Questions and Answers About EMF Electric and Magnetic Fields Associated with the Use of Electrical Power.
January 1995.

Your EMF Environment

Q. What are some typical EMF exposures?

A. First, "exposure" must be defined. Scientists are still uncertain about the best way to do this, because experiments have shown that several aspects of the fields may be relevant to biological effects. Should exposure be an average of changing magnetic field levels over some time period, or should it focus only on time spent in high fields above some threshold value? Are rapid field changes important? Does the frequency content play a role? Even though the average field level has been used widely to represent EMF exposure, it is possible that other definitions may relate more closely to any possible effects.

Second, EMF in the environment is very complicated. We are usually exposed to EMF from a large number of sources every day. Fields change both in time and space. A person's EMF exposure depends to a large degree on what he or she is doing in the field at the time.

Several kinds of small meters are now available that can be carried or worn by a person to record magnetic field exposures automatically. The figure below is an example of data collected with one of these meters. The magnetic field was measured every 24 seconds over a 24-hour period. For this person, field exposure at home was very low. The occasional spikes (short exposures to high fields) occurred when the person drove or walked under or over power lines or was close to appliances in the home or office.

Some studies have used these automatic gaussmeters to measure human exposure to magnetic fields (see picture above). These studies tend to show that appliances and building wiring contribute to the low-level background magnetic field exposure that most people receive. People living close to large power lines tend to have higher overall field exposures. However, as shown (97K gif), there is much individual variation among homes.

In this graphic we see a random sample of the magnetic field exposure of an employee over a 24-hour period. This person works in an office with a computer and lives in an all-electric "very low current configuration" house.