, boots and breathing apparatus. Although this

ppe will provide protection to its user in line with approved

national and international standards, it is crucial to acknowledge that ppe has a performance limitation and that individual firefighters have different physiological limitations. It should not be assumed that firefighters are immune to the effects of working in a fire-impacted environment. Indeed, it is the fact the firefighters and firefighting equipment have limitations that has helped to inform the content of typical prescriptive fire and rescue service access guidance (e.g. limitations on hose distance coverage, and thus travel distances and related retreat paths, to the furthest points of a building).

This can therefore be an important factor when designing performance-based solutions for buildings that move away from prescriptive guidance. What needs to be avoided as much as possible is creating a scenario that has the potential to be impractical and/or onerous on firefighters and their ppe. Although recent research into this specific area is currently limited (in relative terms), information relating to the potential limitations of ppe, firefighter physiology and firefighter tenability is available to provide engineers with a good understanding of the background issues and a benchmark for design purposes. Fire Research Technical Reports 1/2005 (ODPM, 2004a) and 2/2005 (ODPM, 2004b) in particular provide in-depth commentary on the potential physiological demands that can be placed on firefighters undertaking different firefighting and search and rescue activities and the different influences that can limit performance. As part of this, the relationship between an individual firefighter’s exertion, physical response and ppe is acknowledged; for example, when undertaking demanding work, a firefighter’s body temperature may increase along with breathing demand from their breathing apparatus (which has a limited duration of operation, depending upon the user), with their overall effective safe (tenable) working time being relatively short. Where fire engineered design solutions propose to consider an assessment of firefighter tenability as part of the justifications being put forward, it is imperative that discussions are had with the local fire and rescue service in order to agree reasonable and conservative assessment criteria as part of the approach being adopted. This again would ideally be incorporated into a qdr process; PD 7974-5 (BSI, 2014a) provides a useful reference in regard to this issue. One example from the UK where the limitations of firefighter ppe and physiology have been expanded upon further in a specific design context is found in the best practice design guidance contained in the Smoke Control Association’s (SCA) guide to smoke control in residential common escape routes (SCA, 2015: section 5.3). Within this document, where performance-based fire engineered solutions are being developed to justify extended travel distance within the common corridors of residential apartment buildings, designers need to specifically (and quantitatively) assess conditions within the corridors during fire scenarios to ensure that they remain appropriately tenable for both escaping occupants and attending firefighters. In the case of the latter, maximum air temperature (°C), maximum radiated heat flux (kW · m–2) and exposure time that firefighters are subjected to in the corridor space need to be assessed against defined acceptance criteria to demonstrate that reasonable measures are being provided to facilitate fire and rescue service access.

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operate a single hose line when attending an incident (note that for a fire in a high-rise building it would typically be expected that two hose lines, a primary and a secondary safety, would be required to commence firefighting). This, coupled with the fact that a single fire appliance will only carry a certain amount of hose, means that engineers and designers need to carefully assess the knock-on resource implications for the fire and rescue service of any proposal to extend:

Firefighting

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Table 13.1  Exposure limits for firefighters under various conditions (Reproduced with permission from Society of Fire Safety, 2014.) Hazardous condition

Extreme condition

Critical condition

Maximum time (minutes)

25

10

1

< 1

Maximum air temperature (°C)

100

120

160

235

1

3

4–4.5

> 10

Temperature: 120 ºC

Radiation: 3.0 kW·m–2

Exposure limit <10 mins

1.5 m

Maximum radiation (kW·m–2)

Figure 13.1  Example exposure limits in hazardous conditions up to 10 minutes, with conditions measured at 1.5 m relative to the floor level (After Society of Fire Safety, 2014, with permission.)

The acceptance criteria in this case have been derived from exposure limits used by the Australasian Fire Authorities Council, as outlined by the Society of Fire Safety (2014) (Table 13.1). The suggested firefighter tenability criteria can be summarised as shown in Figure 13.1 Although the SCA guidance document is specific to residential applications, the broad fire engineering themes and concepts outlined within it relating to the demonstration of firefighter tenability could potentially be applied to other building uses. There may also be cases where visibility through smoke needs to be considered in relation to firefighter tenability; for example, BS 7346-7: 2013 (BSI, 2013a: clause 10) requires a 10 m visibility criterion to be applied when demonstrating the performance of impulse jet fan smoke ventilation systems being used in car parks to assist firefighting access.

13.4.4

Other equipment considerations

In addition to their own ppe and hose equipment, firefighters may need to transport and use other equipment (e.g. ladders or breaking-in gear) for use during an incident. This can be a key consideration in some cases when designing firefighter access routes from perceived fire appliance arrival positions to and around buildings. It needs to be remembered that firefighters will in most cases have to physically carry all necessary equipment, thus it is important to ensure that such access routes are reasonably limited in distance, intuitive in terms of wayfinding and reasonably dimensioned to permit relatively easy transportation of resources and equipment. Assumed fire and rescue service vehicle parking locations also need to be practical.

Advances in technology

Like many industries, technology associated with firefighting is always evolving and progressing, with standards improving, more efficient and safer equipment being developed and new equipment being introduced to react to emerging challenges posed by the modern built environment. While some technological advances can be adopted relatively quickly, caution must be exercised by fire engineers and any other stakeholders so as not to presume that the local fire and rescue service for a particular area will have access to (or the budget or demand to acquire) all forms of cutting-edge firefighting equipment. The adoption of new equipment and techniques may also not be universally accepted between different fire and rescue services. In some cases, advancements in technology are adopted relatively slowly by fire and rescue services. An example of this could be the availability and use of positive pressure ventilation (ppv) equipment and tactics by different fire and rescue services in the UK. At the extreme end, some technologies may be so specialised or unique that they are only adopted in certain areas or where they are absolutely warranted. An example of this could be the development of the Martin ‘First Responder’ Jetpack product (Martin Aircraft Company, no date), which may soon enter use to assist firefighters responding to incidents in Dubai. Similarly, the development of higher reach fire appliances, such as the Bronto Skylift High Level Articulated (HLA) aerial platform (Bronto Skylift, no date), which can vertically extend to 81–112 m, can offer enhanced high-rise firefighting capabilities. However, such appliances may only be appropriate (or be able to be practically put into service) for a relatively small number of fire and rescue services. Cutting extinguishing techniques, utilising equipment such as the coldcut Cobra (originating from Sweden) or Pyrolance (USA), enables firefighters to attack a fire from outside the fire compartment by using high-pressure water to cut through walls and building fabric and apply water spray through the resulting holes. Overall, what needs to be remembered is that while fire and rescue services will always use a similar base level of equipment (pumping appliances, hose lines and so on), engineers and designers may need to be aware of and account for emerging technologies and new practices or tactics being implemented by the local fire and rescue service as part of their building or site design.

13.5

Fire and rescue service notification and response

13.5.1

Local fire and rescue service resource variations

It is important to understand the level of local fire and rescue service coverage to a building as this can vary significantly depending upon geographical area. In addition, due to increasing economic and resource pressures on fire and rescue services in many areas, the current level of coverage

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Routine condition

13.4.5

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The local fire and rescue service may provide full-time and/or retained fire coverage to an area. Retained fire stations (which are common in some countries, including the UK and Ireland) are staffed by professional firefighters, who may have other employment elsewhere but respond to emergency incidents within their local area when necessary. Although not as common, volunteer-staffed fire stations may also be present (such as in parts of Germany, France and the USA), or a private fire and rescue service (part or fully private) may serve the site in question. It is usual for all forms of fire station to have attendance time targets. There will, however, be differences in the level of coverage that different geographical areas receive, in terms of how quickly the fire and rescue service could potentially arrive to deal with an incident and what resources and equipment they would have available to them. For example, a fire and rescue service in an urban metropolitan area could be expected to provide a quicker response and more immediate resources than one located in a remote rural area. While the distance to the nearest fire station will be a consideration for fire engineers, in most cases the fire engineer should not rely solely upon a response from this fire station as a means to justify a proposed scheme. It will always be possible that the resources located at the fire station are responding to another incident elsewhere. Therefore, where required and possible, it would be more resilient to consider assessing the following information in relation to the relevant local fire and rescue service: ——

average time for emergency calls to be responded to

——

average time for firefighters to be mobilised and leave the fire station

——

average time for the first and second fire appliances to arrive at an incident

——

what the expected predetermined attendance (pda) could be, and what implications this may have for the scheme in question

——

what the potential, reasonable worst-case scenarios for all the above could be, and how these might need to be considered as part of a sensitivity analysis.

Information relating to the above can often be requested from the local fire and rescue service, and in some cases is publicly available (via the internet) as part of fire and rescue service performance target and response time statistics reports. In regard to the pda mentioned above, another common perception is that the fire and rescue service will immediately mobilise a multitude of fire appliances and resources, sufficient to deal with the worst-case fire incident in a building. For most incidents, this is not the case; the fire and rescue service will usually only mobilise those

resources on their pda record for a building, with this often being limited (e.g. a single pump appliance). Upon arrival at an incident, the officer in charge of the initial fire and rescue service attendance will then call for additional resources should they be required.

13.5.2

Improving fire and rescue service notification

To increase the potential for early attendance by the fire and rescue service, in support of a building’s life safety and/or property protection strategy, the fire engineer should consider the use of automatic transmission of signals from the building fire detection and alarm system to a suitable alarm receiving centre. By considering the factors outlined in section 13.5.1, along with the hours during which the building in question is occupied and the reliability of manual means of notification (e.g. use of telephones by onsite staff), the building fire strategy may determine that the provision of a more resilient arrangement for the early summoning of the fire and rescue service is required due to the risks posed by the building’s use and occupancy. Often this is most easily achieved through the automatic transmission (via a monitored link) of fire detection and alarm system signals to an alarm receiving centre, from where a quick response to a potential fire incident and the summoning of the fire and rescue service can be efficiently completed. An alarm receiving centre could be located in, for example, a continuously staffed fire and security room on the same site as the building requiring protection (as found in some shopping complexes and hospital sites) or in a third party commercially operated centre. The use of an alarm receiving centre will provide a more reliable and resilient means to react to a fire detection and alarm signal from a building, and can therefore help to compress the timeline involved in getting adequate fire and rescue service resources to an incident. Example design and procedural guidance relating to automatic transmissions from a fire detection and alarm system to an alarm receiving centre can be found in BS 5839-1: 2017 (BSI, 2017b: clause 15), and requirements for alarm monitoring and receiving centres are covered in BS EN 50518: 2013 Parts 1 to 3 (BSI, 2013b, 2013c, 2013d) and BS 8591: 2014 (BSI, 2014b).

13.6

Fire service vehicle access and water supplies

13.6.1

Roadway access

It is important to ensure that fire and rescue service vehicles can access a site and get close enough to a building via appropriately sized and constructed roadways in order to commence fire and rescue operations. This should include consideration of associated landscaping, building overhangs, the need to drive over or under features such as bridges, and so on. The extent to which fire and rescue service vehicle access is required depends on whether external (see section 13.8) or internal (see section 13.9) firefighting measures are appropriate and what type of fire

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may be under review and subject to change. Therefore, understanding where local fire stations are situated and what resources they have could be relevant to the development of the building fire strategy in terms of what initial resources will be available and the time it will take for the fire and rescue service to attend an incident (and factoring in a suitable margin of safety, should the building fire strategy rely upon this).

Fire safety engineering

Firefighting

13-7

Table 13.2  Fire and rescue service vehicle route specification (UK) (BSI, 2017a) Appliance type

Min. width of gateways / m

Min. turning circle between kerbs / m

Min. turning circle between walls / m

Min. clearance height / m

Min. carrying capacity / t

Pump

3.7

3.1

16.8

19.2

3.7

12.5

High-reach

3.7

3.1

26.0

29.0

4.0

17.0

Note: Because the weight of high-reach appliances is distributed over a number of axles, it is considered that their infrequent use of a carriageway or route designed to 12.5 tonnes is not likely to cause damage. It would therefore be reasonable to design the road base to 12.5 tonnes, although structures such as bridges should have the full 17 tonnes capacity.

and rescue service vehicle response needs to be planned for. Ultimately, this will be driven by the size, height, location, geometry and occupancy of the building in question. Ensuring the provision of adequate fire and rescue service vehicular access should be considered by all relevant designers and stakeholders at a very early stage in the design process for a building, to ensure that the necessary external and internal fire and rescue service access arrangements can be supported. In particular, design schemes involving podium access need to be very carefully considered to avoid imposing onerous expectations on firefighters, in terms of having to conduct firefighting operations in areas remote (physically, visually and communication wise) from the locations accessible to fire and rescue service vehicles.

space needs to be provided to allow these vehicles to negotiate corners. This is often assessed for new routes and roadways by completing a swept path analysis. ——

Dead-end access roads: Limits are often placed in national and international design guidance on the distance along which the fire and rescue service drivers are expected to reverse their vehicles before being able to drive forward away from a building or site. For example, in the UK-specific context, a dead-end access road distance of 20 m is typically considered the limit under BS 9999 (BSI, 2017a: clause 21.3), while under International Fire Code guidance the limit is 150 feet (ca. 45 m) (ICC, 2017: Appendix D). When such limits are exceeded, suitably sized turning circle or hammerhead facilities should be provided to allow fire and rescue service vehicles to turn around and drive forward from the dead-end road. While some of these deadend distance limits have historic origins (e.g. the UK limit of 20 m originates from the time when fire and rescue services used horses to pull their engines), they do have a practical relevance in the modern era. Managing fire and rescue service resources during an incident can be complicated; thus, as fire appliances carry all relevant personnel and equipment, reasonable measures need to be provided to ensure that resources can be moved relatively easily if required. In some scenarios, it may be possible for the fire engineer to justify dead-end access road distances that exceed relevant local limits based on the provision of other building-specific compensatory measures. Such measures could include the voluntary provision of a robust suppression system in a building where suppression is not required for other reasons, or wider access roads to permit easier vehicle reversing. In some cases, measures such as these could assist in obtaining agreement by the local fire and rescue service to an extension to the road distance.

——

Working area: While providing the roadways to minimum dimensions, such as those shown in Table 13.2, will get the fire and rescue service vehicles close to a building, it must be remembered that firefighters will require a working area in order to unload personnel and stowed equipment from the appliance for use. Therefore, it may be best practice to provide some additional room around perceived fire appliance parking positions (e.g. in zones designated for perimeter access or where fire appliances will be parking near to designated building entry points or fire mains inlets) to allow for this to be done easily. This may be of

The design guidance applicable in a particular geographical area will often specify, in broad terms, what dimensions and carrying capacity fire and rescue service vehicle access routes should have. For example, BS 9999 (BSI, 2017a: clause 21.3) provides guidance on how these routes should be designed for the two most common fire appliance types used in the UK, as shown in Table 13.2. Checks should be made to ensure that inspection covers (such as those used by public utilities) and other similar features that may be incorporated into the roadway design are capable of carrying the expected carrying capacity weights. For those designing roadways and vehicle access for a site or building, it should be remembered that fire appliances are not standardised; the size and weight and equipment carried may differ between appliance types within a fire and rescue service, and may differ further regionally, nationally and internationally. Some fire and rescue services use more specialised vehicles than others; a consideration which may also need to be factored into the design of roadways. Relevant vehicle dimensions and details should therefore be confirmed with the local fire and rescue service where appropriate. Other design considerations that may need to be checked as part of ensuring that adequate fire and rescue service vehicle access can be facilitated include the following: ——

Roadway gradients: There may be local roadway gradient design limits that must be observed. For example, in the UK, hardstanding areas for highreach appliances should not exceed a 1 in 12 gradient, and gradients of 1 in 4 should be avoided for fire and rescue service vehicle access in general.

——

Vehicle turning and sweep circles: When designing access routes, allowances should be made for fire appliance turning and sweep circles as additional

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Min. width of road between kerbs / m

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Fire safety engineering

particular relevance if it is proposed that only a single-lane access road is to be provided. Roadway markings: For some sites it may be necessary to consider the use of roadway markings to impose traffic restrictions (such as no parking areas or hatched zones for emergency vehicle use only) or, in some extreme cases, such as found in North America, the use of fire lanes on roadways. Similarly, if a fire and rescue service roadway is proposed to pass through a pedestrianised area, a clear fire path should be planned and identifiable (perhaps using different surface materials or markings) to ensure that it is not obstructed.

——

Posts and bollards: Any posts or bollards installed across roadways used for fire and rescue service access (to restrict use by other vehicles) should usually be of the removable or collapsible (fixed hinged) type, with standard ‘fire brigade’ padlocks used to secure them in the up position. Any proposed use of flexible or electronically retractable posts or bollards needs to be carefully considered, and design details discussed with the local fire and rescue service.

——

Use of security gates across a roadway or vehicle access point: Gates are often used to restrict access to larger sites, but to prevent any delay being caused to fire appliances, ideally only one gate barrier should be used. This should be secured by a means that can be easily and quickly opened by the fire and rescue service (e.g. use of a single ‘fire brigade’ padlock or, where electronic gate locks are used, a drop-key mechanism). For some buildings or sites, there may be a 24-hour security presence, where gates are opened via a central control system; the relevant details and protocols associated with this may need to be agreed with the local fire and rescue service.

——

Traffic calming measures: Features such as speed humps can significantly increase fire and rescue service attendance times, depending on the length of roadway over which the traffic calming measures are proposed, and on their design, number and spacing.

If there is any doubt as to what local regulatory and fire and rescue service requirements are in place in relation to the above items (or similar roadway features), the local fire and rescue service, and possibly the local traffic authority, should be consulted. As outlined in section 13.5.1, while pumping and high-reach appliances are often the most common forms of vehicles used by fire and rescue services, there may be a need to plan for the attendance of other specialised appliances for some buildings or sites. This should also be discussed with the local fire and rescue service in the event of any doubt.

13.6.2

The most common and effective means of providing supplementary and resilient water supplies is via a hydrant connected to a water main. These often take the form of underground hydrants (e.g. to BS 750: 2012 (BSI, 2012a) or BS EN 14339: 2005 (BSI, 2005a)), but could also be presented as pillar hydrants (e.g. to BS EN 14384: 2005 (BSI, 2005b), with these provided by the relevant local water authority from street water mains or by the building or site developer or owner as a private hydrant. Alternatively, where no piped water supply can be provided, a charged static tank or natural water source (river, pond or similar) could be considered acceptable provided that it provides adequate capacity for the building, site or risk in question and is agreed with the local fire and rescue service. Guidance in Approved Document B Volume 2 (HM Government, 2013) recommends a capacity of at least 45 000 litres, but it is suggested that the adequacy of this would need to be assessed on a project-specific basis (particularly as some alternative sources of water may increase time delays to effective firefighting due to the need for additional specialist equipment or the need for water relay). Figure 13.2 illustrates how the fire and rescue service will typically connect a pumping appliance to a hydrant. To connect a standpipe to an underground hydrant (for example), the firefighter has to collect a standpipe, key and bar from a locker on the pumping appliance, run to the hydrant, lift the pit lid, take the blank cap off the outlet, screw the standpipe onto the outlet, fit the key onto the

Collecting head

External water supplies and hydrants

Carrying water to an incident enables the fire and rescue service to apply the first jet or spray to the fire with least delay. However, the water supply carried in the tanks of pumping appliances is limited; capacity is typically between 1000 and 2000 litres. Using a 12.5 mm nozzle at

Figure 13.2  Water from a hydrant via a standpipe and a line of hose of one length to the collecting head of a pump and then from a delivery valve via a line of hose of two lengths to a branch or nozzle (Note: the hose connection between the hydrant and fire appliance may be twinned depending upon local fire and rescue service procedures.)

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——

2.5 bar nozzle pressure, the rate of delivery will be approximately 160 litres of water per minute (this figure should be taken as a guide only; e.g. some modern multi-flow nozzles for use with layflat hose can deliver 360–750 litres per minute). Therefore, with a 1000 litre tank and a delivery flow of 160 litres per minute, the water would be exhausted within 6 minutes. The significance of these figures for preplanning is that if a fire cannot be extinguished within that time period, additional water supplies need to be established to maintain an unbroken attack on the fire. The building type also has an influence on the requirements for a water supply; for example, for a highrise building, a water supply must be secured to charge fire mains before firefighters can be committed to the fire compartment, thus additional water supplies will be needed.

Firefighting

Securing an uninterrupted water supply is one of the critical actions that the fire and rescue service will complete upon arrival at an incident. Ensuring that an appropriate supply is available should therefore be identified as part of a building’s or site’s fire strategy. For new developments, formal consultation may be needed with the local water authority and the local fire and rescue service (which are likely to have a specialist water department) to ascertain the adequacy of existing supplies and to identify where new hydrants may be required. The legislative requirement to provide hydrants can be a complex issue. For example, in England and Wales, while there is guidance contained in design documents supporting the Building Regulations, it is actually the Fire and Rescue Services Act 2004 that is explicit in stating that the fire and rescue authority must secure an adequate supply of water in the event of fire. The Act states that if securing a supply requires making an agreement with a water undertaker to provide hydrants, it is the responsibility of the fire and rescue authority to pay the water undertaker. There is no qualification in this that differentiates between whether the hydrants are on public or private land, although it is usual for hydrants on private property to be paid for by the developer or owner. However, it is standard policy within all fire and rescue services in the UK that it should be made clear to developers and owners that the fire authority cannot be expected to meet the expense of providing water supplies for special premises where this would be out of all proportion to the remainder of the risk in an area. Further information relating to the legislative background and general requirements for hydrants is provided in the National Guidance Document on the Provision of Water for Fire Fighting (LGA and Water UK, 2007). The location of hydrants should be such that they are near to fire and rescue service appliance parking positions, near to building entry points and readily accessible. Hydrants should be located in a prominent position and clearly signed, and not camouflaged in surrounding landscaping. Approved Document B guidance suggests that a reasonable provision for a building not provided with fire mains

would be a hydrant located within 90 m of an entry point to the building and not more than 90 m apart or, for a building fitted with a dry rising main, within 90 m of the fire main inlet connection (assumed for a building with a compartment of more than 280 m2 that is more than 100 m away from an existing hydrant) (HM Government, 2013: section 15.7). BS 9990: 2015 guidance (BSI, 2015a: clause 5), which covers the provision of private hydrants, adds to this by stating that hydrants should be positioned no less than 6 m away from the building or risk in order to offer some protection from falling debris and other possible occurrences during a fire. For comparison, NFPA 24 (NFPA, 2013: chapter 7) gives the general recommendation that hydrants ‘shall be spaced in accordance with the authority having jurisdiction’ and ‘for average conditions hydrants shall be placed at least 40 feet (12.2 m) from the building protected’. In terms of flow rate for hydrants, typical building design guidance is relatively silent on specific requirements; for example, BS 9999 (BSI, 2017a: clause 22.2) limits recommendations to ensuring that hydrants are capable of delivering a ‘sufficient flow of water to enable effective firefighting to be undertaken’. In terms of assessing whether a hydrant flow is sufficient for firefighting, example data produced in the National Guidance Document on the Provision of Water for Fire Fighting (LGA and Water UK, 2007: Appendix 5) show that there can be quite diverse requirements, depending upon the type of building and risk in question; this is summarised in Table 13.3. This variation in potential flow rate demand between different uses demonstrates the importance of liaising with the local water authority and fire and rescue service when providing new or assessing existing hydrant installations. For more complex schemes, where water supplies are deemed to require more in-depth analysis to support a specific fire engineered design solution, PD 7974-5 (BSI, 2014a: clause 8 and Annex A) provides a detailed commentary and suggested methodology for the assessment of water demand and efficient flow rates. Table 13.3  Recommended ideal hydrant flow rates (LGA and Water UK, 2007) Type of structure

Flow rate / litre · s–1

Distance from risk / m

Housing: not more than two floors

8

Not stated

Multi-occupied housing: not more than two floors

20–35

Not stated

Lorry/coach parks, multistorey car parks, service stations

25

90

20 35 50 75

Not Not Not Not

Shopping, offices, recreation and tourism

20–75

Not stated

Village halls

15

100

Primary schools and single-storey health centres

20

70

Secondary schools, colleges, large health and community facilities

35

70

Industrial estates:   up to 1 hectare   1–2 hectares   2–3 hectares   over 3 hectares

stated stated stated stated

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false spindle, fit the bar into the key, turn on the water to flush the hydrant and then turn off the water. For planning purposes, may be reasonable to assume a time of 30 seconds to collect the equipment off the pumping appliance and 30 seconds of work at the hydrant (1 minute). If the hydrant is 20 m from the pump (equivalent to a single length of hose; in some cases, two lengths of hose twinned between the fire appliance and hydrant will be required), it will take the firefighter a total of 20 seconds to run to the hydrant and back. On return to the pump, the firefighter will collect a length of hose, run back to the hydrant, connect the hose to the standpipe and run back to the pump, paying out the hose (a further 20 seconds). The firefighter will then run back to the standpipe (10 seconds) and turn on the water (10 seconds). It is appreciated that hydrant pits sometimes contain debris that must be removed before the hydrant can be used, and this would extend the time considerably. However, as with all planning assumptions, the above figures have assumed a hydrant pit in good order. Using these figures, the total time available for one firefighter to obtain a feed from an underground fire hydrant to a pump where the hydrant is 20 m from the pump could reasonably be considered as being 2 minutes.

