Local Indoor & Site Sources of EMF Affect Site EMF Surveys InspectAPedia® -
How small or local site or indoor EMF sources affect EMF property & power line surveys
Sources of error and variability in electromagnetic field strength measurement surveys
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Here we describe the identification & measurement of local outdoor or indoor EMF electromagnetic field sources as part of a recommended procedure for performing electromagnetic field (EMF) or
electro-magnetic radiation EMR measurements in gauss or milligauss. We discusses
sources of error and variation in EMF measurements and we review and make suggestions for using several low-cost EMF
measurement devices to determine the instantaneous electromagnetic field exposure.
The information provided here is for research and study purposes. The author makes no representation of unique
expertise on this topic, other than having field experience in EMF measurement, having studied technical literature and
having conversed with other experts and authors in the field for a number of years. Readers are urged to consult expert sources and to give any suggestions regarding these notes to the author.
Other sources of electromagnetic fields may be greater than a power transmission line,
may confuse readings, and might in some cases deserve attention.
Electrical appliances commonly found in Buildings (TV's, toasters, clocks, microwave ovens, electric motors),
generate their own electrical fields, in some cases pretty strong ones.
However remember that the field strength
falls off as the square of the distance from the source.
And remember that an appliance generates a field
when it's electrically active or "turned on."
So unless your toaster is running 24-hours a day, and unless
you're sleeping with your head next to the toaster, the fact that it generates an electrical field (while you're
making toast) is, from an EMF health exposure view, pretty unimportant.
We conclude that power-company funded studies which focus attention on home appliances are simply funding a red herring to distract already-frightened consumers, but we also emphasize that in most cases the fear that some people have about EMF exposure is not appropriate and that other more dangerous hazards may be present.
But having investigated a number of interesting cases and complaints,
we have found cases where specific items in buildings were creating a strong and constant electromagnetic
field. Occupants who wish to take the EPA's advice of "prudent avoidance" (that means avoid without going to
extreme measures and without panic), might use their new EMF meter to look at the following cases:
An electrical service entry cable (SEC) running down the outside of a home happened to be on a wall against which, inside, an
infant's bed headboard was placed.
The distance separating the infant's head from the SEC was thus only about
10", and at the pillow I found a very strong EMF. Solution for prudent avoidance: move the bed away from this building wall to a different location.
Moving even three or four feet away from this line usually reduces the measurable EMF field strength from the electrical service entry cable to below the range of detection.
we have found exceptions to that rule where metal building piping or steel beams (or in one case sewer piping) appear to carry EMF to other locations more distant from the source.
A bedroom had been built on a converted porch. The SEC and electric meter were enclosed in a wooden "box" and
chaseway which was right next to the bed's headboard.
EMF measurements and solution were the same as for the
case above.
Steel piping carrying electrical fields from other locations in a building: In an basement apartment of a large building I found very strong EMF measurements near the ceilings of the
apartment. I observed that steel building water pipes ran close and parallel to a large bank of 24 electrical
meters serving the building. Apparently the electrical fields at the SEC wiring and meters were being picked up
and transmitted across the building by its plumbing.
Steel sewer piping carrying electrical fields: At a suburban community local road which was crossed by a high voltage power transmission line, I found that
the entire street appeared to generate a strong EMF. We observed that the street contained a large buried steel
sewer line that appeared to conduct the EMF away from and at right angles to the power line. There was no measurable
effect from the street's field at the nearby homes themselves.
A home's aluminum siding appeared to be showing a strong EMF. I found that improper electrical wiring, including
a defective clothes dryer and improper grounding of the electrical system was causing some of the siding to actually
carry current when the dryer was operating.
Other safety hazards may much more dangerous than EMFs: a final and really important example: while measuring EMF's at properties, or while performing other types
of environmental inspections, I have often found sever immediate hazards such as unsafe chimneys, boilers without
relief valves, combustible gas leaks, or dangerous electrical or fire hazards. It would be foolish to become so
focused on an concern for electromagnetic fields (EMF) that one failed to notice immediate and severe threats
to life and safety.
Some studies by some experts have suggested a possible link between exposure to electromagnetic fields and various
cancers or other health problems. Other studies suggest that no definite correlation could be demonstrated. It is
likely that the jury will be out on this matter for some time, for both economic and political reasons.
Our photo shows an uncommon exposure to an electrical field: the electrical meter and service entry cable produce a field which can be detected up to perhaps two to four feet away. But the history of construction at a building can bring surprises.
