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Electromagnetic fields: the invisible threat.

Electromagnetic fields (EMFs) are electrically generated lines of force that, although invisible, can have very real disruptive effects. They can compromise the productivity of computer systems and the security of financial data and automated transactions. And though there are no definitive studies on the human-health consequences of short- and long-term exposure, there is enough uncertainty to warrant concern. Inasmuch as almost all buildings are subject to some degree of exposure, risk managers should understand how EMFs can affect an office environment and, when necessary, take early measures to reduce or eliminate the risks.

The first step in dealing with the challenge is identifying EMF sources. Magnetic fields within a building emanate from transformers, network protectors, secondary feeders, switchgears and panels. Improper wiring can inject ground currents onto metal conduits, water pipes, building steel and heating/ventilating/air-conditioning (HVAC) ducts, Regardless of the location of the source, be it in the basement or the 15th floor, these fields can be a challenge throughout a building.

Outside sources can also produce EMF problems. Buildings near transmission lines, subways and electrified-rail systems can experience high magnetic field levels. On roofs and upper floors, radiated energy from nearby antennas and microwave dishes can be potentially dangerous. Furthermore, as wireless local area networks, cellular telephones, microwave and other forms of radio-frequency communications become more common, so will the associated problems and health risks.

Field Surveys

A detailed site survey, generally conducted by an electrical engineer, can locate the origin of magnetic fields and evaluate the potential effects on the building environment, equipment and people. There are three types of commercial EMF surveys:

In a spot survey, levels are recorded in areas such as the center of offices, work areas and electrical equipment rooms, and around the property.

A contour survey will record field levels at one-foot intervals along selected paths (e.g., in a back-and-forth pattern within a large room, the outside perimeter of a building or property line, or perpendicular from an overhead transmission line or electrified train track). The recorded data is processed and plotted in two- or three-dimensional color images that present a clear picture of the invisible flux.

Finally, in a dosimetric survey, a gaussmeter, which is used to measure the resultant magnetic flux density emanating from electric power sources in milligauss (mG), is placed at a fixed location or attached to a test subject. Exposure levels are recorded in timed increments to show accumulated exposure and level changes over a defined period.

After a survey is completed, the engineer should provide comprehensive report that includes recorded contour measurements (with color graphics) of the surveyed areas, including selected equipment measurements, noted wiring violations and current grounding and plumbing problems-, detailed drawings of the property, building(s) and nearest electrical sources; risk assessment information; and recommended mitigation measures and estimated costs.


Depending on the survey results, a company may decide to implement one or more mitigation solutions. There are five basic strategies:

* Installing a dielectric coupler should eliminate excessive AC power magnetic fields emanating from water service lines (plumbing currents caused by an electrical current attaching itself to metal water pipes).

* Locating and correcting the ground current sources (code violations or shorts) should solve excessive AC power magnetic fields emanating from the building steel, HVAC ducts, metal pipes or conduits.

* Prudent avoidance requires that people or the magnetic source be moved to a safe distance (EMF exposure diminishes quickly with distance). However, in government and commercial buildings, it is highly unlikely that rentable, productive or living space will be vacated permanently to solve an exposure challenge.

* Magnetic field cancellation technology can be implemented if unacceptable levels originate from outside a building. In this approach, a passive wire or active loop cancellation system is set up between the building and EMF source. (Building size can severely limit this strategy.) Radiated radio/microwave signals can be mitigated b), the application of special conductive window coatings electrically grounded to aluminum/copper foils or by using conductive paints on the walls and floors.

* Magnetic shielding is the only viable solution when AC power magnetic field levels exceed 10mG and empty space cannot be used as a barrier between people, computers and the source. Two approaches can be used:

Shielding the source is the most effective (and least expensive) solution. However, if there are multiple magnetic field sources or the sources are not readily accessible (e.g., underground or spread out behind walls), it may not be economically feasible to do so. The solution then is to shield the area in which people work and EMF-sensitive equipment is used.

One recent example of a successful area shielding project involved a New York City community college where peak readings in a fitness center were far above acceptable levels. The fitness center -- which was also used for day care -- was located directly over transformers, network protectors, feeders and switchgears.

A contour survey was performed to ascertain the levels of magnetic-field penetration throughout the room. from the results, it became clear that it would be impractical to shield each source and that protecting the room from the sources below would be more effective. To achieve the acceptable levels, the engineering team covered the floor and all four walls with a specially created multilayer, three-substrate shield of welded aluminum plates and multiple layers of silicon-iron and mumetal sheets.

It should be noted, however, that one solution often does not solve all problems. Every shield will require different materials and layering, and the area to be shielded will be dictated by field levels.

The best, and by far the most cost-effective, approach to containing EMFs is to implement appropriate shielding mechanisms in the design stage. (Mitigation can be four times as costly after the fact.) Any business relying on computer-related technology or high-speed communications systems will benefit by identifying EMFs and radio-frequency interference before building, leasing or renovating a facility. If levels are unacceptable, shielding systems should be installed before occupancy. Any area where computers are to be used should measure less than 10mGs one meter above the floor over 95 percent of the area occupied by computers (less than five mGs if 21-inch monitors are used), These performance standards should be written into any lease or rental agreement or new construction/renovation contract. The language should also specify who will be responsible for maintaining these standards. Finally, buildings should be certified clean every two years.

EMFs are n unpleasant, aggravating and possibly harmful byproduct of the technologically-driven world we live in, but with proper vigilance and appropriate strategies their effects in the workplace can be minimized. As is often the case in managing risk, however, the best time to address the problem is sooner, not later.
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Author:Vitale, Lou
Publication:Risk Management
Date:Jul 1, 1998
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