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By Mohammed Osama Abdel Rahman El Samadony
Preface There is much public concern about the issues surrounding the effects of electromagnetic fields on health – in particular, the potential health effects of new communication technologies such as mobile telephones. This report extensively describes what electromagnetic fields are, where they are found, and what is being done to investigate their potential for affecting our health. There are maximum exposure limits that are reviewed in the light of scientific researches.__________________________
CONTENTS Chapter 1 – Introduction………………………………………………….. 1.1 Overview 1.2 The growing concern
5 5 6
Chapter 2 – Characteristics of Electromagnetic fields ……………….… 2.1 Physics of EMFs 2.2 The electromagnetic spectrum
7 7 9
Chapter 3 – Sources of Electromagnetic field …………………………... 3.1 Natural sources 3.2 Man-made sources
10 10 16
Chapter 4 – EMF Impact on Environment ………...…………………….. 4.1 Human being 4.2 Animals 4.3 Vegetation 4.4 Aquatic Life
24 24 28 29 30
Chapter 5 – Standards and Guidelines ….…………………..………….....
ELF EMF ICNIRP IEEE NIR RF UV WHO
Extremely Low Frequency Electromagnetic Field International Commission on Non-Ionizing Radiation Protection Institute for the Electric and Electronic Engineers Non-Ionizing Radiations Radiofrequency Ultraviolet World Health Organization
INTRODUCTION 1.1 Overview: Recent years have seen an unprecedented increase in the number and diversity of sources of electric and magnetic fields (EMF) used for individual, industrial and commercial purposes. Such sources include televisions, radios, computers, mobile cellular phones, microwave ovens, radars and equipments used in industry, medicine and commerce. All these technologies have made our life richer and easier. Modern society is inconceivable without computers, television and radio. Mobile phones have greatly enhanced the ability of individuals to communicate with each other and have facilitated the dispatch of emergency medical and police aid to persons in both urban and rural environments. Radars make air traveling much safer . Simultaneously, these technologies have brought with them concerns about possible health risks associated with their use. Such concerns have been raised about the safety of cellular mobile telephones, electric power lines and speed-control radars. Scientific reports have suggested that exposure to electromagnetic fields emitted from these devices could have adverse health effects, such as cancer, reduced fertility, memory loss, and adverse changes in the behaviour and development of children. However, the actual level of health risk is not known, although for certain types of EMF it may be very low or non-existent. 5
There is also confusion about the biological effects of non-ionizing radiations (e.g radio waves, microwaves, etc.) versus ionizing radiations such as X-rays and gamma rays . The conflict between concerns about possible health effects from exposure to EMF and the development of electricity supply and telecommunications facilities have led to considerable economic consequences. For example, electrical utilities in many countries have had to divert high voltage transmission lines around populated areas and even halt their construction. The installation of base stations for mobile telephone systems has been delayed or has met opposition from the public because of concerns that the RF emissions from these base stations might cause cancer in children. In the United States, for example, 85% of the total number of base stations needed have yet to be constructed . Measures to significantly reduce electric and magnetic fields in the environment, below what is now commonly accepted, are costly. It has been estimated that concerns about EMF and health are now costing the United States economy alone about US$ 1 billion annually. However, if unacceptable health risks do occur, costly prevention measures will be required .
1.2 The Growing Concern: In the last two decades, awareness has increased for this health hazard problem and many institutions both public and private, expressed great interests in the electromagnetic fields impact on environment as a global issue and the human health as specific issue, resulting in a more precise
definitions for the problem and standards that ensures its elimination or reduction. All over the world, numerous studies have been carried out on the possible effects of electromagnetic fields on humans, animals, plants and cell or tissue cultures, and a series of large-scale epidemiological surveys has also been conducted. Based on these research results and upon evaluations of biological effects that have been established to have health consequences, The International Commission on Non-Ionizing Radiation Protection (ICNIRP) developed a guidline for emf exposure limits . Disparities in EMF standards around the world have caused increasing public anxiety about EMF exposures from the introduction of new technologies. Therefore, the World Health Organization (WHO) commenced a process of harmonization of electromagnetic fields (EMF) standards worldwide. Future standards will be based on the results of the WHO's International Electromagnetic Field Project .
