Published June 6, 2006

In an effort to better combine the editorial content of our magazine with our newly developed and retooled on-line presence, we have decided to expand Harlan's RF and microwave engineering advice into a monthly feature that appears in Microwave Journal.

Harlan has selected one question from his "Ask Harlan" column to be featured in the March issue. Harlan will be monitoring the responses and will ultimately choose the best answer to the question. Although all of the responses to the featured question will be posted on our web site, we plan to publish the winning answer in the May issue.

You be the expert: The answers to the May Question of the Month are below

Verne Reynolds has submitted this month's question:

Dear Harlan,
My wife wants to know if she is endangered by radiation from our stove-top kitchen microwave. When cooking, her face may only be a foot away from the microwave, for minutes at a time. Is she in any danger? Are there any long-term effects we should be concerned with?

From: John Osepchuk, Full Spectrum Consulting

1. She is in no danger. 2. There are no long-term effects to be worried about. These conclusions are supported by the following: 1. The typical microwave oven leakage with food in the oven is about 0.1 mW/cm2 at 5 cm from the oven. 2. Federal regulations limit this leakage to 5 mW/cm2 at 5 cm. 3. Even if leakage (emission) is at 5 mW/cm2, the intensity drops off at one foot to at most 0.5 mE/cm2, which is well below the safe exposure limit for the general public in the just-issued IEEE C95.1-2005 Standard, which in itself incorporates a very large safety factor much greater than 10 against harm. The C95.1 limit is 1 mW/cm2 but this is a whole-body average and also averaged over any 30 minutes. 4. Note that at the FDA limit the oven is leaking (radiating) the order of 1 W of microwave power. This is much smaller than the microwave diathermy power of up and even greater than 125 W, applied to millions of patients, at various places including the head, for beneficial purposes. This power is also comparable to the power (up to 0.6 W) radiated from cell phones, which are held to the head whereas the microwave oven is not brought close to the head. 5. Historically, electrophobia, based on poor-quality research, has caused fear of microwave ovens, police radar, VDTs, power lines and now cell phones and wireless base stations. Over time all of these fears have been judged baseless by scientists, the government and the general public.

From: Mikael Carlsson, Student

The microwave leakage is generally below the guideline for the safety limit, less than 5 mW/cm2 measured 5 cm from the oven. This limit is far below the known levels of radiation causing injury. If you are even further away (say one feet, ~ 30 cm which is about 6 times that distance) the radiation would have dropped to 1/36, or 0.14 mW/cm2 (drop as square of distance). According to the safety limits there should be minimum effects of injury for normal use and in the long term.

From: Nagaraju Nerella, Conexant Systems

The radiation caused by microwaves is quite dangerous. It leads to long-term effects on the body and genetics. Microwave radiation is odorless, invisible and therefore hard to detect. Microwave oven radiation is present whenever a microwave oven is turned on. The microwave energy causes the water molecules in the food to vibrate rapidly. This rapid vibration produces heat, which, in turn, cooks the food. It can also penetrate through living tissue, which is why exposure is harmful to our health. Once you turn off the oven, the microwaves disappear. Until then, however, you may be exposing yourself to dangerous levels of radiation leakage. A microwave oven has in it a magnetron, which is a radio transmitter. If it was on a radio mast (do not try this) it would be able to send radio signals a long way. However, it is inside a metal box, which keeps the signal in. The frequency of the transmitter is 2450 MHz (megahertz), which is a wavelength of 12 cm (that is why it is microwaves). The radiation level inside the microwave oven will be very high but the outer radiation will be less and it will meet FDA regulations. Over a long period of usage, the radiation from the oven will be more than 10 percent from the study, which is dangerous. When your wife's face is very close to the oven, and if the microwave oven is not in compliance with FDA regulations, there may long-term effects. From the conclusions of Swiss, Russian and German scientific clinical studies, we can no longer ignore the microwave oven sitting in our kitchens. Based on this research, we will conclude this article with the following: 1). Continually eating food processed from a microwave oven causes long term - permanent - brain damage by "shorting out" electrical impulses in the brain [de-polarizing or de-magnetizing the brain tissue]. 2). The human body cannot metabolize [break down] the unknown by-products created in microwaved food. 3). Male and female hormone production is shut down and/or altered by continually eating microwaved foods. 4). The effects of microwaved food by-products are residual [long term, permanent] within the human body. 5). Minerals, vitamins and nutrients of all microwaved food is reduced or altered so that the human body gets little or no benefit, or the human body absorbs altered compounds that cannot be broken down. 6). The minerals in vegetables are altered into cancerous free radicals when cooked in microwave ovens. 7). Microwaved foods cause stomach and intestinal cancerous growths [tumors]. This may explain the rapidly increased rate of colon cancer in America. 8). The prolonged eating of microwaved foods causes cancerous cells to increase in human blood. 9). Continual ingestion of microwaved food causes immune system deficiencies through lymph gland and blood serum alterations. 10). Eating microwaved food causes loss of memory, concentration, emotional instability and a decrease of intelligence. For more information, visit:

