EMF are produced through both natural and man-made means. The earth is the largest single source of static magnetic fields. The human heart and brain produce a magnetic field as well. This page only discusses man-made magnetic fields. Electricity produces two types of alternating fields. Whenever there is a flow of electricity both electric and magnetic fields are created. Electric fields can be shielded by materials such as wood, metal, trees or shrubs. Magnetic fields pass through most materials and objects.
Research for possible adverse (and beneficial) health effects has been conducted on EMF and several thousand papers have been published. More than two dozen panels of independent scientific experts have reviewed this research. They represent the most authoritative efforts to put all the science on EMF into perspective and have found that the research is inconclusive and inconsistent.
Magnetic fields are measured using a handheld meter called a gauss meter. In the United States, magnetic fields are measured in units called Milligauss (mG). When measuring magnetic fields, you may notice that the levels vary in different areas of the same room. These variations may be due to wiring in the walls or to changes in the amount of electricity being used.
The strength of a field depends on the voltage level and the amount of current flow. The amount of current flowing through a power line varies as the demand for electric power changes. The strength of a magnetic field falls off sharply as you move away from its source, whether it is an electrical appliance or a power line.
Although the public tends to focus on exposure from transmission lines, for most people, exposure to magnetic fields comes more from appliances and household wiring. (Measurements In Milligauss (mG) Source: "EMF In Your Environment" EPA, 1992)
|6 inches away (mG)||2 feet away (mG)|
|Directly under/overhead transmission lines||6-100 mG|
|100 feet away from overhead transmission lines||0.5-15 mG|
|Directly over underground distribution lines||20-40 mG|
|20 feet away from underground distribution lines||4-10 mG|
*Typical of EMF strengths from NPC power lines measurements in milligauss (mG)