13-9

13-10

Fire safety engineering

13.7

Internal water supplies: fire mains

of fire main, which can be referred to using a number of different terms.

Fire mains are fixed installations provided within a building to assist with the supply of water for firefighting, helping to reduce hose lengths and fire and rescue service intervention times. As shown in Table 13.4, there are various types Table 13.4  General terminology used for fire mains in buildings (examples) Type of installation

Terms used in UK

Terms used in USA

Internal firefighting water main

Fire main, rising/falling main or internal main

Standpipe system

Pipework that is normally empty of water

Dry riser/faller

Manual dry

Pipework that is filled with pressurised air

No equivalent in UK

Hybrid mains; automatic dry and semi-automatic dry

Pipework that is filled with water but has no other supply

Charged dry main or damp main

Manual wet

Pipework that is filled with water and has additional water supplies to sustain a firefighting attack

Wet fire main, wet riser/faller

Automatic wet

Table 13.5  Typical criteria for internal fire mains (summary examples UK) Design guide

Building use

Floor area

Top floor height or lowest floor depth*

Type of fire main

Typical location of fire main outlets or landing valves

ADB / BS  9991

Residential flats (where the hose distance from the pumping appliance to the furthest point of the furthest dwelling exceeds 45 m)

N/A

< 18 m in height

Refers to BS 9990; typically dry

Protected staircase landings

BS 9991

Residential flats

N/A

18–50 m in height and/or –10 m deep

Dry

Firefighting staircase landings

BS 9991

Residential flats

N/A

≥ 50 m in height

Wet

Firefighting staircase landings

ADB

Shop, commercial, assembly, recreational or industrial use

≥ 900 m2 storey over 7.5 m in height

≥ 7.5 m in height

Refers to BS 9990; typically dry

Firefighting lobbies

ADB

All buildings

≥ 900 m2 (each basement storey)

Two or more basement storeys

Refers to BS 9990; typically dry

Firefighting staircase landings for residential flats, firefighting lobbies for all other uses

ADB

All buildings

N/A

18–50 m in height and/or –10 m deep

Dry

Firefighting staircase landings for residential flats, firefighting lobbies for all other uses

ADB

All buildings

N/A

≥ 50 m in height

Wet

Firefighting staircase landings for residential flats, firefighting lobbies for all other uses

NFPA 1

All buildings

N/A

3 floors high or 15 m in height

NFPA 5000

All buildings

N/A

4 floors high/deep

BS 9999

All buildings within the scope of the document

N/A

11–18m in height

Dry

Firefighting lobbies

BS 9999

All buildings within the scope of the document

N/A

18–50 m in height

Dry

Firefighting lobbies

BS 9999

All buildings within the scope of the document

N/A

≥ 50 m in height

Wet

Firefighting lobbies

Floor landings

* Floor heights and depths are measured above and below fire and rescue service access level. Note: ADB refers to Approved Document B Volume 2 design guidance (HM Government, 2013).

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13.7.1 General

It can be seen in Table 13.5 that different guides recommend the installation of a dry fire main at varying floor heights; in the UK this is where (depending upon the guidance being applied and building use) the top occupied floor height above fire and rescue service vehicle access level is more than 7.5 m, 11 m or 18 m, where hose distances from the perceived fire appliance parking position to the furthest point of the furthest dwelling exceed 45 m (for residential flats), or where there are large or deep

Firefighting

13-11

13.7.2

Dry fire mains

Dry fire mains consist of a pipe installed vertically through a building with an inlet breeching provided at fire and rescue service vehicle access level and outlets, with hand-controlled valves (known as landing valves), on each floor (Figure 13.3). On arrival, the firefighters connect hoses from a hydrant to a pump appliance and from the pump appliance to the fire main inlet, then charge the main with water. Other firefighters go to a floor (in an above-ground context, one or two floors below the fire floor initially, to establish a bridgehead, which is usually a protected area, from which firefighting crews can then be committed to tackle the fire), connect their hoses to the outlet and run out the hose to the fire. Fire mains that serve above-ground floor levels are known as dry rising mains, while those that serve below-ground floor levels are known as dry falling mains. In the UK, BS 9990 (BSI, 2015a) (with supplementary references to BS 5041) provides guidance on the design, installation and maintenance of fire mains. Dry fire mains typically have pipework diameters of 100 mm or 150 mm. Breeching inlets for dry risers are located on an external wall as close as possible to the installation and relevant fire and rescue service access point into the building, and there should be access for a pumping appliance within 18 m of each fire main inlet. The breeching inlet box should be positioned with its lower edge between 400 mm and 600 mm above ground level. Where a 100 mm dry fire main is provided, a two-way breeching inlet should be fitted, and for 150 mm

Automatic air release

Landing valve

risers, a four-way inlet should be provided. The door of the inlet box should be secured and should be clearly indicated with appropriate signage (e.g. ‘DRY RISER INLET’). A drain valve should be incorporated into the breeching inlet unless the main also feeds landing valves below the inlet level. An automatic air release valve should be fitted at the highest point on dry risers to permit the riser to be charged with water without the need to open any landing valves. NFPA 14: Standard for the installation of standpipes and hose systems (NFPA, 2016) contains similar design guidance, although there are three classes of ‘standpipe systems’ that can be applied when using this document, dependent upon the building or scenario in question. A dry fire main can also be ‘charged’, i.e. permanently filled with water, which is sometimes known as a ‘damp fire main’ or ‘manual wet fire main’. The primary benefit of providing such an arrangement is that the fire and rescue service do not need to fill the fire main with water, thereby ensuring there is no delay in deploying firefighting jets to tackle the fire. However, this arrangement tends only to be applied where extensive fire main installations are proposed for a building or site. The permanent charging of the fire main should be discussed with the local fire and rescue service. Horizontal dry fire mains (involving a horizontal length, with no vertical rise or fall to other floors) have also been applied on design schemes. However, they have limited application, related to: their potential to cause confusion among attending fire crews; the fact that, while they may be able to deliver water across a significant horizontal distance, firefighters with all their required equipment still need to travel across the same distance; and issues relating to practical drainage and maintenance. The landing valves (also known as outlets) for fire mains are typically located in close association with the protected firefighter access routes provided in a building. For example, it is common in the UK for the landing valves to be provided within the firefighting lobbies provided to the firefighting access stair in commercial buildings, and within the firefighting access stair enclosure for residential buildings. The landing valves themselves should be positioned in a manner that enables ease of access and the running out of what will become a charged hose line, and ensures they do not obstruct or become obstructed by door openings. Additionally, landing valve height, protection and security should also be considered; for example, BS 9990 (BSI, 2015a) recommends that the lowest part of the valve is positioned no lower than 750 mm above floor level, that the valve is preferably protected by an appropriate box to BS 5041-2: 1987 (BSI, 1987), and that precautions should be taken against vandalism and theft of the landing valves. Any alternative landing valve locations (that deviate from the expectations of local or national fire safety design guidance) should be discussed and agreed with the local fire and rescue service.

13.7.3

Drain valve Figure 13.3  Schematic of a dry rising fire main

Breeching inlet at ground level

Hybrid fire mains

In addition to the dry and charged dry mains common in the UK, NFPA 1 (NFPA, 2018a) also describes two hybrid dry and wet systems, known as an automatic dry standpipe system and semi-automatic dry standpipe system. Both systems consist of a dry main that is filled with pressurised air. When a landing valve is opened, water flows into the

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multiple basement levels present. Where the top occupied floor height exceeds 50 m, a wet fire main is required in order to ensure that water can be adequately pumped vertically up the building. Fire mains can also be a useful tool for fire engineers wishing to enhance (as part of a wider fire strategy) the firefighting provisions in a building that would not otherwise be required under typical design guidance to have a fire main.

13-12

Fire safety engineering

system piping automatically. The water supply for these systems must be capable of supplying the system demand.

Wet fire mains

Wet fire mains in the UK are known as ‘automatic wet’ standpipe systems in NFPA codes. A wet fire main is similar in construction and layout to a dry fire main except that the system is connected to a permanent water supply that is capable of supplying the system demand automatically. This may be a direct connection to a water company main, where this is permitted and is of sufficient capacity, but more commonly consists of a water tank and either a pumping facility or gravity feed or both. In the UK, BS 9990 (BSI, 2015a) guidance calls for wet fire mains to be fed by two interconnected tanks of equal capacity, having a total minimum capacity of 45 000 litres, with the tanks automatically supplied from a mains water supply. The tanks and water mains feed should be capable of maintaining a flow of water to supply two firefighting hose lines for 45 minutes when water is being used at a total rate of 1500 l · min–1, with two pumps (duty and standby) provided to feed the system with a running pressure of 8 (±0.5) bar per landing valve when the landing valve is fully open. Wet fire mains are suitable for buildings of all heights but are essential when the highest floor is more than 50 m above fire and rescue service access level. This is due to the excessive pressure at which the fire and rescue service would need to pump and the delay in delivering water to the highest point in the riser. The benefit of wet fire mains is that a supplementary water supply via fire service pumps may not be necessary. If a supplementary water supply is necessary, the time available to obtain the supply is extended. Because of the need to provide sufficient pressure in the upper sections of wet risers, the pressures in the lower parts of the riser may be excessive. If this is the case, it may be necessary to limit the delivery pressures so as to avoid dangerously high pressures in firefighting hoses. Pressure control can be achieved by the provision of a pressure relief connection built into the delivery side of the landing valve that is permanently connected to a waste pipe. Valves can be calibrated to give different inlet–outlet pressure differentials, as appropriate for specific locations within the riser. An alternative type of landing valve for wet risers incorporates a ‘dead shut-off ’ pressure-reducing valve and requires no drain connection. For example, BS 9990 recommends pressure-reducing valves be provided to regulate the flow and pressure to 750 (±75) l · min–1 at 8 (±0.5) bar per landing valve, with the system designed so that the static pressure in any hose line connected to a landing valve does not exceed 12 bar when the nozzle is shut off. The landing valve/outlet location for a wet fire main system should meet the same standards as for dry fire main systems, as outlined in section 13.7.2. An emergency tank filling connection for fire and rescue service use may be necessary to take account of circumstances when the automatic infill is out of action. BS 9990 recommends that this should typically take the form of a breeching inlet (positioned in a prominent location on the face of the building) connected to a delivery pipe of not less

13.7.5

Additional considerations relating to fire main landing valves

There are clear differences within and between national guidance relating to the positioning of fire main landing valves. For example, the recommendations in Approved Document B (HM Government, 2013) and BS 9999 (BSI, 2017a) vary depending on whether or not the landing valve is located in a firefighting shaft or protected stairway and whether or not a building is sprinklered. The recommendations are also significantly different to the NFPA 1 (NFPA, 2018a) recommendation that landing valves should be located at each intermediate landing between floor levels in every required exit stairway. NFPA 1 also recommends considerably more landing valves than Approved Document B. For many building and fire main systems, designs achieving compliance with the minimum standards outlined in local and national standards will suffice. However, for some fire engineered buildings it may be appropriate to further consider where fire main landing valves are located and/or whether the provision of additional landing valves would bring clear benefits to a scheme (through the subsequent enhancing of firefighter access arrangements). Research in England in 2004 (ODPM, 2004b) assessed the physiological limits of firefighters in a series of controlled experiments. Essentially, these experiments tested the maximum distance it was considered possible to penetrate into a fire compartment for the purposes of fighting a fire and searching for a casualty. The research determined that heat strain among the firefighters was the greatest single source of performance limitation. It was further determined that the most significant effect on heat strain was the number of stairs that had to be climbed while wearing standard ppe, standard-duration breathing apparatus or extended-duration breathing apparatus and carrying firefighting and rescue equipment. As a result of the trials, the research suggested that firefighters should be able to penetrate into a fire compartment to rescue a casualty, where no stair climbing is required to access the point of entry, for a maximum distance of 34 m. This distance was reduced if firefighters had to climb stairs beforehand. For example, climbing two floors reduced the penetration distance to 32 m, and climbing 10, 20 and 30 floors reduced the penetration distance to approximately 25 m, 20 m and 12 m, respectively. It should be noted that this research dealt with simulated incidents, and there are no data on actual fire incidents that suggest that travel distances up to 45 m into a fire compartment are excessive. Therefore, it was deemed that the distances firefighters are able to travel are primarily dependent upon the number of floors climbed, and that travel distances within fire compartments should be based on a standard that considers both the (nonoperational) research and the practical experiences of actual firefighting.

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13.7.4

than 100 mm diameter that enters the wet fire main tank(s) above the maximum water level. Any such inlet provided should be clearly indicated with appropriate signage that ensures it is identifiable as the wet fire main infill.

Firefighting

When firefighters exit a firefighting lift two floors below the fire floor, they undertake two key tasks: (a)

establishing a bridgehead on that floor, and

(b)

the officer in charge considers where it is safe to connect the primary and secondary hose lines to the fire main landing valves; ideally, the primary hose line would be connected to a fire main landing valve on the floor below the fire floor, with the secondary (safety) hose line connected to the fire main landing valve on the fire floor.

It is clear from the above that, if only one landing valve is to be installed for each staircase, the optimum location for that landing valve is within the staircase enclosure. This will ensure that only the fire-resisting doors to the fire floor are held open by the hose line passing through them and will shorten hose lines. Arguably, locating landing valves within stair enclosures also increases the possibility that firefighters can use the landing valve located on the fire floor. There is also merit in the NFPA 1 recommendation that landing valves should be located at each intermediate landing between floor levels rather than at floor levels. This would remove the need for landing valves at the full floor levels, and would mean that hose lines could be connected half a floor below the fire floor rather than one or two full floors below, thereby reducing the lengths of hose lines and reducing congestion on staircases (including potentially not disrupting wheelchair refuges). If it is proposed to provide more than one fire main landing valve per level for each staircase (to enhance firefighter water supply and access arrangements by helping to reduce potential hose and travel distances), this could be presented in several different arrangements, such as: ——

a twin landing valve connection within the staircase enclosure at each level

——

a single landing valve each within the staircase enclosure and within the associated protected lobby at each level

——

a single landing valve within the staircase enclosure and a single landing valve installed adjacent to the door to the fire compartment, for those occasions when it is safe to enter the fire compartment without a charged hose line.

Where it is proposed to provide more than one fire main landing valve per staircase per level, the arrangements should be discussed and agreed with the local fire and

rescue service to ensure there is confidence in operational procedures expected to be applied, hose line distances and resourcing, and travel distances.

13.7.6

Foam inlets

A foam inlet system consists of an inlet box housing a foam inlet adaptor that is connected to a length of distribution pipework, which then terminates in one or more fixed foam pourers or discharge outlets. In the UK, design guidance relating to the design of these systems can be found in BS 5306-1 (BSI, 2006). These systems are provided to assist the fire and rescue service in fighting fires involving oil storage tanks or oil-fired boilers that are either situated below ground level or are inaccessible from outside. Where a fire strategy deems that such an installation is required, the foam inlet breeching connection at the fire and rescue service access level should be positioned in a prominent and practical location (e.g. within 18 m of a practical fire appliance parking position), with this being clearly indicated with appropriate signage.

13.8

External firefighting access (perimeter access)

Design standards attempt to ensure that the fire and rescue service can reasonably reach the exterior of a building in order to efficiently commence firefighting operations. The ideal scenario is to afford access to all sides of a building. The reasons why external access is required are best summarised in clause 16.1 of Approved Document B Volume 2 (HM Government, 2013), which states that it is needed to enable high-reach appliances to be used and to enable pumping appliances to supply water and equipment for firefighting and search and rescue activities. The extent to which external access is required is, however, driven by the size and height of a building. In the UK context, buildings less than 11 m in height, as measured to the highest occupied storey, need to facilitate access for pumping appliances, while those over 11 m in height need to be designed to facilitate access for highreach appliances. This acknowledges that the portable ladders typically carried on pumping appliances have a limited reach. Depending upon the size of the building (in terms of total area, m2), a percentage of the building perimeter must then be made available for fire and rescue service access, with this ranging from 15% to 100%. The fire and rescue service should then be able to access the building from adjacent to the designated perimeter elevation. Where access for high-reach appliances is required, designated hard-standing areas need to be provided and must be free from overhead obstructions (such as cables, trees etc.). Key to providing the adequate perimeter access percentage is ensuring that there are entry points into the building on any elevations that have a designated perimeter access zone (within 18 m of a practical fire appliance parking position). BS 9999 (BSI, 2017a: clause 21.1) calls for suitable entry door(s) not less than 750 mm in width to be provided so that there is no more than 60 m between each

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It is standard operating practice within the UK for firefighters to travel up a high-rise building in a firefighting lift and to exit that lift two floors below the fire floor. Although the research referred to above suggested that if firefighters climbed two floors they should not travel more that 32 m into a fire compartment, this is not supported by assumptions made in typical design guidance, where hose coverage distances of 45 m and 60 m can be acceptable, depending upon the circumstances. In fact, if the two floors and 32 m recommendation were accepted as a standard, it would mean that fire mains should be installed in the majority of buildings above two floors in height.

13-13

13-14

Fire safety engineering ——

buildings more than 11  m but less than 18  m in height; firefighting shaft to include an escape stair and unvented firefighting lobby with a fire main

——

buildings intended to be used as shops, factories or for assembly and recreation where the height of the topmost storey exceeds 7.5  m, with the floor area of any storey above the ground storey not less than 900  m2; firefighting shaft to include a firefighting stair and firefighting lobbies with a fire main

In some geographical areas, alternative methods of facilitating perimeter access for the fire and rescue service can be required. For example, access ‘holes’ can be provided at regular intervals in the building facade (as mentioned in the Spanish Technical Building Code), which are seen to offer benefits.

——

buildings or parts of buildings where the height of the surface of the floor of the topmost storey (excluding any storey consisting entirely of plant rooms) exceeds 18 m; firefighting shaft to include a firefighting stair, firefighting lobbies with a fire main, and a firefighting lift

As part of developing an external access strategy, appropriate access should also be afforded to any fire system inlet connections positioned on the building perimeter which the fire and rescue service personnel may need to use. Common inlet connections that may need to be considered include dry rising main inlets, wet rising main inlets and suppression system inlets. Hose distances from the perceived fire appliance parking position to such inlet connections need to be minimised. In the UK, for example, the distance between the pumping appliance parking position and a dry rising main inlet should be limited to 18 m, which equates to one hose length (see section 13.4.2).

——

buildings where the depth of the surface of the floor of the lowermost storey exceeds 10 m; firefighting shaft to include a firefighting stair, firefighting lobbies with a fire main, and a firefighting lift

——

buildings where there are two or more basement levels, each with a floor area exceeding 900  m2; firefighting shaft to include a firefighting stair and firefighting lobbies with a fire main.

13.9 13.9.1

Internal firefighting access

The recommendations in BS 9999 (clauses 20.1.2 and 20.1.3) for the number of firefighting shafts include the following: ——

At least two firefighting shafts should be provided in buildings with a storey of 900 m2 or more in area and should be located to meet the maximum hose distances set out in (a) and (b) below: (a)

If the building is fitted throughout with an automatic sprinkler system in accordance with BS EN 12845, then sufficient firefighting shafts should be provided such that every part of every qualifying storey is no more than 60 m from a fire main outlet in a firefighting shaft, measured on a route suitable for laying hose.

(b)

If the building is not fitted with sprinklers, then every part of every qualifying storey should be no more than 45 m from a fire main outlet contained in a protected stairway and 60 m from a fire main in a firefighting shaft, measured on a route suitable for laying hose.

Provision of firefighting shafts

Reasonable access into and within a building must be provided for firefighters to enable them to undertake efficient firefighting activities. The main factor determining the level of access and dedicated facilities required to assist the fire and rescue service is the size and height of the building in question. For some buildings, the provision of adequate external (perimeter) access along with the access offered by the normal means of escape routes will be acceptable. For other buildings, such as those with deep or multiple basement levels or those that are tall and beyond the reach of fire service ladders, more onus is placed on firefighting occurring inside the building, thus special access facilities and, often, enhanced fire compartmentation need to be provided. The most common facility provided within a building to improve firefighting capability is a firefighting shaft. Depending upon the specifics of the building involved, a firefighting shaft will provide a package of fire protection measures and installations to help facilitate internal firefighting. Local and national fire safety design guidance sets out criteria for where firefighting shafts (or equivalent) need to be provided. For example, in the UK, BS 9999 (BSI, 2017a) recommends the provision of at least one firefighting shaft in each of the following types of buildings:

Note: qualifying storey means a floor with a height of more than 18 m, or basements more than 10 m in depth. Note: in order to meet the 45 m hose criterion in (b), it might be necessary to provide additional fire mains in escape stairs. This does not imply that these stairs need to be designed as firefighting shafts. Note: it is not necessary for lobbies to be provided to escape stairs solely to accommodate dry riser outlets. The riser outlets may be sited on landings or half-landings to the stair, provided that sufficient space is available for their use by firefighters without obstructing the opening of doors.

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door and/or the end of the elevation. It is then assumed that the provision of this perimeter access along with the access offered by the normal means of escape for a building will provide reasonable access for firefighting. Note that there is no requirement to consider the nature and quantity of facade openings (e.g. windows) on the upper floors of a building; however, in some cases (e.g. for a building with no windows, or with double- or triple-glazed fixed shut windows) where an engineered approach is being taken in relation to firefighting access, it would be advisable to consider the practicalities of firefighting externally.

Firefighting

13-15 (b)

Note: where exact hose distances are not known, direct distances should be taken as two thirds of the hose distance.

——

A firefighting lift installation includes the lift car itself, the lift well and the lift machinery space, together with the lift control system and the fire and rescue service communications system. The installation should conform to BS EN 81-72: 2015 (BSI, 2015b) or BS 9999 (BSI, 2017a). Water protection measures (e.g. raised threshold, drainage grid, sloping floor) to prevent the ingress of water into the lift shaft entrances along with water protection measures within the lift shaft itself will need to be provided as part of the installation.

——

Passenger lifts should not be located within a firefighting shaft unless the lift cars are constructed in accordance with BS EN 81-72, are clearly and conspicuously marked with a notice stating ‘FIREFIGHTING LIFT: Do not use for goods or refuse’, and have access only from a firefighting lobby.

——

Goods lifts and service lifts should not be located within firefighting shafts.

——

If a firefighting shaft contains a firefighting lift, the firefighting stair in that shaft should serve every storey served by the firefighting lift.

——

Dedicated fire and rescue service communications (e.g. a fire telephone system to BS 5839-9: 2011 (BSI, 2011)) may be required.

NFPA 5000 (NFPA, 2018b) does not differentiate between escape staircases and firefighting shafts (called ‘smokeproof enclosures’ in NFPA 5000), i.e. every escape staircase is considered to be suitable as a firefighting staircase.

13.9.2

Design considerations for firefighting shafts

To provide context, BS 9999 (BSI, 2017a) broadly recommends that the following key provisions are incorporated into the design of a firefighting shaft: ——

A firefighting shaft may consist of lobbies and a staircase within a protected enclosure (120 minutes fireresisting) and may also include a firefighting lift.

——

Firefighting shafts should serve every storey through which they pass and be located such that every part of every storey, other than the fire and rescue service access level, is no more than 60 m from the fire main outlet.

——

Only services associated with the firefighting shaft should pass through or be contained within the firefighting shaft. A firefighting shaft should not contain any cupboards or provide access to service shafts serving the remainder of the building.

——

Firefighting lobbies and stairs should be provided with facilities for smoke control (natural smoke ventilation, mechanical smoke ventilation or pressurisation, depending upon application).

NFPA 5000 (NFPA, 2018b) describes a firefighting shaft as a ‘smokeproof enclosure’. The source documents should be read for the detail of design and construction, but the following general standards are recommended in the documents:

——

Fire mains to BS 9990 to be provided.

——

——

Firefighting lobbies and stairs should be provided with emergency lighting.