An outside porch first enclosed this electrical meter; later the porch was enclosed and converted to a bedroom. Our model shows that someone sleeping on the side of the bed next to the electrical meter was likely to be sleeping in an EMF that could easily have been avoided: move the bed to an opposite wall.
Small absolute health risk from EMF: Most researchers indicate that where a risk is present, the absolute risk level from EMF is likely to be small, and
less than other less obscure hazards. (Automobile accidents, trip and fall, fire, and shock hazards, smoking and other
health risks.) Consumers should not let focus on a specific emotionally-charged hazard distract them from these other
more mundane but more dangerous concerns.
Often but not always, the relative strength of
such fields falls off in much shorter distance than that from power transmission facilities. However in some instances
where occupants wish to maintain prudent avoidance, it is possible to make a significant reduction in exposure by small
changes in arrangement of devices or locations of working or sleeping areas.
Instead of contacting us with a request to perform EMF Electromagnetic or RF Radio Frequency Field Strength measurements, in most cases it is more economical and convenient for a property owner to purchase their own instrument, making measurements under varying conditions. See Recommended EMF Measurement Procedure for details of how to collect EMF measurement data.
Please do not contact us with a request buy EMF or RF measuring equipment. We do not sell anything. To do so would be a conflict of interest for this website. See Evaluation of Low-Cost EMF Instruments where we describe several low-cost and reasonably accurate EMF measurement devices that are readily available. See Radio Frequency RF Detection Meters where we describe several low-cost and accurate radio frequency or RF detection and measurement devices suitable for radio, TV, cellphone, microwave, and similar signals.
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Additional technical contributors & reference sources for this article are listed below.
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"Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields", Federal Communications Commission, Office of Engineering and Technology, US FCC, OET Bulleting 56, 4th Edition, August 1999
" Many consumer and industrial products and applications make use of some form of
electromagnetic energy. One type of electromagnetic energy that is of increasing importance
worldwide is radiofrequency (or "RF") energy, including radio waves and microwaves, which
is used for providing telecommunications, broadcast and other services. In the United States
the Federal Communications Commission (FCC) authorizes or licenses most RF
telecommunications services, facilities, and devices used by the public, industry and state and
local governmental organizations. Because of its regulatory responsibilities in this area the
FCC often receives inquiries concerning whether there are potential safety hazards due to
human exposure to RF energy emitted by FCC-regulated transmitters. Heightened awareness
of the expanding use of RF technology has led some people to speculate that "electromagnetic
pollution" is causing significant risks to human health from environmental RF electromagnetic
fields. This document is designed to provide factual information and to answer some of the
most commonly asked questions related to this topic." - original source: U.S. Federal Communications Commission Office of Engineering and Technology, http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf
EMF RF FIELD & FREQUENCY DEFINITIONS RF and EMF measurement tools need to be properly chosen to measure the particular type and frequency of RF or EMF signal that is of interest. 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.
US Environmental Protection Agency, Office of Pesticides
and Toxic Substances, TSCA Assistance Office (TS-799), 800-424-9065
or 202-554-1404.
"Evaluation of Potential Carcinogenicity of Electromagnetic Fields,"
EPA Report #EPA/600/6-90/005B October 1990. EPA: 513/569-7562.
"Biological Effects of Power Frequency Electric and Magnetic Fields"
background paper, prepared as part of OTA's assessment of "Electric Power
Wheeling and Dealing: Technological Considerations for Increasing Competition,"
prepared for OTA by Indira Nair, M. Granger Morgan, H. Keith Florig, Department
of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA
15213
"Biological Effects of Power Line Fields," New York State Powerline
Project. Scientific Advisory Board Final Report, July 1, 1987.
"Extremely Low Frequency (ELF) Fields," Environmental Health
Criteria 35. World Health Organization, Geneva, 1984.
"Electric and Magnetic Fields at Extremely Low Frequencies:
Interactions with Biological Systems. In: Non ionizing Radiation Protection,
World Health Organization, Regional Office for Europe, Copenhagen, 1987.
"Electric and Magnetic Fields from 60 Hertz Electric Power: What do
we know about possible health risks?," Department of Engineering and Public
Policy, Carnegie Mellon University, Pittsburgh, PA 15213 1989.
"Electromagnetic Fields Are Being Scrutinized for Linkage to
Cancer," Sandra Blakeslee, New York Times, Medical Science section, April
2, 1991
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