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Guide to Electromagnetic Field Surveys - a Recommended EMF Measurement Procedure Enter your search terms Submit search form   Search This Website - InspectAPedia.com

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.

Also see Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

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 EMFSURVY.XLS in DJ Friedman's ASHI-COMPUTER.LIB for a list 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.

Introduction to Electromagnetic Field EMF Radiation Measurement at Buildings

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.

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.

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.

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.

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 my 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.

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 devices and areas where strong EMF can be measured. 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.

Finally, in order to permit comparison of measurements (and studies) it is important not only to have line load data available (for researchers) but also that site measurements are made in a very consistent manner from building to building. To do otherwise would make it impossible to compare conditions at one property with those at another, even if both properties are equidistant from the same power line and even if both measurements were made at the same moment.

An Overview of an EMF/EMR Measurement Survey Procedure

Magnetic fields are directional; measurements are affected by position as well as location of the instrument within the area being examined, and by the distance of the instrument from the field source. Our field experience strongly suggests that results are quite variable depending on the particular direction aimed and positions held when using the measuring instrument.

Therefore, and consonant with recommendations from the manufacturers, each of our "measurements" is derived from at least three instrument readings, holding the instrument pointed at a suspected field source (e.g. nearby power line), pointed straight up, and held horizontally. Horizontal and vertical measurements are recorded as the highest obtained following a 360 degree scan of the area with the instrument held in that position.

During such a rotation in the presence of a strong magnetic field we find reading levels ranging widely. We warn you that measurements made by another professional will not duplicate our results unless our exact procedure is used with an instrument of similar performance at the identical locations. However our experience is that measurements with similar instruments in approximately the same locations and circumstances, produce results which are quite close.

For each instrument reading we record location, position, meter sensitivity settings, meter readings, and estimated distance to the suspected field source, if any. We also record observations of devices such as TV's or computers if they are seen operating nearby.

For the analog device measurements, actual meter readings are converted to milli/microgauss using tables provided by the instrument manufacturer based on the sensitivity range to which the instrument was set at time of use. A range of sensitivity settings are required to protect this very delicate instrument from being damaged by the fields being measured. The manufacturer describes a mathematical procedure which we follow to combine these data into a single field level number for an area being measured.

For the digital device measurements, actual measurements are read on the instrument in gauss or milligauss, depending on a field strength sensitivity selection on the meter.

Variability and Inaccuracy Problems When Measuring Electromagnetic Field Exposure

As with any potential poison, our concerns are first to establish a dose-relationship to effects of the poison, and next to establish a reliable way to measure the actual dose or exposure that a person may experience.

EMF polarity and shape

Electromagnetic fields are created around power transmission lines by the passage of high levels of current through the transmission line wires themselves. A power-line generated electromagnetic field has polarity and shape, roughly spherical around a power line.

The problem of the electromagnetic field having polarity and shape means that some early or low-cost EMF measuring devices will give widely varying field strength measurements depending simply on the physical orientation of the device when the measurement is made - that is, what direction you point the instrument affects its reading. But don't think that pointing directly towards the power line wires overhead gives the maximum reading. It may not, due to field polarity. More costly EMF meters have multiple sensors to overcome this defect.

EMF strength effects and distance from the electromagnetic field source

The strength of an electromagnetic field diminishes as the square of the distance one is from the power line or field source. So in general, walking closer to a power transmission line will give a higher reading. But near a large power transmission line, since the electrical field has a "shape" and since a building owner's property line may not be exactly parallel to the power transmission lines themselves, I've found that field strengths along a line parallel to the edge of a property may vary widely.

Power transmission facility design also affects the strength of the EMF generated. Load or phase balancing for overhead transmission lines, distance between electrical conductor wires, and the choice to use buried transmission lines (which I believe are much more costly to install) can make a very significant difference in the measurable EMF.

