Sources of Man Made
Low frequency Safety Standards
Extremely low frequency (ELF; frequencies below 3 kHz) field strengths are measured in terms of the individual electric and magnetic components.
Electric ELF fields are related to the voltage in conductors and are measured in volts per meter (V/m). Electric fields are present even if there is no current flowing. For example, an electric blanket will generate an electric field if plugged in, even if it is not turned on.
Magnetic fields are generated by the flow of current through conductors - the stronger the current the stronger the magnetic field. Magnetic field strengths are measured in the unit of milligauss (mG, 1/1000 of a gauss) since the gauss is a very big unit. Some scientists prefer another unit of measure called microtesla (µT, one millionth of a tesla); mG and µT relate to one another as follows: one µT equals 10 mG.
Most of the debate going on over acceptable thresholds of ELF fields is expressed in terms of magnetic field strengths. This is because the principal concern over the potential health effects relates to the magnetic component of the field. It's virtually impossible to shield, even with materials such as bricks, concrete, lead and earth. It penetrates deeply into cells, tissues, organs and the body of any person exposed. This is why placing electrical transmission lines underground will not in itself reduce magnetic
field exposures unless special engineering and design (shielding, phase cancellation, etc) are employed. The electric field, on the other hand, is much more effectively shielded; a house will shield out around 90 % of an electric field.
ELF fields envelop the surrounding space of a conductor or electrical device in the same way as the
earth's magnetic field
surrounds the planet. EMFs are not limited to power lines - they surround us in our work environment and homes, generated by hundreds of different appliances such as cell phones and cordless phones, computers, laser printers, photocopiers, radar equipment, halogen and fluorescent lighting, hair dryers, vacuum cleaners, TV sets and stereo equipment, electronic games, electric shavers, electric blankets and heaters, food processors, coffee grinders, refrigerators, washers, tumble dryers, microwave ovens, and so on. ELF field strength can be measured with a gaussmeter, a fairly inexpensive device which can usually be purchased. Most utility companies are now willing to come to your home without charge to test EMF levels with a gaussmeter.
ELF field strengths drop off quickly with distance, and exposures to many appliances may be brief. However, research has indicated that even weak and short exposures have an effect, the effects seem to be cumulative, and multiple on/off exposures may induce stronger effects than continuous exposures.
Table 1 shows the international standards and safety guidelines established by the International Commission on Non-Ionizing Radiation Protection.
Table 1: ELF safety standards.
These exposure standards were established in 1990, more or less arbitrarily. The problem with these standards is that numerous scientific studies have shown significant biological effects induced by EMF at field strengths thousands of times below these safety standards.
Epidemiologic studies have reported a
substantially increased risk of cancer at much lower field strengths. In two Swedish residential studies published in 1993 and 1994, up to 3.8 times the expected rate of cancer was found in persons residing near power lines with time-weighted exposures of up to 4 mG [ref. 2 and 3]. In a Danish residential study published in 1994, up to five times the expected rate of all cancers was found in people residing near power lines [ref. 4]. In a Swedish occupational study, up to 5 times the expected rate of cancer was found in persons exposed to EMFs on the job.
On the weight of these studies, the Swedish government has stated that it will act on the assumption that a relationship exists between EMF exposure and childhood cancer, and a safety standard of 2 mG has been suggested.
To the average person, household and office appliances represent a more significant source of EMF exposure than power lines. Table 2 below show some examples of ELF field levels emitted from appliances and devices.
As it appears from this table, many appliances emit EMFs at intensities well above the 2 mG limit considered the de facto safety standard by Swedish authorities.
Table 2: Typical ELF levels in mG (50/60 Hz) emitted by appliances and devices.
Nature's sources of
oscillating low frequency EMFs
are few and extremely weak; the only sources are the sun, distant radio stars and other cosmic RF sources, and the terrestrial sources originating from lightning primarily in the tropics. Even the sun can not be considered a strong source of energy in the non-ionizing spectral region, making natural ambient levels so low that the possibilities of biological or even health effects are negligible [ref.1].
We will never experience that "quiet" world again. The greatest changes have all come after World War II with a trend towards the use of higher energy radiowaves for long-distance communication and electronic devices of all types. Since then nearly every human action has involved an electrical appliance, and today we are all awash in a sea of artificial electromagnetic energies living species have never experienced before.
The human species has changed its electromagnetic exposures more than any other aspect of the environment. For example, with the explosion in radio and TV broadcasting stations, radio telephone networks, cordless phones and cell phones, the density of radio waves and microwaves around us is now many millions of times higher than the natural levels in the same spectral region.