CHARACTERISTICS OF ELECTOMMAGNETIC FIELDS 2.1 Physics Of EMFs: When current flows in a wire, there is also a magnetic field generated around it, which is the fundamental concept behind an electromagnet . This magnetic field radiates away from the wire in a circular fashion (Fig. 1). The combination of these two fields is what we call an electromagnetic field (EMF) . The electric field describes the force created by electric charges, and the magnetic field describes the force caused by moving charges in the form of electric current.
Fig. 1 Electromagnetic field around a conductor .
Electric fields are produced by voltage and increase in strength as the voltage increases. The electric field strength is measured in units of volts per meter (V/m). Magnetic fields result from the flow of current through wires or electrical devices and increase in strength as the current 8
increases. Magnetic field strength is usually measured in units of ampere per meter (A m–1). A related quantity is magnetic flux density, measured in tesla (T). The other unit frequently seen in the literature is milligauss (10 mG = 1 μT) .
The electric and magnetic fields that combine to form an electromagnetic wave travel at right angles to each other and to the direction of motion. In following figure (Fig. 2), imagine this electromagnetic wave front jk jjjj
traveling to the right of the page. The electric field ( E ) in this illustration consists of waves that rise and fall in a vertical plane, while the waves of jjk jjjj
the magnetic field ( H ) vibrate back and forth on a horizontal plane. These waves, vibrating at right angles to each other, are inseparable and cannot be defined individually. In other words, an oscillating field of electrical energy will always create a magnetic field, and a moving magnetic field will always create an electrical field; one causes and depends on the other, and, together they form electromagnetic radiation .
Fig. 2 A schematic view of an electromagnetic field propagating along the Z-axis. jk jjjj jjk jjjj The electric E and magnetic H fields oscillate in the x-y plane and perpendicular to the direction of propagation .
In general, the electricity supply produces undistorted sinusoidal waveforms with a frequency of 50-60 Hz. However, in some situations the EMFs may contain additional frequency components called harmonics, which are multiples of the fundamental frequency. Electric fields are shielded or weakened by materials that conduct electricity, even materials that conduct poorly, including trees, buildings, and human skin. Magnetic fields, however, pass through most materials and are therefore more difficult to shield. Both electric fields and magnetic fields decrease rapidly as the distance from the source increases (Fig. 4).
Fig. 4 Magnetic Field Strength Decrease with Distance (a) Magnetic field near the ground for some typical overhead power lines . (b) Magnetic field for typical photocopier .
2.2 The Electromagnetic Spectrum: One of the main characteristics which define an electromagnetic field (EMF) is its frequency or its corresponding wavelength. Fields of different frequencies interact with the body in different ways. One can imagine electromagnetic waves as series of very regular waves that travel 10
at an enormous speed, the speed of light. The frequency simply describes the number of oscillations or cycles per second, while the term wavelength describes the distance between one wave and the next. The frequency of an electromagnetic wave is simply the number of oscillations which passes a fixed point per unit of time. It is measured in cycles per second, or hertz. One cycle per second equals one hertz (Hz). Large divisions commonly used to describe radio frequency (RF) fields include the kilohertz (kHz), or one thousand cycles per second; the megahertz (MHz), one million cycles per second; and the gigahertz (GHz), one billion cycles per second. Hence wavelength and frequency are inseparably intertwined; the wavelength is inversely proportional to the frequency. The middle of the AM broadcast band, for example, has a frequency of one million hertz (1 MHz) and a wavelength of about 300 meters. Microwave ovens use a frequency of 2.45 billion hertz (2.45 GHz) and a wavelength of 12 centimeters . Many properties of EMF depend on its frequency. For example, heating (thermal) effects are produced at microwave and infrared frequencies, and the ability to knock electrons from atoms (ionization) appears at X-ray and gamma ray frequencies. An electromagnetic wave consists of very small packets of energy called photons. The energy in each packet or photon is directly proportional to the frequency of the wave: The higher the frequency, the larger the amount of energy in each photon . The electromagnetic spectrum (Fig. 5) encompasses a wide variety of electromagnetic fields, including static fields, radio frequency fields, 11
