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WHAT ARE EMFs? - What are Electromagnetic Fields - EMFs? This document discusses common sources of exposure to electromagnetic fields and methods to reduce exposure, as well as mentioning some exposure standards.
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EMFs are invisible lines of force created whenever electricity is generated or used. EMFs are produced by power lines, electric wiring, and electric equipment and appliances. The frequency of EMFs is measured in hertz (Hz, or cycles per second).
People are exposed to both electric and magnetic fields, but scientists are most concerned about magnetic fields. This fact sheet deals only with magnetic fields that have frequencies near 60 Hz the frequency of electric power in North America.
Static magnetic field around a bar magnet.
While this NIOSH document is focused on the workplace it is of interest to home owners as well. Everyone in our modern society is exposed to the electric and magnetic fields (EMFs) that surround all electric devices. Readers should also see Electromagnetic Radiation Field EMF SURVEY Procedure and where property values may be affected by the presence of nearby power transmission lines, see Enviro-Scare, the Cycle of Public Fear.
Recently, scientific studies have raised questions about the possible health effects of EMFs. This fact sheet answers frequently asked questions about EMFs in the workplace.
You can use this information to help identify EMF sources at work and to take simple steps for reducing exposures. However, you cannot use this information to judge the safety of your exposures, since the scientific evidence does not yet show whether EMF exposures are hazardous. [This is a NIOSH document. Also see More Information about Electromagnetic Fields below.] Also see EMF RF FIELD & FREQUENCY DEFINITIONS for a simple explanation of different types of radio frequency (RF) and electromagnetic frequency (EMF) types and where they are found.
Workers may be exposed to high magnetic fields if they work near electrical systems that use large amounts of electric power (for example, large electric motors, generators, or the power supply or electric cables of a building).
High magnetic fields are also found near power saws, drills, copy machines, electric pencil sharpeners, and other small electric appliances.
The strength of the magnetic field depends on equipment design and current flow not on equipment size, complexity, or voltage. Though some electric equipment produces EMFs of other frequencies, most health research has considered only frequencies near 60 Hz.
[Click to enlarge any image]
The EMF exposures for many jobs have not been measured, but the following table shows average exposures to magnetic fields for typical workers who use electric equipment. Exposures during a work shift vary with the strength of the magnetic field, the worker s distance from the EMF source, and the time the worker spends in the field. For comparison, the table also lists worker exposures off the job.
Average magnetic field exposures for various types of workers (in milligauss*
Average daily exposures Type of worker Median** Range Workers on the job: Clerical workers without computers 0.5 0.2 - 2.0 Clerical workers with computers 1.2 0.5 - 4.5 Machinists 1.9 0.6 - 27.6 Electric line workers 2.5 0.5 - 34.8 Electricians 5.4 0.8 - 34.0 Welders 8.2 1.7 - 96.0 Workers off the job (home, travel, etc.) 0.9 0.3 - 3.7*Magnetic fields are often measured in gauss or milligauss (one thousandth of a gauss = 1 milligauss).
**The median is the middle measurement: half the workers have average daily exposures above this point and half below.
Studies have shown that some workers exposed to high magnetic fields have increased cancer rates. But such associations do not necessarily show that EMF exposures cause cancer (any more than the springtime association of robins and daffodils shows that one causes the other). Scientists have looked carefully at all the EMF evidence, but they disagree about the health effects of EMFs except to say that better information is needed.
EMF EFFECTS - What DO studies show about the health effects of Electromagnetic Fields - EMFs in workers?
The most important data come from six recent studies of workers wearing EMF monitors to measure magnetic fields. All but one study found significantly higher cancer rates for men with average workday exposures above 4 milligauss.
However, the results of these studies disagree in important ways such as the type of cancer associated with EMF exposures. So scientists cannot be sure whether the increased risks are caused by EMFs or by other factors.
A few preliminary studies have also associated workplace EMFs with breast cancer, and one study has reported a possible link between occupational EMF exposure and Alzheimer s disease.
The data from all of these studies are too limited for scientists to draw conclusions. However, a national research effort is under way, and more study results are expected in a few years.
Because of the scientific uncertainty, no Federal limits for worker exposures to EMFs have been recommended or established in the United States.
Two private organizations have developed guidelines to protect workers from the known effects of extremely high exposures (that is, those more than 1,000 times the exposures typically found in occupational environments). However, these guidelines do not address the possible health effects of the low EMF exposures usually found on the job.
Because some studies have associated high magnetic field exposures with increased cancer risks, the government will continue studying EMFs.
While research continues, concerned workers and employers might consider the following simple, inexpensive measures for reducing EMF exposures:
NIOSH has been evaluating the possible health effects of EMFs since 1991. NIOSH scientists have measured the fields in workplaces where employees are concerned about their EMF exposures; they are also studying the biological effects of EMFs. In addition, NIOSH scientists work cooperatively with researchers in universities and other Federal agencies to share their study results. These cooperative efforts have increased recently under the National EMF Research and Public Information Dissemination (RAPID) program.
"NIOSH Fact Sheet: EMFs in the Workplace," DHHS (NIOSH) Publication No. 96-129, is available from:
NIOSH Publications Dissemination,
Fax: (513) 533-8573
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