Radiation Protection

quick links

contact

For more information please get in touch with ARPANSA

Magnetic & Electric Fields From Power Lines

Transmission lines

On balance, the scientific evidence does not indicate that exposure to 50 Hz EMFs found around the home, the office or near power lines is a hazard to human health.

This Page:

Sources of Electromagnetic Fields

There is a general perception amongst many in the community that there are health risks resulting from exposure to electromagnetic fields (EMF) from power lines. All alternating electric currents generate electric and magnetic fields, collectively known as EMFs (sometimes, incorrectly referred to as electromagnetic radiation). The electric field is proportional to the voltage (which can be considered as the pressure with which electricity is pushed through the wires). The magnetic field is proportional to the current, that is, to the amount of electricity flowing through the wires. The direction of the current, and therefore that of the magnetic field, changes 50 times per second (that is, at 50 Hz).

These fields emanate from the wires delivering electricity to our homes and all devices which use electricity in the home. Many people are concerned about the alleged link between exposure to magnetic fields, in particular, and an increased risk of contracting cancer. These concerns are raised when stories appear in the media in which the words radiation and cancer are emphasized, especially when children are also involved.

Electric fields are shielded by many common building materials and the earth but the shielding of magnetic fields is more difficult and can be very expensive. Usually, the easiest way to reduce exposure to magnetic fields is to increase the distance from the source, particularly for fields generated by appliances.

Magnetic fields generated by power lines decrease with distance and this happens more quickly when the individual wires are closely spaced, either in a bundled overhead cable or when buried. Where the wires are close together, the magnetic fields from electric currents flowing in opposite directions cancel more completely. Overhead and underground power lines will often produce similar levels of magnetic fields on nearby streets and paths. In some cases the fields from underground cables may be greater. Underground power lines will usually produce lower fields at the distance of nearby houses.

Power lines include transmission lines (mounted on large steel towers) and distribution lines (mounted on concrete or wood poles placed on the road reserve).

Transmission lines generate both strong electric fields and strong magnetic fields. Distribution lines generate weak electric fields, but can generate strong magnetic fields.

Top of Page

Health Effects?

Human studies have consistently shown that there is no evidence that prolonged exposure to weak electric fields (such as those found in the home or in most workplaces), results in adverse health effects. Whether chronic exposure to weak magnetic fields is equally harmless remains an open question. There is no evidence that these fields cause immediate, permanent harm.

Laboratory studies on animals and cell cultures have shown that weak magnetic fields can have effects on several biological processes. For example, they may alter hormone and enzyme levels and the rate of movement of some chemicals through living tissue. By themselves, these changes do not appear to constitute a health hazard. We do not know if, in the long term, they may have an effect on the incidence of cancer or other adverse health effects. While most studies have produced inconclusive results or no increased cancer incidence in laboratory animals following exposure to EMFs, a few studies have indicated an increased incidence.

Another way to find out whether EMFs affect human health is to conduct relevant studies on human populations.

Top of Page

Human Studies

To determine if there is a health risk from some, as yet, unknown cause, science uses the discipline called epidemiology. Epidemiology is the study of occurrence and distribution of disease in the population (or community). The first major benefit to mankind from this science came in 1855. John Snow, a British physician, observed that death rates from cholera were particularly high in areas of London which were supplied with drinking water which had been extracted from the Thames River at points adjacent to sewage outfalls. He proposed that cholera was transmitted by an unknown agent through sewage. This discovery eventually led to proper treatment of sewage.

To do this type of study for EMFs and cancer, two groups of people need to be compared: one group which has, in the past, been exposed to EMFs while another group (the control group) has not. Because everyone in the community has been exposed, to some extent, to these fields, the exposed group is usually made up of people who live near to power lines, while the non-exposed group live further away. An observation is then made as to whether there are more cancers in the exposed group than in the non-exposed group. Simple? Unfortunately, it is not and that is why the controversy remains.

Epidemiology

The epidemiology of cancer is difficult for the following reasons:

  • There is a long latency period (delay) of 5 to 20 years or more between exposure and onset of the disease. Cancer usually occurs in old age because of the long latency period.

  • Cancer is found amongst people who have not been exposed to the causative agent because the disease is naturally occurring. For this reason carcinogenic (cancer causing) agents are often given a relative risk. Cigarette smokers for example have 10 to 30 times the risk (relative risk) of contracting lung cancer as do non smokers.

  • Not everyone who is exposed will get a cancer. Cancer incidence is relatively rare, except amongst the elderly.

  • There are many factors which can increase the risk of cancer. For example; poverty, cigarette smoking, alcohol consumption, occupation, gender, race, lifestyle and age.

  • The cause of most cancers is not known. The occurrence of cancer in an exposed group seems to be a random process. Not all cigarette smokers get lung cancer and perhaps that is why people continue to smoke despite the warnings. They are playing a lottery with their lives.
Top of Page

For the above reasons, to do an epidemiological study between an exposed and non exposed group for a possible cancer risk factor, one needs to meet the following criteria:

  • A large number of people must be included in the study (not everyone exposed gets a cancer).

  • The two groups must be matched in every respect except exposure to the agent under test (there are many risk factors for cancer).

  • The two groups must be monitored for a long time (long latency period for cancer).

  • Since cancer incidence is random, a statistical (mathematical) analysis of the results must be performed. This analysis will result in a relative risk factor (see above).

There are several ways in which these studies can be performed. Because of the time and cost savings involved, a retrospective cohort (group of associates) study is the most common method for EMF exposure. In this type of study a group of people who have been exposed to the agent under test and a similar group who have not been exposed are compared. One might choose electrical linesman and compare them with their next door neighbour, for example. This type of study is fraught with pitfalls, such as:

  • The exposed group have not had their exposure, to the agent under test, measured. It is assumed because of their occupation or proximity (say to powerlines) that they are more exposed than the control group.