ultraviolet (UV) radiation, visible light and X-ray radiation. Electromagnetic waves at low frequencies are referred to as "electromagnetic fields" and those at very high frequencies are called "electromagnetic radiations". According to their frequency and energy, electromagnetic waves can be classified as either "ionizing radiations" or "non-ionizing radiations" (NIR) . a) Ionizing radiations: The frequency of ionizing radiation is measured in millions or trillions of hertz (cycles per second). The energy contained in a given photon is proportional to its frequency, which means that the higher the frequency, the higher the energy. The tremendous photon energy of X-rays and gamma rays (because of their extremely high frequencies) is capable of changing the internal structure of atoms and molecules, as well as being immensely penetrating. This is the sort of radiation we associate with radioactive substances such as uranium, radium, and radiation emitted during atomic and thermonuclear explosions. Ionizing radiation has sufficient energy to cause actual chemical changes to take place within the molecular structure of matter, damaging the cells of living tissues by creating electrically charged, or “ionized,” molecules, and causing genetic mutations. These deadly rays are particularly dangerous because they are initially imperceptible, causing little or no temperature rise within the exposed matter, and since their damaging effects are cumulative, even slight exposure is hazardous. b) Non-ionizing radiations: Non-ionizing radiations is a general term for that part of the electromagnetic spectrum which has photon energies too weak to break atomic bonds. They include ultraviolet (UV) radiation,
visible light, infrared radiation, radiofrequency and microwave fields, extremely low frequency (ELF) fields, as well as static electric and magnetic fields. Even high intensity NIR cannot cause ionization in a biological system. NIR, however, have been shown to produce other biological effects, for instance, by heating, altering chemical reactions or inducing electrical currents in tissues and cells.
Fig. 5 Electromagnetic spectrum—Types of EMF Radiation.
SOURCES OF EMFs The sources of power frequency EMFs are divided broadly into those produced by natural processes and those generated by human activity. Naturally occurring EMFs arise from electrical processes associated with the Earth and the atmosphere. In most environments the dominant source of exposure is that associated with the generation, transmission and use of electricity. People are exposed directly through the use of electrical appliances or equipment, or incidentally through working close to heating systems and power supplies.
3.1 Natural Sources: 3.1.1 Sun radiation: The Sun emits energy in the form of electromagnetic radiation. We see this radiation as light in the visible region and feel it at infrared wavelengths as 'heat'. Other radiation is also emitted as X-rays and radio waves. All of these are electromagnetic waves and are part of the electromagnetic spectrum . The proportion of each type of radiation emitted by the sun is shown in the diagram (Fig. 6): Several measurements made in high quote atmosphere show that a surface of 1 cm2, adsorbing solar energy perpendicularly to the solar rays, adsorbs a heat quantity of 1983 calorie for each minute. This number is said solar constant. Being 1calorie = 4184 joule the solar constant in the International System is given by 1380 Joule per m2 and per sec. These 14
data corresponds to an electrical field of 700 V/m and to a magnetic field of 2.5 microtesla. The centre of the spectrum of the solar radiation is given by a wavelength of 510 nm corresponding to green light .
Fig. 6 Electromagnetic radiation from the sun.
3.1.2 Electric and magnetic field of the earth: Static electric and magnetic fields (constant fields) of significant field strength have always existed on this planet. The movement of air in the atmosphere and the ionising effect of cosmic radiation in the higher regions, the ionosphere, create a field of direct electric current between the surface of the Earth and the ionosphere. Under normal weather conditions, the field strength near the ground is around 100-500 V/m, whereas it can rise to 20,000 V/m (20 kV/m) during storms. Alternating currents at frequencies used in energy supply are practically non-existent. The natural background field strength at 50 Hz is only 0.1 mV/m. This natural static geomagnetic field (Fig. 7) varies in strength from 35 to 70 microtesla (µT) and is enough to deflect compass needles, and assist in the navigation and migration of some birds and fish. This constant field is created by circular action in the Earth's core. Extremely high field 15
strengths can occur in the vicinity of lightning (up to 1 T, which can cause heart failure in humans). Small variations in flux density are induced by the solar wind, which distorts the earth's magnetic field due to its streams of charged particles. Furthermore, global storm activity also results in high-frequency components within the magnetic field. However, these are so small that at 50 Hz the alternating field component is merely 10-6 µT .
