-From the book on CD-ROM,

The COMPLETE MICROWAVE OVEN SERVICE HANDBOOK
Operation, Maintenance, Troubleshooting and Repair

Copyright © 1989-2013 J. Carlton Gallawa . All Rights Reserved WorldwideLearn how to repair commercial and residential microwave ovens

3.1 INTRODUCTION

In 1926, Soviet naturalist Vernadskii wrote, "We are surrounded and penetrated, at all times and at all places, by eternally changing, combining, and opposing radiations of different wavelengths." He was referring to electromagnetic radiation emanating from the sun and other sources in earth’s galaxy that finds its way into our atmosphere. Vernadskii had no way of knowing that within fifty years his observation would apply as well to radiation generated here on earth by his fellow man. —Paul Brodeur, The Zapping of America, (Norton, 1977) p. 15.

Since the development of radar, man’s ability to generate and harness microwaves has resulted in such a proliferation of devices using microwaves that today virtually everyone on earth is affected by them to some degree. Some environmentalists call it "electronic smog," and one United States government agency warned that the levels Americans are exposed to every day, without even being aware of it, may be dangerous.

Particularly in some urban areas, microwave and related radiation is estimated to be up to a billion times or more as great as that which naturally exists in the environment. And sources of this kind of radiation are increasing rapidly.

Airports have navigational systems that use microwaves, and police radar operates on microwave frequencies. Television, telephone, and computer signals are transmitted by microwaves. Broadcasting, surveillance, and communications satellite systems utilize microwaves, as do some air pollution monitoring systems. Motorist-aid call boxes along the highway, many burglar alarm systems, and some automatic garage door openers work because of microwaves.

The world of medicine uses them for sterilization, to retard tumor growth, and to treat sore muscles. Industry and science each have their own uses for microwaves. Researchers in Canada have developed an aircraft that can stay aloft for months at a time without fuel. The plane is powered by electricity, which is beamed up as microwave energy, then converted back into electrical energy, which powers the engine. The military, by far the largest users of microwave devices in today’s world of electronic warfare, employ microwaves for such things as guidance systems for nuclear missiles and antimissile missiles, range finders for tanks, and for eavesdropping.

The Soviets allegedly used microwaves to irradiate the American Embassy in Moscow. Conversely, American warships would, reportedly, pull alongside Russian surveillance trawlers on the high seas, turn on their radars at full megawatt power, and "paint" the Soviet vessels with radiation. This would burn out the trawlers’ electronic listening devices, and probably accounts for the fact that Russian sailors were seldom seen on deck. — Paul Brodeur, The Zapping of America, (Norton, 1977) p. 308.

This era of energy pollution has brought about growing concern regarding the potential risks involved in exposure to low-level microwave radiation, in particular from microwave ovens, the most common consumer use of microwave energy. With the skyrocketing popularity of microwave ovens, some are seriously questioning the wisdom of bringing these microwave-emitting devices into our homes when the effects of microwaves on the human system are not yet completely understood. Extensive research that began particularly in the mid-1970’s in the United States, and as far back as the 1930’s in Russia, is now rendering some interesting and controversial results.

3.2 MICROWAVES—HOW DANGEROUS ARE THEY?

If microwaves in an oven can cook a piece of beef, they will also have the same effect on human tissue if 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. Just as it is the heat produced by a hot stove that causes the careless cook to voice a sudden unsavory expletive, so too, 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. Exposure to high levels of microwaves can cause cataracts. Also, the stomach, intestines and bladder are especially sensitive to thermal damage from high levels of microwaves. Likewise, the testes are very sensitive to changes in temperature, since sperm can be formed only at temperatures lower than that of the body itself. Thus, accidental exposure to high levels of microwave energy can alter or kill sperm, producing temporary sterility. The question is: How intense would levels of microwave energy have to be to create such a danger?

3.3 MEASURING MICROWAVES

The power density of microwaves is determined by measuring the amount of energy that flows through one square centimeter (a square centimeter is about the size of an aspirin tablet) of space in one second. Western scientists believed that serious injuries could result only at levels of 100 Milliwatts per square Centimeter (mw/ cm2) or higher. It was theorized that a built in safety factor of 10 times would be a safe margin. So, in the mid-1950’s a voluntary industry standard of 10 mw/cm2 (or, one-tenth of 100 mw/cm2) was adopted.

