Microwave Ovens

MICROWAVES  used in microwave ovens oscillate at 2450 million cycles per second (MHz). On the  frequency spectrum  , that region is located at the lower end of the radar band, slightly above the frequencies used for UHF (ultra-high frequencies) TV channels, and safely within the  NON-ionizing region.  However, it is important to note: Although microwaves do not carry enough energy to be  ionizing,  they can be dangerous.

Energy.

If microwaves can cook a piece of beef, these waves will also have the same effect on human tissue if it is exposed to high enough intensities for a long enough period of time. Certain body organs are particularly sensitive to this thermal effect. "Thermal" means heat. Thus, it is the heat produced by a hot stove that causes the careless cook to utter a sudden unsavory expletive. Likewise, it is the heat generated by the microwaves that creates the hazard in this case.

For example, if the lens of the eye were exposed to excessive heat from microwaves, its circulatory system would be unable to provide sufficient cooling, and it would cook like the white of an egg. Also, the stomach, intestines, and bladder are especially sensitive to thermal damage from high levels of microwaves. Similarly, the testes are very sensitive to changes in temperature, because sperm can be formed only at temperatures lower than that of the body itself. Therefore, accidental exposure to high levels of microwave energy can alter or kill sperm, producing temporary sterility.

What Are Safe Levels of Exposure?

No one really knows for sure. Several American laboratories have found that low level exposure to microwaves can cause cumulative effects to the eyes, resulting in cataracts. Research also reports a reduction in personnel efficiency, and even a possible link to cancer. As painstaking experimentation continues, one thing is certain: There is a non-thermal effect from microwaves that many people are exposed to on a daily basis. What degree of danger does this non-thermal effect represent? The answer to that question has to do with the controversial difference between a simple biological effect , and a serious biological hazard. For example, a reduction in the ability to perform certain tasks may be the effect, but at what point does that effect constitute a hazard?

The effects of long term exposure to low levels of microwaves, and their significance to human health, will become clear only after large numbers of people who are being exposed to microwaves are studied for many years. Studies are being done with animals, but it is difficult to translate the effects of microwaves on animals to possible effects on humans. With animals, for example, researchers find it difficult to simulate the conditions under which people use microwave ovens. Because no one can say with certainty what levels of exposure are save, the course of wisdom is, as one U.S. Government spokesman pointed out, to avoid "exposure to any unneeded radiation.

How Far Away Is Safe?

One pertinent characteristic of microwaves is that they disperse and dissipate very quickly in the atmosphere. Under Federal guidelines set by the Department of Health and Human Services (DHHS), the maximum allowable leakage from a microwave oven [after the sale] is 5 milliwatts [or 5 thousandths of a watt] per square centimeter [or within the area the size of an aspirin tablet], as measured at about 2 inches from the oven surface. However, as you move away from the oven, the level of exposure to any energy that may be leaking decreases dramatically. This may be likened to the difference between holding your hand just inches above a burning candle, and then moving it 10 or 12 inches away.

To illustrate: Let's say you are standing just 2 inches away from an operating microwave where you are being zapped by 5 milliwatts of microwave radiation. Then, you wisely step back to a distance of 20 inches, or roughly an arm's length away. Your level of exposure would drop by a factor of 100 [the square of the distance] to an infinitesimal .05 milliwatts. When you consider that the typical cooking power of a microwave oven is in the range 600 to 700 watts, and even higher in some models, .05 milliwatts is clearly a tiny amount.

Unsettling Reports

Yet, the question remains: Is exposure to low levels of microwave radiation dangerous to humans? Soviet research has yielded some rather unsettling reports. Rather than concentrating on the effects of high-intensity levels, scientists in the U.S.S.R have focused their efforts on the effects of prolonged or repeated exposure to low levels of microwaves. Their studies show that long-term exposure to low levels of microwave energy could result in unpleasant effects that are not attributable to the thermal (heating) effect alone. So, the U.S.S.R and other European countries have set their own strict guidelines for microwave safety, concluding that Western safety standards are simply not safe.

For instance, Russian workers are required to wear special goggles any time they are temporarily exposed to a microwave radiation level of 1 milliwatt per square centimeter. Remember, the U.S. Federal Standard is 5 milliwatts per square centimeter. (It should be noted that some manufacturers have voluntarily established their own, more stringent, standards. For example, Amana, Menumaster, Caloric, Modern Maid, and Sharp have lowered the maximum allowable leakage from 5 mw/cm 2 to 4 mw/cm 2 .)

Inasmuch as the significance for humans of repeated exposure to low levels of microwave radiation is still unclear, there is enough evidence to warrant certain commonsense precautions:

   1. Stay at least an arm's length away from an operating microwave oven
   2. Do not operate an oven when it is empty
   3. Do not operate an oven if the door will not close properly or is in any way damaged
   4. Never tamper with the safety interlock switches or the fuse

My thanks to the author J. Carlton Gallawa