Fig. 7 Natural electric (direct) and magnetic (constant) fields .
3.2 Man-Made Sources: 3.2.1 Power lines: Power transmission lines bring power from a generating station to an electrical substation. Power distribution lines bring power from the substation to your home. Transmission and distribution lines can be either overhead or underground. Overhead lines produce both electric fields and magnetic fields. Underground lines do not produce electric fields above ground but may produce magnetic fields above ground.
Power transmission lines: High voltage lines in most of the world have a voltage of 132 kV to 380 kV and a frequency of 50 to 60 Hz. Typical EMF levels for transmission lines are shown in the chart (Fig. 8). The distance at which the magnetic field from the line becomes indistinguishable from typical background levels differs for different types of lines .
Fig. 8 Typical EMF Levels for Power Transmission Lines. These are typical EMFs at 1 m above ground for various distances from power lines .
Electric fields from power lines are relatively stable because line voltage doesn’t change very much. Magnetic fields on most lines fluctuate greatly as current changes in response to changing loads. Magnetic fields must be described statistically in terms of averages, maximums, etc. The magnetic fields above are means calculated for 321 power lines for 1990 annual mean loads. During peak loads (about 1% of the time), magnetic fields are about twice as strong as the mean levels above. The graph shown (Fig. 9) is an example of how the magnetic field varied during one week for one 500-kV transmission line .
Fig. 9 Magnetic Field from a 500-kV Transmission Line Measured Every 5 Minutes for 1 Week
Power distribution lines: Typical voltage for power distribution lines ranges from 4 to 24 kilovolts (kV). Electric field levels directly beneath overhead distribution lines may vary from a few volts per meter to 100 or 200 volts per meter. Magnetic fields directly beneath overhead distribution lines typically range from 10 to 20 mG for main feeders and less than 10 mG for laterals. Such levels are also typical directly above underground lines. Peak EMF levels, however, can vary considerably depending on the amount of current carried by the line. Peak magnetic field levels as high as 70 mG have been measured directly below overhead distribution lines and as high as 40 mG above underground lines .
Power substations: In general, the strongest EMF around the outside of a substation comes from the power lines entering and leaving the substation. The strength of the EMF from equipment within the substations, such as transformers, reactors, and capacitor banks, decreases rapidly with increasing distance. Beyond the
substation fence or wall, the EMF produced by the substation equipment is typically indistinguishable from background levels. 3.2.2 Household appliances: In our houses there are many appliances which once activated create electromagnetic fields. These fields typically act over a small area (diameter of one meter, more or less). Some examples working at extremely low frequencies (ELF = 3-3000 Hz) are: electric razor, Hoover, hairdryer, washing machine, florescent, lamp, refrigerator, toaster, iron and so on. Microwave ovens and others work at RF frequency . Magnetic fields close to electrical appliances are often much stronger than those from other sources, including magnetic fields directly under power lines. Appliance fields decrease in strength with distance more quickly than do power line fields. The following table (Table 1) lists the EMF levels generated by common electrical appliances . Table 1 Typical magnetic field strength of household appliances at various distances .