——

Firefighting lobbies should have a clear floor area of not less than 5 m2. The clear floor area should not exceed 20 m2 for lobbies serving up to four lifts, or 5 m2 per lift for lobbies serving more than four lifts. All principal dimensions should be not less than 1.5 m and should not exceed 8 m in lobbies serving up to four lifts, or 2 m per lift in lobbies serving more than four lifts.

A stair enclosure designed to limit the movement of products of combustion produced by a fire. The smokeproof enclosure can be ventilated naturally, by mechanical ventilation incorporating a vestibule, or by pressurising the enclosure.

——

A smokeproof enclosure shall be enclosed from the highest point to the lowest point by barriers having 2-hour fire-resistance ratings.

——

Access to the smokeproof enclosure shall be by way of a vestibule or by way of an exterior balcony unless the smokeproof enclosure consists of a pressurised enclosure. Every vestibule shall have a net area of not less than 16 ft2 (1.5 m2) of opening in an exterior wall facing an exterior court, yard or public space not less than 20 ft (6.1 m) in width. Every vestibule shall have a minimum dimension of not less than the required width of the corridor leading to it and a dimension of not less than 72 inches (183 cm) in the direction of travel.

——

Where a vestibule is used, it shall be within the 2-hour fire-rated enclosure and shall be considered part of the smokeproof enclosure.

——

In buildings containing flats, protected smokeventilated common corridors or lobbies are expected to protect the firefighting stairs without the need to provide additional dedicated ventilated lobbies. However, where a firefighting shaft is pressurised, a lobby should be provided.

——

Entry to a firefighting shaft at fire and rescue service access level should be available either: (a)

directly from the open air whenever possible, i.e. be sited against an exterior wall, or

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Note: where the firefighting shaft or firefighting stair is not adjacent to a perimeter wall, an assessment should be made as to whether more than one inlet needs to be provided. If two or more inlets are provided, they should be sufficiently remote from one another to provide viable alternative locations from which to charge the fire main.

by way of a protected corridor not exceeding 18 m in length. The corridor is deemed to be part of the firefighting shaft, and any access to it from the accommodation should be by way of protected lobbies, with the corridor being 500 mm wider than is required for means of escape purposes to permit firefighters to move towards the firefighting shaft while occupants are escaping.

13-16 ——

Fire safety engineering

13.9.3

Assessing the provision and design of firefighting shafts: alternative approaches

It may be possible to develop a firefighting access strategy where the provision and design of the firefighting shafts deviates from standard fire safety design guidance by considering the specifics of the building in question and risks present. Common examples of design deviations include the following: ——

Rationalising or reducing the number of firefighting shafts by ensuring there is good hose coverage from the firefighting shafts that are being provided (often linked to the shape of the building in question). For tall buildings, the impact of this approach on the potential for conflict between occupant egress and firefighter access needs to be considered.

——

Variations to protected corridors that lead from external to an inboard firefighting shaft (e.g. in terms of level of fire resistance applied, requirements for lobby protection to the protected corridor, length and firefighter travel distance within the protected corridor).

——

Proposed provision of firefighting lobbies larger than 20 m2 in area.

——

Proposed use of firefighting lifts for other functions, and proposal for firefighting lifts not to serve all floors. Firefighting tactics and the potential locations of bridgeheads need to be considered for the latter.

——

Introduction of a new firefighting shaft or refurbishment of a current firefighting shaft within an existing building, where not all aspects of the current firefighting shaft can practically achieve compliance with BS 9999 guidance. This could include the application of supplementary guidance, such as BS 8899: 2016 (BSI, 2016), in relation to proposed upgrading of existing lifts for firefighter use.

——

Deviation from the BS EN 81-72 (BSI, 2015b) suggestion that the vertical speed of firefighting lifts should be such that floors in a building can be accessed within 60 seconds; for some high-rise buildings, this may not be physically possible due to the limits of lift equipment and the sheer height of the building in question.

Where such deviations are proposed, it would be expected that a specific project assessment is completed in relation to the potential impact that the deviations could have on firefighter safety, and the safety of other relevant persons, with the proposals then being discussed and agreed with the local fire and rescue service.

13.10

Smoke control measures for firefighting

Heat and smoke build-up from a fire within a structure can adversely impact the ability of the fire and rescue service to carry out firefighting and search and rescue activities. Therefore, smoke control measures (see chapter 10) can be employed in certain areas of a building to help protect, or improve tenability in, firefighter access routes to support life safety and property protection strategies. Such systems can, therefore, prove to be critical where fire engineering is being applied to a building. In the UK, areas that are typically afforded dedicated smoke control measures that can benefit firefighter access are as follows: ——

Firefighting shafts: Natural smoke ventilation shafts, mechanical smoke ventilation shafts (lobby extract) and pressurisation (to BS EN 12101-6: 2005 (BSI, 2005c)) are all typically used to protect firefighting stairs, firefighting lifts and firefighting lobbies in buildings, depending upon the individual circumstances. Firefighting shafts are fundamental infrastructure required for tall and/or deep buildings; therefore, ensuring that there is a robust and resilient means of smoke ventilation to protect these vital fire and rescue service access routes and facilities is a key aim.

——

Basement floors: Fires in basements can present exceedingly onerous conditions for firefighters as the products of combustion will often want to leave the fire compartment by the same access routes that firefighters need to use to get to the seat of the fire. Except for basements that are less than 200 m2 in area and less than 3 m below ground level, it is expected that a means of smoke ventilation is provided to help alleviate conditions should a fire occur. As outlined in section 18 of Approved Document B Volume 2 (HM Government, 2013), this could take the form of natural smoke outlets (e.g. vents providing a minimum combined area of 1/40th of the floor area or storey they serve, covered by a stallboard, breakable panel or pavement lights) or a mechanical smoke extract system (provided an adequate suppression system is present, such as sprinklers, with the smoke extract system providing a minimum of 10 air changes per hour using equipment rated to 300 °C).

——

Car parks: There are three broad approaches to providing smoke ventilation to car parks (which are structures that can contain a relatively high potential fuel load), as outlined in section 11 of Approved Document B Volume 2: (a)

design the car park as an open-sided car park, with each storey being naturally vented via permanent openings to external with an area not less than 1/20th of the floor area at that level (with at least half of the vents split equally on two opposing walls), or

(b)

where not designed as an open-sided car park, each car parking level should be vented by permanent openings at high level with an aggregate free vent area of not less

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Every smokeproof enclosure shall discharge into a public way, into a yard or court having direct access to a public way, or into an exit passageway. Such exit passageways shall be without openings other than the entrance from the smokeproof enclosure and the door to the outside yard, court or public way. The exit passageway shall be separated from the remainder of the building by a 2-hour fire-resistance rating.

Firefighting

13-17

(c)

where not designed as an open-sided car park and where opportunities to provide permanent openings for natural ventilation are limited, the car park should be mechanically ventilated. Methods of providing mechanical ventilation in car parks, as covered in BS 7346-7 (BSI, 2013a), include ducted mechanical systems for smoke clearance, impulse fan systems for smoke clearance, impulse fan systems for protecting means of escape, impulse fan systems for assisting with firefighter access, and smoke and heat exhaust ventilation systems.



In all the above cases, the smoke ventilation provisions will provide benefits for firefighting, albeit to different degrees of effectiveness.

——

Residential apartment common corridors and staircases: As outlined in BS 9991 (BSI, 2015c), Approved Document B Volume 2 (HM Government, 2013) and guidance published by the Smoke Control Association (SCA, 2015), common staircases, corridors and lobbies in residential apartment buildings require a means of smoke control. Depending upon the size and configuration of the building in question, this could range from a simple, automatic opening natural smoke vent to external, all the way through to a mechanical smoke ventilation system utilising multiple smoke shafts. For standard applications for apartment buildings 18 m or less in height, the provision of smoke control is primarily for the protection of the stairs, for means of escape and firefighting purposes. However, once buildings exceed 18 m in height (at which point firefighting shafts are required) and/or where extended common corridor travel distances are involved, the smoke control provisions become more extensive. This is to provide increased protection to the common areas and to offer increased resilience to the occupant escape and firefighter access routes.

——

——

Shopping malls: In covered shopping complexes, there is the potential for smoke from a fire in one unit to compromise adjacent units and the wider mall, posing a significant hazard to both occupant means of escape and firefighter access. Therefore, having automatic means of smoke control in covered shopping complexes is crucial to prevent smoke logging the building. Depending on the size of the shopping mall, smoke measures may be required in the public common mall areas, individual shopping units, other occupancies and non-public areas. The form of smoke control may be natural, mechanical (powered) or pressurisation. BRE Report BR 368 (Morgan et al., 1999) provides useful background and design information relating to smoke control systems appropriate for shopping malls, including considerations relevant to fire and rescue service access. Atrium spaces: Where there are open spaces or voids passing through floors within a building, there is an obvious higher potential for smoke spread in the event of a fire. Under guidance such as that contained in Annexes B and C of BS 9999 (BSI,

There are other, less obvious buildings where smoke control measures may be present and which can be used to assist firefighting activities. For example, natural or mechanical smoke ventilation measures can be found in theatres and in some warehouse types (e.g. some selfstorage or high-bay storage warehouses). When developing a fire strategy that is required to propose smoke control measures for a building under local or national design criteria and/or where smoke control is desired to fulfil a property protection or business continuity aspiration, it is important to clearly define the objective of the smoke control system. As part of this the method of smoke control should also be defined, with the performance goals and design criteria or specification clearly established. Where smoke control measures are present to support fire and rescue service access, three key items should be considered as part of designing, installing and handing over the relevant system(s): ——

Automatic operation of the smoke control system(s) is preferable, where possible and practical. Firefighters attending a fire incident may have neither the time nor the knowledge or experience to engage with the manual operation or adjustment of a smoke control system. Configuring the smoke control system to operate automatically will therefore help to reduce the potential for confusion and for delay to firefighting intervention.

——

Where manual override controls for firefighter use are provided for a smoke control system, these should be intuitive in function or use, and positioned in an appropriate location that is easily accessible and in a place of relative safety.

——

Clear and concise system operation information should be kept on site in an appropriate manner for firefighter reference, to enable interaction with the system.

13.11 Communications For large and complex buildings, the provision of additional, reliable communication equipment for the fire and rescue service should be considered. Radio equipment is carried and used by firefighters, but this equipment has its limitations, and it can be significantly affected by the built environment, particularly in tall and deep structures.

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2017a), smoke control measures are often required in atrium spaces to protect occupant means of escape. These measures can also be used to assist with firefighter access. Even where dedicated smoke control for means of escape is not required, smoke clearance provisions may still be provided (e.g. for atria 18 m or less in height: natural exhaust vents with an area of not less than 10% of the maximum plan area of the atrium; and for atria more than 18 m in height: mechanical smoke ventilation providing a minimum of four air changes per hour in a sprinklered building with a controlled fire load at the atrium base or six air changes per hour in an unsprinklered building).

than 1/40th of the floor area at that level (with at least half of the vents split equally on two opposing walls), or

13-18

Fire safety engineering

In some certain circumstances (e.g. underground transport infrastructure and high-rise buildings, where construction materials may limit the broadcasting of radio communications), fire and rescue service radio communications may need to be supported through the use of a ‘leaky feeder’ installation. In its simplest form, this involves the provision of an appropriate cable and amplifiers: the cable is able to receive and emit radio waves, thus acting as an extended antenna and allowing two-way communication.

strategy. For example, in an ultra-high-rise building, firefighters may utilise high-speed lifts to go from the access level to the refuge floor below the fire floor, and then utilise the firefighting lift(s) from this refuge floor to work their way further up the building. Where the provision of refuge floors is being considered for a building, there should be a coordinated approach between the fire engineer and the building services engineer in relation to the additional provisions that may be required (in terms of active and passive fire safety measures, additional welfare facilities, emergency power, communications etc.). Discussions should also be had with the local fire and rescue service in relation to the different potential evacuation scenarios and the fire and rescue service access strategy.

The need to provide additional communication equipment in a building for fire and rescue service use should be discussed with the local fire and rescue service, particularly when the provision of leaky feeder technology is being considered.

13.13

13.12

13.13.1 Background

Refuge floors and firefighter access

With buildings tending to increase in height on a global scale, and the emergence of ultra-high-rise buildings, designers and engineers need to consider the impact that vertical travel within such buildings has on both occupant evacuation and firefighter access. While some ultra-high-rise buildings, such as the Petronas Twin Towers, rely on high-speed lifts for occupant evacuation, others have protected ‘refuge floors’ or ‘refuge rooms’ at strategic levels within a building, for the occupants to evacuate to in the event of a fire. These refuge floors are places of temporary refuge. They are highly fire protected (with passive and active measures) and have their own independent air supplies. For example, in Taipei 101 there are two pressurised fire safety corridors on each floor, which connect to separate pressurised emergency staircases that provide access to two refuge rooms on every eighth floor. In the Shanghai World Financial Centre, every 25th floor is constructed as a refuge floor, with sufficient space to hold every occupant from 24 other floors at a density of 0.3 m2 per person. Lift installations known as ‘occupant egress elevators’ stop at every refuge floor. The Shard in London also adopts a refuge floor approach, along with the use of evacuation lifts. The use of refuge floors potentially means that the evacuation of a building can be completed in a more controlled and efficient manner, and avoids placing onerous physical demands on the occupants (in terms of being expected to evacuate tens of storeys down to final exit level). In turn, this can have a benefit in that there will potentially be less conflict between occupant egress and fire and rescue service access (e.g. within the stair enclosures and lobby areas), and it can help to minimise any adverse impacts on staircase pressurisation systems (which are often used in taller buildings, but performance can be reduced with the opening of multiple stair enclosure doors during occupant escape). The fire and rescue service may also be able to utilise the protected refuge floors as part of their access

Firefighting timelines and an engineered approach

For some fire engineering design solutions, it may be desirable to interrogate in detail the assumptions relating to the predicted timings for attendance to and firefighting activities within a building by the fire and rescue service (or other trained personnel expected to engage in firefighting). The aim of this is to gain a more accurate appreciation of how long it could reasonably take for firefighting to commence for a specific type of fire incident or scenario. Where such an analysis is required, it will be necessary to consider what level of detail is appropriate. In some cases, a relatively simple analysis may be suitable, where only broad events and actions are considered. In other cases, a very detailed analysis could be needed, where the anticipated activities of specific groups of (or individual) firefighters need to be accounted for. In all cases, it is important to consider and demonstrate a reasonable margin of safety, keeping in mind that there could be potential future changes to local fire and rescue service resourcing and response, which may have an impact on the validity of an analysis completed at a particular point in time. As can be seen in the preceding sections of this chapter, the objectives and process of successful tactical firefighting involve a complex interrelationship of many different variables. For a building fire, considerations that might influence the firefighting timeline could include, among others: ——

What is the potential fire scenario that needs to be considered?

——

How is the fire incident potentially detected, and how is the local fire and rescue service notified or summoned?

——

Where is the building or area in question located?

——

What is the expected local fire and rescue service attendance in terms of type of predetermined

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The most common means of providing supplementary communication equipment is a fire telephone system (e.g. to BS 5839-9 (BSI, 2011)). Telephones, as part of a dedicated linked network, can be positioned in protected firefighter access routes, such as the firefighting lobbies on each floor.

Firefighting attendance, resources (type of fire cover, personnel, equipment) and response time? How might this escalate?

give access to a compartment from a staircase in which there are fire main landing valves.

How do the local fire and rescue service gain access to the site or building? Who might meet them on arrival? What level of premises information is available to firefighters?

The speed and ‘weight’ of fire service attendance The location of the nearest fire stations and the system of staffing will enable pump appliance fire crews to arrive outside the building within 10 minutes of the time of call. Additional fire pumps could take up to 30 minutes to arrive.

——

What is the size, height, shape, occupancy, content, layout, etc. of the building?

——

What external water supply arrangements (e.g. hydrants) are available?

Fire scenario

——

Are any specific facilities for firefighting (e.g. firefighting shafts, fire mains) provided for the building? What other relevant passive and active fire safety systems are present?

——

How will firefighting equipment and personnel be able to be transported in and around the building? What are the travel distances within the building, both horizontally and vertically? How long could the transportation of equipment and personnel take?

Because of the occupancy and fire compartmentation, any fire that occurs should be (worst credible case) contained within a compartment or sub-compartment so that it will be limited to a size that can be controlled by two firefighting jets for a period of 120 minutes.

——

How will the factors listed above potentially influence the decision-making of attending firefighting crews, in terms of committing resources and commencing fighting the fire with appropriate extinguishing media?

The number of variables that will need to be considered when developing the perceived firefighting timeline will be highly case specific. It is recommended that the timeline is developed through a qdr process, with the fire engineer liaising with the local fire and rescue service and other relevant authorities having jurisdiction.

Arrival protocol and entry preparation time The fire alarm system and indicator board together with the fire safety management system within the building should mean that the fire crews will know which access door(s) to use and the firefighting lift should be waiting at ground floor access level. Interrogating the fire alarm panel (and/or receiving information from a representative of the building management) by the fire officer in charge should take no more than 3 minutes, by which time the fire crew should have collected all necessary equipment from the fire pump. Positions for hose lines/stopping jets

The aim and objective of compiling a firefighting timeline as part of a fire engineered solution should be clearly declared, and the events and activities that form part of the timeline should be collated and assessed in a logical and chronological order.

The configuration of the floors means that it would be necessary to commence firefighting operations from two directions utilising two firefighting shafts.

PD 7974-5 (BSI, 2014a) provides useful background information on different variables that could influence a firefighting timeline, as well as suggested firefighter task analysis and intervention modelling. Related to this, and as discussed by Halstead (2016), there may in some circumstances be scope to utilise computer modelling software to help assess potential firefighting intervention and timelines, albeit that this approach is currently in its infancy.

‘Fire safe’ access routes within floor areas have been established by utilising protected corridors.

13.13.2

In this example, it is assumed that firefighters would initially use the firefighting lift to ascend from access level to the firefighting bridgehead located two floors below the fire floor. They will then use the staircase to work their way from the bridgehead up to the fire floor.

Worked example for a high-rise building

The following presents an example firefighting timeline for a theoretical high-rise building. It should be treated as an indication of what a simple assessment of the relevant firefighting events and activities could entail. This example is provided for illustrative purposes only. The building A high-rise building with floors of a size and layout that require four firefighting shafts to ensure every part of every storey is within 50 m of the fire-resisting doors that

‘Fire safe’ access routes

Firefighting lift and staircase The firefighting lifts within the building can access all floors within 60 seconds. If ascending via a staircase, a base of 30 seconds per floor, increasing by 15 seconds for each floor, could be used for the calculations.

Therefore, for this example: ——

time for firefighters ascending in firefighting lift to bridgehead = 60 seconds

——

time for firefighters to walk up firefighting staircase to fire floor from bridgehead = 60 + 15 seconds.

Calculation of fire attack timeline

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——

13-19

13-20

Fire safety engineering

Table 13.6  Example fire attack timeline Event

Time / seconds

Initiation to fire detection

120 10

Processing by central monitoring station

60

Receipt of call by fire service mobilising control

10

Transmission to fire station and response

60

Travelling time of fire service

600

Arrival protocol and entry preparation time

180

Firefighter travel in firefighting lift

60

Firefighter travel walking up two flights of stairs to fire floor

75 Total: 1175 (approx. 20 min)

The calculation of the fire attack timeline for this simple worked example is shown in Table 13.6. Discussion of timeline results for worked example If the worst credible case, adjusted by a factor of 2, suggested that the fire and rescue service must commence applying water to the fire within 40 minutes of discovery of the fire, the above figures would mean that the horizontal distance from the fire pump to the firefighting lift and from the staircase landing to the point at which the firefighting jet is applied must be traversed within 20 minutes. Clearly, the travelling time from the staircase landing to the point at which the firefighting jet is turned on is the more onerous, as firefighters will have to run out hose and enter a hazardous environment dragging the hose with them. The travelling time from the fire pump to the lift will be in clear air and carrying equipment rather than running out hose, and a greater distance can therefore be covered in a shorter time. It is obviously beneficial for all travel times to be as short as possible. However, if the limitations of the site or the designed use of the building calls for extended travel times, it is considered reasonable to allocate times, and thereby distances, on a 3 : 1 basis, i.e. if the available time is 20 minutes then 5 minutes could be allocated for travel from the fire pump to the lift and 15 minutes allocated for travel from the staircase landing to the point at which the jet turned on. Obviously, if any of the individual times are extended, then the whole timeline is altered. This may result in a need to provide further passive or active fire safety measures to help compensate for the extended timeline and provide an increased margin of safety, such as installing an automatic sprinkler system.

13.14

Firefighting and environmental protection

Although life safety and property protection are usually the main focuses for building fire strategies, in some cases specific consideration needs to be given to the interaction between fire safety, potential firefighting activities and

Fire-related incidents can potentially have a significant impact on the environment, with contaminated water run-off, hazardous substance leakage or release, and smoke emission posing the most significant concerns. Fire and rescue services have had to adjust to these concerns and implement new techniques to minimise potential environmental damage resulting from firefighting operations. In the UK, this is reflected in the detailed guidance contained in the Environmental Protection Handbook for the Fire and Rescue Service (DCLG, 2016). Similarly, operators of buildings or sites of certain types or uses may also need to consider specific environmental protection measures on site in the form of provisions that minimise the outbreak and spread of fire to begin with, and then to assist the fire and rescue service in accessing the building or site and then controlling and extinguishing a fire with as little damage as possible. Such measures could include, for example, the strategic use of fire suppression systems, the use of bunds and/or containment tanks, the provision of enhanced fire and rescue service access roadways and water supplies, and protection measures for drainage systems or watercourses found on site. Where enhancements to building or site fire protection measures for environmental protection are required by national legislation, these often need to be incorporated into the overall fire strategy to ensure that a consistent and complementary design solution can be delivered, and that it still satisfies the minimum accepted standards for life safety. Fire engineers should therefore be cognisant of this, and they may need to liaise with additional authorities having jurisdiction (e.g. the Health and Safety Executive and/or the Environment Agency), as well as the local fire and rescue service where the need arises.

13.15

Provision of information for the fire and rescue service

For any building, the provision of appropriate and adequate premises information for the local fire and rescue service can help to facilitate efficient firefighter access and response, and help responders to an incident understand a building’s layout and fire safety systems. This can be of particular importance for buildings containing fire engineered design solutions or systems, high fire risks or where bespoke arrangements within the building may present firefighters with scenarios that they may not be familiar with.

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Actuation of fire detector to transmission of alarm

environmental protection. For example, this can arise for some buildings used in the processing of waste materials or chemical production, where ensuring adequate environmental protection for many reasons, including fire, is a key objective for stakeholders. In recent years, societal understanding and expectations for the protection of the environment and what constitutes sustainable development have increased. This has led to the implementation of specific environmental protection legislation, which has had an influence on fire safety.

Firefighting

13-21

There are different methods of collating, formatting and providing information on site for firefighter reference. The easiest forms are:

——

the provision of concise premises plans and supporting hazard/risk and firefighting facility information at a centralised location within the building (e.g. a 24-hour staffed reception) or in a secure manner external to the building (e.g. a secured, recognisable information box system) the provision of information as part of a fire control centre (see chapter 14).

Whichever method is chosen, it is essential to keep the information provided on site up to date, and that it is in a format that is recognised by the local fire and rescue service. It is therefore recommended that the key personnel liaise where possible with the local fire and rescue service to ensure that the information is presented in an appropriate manner for them, and to initiate any required familiarisation visits to the building or site by local fire crews to gather risk and pre-planning information. As many local fire and rescue services use mobile data terminals (mdts) on their appliances, there may also be opportunities for building or site managers to provide additional supplementary electronic information and plans to the fire and rescue service that can be downloaded to the mdt devices. For buildings where complex fire safety systems are provided, it is also recommended that key personnel (such as the building services engineer or security staff), who may provide 24-hour on-site staff coverage or are available for out-of-hours emergencies, are trained to be familiar with the fire safety systems present, including any dedicated facilities provided for fire and rescue service use. Such trained personnel can provide invaluable assistance to the fire and rescue service in the event of an emergency, in terms of ensuring the efficient transfer of fire safety information and identifying where and how relevant fire safety systems operate.

13.16

First-aid firefighting provisions on site

13.16.1

Objectives of providing first-aid firefighting equipment

Although there would be very limited opportunities to base a fire engineered design solution upon firefighting intervention by the occupiers of a site or building, the provision of first-aid firefighting equipment is still important to the overall fire strategy. For example, when used by correctly trained staff, fire extinguishers have proved to be an effective method of controlling and extinguishing fires of limited size, with their true success rate probably being under-reported due to the reluctance of people to report extinguished fires to the fire and rescue service. When firefighting is undertaken by the occupiers of a building, there is usually a single immediate objective – to extinguish the fire in the shortest possible time. The outcome of an attack on a fire by occupiers will depend on

——

availability of appropriate firefighting equipment

——

appreciation of the size and risk of the task

——

physical ability of staff

——

training assimilated

——

skill level of the individuals involved.

