FMS Articles

Magnetic Fields 101 For Facility Managers
The power of planning: Mitigating Magnetic Field Problems

Magnetic fields are an unseen, and potentially costly, factor that facility managers must consider when organizing, renovating, or selecting new office space. Nearly every commercial and industrial building has certain areas with elevated magnetic fields, some high enough to render the space unusable for today's technology, particularly for computers. The best way for facility managers to avoid costly and embarrassing mitigation is to be knowledgeable about the sources of magnetic fields and the problems they can cause.

What are Magnetic Fields?

Electric and Magnetic Fields (EMF) are the result of the generation, distribution, and use of electricity. These fields exist in different frequencies and waveforms, and are not always static. At most frequencies, the electric and magnetic fields operate together, but at the lowest frequencies, including those caused by electrical power, called the Extremely Low Frequency (ELF), they operate independently; it is possible to shield the electric field without affecting the magnetic field.

Magnetic and electric fields are “vector” quantities, which means that they have both field strength and direction. The electric field is generated by voltage, and, since voltage is relatively stable, the strength of the electric fields produced by power systems are relatively constant over time. Magnetic fields, however, are produced by electric current and will vary proportionately to the amount of current being used. Consequently, industrial and commercial buildings, which have areas of high concentration of high current, particularly at the entrance to the building, will have high magnetic fields in these areas.

The primary difference between electric fields and magnetic fields is that electric fields are blocked by most common building materials, while magnetic fields are extremely difficult to block. Accordingly, most of the issues regarding EMF center on magnetic fields. In commercial buildings, the average level of magnetic fields will vary between a range of 0.5 and 4 milliGauss (mG), depending on location. In areas of high current concentration, values greatly above these are common.

From the view of the real estate industry, the concern about magnetic fields falls into two categories: equipment interference and health problems. Both of these issues revolve around the field strength of EMF, but a host of other metrics can play a part, including frequency of exposure, intermittency, how often and how much the exposure changes over time, and harmonics. The location and strength of elevated fields and how to rectify the problem are critical tools of the real estate professional, since problems arising from equipment interference will often cascade into a series of occupancy problems, leading to diminished utility and value of the building.

Sources of Magnetic Fields

Devices that carry heavy Alternating Current (AC) are the most obvious sources of magnetic fields: transmission lines close to the building, transformer and network protection vaults, electric service panels, circuit boxes, and bus ducts. Less obvious sources include conduit running through the walls or floors, wiring errors, fluorescent lights, and other high-current electrical equipment.

Magnetic fields from Direct Current (DC) can be generated by passing trains, elevators, or standby power supplies. The magnets frequently used in MRI and NMR equipment in commercial or health facilities are also sources of magnetic fields from DC. A source unknown to many property managers is a building's steel structure, which may have become magnetized during construction, and now generates its own DC field. In some situations, a combination of AC and DC sources can cause both types of fields to occur in the same area. For example, trains and elevators, which combine high AC or DC current-flow with a quickly moving object, are responsible for both causing and disturbing a field, and thus, create even more complicated interference scenarios.

Equipment Interference

Computer monitors are the most frequently cited example of equipment that is receptive to interference from magnetic fields. Elevated magnetic fields can cause the screen to jitter, flicker, or distort. New, larger, and more sophisticated monitors are the most sensitive to the effects of EMF and can display problems in fields as low as 3 to 5 mG. Almost all monitors will become unstable in fields above 10 mG. CPUs, peripherals, and data networks can all potentially become unstable in elevated magnetic fields. Broadcast and audio equipment will actually emit a noise indicative of interference. It is usually an audible "hum."

Medical equipment is not immune to the effects of magnetic fields either: EEG, EKG, EMG, scanning equipment, and electron beam microscopes are all exquisitely sensitive to external fields. Implanted personal medical devices, such as pacemakers and insulin delivery systems, can be affected by elevated magnetic fields.

Planning is Essential

The best strategy for dealing with a magnetic field problem is to plan for it; the first line of defense is planning the building's space allotment. Because magnetic fields generally will diminish quickly over distance, keep sensitive equipment away from large sources of EMF.

Be aware of the locations of transformers, service panels, and elevators in your facility. If possible, map heavy current-carrying conductor runs in the walls and floors. While areas immediately adjacent to heavy current-carrying devices may not allow optimal use of sensitive equipment, they can be designated as low-technology areas, such as for storage space or as a conference room.

If renovations are planned for the building, especially if they include any alterations to the building's power system, it is advisable to evaluate the potential for increased field levels in the newly constructed or improved space.

Identifying Problems

Often, magnetic field interference problems will emerge after a building has been remodeled or upgraded. This usually occurs if spaces previously not used for computer or medical technology are now designated for such use. If computer monitors and other sensitive equipment begin to display signs of instability, you should suspect EMF problems.

Once you encounter signs of elevated magnetic fields, your first course of action is to determine the source. The source and strength of the fields will determine which mitigation options are available to you. Fields concentrated in a specific area will most likely reveal an obvious source, such as a transformer vault. Moderately elevated fields that are spread out over a large area may suggest, however, a net-current problem from wiring errors.

To evaluate your situation, it is advisable to get a survey taken of the fields. Your local electric utility may be able to provide a low or no-cost preliminary survey. Another option is to rent or buy a magnetic field meter. There are several inexpensive and reliable AC field meters available, but DC fields require a separate meter that can be quite costly. It may also be worthwhile to get a professional, independent company to conduct a survey that will provide detailed information; the best of them will include an appropriate mitigation plan.

Managing the Problem

If mitigation is in order, in many cases, the first and least expensive option is to increase the distance between the affected device(s) and the source. Magnetic fields generally diminish quickly with distance, so moving a monitor, or even an office, further from a power source may solve the interference problem. Unfortunately, in many situations this option has the downside of diminishing the utility of prime office space.

The next option to consider is lowering the fields that are being created through engineering techniques that can increase the natural cancellation of the fields. It may be possible to decrease the fields by reconfiguring the transformer arrangement or by compacting the cabling. In situations where the source is wiring errors, decreased fields are achieved by isolating and correcting the errors, which will enable the natural cancellation of the fields.

Finally, area, source or device shielding may be considered. Area or source shielding can be expensive, but can effectively and permanently restore the utility and value of an affected space. Device shielding may provide an effective solution if just a couple of monitors are affected or if the source is transmission lines running outside the building.

Contact with magnetic fields may be unavoidable, whether it's naturally occurring or artificially generated. In addition, our use of electricity is increasing at the rate of about two percent a year as our dependence upon technology grows, so our production of EMF is rising. These two factors, plus our increasing workplace density, make magnetic field interference a concern for today's facilities, many of which already have areas of elevated magnetic fields. Engineers and architects are studying the creation of "low-EMF" buildings, facilities designed to be immune to magnetic field interference problems. Until we are managing those, however, the answers lie in awareness and planning during the layout or renovation of a facility to prevent costly mitigation. If mitigation is necessary, knowledge about the issues can speed diagnosis of the problem and lead to finding the most effective solution.

Michael L. Hiles is president of the Los Angeles-based Field Management Services. With a background in electrical engineering, he has served in a number of capacities in the television, telecommunications, videographic, and teleconferencing systems industries. He regularly speaks about topics involving magnetic fields. He can be reached at Michael.Hiles@FMS-Corp.com.