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1. What are EMFs?
Power lines, electrical wiring, and appliances all produce electric and magnetic fields. EMFs are invisible lines of force that surround any electrical device. Electric and magnetic fields have different properties and possibly different ways of causing biological effects. Note that while electric fields are easily shielded or weakened by conducting objects (trees, buildings, and human skin), magnetic fields are not. However, both electric and magnetic fields weaken with increasing distance from the source.
The electromagnetic spectrum covers an enormous range of frequencies. These frequencies are expressed in cycles per second (Hz=Hertz). Electric power is in the extremely low frequency range which includes frequencies below 3000Hz. (60Hz in North America, 50Hz in most other places). The higher the frequency, the shorter the distance between one wave and the next, and the greater the amount of energy in the field. Microwave frequency fields, with wavelengths of several inches, have enough energy to cause heating in conducting material. Still higher frequencies like X-rays cause ionization- the breaking down of molecular bonds, which damages genetic material. In comparison, power frequency fields have wavelengths of more than 3100 miles (5000 km) and consequently have very low energy levels that do not cause heating or ionization.
Yes, the earth produces EMFs, mainly in the form of DC (also called static fileds). Electric fields are produced by thunderstorm activity in the atmosphere. Near the ground, the DC electric field averages less than 200 volts per meter. Much stronger fields, typically about 50,000 volts per meter, occur directly beneath electrical storms.
AC fields create weak electric currents in the bodies of people and animals. This is one reason why there is a potential for EMFs to cause biological effects. Currents from electric and magnetic fields are distributed differently within the body. The amount of this current, even if you are directly beneath a large transmission line, is extremely small. The current is too weak to penetrate cell membranes; it is present between the cells.
5. What are transmission lines?
Transmission line are high-voltage power lines. The high voltage allows electric power to be carried efficiently over long distances from electrical generation facilities.
Several studies have reported increased cancer risks for jobs involving work around electrical equipment. About 50 studies have now reported statistically significant increased risks for several types of cancer in occupational groups presumed to have elevated exposure to EMFs.
Not necessarily. Although use of electricity has increased greatly over the years, EMF exposures have probably not increased in the same way. Changes in the way that buildings are wired and in the way electrical appliances are made have in some cases resulted in lower magnetic field levels. Rates for various types of cancer have shown both increases and decreases through the years.
Several studies have looked for EMF effects on pregnancy outcomes and general health. Various EMF sources have been studied for possible association with miscarriage risk: power lines and substations, electric blankets and heated water beds, electric cable ceiling heat, and computer monitors or video display terminals. Some studies have correlated EMF exposure with higher than expected miscarriage rates; others have found no such correlation. Epidemiologic studies have revealed no evidence of an association between EMF exposure and birth defects in humans.
Yes, worldwide, there are about 200 studies under way or planned involving magnetic and/or electrical fields.
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This page was updated on October 13, 2006