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Non-ionising radiation and ELF electromagnetic fields FAQs

What is non-ionising radiation?

Non-ionising radiation (NIR) is the term given to the part of the electromagnetic spectrum where there is insufficient quantum energy to cause ionisations in living matter. It includes static and power frequency fields, radiofrequencies, microwaves, infra-red, visible and ultraviolet radiation.

 

What are electromagnetic fields?

Electromagnetic fields (EMFs) arise from electric charges and the strength of a field at a point depends upon the distribution and behaviour of the charges involved. The term EMF as used here covers fields in the frequency range below 300 gigahertz (GHz). Electromagnetic fields include static fields such as the Earth's magnetic field and fields from electrostatic charges, electric and magnetic fields from the electricity supply at power frequencies (50 Hz in the UK), and radio waves from TV, radio and mobile phones, radar and satellite communications. At the higher frequencies the electric and magnetic fields are coupled together and as the frequency decreases the coupling decreases. At 50 Hz used for electricity generation it is appropriate to think in terms of separate electric and magnetic fields. The part of the electromagnetic spectrum from 0 to 300 Hz is often termed extremely low frequency (ELF). Electromagnetic fields as described here have insufficient energy to damage DNA in the cell nucleus directly.

 

What are the main contributions to people's exposure to ELF (power frequency) EMF?

The main sources of power frequency electromagnetic fields are related to the transmission, distribution and use of electricity. Transmission power lines in the UK operate principally at 400 kilovolts (kV) and 275 kV, and distribution lines operate at 132 kV, 66 kV, 33 kV, 11 kV and 400 V. Underground cables and substations can also be sources of exposure. Away from power lines, power frequency EMF in homes arise from currents and voltages associated with distribution circuits and household electrical wiring, and the use of appliances. The strength of EMF tends to fall rapidly with distance. The relative contribution of these sources to residential exposure in the UK is variable and depends on individual home circumstances. Power frequency EMF are also produced from the use of electricity in the workplace and from electrified transport systems.

 

How are people protected from possible health effects of ELF EMF?

At extremely low frequencies, guidelines on restrictions on exposure to EMF have been developed that are based on the avoidance of established biological effects of electromagnetic fields. These include the effects of induced currents in the body and the risk of painful spark discharge. NRPB recommended the adoption of the guidelines published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). This recommendation is supported by a comprehensive review of the scientific literature on biological effects, human health and research on dosimetry. The ICNIRP reference levels for external fields are used at the initial stage of assessing compliance with restrictions on exposure. The levels for exposure to 50 Hz electric and magnetic fields are 10 kV m-1 and 500 µT for occupational exposure, and 5 kV m-1 and 100 µT for public exposure. The exposure restrictions advised by ICNIRP have been incorporated into a European Council Recommendation on public exposure, which the UK supported.

 

What are the established health effects associated with exposure to ELF EMF?

 

Power frequency magnetic fields induce currents in the body including the central nervous system. At levels much higher than those experienced by the general public they can affect the control of movement and posture, memory, reasoning and visual processing. Power frequency electric fields induce currents in the body and can also result in direct perception effects due to alternating electric charge induced on the surface of the body causing for example body hair to vibrate. In addition indirect effects such as microshocks can occur in strong electric fields through contact between a person and a conducting object.

 

How does the HPA ensure that the guidelines are based on the most recent and up-to-date science?

The Health Protection Agency keeps the results of EMF health studies under constant review through its involvement with international bodies, through AGNIR and through the work of its own specialist scientific staff. This ensures that the guidelines for limiting exposure are based on the best available scientific information.

NRPB, now the Radiation Protection Division of HPA, has published advice on limiting exposure to electromagnetic fields and has recommended the adoption in the UK of the ICNIRP guidelines. The advice is supported by a comprehensive review of the science related to EMFs and health.


 

What typical levels of power frequency magnetic fields are people exposed to at home?

The magnetic field levels encountered in UK homes are typically in the range 0.01–0.2 µT or 10–200 nanotesla (nT). The highest levels in homes usually occur close to operating appliances and electrical wiring. Sources outside the home can also contribute to exposure because common building materials do not shield magnetic fields. The lower 'background' level away from appliances usually comes from distribution circuits outside the home. Magnetic field levels may increase to a few microtesla close to domestic appliances or in homes beneath power lines.

 

What typical levels of power frequency electric fields are people exposed to at home?

Electric fields in the home come largely from appliances and wiring inside the home. The typical background range expected in UK homes is 1–20 volts per metre (V m-1) and this may increase to a few hundred volts per metre close to domestic appliances and power cables. These levels are small fractions of guideline levels. Sources of electric field outside the home are relatively unimportant inside homes because buildings provide strong screening. Electric fields are readily perturbed by conducting objects and this also causes levels to vary in homes.

 

What levels of power frequency electric fields are people exposed to beneath power lines?

Electric field strengths of up to several kilovolts per metre might occur outside a home located directly beneath some of the very high voltage power lines. Inside the home, the field strength reduces typically to a few tens of volts per metre because of shielding.

 

How is EMF exposure determined?

Instruments can be used to measure electric and magnetic field strengths to which people are exposed. A common measure used in many EMF epidemiological studies is the time-weighted average (TWA) exposure – a measure of the field strength combined with duration of exposure. It has been estimated from the UK Childhood Cancer Study (UKCCS) that less than 3% of children in the UK have a TWA exposure of 0.2 µT or more and about 0.5% exceed 0.4 µT. Exposure to high field strengths for short periods and low field strengths over a much longer period can be numerically equivalent when expressed as TWA.

 

Is TWA exposure the appropriate metric?

The epidemiological studies carried out so far have tended to use TWA exposure as the most robust metric because of the absence of a plausible biological mechanism for adverse health effect at environmental levels. However other metrics, such as peak values, time above thresholds, number of excursions and presence of transients, may be investigated in future studies.


Last reviewed: 8 September 2008