In 1971, due to the concern of the Department of Health, Education and Welfare (now the Department of Health and Human Services), the standard for allowable leakage from microwave ovens in the United States was set by law to the present, more stringent, levels of 1mw/cm2 (at a distance of five centimeters--see Section 15.7) prior to acquisition by a purchaser, and 5mw/cm2 thereafter. These safety standards were based on the belief that the only danger from exposure to high-intensity microwave energy was a thermal or overheating effect.

3.4 SOVIET STANDARDS

In the U.S., exposure standards were being developed mainly under the American National Standards Institute by a broad group of scientists and by representatives of users and manufacturers. While in East European countries and, in particular, Russia, the exposure standards were being determined by a specialized research institute on occupational health. Rather than concentrating on the effects of high-intensity levels, ‘Soviet scientists were focusing their efforts on the lesser-known effects of prolonged or repeated exposure to low levels of microwaves. Their research, which began quite some time before that of their Western counterparts, has yielded some rather unsettling reports. Soviet studies show that long-term exposure to low levels of microwave energy could result in unpleasant effects that are not attributable to over-heating (or thermal effect) alone. These effects could be seen at exposure levels at and below 10mw/cm2, which is the occupational safety standard in the U.S.

The USSR, and other European countries, has thus set their own strict guidelines for microwave safety, concluding that Western safety standards are simply not safe. For example, Russian workers are required to wear protective goggles any time they are temporarily exposed to a microwave radiation level of 1mw/cm2, a level routinely allowed to leak (although in recent years, rarely does) from U.S. microwave ovens.

These reports have provoked a reexamination of Western safety standards and heightened experimentation. Several American laboratories have since found low-level exposure to microwaves to cause cumulative harmful effects on the eye, such as cataracts. (Cumulative means that one low-level dose in itself would not be enough to affect you, but if you add another and another, and so on, then eventually the effects would be seen.) Research also reports a reduction in personnel efficiency, and in the ability to perform certain tasks, and even a possible link to cancer. Thus, while not all the research is complete, there has been enough evidence in support of Soviet findings to likely cause an eventual toughening of U.S. standards.

3.5 WHAT ARE SAFE LEVELS OF EXPOSURE?

No one really knows for sure how to interpret the emerging results as painstaking experimentation continues. One thing they do know, however, is that there is a non-thermal effect from microwaves at levels that many people may be exposed to on a daily basis. What degree of danger does this non-thermal effect represent? The answer to that 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?

So, what are safe levels of exposure to microwaves? While vigorously warning of the invisible dangers involved with non-ionizing radiation, Dr. Milton M. Zaret, a professor of ophthalmology, and a long time student of the biological effects of microwaves, answers: "I have no idea what a safe level is, I don’t think anyone in the world knows what a safe level is."

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. For example, researchers find it quite difficult to simulate the conditions (with animals) under which people use microwave ovens. Since no one can say with certainty what levels of exposure are safe, the course of wisdom would be, as a U.S. government spokesman pointed out, to avoid "exposure to any unneeded radiation.’’

3.6 HOW FAR AWAY IS SAFE?

One pertinent characteristic of microwaves is that they disperse and dissipate very quickly in the atmosphere. For example, the maximum allowable leakage from a microwave oven (after the sale) is 5 milliwatts of microwave radiation per square centimeter at approximately 2 inches from the oven surface. However, as Figure 3-1 illustrates, 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 holding your hand immediately above a burning candle as opposed to holding it 4, 8 or 12 inches away. Say you are standing 2 inches away from a microwave oven, and are being "zapped" by 5mw/cm2 of microwave energy, then you wisely step back to a distance of 20 inches or roughly an arm’s length. Your level of exposure would drop by a factor of 100, (the square of the distance) to .05mw/cm2, a level compatible even with stringent Soviet standards, (present Soviet occupational standard allows up to 0.1mw/cm in no more than two hours). However, it must be noted that Czech scientists have reported some effects even at these infinitesimal levels. This, combined with the opinion of Russian scientists that microwave effects are cumulative, certainly underscores the need for consumers and servicers alike to observe certain common sense precautions.

• Stay at least an arm’s length away from the front of an operating oven. This is especially so with pregnant women according to a U.S. government agency, which states that the human fetus is "probably the most sensitive segment of the population potentially exposed to microwave radiation." Children represent another sensitive segment of the population. Never should anyone, and especially children, stand gazing into, or directly against an operating microwave oven.

• If the door of an oven will not close properly, is bent, warped, tampered with, or otherwise damaged in any way, DO NOT OPERATE the oven unless you are a qualified servicer with an approved RF survey meter in hand.

