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Extremely low frequency electric and magnetic fields
Extremely low frequency (ELF) electric and magnetic fields exist wherever electricity is generated, transmitted or distributed in powerlines or cables, or used in electrical appliances.
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Extremely low frequency (ELF) electric and magnetic fields (EMF) occupy the lower part of the electromagnetic spectrum in the frequency range 0-3000 Hz. ELF EMF result from electrically charged particles. Artificial sources are the dominant sources of ELF EMF and are usually associated with the generation, distribution and use of electricity at the frequency of 50 Hz in Australia or 60 Hz in some other countries. The electric field is produced by the voltage whereas the magnetic field is produced by the current. The properties of ELF electric and magnetic fields are described in detail in the World Health Organization's Environmental Health Criteria 238 Extremely Low Frequency Fields.
Measurements of ELF EMF are performed in order to characterise emissions from sources and exposure of persons or experimental subjects. The strength of the electric field is measured in units of volts per metre (V/m). The strength of the magnetic field is measured in units of amperes per metre (A/m) but is usually expressed in terms of the magnetic flux density measured in units of tesla (T) or microtesla (μT). Another unit which is commonly used to measure the magnetic field is the gauss (G) or milligauss (mG), where 1 G is equivalent to 10⁻⁴ T (or 1 mG = 0.1 μT).
ELF EMF is produced by both natural and artificial sources. Naturally occurring ELF EMF is associated with atmospheric processes such as ionospheric currents, thunderstorms and lightning. Artificial sources are the dominant sources of ELF EMF and are usually associated with the generation, distribution and use of electricity at the frequency of 50 or 60 Hz. Powerlines, electrical wiring and common appliances (electric blankets, televisions, hair-dryers, computers, etc.) all produce ELF EMF.
The widespread use of electricity means that people are exposed to ELF electric and magnetic fields in the home, in the environment and in the workplace. Residential exposure to ELF fields depends on many factors, including the distance from local powerlines, the number and type of electrical appliances in use in the home, and the configuration and position of household electrical wiring. Background magnetic fields in the home are usually around 0.1 µT. Background electric fields in the home can be up to 20 V/m. In the vicinity of some appliances, the instantaneous magnetic field values can be as much as a few hundred microtesla and the electric field several hundred volts per metre. At ground level, directly below powerlines, magnetic fields reach as much as 20 µT and electric fields can be between several hundred and several thousand of volts per metre (~100 V/m - ~10 kV/m).
Exposure in the workplace can vary. In the electrical supply industry, workers may be exposed to magnetic fields which can exceed 2,000 µT and electric fields up to 30 kV/m. Office workers are usually exposed to much lower level fields when using equipment such as computers and photocopying machines. There is evidence however that workers in some non-electrical occupations can also be exposed to elevated EMF, for example workers in the garment industry have been shown to be exposed to levels greater than 10 µT.
It is known that acute exposure to ELF EMF at high levels can affect the function of the nervous system. However, exposure to high levels of ELF EMF is extremely rare apart from medical exposures to patients and some specialised occupational exposures. They will not occur in people during their day-to-day living and should not occur at work.
There is no established evidence that ELF EMF is associated with long term health effects. There is some epidemiological research indicating an association between prolonged exposure to higher than normal ELF magnetic fields (which can be associated with residential proximity to transmission lines or other electrical supply infrastructure, or by unusual domestic electrical wiring), and increased rates of childhood leukaemia. However, the epidemiological evidence is weakened by various methodological problems such as potential selection bias and confounding. Furthermore this association is not supported by laboratory or animal studies and no credible theoretical mechanism has been proposed.
Health effects related to ELF fields are described further in the ARPANSA fact sheet Electricity and Health.
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has issued Guidelines for Limiting Exposure to Time-Varying Electric and Magnetic Fields (1 Hz -100 kHz) (PDF 641 kb) which are aimed at preventing the established health effects resulting from exposure to ELF EMF. The ICNIRP ELF guidelines are consistent with ARPANSA’s understanding of the scientific basis for the protection of the general public (including the foetus) and workers from exposure to ELF EMF. Details about ICNIRP and a link to the ICNIRP ELF guidelines are available at International Best Practice.
- The World Health Organization’s fact sheet Exposure to Extremely Low Frequency Fields
- The International Commission on Non-Ionizing Radiation Protection
- Public Health England in the UK