More and more attention by the news media is currently being devoted to electromagnetic fields. Whenever electricity is present, there are both electric fields and magnetic fields. These fields, when taken together, are referred to as electromagnetic fields, or EMF. They exist around electrical transmission lines, transformers on poles, house wiring, appliances, electronic equipment, and so on. An epidemiological study published in 1979 concluded that children living in Denver near certain power lines that were exposed to electromagnetic fields with a magnetic field strength of 2–3 milligauss (mG) were twice as likely to develop leukemia than children living in houses without such exposure. The conclusions of the above study were not universally accepted by the scientific community; some researchers felt that the study was flawed and not scientifically sound. In the early 1980s, the scientific community began looking extensively into whether exposure to electromagnetic fields is dangerous to a person’s health. The complexity of the problem is compounded by the fact that the results vary according to the characteristics of the electromagnetic field, such as frequency, intensity, field orientation, period of exposure, and whether the field is continuous or pulsed.
The studies to date have not resulted in definite conclusions. They have shown that there is a statistical association between electromagnetic fields and cancer. However, they have not shown that the fields are involved in causing cancer. Based on all available information, many scientists have concluded that more research is needed before they can understand how EMF interacts with the human body to cause health effects and whether there is indeed a risk from exposure to EMF. Also, since not enough is known about which elements of the exposure are important to health, a safe exposure level has not been established.
Both electric fields and magnetic fields are being studied. However, more attention is being focused on magnetic fields because they can penetrate through common objects as thick as concrete walls without losing their strength whereas electric fields can be shielded by materials like wood, aluminum, or insulation around the wires. Although the potential risks and exposure levels have not been determined, it might be useful to know what some of the typical background levels are near transmission and distribution lines, near a pole mounted transformer, and in the yard of a house several hundred feet away from those power sources. The figures in TABLE 20-2 are from a very small sample and are not statistically significant. They can also vary considerably, depending on the electrical load. Nevertheless, they are based on actual measurements by a colleague, Dan Friedman, in New York.
How does all of the above affect a person contemplating purchasing a home near power lines or an electrical substation? You can have measurements taken to determine the magnetic-field intensity in and around the house to see if the readings are within typical background levels. A few home inspectors provide this service. Unfortunately, as of this writing, no government regulation or scientific recommendation helps answer the question. Until the research is complete, it is premature to recommend any course of action. Nevertheless, prudent avoidance should be considered, because until the cloud of uncertainty is removed, this problem can affect the resale value of these homes.
Table 20-2. Typical strengths of magnetic fields.
Range Source (milligauss)
High voltage transmission lines (within “right of way”) 12–900
Local power distribution lines
(within “right of way”) 0.1–10 Pole mounted transformer (at 25’ from source) 0.3–2.3
Service entry line
(at 20’ from source) 0.3–0.77 Electric meter at house (at 6” to 3’ from source) 1.0–7.0*
Front, rear, and side yards around house (several hundred feet from source) 0.0–0.5
*Numbers are inversely related to distance from source.