• Never operate an oven when it is empty. This creates a no-load condition, which can damage the oven and cause excess leakage.

• Never inactivate, interfere with, or try to adjust the built-in safety interlock system of an oven, unless you are properly equipped and qualified to do so. Tampering with safety interlocks would be as foolish as disconnecting the brakes on a car.

• The Food and Drug Administration recommends that microwave ovens not be used in home canning. It is believed that they do not produce or maintain temperatures high enough to kill harmful bacteria.

Observing these safety suggestions, as well as others that will be presented in subsequent chapters of this book, will help to minimize exposure levels and the risk of serious accidents.

—Our thanks to the publishers of AWAKE! Magazine. Much of the preceding information was adapted from the 3/22/81 (pp. 13-15), 4/22/81 (pp. 12-15), and 5/22/81 (pp. 27-28) issues of AWAKE!

3.7 MICROWAVES AND CARDIAC PACEMAKERS

It has been a subject of great concern, especially for many heart patients, that stray leakage from microwave ovens could interfere with the proper operation of their cardiac pacemakers. The fact is, there are at least 20 other known sources of electromagnetic interference that could also cause a pacemaker to malfunction if it were non-shielded. RF interference is generated by such common items as: electric shavers, auto ignition systems, walkie-talkie radios, fluorescent lights, and dial telephones. Many more of these electronic interference-emitting products are commonplace items even in hospitals; diathermy, electro-surgical units, electric bed motors, elevators, personnel pagers, electric heaters and heating pads, to mention a few.

The problem has been resolved, for the most part, with the development of a new shielded pacemaker. Since microwaves, or any other type of electronic interference, cannot penetrate their stainless steel casing, the possibility of harm to people who wear these modern heart pacemakers is extremely remote. In an effort to determine the overall susceptibility of these units to electromagnetic interference, U.S. government agencies contacted all known U.S. manufacturers of cardiac pacemakers. Their findings indicate that less than 1% of all pacemakers are sensitive to electronic interference and this number is rapidly decreasing. Apparently, the external demand type of pacemaker continues to be a particularly sensitive device, so wearers of this type of pacemaker should avoid all possible sources of electronic interference. In fact, all patients with pacemakers would be well advised to contact the manufacturer of the unit and consult with their physicians for the final word on this matter.

While signs that warn "MICROWAVE IN USE" are not a federal requirement, local administrations or establishment owners may prefer to display such signs for various reasons. For example, some may display warning signs for their own protection (like a "watch your step" sign), to avoid the possible psychological trauma that could be suffered by an unwary pacemaker patient who suddenly discovers that he is sitting next to an operating microwave oven.

3.8 RADIATION INJURIES FROM MICROWAVE OVENS?

A 1986 report on microwave oven radiation by, among others, the Food and Drug Administration, has this to say: "There have been allegations of radiation injury from microwave ovens. The injuries known to FDA, however, have been injuries that could have happened with any oven or cooking surface. For example, people have been burned by hot food, spattering grease, or steam from food cooked in a microwave oven.

3.9 COLOR TELEVISION EMISSIONS

While not necessarily related to microwave safety, these types of emissions merit brief consideration because they are in the same family as microwaves, and are very often the subject of consumer concern.

Emissions from color TV sets are of the nature of X-rays, which are more serious and penetrating than low-level microwaves. However, modern circuitry improvements, combined with the stringent regulatory control of the Food and Drug Administration (FDA), have brought color TV emission levels to below that of certain natural background radiations. Just as there is a greater risk of excessive leakage from older, or improperly serviced, microwave ovens, so too, the same potential hazard exists with color television sets. In either case, it would be the course of wisdom to observe appropriate precautions. Use discretion when buying a used color TV set or microwave oven. Selection of a repairman should be done with scrutiny. And, sit or stand no closer to the unit than is necessary.

A Final Word

As with so many modern conveniences, the benefits must be weighed against the hazards, the risks against the rewards. Sometimes this can be a delicate and a controversial balance. So, while these devices must be used at one’s own risk, the application of common sense and caution will certainly minimize the risk factor in this balance. A growing knowledge and understanding of electromagnetic radiation is producing a better perspective, enabling a more clear definition of just what the balance is in each case and allowing each person to draw his or her respective a conclusions accordingly. Meanwhile, the controversy, the debate, and the research continue.

And, so do the repairs...

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Copyright © 1989-2013 J. Carlton Gallawa . All Rights Reserved Worldwide