  • It is difficult to find a control group which has the same mix of characteristics so that confounding (confusing) factors do not interfere with the result.
Top of Page

EMF Study Results

The results of all EMF studies to date have indicated either no association or a weak association with adverse health effects. Those studies which do indicate an increased risk of health effects claim a relative risk of 2 to 3. That is as a result of exposure to powerline electromagnetic fields the risk of contracting a cancer is two to three times the risk for a non exposed person. Because of the relative risks found (most epidemiologists consider a single study with a relative risk ratio less than 3 as not significant) there is room for debate about whether a health hazard exists at all.

At this point it is necessary to discuss the meaning of the word association as it is used in epidemiology. Association does not mean causation. The fact that the air temperature rises when the cock crows is an association. We know that it is the rising of the sun that causes the temperature to rise, not the cock. To pass from association to causation the results of these studies should meet most if not all of the following criteria:

  • The risk ratio should be high, usually 5 or greater.

  • The studies should consistently demonstrate an association.

  • There should be an association between the exposure and a specific disease. The association should not refer to cancer in general but a specific cancer; eg leukemia and brain cancer together is acceptable but not leukemia in one study and brain cancer in another.

  • There should be a demonstrable dose effect. A dose effect means that as you increase exposure to EMF the number of cancers increases.

  • There is a biological mechanism by which the agent under test can cause the associated disease; eg. cholera is caused by a bacterium, lung cancer is caused by the chemical carcinogens in tobacco tar.
Top of Page

To date all of the epidemiological studies on exposure to EMF do not meet these criteria. The evidence is either weak or absent. In particular:

  • The relative risk ratio for those studies which do show an association is usually less than 3.

  • The studies are inconsistent. Many studies show no effect.

  • The health effects vary. Some studies show an increase in brain cancer while others show an increase in leukemia.

  • No dose effect has been demonstrated.

  • No biological mechanism is known for induction of cancer from exposure to EMF's.

It is for these reasons that the majority of scientists, and Australian radiation health authorities in particular, do not regard chronic exposure to 50 Hz electric and magnetic fields at the levels commonly found in the environment as a proven health risk. Moreover, the evidence we have is inconclusive and does not allow health authorities to decide whether there is a specific magnetic field level above which chronic exposure is dangerous or compromises human health.

Some authorities advocate a policy of minimizing exposure wherever possible, providing this can be achieved at reasonably modest cost. Since this is essentially a question of judgement, such decisions are best left to the individual. Simple steps to reduce exposure are:

  • using an electric blanket to warm the bed and switching it off before climbing in will virtually eliminate what could be a significant exposure;
  • locating bedrooms towards the rear of the house reduces dramatically the exposure due to distribution lines in front of the house;
  • moving a bed away from an external wall which has an electric hot water service on the other side will also reduce exposures;
  • a distance of about 50 cm between a video screen and the user usually results in an exposure not very different from those found elsewhere in the environment.
Top of Page

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 (1,000 mG - milligauss) and for occupational exposure (whole working day) is 0.5 millitesla (5,000 mG). Note 1.

The NHMRC notes that "although there are limitations in the epidemiological studies that suggest an increased incidence of cancer among children and adults exposed to 50/60 Hz fields, the data cannot be dismissed. Additional study will be required before these data can serve as a basis for risk assessment". In other words, because the research data do not indicate an exposure level at which a cancer risk exists (assuming that such a risk exists at any level), it is simply not possible to determine an exposure limit below which that risk would disappear. Hence, the above NHMRC limits do not apply to the avoidance of cancer risk resulting from chronic exposure to 50 Hz magnetic fields.

Residential Exposures

Exposure levels to EMFs around the home are in the range of 0.01 - 0.25 µT (microtesla = 0.1 - 2.5 mG). For homes near powerlines, these levels may be as high as .5 - 1 µT (5 - 10 mG). Immediately under the powerline, magnetic field levels of 6 - 10 µT (60 - 100 mG) may be found. Note 2.

Top of Page

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 localized 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 Note 2.

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 minimize the exposure level for all staff. However, particular situations may require particular solutions and the local electricity supplier or the Energy Networks Association should be consulted.

The Doll Report

The NRPB (National Radiation Protection Board - UK) Advisory Group on Non-ionising Radiation (AGNIR) headed by sir Richard Doll produced a report titled, ELF Electromagnetic Fields and the Risk of Cancer in March 2001. The report concluded that; unless ... further research indicates that the finding is due to chance or some currently unrecognised artefact, the possibility remains that intense and prolonged exposures to magnetic fields (from powerlines) can increase the risk of leukaemia in children. The inconclusive nature of this finding is due to the low relative risk and the lack of supporting evidence such as a biological mechanism or dose response curve etc.

Top of Page

More information from ARPANSA

External links

Notes

Note 1  The earth's magnetic field has a strength of about 50µT (500 mG). This figure is included to help the reader obtain a feel for what the units mean. The earth's magnetic field is not changing direction at 50 to 60 times per second and is therefore not comparable to powerline fields as far as health effects are concerned. N.B. 10 milligauss = 1 microtesla.

Note 2  ARPANSA offers a magnetic field meter for hire which can be used to measure exposure to such fields. Details on hiring the magnetic field meter including cost and postage charges can be found on the EMF meter hire page.

Adobe Acrobat Reader is needed to view PDF files

Acrobat image

The free Adobe Acrobat Reader is available from Adobe's website

 

Top of Page