EMF strength variation and seasonal or time of day variations in electrical power usage levels

But distance from the power transmission line, while important, is not the only important factor. The strength of the electromagnetic field varies dramatically as the current passing through the power line varies.

Thus in the middle of summer in the Northeastern United States, when many people are running air conditioners and thus the load on the electrical grid is high, a lot of current is passing through the power transmission lines, and the EMF strength will be quite high - thus extending further from the power lines and being measurable at higher levels than it will during times of low electricity usage. Therefore no single instantaneous EMF measurement at a particular spot may be quite repeatable.

A power transmission company can tell you the kilovoltage that a given transmission line is designed to carry. This is not enough data to calculate exposure or risk. One would need to know the actual minute-to-minute load on the transmission line to be able to predict the probable EMF strength during those intervals. The absence of this data has plagued attempts to correlate proximity to power transmission lines, EMF exposure, and health risks. The "Swedish study" mentioned herein was able to overcome this difficulty and obtain actual usage data and thus was able to calculate the actual EMF exposure levels.

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.

But having investigated a number of interesting cases and complaints, I've 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.
  
  
• 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.
  
  
• 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.
  
  
• 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.
  
  
• 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.

A Recommended Electromagnetic Field Measurement Procedure

1. Outside Measurements

a. At perimeter of the property at a point closest to a suspect source such as a power transmission or distribution line

b. At the electric meter at distance of 12" (confirms equipment is responding)

c. At targets of opportunity such as pole-transformers near building, below service laterals to building.

d. In street in front of building, or other apparently neutral location more than 1000 meters from the power line of interest, to determine an apparent ambient or background level (commonly 0 to .5 mG, larger near local power distribution wiring under some conditions)

Also Document:

e. Estimated or measured distance from nearest point on building to point directly below nearby power line

f. Same, for distance from corners of building to point e. above.

2. Inside

If the outside of the building is in a strong EMF, all measurements inside the building might be expected to produce the identical number. However if the inspector agrees to a detailed site survey I recommend spot checks in every room as well as at obvious common interior targets of interest (such as an electrical device which is normally kept "on" and which is close to the head of a bed (clocks).

You will observe that while there may be a strong field close to a clock, the field will fall off to undetectable in 2 feet or so. Toasters are a "red-herring" and need not be measured unless the client indicates that someone sleeps with their head in or on the toaster and that it's kept on for long periods of time each day.

Other indoor targets of opportunity in residential properties:

- Bedroom walls adjacent to electrical service equipment, refrigerators, or computers if left on 24 hours.

- Bedroom walls inside of outside location of electrical service entrance cables.

- Every bedroom heated by electric radiant panels in ceiling or floor -

I've found very strange anomalies in some rooms, possibly due to damaged equipment or improperly installed wiring.

- Sleeping areas (or areas where people spend many hours daily) traversed by steel piping or ducting which in turn passes by electrical equipment.

Commercial properties have special targets of opportunity:

Local power distribution systems, electric meter buses which may produce a field which is further distributed by building plumbing or wiring

Special high-amp equipment such as X-ray machines, computer equipment, compressors

Given the ease with which electrical components within a building can be relocated or modified, field inspectors are strongly warned to absolutely refuse to permit clients to assert that the sample measurements made are a comprehensive or exhaustive study of a property.

3. Measurement procedure

- Document date, time, location, weather conditions (hot means air conditioners are running and load may be higher; time means it is at least theoretically possible to correlate the measurement results with actual load data if the power company would provide it)

- Document distance from measurement location to suspected source of

EMF and identify that source

- Document any reports of medical anomalies (if anyone volunteers such information or if your procedure or study permits its collection)

For position-insensitive equipment, a single reading is usually provided, directly in mG.

For position sensitive equipment you'll find an enormous range of response depending on the angle and direction in which you hold the measurement device.

While this type of instrument is more work to use (see calculations below and in spread sheet) it provides more clear indication of when you're approaching a field. Some instruments do not provide a reading directly in mG and you'll have to simply record the "raw" measurements and to convert them later.