From: Sandeep Satav, RCI

1. After starting the microwave, she should not be very close to it because if the door accidently opens she may get a few RF burns. If the microwave has a good shielded door with 'Locking-alarm-while On' facility, it is safe enough. 2. Even a little dose of RF over a long period may cause some illness like an eye-problem, grey hair, etc. The woman should not look into the microwave from a close distance through its window. You can contact the microwave vendor to see if they have provided see-through shielding. 3. Long-term effects like cancer, etc., are not yet confirmed, but it is always advised to handle it with the above precautions.

From: Peter van der Velden, Philips Semiconductors

A microwave emits waves. Although these are well shielded by the casing of a microwave, remember that waves have a wavelength. The shorter this length, the easier it penetrates the body. Now the "heat-waves" of a fire or central heating are much shorter and do slightly penetrate, thus heating up your body. The even shorter wavelength of UV can harm the body and X-ray waves do penetrate the body so exposure should be limited. So the waves of a microwave do not harm. The wavelength is too long to be harmful. Although microwaves are able to warm up products, shielding prevents products or people outside this appliance to warm up.

From: Robert Johnson, L-3 Communications

Microwave ovens have long been covered under a Federal Regulation (21 CFR 1030.10) that limits emissions to limits well within international exposure limits for humans. Ovens must emit less than 5 mW/cm^2 at a distance of 5 cm (the average distance between the end of the nose and the human eye!) after purchase. This contrasts with exposure standards such as IEEE C95.1, wherein a person could be exposed to as much as ~8 mW/cm^2, averaged over the whole body, continuously. Also, remember the inverse square-law of radiation comes into effect here and says that when you double the distance the power will decrease by a factor of four. So at 10 cm distance levels will probably be less than 0.25 mW/cm^2 and so on at greater distances. Therefore, emission limits are very conservative and practically guarantee that human exposure limits will never be exceeded. As far as long-term exposures are concerned, there are no reputable, repeatable experiments that prove long-term exposures have any health consequences, when exposures are maintained within limits like those published by the IEEE, ICNIRP or Safety Code 6 (Canada). Just make sure you don't overheat the food and burn yourself, which seems to be the number one hazard!

From: Hongfei Yao, Aerospace Long March Launch Vehicle Technology Co.

Usually, most stove-top kitchen microwave radiation will be blocked by the gate. However, it can still leak. I suggest that she stand further away. When exposed under microwave radiation for a long time, one may feel uncomfortable or get a headache.

From: Xie Maoxu, ZTEIT

I assume you mean the radiation from the microwave oven in your kitchen. Microwave radiation can cause body tissue to heat. Absorption of electromagnetic energy causes electrical currents to flow in the semi-conducting material of exposed human flesh. Significant heating can occur when the currents rise above a threshold level. Excessive heating can lead to damage in biological tissue. But, as a product with certification of authority in the market, the radiation level of microwave ovens must be in a safe range. So don't worry about the radiation unless your wife is pregnant. At the very least, you can stay away from your kitchen when the oven is working.