3 cm distance (µT)
30 cm distance (µT)
1 m distance (µT)
0.5 – 1.7
0.01 – 0.25
2.5 - 50
0.04 – 2
0.01 – 0.15
16 – 56
8 – 30
0.12 – 0.3
0.01 – 0.03
3.5 – 20
0.6 – 3
0.07 – 0.3
0.8 – 50
0.15 – 3
0.01 – 0.15
73 – 200
0.25 – 0.6
3.2.3 Working appliances: 19
Exposure assessment studies so far have shown that most people’s EMF exposure at work comes from electrical appliances and tools and from the building’s power supply. People who work near transformers, electrical closets, circuit boxes, or other high current electrical equipment may have 60-Hz magnetic field exposures of hundreds of milligauss or more. In offices, magnetic field levels are often similar to those found at home, typically 0.5 to 4.0 mG. However, these levels can increase dramatically near certain types of equipment . The following figures (Fig. 10) are examples of magnetic field exposures determined with exposure meters worn by four workers in different occupations. These measurements demonstrate how EMF exposures vary among individual workers. They do not necessarily represent typical EMF exposures for workers in these occupations.
Fig. 10 Magnetic Field Exposures of Workers (mG)
Table-2 may give a general idea about magnetic field levels for different jobs and around various kinds of electrical equipment. It is important to remember that EMF levels depend on the actual equipment used in the workplace. Different brands or models of the same type of equipment can have different magnetic field strengths. It is also important to keep in mind that the strength of a magnetic field decreases quickly with distance . Table 2 EMF Measurements During a Workday .
3.2.4 Telecommunications and transmission antennas: Electromagnetic fields are also generated by high frequency technology. In telecommunications there are many categories of appliances: radio and TV towers, space communications, direct radio communications, mobile phone base-stations, radar, electric blankets, radios, TVs, computers, mobile phones and so on. 21
Nowadays, mobile telephony is commonly used all over the world. This wireless technology relies upon an extensive network of fixed antennas, or base stations, relaying information with radiofrequency (RF) signals. Over 1.4 million base stations exist worldwide and the number is increasing significantly with the introduction of third generation technology . Mobile phone handsets and base stations present quite different exposure situations. RF exposure to a user of a mobile phone is far higher than to a person living near a cellular base station. However, apart from infrequent signals used to maintain links with nearby base stations, the handset transmits RF energy only while a call is being made, whereas base stations are continuously transmitting signals. Handsets: Mobile phone handsets are low-powered RF transmitters, emitting maximum powers in the range of 0.2 to 0.6 watts. The RF field strength (and hence RF exposure to a user) falls off rapidly with distance from the handset. Therefore, the RF exposure to a user of a mobile phone located 10s of centimeters from the head (using a "hands free" appliance) is far lower than to a user who places the headset against the head. RF exposures to nearby people are very low . Base stations: Base stations transmit power levels from a few watts to 100 watts or more, depending on the size of the region or "cell" that they are designed to service. Base station antenna are typically about 20-30 cm in width and a meter in length, mounted on buildings or towers at a height of from 15 to 50 meters above
ground. These antennas emit RF beams that are typically very narrow in the vertical direction but quite broad in the horizontal direction. Because of the narrow vertical spread of the beam, the RF field intensity at the ground directly below the antenna is low. The RF field intensity increases slightly as one moves away from the base station and then decreases at greater distances from the antenna . Typically within 2-5 meters of some antenna mounted on rooftops, fences keep people away from places where the RF fields exceed exposure limits. Since antenna direct their power outward, and do not radiate significant amounts of energy from their back surfaces or towards the top or bottom of the antenna, the levels of RF energy inside or to the sides of the building are normally very low. Other RF sources in the community: Paging and other communications antenna such as those used by fire, police and emergency services, operate at similar power levels as cellular base stations, and often at a similar frequency. In many urban areas television and radio broadcast antennas commonly transmit higher RF levels than do mobile base stations.
EMF IMPACT ON ENVIRONMENT Protection of the environment and conservation of nature has become matter of great interest to the public, as well as to governments. Public concern about environmental exposure to EMF has ranged from claims of reduced milk production in cows grazing under power lines to damage to trees near high power radars. Therefore, the Impact of Electromagnetic on environment was studied in numerous researches. A review of the results of such studies is summarized as follows: 4.1 Human being: "Electro-smog" is the buzzword which has directed public awareness towards technical field emissions in recent years. All over the world, numerous studies have been carried out on the possible effects of electromagnetic fields on humans, animals, plants and cell or tissue cultures, and a series of large-scale epidemiological surveys has also been conducted. The effects of electromagnetic fields generally depend on the frequency and intensity, but also on individual characteristics such as body size or angle towards the field . Findings have been largely substantiated with regard to the effects of induced eddy currents at higher and medium-range field strengths (Fig.
