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How to make EMF measurements: This paper discusses a recommended procedure for performing electromagnetic field (EMF) or electro-magnetic radiation EMR measurements either by engaging a professional or by consumers using low-cost instruments which measure EMF exposure levels 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.
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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.
Health professionals, epidemiological experts, and in the case of EMF, electrical engineers can offer competent, expert advice which should be considered before any costly or risky actions are taken regarding this or other environmental topics.
This information is has not been sanctioned nor technically reviewed by the American Society of Home Inspectors. Use it at your own risk.
Readers are urged to consult expert sources and to give any suggestions regarding these notes to the author.
Readers may want to see our EXCEL Spreadsheet EMS_Survey_Sample1.xls for an example of common locations and measurement points.
This spread sheet includes computations necessary to produce mathematically valid measurement results for those who are using position-sensitive instruments.
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.
Property valuation impact of EMF: However our experience with a number of environmental issues is that economic and other risks (property marketability, stress-related illness, legal concerns) pertain for all "potential" environmental health issues, regardless of the legitimate, demonstrated health exposure.
If homes or schools were immediately adjacent to a power sub-station such as the one shown in our photo from Dutchess County, NY the nearest properties may show a strong EMF. This power substation is of the sort discussed in sensationalist and scary books on this topic.
This particular power substation does not have homes adjoining its property; but nonetheless, some buyers of homes in the neighborhood may be nervous about this facility.
Property owners and consumers would be wise to be as accurately and calmly informed as possible. The emotional fear that motivates some consumers subjects them to risk of economic profiteering by less than totally scrupulous "investigators" in some instances. A professional hazard investigator should be personally committed to being as informed and professionally neutral as possible.
The EMF Field strength at any given moment depends on the load on the power line: A serious problem has limited research and conclusions regarding possible hazards of electromagnetic fields in the U.S.: the lack of publicly available load data. EMF field strength varies depending on the load on the system/conductors. Measurements made at different times and under different conditions will vary widely.
Additional explanation of the causes of variation and error in measurements of electromagnetic fields can be found at my article on Enviro-Scare and EMF this website.
In our opinion if you can establish any field measurement at a property it is likely that under some conditions the field strength will be greater than the time of your measurement. Further, even if you measure no field effects, if the property is close to large power transmission or some power distribution lines, it is possible that at some times and conditions it's in a measurable field.
Distances from power lines and EMF field strength: The distances for common field strengths and power lines are available in a number of EPA documents, such as "Evaluation of the Potential Carcinogenicity of Electromagnetic Fields," EPA/600/6-90-005B October 1990 (DRAFT review copy), page 2-21.
For example, the field strength of a 500 KV Transmission line begins to fall off measurably at 50 meters, but does not fall off below 1 mG until distances nearing 1000 meters.
Keep in mind that independent of proximity to power transmission facilities, a careful survey of conditions in any building may reveal other devices like home appliances or electrical service entry cabling: areas where strong EMF can be measured from distances of a few inches to several feet away.
Also keep in mind that based on our own field experience, we note that it would be unusual in any urban or suburban environment to find ambient EMF levels below one or two milligauss.
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.
Power companies in the US have been singularly uncooperative in providing actual load data, making it difficult to establish a dose-exposure relationship between exposure to EMF and occurrence of disease. This is why the Swedish studies are so important. There the government cooperated with researchers in providing load data, permitting clear establishment of exposure to occurrence relationships.
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. In this series of articles we describe how to make measurements using a consistent approach and using good documentation.
See Recommended EMF Measurement Procedure for details of how to collect EMF measurement data.
Following good procedure and using instruments properly are two steps towards making accurate, repeatable EMF measurements. But because the signal transmission for RF sources such as radio, TV, or cell towers, the load on a power transmission line is not under control of an individual property owner, and because the EMF strength varies as the power transmission line load varies, it is important to have an idea of that condition as well when attempting to characterize EMF exposure at a specific location.
In contrast, EMF measurements are quite accurate and repeatable at other EMF sources such as close to electrical appliances and service entry cables.
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. These devices are readily available from many electrical equipment and home inspection equipment suppliers.
A clear summary of EMF risks and characteristics is at "Magnetic Field Exposure and Cancer: Questions and Answers [ copy on file as /emf/EMF_Fact_Sheet_NCI_NIH.pdf ] - ," National Cancer Institute, U.S. National Institutes of Health.
Continue reading at EMF SURVEY REPORT INTERPRETATION or select a topic from the More Reading links shown below.
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