For Position-sensitive instruments, three readings are necessary. I use these:

- Horizontal (spin through 360 degrees and record highest reading)

- Vertical (same as above)

- Pointed towards suspected source (e.g. distant power line)

To compute the actual point measurement, each of these numbers, once converted to mG, must be squared, the three squares added, and the square root taken of the sum. This is because the measurement scale is not linear, so a direct raw average would be incorrect. In the EXCEL worksheet you'll see that provision is made for recording raw data points as well as the individual mG readings.

Interpreting Electromagnetic Field Strength EMF Survey Results

It is very dangerous for untrained personnel to express opinions for which they have no scientific basis. There are very few standards for allowable exposure to EMF. The health studies are, according to some experts, inconclusive. Some health studies showed an increase in childhood leukemia and other diseases at long exposure to field strengths as low as 1 or 2 mG. However, keep in mind that "doubling" the risk of a disease may in some cases be doubling a number that was extremely small to start with. Doubling a very small number yields still a very small number. If your clients are worried about EMF but smoke, or don't fasten seat belts, or have dangerous stair or railings, their attention has been misdirected.

Pending acceptance of conclusive research by the scientific and engineering community at large, the most accurate position which can be taken by a consultant is that this is a controversial subject. There may be a health risk, that there are definitely economic risks, and that clients should not let this topic distract them from attending to other high risks that may be at a given property.

While the health risks remain under argument, with some recent studies suggesting that there may really be a risk, it is possible to infer whether or not a given property is likely to be exposed to EMF:

1. Any property which uses electrical devices will have at least some measurable fields. If the fields are continuous and close to people the people may be exposed. (EG. sleeping with head 8" from the electric meter-- you can move away, or sleeping in a building 50 ft from a 500KV power transmission line--you cannot move away within the building to escape the field)

2. If I measure *any* detectable field outside and all around a building attributable to a nearby power line, it is very likely that at times the building and its interior are exposed to more powerful fields (when load on the line is greater)

3. If I can measure *no* EMF at a given property (attributable to a power line which is nearby) but if the line is within 1000 meters of the building (at 500KV)

I contend that it's still quite possible that under some conditions (of heavy load) the building will be in a field. As field strength falls off with the square of the distance, and as field strengths are less for smaller transmission and distribution lines, this 1000 meters is not a sacred distance.

This material represents research thinking. Anyone having any comment, content correction or suggestion is welcome to contact the author.

Evaluation of and Advice for Using Some Low-Cost Electromagnetic Field Measurement (EMF) Instruments for Consumer Use

For added confidence in our measurement results, we use two independent measurement instruments - a Safeco(TM) analog meter and a Walker ScientificTM digital meter.

Both instruments measure magnetic fields which may be generated from power lines, transformers, household wiring, computers, TV's, and other electric devices. Measurements made by these devices should be considered as a general screening procedure designed to discover the possible presence of magnetic fields in and around the building or site. Such measurements are not exhaustive. Before making decisions involving any significant expense we recommend that additional instrumentation and expertise be considered.

The WalkerTM digital meter provides a direct readout of field strengths in gauss or milligauss. The Safeco(TM) analog meter permits visual observation of field orientation and strength, but requires mathematical computations to develop a final field strength number.

Our staff are not experts in electromagnetic fields. As the first and currently the only home inspection professional firm to offer this service in our area we have relied on the quality of instrumentation, information and consulting provided by the manufacturer, and field experience at a range of buildings and environments.

Accuracy and Calibration of Electromagnetic Field Measurement Instruments

SafecoTM analog EMF ELF EMR meter

Used in its "C" or "ELF" range to screen an area for magnetic fields typically generated by power transmission lines, secondary lines, power transformers, and household wiring (Extremely Low Frequency, or ELF) our test instrument measures magnetic field strength across seven scales from .3 milligauss to 302 milligauss.