11), and these have formed the basis for the limit values in protective legislation .
Fig. 10 Schematic Distribution of Eddy Currents Induced by Magnetic Fields of Longitudinal and Transversal Orientation Towards the Body .
An external magnetic field induces eddy currents in the human body on a circular plane perpendicular to the direction of the field. Similarly, an electric field creates a flow in the body which follows the same direction as the field: under high overhead voltage lines, for example, the flow would be from head to foot - and vice-versa (alternating field!). These field-induced flows are recognized as the predominant cause of biological effects at low-frequency fields. Above certain trigger values, the induction flows, just like direct body current, cause effects which can damage the organism . Table 3 Biological Effects of Different Current Densities at 50 Hz .
Electromagnetic waves can be characterized by their wavelength, frequency, or energy. The three parameters are interrelated. Each influences the effect the field may have on a biological system. The International EMF Project of WHO is addressing the health concerns raised about exposure to radiofrequency (RF) and microwave fields, extremely low frequency (ELF) fields, and static electric and magnetic fields. These electromagnetic fields can produce different biological effects that may lead to health consequences . Radiofrequency (RF) fields: are known to produce heating and the induction of electrical currents. Other less established biological effects have also been reported . RF fields at frequencies above about 1 MHz primarily cause heating by moving ions and water molecules through the medium in which they exist. Even very low levels of RF energy produce a small amount of heat, but this heat is carried away by the body's normal thermoregulatory processes without the person noticing it. A number of studies at these frequencies suggest that exposure to RF fields too weak to cause heating may have adverse health consequences, including cancer and memory loss. Identifying and encouraging coordinated research into these open questions is one of the major objectives of the International EMF Project. RF fields at frequencies below about 1 MHz primarily induce electrical charges and currents which can stimulate cells in tissues such as nerves and muscles. Electrical currents already exist in the body as a normal part of the chemical reactions involved in living. If RF fields induce currents significantly exceeding this
background level in the body, there is a possibility of adverse health consequences. Extremely Low Frequency (ELF) electric and magnetic fields: The primary action in biological systems by these fields is the induction of electrical charges and currents. This mechanism of action is unlikely to explain the health effects, such as cancer in children, reported to occur from exposure to "environmental" levels of ELF fields. ELF electric fields exist whenever a charge (voltage) is present, regardless of whether any current is flowing. Almost none of the electric field penetrates into the human body. At very high field strengths they can be perceived by hair movement on the skin. However, some studies suggest that exposure to low levels of these fields is associated with an increased incidence of childhood cancer or other health consequences. Other studies do not. The International EMF Project is recommending that more focused research be conducted to improve health risk assessments. ELF magnetic fields exist whenever an electric current is flowing. They easily penetrate the human body without any significant attenuation. Some epidemiological studies have reported associations between ELF fields and cancer, especially in children, but others have not. Research on effects of low-level (environmental) ELF fields is currently underway, including that monitored and encouraged by the International EMF Project . Static electric and magnetic fields: While the primary action in biological systems by these fields is the induction of electrical charges
and currents, other effects have been established to occur that could potentially lead to adverse health consequences, but only at very high field strengths. Static electric fields do not penetrate into the body, but can be perceived by skin hair movement. Except for electrical discharges from strong static electric fields, they do not seem to have significant health effects . Static magnetic fields have virtually the same strength inside the body as outside. Very intense static magnetic fields can alter blood flow or change normal nerve impulses. But such high field strengths are not found in everyday life. However, there is insufficient information about the effects of long-term exposure to static magnetic fields at levels found in the working environment. Safety Standards: In order to ensure that human exposure to EMF should not have adverse health effects, which man-made EMF generating devices are safe and their use does not electrically interfere with other devices, various international guidelines and standards are adopted .
