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Introduction
Just over 100 years ago, human exposure to electric and magnetic fields was limited to those fields arising naturally. Within the last 50 years there has been a dramatic growth in the use of electric power and valid questions are now being raised concerning safe levels of exposure to man-made electric and magnetic fields.
What are electric and magnetic fields (EMF)?
A small piece of iron held near a magnet will move towards and attach itself to the magnet. The iron is attracted to the magnet because of the magnetic field which surrounds it. The earth itself is a huge magnet, and it is the earth's magnetic field which, for example, controls the direction of the needle on a compass.
Electricity also produces fields:
- A field called the electric field occurs when an electric charge or voltage is present and results from the force electric charges exert on each other.
- A magnetic field is produced by the movement of the electric charge, that is, by the flow of electric current. The magnetic field effect is used in electromagnets and electric motors.
Plug an ordinary lamp into an electric outlet; the voltage on the lamp cord produces an electric field. Switch the lamp on and the current flow through the cord produces a magnetic field. The higher the voltage, the stronger the electric field. The higher the current, the stronger the magnetic field.
Unlike natural fields, which remain relatively constant, fields produced by electrical equipment usually change rapidly with time. Electricity in Australia is supplied as alternating current at a frequency of 50 cycles per second. This means that the electric and magnetic fields reverse their direction 50 times every second.
How are we exposed to EMF?
Electric and magnetic fields (EMF) come from anything which produces, carries or is powered by electricity. This means there are fields associated with large and small powerlines, wiring in homes and places of work, and all electrical appliances. The table below lists several sources of EMF, with typical strengths of the fields to allow comparisons.
Typical field strengths from EMF sources
| Source | Electric field strength* |
Magnetic field strength+ |
| 275,000 volt transmission line | ||
| - directly underneath |
3
|
0.5 to 2.5
|
| - edge of easement |
0.3
|
0.1 to 0.5
|
| 66,000 volt distribution line | ||
| - directly underneath |
0.4
|
0.5 to 2.0
|
| - edge of easement |
0.04
|
0.1 to 0.3
|
| Various appliances | ||
| - electric blanket at surface |
2
|
1.0 to 3.0
|
| - vacuum cleaner at 1 metre |
0.002
|
0.1 to 2.0
|
| - hairdryer at 30 cm |
0.04
|
0.1 to 7.0
|
| - iron at 30 cm |
0.06
|
1.2 to 3.0
|
| - toaster at 30 cm |
0.04
|
0.6 to 7.0
|
| - video display unit (VDU) at 50 cm in front |
0.01
|
0.05 to 0.4
|
* measured in kilovolts per metre (kV/m) + measured in microTesla (uT)
The following information has been sourced from the Australian Radiation Protection and Nuclear Safety Agency website.
Australian exposure guidelines
There are currently no Australian Standards regulating exposure to these fields. The National Health and Medical Research Council has issued Interim guidelines on limits of exposure to 50/60 Hz electric and magnetic fields.
These guidelines are aimed at preventing immediate health effects resulting from exposure to these fields. The recommended magnetic field exposure limit for members of the public (24-hour exposure) is 0.1 millitesla (mT) or 1,000 milligauss (mG), and for occupational exposure (whole working day) is 0.5 mT (5,000 mG).
Residential exposures
Exposure levels to EMFs around the home are in the range of 0.01–0.25 microtesla (µT) or 0.1–2.5 mG. For homes near powerlines, these levels may be as high as 0.5–1 µT (5–10 mG). Immediately under the powerline, magnetic field levels of 6–10 µT (60–100 mG) may be found.
Workplace exposures
The widespread use of electricity means that in all workplaces, there will be levels of magnetic fields that would be considered 'normal'. However, there are also localised sources of magnetic fields in the workplace such as electrical substations in the basement, power cables in the walls or floor and distribution lines close to the building. The field levels close to these sources will be relatively high and may cause computer screens to shimmer, for example. These levels may exceed the NHMRC limit.
The only remedies currently available to reduce these fields, and the resultant exposure, is a combination of shielding and relocating the source (both very costly), or relocating the employees (also potentially costly). The general aim of any field reduction program is to minimise the exposure level for all staff. However, particular situations may require special solutions and the local electricity supplier or the Energy Networks Association should be consulted.
Is there a health hazard?
The main hazard to be avoided with electricity is fatal electric shock from direct contact with conductors.
In addition, if you stand beneath a high-voltage powerline you may experience nuisance spark discharges between your body and an insulated or poorly earthed conducting object such as a metal fence or shed.
The above effects are well established and understood. However, in recent times concern has been expressed by some scientists and members of the community that EMF may be responsible for certain long-term health hazards, especially cancer.
Hundreds of scientific studies have been conducted on this topic throughout the world over the last 25 years. The studies have been of two types: research on human populations; and laboratory based research on animals, isolated cells and tissues.
In general, the results of the laboratory studies show no good evidence that exposure to 50-Hz EMFs cause or promote cancer, nor do human studies in general.
On the basis of the research findings, the International Agency for Research on Cancer (IARC) classified magnetic fields as 'possibly carcinogenic', a classification shared with coffee, pickled vegetables, bitumen, engine exhaust and hundreds of other substances.
The World Health Organization is advocating the use of precautionary measures to reduce the individual's exposure to magnetic fields during this time of scientific uncertainty. This is consistent with the way other 'possibly carcinogenic' substances are managed. Individuals may reduce their exposure by minimising the use of certain electrical appliances, or increasing the distance to sources of high magnetic fields.
EMF meter hire
The Radiation Protection Branch has two magnetic field meters available for hire by South Australian residents. Please contact the branch if you wish to hire a meter.
Further reading
- GreenFacts
- International Agency for Research on Cancer
- World Health Organization
- Australian Radiation Protection and Nuclear Safety Agency
Last modified: 03/01/2012 09:54 am
