EMF IN YOUR ENVIRONMENT

What are electric and magnetic fields (EMFs)? What common EMF sources do we encounter during a typical day? This publication compares the strength of 60 hertz magnetic fields produced by common electrical items and shows you how their strength diminishes as you move farther away from them.

We still have a great deal to learn about electric and magnetic fields (EMFs). We really don't know if typical, everyday exposures to EMFs affect human health. Some studies indicate that they might -- others suggest otherwise. Most of the recent research on possible biological effects of 60 hertz EMFs suggests that the magnetic, rather than the electric, fields are more likely to produce significant effects. Therefore, this publication focuses on them. The information presented here has to do with the strength of the magnetic field; however, we aren't certain that the strength of the field is the only important consideration. It may turn out that other factors are also important, such as how long the exposure lasts or whether particular characteristics of the field change rapidly. Future research is likely to reveal that the information given in this publication is only part of the story -- that is the chance we take in providing a public information document this early in the study of a complex environmental health issue.

What Are Electric and Magnetic Fields?

Electric charges create electric fields. Electric charges which move (i.e., electric current) create magnetic fields. An appliance that is plugged in, and therefore connected to a source of electricity, has an electric field even when the appliance is turned off. To produce a magnetic field, however, the appliance must be not only plugged in, but also operating, so that the current is flowing.

This illustrates the point that the higher the frequency, the shorter the wavelength. The wavelengths are infinitely long at the bottom and infinitesimally short at the top of the spectrum so, obviously, the drawing cannot be done to scale.

The electric current we use in our everyday life produces certain kinds of electric and magnetic fields. There are many other kinds of electric and magnetic fields as well, found throughout nature. The term "electromagnetic" field implies that the electric and magnetic fields are interrelated.

These fields can be characterized by either their wavelength or their frequency, which are related. The amount of energy an electric or magnetic field can carry depends on the frequency and wavelength of the field. The wavelength describes how far it is between one peak on the wave and the next peak. The frequency, measured in hertz, describes how many wave peaks pass by in one second of time.

The Electromagnetic Spectrum

If you take all the different kinds of electromagnetic fields we know about and place them on a chart, from the lowest frequency (i.e., lowest energy) to the highest, you have a chart of the electromagnetic spectrum. (See chart on the previous page.) The low end of the spectrum includes electric and magnetic fields produced by everyday electrical appliances. At the top of the spectrum are X-rays and gamma rays.

When you hear about "EMFs" in the news media, the term usually refers to electric and magnetic fields at the extremely low frequency (or ELF) end of the spectrum, such as those associated with our use of electric power. The term "EMF" can be used in a much broader sense as well, encompassing electromagnetic fields across the spectrum. When we use "EMF" in this brochure we mean extremely low frequency (ELF) electric and magnetic fields. We should note that in the ELF range, electric and magnetic fields are not coupled or interrelated in the same way that they are at higher frequencies, so it is actually more accurate to refer to them as "electric and magnetic fields" rather than as "electromagnetic fields." In the popular press, however, you will see both terms used, abbreviated as "EMF."

Electric fields from most appliances primarily create charges or current on or near the surface of the body and not in the internal organs. Magnetic fields, however, pass through the body and actually induce electrical currents within the body. We don't know exactly what effect, if any, this has on the different internal organs, but many studies are now underway to find out.

60 Hertz Electric And Magnetic Fields

It is relatively easy to shield people from exposure to electric fields using commonly available materials. Magnetic fields, however, can pass through anything. Even though both are present around appliances and power lines, more recent interest and research have focused on potential health and biological effects of magnetic fields of various strengths.

This publication presents information regarding magnetic fields associated with 60 hertz alternating current (AC) electric power -- that is, the kind of electric power we use in North America which flows back and forth or alternates at a rate of 60 times per second (60 hertz). We will not focus here on equipment that is powered by "direct current" (DC) such as battery-operated appliances. The magnetic fields created by direct current are primarily static; that is, they do not vary with time as do AC fields. Direct current (DC) magnetic fields have not raised as many questions about potential health concerns as have the time-varying fields created by alternating current (AC). We should point out, however, that some DC-powered equipment can produce alternating magnetic fields, but these are usually not 60 hertz fields.

