Introduction
What are electric and magnetic fields (EMF)?
How are we exposed to EMF?
Is there a health hazard?
Typical field strengths from EMF sources
Reference
Further web reading
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. In the table overleaf
several sources of EMF are listed along with typical strengths
of the fields to allow comparisons.
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 well-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. However, in 2001, after reviewing
all the relevant research, both the International Agency for Research
on Cancer (IARC) and a UK expert group on non-ionising radiation
concluded that exposure to prolonged and relatively high levels
of magnetic fields may increase the risk of leukaemia in children.
Specifically, children with average daily exposures of more than
0.3 to 0.4 uT were found to have a leukaemia risk of 2 in 20,000
per year, whereas children with lower exposures had a risk of
1 in 20,000. On the basis of the research findings, 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 Organisation 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.
The Radiation Protection division has two magnetic field meters
available for hire by South Australian residents. Please contact
the division if you wish to hire a meter.
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)
Reference
National Health and Medical Research Council (NHMRC): 'Interim
Guidelines on Limits of Exposure to 50/60 Hz Electric and Magnetic
Fields (1989)'.
Further web reading
GreenFacts
www.greenfacts.org/power-lines/index.htm
IARC
http://monographs.iarc.fr/ENG/Monographs/vol80/volume80.pdf
World Health Organization
www.who.int/docstore/peh-emf/publications/facts_press/efact/efs263.html
This page was last modified 23-09-2008
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