The type and quantity of first-aid firefighting equipment provided for a site or building is often determined through fire risk assessment, to ensure that the most appropriate form of fire extinguishing media is provided for the type of fire incident that might potentially occur. The ongoing testing and maintenance of firefighting equipment provided on site is obviously crucial, to ensure that the equipment is in good working order at all times. Where the provision of first-aid firefighting is deemed necessary for different areas and risks, it should be provided in accordance with whatever code is appropriate for the country or region in which the site or building is situated. Adequate training must be given to designated personnel who may be expected to use such equipment (e.g. BS 5306-8: 2012 (BSI, 2012b) calls for at least one water-based fire extinguisher per 200 m2 suitable to the risk, and people should not have to travel more than 30 m to reach one). This training should not only deal with how to operate the different types of fire extinguishing equipment present, but should also include: ——

an assessment of the physical capability of staff to carry and operate the different equipment

——

the maximum distance it is reasonable for individuals to carry a fire extinguishers etc. in order to use them

——

the necessity of maintaining a route to safety so that the operator can turn away from the fire and escape, and

——

an indication of the maximum size of fire the trained personnel may try to extinguish (expressed in common terms, such as a single waste paper basket).

All training should be repeated on an appropriate routine periodic basis depending on the risk (e.g. annually). In certain circumstances, it could be argued and justified through risk assessment that a building may not be required to be provided with first-aid firefighting equipment. An example of such a circumstance could be in residential blocks of flats, where there are no trained members of staff present.

13.16.2

Examples of common first-aid firefighting equipment

There are many types of first-aid firefighting equipment and technologies in use (rated for use on different fire sources), but in broad terms the most common types fall into the following groups:

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——

the availability and competency of trained staff to take action based on:

13-22 ——

(c)

(d)

(e)

——

——

water spray (with additives to permit enhanced capability and reduced cylinder size) – can typically be used on organic solid materials, such as wood, paper, plastics, etc. water mist – can be used on a broad spectrum of fire types depending upon class rating dry powder – can typically be used on organic solids, and on liquids such as grease, oil and petrol foam (aqueous film-forming foam (afff)) – can typically be used on solids, liquids and some electrical fires, depending upon rating

(f)

carbon dioxide – can typically be used on live electrical equipment

(g)

wet chemical – can typically be used on oils and fats.

Fixed hose reel installations (e.g. to BS 5306-1 (BSI, 2006)): Comprise a small-bore hose on a reel or drum, connected to a permanent water supply, and can typically be used on solid materials such as wood, paper, plastics etc. These are provided primarily for use by designated trained personnel within a building, but may also be used by the fire and rescue service. Fire blankets (e.g. to BS EN 1869: 1997 (domestic) (BSI, 1997) or BS 7944: 1999 (industrial) (BSI, 1999)): Use a fire-resisting material to smother flammable liquid fires of a relatively small size. Fire buckets: A simple bucket which can be filled with water or sand. The latter is the most common, with sand being used smother and contain potential small flammable liquid fires.

13.16.3

Special circumstances and equipment

For some sites or buildings there may be high-risk activities or legislative requirements present where enhanced or more robust first-aid firefighting equipment is deemed necessary to ensure a reliable rapid response to a developing fire incident. In an extreme case, this could involve the provision of dedicated personnel who have been provided with a firefighter level of training, and who have access to appropriate ppe and portable and/or fixed firefighting equipment on site to assist with commencing firefighting intervention as soon as possible. While this type of arrangement is mainly associated with specialist industries (e.g. some areas of the atomic industry, aviation industry, industrial processing, offshore/ marine environments), the fire engineer and building service engineer should be aware that such specialist arrangements can exist in other building types.

References Bronto Skylift (no date) HLA articulated aerial platforms [online] http:// www.brontoskylift.com/en/hla (accessed May 2016) BSI (1987) BS 5041-2: 1987 Fire hydrant systems equipment. Specification for landing valves for dry risers (London: British Standards Institution) BSI (1997) BS EN 1869: 1997 Fire blankets (London: British Standards Institution) BSI (1999) BS 7944: 1999 Type 1 heavy duty fire blankets and type 2 heavy duty heat protective blankets (London: British Standards Institution) BSI (2002) PD 7974-0: 2002 Application of fire safety engineering principles to the design of buildings. Guide to design framework and fire safety engineering principles (London: British Standards Institution) (Note: PD 7974-0: 2002 has been replaced by BS 7974: 2019) BSI (2005a) BS EN 14339: 2005 Underground fire hydrants (London: British Standards Institution) BSI (2005b) BS EN 14384: 2005 Pillar fire hydrants (London: British Standards Institution) BSI (2005c) BS EN 12101-6: 2005 Smoke and heat control systems. Specification for pressure differential systems. Kits (London: British Standard Institution) BSI (2006) BS 5306-1: 2006 Code of practice for fire extinguishing installations and equipment on premises. Hose reels and foam inlets (London: British Standards Institution) BSI (2011) BS 5839-9: 2011 Fire detection and fire alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of emergency voice communication systems (London: British Standards Institution) BSI (2012a) BS 750: 2012 Specification for underground fire hydrants and surface box frames and covers (London: British Standards Institution) BSI (2012b) BS 5306-8: 2012 Fire extinguishing installations and equipment on premises. Selection and positioning of portable fire extinguishers. Code of practice (London: British Standards Institution) BSI (2013a) BS 7346-7: 2013 Components for smoke and heat control systems. Code of practice on functional recommendations and calculation methods for smoke and heat control systems for covered car parks (London: British Standards Institution) BSI (2013b) BS EN 50518-1: 2013 Monitoring and alarm receiving centre. Location and construction requirements (London: British Standards Institution) BSI (2013c) BS EN 50518-2: 2013 Monitoring and alarm receiving centre. Technical requirements (London: British Standards Institution) BSI (2013d) BS EN 50518-3: 2013 Monitoring and alarm receiving centre. Procedures and requirements for operation (London: British Standards Institution) BSI (2014a) PD 7974-5: 2014 Application of fire safety engineering principles to the design of buildings. Fire and rescue service intervention (Sub-system 5) (London: British Standards Institution) BSI (2014b) BS 8591: 2014 Remote centres receiving signals from alarm systems. Code of practice (London: British Standards Institution) BSI (2015a) BS 9990: 2015 Non automatic fire-fighting systems in buildings. Code of practice (London: British Standards Institution) BSI (2015b) BS EN 81-72: 2015 Safety rules for the construction and installation of lifts. Particular applications for passenger and goods passenger lifts. Firefighters lifts (London: British Standards Institution) BSI (2015c) BS 9991: 2015 Fire safety in the design, management and use of residential buildings. Code of practice (London: British Standards Institution) BSI (2016) BS 8899: 2016 Improvement of fire-fighting and evacuation provisions in existing lifts. Code of practice (London: British Standard Institution)

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Portable fire extinguishers (e.g. to BS 5306-8): Types of portable fire extinguisher include: (a) water – can typically be used on organic solid materials such as wood, paper, plastics etc. (b)

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Fire safety engineering

Firefighting BSI (2017a) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution)

DCLG (Department for Communities and Local Government) (2008) Fire and Rescue Manual – Volume 2: Fire Service Operations – Incident command (3rd edition) (Norwich: The Stationary Office) DCLG (2016) Environmental Protection Handbook for the Fire and Rescue Service [online] https://www.ukfrs.com/sites/default/files/2017-09/Environment%20Agency%20and%20DCLG%20environmental%20handbook. pdf (accessed November 2017) DCLG and CFRA (Chief Fire and Rescue Adviser) (2011) Fire and Rescue Service Operational Guidance. Generic Risk Assessments. GRA 3.1: Fighting fires in buildings. Section 1.0 (Norwich: The Stationary Office) Halstead S (2016) ‘Firefighting engineering’ International Fire Professional 18 22–26. HM Government (2013) The Building Regulations 2010 Approved Document B: Fire Safety. Volume 2: Buildings other than dwellinghouses (2006 edition incorporating the 2007, 2010 and 2013 amendments) (Newcastle upon Tyne: NBS) (Note: further amendments published as a separate document, April 2019) IAFC and NFPA (International Association of Fire Chiefs and National Fire Protection Association) (2016) Evidence-based Practices for Strategic and Tactical Firefighting. (Burlington, MA: Jones & Bartlett Learning) ICC (2017) 2018 International Fire Code (Country Club Hills, IL: International Code Council) LGA and Water UK (2007) National Guidance Document on the Provision of Water for Fire Fighting (3rd edition) (London: Local Government Association and Water UK) Martin Aircraft Company (no date) First Responder Jetpack [online] http://www.martinjetpack.com/sales/manned-jetpack0.html (accessed December 2017)

Morgan HP, Ghosh BK, Garrad G, Pamlitschka R, De Smedt J-C and Schoonbaert LR (1999) Design methodologies for smoke and heat exhaust systems BRE Report 368 (Garston, Watford: BRE Press) NFPA (2013) NFPA 24 Standard for the installation of private fire service mains and their appurtenances (Quincy, MA: National Fire Protection Association) NFPA (2016) NFPA 14 Standard for the installations of standpipes and hose systems (Quincy, MA: National Fire Protection Association). NFPA (2018a) NFPA 1 Fire Code (Quincy, MA: National Fire Protection Association) NFPA (2018b) NFPA 5000 Building Construction and Safety Code (Quincy, MA: National Fire Protection Association) NRC, ICC, DBH and ABCB (National Research Council of Canada, International Code Council, Department of Building and Housing New Zealand, Australian Building Codes Board (2005) International Fire Engineering Guidelines – Edition 2005 (Canberra: Australian Building Codes Board) ODPM (Office of the Deputy Prime Minister) (2004a) Operational Physiological Capabilities of Firefighters: Literature review and research recommendations. Fire Research Technical Report 1/2005 (London: Her Majesty’s Stationery Office) ODPM (2004b) Physiological Assessment of Firefighting, Search and Rescue in the Built Environment Fire Research Technical Report 2/2005 (London: Her Majesty’s Stationery Office) SCA (Smoke Control Association) (2015) Guidance on smoke control to common escape routes in apartment buildings (flats and maisonettes). Revision 2 (Reading: FETA) Society of Fire Safety (2014) Practice Note for Tenability Criteria in Building Fires, version 2.0 (Barton, ACT: Engineers Australia)

This publication is supplied by CIBSE for the sole use of the person making the download. The content remains the copyright property of CIBSE

BSI (2017b) BS 5839-1: 2017 Fire detection and fire alarm systems for buildings. Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises (London: British Standards Institution)

13-23

14-1

14

Fire safety management

The importance of fire safety management should not be underestimated. Even with the most comprehensive fire safety provisions that modern technology can provide, it is essential that there is adequate management of fire safety to ensure that the occupants of a building reach a place of safety in the event of fire and to avert disaster. In many multi-fatality disasters, poor fire safety management has been found to be a significant contributing factor. Different countries around the world have adopted and apply different requirements, recommendations or standards in their approach to fire safety. Most countries have some regulations governing the design and construction of the building for fire safety; fewer have regulations that relate to the management of the building. Within Europe, the ‘Workplace Health and Safety’ Directive (89/391/EEC) includes fire safety and provides functional high-level requirements to achieve fire safety through the management of the premises. The individual countries that are subject to the Directive have each implemented the Directive in their own way.

The fire safety manager is the person who carries out the job of fire safety management within the building. In a small building, this task might only be a small part of the manager’s job. In a large, complex building, this task may be a full-time job with a team of staff. Within the UK, the fire safety manager may be the ‘Responsible Person’ for the building or occupancy specified in the Regulatory Reform (Fire Safety) Order 2005 (in England and Wales, or the relevant Regulations in Scotland and Northern Ireland). (Note that different terms for ‘Responsible Person’ are used outside England and Wales, such as the ‘Duty Holder’.) In other buildings, the fire safety manager will be a ‘Competent Person’ appointed by the ‘Responsible Person’. In this latter case, the Responsible Person will be the entity that retains the legal responsibility to comply with the fire safety law. The legal responsibility cannot be delegated to the Competent Person who has been appointed to assist the Responsible Person in executing the requisite duties. The designer needs to ensure that the overall design of a building assists and enhances the job of the fire safety manager. Also, the fire safety manager needs to be aware of the fire safety provisions designed into the building.

Note, however, that in response to the movement of people within Europe, hotels have been given special status with respect to fire safety (Council Recommendation 86/666/ EEC) and guidance on hotel fire safety management is available (HOTREC, 2010).

Detailed guidance on fire safety management is contained in British Standard BS 9999: 2017 (BSI, 2017).

Within the UK, effective fire safety management, and the key tasks that this entails, are specified as legal requirements (in England and Wales) under the Regulatory Reform (Fire Safety) Order 2005 (SI 2005/1541) (and in the Fire Safety (Scotland) Regulations 2006 (SSI 2006/456) or the Fire Safety Regulations (Northern Ireland) 2010 (SR 2010/325)).

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legal obligations and statutory duties

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designing for a manageable building

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construction to handover

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the fire safety manual

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authority and responsibilities of the fire safety manager

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communication

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fire prevention

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ensuring that systems respond properly in a fire emergency

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planning for a fire emergency

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management of a fire emergency

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other planning issues

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changes to a building

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fire control centre.

Fire safety management here encompasses the whole of the management of fire safety. It comprises the management activities that ensure that the incidence of fire in a building is minimised, but that, when a fire does occur, all of the passive, active and procedural fire safety systems are in place and operating properly. Fire safety management primarily concerns the life safety of building occupants and firefighters but can also concern the protection of property, heritage and environment. It is a process that covers the entire life cycle of the building, i.e. from design to construction, handover, occupation, changes of use etc., through to demolition. It is essentially concerned with building occupation. It is not simply about maintenance of fire safety systems.

This chapter covers the following aspects of fire safety management:

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14.1 Introduction

14-2

14.2

Fire safety engineering

Legal obligations and statutory duties

Within the UK, these include the Building Regulations 2010 (SI 2010/2214), as amended, the Health and Safety at Work etc. Act 1974, the Regulatory Reform (Fire Safety) Order 2005, the Fire Safety (Scotland) Regulations 2006, the Fire Safety Regulations (Northern Ireland) 2010, the Construction (Design and Management) (CDM) Regulations 2015 (SI 2015/51), the Equality Act 2010, local acts, environmental acts and, in some premises, the Petroleum (Consolidation) Regulations 2014 (SI 2014/1637). Some older buildings will have been previously subject to the Fire Precautions (Workplace) Regulations 1997 (SI 1997/1840) and the Fire Precautions Act 1971 (now repealed). (Fire certificates issued under the Fire Precautions Act no longer have legal standing, and risk assessments carried out under the Fire Precautions (Workplace) Regulations need to be carried out afresh as the detailed requirements have changed.) In England and Wales, the Department for Communities and Local Government (DCLG) has published a series of guides in support of the Regulatory Reform (Fire Safety) Order 2005 (DCLG, 2012). Similar guides are available in Scotland (Scottish Government, 2017). Managers have to be aware of the statutory requirements (for all buildings except private domestic premises but including houses in multiple occupation and common areas in apartment buildings) concerning the maintenance of the means of escape, fire warning systems, portable fire extinguishers, escape lighting, fire safety instructions to staff etc. In many countries, there is a legal requirement to consult the local building and fire authorities prior to the implementation of extensions or alterations within the building and for necessary approvals under planning acts that control external elevations of buildings. For fire engineered buildings, in particular, where good management is often a significant element of the safety system, the ways in which the legal obligations and duties are satisfied should be properly documented.

14.3

Designing for a manageable building

14.3.1 Pre-planning Although the formal responsibilities of the designer and the fire safety engineer largely end once the building is completed and occupation and/or use has commenced, many, if not all, of the systems included will impose

In practice, therefore, the fire safety engineer can assist the work of the fire safety manager by ensuring that: ——

active fire safety systems are able to be properly maintained and tested

——

passive fire safety systems are not likely to be made ineffective

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design assumptions regarding the use and management of the building are sound, e.g. that they correctly anticipate the type of occupancy or the fire load, or provide for flexibility in the use of the building.

Therefore, wherever possible, the key management issues relating to any new project should be identified at the earliest possible stage in the process, ideally at the concept stage, and properly taken into account. It is important at this early stage to initiate liaison with other agencies, such as building control officers, fire safety officers, health and safety inspectors and insurers. The designer should become familiar with the responsibilities and tasks of the fire safety manager so that these issues can reasonably be taken into account in the design (see section 14.4). In England and Wales, the designer needs to be aware of Regulation 38 of the Building Regulations 2010, entitled ‘Fire safety information’ (see section 14.5.1).

14.3.2

Management input at the design stage

It is a principle of good fire safety design that buildings should be designed and equipped so that in an emergency the occupants of the building can make their way easily to a place of safety. This requires the designers to take account of human behaviour, in particular in emergency situations, and seek to use this behaviour to lead people to safety, rather than design a complex system which requires a rapid learning process by the occupants at a time of stress. There is therefore a need for the fire safety systems to be appropriate for what people actually do, not what the designer would like them to do. A clear statement of the design requirements for the management of a building has to be developed and conveyed to the design team (architect, designer and fire safety engineer), otherwise there is a danger that the new building will need extensive modifications to cater for conditions that were not anticipated by the designers. A design that does not fulfil the management brief can adversely affect running costs, staffing levels and the general safety and efficiency of the building. Fire safety systems need to be considered as an inherent part of the basic design, and not as supplementary to other aspects, such as services or finishes. Where there are

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The senior management of the building need to identify and meet legal requirements and statutory duties imposed upon them by various regulations, orders and acts that impact on the management of fire safety. The relevant regulations, orders or acts applying to the management of fire safety will nearly always be those of the country or jurisdiction in which the building is located.

management responsibilities. The job of the fire safety manager will be made more difficult if the fire safety design conflicts with the normal, everyday use of the building (e.g. by placing fire doors across through routes) or fails to take account of real behaviour during an incident, such as counter-flows in escape routes as parents search for their children.

Fire safety management

An important aspect of design team management is the coordination of the specialists who are designing systems that will have to interact. Wherever possible, checks should be carried out to ensure that the systems are compatible and that, when changes are made, any consequential effects are accommodated so that the overall objectives will still be satisfied. Where the project is a speculative build, without a particular occupier, or even a particular use, in mind, then it may be appropriate to design with minimal management requirements. Other aspects to consider will be the management of environmental issues and the long-term implications of the proposed design for management over the life of the building.

14.3.3

Designing for the management of fire prevention

By careful and considered design or location, the designer or fire engineer can provide the building with facilities and equipment that can assist the fire safety manager in carrying out their fire prevention duties (see section 14.8). In particular, the designer can assist the fire safety manager with the housekeeping in the building (see section 14.8.1). A significant way of preventing fire incidents is to correctly maintain non-fire equipment that might start a fire and to control the storage and use of materials that might allow a fire to develop and spread. The designer should therefore consider the manager’s need to inspect and maintain the following items (the list is not exclusive): ——

potential sources of ignition, such as gas, oil and electrical heating installations

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electrical and gas installations

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other heat-dissipating equipment

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equipment in voids and cavities, such as heating, ventilation and air-conditioning (hvac) and cavity barriers

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furniture, furnishings, decor and equipment

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floor coverings, scenery, props, curtains and drapes

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other equipment that has particular fire risks.

The designer can assist the manager in a number of ways to reduce the likelihood of arson and to mitigate the effects if it does occur. One option is for the designer to provide good security arrangements in the building to reduce the risk of arson. However, the designer will have to bear in mind the possible conflict between security and means of escape (see section 14.8.3).

14.3.4

Designing for the management of fire protection

By careful and considered design or planning, the designer or fire engineer can provide the building with facilities and equipment that can assist the fire safety manager. This includes ensuring that the fire protection systems can be kept fully functional and designing provisions that will allow effective evacuation.

14.3.5

The provision of safety systems

All safety equipment should be readily available, reliable, testable, durable, resilient, repairable and maintainable. Fire safety systems requiring inspection, maintenance, testing or repair are detailed in section 14.9.1.

14.3.6

Designing for change of use

The designer needs to consider whether the building is being designed to accommodate a specific occupancy with a defined management regime. The designer may wish to provide a greater level of designed-in safety with the least possible dependence on management so as to allow for maximum flexibility in the future use of the building.

14.4

Construction to handover

14.4.1 Construction Many fires occur during construction, often in the latter part of a project nearing completion, partly due to the nature of the work being carried out, which often includes hot work, partly due to the necessarily complex management regime and partly due to the level of fire protection measures, which, although fitted, may not be operable. Fire safety on construction sites, including fire safety management, is covered in detail in chapter 15.

14.4.2

Fitting-out and speculative builds

Management during fitting-out will need to consider most of the same issues as for the construction phase, although different processes may be employed, since fire safety systems may still not be in place or operational. Again, particular care is needed during any hot work, and to avoid blocking escape routes. Some buildings will be speculative and the identity of the occupier will not be known at the time of construction. Such buildings must either be well-equipped with fire safety provisions and require the minimum of fire safety management from the eventual occupiers, or the management assumptions or implications must be stated in the fire safety manual as a limitation on the eventual use of the building.

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conflicts of interest, compromises may be necessary. In any case, a flexible approach is essential if novel problems are to be solved. It should be recognised that there can be conflicts between the fire safety requirements and the normal use of the building or with building services or other safety systems.

14-3

14-4

14.4.3

Fire safety engineering

Approvals and certification

14.4.4

Commissioning and handover

Before accepting the building for occupation, it is essential that the safety of the staff, public and construction personnel, if the building is being completed in phases, is assured. The design and construction of the building and the systems installed in it need to be recorded in the fire safety manual. In any case, fire safety systems, as with any other components of a building, must, in England and Wales, satisfy Regulation 7 of the Building Regulations 2010 (Materials and workmanship) (HM Government, 2013; Welsh Government, 2013), ), as amended by the Building (Amendment) Regulations 2018 (HM Government, 2018). Guidance on the commissioning and handover of fire safety systems is given in appropriate British Standards and other guidance documents. On completion of the fire safety system, the complete installation must be checked for conformity with the approved drawings and system design. The handover procedure should include operation of the system.

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to demonstrate that the safety system design objectives have been achieved

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to identify any problems of detail which were not considered in the original design

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to demonstrate that the design has been properly implemented

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to identify any problems with interactions, or failures to interact

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to provide management with the opportunity to operate the systems

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to inspire confidence in the users of the building

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to offer reassurance, and training opportunities, to the fire service.

The fire safety management team must be provided with information on all installed active and passive fire safety systems incorporated into the building, compiled in the fire safety manual, including: ——

documentation from contractors and manufacturers (including any instructions, guarantees and test certificates) and spare parts

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as-built drawings and specifications and equipmentoperating parameters and record drawings

All the fire safety systems need to be individually tested to establish that the final installation complies with the specified design, is functioning properly and is ready for acceptance testing. A written record must be kept confirming that the installation of each system component is complete and that the component is functional.

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instructions on the use, planned maintenance and testing of the systems

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the results of acceptance tests (which may involve the regulatory authorities and insurance company representatives).

Acceptance testing has to demonstrate that the final integrated system as installed complies with the specified design, has been properly installed or fitted, and is functioning correctly. The details and findings of acceptance tests should be recorded and verified. The extent and form of any acceptance tests should be agreed with the enforcing authority at the design stage.

All components of any installed safety system for which the tenant is responsible need to be operational and compatible with the systems common to the complex before the tenant occupies their unit. The design and construction of the building and the systems installed in it need to be fully documented for handover to the management team on completion.

Arrangements for standby power supplies need to be checked and tested.

The fire safety manual needs to be prepared.

Wherever possible, the appropriate members of the management team should be available during the handover period to ensure that a clear understanding of every aspect of the building is passed on.