Other Electromagnetic Frequencies

Although the information presented here has to do with the low frequency magnetic fields associated with 60 hertz electrical current, we should note that some appliances, such as microwave ovens, baby monitors, and video display terminals, use 60 hertz electrical energy to create other electromagnetic frequencies.

The measurements we give for microwave ovens, for example, describe the magnetic field that results from the 60 hertz electrical current used to operate the oven. We are not describing the magnetic field associated with the approximately three billion hertz microwaves inside the oven which heat the food and from which people are protected when the door is secured properly.

Oddly enough, we can be easily shielded from the higher frequency microwaves' magnetic fields, but not from the 60 hertz magnetic fields. This is because even though the microwave's frequency is higher, its length is much, much shorter (about 1 cm) than the wavelength of a 60 hertz field (about 5000 kilometers). The shorter wave can be blocked by materials such as thin metal sheets, whereas the much longer wave cannot.

Potential Health Concerns Associated With Electric and Magnetic Fields

Electric and magnetic fields from 60 hertz electric power (as well as microwaves and radio waves) are sometimes called non-ionizing radiation. The term "radiation" simply means energy transmitted by waves. "Ionizing" radiation has enough energy to strip electrons from atoms. (X-rays are a form of ionizing radiation.) Extremely low frequency EMF cannot do this. Higher frequency non-ionizing radiation, such as microwaves, can heat up biological tissue by vibrating molecules. The lower frequency 60 hertz EMFs cannot. Because of their relatively lower energy, 60 hertz EMFs were not, until recently, thought to be connected with any potential health problems.

There are no national standards in the United States for exposure to 60 hertz electromagnetic fields. Several states have formally adopted standards to limit the permissible magnetic strength along rights of way of electric transmission lines. Federal legislation has been enacted to establish and support national EMF research and public information programs, but no exposure standards have been proposed.

Some recent scientific studies have suggested a link -- a statistical association -- between exposure to 60 hertz EMFs and specific types of cancer, primarily leukemia and brain cancer. Other studies have found no such association (see Appendix B). In a sense, this can be compared to circumstantial evidence in a court of law. Laboratory studies have shown electromagnetic fields to affect cells in various ways, but whether these effects are important in terms of human health is still not clear. Almost everyone involved in EMF research agrees that much more needs to be learned before conclusions can be reached about the relative safety or harm of 60 hertz EMF exposure.

Some people doubt that the EMFs generated by 60 hertz electrical appliances and internal household wiring have any significant effect on human health, because they know that the earth's magnetic field, to which we are all constantly exposed, is stronger (sometimes over 100 times stronger) than the magnetic fields produced by many of the appliances listed in this publication. However, the earth's magnetic field is primarily a DC field rather than a time-varying field. Our bodies seem to react differently to these different types of fields so comparing them can be misleading.

At this point, we are not at all sure that exposure to EMFs such as we find in our everyday environment has an adverse effect on our health. However, we cannot say with certainty that such exposure is safe for us, either. More research is needed -- and is underway. Meanwhile, many people have expressed an interest in having information about everyday sources of EMF exposure. This booklet is in response to that interest.

MAGNETIC FIELD MEASUREMENTS OF EVERYDAY ELECTRICAL DEVICES

Appliances and Magnetic Field Strengths

Magnetic fields from individual appliances can vary considerably, depending on the way they were designed and manufactured. One brand of toaster, for example, may generate a much stronger magnetic field than another. The strength of the magnetic field is measured in units of gauss (G) or milligauss (mG). A milligauss is 1/1000th of a gauss. (The international standard unit is microtesla which is the same as 10 milligauss.)

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