Used in its "A" or "VLF" range to screen an area for magnetic fields typically generated by televisions and computers (Very Low Frequency, or VLF) our test instrument measures from .12 microgauss to 8312 microgauss. 1000 microgauss = 1 milligauss = 80 milliamps per meter.

The accuracy of this instrument itself is <145> 5%, which is typical for portable, hand-held electronic devices. The instrument is calibrated by the manufacturer using a Holaday 3600 for ELF fields. That instrument is available for additional measurements if necessary.

Measurements of ELF (around 60 Hz) will be confounded if there is nearby VLF (such as from a TV or Computer). We attempt to discover and will record the presence of such devices if seen, but we cannot guarantee that there were no such devices operating in or around the property being examined at the time of our tests. Generally such devices create a measurement problem only if they are within 15-20 feet of our instrument. We verify that a suspect high reading is not coming from a TV or computer by flipping from the "C" to "A" range - if the reading does not change significantly then there is VLF interference from a TV or Computer.

The Safe MeterTM is manufactured by Safe Computing CO., 368 Hillside Ave., Needham, MA 02194 800/222-3003.

The Walker Scientific ELF-50D Digital Meter

The Walker Scientific ELF-50 tm Digital Meter is a portable handheld instrument designed and calibrated to measure low level 50Hz or 60Hz electromagnetic fields generated by power lines, TV sets, video display terminals (VDT's), home appliances, industrial machinery, and similar devices.

The low-range instrument setting measures field measurements from 1 to 20 milligauss. This is the range in which most measurements are performed and it is the range within which current literature on this topic discusses possible health effects. The high-range instrument setting is used to measure fields from 10 milligauss to 20 gauss.

As with our analog instrument, the readings obtained with this device depend on the position with which it is held in the field being measured as well as the field strength.

The manufacturer provides a certificate of test and calibration certifying that the instrument has been tested to meet or exceed its published specifications. A copy of this certification is available for your inspection.

This instrument is manufactured by Walker Scientific, Inc., Rockdale St., Worcester, MA 01606 508-852-3674 / 853-3232 / 800-962-4638 / 508-856-9931 FAX.

Field Calibration of EMF Measurement Instruments

Our standard measurement procedure includes confirming normal instrument operation by measuring a known common field source - the electric meter at each property as well as at a baseline meter. We measure at 1' and 2' distances from the electric meter, typically finding a field strength between 2 and 7 milligauss in those areas.

Calibration of EMF Measurement Instruments With Electric Power Company Instruments for Measuring Electromagnetic Field Strength

We have compared our test measurements of specific sites with those obtained by local electric utility company representatives and have found our measurements and theirs to be in close agreement.

[Measurements made at the same electric meter at the same distances produced results within 7% of one another. Most power utility companies use equipment which is more sophisticated (and costly) than our own and their personnel may have additional training. See AHS Report #I9189105]

References for Electromagnetic Fields and Cancer Risk/Carcinogenicity

• Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear About Environmental Issues - online document by DF
• A Procedure for Measuring EMF electromagnetic fields online document by DF
• Consumer Product Safety Commission, 800-638-CPSC.
• 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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More Information on Building Diagnostic Inspections and Repairs

• Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues
• Electromagnetic Fields in the Workplace sample very good NIOSH document online, links to other NIOSH docs.
• Environmental Concerns in Buildings, hazards: allergens, asbestos, brownfields, - above ground or buried oil storage tanks, - A Procedure for Measuring EMF electromagnetic fields, - Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues - toxic gases & odors, IAQ, lead paint, - toxic mold inspections, - mold test kits - how to send a mold sample to our lab using an inexpensive and superior method - radon, sick buildings, UFFI (urea formaldehyde foam insulation), - sewage septic backup contamination testing & cleanup - water testing for bacteria, lead, etc.
• Electromagnetic Field Surveys & Hazards full list of our links to services and technical articles

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