14.5

Fire safety manual

14.5.1

Purpose and contents of the fire safety manual

(Note that the fire safety engineer will not normally be present at handover and responsibility for conveying an understanding of the fire safety aspects will often fall to the architect. However, wherever possible, the fire safety engineer should be involved in the handover.) All installed safety systems need to be operational before the building (or part of the building) is accepted and any units are handed over to tenants in mixed user developments and premises in different occupation. All installed safety systems need to be commissioned and, where appropriate, tested by full commissioning tests involving fire and/or smoke, with the appropriate members

The designer of a large or complex building has a responsibility to document and communicate the design for the benefit of the management of those premises. All this relevant information needs to be included in the fire safety manual (which should be a ‘live’ file or folder of documents), which will provide a clearer understanding of the responsibility for ensuring that a high standard of safety is maintained. It should be available for inspection or tests by auditors and regulators. The fire safety manual should provide:

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All documentation relating to approvals and certification must be made available to the fire safety manager and included in the fire safety manual (see section 14.5).

of the management team present. Such tests have the following purposes:

Fire safety management a permanent means of communication between the designer and successive fire safety managers

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a full description of the assumptions and philosophies that led to the fire safety design, including explicit assumptions regarding the management of the building, housekeeping and other management functions

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exterior and interior access for the fire service and planned procedures agreed with the fire service

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planned procedures for salvage

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firefighting equipment

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communication systems

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a full description of the active and passive protection systems in the building

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fire prevention, and security and arson prevention

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a complete account of all the other design aspects that have a direct bearing on the fire safety management

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any IT system used to manage the manual (e.g. maintenance schedules, record keeping)

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an ‘operator’s manual’, containing inspection, maintenance and repair manuals for the fire safety systems

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information relevant to the Construction (Design and Management) Regulations 2015 (in the UK, or their equivalent elsewhere)

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interactions with security, building management, other safety systems etc.

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information required under the Construction (Design and Management) Regulations 2015 (in the UK, or their equivalent elsewhere) for the safety plan

information relating to certification and/or licensing, with copies of all certificates and licences

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information relating to any fire certificates or licensing

(within the UK) information relating to the Regulatory Reform (Fire Safety) Order 2005, the Fire Safety (Scotland) Regulations 2006 or the Fire Safety Regulations (Northern Ireland) 2010

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——

continuing control and audit plans

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a ‘log book’ of all events that occur over the life of the building that relate to fire safety.

further information etc. relating to other reasons for protecting the building (property, contents, fabric, heritage, environment)

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proposed testing regime for the manual.

The fire safety manual should contain details of the following items: (a)

(b)

Part 2: Operational records ——

the safety management structure, and any changes to the management structure

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access statements for people with disabilities (in the UK, to meet obligations under the Equality Act 2010)

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the testing of fire safety systems, including acceptance tests

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the results of monitored fire drills

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training and education records

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maintenance records (of all heat-dissipating equipment, other equipment that presents a fire risk and fire safety equipment)

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a description of the active and passive fire safety measures and details of their integration

a log of contractors’ and/or workers’ attendance and the issuing of hot work permits

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changes to the building structure

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any identified fire risks, and particular hazards for firefighters

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changes to building systems

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planned inspection, maintenance and testing schedules

information relating to regulatory requirements (e.g. fire safety risk assessments, Building Regulations approvals)

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control systems utilised throughout the building

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feedback from staff, occupants or other users of the building

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any fire incidents

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critical transportation routes for building services

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any ‘near-miss’ events

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the site plans, showing escape routes, assembly points and/or muster stations

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any false alarms and evacuations

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records of any appeals or prosecutions

Part 1: Design information ——

fire safety policy statement endorsed by the highest level of management

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fire safety specification for the building, supported by layout plans

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a description of the computer models that have been used to derive the safety design and the assumptions, inputs and outputs to any computer models used

—— ——

any quantitative or qualitative risk assessments and sensitivity analyses

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14-5

14-6

Fire safety engineering results and changes following reviews and testing of the manual

are being properly carried out, and should be monitored by senior management.

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inventories of flammable materials

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details of any operations that have a high fire hazard.

Records of the reviews and of any changes made should be kept. If an it system is used to manage the manual, then regular checks should be made to ensure that the requirements are being met.

In England and Wales, the designer needs to comply with Regulation 38 of the Building Regulations 2010, ‘Fire safety information’. This requirement stipulates that sufficient information must be recorded to assist the eventual owner, occupier or employer to meet their statutory duties under the Regulatory Reform (Fire Safety) Order 2005. This is specified as ‘information relating to the design and construction of the building or extension, and the services, fittings and equipment provided in or in connection with the building or extension which will assist the responsible person to operate and maintain the building or extension with reasonable safety’. Where this information is provided, it will underpin the fire safety manual.

14.5.2

Location, access and maintenance of the fire safety manual

The fire safety manual should be kept in a secure and fireproof container on the premises. It should be readily accessible to fire officers attending an incident. At least one duplicate, fully maintained identical copy should be retained in a separate stated location away from the premises (i.e. not at risk from a fire on the premises). The manual should be available for inspection by the fire enforcement authority or other relevant enforcing authority on request. However, it is not intended that the fire safety manual should be in lieu of the fire safety risk assessment required (in the UK) as a part of the Regulatory Reform (Fire Safety) Order 2005, the Fire Safety (Scotland) Regulations 2006 or the Fire Safety Regulations (Northern Ireland) 2010, although the manual will contribute to this. The fire safety manual should be kept up to date by the fire safety manager or a competent person nominated for the task, so that the information is included within one week of any event. It should be updated, as appropriate, to record feedback from staff and other users of the building. Records of any reliability problems with particular equipment should be kept.

14.5.3

Review and testing of the fire safety manual

The fire safety manual needs to be reviewed and its procedures tested annually, or whenever alterations are made to the building, in accordance with a documented procedure. If possible, this should be undertaken periodically by an independent auditor. Most of the testing should be a matter of routine activity for the management, to ensure that prescribed activities

Inspection routines should make provision for all fire safety systems installed in the building, including systems installed in tenant units and other occupancies. There should be a full monitored building evacuation drill at least once a year to test all of the systems and procedures in the manual. Such evacuations should always be carried out shortly after the first full occupation of a new building. If the interval between these drills is more than about 12 months, consideration should be given to conducting a monitored evacuation in the interim period. The purpose of any test exercise or drill should be clearly defined by management, and explained to the staff, so that it can be assessed afterwards. The records of fire drills etc. should be made available for scrutiny by the enforcing authority.

14.6

Authority and responsibilities of the fire safety manager

The fire safety manager is the person in overall control of the premises while people are present, or the person with direct responsibility for fire safety. The fire safety manager may exercise this responsibility in their own right, e.g. as the owner, or it may be delegated. Whatever the building size, there should be no doubt as to the identity of the person with whom the responsibility lies. The fire safety manager needs to have sufficient authority and powers of sanction to ensure that standards of fire safety in the complex are adequately maintained. These powers may extend to closing the building to the public, restricting its use or shutting down normal operations. The appointed manager must have access to sufficient resources to ensure that essential repairs or maintenance are carried out. The fire safety manager has responsibility for the following: ——

being aware of all of the fire safety features provided and their purpose

——

being aware of any particular risks on the premises

——

being aware of their responsibilities towards people with disabilities

——

being conversant with the legal duties, codes or regulations that apply and all terms, conditions and restrictions imposed by any licence

——

being in attendance on the premises, or ensuring that some other competent person delegated in writing is in attendance, whenever the public are present or when the building is occupied

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Fire safety management liaising with, and where necessary seeking the advice of, the fire authority and the licensing authority

——

dealing with individuals who sabotage or tamper with safety systems (for example, because they are inconvenient), who ignore any non-smoking policy or who block exits

——

(in the UK) as a Competent Person, conducting the fire risk assessment required under the Regulatory Reform (Fire Safety) Order 2005, the Fire Safety (Scotland) Regulations 2006 or the Fire Safety Regulations (Northern Ireland) 2010.

Other responsibilities of the fire safety manager include: ——

carrying out routine maintenance and testing of fire safety equipment

——

maintaining documentation for the fire safety manual, such as training records, drill records, information on ‘near-miss’ events

——

developing a fire strategy appropriate for the particular risk

——

in the role of a Competent Person, seeking to ensure compliance with appropriate codes, regulations, terms or conditions

——

responding to any rare or unexpected events that could increase the risk of fire or affect the evacuation procedures, e.g. by limiting the number of people permitted on the premises

——

notifying the authorities of any changes that will affect the fire precautions in the building, e.g. structural alterations, extensions, alterations to internal arrangements or a new practice of keeping explosives or highly flammable materials on the premises.

In addition, for larger buildings and complexes, the fire safety manager is responsible for: ——

appointment of fire marshals/fire wardens

——

appointment or delegated appointment of members of any site fire team

The management teams of all individual units and other occupancies need to understand that their own fire safety responsibilities are in no way diminished by the existence of a further tier of management with a wider span of control. In particular, it is necessary that a clear understanding exists on the subject of emergency procedures to ensure that no element of these procedures is neglected, and no element is unreasonably duplicated where this could cause confusion in an emergency. Where the fire safety management is outsourced, e.g. as part of the facilities management arrangements, then the final responsibility will still reside with the person responsible within the main organisation.

14.7 Communication Good communication is the key to successful management. Large, crowded, complex buildings represent a significant potential for loss of life in fire, and therefore demand the highest standards of management to ensure that risks are anticipated and covered by the best possible systems for life safety and property protection. It is the responsibility of the fire safety manager to ensure that all necessary and appropriate communication systems are in place to deal with any fire incident. This includes both equipment and chains of command, especially if it is intended that first alarms be investigated before sounding warnings, or if control room staff are taking decisions based on many channels of information. The communication strategy must include contingency planning, e.g. for abnormal occupancy loads, or for absent staff or equipment failure. Such systems should be tested and audited as part of the testing of the overall fire safety procedures. Other issues that need to be considered are: ——

the communications structure, in particular where there is a cascade decision-making process involving a number of levels of management

——

maintenance and routine testing of systems

——

testing of ‘emergency conditions’

——

the selection of languages to use in voice messages

——

development of the training policy for the building

——

ensuring that staff have the necessary competencies

——

special provisions for people with sensory disabilities

——

arranging training and maintaining training records

——

contingency planning (i.e. while fire safety facilities, equipment or systems are faulty or otherwise non-operational).

——

organising audits by an independent third party

——

organising periodic internal audits to review current fire safety management procedures and the effect of changes in personnel or building use

——

ensuring the effectiveness of automatic fire safety systems, even after a change in building use

——

consideration of and, if appropriate, preparation of disaster plans, where a fire incident could affect the local community.

14.8

Fire prevention

The task of fire prevention involves attempting to avoid fires occurring and working to create an environment in which fires are prevented from starting. The fire prevention tasks of the fire safety manager include: ——

monitoring the behaviour of occupants

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Fire safety engineering

14.8.1 Housekeeping

monitoring any smoking policy

——

housekeeping

——

routines for the disposal of waste

——

minimising hazards of combustible contents, furnishings and surface finishes

——

minimising hazards of materials, components and elements of construction

——

establishing purchasing standards for furniture, furnishings and fittings

——

seeking to avoid conditions which could lead to gas and dust explosion hazards

——

maintenance of furniture, furnishings, decor and equipment

——

keeping combustible materials separate from possible ignition sources

——

reviewing and appraising the risks, i.e. how a fire might start, spread and its consequences

——

storing flammable liquids, paints and polishes in appropriate containers

——

routine checks, inspections, tests and monitoring the maintenance of equipment that could cause fires (especially heat-generating equipment), chaffing of cables, self-heating and fuel supplies

——

recognition of potential hazards

——

monitoring proper waste control

——

cleaning, including build-up of dust on machinery or extract ducts

——

checks on electrical machinery overload

——

clearing waste from the outside of the building

——

checking ‘dark’ areas (e.g. cinemas, darkrooms)

——

out-of-hours checks, or checks after closing time

——

other routine precautions.

——

maintaining integration of the fire safety system with other systems (e.g. ventilation)

——

assessing the risks from new equipment, new business processes or changing and new technologies

——

issuing work permits

——

training and education

——

establishing and maintaining out-of-hours inspection and security procedures

——

security.

The task requires vigilance and, in larger buildings and complexes, may need separate teams to cover all of the possible areas of hazard. Regular inspections should be carried out and logged in the fire safety manual, and any problems found and remedial action taken stated. It is probable that surreptitious smoking presents the greatest fire risk, especially by members of the public and staff in back rooms, store rooms and other areas not in continuous view of supervisory staff. The best recommendation that can be made is that, for those premises where smoking is still permitted by law, smoking be prohibited other than in designated smoking areas and that fire-safe ashtrays and bins are provided. For those premises where smoking is not permitted by law, then continuous vigilance is needed. Outside contractors can pose a greater fire risk than a firm’s own employees. They are not as familiar with the premises as the people permanently employed by the firm. Therefore, they cannot be expected to know the fire risks, necessary precautions and correct action to take in the event of fire. Yet, these contractors may have to carry out operations which are much more hazardous than those normally occurring on the premises, e.g. hot work. Efforts should be made to make contractors and subcontractors aware of the risks involved in their work. All activities of outside contractors should be strictly supervised and controlled, and management should ensure that all necessary precautions against fire are taken.

Good housekeeping will reduce the chances of fire starting or developing. It is vital that all employees are aware of the particular risks associated with hazardous substances and practices that may be encountered in the premises, especially in factories and warehouses. Where additional risks are introduced anywhere in the building, e.g. the introduction of car displays and Christmas grottoes inside shops, advice on their specific protection needs to be obtained from the appropriate authority. Housekeeping measures include:

Good housekeeping is essential to reduce the chances of fire and smoke spreading and escape routes being blocked, and measures must include: ——

ensuring that escape routes are kept clear and are available for use at all times when the building is occupied

——

ensuring that fire doors which should be kept closed are kept closed and are not obstructed

——

ensuring that fire doors on hold-open devices are operable, are not obstructed and are closed at night

——

preventing warning signs or wayfinding guidance lighting from becoming obscured

——

carrying out general inspections of all the fire safety equipment.

Management procedures should ensure that control is exercised over the parking of commercial vehicles on service roadways that are also used for fire service access, so that fire appliances are not obstructed in an emergency and are able to proceed to within the required distance of any fire main, foam or other inlets. In the interest of security, it may also be considered necessary to restrict unauthorised entry via such roadways, in consultation with the fire authority.

14.8.2

Training and education

An essential task of the fire safety manager is the training of all staff, including part-time, security and cleaning staff,

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Fire safety management

All staff need to be trained in basic fire prevention, risk awareness, smoking policy, process shutdown, good housekeeping and reporting procedures. Fire safety training needs to commence on the first day of appointment of new staff and continue in the form of regular refresher training.

14.8.3 Security Arson fires can start with a rapid burning material, such as petrol, and the arsonist can start fires in several places simultaneously so that the alternative escape routes normally provided in a building are blocked. Building management can reduce the risk of serious fires by arson by using a number of methods to reduce the likelihood of arson and to mitigate the effects if it does occur. These include: ——

management awareness of vulnerability to arson

——

security against intruders

——

intruder detection

——

control of ignition sources and easily ignitable materials

——

fire detection throughout the building

——

fire suppression systems throughout the building

——

segregation of risks

——

effective staff training

——

closed-curcuit television (cctv) to deter deliberate fire-setting.

Good security arrangements will reduce the risk of arson. However, the fire safety manager needs to be aware of the possible conflict between security and means of escape and must ensure that the security arrangements do not prevent occupants from exiting the building to reach a place of safety or hinder the entry of the fire service into the building to fight the fire or effect the rescue of occupants. In certain circumstances, the need to restrict the occupants’ ability to leave the premises must be integrated with the provision of adequate and manageable emergency egress.

14.9

Ensuring systems respond properly in a fire emergency

Another task of the fire safety manager is to ensure that all of the safety systems respond properly in a fire emergency. This task includes: ——

housekeeping (see section 14.8.1)

——

seeking to ensure compliance with relevant codes or regulations, as appropriate

——

maintenance of structural and/or passive safety systems

——

routine inspection, maintenance and testing of active systems

——

testing under simulated ‘emergency’ conditions

——

safety audits and inspections

——

recording and taking appropriate remedial action following false alarms

——

learning from drills, false alarms and near-miss events, i.e. using false alarms and near-miss events as data

——

revising safety plans and updating the fire safety manual.

In addition, for larger buildings and complexes, this task includes: ——

ensuring that systems mesh properly with the emergency procedures

——

integration of the fire safety systems

——

maintaining integration of the fire safety system with other systems (e.g. ventilation).

14.9.1

Fire safety maintenance and testing

It is essential for the safety of the occupants of a building that all fire safety equipment is checked frequently. Planned inspection, maintenance and testing procedures need to be established and used to ensure that all fire protection systems can operate effectively when required. Maintenance needs to be carried out in accordance with the relevant British Standards or manufacturer’s instructions at the recommended time intervals. The testing and inspection of these systems should be carried out by competent persons. Fire safety equipment that needs to be checked regularly includes the following: ——

fire detection and alarm systems (see chapter 8)

——

fire suppression systems (see chapter 11)

——

smoke control systems (see chapter 10)

——

means of escape systems (see chapter 7)

——

structural and/or passive elements

——

firefighters’ systems (see chapter 13)

——

control systems and power supplies, including emergency power arrangements

——

access to the building and its surroundings (see chapter 13)

——

communications systems.

In addition to being responsible for daily checks on the premises prior to the admission of the public, it is also the

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in fire prevention. This training aims to ensure that each member of staff takes the appropriate actions to minimise the likelihood of a fire starting. In a complex, the training should include the tenants of every unit and other occupancy in the complex.

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Fire safety engineering place of safety quickly, without injury or distress. This requires that occupants react promptly to any alarm, and also that they exit the building by the most efficient route. To facilitate this result, the fire manager is responsible for: ——

staff training and fire drills, including full evacuations

——

reviewing all plant and equipment interface controls, to ensure that they mesh correctly with the procedures

Alterations or modifications to an existing installation should not be carried out without consultation with the enforcing authority and, where possible, the original system designer or installer or other qualified persons. This is particularly important where systems are combined and depend on a sequence of control events.

——

continual inspections and testing of systems and emergency procedures, including major incident simulations

——

testing under simulated emergency conditions

——

carrying out safety audits and inspections

The manager needs to be aware that safety equipment can itself be a hazard, e.g. poorly maintained fire doors can cause injury. Where necessary, equipment may need to be replaced, but without reducing the safety of the building. Similarly, equipment that is not reliable, or that is regularly vandalised or abused due to poor or inappropriate design, may need to be replaced.

——

responding to false alarms

——

learning from and recording drills, false alarms, near-miss events and minor incidents

——

reviewing all staff duties and training procedures

——

checking the records, as-built drawings and specifications for all fire protection measures

When repairs or alterations are made to the building structure, it should be ensured that compartment walls or other passive fire protection systems are reinstated if damaged, especially those that are hidden in voids.

——

collating feedback from, and issuing it to, participants, staff, other occupants etc. after drills

——

managing the site fire team

——

monitoring and recording information in the fire safety manual and revising safety plans.

All fire safety installations need to be tested individually, but interdependent fire safety installations need to be tested collectively to demonstrate satisfactory interfacing/ interlinking etc.

Any alterations, additions, repairs or modifications to services and equipment need to be carried out only by competent persons. Contingency plans must be prepared to cope with equipment failures or other problems, such as a failure in the water supplies for the sprinkler system. The maintenance of furniture, furnishings, decor and equipment is as important for the safety of occupants as is the maintenance of the fire safety equipment. Contents and equipment affect the likelihood of fire occurring, its development and subsequent events. Diligent attention to detail can minimise the risk of fire. Floor coverings, furniture, furnishings, scenery, props, curtains and drapes should be maintained to the appropriate standards of fire retardancy and in a condition that does not reduce overall fire safety. In addition, well-maintained floor coverings reduce the risk of persons tripping during any emergency evacuation. A record of all tests and checks, and any defects remedied, needs to be made in the fire safety manual.

14.10

Planning for a fire emergency

Having a fully developed and effective emergency plan is a key part of effective fire management. In the UK, such a plan is a requirement of the Regulatory Reform (Fire Safety) Order 2005 or the relevant regulations in Scotland and Northern Ireland. It is the responsibility of the fire safety manager in planning for a fire emergency to seek to ensure that in the event of a fire all occupants escape to a

Specific tasks relating to plans include: ——

developing and maintaining emergency plan(s), including evacuation plans, personal emergency evacuation plans (peeps), victim support and emergency accommodation plans

——

planning for bad weather, including evacuation into hostile weather conditions

——

planning for the mitigation of potential environmental impact of fire

——

risk management, contingency planning, re-start planning

——

contingency planning for salvage and damage control.

Planning should include liaison with the external fire brigade, and, if appropriate, provision of an ‘emergency pack’, prepared in collaboration with the fire authority, containing essential information for firefighting, and indicating escape routes and special hazards, including a clear set of plans, ideally laminated, indicating key hazards and shut-off switches in the building.

14.10.1

Training and education

An essential sub-task of the fire safety manager is the training and education of all staff to ensure that, in a fire emergency, they each take appropriate actions to safeguard occupants and facilitate safe escape. This training is in addition to training in fire prevention (see section 14.8.2) and should include:

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fire safety manager’s responsibility to ensure that all fire safety equipment is adequately and routinely maintained and tested. Failure to maintain any one of the fire safety provisions in effective working order could negate the whole fire safety strategy.

Fire safety management the fire emergency plan

——

the action to be taken on discovering a fire

——

exits and exit routes

——

raising the alarm, including the location of alarm indicator panels

——

the action to be taken on hearing the fire alarm

——

the arrangements for calling the fire service

——

the location, selection and use of firefighting equipment

——

knowledge of the escape routes, refuges and exits, especially those not in regular use

——

appreciation of the importance of fire doors and of the need to close all doors at the time of a fire and on hearing the fire alarm

——

procedure for process shutdown and shutting down of non-essential equipment, stopping machines and processes and isolating power supplies, where appropriate

——

assisting other occupants who may be unfamiliar with the building or fire safety systems

——

evacuation procedures

——

evacuation of the building (this will include reassuring any members of the public, escorting them to exits and encouraging them to get well clear of the building).

Details of all training and instruction given and received should be recorded in the fire safety manual (e.g. the date of the instruction or exercise and its duration; the name of the trainer or instructor, the name of the person receiving the training or instruction and the nature of the instruction, training or drill). The basis of fire safety in any premises is the fire emergency plan. Staff need to know how to act on discovery of fire or on the raising of the alarm. It is essential that the management team draws up an effective routine which covers all situations, from a false alarm to a major incident. The fire routine must take into account the types of activities that take place in the premises, the fire precautions that are provided and, above all, the fire warning and communications systems that are available and the emergency actions that will be required. The core of the fire emergency plan will be the actions to be taken in the event of fire. A fire emergency plan should be developed that keeps the procedures as simple as possible and minimises the decisions that need to be made to cope with a particular incident. A fire emergency plan should be carefully devised for each building, taking into account the uses to which the premises are put and, in particular, the means of giving warning and the means of communication. This fire emergency plan should take account of the relationship between the trained staff and other occupants, the familiarity of occupants with the building, and the availability of fire marshals or a site fire team. The production of the fire emergency plan should take account of the needs of all occupants, including those at

special risk (such as people with disabilities, the elderly, the infirm and children), and make suitable arrangements for their assistance. All staff should be familiar with the fire emergency plan and evacuation procedures and prominent ‘fire instruction’ notices should be displayed in all staff areas. These should state the essentials of the action to be taken on discovering a fire and on hearing the fire alarm, and should be placed in conspicuous positions in all parts of the building. Key members of staff should have specific roles relevant to the fire emergency plan. Designated staff who require master keys to assist in an evacuation should carry them at all times. In some cases, the fire authority or competent salvage professional should be consulted regarding the fire emergency plan. A key issue for training and the fire emergency plan will be how to decide whether the fire service should be called in from outside. Many minor fires will not appear to be (and will not be) life-threatening and might be successfully extinguished with portable firefighting equipment. However, nearly all large fires start off as small fires, and if this initial judgment is faulty, then disaster can follow.

14.10.2

Evacuation management

Fire alarms in most smaller buildings are best operated in a ‘single stage’ mode, in which the actuation of a call point or detector gives an instantaneous warning from all fire alarm sounders for an immediate evacuation. In large or complex buildings, a staged evacuation procedure may be adopted, in which the operation of a call point or detector gives an evacuation signal on the storey or zone affected, and an ‘alert’ warning signal sounds in all other parts of the premises. The decision to evacuate the remainder of the occupants then rests with the management and/or the fire service. It is essential that adequate means of communication between storeys or zones is provided. A public address system or voice alarm is the most suitable way to control the evacuation process if fire alarm sounders are not used (but see chapter 8). The evacuation process can be phased evacuation, in which different parts of the building are evacuated in a controlled sequence of phases; first, the original fireaffected storey or zone, then the remainder of the building in various phases. A phased evacuation will normally require at least a two-stage alarm system to give ‘alert’ and ‘evacuate’ signals, or ‘staff alarm’ and ‘evacuate’ signals. The escape stairs in the building will have been designed specifically for phased evacuation and the evacuation will normally be coordinated from a fire control centre with directive public address announcements, aided, where appropriate, by colour cctv. Where horizontal evacuation is planned, and/or the use of temporary refuges, then appropriate evacuation procedures will be needed. In general, evacuation procedures would not be intended to cope with extreme events which may require simultaneous evacuation.