4.2 Animals Most studies of EMF effects in animals have been conducted to investigate possible adverse health effects in humans. These are usually performed on standard laboratory animals used in toxicological studies, e.g. rats and mice, but some studies have also included other species such as like short-living flies for the investigation of genotoxic effects. The subject of this information sheet, however, is whether EMF can have harmful impacts on species of wild and domestic animals. Under consideration are: 28
Species, in particular certain fish, reptiles, mammals and migratory birds, which rely on the natural (geomagnetic) static magnetic field as one of a number of parameters believed to be used for orientation and navigational cues Farm animals (e.g. swine, sheep or cattle) grazing under power lines (50/60 Hz) or in the vicinity of broadcasting antennas Flying fauna, such as birds and insects that may pass through the main beam of high power radio-frequency antennas and radar beams or through high intensity ELF fields near power lines. Studies performed to date have found little evidence of EMF effects on fauna at levels below ICNIRP’s guideline levels. In particular, there were no adverse effects found on cattle grazing below power lines. However, it is known that flight performance of insects can be impaired in electric fields above 1kV/m, but significant effects have only been shown for bees when electrically conductive hives are placed directly under power lines. Un-insulated un-earthed conductors placed in an electric field can become charged and cause injury or disrupt the activity of animals, birds and insects. 4.3 Vegetation Field studies of 50-60 Hz exposure to plants and crops have shown no effects at the levels normally found in the environment, nor even at field levels directly under power lines up to 765 kV. However, the variability of parameters associated with environmental conditions that affect plant growth (e.g. soil, weather) would likely preclude observation of any possible low-level effects of electric field exposure. Damage to trees is well known to occur at electric field strengths far above ICNIRP’s levels due to corona discharge at the tips of the leaves. Such field levels are found only close to the conductors of very high voltage power lines. 29
4.4 Aquatic Life Although all organisms are exposed to the geomagnetic field, marine animals are also exposed to natural electric fields caused by sea currents moving through the geomagnetic field. Electro-sensitive fish, such as sharks and rays in oceans and catfish in fresh water, can orient themselves in response to very low electric fields by means of electro-receptive organs. Some investigators have suggested that human-made EMF from undersea power cables could interfere with the prey sensing or navigational abilities of these animals in the immediate vicinity of the sea cables. However, none of the studies performed to date to assess the impact of undersea cables on migratory fish (e.g. salmon and eels) and all the relatively immobile fauna inhabiting the sea floor (e.g. molluscs), have found any substantial behavioural or biological impact.
STANDARDS AND GUIDELINES A number of national and international organizations have formulated guidelines establishing limits for occupational and residential EMF exposure. The exposure limits for EMF fields developed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) - a non-governmental organization formally recognized by the World Health Organization (WHO), were developed following reviews of all the peer-reviewed scientific literature, including thermal and nonthermal effects. The standards are based on evaluations of biological effects that have been established to have health consequences. The main conclusion from the WHO reviews is that EMF exposures below the limits recommended in the ICNIRP international guidelines do not appear to have any known consequence on health. The exposure guidelines may differ by a factor of more than 100 between some former Soviet countries and Western countries. Because disparities in EMF standards around the world have caused increasing public anxiety about EMF exposures from the introduction of new technologies, WHO commenced a process of harmonization of electromagnetic fields (EMF) standards worldwide. Future standards will be based on the results of the WHO's International Electromagnetic Field Project . 31
Despite of criticizing of the ICNIRP international guidelines as lacking clear interpretation on exposure safety or direct application to equipment in existence, these guidelines is based on scientific results from all over the world and is considered the sole authorized scientific guidelines to follow. Consequently, the majority of national standards draw on the guidelines set by ICNIRP. Electromagnetic field levels vary with frequency in a complex way. Listing every value in every standard and at every frequency would be difficult to understand. Table-4 is a summary of the exposure guidelines for the three areas that have become the focus of public concern: electricity in the home, mobile phone base stations and microwave ovens. These guidelines were last updated in April 1998 . Table 4 Summary of the ICNIRP exposure guidelines .