From: Jim Assurian, Reactel Inc.

I think the only danger and long-term effects are in eating microwave burritos, chicken fingers and pizza. In reality, as long as the door is intact and has no visible damage, close proximity to a microwave oven in action should be relatively safe.

From: William Howell, US Air Force

She is not in danger if the microwave is in good working order. There is a shielding screen on microwaves that filters out the frequency of the microwave signal. There should be no long-term side effects to worry about. In my opinion a cell phone, which transmits microwave frequencies right next to your brain, is much more dangerous than your kitchen microwave.

From: Nag Elmin, Fac of Engineering

In principal the door is well closed and no radiation comes out. If there is a problem with the door and radiation leaks out, maybe there will be problems of extensive heating.

From: Atilla Alpay, Turksat

There is no danger because the specific absorption rate (SAR) at 5 cm from the oven where the emission is around 5 mW/cm2 is found to be 0.256 W/kg. If it is measured as close to the front door (if we touch) the SAR is around 7.95 W/kg. This gives an estimated SAR of 0.0056 W/kg at a distance of 30 cm from the oven. These figures show that there is no negative effect on the human body.

From: Gavin Lewis, QinetiQ

In essence, the woman in question is not in danger. The door of the microwave contains an EMI gasket to shield the user from radiation. When the door closes, a seal is formed, completely enclosing the microwave energy within a metal shield, analogous to shields or "cans" that can be found on printed circuit boards. Although some energy inevitably leaks out, it is well below the specified limits set for electromagnetic field exposure. However, one word of caution: The EMI gaskets on some older microwaves have been known to degrade with time. Although this is very unlikely, for peace of mind, microwave oven radiation meters can be purchased cheaply from certain hardware stores that will indicate a broken seal. I hope that helps.

From: Andrew Gibson, Wireless Dynamics Inc.

As long as the microwave oven is in good repair there should be no danger. There are low cost meters available for well under $50, though one should check for reviews and opinions before putting much trust in them. A low cost (cheap) 2.5 GHz cordless phone could also act as a relative indicator between different operating microwave ovens; the less interference the less leakage.

From: Hussam Al-Zaaterah, Aces Co.

No, the microwave signal cannot pass through the stainless steel grid to the outside of the microwave oven.

From: Kashif Naveed, TUoL

Yes, there is potentailly danger of microwave radiations causing skin cancer because not 100 percent of the radiations are internally reflected. The distance should be increased by around 200 percent (for example, a distance of three feet may be enough for the radiations to attenuate to a level where she could be safe).

From: Anil Deshpande, Avantel Softech Ltd.

No, there are no long-term effects. The radiation given out from the oven is non-ionizing radiation leakage and less than 5 mW/cm2 at approximately two inches from the surface of the oven. This is far below the exposure level that is currently considered to be harmful to human health. The radiation produced by a microwave oven is non-ionizing. As such, it does not have the same cancer risks associated with ionizing radiation such as X-rays, ultraviolet light and nuclear radioactive decay. As a comparison, a GSM mobile phone may emit up to 1 W at 1800 MHz, which is 3.2 mW/cm2 at 5 cm. Whether or not cellular phones are hazardous to the health is also controversial.

From: Mrac Hunter, Pathwave Corp.

Providing the microwave itself is not damaged, things to look for are the door not fitting properly, missing parts inside and out, window screens or burned areas inside and out. One can check for major RF leaks with the use of a florescent light bulb (the electrons will excite the gasses and the bulb will glow). She could be getting more radiation by sitting down in front of the TV tube. Your wife will be just fine and there is no long-term danger with the microwave ovens that are built to meet the standards that are in place.

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