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Fire safety engineering

The sophistication of the fire alarm system and public address arrangements are major factors when considering evacuation procedures in large or complex buildings.

Members of the public may need to be guided to a suitable exit as, otherwise, they tend to follow the same route that they used to enter the building, or they may be disorientated or unaware of the location of exits. If they arrived by car, they are likely to try to return to it. Parents and children who have been separated will tend to seek each other so as to leave together. People will often attempt to carry out normal activities when faced with an unexpected situation. Careful attention must be given to the wording and delivery of both live and pre-recorded messages, not only to provide reassurance and relevant information, but also to convey the sense of urgency necessary to motivate people to move promptly in the safest direction when required.

14.11

Management of a fire emergency

Actions in the event of fire for which fire emergency planning is appropriate include: ——

action on discovery of a fire

——

warning and evacuation signals

——

calling the fire service, providing information and advising them

——

initiation of evacuation

——

fighting the fire and other staff activities

——

evacuation procedures

——

meeting the fire service, providing information and advising them

——

completion of evacuation.

Other issues to consider include: environmental protection, security, salvage and damage control, protecting the building contents, protecting the building fabric and recording lessons learned. The following procedure provides the basis for any plans that are developed for a specific building: (a)

Operate the fire alarm system and alert employees, or selected employees, and any control room, to the emergency.

(b)

Call the fire service.

(c)

Establish the location and apparent extent of the fire and assess the situation.

(d)

Organise and effect the movement and/or evacuation of the public and staff as determined by item (c).

(e)

Take steps, consistent with the safety of individuals, to fight the fire or contain it.

Ensure that people with peeps are able to put their plan into action and that assistance is given to those using temporary refuges.

(g)

Ensure that everyone assembles at a place of safety and is accounted for so that, if anyone is missing, the fire service can be informed on their arrival. Ensure that people do not re-enter the building.

(h)

Ensure that, on the arrival of the fire service, every assistance is given to enable them to attack the fire effectively, and in particular inform the fire service of the situation regarding the safety and whereabouts of the occupants of the building.

(i)

Implement any pre-planned procedures with respect to care of evacuees, salvage, environmental protection etc.

(j)

Initiate the pre-planned recovery process.

14.12

Other planning issues

Other planning issues may involve plans for limiting loss and damage to building structure, contents, the environment and business operations. Plans may involve actions to be taken both during and after the fire emergency. In certain cases, these may include planning for the salvage of identified valuables during the incident. The fire safety manager may wish to consider measures to facilitate the post-fire operation of the business or functioning of the building, including arrangements to keep duplicates of business records off-site. This might be as simple as preparing a list of contacts, but could include having arrangements in place for using alternative premises. For other types of occupancy or businesses, more detailed planning may be appropriate. Re-start planning for the business may form part of the overall risk management. The fire safety manager may also wish to consider plans for the protection of the building structure, its contents and the environment. Building fabric and property protection will be a particularly important issue for heritage buildings. It must be recognised that, while it is often the case that protecting occupants will also protect contents etc., there may be conflicts of interest and in such cases life safety must take precedence.

14.13

Changes to a building

Changes to a building include extensions, alterations, refurbishment, change of use, disuse, or decommissioning and demolition, all or any of which can affect the fire risk.

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Directive messages provide the occupants with the clear, prompt and accurate information they need to move safely without delay. The use of public address systems should not be restricted to coded staff messages.

(f)

Fire safety management

14.13.1

Extensions, alterations and refurbishment

——

the fire safety arrangements within the building, to ensure that they are not adversely affected by maintenance work or alterations (especially in hidden spaces or voids), and

——

procedures to avoid fire occurring, particularly in relation to hot work, such as welding or cutting.

During maintenance work, and particularly when alterations are being carried out in buildings that remain occupied, appropriate arrangements should be made to safeguard the integrity of escape routes and the operation of all fire protection facilities. Approval should be obtained from the local building and fire authorities, where appropriate, before the implementation of extensions or alterations within the building (DCLG, 2007). Management should ensure that arrangements are made for the instruction and supervision of contractors and workers in maintaining fire safety; in particular, that they implement good safety practices, that they understand the actions to be taken in case of fire and that they are made familiar with appropriate escape routes. In many situations there will be a need for strict documentation and a permit system for contractors carrying out any kind of structural work. Any form of hot work should be the subject of specific approval and insistence on appropriate safeguards. Before any hot work is carried out, a thorough safety check should be made in the area where the work is to be undertaken, and adjacent areas, to see that flammable materials are either removed to safety or protected. Suitable portable fire extinguishers should be provided adjacent to the hot work area. A further check should be carried out immediately after work has finished for the day to ensure that the area is safe. No hot work should be allowed in or near the building unless a hot work permit has been issued. The permit will be issued only if the fire safety manager is satisfied that no satisfactory alternative method is feasible and that the contractor understands and can carry out their responsibilities with regard to the following issues: ——

preparation of the place of work

——

care and attention during work

——

leaving the workplace clean and safe

——

the need for a check of the area after the job is completed and for a final check at a later time.

Issue of a permit for hot work should also be dependent on: ——

the contractor receiving training in the operation of available fire extinguishers

——

the availability of a safety officer (if appropriate)

——

particular precautions being put in place where special risks are present in the premises.

A log of the contractors’ attendance should be maintained so that, at any time, the number and location of all personnel can be determined.

14.13.2

Change of use

Any occupiers of a building will be subject to the management requirements specified at the design stage and recorded in the fire safety manual. Where there is a change of use of the building, or where the scale of the operation within the building changes, then the fire safety management requirements specified will have to be carefully re-examined and assessed for the new use. Unless the management assumptions and the level of management specified prove to be appropriate for the new use, changes will have to be implemented. These changes could either be to the management structure or could involve the provision of additional facilities or equipment, retrofitted to the building. Following a change of use, the building will be subject to review by various regulatory bodies and they will need to be assured that an appropriate level of fire safety has been reinstated within the building. For buildings in the UK subject to the Regulatory Reform (Fire Safety) Order 2005 (England and Wales), the Fire Safety (Scotland) Regulations 2006 or the Fire Safety (Northern Ireland) Regulations 2010, a review of the fire safety risk assessment will be necessary.

14.13.3

Units in disuse and decommissioned areas

For units in disuse and decommissioned areas, routine inspection by staff should be intensified to prevent careless practice and to ensure that fire protection systems remain fully operative (where appropriate). In cases where these units/areas are not physically separated from the rest of the building, they should either have an operational sprinkler system or be partitioned off from the rest of the building by appropriate fire-resisting construction.

14.13.4

Disused or decommissioned buildings

Disused or decommissioned buildings do not present a very great risk to life. Any fire safety management of such a building should focus on the prevention of fire starting and should include measures to: ——

ensure that all power supplies are disabled

——

remove any material that might self-ignite

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Experience has demonstrated that fires are more likely to occur when general maintenance work or alterations are being carried out to a building, most notably when work is being carried out by external contractors. The activities of all external contractors should be strictly supervised and controlled, and management should ensure that all necessary precautions against fire are taken. It is therefore particularly important that guidance is given to both general maintenance staff and external contractors on:

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Fire safety engineering

——

remove any material that might be subject to an arson attack

——

maintain security to prevent arson attacks.

Buildings being demolished

——

Control systems showing the location of the incident and the status of all automatic fire protection installations and facilities.

——

Override provision associated with all automatic fire protection installations and facilities (other than those that have to be located either adjacent to their equipment or elsewhere where local control is needed, e.g. overrides for gaseous fire extinguishing systems or the sprinkler system main, or floor-isolating valves).

——

Override provision for air conditioning systems or ventilation systems involving recirculation of air.

——

A communication system, in the UK conforming to BS 5839-9, providing a direct link between the control room and all firefighting lobbies, fire and rescue service access points and refuges for people with disablilities.

——

An exchange telephone with direct dialling for external calls.

The management of fire safety in buildings that are being demolished will be very similar to that required during construction (see chapter 15). There will be significant risks of ignition in a building where many or most of the fire protection systems are either disabled or missing.

14.14

Fire control centre

In all buildings designed for phased evacuation, and in large or complex buildings, a fire control centre should be provided to enable the fire and rescue service to assist the premises management in controlling an incident immediately on arrival. The fire control centre should be either: (a)

a room dedicated solely as a fire control centre or

——

(b)

combined with the management central control room.

Facilities to broadcast information via public address system to occupiers of the building.

——

The fire control centre should be adjacent to a fire and rescue service access point, or other location agreed with the fire and rescue service, and it should be readily accessible, preferably directly from the open air. If this is not practicable, the route to the fire control centre should be protected.

Controls and monitor screens for cctv, if provided for the control of evacuation (the use of cctv can greatly assist in the management of emergencies).

——

The fire emergency plan for the building.

——

Keys or other devices required to facilitate access throughout the building and to operate any mechanical and electrical systems.

——

Floor plans of the building.

——

Means of contacting principal staff and/or building services engineers.

——

A means of sounding the alert signal throughout the building.

——

A clock to time phases of evacuation.

——

A visual indication showing the status of evacuation in those parts of the building where an evacuation signal has been given.

——

A wall-mounted writing board with suitable writing implements for displaying important information.

——

Refreshment facilities for personnel involved in the incident.

Because of the potential need for the fire control centre to be operational over an extended period of time, it should be separated from the remainder of the building by two-hour fire-resisting construction and should incorporate facilities to enable it to function as normal during an emergency. The fire control centre should be provided with a threehour non-maintained system of emergency lighting supplied from a source independent of the normal lighting, to enable the control centre to operate satisfactorily in the absence of the normal lighting supply. Throughout the building, a reliable means of communication with the fire control centre – either a fire telephone system or a radio telecommunication system acceptable to the fire authority – should be provided for use by the management of the building in conjunction with the fire control system to control evacuation procedures and for communication between fire and rescue service personnel. Fire telephone systems in the UK should conform to BS 5839‑9: 2011 (BSI, 2011). The fire control centre should be equipped with the following: ——

All control and indicating equipment for the fire alarm and other fire safety systems for the building. This should include a facility to sound the evacuation signal in each evacuation zone throughout the building, with the option to signal a total evacuation. However, this would not be feasible where the stairs provided are designed to cope with phased evacuation only. The option to cancel any automatic

The control centre should be staffed by a competent person, familiar with the use and operation of the installed equipment, whenever the building is occupied. Particular attention should be paid to the human factors involved in running a control centre in an emergency. The design should support the interface with control centre operators to enable them to take control of the emergency efficiently and effectively. The control of building systems, such as fire, security and general building services control, is increasingly being integrated into single building management systems. In view of the increasing use of these systems, it is important that the integrity of the building management system is at least as good as the integrity of the individual systems that

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14.13.5

sequencing of phases of an evacuation procedure, except for the initial phase, should be provided.

Fire safety management

DCLG (2007) Building Regulations and Fire Safety Procedural Guidance (4th edition) (London: RIBA Publishing) DCLG (2012) HM Government. Fire safety law and guidance documents for business [online] https://www.gov.uk/government/collections/fire-safetylaw-and-guidance-documents-for-business (accessed November 2017) HM Government (2013) The Buildings Regulations 2010: Approved Document 7. Materials and Workmanship (Newcastle upon Tyne: NBS)

References

HOTREC (2010) Guidelines to fire safety in European hotels. Hotel fire safety MBS (management, building and systems) methodology Version 1st February 2010 (Brussels: HOTREC)

BSI (2011) BS 5839-9: 2011 Fire detection and fire alarm systems for buildings. Code of practice for the design, installation, commissioning and maintenance of emergency voice communication systems (London: British Standards Institution)

Scottish Government (2017) Fire law. General guidance [online] http:// www.gov.scot/Topics/Justice/policies/police-fire-rescue/fire/FireLaw/ GeneralGuidance and http://www.gov.scot/Topics/Justice/public-safety/ Fire-Rescue/FireLaw/FireLaw/SectorSpecificGuidance (accessed November 2017)

BSI (2017) BS 9999: 2017 Fire safety in the design, management and use of buildings. Code of practice (London: British Standards Institution)

Welsh Government (2013) The Buildings Regulations 2010: Approved Document 7. Materials and Workmanship (Cardiff)

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it incorporates. This is essential to ensure that the highest standards of security, safety and reliability are achieved where systems have been integrated. Clear differentiation should be provided, where possible, between fire, security and building management systems within the control centre.

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15-1

15

Fire safety on construction sites

It was reported that the fires at London’s Minster Court (1991) and Broadgate Phase 8 (1990) accounted for £138.5 million of the £143 million total for fire losses on construction sites between 1984 and 1991 in the UK (Fire Prevention, 1992a; SCI, 1991). In response, a code of practice for fire prevention on construction sites was produced, Fire Prevention on Construction Sites: The joint code of practice on the protection from fire of construction sites and buildings undergoing renovation (FPA, 2015). In addition, the Health and Safety Executive (HSE), which has powers over fire precautions on construction sites, has published guidance on managing fire safety during construction and identifying the responsibilities for those concerned (HSE, 2010). The application of either may be required by insurers, depending on the scale of the works and the risks involved. The increasing use of timber construction poses an ever greater fire risk in the construction industry. A report by the Greater London Authority (GLA) suggests that timber construction now makes up approximately 24% of all new housing projects in the UK and approximately 12% of all construction site fires in London (GLA, 2010). The high fire loads inherent in timber-framed buildings and the difficulties associated with providing fire compartmentation prior to completion has led to a number of severe fire incidents in recent years. As with completed buildings, there is a conflict between the building user and the regulatory controls designed to limit the incidence of fire. The designer, contractor and building user do not really believe that their building will ever be involved in a fire, whereas the regulating authorities assume that a fire will occur at some stage during the life of the building and require that the building be designed accordingly. However, the extent and cost of fire damage and the resulting disruption to the construction process, as well as the commercial consequences of delayed handover, can be significant. Therefore, it is important to clarify the issues surrounding site fires and to emphasise where attention should be focused. Furthermore, the transient and changing nature of construction sites makes it harder to police them and to ensure that an appropriate level of safety is provided.

15.2

Motivation for provision and maintenance of fire precautions

15.2.1

Personal responsibility

An increased awareness of the possibility of fire and its consequences is required. Despite past incidents, there is

still a lack of belief that such events will happen (Fire Prevention, 1992b). The conflict between the need for fire precautions generally and resistance to having to adopt them due to their maintenance requirements not only exists in completed buildings but also during construction. An effective way of increasing awareness is to assign responsibility for the outcome of failure to provide adequate fire precaution. Where it is unrealistic for individuals to bear this responsibility, it should be borne by their employers.

15.2.2

General fire training and security

The building process is varied and complex and often conflicts with the need to provide and maintain fire precautions. An effective form of detection and control, proven in health-care premises particularly, is the presence of alert persons. Of the many fires which start in health-care premises, few get out of hand because they are detected by persons trained to respond and are therefore tackled at an early stage. One solution to the need for provision and maintenance of fire precautions on building sites may be to employ trained persons to monitor the site and take appropriate action when fires are detected. This may be more cost effective than stipulating temporary measures or overspecifying permanent ones to serve during construction. Such persons could be provided by private security contractors or, alternatively, suitably trained persons could be sought as part of the professional responsibility of the developer or contractor. There may be a need for a team of on-site professionals, who could respond to any fire incidents. General awareness of the risk of site fires would be increased by contractors offering improved levels of training in firefighting. Contractors could then ensure that a minimum number of suitably trained staff are present on site during construction. The provision of trained fire watchers can be justified in view of the potential losses arising from inadequate provision. This is not a new concept, it is employed in certain hazardous industries and during national emergencies. Aside from offering financial incentives for fire detection and control duties, the necessity for the role could be backed by requirements from the HSE, the fire brigades and the building control authorities.

15.2.3

Life safety

It is of primary importance to maintain the record of zero lives lost in recent construction site fires in the UK. The

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15.1 Introduction

15-2

Fire safety engineering

Many provisions and recommendations contribute to life safety. It would not be helpful to distinguish any as unique or of more importance than others, but particular items that should be addressed as part of a life safety strategy are: ——

escape routes

——

detection and alarm

——

ventilation for smoke relief

——

emergency lighting and signage

——

compartmentation.

Obviously, the management and signage of escape routes is essential, but emergency lighting on construction sites often fails to meet satisfactory standards.

15.3

Long-term objectives

15.3.1

Assimilation of fire precautions into routine site practice

The long-term objective of effective site fire precautions should be to maintain the status quo of no fatalities resulting from construction site fires, a reduction in the number of site fires, and a reduction in losses and insurance claims. In achieving this objective, it is important not to make the construction process more onerous – indeed, the more onerous the fire prevention measures, the more likely they are to be ignored or overridden. The objectives should include the assimilation of site fire precautions in the most unobtrusive manner possible, ensuring that their effectiveness is commensurate with the risk. They should be as effective during construction, when the risk is high, as they will be in the completed building.

15.3.2

Improved fire awareness

While the risk to firefighters and construction workers is significant, particularly on high-risk sites, such as the construction of timber-framed buildings, to date there has been little risk of loss of life from construction site fires in the UK. Moreover, the emotive dimension present in dwelling fires is absent from construction site fires. Therefore, the incentive for improving construction site fire safety lies mainly with insurers, who bear the cost of reinstatement, and with the client, who has an interest in seeing projects completed, ready for occupation. Substantial losses are also incurred by delays to future business activities.

15.5

UK legislation

In England and Wales, the construction of new buildings and the alteration of existing buildings is controlled by the Building Regulations 2010, as amended, and by some remaining local acts. The principal legislation relevant to existing buildings in England and Wales is the Regulatory Reform (Fire Safety) Order 2005, known as the Fire Safety Order, which applies to both occupied buildings and construction sites. Similar legislation applies in Scotland (Building (Scotland) Regulations 2004 and Fire (Scotland) Act 2005) and Northern Ireland (Building Regulations (Northern Ireland) 2012) (see section 3.4). In the course of construction, the Health and Safety at Work etc. Act 1974, the Construction (Health, Safety and Welfare) Regulations 1996 (regulation 18), the Construction (Design and Management) Regulations 2015 and the Management of Health and Safety at Work Regulations 1999, as amended, apply, the enforcing authority generally being the HSE. In non-segregated sites, both the HSE and the fire service may have an enforcing role. Under the Fire Safety Order and these acts and regulations, the person who has control of the site has a duty to keep the workplace, including any temporary buildings and temporary accommodation units, in a safe condition. This duty includes the identification of risks, preservation of safe means of escape, maintenance of fire safety equipment, and the provision of training, supervision and information to ensure health and safety (HSE, 1993). Employees must be conversant with fire drills and fire precautions. The Fire Safety Order identifies the appropriate enforcing authority.

Petrochemical and other hazardous industries have considerable experience in assessing risks and ensuring that their staff are aware of such risks. Similar principles need to be applied to the construction industry to ensure that an adequate level of safety is provided and that staff understand the risks and the safety features provided.

Safety precautions for the special processes taking place during construction and for the storage and use of dangerous substances and materials are addressed in legislation, such as the Highly Flammable Liquids and Liquefied Petroleum Gases Regulations 1972 and the Petroleum (Consolidation) Regulations 2014.

15.4

15.6

Implications of site fires

There are environmental issues associated with site fires besides pollution, such as the wastage of materials and workmanship. However, in financial terms, there need be little cause for concern, provided that insurers continue to cover losses. Furthermore, the workforce may continue to be employed on a site following a fire, and materials suppliers may also continue to benefit.

Aspects to be considered

There are several aspects that should be considered with respect to fire safety on construction sites, including the following: ——

Role of the designer: An appreciation of the fire hazards during construction should be part of the designer’s brief (see also section 15.8).

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provision and maintenance of means of escape is vital, but may conflict with construction activities. The financial losses incurred from recent incidents are bad enough; the loss of life of operatives or firefighters must be avoided.

Fire safety on construction sites Fire precautions: Precautions required during construction should be incorporated into the design in the most economic manner possible and with the least disruption to the building process.

——

Fire strategy report: The contractor should be cognisant of the fire strategy for the completed building, which provides guidance on the intended fire precautions and highlights particular problems and provisions in the design. This knowledge will assist in the development of construction fire risk assessments and in the provision of appropriate fire precautions.

——

Performance requirements for site fire precautions: Fire risks during construction should be identified and managed to avoid them being significantly increased. Contractors should undertake risk assessments and produce manuals and work procedure documents to record their solutions to these issues, highlighting the use of temporary measures and maximising the use of provisions intended for the completed building.

——

Fire awareness: The workforce must be made aware of the risk of fire and be encouraged to undertake fire safety training.

——

Revisions to conditions of contract: Contracts should address legislation and standards, such as the Fire Safety Order, NFPA 241 (NFPA, 2013) or other applicable standards and published guidance. They should include performance requirements for fire precautions and safety, method statements relating to the planning of fire precautions, and the necessity for appointing appropriately qualified fire wardens. Tender submissions and interviews should address these issues.

15.7

Objectives of fire precautions during construction

15.7.1 Background It is understandable and commendable that most of the guidance and legislation on fire precautions during construction is aimed at providing a safe environment for construction staff. That there have been no actual casualties in the UK in recent incidents suggests that existing life safety provisions have probably been adequate. However, this situation will remain satisfactory only if the present standard of vigilance is maintained, and increased when the fire risk is greater, such as during the construction of timber-framed and high-rise buildings. However, in terms of overall fire damage, the situation is much less satisfactory, and this aspect of construction fire safety needs urgent attention. The risk to neighbouring buildings and persons posed by timber-framed buildings can be greater than would generally be encountered in standard construction practices and the spread of fire deserves additional consideration. Organisations such as the Structural Timber Association in the UK provide guidance on such matters as the safe

separation distances that should be maintained between adjoining buildings.

15.7.2

The case for action

Clearly, there is a general level of awareness of the dangers from fire on building sites; however, even given the unlikely assumption that existing building sites have been protected to the standards recommended by available guidance, fires within buildings undergoing works have happened and the resulting financial losses have been significant. Therefore, it is clear that existing guidance is either ignored, misunderstood, inadequate or does not address the issues that have previously resulted in large losses. The need to focus on these issues in order to improve the situation is justified by the losses experienced, both capital and consequential, particularly from smoke damage, delays in completion and future business disruption.

15.7.3

Temporary and permanent provision

The completed building will ideally incorporate suitable fire precautions to limit damage effectively in the event of a fire. However, it must be remembered that statutory fire precautions are weighted towards life safety rather than property protection. Nonetheless, during building works, it would be advantageous to be able to rely as much as possible on the fire precautions for the completed building rather than introducing temporary measures. Although relying on the final provisions may add costs due to out-of-sequence working, these are often likely to be less than the cost of equivalent temporary provisions. The use of some temporary provisions will probably be inevitable, but the aim should be to keep these to a minimum. The intention would be to install the fire precautions as the work progresses, to preserve them during the works and to leave them in good order upon completion. They would then assume their intended role of protecting the completed building. This approach offers advantages in programme reduction and subsequent time savings. The alternative option is to introduce extra fire precautions during the works and either leave them in the completed building or remove them before handover. It must be appreciated that the hazards in a completed building and one under construction or repair are not the same, and it is generally accepted that they are greater during construction. This will be apparent from the ongoing risk assessments and can be catered for by recognising the increased danger and increasing vigilance accordingly. If it is considered essential to provide additional temporary fire precautions, the maintenance and effectiveness of such measures are more likely to be ensured if they are active, such as detection and firefighting facilities, rather than passive measures, such as temporary partitions. Passive provisions are prone to damage, although they can be easily inspected; active systems are less prone to damage but need to be maintained.

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——

15-3

15-4

15.7.4

Fire safety engineering

Criteria for fire precautions

——

that suitable measures should be taken to avoid fires from starting

——

the need to detect fires at an early stage

——

provisions for raising an alarm and evacuating the building

——

control of fire size by active or passive measures

——

access and facilities for fire brigade intervention.

