Magnetic Fields and Cancer
60Hz electric and magnetic fields have brought fears of cancer and various disorders to many homes. The new classification of magnetic fields as a class 2B carcinogen by IARC (International Association of Research on Cancer) has amplified that fear for many. Most laboratory experiments on cell cultures and animals have failed to demonstrate a link between magnetic fields and health effects. There are experiments that do show some biological effects, however they have failed to be replicated by other research groups or are of an unknown health significance.
Some epidemiological studies (studies based totally on statistics and patterns of disease) have shown a small increased risk of childhood leukaemia. The chances of a child having leukaemia are approximately 1 in 100,000. Should the result from these studies prove to be true, the risk would increase to approximately 1.5 to 3 in 100,000 (up to a 3 fold increase). Since this type of cancer is extremely rare, and due to other factors such as bias of the researchers in selecting their subjects, the outcome of the laboratory experiments tend to carry more weight.
In regards to the recent classification by IARC, magnetic fields find themselves in the same category as coffee and pickled vegetables. There are 5 classifications: 1, 2A, 2B, 3 and 4. Only one item is classified as a definite non-carcinogen. Class 1 is carcinogenic and class 4 is non-carcinogenic. Class 2A means the substance or agent is probably carcinogenic but there is not enough proof to put it in class 1. Class 2b means that the substance or agent is a possible carcinogen but there is insufficient proof to put it in class 2A. Keeping in mind that it is almost impossible to prove that something is not carcinogenic, it is not surprising to see magnetic fields in the class 2B category. The epidemiological studies were largely responsible for the classification as a precautionary measure. For more information, visit the IARC web page.
Magnetic Fields and Power Lines
Typically, levels in the homes are quite low, except in close proximity to appliances. Homes located near power lines do not usually have much higher fields. Fields from power lines decay rapidly with distance so that at 100m distance they are not much more than background field levels.(At 100 metres from a big 500kV power line, the magnetic field drops to a value of 1 one hundredth of its peak value directly under the power line.) Magnetic fields, unlike electric fields are not absorbed by most materials. Shielding magnetic fields in a home is extremely costly and not very beneficial since the fields are already low.
What do magnetic fields do in our bodies?
Magnetic fields induce electric currents in our bodies and are only dangerous at levels where the current is large enough to cause stimulation of the muscles. Though the effects of muscle stimulation are short term and in themselves not really harmful, they could hinder movements of the body and cause an accident. Incidentally, have you noticed all those ads on TV for devices like the "AB-TRONIC"? These are devices that intentionally inject electric currents in the body to stimulate the muscles to contract. Supposedly this helps you lose weight. The interesting thing is that people are PAYING with their own cash to have their muscles stimulated by currents yet they would probably cringe at the thought of living near a power line where the induced currents from the magnetic fields would probably be thousands of times lower.
The extremely high levels of magnetic field that could cause muscle stimulation are not generally available to the general public. They are only found in industrial situations where equipment utilizing large electric currents produce them. Another risk from exposure to high fields is a shock. The shock occurs by touching an ungrounded fence or metal object that is in the presence of a high electric or magnetic field. The object becomes energized to a certain voltage which may be high enough to force current flow through your body when you touch it. These are called contact currents. A scenario where they might occur is if you parked a big truck under a really big power line (say 500 kV) and touched the truck while standing on the ground. There should always be signs indicating high fields in these areas.
What is the difference between electric and magnetic fields?
Electric fields are always present when an appliance is plugged into a wall outlet. They are easy to shield by using metal and other materials. Magnetic fields are caused by current flow while electric fields are caused by voltage. You can have an electric field without a magnetic field but generally you cannot have a magnetic field without an electric field except in the case of permanent magnets. Magnetic fields are much harder to shield than electric fields (requires special materials). Because of the design of measuring instruments, electric fields are easy to measure at high frequencies but hard to measure at low frequencies and require more sophisticated instruments. In contrast, magnetic fields are easy to measure at low frequencies, but impossible to measure at ultra high frequencies. Since there is a relationship between electric and magnetic fields in the far field region, and because the far field region is much closer to the source at high frequencies, the magnetic fields can still be determined.
Are there safety guidelines to protect citizens from power lines?
There are no safety codes for 60Hz magnetic or electric field exposure in Canada. Safety Code 6 only covers from 3KHz to 300GHz. At the lower frequencies, there is not enough energy in the fields to create a heat rise in the human body.
Coming soon: Pictures, survey results and diagrams. Future projects: maps of magnetic fields near power lines and in residential neighbourhoods.