European power frequency
Mobile phone base station frequency
Power density (W/m2)
Power density (W/m2)
Power density (W/m2)
Electric Magnetic field field (µT) (V/m) Public exposure limits
Microwave oven frequency
Some practical information will help to relate to the international guideline values given above. In the following table (Table 5), the most common sources of electromagnetic fields are listed. All values are maximum levels of public exposure . Table 5 Typical maximum public exposure for the most common sources of electromagnetic fields.
Source Typical maximum public exposure Electric field (V/m)
Magnetic flux density (µT)
Mains power (in homes not close to power lines)
Mains power (beneath large power lines)
Electric trains and trams
TV and computer screens (at operator position)
Typical maximum public exposure (W/m2) TV and radio transmitters
Mobile phone base stations
Due to public anxiety in Egypt about mobile base stations, the National Telecommunications Regulatory Authority, National 33
Telecommunications Institute, Ministry of Health and Population, and Ministry of State for Environmental Affairs have thus jointly produced a modified manual of the required standards for installing mobile phone base stations, up-to-date with the latest developments in communications and information technology. This tripartite protocol lists twelve conditions for the construction of cell sites as follow: 1. A cell site must be constructed on a building that is 15 - 50 meters high from surface, with the possibility of exceptions in case this is not available. 2. The antenna must be higher than the other surrounding buildings within a range of 10 meters. 3. The roof of the building on which the antenna is to be fixed must be made of enhanced concrete. 4. It is not permissible to fix more than one antenna on a single post. 5. The distance between two cell sites must be at least 12 meters. 6. The distance between the antenna and the utmost reach of humans must be at least 6 meters. 7. Antennas may not be fixed on roofs that are not made of concrete. 8. Antennas may not be fixed on independent buildings, such as hospitals. 9. Sites must have a fence at a distance of 6 meters from all directions. 10.Companies must adhere to the standards endorsed by the American Institute for Measurements and the Institute for the Electric and Electronic Engineers (IEEE). The maximum permissible power density a human being can be safely exposed to must not exceed 0.4 mW/cm2 (900 MHZ - 1800 MHZ). 11.Antennas may not be directed towards schools.
12.Finally, Approval certifications that must be obtained are cited.
REFERENCES 1. WHO, “Electromagnetic Fields and Public Health: the international EMF project,” Fact Sheet No. 181, World Health Organization, May, 1998. 2. WHO, “WHO : Standards and Guidelines,” available at http://www.who.int/entity/peh-emf/standards/en/ 3. Brooks D., “Electromagnetic Field Basics,” available at http://www.mentor.com/pcb/tech_papers.cfm. 4. “The Complete Microwave Oven Service Handbook, Operation, Maintenance, Troubleshooting and Repair,” Micro-Tech Production, 2000. 5. NIEHS and NIH, “Electric and Magnetic Fields Associated with the Use of Electric Power,” National Institute of Environmental Health Sciences National Institutes of Health, 2OO2. 6. ESB, “Electric and Magnetic fields in the Environment,” Electric and Magnetic fields in the Environment, Ireland, 1999. 7.
“Berlin Digital Environmental Atlas 08.05 Electromagnetic fields,” available at http://www.stadtentwicklung.berlin.de/umwelt/umweltatlas/ed805_02.htm.
8. NRPB, “Health Effects from Radiofrequency Electromagnetic Fields,” National Radiological Protection Board, Vol. 14, No. 2, 2003. 9. WHO, , “Typical exposure levels at home and in the environment,” available at http://www.who.int/peh-emf/about/WhatisEMF/en/index3.html. 10. WHO, “Electromagnetic fields and public health: mobile telephones and their base stations,” Fact Sheet No. 193, World Health Organization, June, 1998. 11. WHO, “Electromagnetic Fields and Public Health: Physical Properties and Effects on Biological Systems,” Fact Sheet No. 182, World Health Organization, may, 1998.