These provisions, all of which will be required in the finished building, can be incorporated at an early stage in the construction programme and maintained as the building work develops. The fire precautions required during building works can then be established based on analysis of the various activities taking place and the availability of the fire precaution measures intended for protection of the completed building. Additional protection during works may be necessary to reduce the risk to an acceptable level. In defining such a level, it would not be appropriate to attempt to quantify it rigorously, by a statistical representation of time related to hazard, for instance. However, this should be borne in mind when evaluating proposals. For example, the storage of hazardous materials for a short period may be acceptable with strict management in a non-fire-rated area. However, if such storage were needed over an extended period, then the use of a secure fire-resisting enclosure would be expected.

15.8

Designer’s responsibility

15.8.1

HSE guide: Fire Safety in Construction

The HSE’s own guidance, Fire Safety in Construction, is a very thorough document and could be applied to address the subject matter of this section (HSE, 2010). However, in considering the responsibilities of all entities associated with construction, it is appropriate in this Guide to emphasise the designer’s role. Appendix 4 of the HSE guide is entitled ‘Who does what?’ and is summarised in this section.

15.8.2

Fire performance of construction materials

Designers should be aware of the fire performance of their preferred materials during storage, construction and in the completed building. Following analysis, it may be decided that the use of less hazardous materials or processes would be more appropriate.

Reducing ignition sources

Minimising the need for hot work is the most crucial area, although control of on-site ignition sources is more in the domain of the contractors. The need for welding on-site can be reduced by specifying bolted rather than welded steel sections and by the use of off-site fabrication. Another area for risk reduction is the use of threaded or push-fit plumbing rather than brazed jointing.

15.8.4

General fire safety precautions

Fire safety measures required in the completed building can often be provided in the early stages of construction. General fire safety precautions worthy of attention include the following: ——

Operational fire mains and access for personnel and vehicles to the inlets will greatly improve firefighting capabilities.

——

Compartmentation required in the finished building should be implemented as early as possible.

——

Early provision of escape and firefighting stairs enhance both safety and firefighting capabilities.

——

Fire doors, if shut during a fire, are very effective in controlling fire and smoke spread; where they are provided to protect escape and firefighting stairs, their early installation is beneficial.

——

Alarm systems will provide early warning of a fire situation, but should be suitable for installation in dusty environments.

The early provision of these facilities, although conceptually possible, may have an impact on other design features. An appreciation of their benefits may allow their incorporation early in the process, if raised at a suitable stage during the design phase.

15.8.5

Emergency procedures

Provision and maintenance of first-aid firefighting equipment and training regimes may be outside the scope of the designer’s responsibility, but designers can address the provision of suitable access to the site and within it. A suitable route into and around the site would be beneficial for general construction purposes, and could be kept clear for firefighting access. With higher risk projects, e.g. those below ground and tall structures, particular attention to this aspect is warranted.

15.8.6

Temporary accommodation units

Space should be allowed for temporary units when considering the general layout of the site. Locating them outside the structure is optimal but, if this is not achievable, the most suitable locations would include consideration for means of escape, fire spread and firefighting access.

15.8.7

Sleeping accommodation

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Based on the premise of maximising dependence on permanent, rather than temporary measures, fire precautions during construction may be considered using the same criteria as those anticipated for the completed building. These criteria include:

15.8.3

Fire safety on construction sites

15.9

Building construction works

Method statements and works sequencing should consider and take into account the following fire safety issues.

15.9.1 Compartmentation The need to provide and maintain fire compartmentation at the early stages of construction should be emphasised. If self-closing fire doors protecting shafts and other vertical connections are vulnerable to damage, they should be provided with hold-open devices operated by a fire detection system. The provision of compartmentation is likely to be a major part of the fire strategy for a completed building. During construction, it may be provided only partially, or not at all. During the fire at Minster Court, compartmentation intended for the completed building was impaired, with the result that fire spread up a protected shaft because doors were held or left open without closing devices (Fire Prevention, 1992c). Furthermore the atrium was not enclosed, as it would have been once the building was complete, which resulted in further fire and smoke spread. The need for the progressive installation of compartmentation is even greater in timber-framed buildings, particularly those using cross-laminated timber products where the risk to firefighters, construction workers and adjoining properties is greater. The Colindale fire in London in 2006 revealed the speed at which a large fire can develop in a partially constructed timber-framed building (GLA, 2010). Testing of timber-framed buildings has highlighted the need to ensure that approved methods of fixing fire-rated elements are used; organisations such as the Structural Timber Association in the UK provide further guidance on fire safety for these types of structures.

15.9.2 Ventilation The control of smoke, to assist escape, as assistance to the fire brigade in identifying the fire source or as a means of clearing a building, would normally form part of the fire strategy for a completed building. During the Minster Court fire, smoke control systems were not operating (Fire Prevention, 1992c). Smoke spread up the atrium, accumulating at the top, causing considerable damage to the upper floors, until the atrium roof failed. The need to provide and maintain smoke ventilation at the early stages of construction should be considered where possible.

15.9.3 Firefighting 15.9.3.1 Construction Construction sites associated with timber structures can present an unexpected risk to attending fire and rescue service personnel, and fire authorities should be notified of such projects before work begins on site. If fire stopping and compartmentation is incomplete when a fire starts, fire spread and growth can be rapid. The Colindale fire in London in 2006 highlighted the severity of fires involving timber-framed buildings during construction (GLA, 2010). Within nine minutes of the fire being detected, all parts of the six-storey building were alight and the building collapsed 14 minutes later. The fire was so severe that 100 firefighters attended the incident and, at times, were not able to get within 50 m of the building. This fire, and several others involving timber structures in the UK, resulted in an inquiry by the London Assembly in 2010 and a number of recommendations regarding the construction of timber-framed buildings (GLA, 2010). Buildings with features such as fake chimneys and fake masonry facades may give the attending fire service a false perception of the type and nature of construction involved. Where construction methods would present an abnormal risk to firefighters, the fire service should be notified of the nature of the site and the risks prior to the commencement of construction activities on site. 15.9.3.2

Firefighting facilities

Firefighting facilities in the completed building, including risers, hydrants and firefighting shafts, should become operable as early as possible during construction to maximise their usefulness. This issue is addressed in the Joint code (FPA, 2015), in NFPA 241 (NFPA, 2013) and in hydrant standards. The provision and maintenance of these facilities during construction is dependent on management commitment but is nonetheless considered possible and worthwhile. 15.9.3.3 Sprinklers Some sprinkler standards call for the installation of functioning sprinklers as construction progresses. Sprinklers should be installed as early as possible and will be of economic benefit if such measures also form part of the completed building. Damage to sprinklers during building works is a matter for site management; however, if needed, they could be guarded or provided with mechanical protection, e.g. recessed. Special precautions may be required in exposed conditions during winter, such as temporary alternative valve sets. Decommissioning of sprinklers already installed must first be discussed with the building owners, responsible persons, where assigned, insurers and fire authorities. It is appreciated that the provision of sprinklers to the relevant standard in a partially completed building poses considerable problems. However, if their contribution to the reduction of construction fire risks is acknowledged, the phasing of the building works could be structured to incorporate them at the earliest opportunity.

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The advice of a fire safety specialist should be sought if there is any doubt about the specification or location of sleeping accommodation on a construction site, as higher fire safety standards are justified.

15-5

15-6 15.9.3.4

Fire safety engineering First-aid firefighting

15.9.4 Detection The early detection of fire in any circumstances is advantageous. On construction sites, detection will alert both those responsible for first-aid firefighting and the fire brigade. Dust levels are likely to be high during building works and the provision of fire detection will require careful consideration due to the potential for false alarms. This aspect must be considered to avoid early mistrust of the installation arising, although the problem can be largely overcome by the choice of detector. On large, complex sites, or where the risk is high, consideration should be given to the use of an automated fire detection system rather than a manually operated system.

15.9.5

Fire loads

Past incidents emphasise the need to address the increased fire load posed by temporary works and the need to maintain the integrity of protected shafts (Fire Prevention, 1992b). The use of less combustible materials for temporary works would reduce the risk of fire spread over combustible protective cladding, scaffold boards and staging. Nonetheless, automatic fire detection and control would provide further assistance in reducing fire damage.

15.9.6

15.10

Management and communication

15.10.1 Management Site management plays an important part in ensuring that fire precaution measures are adopted and site managers may need to ensure that site staff are adequately trained to fight fires. Keeping the fire brigade informed about the development, in terms of access and firefighting facilities as well as the site layout, should form part of the site manager’s duties. The importance of patrolling construction sites, particularly as work nears completion, should be emphasised. Site management will play a leading role in briefing the attending fire brigade on the incident on their arrival.

15.10.2

Fire wardens

The role of a fire warden is to ensure that fire precautions are being observed, and they should be aware of the risks based on an understanding of the behaviour of fire, rather than merely as the application of a set of rules. There needs to be a greater appreciation of the importance of the fire warden’s role. Implementation of this recommendation should not result in the employment of a poorly qualified person to double as the fire safety officer. The better suited the person is to this role, the greater the assurance that fire precautions will be observed. The nature of the job and its responsibilities demand that appropriate safety measures be implemented. The fire warden must receive full support from management in any negotiations that may be necessary, regardless of the contractual implications.

Building separation

Depending on certain factors (see section 3.2.5), the fire strategy will consider the possibility of fire spread between buildings, and will include appropriate measures to mitigate the risk. The fire strategy’s contribution to limiting fire spread will take into account the building’s intended end use, compartmentation and the provision of sprinklers. However, during construction, neither sprinklers nor compartmentation may be functional, and measures to control fire spread will be limited; fire loads may also be higher than they will be on completion.

15.11

Built-in fire precautions

The concept of built-in, or ‘hidden’, fire precautions that cause minimal conflict with the building’s use is not new. However, the more heavily they rely on continuous management, the more likely they are to be ineffective when required. The dangers of having to use an escape route with which one is not familiar are well known and, in an emergency, it is often considered better to leave a building by the route through which it was entered.

Furthermore, designs may require external elevations themselves to include protected areas, but the fact that these are incomplete will mean that they can make no contribution to preventing fire spread to adjoining properties.

The best fire precautions in completed buildings are those that are in harmony with the building’s normal use. Examples include hospitals in which department boundaries coincide with fire compartments, and hotel bedrooms where fire-resisting doors provided for privacy and acoustic needs also ensure sufficient mass to resist fire. Such fire precautions are more likely to be effective when required.

Temporary measures in the form of fire-resisting partitions, facades and enclosures for combustible materials, and the control of combustible materials, may be required on construction sites to avoid fire spread to adjoining properties.

The same considerations apply on construction sites, and appropriate fire precautions, ‘hidden’ in the developing building, should be included where possible. The use of reinforced concrete, for example, provides a level of fire resistance as soon as the formwork is removed.

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There is some evidence that first-aid firefighting facilities, including extinguishers, blankets and fire hose reels, are abused by site staff, but their usefulness is generally accepted. The fact that some fires are not extinguished by first-aid firefighting equipment may be due less to the availability of such equipment and more to a lack of skill or training in their application, or to the nature of the fire at the time of discovery.

This issue is even more critical with timber-framed buildings, due to the potential for a very large fire to occur within a short period.

Fire safety on construction sites

15.12

Partial occupation

15-7

References Fire Prevention (1992a) ‘New construction site code “must succeed”’ 252 (September) 9

Care is needed where it is intended that partial occupation is to take place, in particular where the occupied (or partially occupied) part of the building is residential or incorporates sleeping accommodation. The completed parts of the building are likely to be subject to different legislation from the construction site, and the requirements of such legislation will have to be reconciled with the particular risks of construction.

FPA (2015) Fire Prevention on Construction Sites: The joint code of practice on the protection from fire of construction sites and buildings undergoing renovation (London: Fire Protection Association)

It may be necessary to provide additional and, if appropriate, temporary fire safety measures to assure the safety of those in the occupied parts, especially if sleeping accommodation is provided while construction works continue elsewhere.

NFPA (2013) NFPA 241 Standard for safeguarding construction, alteration and demolition operations (Quincy, MA: National Fire Protection Association)

Fire Prevention (1992b) ‘Getting through construction’ 248 (April) 20 Fire Prevention (1992c) ‘FPA casebook of fires’ 248 (April) 33

GLA (2010) Fire Safety in London: Fire risks in London’s tall and timber frame buildings (London: Greater London Authority) HSE (1993) ID 404/23 General Fire Precautions at Temporary Accommodation Units on Construction Sites (Sudbury: Health and Safety Executive) HSE (2010) HSG168 Fire Safety in Construction (London: HSE Books)

SCI (1991) Structural Fire Engineering: Investigation of the Broadgate Phase 8 fire (Ascot: Steel Construction Institute)

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For some construction projects, in particular where extended timescales are involved, parts of the building may be completed and occupied while construction work continues elsewhere.

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16

Fire safety of building facades

The design of facade systems is a highly specialised area of fire engineering expertise and should only be undertaken by someone who is competent to do so. The Society of Façade Engineering (https://www.cibse.org/society-of-facade-engineering-sfe) is the specialist group within CIBSE that deals with the requirements of façade engineering. Corporate members of the Society have demonstrated their competence in the discipline of façade engineering and have the specialist knowledge to provide advice on cladding and façade engineering requirements. There are hundreds of fire tests defined by UK, European, ISO and US codes and standards. It is vital that reference is made to the correct fire test for the particular use required. Care should be taken in respect of vague terms, such as fire proof, fire safe, fire retardant, fire resistant, and instead a check should be made to determine if the product or system satisfies the performance requirements in the relevant fire test or classification documents referenced in this chapter. Internal fire spread, including requirements for compartment floors, compartment walls and protected shafts, is addressed in chapter 12, smoke ventilation in chapter 10 and sprinklers in chapter 11 of this Guide.

The arrangements in England for full scale fire tests and ‘assessments in lieu of testing’ have recently been the subject of a consultation on severely restricting such assessments, and on banning combustible materials from external elements, which may render full scale testing redundant or significantly curtail its relevance. Such regulatory measures are not limited to the UK. In Australia the states of Victoria and New South Wales have recently introduced new measures to restrict the use of certain products in construction. As a result of this significant regulatory uncertainty, the decision has been taken to publish chapter 16 in online form only. This will allow it to be updated in line with anticipated ongoing government announcements and changes to legislation. It also removes the potential for erroneous guidance on these matters to be available in a more durable and persistent printed form. When substantive information is available, chapter 16 of this Guide may be accessed from the summary page for CIBSE Guide E on the CIBSE website (https://www.cibse. org/knowledge). Given the high likelihood of significant regulatory changes, readers should consider whether it is appropriate to download copies for subsequent use, or access the guidance online to ensure that the latest version is being consulted and applied. Downloaded copies may need to be stored for audit and quality assurance purposes, but it is important that such copies are clearly identified as archive copies and not to be used in a live design or construction environment.

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This new chapter has been added as a result of the fire at Grenfell Tower in Kensington, London, and other largescale international fires involving external facades. This section does not contain speculation regarding the cause and spread of such fires around the world, or the Grenfell fire, which is being addressed by the public inquiry and police investigation.

I-1

Index

acceptance testing 14-4 access for the fire service 13-6 to 13-8, 13-13 to 13-16, 13-18 aerial appliances 13-3 aerosols (extinguishing agents) 11-35 afffs (aqueous film-forming foams) 11-23 ahj (authority having jurisdiction) 1-2, 2-3 to 2-4, 2-5 air change systems 10-1 air leakage from building 10-10 air-tightness of building 10-2 alarm systems see automatic fire detection and alarm systems alarp (as low as is reasonably practicable) 5-3, 5-5, 5-6 alcohol resistant (AL) foams 11-24 alterations buildings 14-12 to 14-13 systems 14-10 alternative exits 7-4 apartment buildings 3-8 to 3-9, 13-17 see also corridors approvals process 2-3 to 2-4, 14-4 approved codes of practice (acops) see codes of practice approved contractors 11-22 Approved Document B 1-1, 2-2, 3-5, 3-7, 7-1, 8-2, 9-2 approved inspectors 3-7 aqueous film-forming foams (afffs) 11-23 argon (extinguishing agent) 11-34 arson fires 14-9 aset (available safe egress time) 7-7 ‘as low as is reasonably practicable’ (ALARP) 5-3, 5-5, 5-6 assembly and recreational buildings 3-10 ASTM fire test standards 12-1 atria 3-10 smoke ventilation 13-17 sprinkler protection 11-15 Australia 2-4, 16-1 authority having jurisdiction (ahj) 1-2, 2-3 to 2-4, 2-5 automatic fire detection and alarm systems 8-1 to 8-18 activating safety measures 8-14 addressable systems 8-6, 8-8 alarm filtering 8-3 audible and visual alarm 8-13 cables 8-14 to 8-15 cause and effect tables 8-3 classification 8-4 to 8-5 construction sites 8-16 to 8-17, 15-6 control equipment 8-13 to 8-16 detector siting and spacing 8-11 to 8-13 detector types 8-8 to 8-11 for dwellings 8-5 to 8-6 fire service notification 13-6 hazardous areas 8-16 life protection 8-4 to 8-5 power supplies 8-15 to 8-16 property protection 8-4 radio-based systems 8-15 sprinkler connected 6-6, 11-20 system types 8-6 zoning 8-7 to 8-8

balanced pressure proportioning 11-25 basement areas 3-4, 13-16 beam detectors 8-9 to 8-10, 8-13 bedrooms see sleeping accommodation behaviour in fires 7-9, 7-9 to 7-11 bladder tanks 11-25 BRE see Building Research Establishment (BRE) B-RISK 6-6 to 6-7 British Standards BS 476-20: 2017 12-1 BS 750: 2006 13-8 BS 5041-2: 1987 13-11 BS 5266-1: 2016 9-3 BS 5306-1: 2006 13-13, 13-22 BS 5306-8: 2012 13-21, 13-22 BS 5499-1: 2002 9-3 BS 5588-7: 1997 3-10 BS 5839: 2013 8-2 BS 5839-1: 2013 8-4 to 8-5, 8-7, 8-8, 8-11 to 8-12, 8-13 to 8-14 BS 5839-1: 2017 13-6 BS 5839-6: 2013 3-8, 8-4, 8-5 to 8-6 BS 5839-8: 2013 8-14 BS 5839-9: 2011 13-18 BS 7346-4: 2003 10-2 BS 7346-7: 2013 13-5 BS 7346-8: 2013 10-1 BS 7944: 1999 13-22 BS 7974: 2001 1-1, 2-2, 4-3, 5-4 BS 8458: 2015 11-28, 11-29 BS 8489: 2016 11-28, 11-29 BS 9990: 2015 13-9, 13-11, 13-12 BS 9991: 2015 13-10 BS 9999: 2017 2-2 building designation 3-1, 3-6 to 3-7, 3-10 fire detection and alarm 8-2 firefighting 13-4, 13-7, 13-9, 13-10, 13-12, 13-13, 13-14, 13-15, 13-17 fire resistance 12-4 fire safety management 14-1 means of escape 7-3, 7-6, 7-7 risk assessment 5-4 smoke ventilation 10-11 BS EN 81-72: 2015 13-15, 13-16 BS EN 1869: 1997 13-22 BS EN 12101-6: 2005 10-8, 10-10 BS EN 12845: 2015 11-5, 11-8, 11-15 BS EN 13565-2: 2009 11-23 BS EN 14339: 2005 13-8 BS EN 15004-1: 2008 11-36 BS PD 7974-5: 2014 13-19 BS PD 7974-7: 2003 5-6, 11-2 building alterations 14-12 to 14-13 building area 3-4 to 3-5 building classification 3-1, 3-2 to 3-3, 3-8 to 3-11 building commissioning and handover 14-4 building contents 3-3, 4-2 building control authority 3-7 building depth below ground 3-4 building design 14-2 to 14-3 ‘built-in’ fire precautions 15-6 designer’s responsibility 15-4 to 15-5 fire resistance rating requirements for building elements 12-3 sprinkler installations 11-14 structural design for fire safety 12-5, 12-6 to 12-7 building designation 3-1 to 3-7, 3-8 to 3-11

building extensions 14-12 to 14-13 building facades see facade systems building handover 2-5, 14-4 building height 3-1, 3-4 building information modelling (bim) 2-3 building life cycle 2-5 to 2-6 building maintenance 14-10, 14-13 building management 14-8, 14-10 building occupancy see occupancy types Building Regulations 2-1, 2-3, 2-5, 3-5, 7-1, 8-1 Building Research Establishment (BRE) BRE 79204 10-11 LPS 1208 12-10 building separation 3-5 construction sites 15-6 and sprinkler protection 11-3 building types see also occupancy types characteristic fire growth times 6-4 escape travel times 7-11 fire load densities 11-6 floor space factors 7-2 travel distances for escape 7-5 building volume 3-5 ‘built-in’ fire precautions 15-6 business resilience 5-8 see also property protection C6 foams 11-25 carbon dioxide (extinguishing agent) 11-34, 11-35 carbon monoxide detectors 8-11 car parks 3-11, 10-6 to 10-7, 13-16 to 13-17 cavity barriers 12-9 certification fire resisting products 12-10 handover documents 14-4 sprinkler systems 11-22 change of use 14-3, 14-13 characteristic growth time 6-4 China 2-4 cladding systems 16-1 Class A foams 11-24 client responsibility 2-5 closed-circuit TV 7-6, 8-11 cmsa (control mode specific application) sprinklers 11-9 codes of practice 1-1, 2-2 construction sites 15-1 emergency lighting 9-1 fire alarm and detection systems 8-2 combustible materials fire load 3-5, 11-6 to 11-7 flame heights 6-15 hazard classification 11-5 to 11-7 hazardous materials 3-3 heat flux for ignition 6-14 to 6-15 heat release rates 6-3 oil and flammable liquids 11-7 combustion 6-1 combustion detectors 8-11 commissioning and handover 11-19 to 11-20, 14-4 common areas 3-8, 8-4, 10-11, 10-12, 13-17 communication systems see also staff training evacuation management 14-11 to 14-12 firefighters 13-18 to 13-19 fire safety management 14-7 lift lobbies 7-6 to 7-7 voice alarm systems 3-5, 7-10, 8-13, 8-14, 14-11 comparative criteria 4-4 compartmentation 3-4, 12-5, 12-7 construction sites 15-5

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Note: page numbers in italics refer to figures; page numbers in bold refer to tables; headings are arranged in letter-by-letter alphabetic order.

available safe egress time (ASET) 7-7

I-2

‘defend in place’ strategy 3-8 demolition work 14-13 Department of Health, Firecodes 3-9 depressurisation systems 10-8 to 10-9 design, building see building design design codes see also codes of practice means of escape 7-2 to 7-7 sprinkler systems 11-5 design fires 4-2, 6-2 to 6-6, 12-6 design information 14-5 design objectives 4-1 to 4-2 design responsibility 2-5 design scenarios 4-2 to 4-3 deterministic criteria 4-4 disabled occupants 3-6, 4-2, 5-9 to 5-10 evacuation 7-5 to 7-6 discounted areas 7-2 discounted exits 7-3 documentation 2-3, 4-4, 14-4 to 14-6 domestic buildings see residential (dwellings) buildings dry mains 13-11 dry powder systems 11-35 ductwork fire dampers 12-10

