ELECTROMAGNETIC FIELDS: YOUR UNINVITED GUEST

J. TERRY TURNER

For apartment property owners and managers, electromagnetic fields (EMFs) are uninvited guests that occupy a variety of spaces. EMFs are an aggravating byproduct of electrical power that managers should understand and be prepared to address.

Compounding the challenge is the fact that EMFs cannot be seen, heard, or felt despite the fact that they can penetrate virtually all objects including buildings and people. Residents become aware of electromagnetic interference (EMI) of alternating current (AC) power sources when they generate screen jitter in computer monitors, noise in stereos, and data errors in magnetic media. There is also conflicting research linking AC power EMFs to health problems, most notably leukemia, cancer, and Alzheimer's disease.

The key to dealing with the EMF challenge is identifying its sources within or outside a building, keeping in mind that they are present in every building. If residents complain of screen jitter or color distortion, data loss, or radio interference, a professional EMF survey can lead to the proper solutions.

WHAT ARE EMF SOURCES?

Magnetic fields emanate from within a building from transformers, network protectors, secondary feeders, switchgears, busway risers, and panels. National Electric Code wiring violations can inject ground currents onto the metal conduits, water pipes, building steel, and HVAC ducts, generating EMI problems throughout the building. This means that while AC magnetic fields are generally located and mitigated near an electrical source, magnetic fields can be a challenge throughout the building. Outside sources can also produce EMFs; buildings near transmission lines, subways, and electrified-rail systems can produce high magnetic field levels.

On many roofs and upper floors of buildings, radiated EMF energy from nearby radio frequency antennas and microwave dishes can exceed minimum acceptable human exposure standards and be potentially dangerous. Furthermore, as wireless computer networks, cellular telephones, microwaves, and other forms of radio frequency communications grow, so will the problems and potential health risks in these buildings.

SELECTING AN EMF SURVEY

Because EMFs are invisible, only a detailed EMF site survey can identify the EMF source(s) and evaluate the potential impact on the building and its environment. Usually the EMF source is obvious because the screen jitters near an electrical switchgear or the screen changes color as a train passes. However, complex problems can be generated by plumbing currents on water pipes, magnetic resonance imaging (MRI) or uninterrupted power supply units, shorted electrical equipment, and nearby antennas and radar.

There are three types of commercial AC power EMF surveys in use today: spot, contour, and dosimetric. A three-axis gaussmeter is used to measure the resultant magnetic flux density emanating from electric power sources in milligauss (mG). Following is a short summary of each type of commercial EMF survey and a description of how each functions: Spot Survey. Levels are recorded in spots such as the center of each office, work area, electrical equipment room, and around the property; Contour Survey. Levels are recorded at one-foot intervals along selected paths. Recorded data is processed and plotted in 2-D or 3-D graphical presentations; and Dosimetric Survey. A gaussmeter is placed at a fixed location or attached to a test subject. Exposure levels are recorded in timed increments over a defined period. This shows accumulated exposure and level changes over time.

Commercial buildings are generally surveyed for AC power magnetic fields using the spot or contour methods. Contour surveys are favored because each room or area can be measured across a variety of points, providing a clear picture of the magnetic field penetration and levels.

Generally, readings below 10 mG will not interfere with computer monitors, electronic cabling, magnetic media, or audio-visual equipment. As for the health consequences of short- and long-term exposure to EMFs, there is no industry agreement or federal standard at this time.

After the AC power EMF survey is completed, an experienced engineer should provide building management with a comprehensive report that includes: Recorded contour measurements of the survey areas, including selected equipment measurements and noted wiring violations, grounding, and plumbing problems; Detailed drawing of the property, buildings, and nearest electrical sources; Risk assessment information and the latest news in EMF research; and Recommended mitigation activities with estimated design and installation costs.

EMF MITIGATION SOLUTIONS

Depending on the EMF survey results, building management may decide to implement one or more EMF mitigation solutions. There are five basic strategies in use today:

Strategy I

If excessive AC power magnetic fields are emanating from water service lines, the installation of a dielectric coupler should eliminate the problem.

Strategy II

If excessive AC power magnetic fields are emanating from the building steel, HVAC ducts, metal pipes, or conduits, locating and correcting the ground current sources should reduce or eliminate the problem.

Strategy III

Prudent avoidance, which requires that people or the AC magnetic source be moved a safe distance away is an option. In commercial buildings, including multifamily properties, it is highly unlikely that rentable space will be vacated permanently to solve an EMF exposure problem.

Strategy IV

If the EMF sources emanate unacceptable levels from outside the building,AC power magnetic field mitigation or RF shielding will have to be implemented. For AC power mitigation, a building can be protected using a passive wire or active loop cancellation system between the EMF source and building. Building size severely limits the use of this mitigation solution.

Radiated microwave signals can be mitigated by the application of special conductive window coatings electrically grounded to foils or conductive paints on the walls and floors.

Strategy V

When AC power magnetic field levels exceed 10 mG and empty rentable space cannot be used as a barrier, magnetic shielding is the only answer. Two approaches can be used in EMF magnetic shielding; either shield the EMF source or shield the room and people.

SHEILDING METHODS

Shielding the source is the most effective and least expensive alternative available for magnetic shields. However, if there are multiple magnetic field sources or they are not readily accessible, it may not be economically feasible to individually shield each source.

The solution then becomes one of shielding the room in which people work and EMF sensitive equipment is used.This solution is selected most often of all the options. U

Turner is vice president with VitaTech Engineering, Montclair, Virginia.