‘Duty Holder’ 2-5 early suppression fast response (esfr) systems 11-9 educational buildings 3-10 emergency lighting 7-16, 9-1 to 9-4 emergency planning and management 14-10 to 14-12, 15-4 emergency wayfinding systems 7-16 empty buildings 14-13 environmental impact 4-2 environmental protection 13-20 escalators 7-7 escape lighting see emergency lighting escape routes see also means of escape alternative 7-4 basement areas 3-4 compartmentation 12-10 individual dwellings 3-8 lighting 9-3 protection 7-5 to 7-7, 8-5 separation 7-4 smoke control 7-8, 10-5 to 10-11 escape stairs capacity 7-3 to 7-4, 7-13 to 7-14 smoke ventilation 10-11, 13-17 escape time 7-7, 7-8, 7-9 to 7-11 pre-movement time 7-9 to 7-11, 7-11 travel time 7-11, 7-11 to 7-14 ESFR (early suppression fast response) systems 11-9 European perspective 2-4 evacuation see also means of escape disabled occupants 7-5 to 7-6, 7-9 escape time 7-8, 7-9 to 7-12 fire drills 14-6 lifts 7-6, 13-18 models 5-8 procedures 14-11 to 14-12 simulation models 7-14, 7-15 strategies 7-1 to 7-2 event tree analysis (eta) 5-5 to 5-6 exits alternative 7-4 final 7-13 exit signs 7-16, 9-3 exit widths 7-3, 7-13 exposure limits for firefighters 13-5 extensions to building 14-12 to 14-13 external fire spread 3-5, 15-6 facade systems 3-5, 16-1 sprinkler protection 11-4 external walls see also facade systems sprinkler protection 11-4 facade systems 3-5, 16-1 failure scenarios 4-2 to 4-3 film-forming fluoroprotein (fffp) 11-24 final exit 7-13 fire alarm and detection systems see automatic fire detection and alarm systems Fire and Rescue Services Act 2004 2-1 fire appliances 13-3, 13-5 fire authority 3-7 fire buckets 13-20 fire control centre 14-14 fire dampers 12-9 to 12-10 fire detection and alarm systems see automatic fire detection and alarm systems fire drills 14-6 fire dynamics 6-1 to 6-17 accumulated ceiling layer 6-11 to 6-14 compartment fires 6-1 to 6-2 design fires 6-2 to 6-6

fire dynamics (continued) effect of sprinklers 6-5, 6-6 to 6-7 fire and smoke modelling 6-7 and fire resistance 12-4 to 12-5 flame calculations 6-14 to 6-16 smoke plumes 6-7 to 6-14 fire emergency management 14-12 fire emergency plans 14-11, 14-12 fire engineering 1-1 to 1-2 fire engineer responsibilities 2-3 fire extinguishers 13-22 firefighters communication systems 13-18 to 13-19 exposure limits 13-5 personal protective equipment (PPE) 13-4 to 13-5 physiological limits 13-4 risks to 5-7 to 5-8 safety 12-7, 13-4 to 13-5, 13-12 travel times 13-19 to 13-20 firefighting 13-1 to 13-24 see also fire services construction sites 15-5 to 15-6 environmental protection 13-20 equipment 13-5, 13-21 to 13-22 high-rise buildings 13-13, 13-19 to 13-20 objectives 13-2 tactical 13-2 to 13-3 timelines 13-18 to 13-20 water supplies 13-8 to 13-11 firefighting lifts 13-15, 13-16, 13-19 firefighting lobbies 13-13, 13-15 firefighting shafts 3-1, 3-4, 10-11 fire mains 13-12 provision 13-14 to 13-16 smoke ventilation 10-11, 13-16 and sprinkler protection 11-3 firefighting staircases 13-15, 13-19 fire growth, effect of sprinklers 6-6 to 6-7 fire growth curves 6-3, 6-4, 6-16 fire growth rates 6-1, 6-2, 6-3 to 6-6 fire hoses 3-4, 13-3 to 13-4, 13-22 fire hydrants 13-8 to 13-9 fire load 3-5 construction works 15-6 equivalent 6-6 hazard classification 11-6 to 11-7 occupancy types 11-6 offices 11-4 to 11-5 fire mains 13-10 to 13-13 fire management plans 14-10 to 14-12 fire models 6-7 fire precautions 3-7 to 3-8 construction sites 15-1, 15-2 to 15-4, 15-6 purpose groups 3-8 to 3-11 standards 3-7 to 3-8 Fire Precautions Act 1971 2-1, 2-6 fire prevention 14-3, 14-7 to 14-9 fire protection engineering, definition 1-1 fire resistance assessment 6-15 to 6-16 fire resistance period 12-2 to 12-3 fire resistance rating requirements for building elements 12-3 fire tests 16-1 measurement 12-1 to 12-2 performance-based design 12-4 to 12-5 performance criteria 12-1 prescriptive vs. performance-based design 12-3 to 12-4 and sprinkler protection 11-3 standards 12-1 fire resisting shutters 12-7 fire risk see risk assessment fire risk assessment 2-5

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compartmentation (continued) protected openings 12-7 to 12-9 sprinkler protection 11-3, 11-5 compartment fires 6-1 to 6-2 fire resistance assessment 6-15 to 6-16 flame spread 6-14 to 6-16 heat flux calculations 6-14 to 6-15 smoke filling times 6-11 to 6-14 competency 2-2 ‘Competent Person’ 14-1 compliance with regulations 11-1, 16-1 concrete construction 12-6, 12-7 Construction (Design and Management) Regulations 2015 2-3, 2-5 construction sites 3-6, 15-1 to 15-7 building separation 15-6 compartmentation 15-5 designer’s responsibility 15-4 to 15-5 fire detection and alarm systems 8-16 to 8-17, 15-6 fire emergency procedures 15-4 firefighting 15-5 to 15-6 fire precautions 15-1, 15-2 to 15-4, 15-6 fire safety incidents 15-1 fire safety management 14-3, 15-6 fire safety responsibility 2-5 legal considerations 15-2 site management 15-6 smoke ventilation 15-5 sprinkler protection 11-14, 15-5 CONTAM 10-9 continuum net-value work diagram 5-5 to 5-6 contractor responsibility 2-5 contractors, fire precautions 14-8, 14-13, 15-1, 15-3 control centre 14-14 control equipment 8-13 to 8-16 control mode specific application (CMSA) sprinklers 11-9 cool gas generators 11-36 corridors firefighters’ safety 13-4 to 13-5 smoke ventilation 10-8, 10-11, 13-17 cost-benefit analysis (cba) 5-5 to 5-7, 5-8 to 5-9 cost and affordability 5-9 remedial works 5-8 to 5-9 cross-ventilation systems 10-6 to 10-7

Fire safety engineering

Index I-3 fluoroketone (extinguishing agent) 11-34 fluoroprotein (FP) foam 11-23 foam systems 11-23 to 11-28 discharge devices 11-26 to 11-27 foam proportioning 11-25 inlets 13-13 system types 11-26 types of foam concentrate 11-23 to 11-25 fp (fluoroprotein) foam 11-23 fuel bed-controlled fires 6-2, 6-6 gaseous fixed fire extinguishing systems 11-32 to 11-35 environmental and safety considerations 11-37 extinguishing agents 11-32 to 11-35 international standards 11-36 to 11-37 maintenance requirements 11-39 to 11-40 system configuration 11-38 to 11-39 system design 11-37 to 11-38 glazing protection 11-4, 11-15 ‘good industry practice’ 5-3 to 5-4, 5-6, 5-9 Grenfell Tower 2-1 guidance documents 2-2 Hackitt Review 2-1, 2-6 halocarbon (extinguishing agent) 11-33 to 11-34 handover phase 2-5, 14-4 hazardous areas 8-16 hazardous materials 3-3, 4-2 hazards analysis 5-4 classification 3-2 to 3-3, 11-5 to 11-7 definition 5-2 Hazen–Williams formula 11-17 healthcare buildings 3-9, 4-1 Health Technical Memorandum 05-02: Firecode 4-1 heat detectors 8-9, 8-11 to 8-12 heat exhaust ventilation 13-16 heat exposure limits 13-5 heat flux calculations 6-14 to 6-15 heat release rates 6-3 to 6-5 condition for flashover 6-5 to 6-6 heat tolerance 7-8 heat transfer to structural elements 12-6 high-reach appliances 13-3, 13-5 high-rise buildings see tall buildings ‘historical’ data 5-7 horizontal evacuation 14-11 hose reels 13-3 to 13-4 hotels 14-1 hot work 14-13, 15-4 housekeeping measures 14-8, 14-10 human factors, behaviour in fires 7-9, 7-9 to 7-11 hvac systems use in smoke ventilation 10-9 hydrants 13-8 to 13-9 hyperthermia 10-4 (informative fire warning) systems 7-14 to 7-15 ignition 6-1 impulse jet ventilation 10-7 incubation period 6-3 to 6-4 inductors (line proportioners) 11-25 industrial buildings 3-11, 11-7 inert extinguishing agents 11-34 informative fire warning (ifw) systems 7-14 to 7-15 institutional (residential) buildings 3-9, 11-21 ifw

insulating materials/products see cladding systems; fire resistance insurance 5-8 insurance standards 3-8 international perspectives 2-3 to 2-4, 3-7 to 3-8 intrinsically safe equipment 8-16 kitchens 11-7 landing valves 13-12 to 13-13 legislation 2-1 to 2-6, 14-2 construction sites 15-2 equal regard for 5-9 life safety protection 3-6, 4-1 to 4-2 construction sites 15-1 to 15-2 fire detection and alarm systems 8-4 to 8-5 fire resistance 12-3 to 12-4 risk assessment 5-3 to 5-4, 5-6 sprinkler protection 11-9 to 11-10, 11-20 to 11-21 lifts firefighting 13-15, 13-16, 13-19 means of escape 7-6, 13-18 liquid inert systems 11-34 to 11-35 lobbies see firefighting lobbies; protected lobbies localised fires 12-5, 12-6 loss prevention 4-2 maintenance building 14-10, 14-13 fire safety systems 11-20, 14-8 to 14-9, 14-9 to 14-10 manual fire alarm systems 8-2, 8-3, 8-5, 8-8 mass optical densities 10-4 means of escape 7-1 to 7-16 see also escape routes; evacuation design codes 7-2 to 7-7 design objectives 7-1 to 7-2 evacuation strategies 7-1 to 7-2 fire safety engineering approaches 7-7 to 7-9 prescriptive approaches 7-1 to 7-16 sprinkler protection 11-3 mechanical smoke ventilation 10-12 mechanical ventilation and air-conditioning systems see HVAC systems mechanised walkways 7-7 Middle East (Gulf States) 2-4 modifications to systems 14-10 mp (multi-purpose) foams 11-24 multiple fatalities 5-6 multiple safeguards 4-2 multi-purpose (mp) foams 11-24 multi-storey buildings see apartment buildings; tall buildings multi-tenancy/multi-occupancy 3-6, 3-8 to 3-9 means of escape 7-9 National Fire Protection Association (NFPA) codes NFPA 1 13-10, 13-11, 13-12, 13-13 NFPA 11 11-23 NFPA 13 11-5, 11-6, 11-7, 11-15 NFPA 14 13-11 NFPA 16 11-23 NFPA 24 13-9 NFPA 25 11-20 NFPA 72 8-2, 8-4, 8-7, 8-12, 8-14 NFPA 92 6-4, 6-5, 10-2 NFPA 101 4-1, 7-1, 7-3, 7-4, 7-5, 9-3, 10-3, 12-3 NFPA 130 10-4

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Fire Safety (Scotland) Regulations 2006 2-5 fire safety design for a manageable building 14-2 to 14-3 objectives 4-1 to 4-2 process 4-3 to 4-4 scenarios 4-2 to 4-3 fire safety engineering design approach 4-1 deterministic approach 1-1 equivalency 1-1 general approach 2-1, 2-2 to 2-3 multiple methods of potential control 11-1 probabilistic approach 1-2 fire safety goals 2-3 fire safety information 2-6, 14-5 to 14-6 fire safety maintenance 2-3, 11-20, 14-8 to 14-9, 14-9 to 14-10 fire safety management 14-1 to 14-14 and building design 14-2 to 14-3 building handover 14-4 changes to a building 14-12 to 14-13 communication systems 14-7 construction sites 14-3, 15-6 documentation 2-3 emergency planning and management 14-10 to 14-12, 15-4 fire prevention 14-3, 14-7 to 14-9 legal considerations 14-2 fire safety manager 14-1, 14-6 to 14-7, 14-9 fire safety manual 2-5, 14-4 to 14-6 fire safety responsibilities 2-5 to 2-6 fire safety review 14-6 fire safety strategy 4-4, 11-1 fire scenarios 4-2 fire separation between buildings 11-3, 15-6 multi-tenancy/multi-occupancy 3-6, 3-8 to 3-9 fire services see also fire authority access within premises 13-14 to 13-16, 13-18 consultation with 13-1 to 13-2 emergency pack 14-10 external access to premises 13-6 to 13-8, 14-8 notification and response 13-5 to 13-6 perimeter access 13-13 to 13-14 provision of information for 13-20 to 13-21 vehicles and appliances 13-3, 13-7 fire size 6-2, 6-7 fire spread see fire growth rates fire stopping 12-7 to 12-8 fire suppression 11-1 to 11-40 fire tanks 13-12 fire tests 12-1 to 12-2, 16-1 fire ventilation see also smoke ventilation fire wardens 15-6 fire watchers 15-1 fitting-out 14-3 flame detectors 8-10 to 8-11, 8-13 flame height 6-15 flame projection from openings 6-15 flameproof equipment 8-16 flame spread 6-14 to 6-16 flammable liquid hazards 11-7 see also foam systems flashover 6-1 to 6-2, 6-5 to 6-6, 6-13 to 6-14 flats and maisonettes 3-8 to 3-9, 13-17 see also corridors floor area 3-4 floor space factors 7-2, 7-2 fluorine-free foams 11-24 to 11-25

I-4

occupancy characteristics 3-5 to 3-6, 4-2, 5-4 occupancy types 3-1, 3-2 to 3-3, 3-8 to 3-11 escape pre-movement times 7-10 to 7-11, 7-11 escape travel times 7-11 to 7-12 fire load 11-6 occupant behaviour 7-9, 7-9 to 7-11 occupant capacity 7-2 to 7-3 occupants firefighting by 13-21 to 13-22 fire prevention 14-8 training and education 13-21, 14-8 to 14-9 office buildings 3-9 to 3-10, 11-4 to 11-5 oil and flammable liquid hazards 11-7 openings flame projection from 6-15 protected 12-7 to 12-9 smoke plumes 6-8 to 6-10 open-plan layout 3-8 operational records 14-5 opposed air flow 10-1 opposed air flow systems 10-7 to 10-8 outsourcing of fire safety management 14-7 overseas regulations 2-4 oxygen reduction systems 11-35 to 11-36 partial occupation 15-7 performance-based design 4-1 to 4-4 personal protective equipment (ppe) 13-4 to 13-5 phased evacuation 3-1, 3-4, 14-11 stair capacity 7-4 pipe closures 12-8 to 12-9 planning for emergencies 14-10 to 14-12, 15-4 post-completion 2-5 post-flashover fires 6-5 to 6-6, 12-4 to 12-5, 12-6 power supplies automatic fire detection and alarm systems 8-15 to 8-16 smoke ventilation 10-7 PPE (personal protective equipment) 13-4 to 13-5 pre-flashover fires 6-3 premix foam units 11-26 pressure differential systems 10-1 pressurisation systems 10-9 to 10-10 probabilistic criteria 4-4 professional competency 2-2 property protection 3-6, 4-2 cost-benefit analysis (cba) 5-6 fire detection and alarm systems 8-4 sprinkler protection 11-20 protected escape routes 7-5 to 7-7, 8-5 compartmentation 12-10 individual dwellings 3-8 smoke ventilation 10-11 protected lobbies 7-5, 7-6, 10-11 protected shafts see firefighting shafts protected stairways capacity 7-13 to 7-14 smoke ventilation 10-11 public evacuation 14-12 pumping appliances 13-3 purpose groups 3-1, 3-2 to 3-3, 3-8 to 3-11 pyrolysis 6-1

qualitative design review (qdr) 4-3 qualitative risk assessment 5-4 to 5-5 quantitative risk assessment (qra) 5-5 to 5-7 rack storage 11-7, 11-17 radiant heat heat flux for ignition 6-1 maximum exposure tolerance 7-8 ‘reasonably foreseeable risks’ 5-2 ‘reasonably practicable’ 5-6 recreational buildings see assembly and recreational buildings refuge areas 7-3, 7-5 to 7-6 refuge floors 7-7, 13-18 refurbishment of buildings 14-12 to 14-13 regulatory approvals 2-3 to 2-4 see also Building Regulations Regulatory Reform (Fire Safety) Order 2005 2-1, 2-5 remedial works 5-8 to 5-9 required safe egress time (rset) 7-7 residential (dwellings) buildings 3-8 to 3-9 see also flats and maisonettes fire detection and alarm systems 8-5 to 8-6 smoke ventilation 10-2, 10-11, 10-12 sprinkler systems 11-21 residential (institutional) 3-9 response time index (rti) 6-6 ‘Responsible Person’ 2-5 to 2-6, 14-1 ‘reverse alarp’ 5-8 rising mains 13-10 to 13-13 risk, definition 5-2 risk assessment 4-1, 5-1 to 5-10 acceptability criteria 5-3 definition 5-2 England and Wales 2-6 hazard classification 11-5 to 11-7 pitfalls 5-8 to 5-10 process 5-2 techniques 5-3 to 5-8 risk matrices 5-4, 5-5 risk profiles 3-1, 3-6 to 3-7, 5-4 risk reduction measures cost-benefit analysis (cba) 5-6 fire prevention 14-3, 14-7 to 14-9 ‘reasonably practicable’ 5-6 RSET (required safe egress time) 7-7 RTI (response time index) 6-6 safety lighting see emergency lighting school buildings 11-22 Scotland 3-7 sd (synthetic detergent) foams 11-23 to 11-24 security construction sites 15-1 fire prevention 14-9 landing valves 13-11 separation distances 3-5, 11-3, 15-6 sfairp (‘so far as is reasonably practicable’) 5-3 shopping malls 13-17 shops and commercial premises 3-10 signage 7-16 simultaneous evacuation, stair capacity 7-3 to 7-4 site boundary see building separation sleeping accommodation 3-6, 7-10, 7-11, 8-13, 8-14 slit extract system 10-12 slot extract system 10-12 smoke in escape routes 7-8 temperature 6-10, 10-3 to 10-4

smoke (continued) toxicity 10-5 visibility in 7-8, 10-4 to 10-5 smoke clearance 10-1, 10-10 smoke control 10-1, 10-11 see also smoke ventilation dampers 12-9 dilution smoke management 10-5 to 10-7 opposed air flow systems 10-7 to 10-8 pressure differential systems 10-8 to 10-10 slot/slit extract system 10-12 smoke-free layer 6-13 system design 10-5 to 10-12 system types 10-5 to 10-12 smoke detection detector as equivalent heat detector 6-6 detector siting and spacing 8-11 to 8-12 detector types 8-9 to 8-10 smoke dilution systems 10-5 to 10-7 smoke extraction see smoke ventilation smoke-free layer 6-13, 7-8, 10-1 to 10-2 smoke hazards 10-3 to 10-5 smoke layer 6-8 to 6-9, 6-11 to 6-14 depths 10-3 temperature 10-4 smoke plumes 6-7 to 6-11, 6-9 air entrainment 6-7 to 6-8 axisymmetric 6-8 ceiling flow 6-11 to 6-12 convective heat release 6-7 flow from an opening 6-8 to 6-10 heat release rate 6-7 heat transfer to building surfaces 6-14 radiant heat transfer 6-14 stratification 6-14 temperature 6-10 volume flow rate 6-10 smoke reservoirs area of reservoir 10-2 screens and curtains 10-2 smoke shafts 10-11 smoke ventilation 10-1 to 10-12 air inlets 10-2 calculations 6-7 computer modelling 10-9 in construction sites 15-5 cross-ventilation systems 10-6 to 10-7 depressurisation systems 10-8 ductwork 12-9 exhaust fan temperature 10-8 to 10-9 extract vents location 6-13 number 10-2 to 10-3 for firefighting 13-16 to 13-17 firefighting shafts 10-11, 13-16 hvac system use in 10-9 impulse jet ventilation 10-7 maximum volumetric flow rate 10-3 mechanical ventilation 10-12 natural ventilation 10-10 to 10-11, 10-11 noise levels 10-5 pressure differentials 10-3 replacement air velocity 10-2 smoke clearance/purging 10-6 smoke-free layer 6-13 and sprinkler protection 11-3 system types 10-1, 10-5 to 10-12 ventilation-controlled fires 6-6 wind overpressures 10-11 to 10-12 smoking 14-8 societal concern 5-7 ‘so far as is reasonably practicable’ (sfairp) 5-3

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National Fire Protection Association (NFPA) codes (continued) NFPA 5000 13-10, 13-15 natural smoke shafts 10-11 nitrogen (extinguishing agent) 11-34 Northern Ireland 3-7

Fire safety engineering

Index I-5 sprinkler protection (continued) speed of activation 11-3 sprinkler heads 11-8 to 11-11 sprinkler pumps 11-18 sprinkler sensitivity 6-6 to 6-7, 11-10 to 11-11 sprinkler spacing and location 11-14 to 11-15, 11-15 system components 11-12 to 11-14 system maintenance 11-20 system types 11-11 to 11-12 tail-end alternate and dry systems 11-12 thermal sensitivity of sprinkler heads 11-10 to 11-11 water supplies 11-17 to 11-19, 11-20 staff training 14-8 to 14-9, 14-10 to 14-11, 15-1 staircases see escape stairs; firefighting staircases standard fire curve 12-1, 12-2 standards see ASTM fire test standards; British Standards; National Fire Protection Association (NFPA) codes standby lighting see emergency lighting statutory requirements see legislation ‘stay put’ strategy 3-8 steady-state fires 6-5 steel construction 12-6, 12-7 storage and other non-residential buildings 3-11 storage risks 11-7, 11-8 structural design for fire safety 12-5, 12-6 to 12-7 structural fire engineering 12-5 supervising station fire alarms 8-5 suspended ceilings position of channelling screens and smoke barriers 10-3 sprinkler protection 11-16 synthetic detergent (sd) foams 11-23 to 11-24 tall buildings 3-1, 3-4 cladding systems 16-1 fire detection and alarm systems 8-17 firefighting 13-13, 13-19 to 13-20 refuge floors 7-7, 13-18 stair capacity for phased evacuation 7-4 temperature, survivable 7-8 testing fire safety manual 14-6 fire safety systems 14-4, 14-9 to 14-10 materials/products 16-1

third-party certification 11-22 timber construction 12-6, 12-7 training of staff 14-8 to 14-9, 14-10 to 14-11, 15-1 transient fires 6-5 travel distances 7-4, 7-12 firefighters 13-4, 13-12 to 13-13 travelling fires 12-5, 12-6 travel times to an exit 7-11 to 7-14 firefighters 13-19 to 13-20 tube-operated systems 11-36 uncertainty in design data 4-3 underground structures 3-4, 3-11 United States (USA) 2-4 see also ASTM fire test standards; National Fire Protection Association (NFPA) codes ‘value of preventing a fatality’ (vpf) 5-6 ventilation see hvac systems; smoke ventilation ventilation-controlled fires 6-2, 6-6 video smoke detection (vsd) 8-11 voice alarm systems 3-5, 7-10, 8-13, 8-14, 14-11 vpf (value of preventing a fatality) 5-6 vulnerable occupants 5-9 to 5-10 see also disabled occupants Wales 2-1, 2-2 wall wetting sprinklers 11-4 water as extinguishent 11-4 water-driven foam metering pumps 11-25 water mist systems 11-28 to 11-32 water supplies firefighting 13-8 to 13-11 sprinkler protection 11-17 to 11-19, 11-20 water mist systems 11-30 water suppression see sprinkler protection wayfinding systems 7-16 wet chemical systems 11-35 wet risers 13-12 ‘what if ’ assessments 4-2 to 4-3 wind overpressures 10-11 to 10-12 window sprinklers 11-4, 11-10 Workplace Health and Safety Directive 14-1 zoning 8-7 to 8-8

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speculative builds 14-3 spontaneous ignition 6-1 sprinkler protection 11-2 to 11-22 approved contractors 11-22 assembly and recreational buildings 3-10 benefits 11-3 building design issues 11-14 colour coding 11-8 commissioning and testing 11-19 to 11-20 compartmentation 11-5 concealed pattern sprinklers 11-9 to 11-10 construction sites 11-14, 15-5 control mode specific application (cmsa) sprinklers 11-9 deluge installations 11-12 and design size fire 11-3 to 11-4 domestic and residential 11-21 dry installations 11-11 to 11-12 early suppression fast response (esfr) systems 11-9 effect on fire growth 6-6 to 6-7 effect on fire size 6-7 extent of protection 11-5 extinguishing mechanism 11-4 to 11-5 fire dynamics 6-5, 6-6 to 6-7 fire engineering approach 11-3 to 11-4 firefighting shafts 11-3 and fire load 11-4 to 11-5 foam systems 11-26 glazing protection 11-4 industrial buildings 3-11 installation design 11-14 to 11-17 installation planning 11-14 institutional (residential) buildings 3-9 life safety protection 11-9 to 11-10, 11-20 to 11-21 location of sprinklers 6-6 occupancy hazard classification 3-2 to 3-3 operating temperatures 11-8 pipework systems 11-13, 11-16, 11-20 pre-action installations 11-12 property protection 11-20 recycling installations 11-12 reliability 11-2 to 11-3 response time 11-10 to 11-11 response time index (rti) 6-6, 11-10 rules and standards 11-5 school buildings 11-22 shops and commercial premises 3-10

CIBSE Guide E 2019

9 781912 034291

Fire safety engineering

ISBN 978-1-912034-29-1

This publication is supplied by CIBSE for the sole use of the person making the download. The content remains the copyright property of CIBSE

The Chartered Institution of Building Services Engineers 222 Balham High Road, London SW12 9BS +44 (0)20 8675 5211 www.cibse.org

Fire safety engineering

CIBSE Guide E