Microwave Ovens And Pacemakers

July 23, 2007

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By Michael D. Shaw

Several months ago, this column discussed the safety of microwave devices, focusing mostly on alleged deleterious effects on pregnant women, and how they might even affect male fertility. Hopefully, the piece allayed readers' fears. Not covered in that article was the widely touted dangers that can befall people with pacemakers, if they venture too near microwave ovens. For the most part, these dangers are now historical curiosities.

All microwave ovens produced for sale in the United States—after October 6, 1971— must meet the Food and Drug Administration/Center for Devices and Radiological Health (FDA/CDRH) performance requirements documented in 21 CFR 1030.10. The regulation states that the ovens may not leak microwave radiation in excess of 1 milliwatt per square centimeter, at 5 cm from the oven surface. It also states that ovens, once placed into service, may not leak microwave radiation in excess of 5 mW/cm² at 5 cm from the oven surface. Several manufacturers have set their own standards to be more stringent than these.

The regulation has many other provisions, pertaining to safety interlocks, warning labels, and testing methods. Refer to this webpage for more details.

Note that the regulatory levels are far below the amounts known to cause harm. Furthermore, as you move away from an oven, the level of any leaking microwave radiation that might be reaching you decreases dramatically. For example, someone standing 20 inches (51 cm) from an oven would receive approximately 1 percent of the amount of microwaves received at 2 inches (5.1 cm).

Fortunately, the ovens are quite resistant to leaking microwave radiation. The literature documents two typical instances of leakage exceeding the FDA/CDRH standard. In the first case, there was a puncture of the protective metal grid at the viewing window, caused by an exploding metal food container. The second oven had a defective door seal as a result of dropping the oven off the top of a refrigerator.

Interestingly, the holes in the metal grid prevent the escape of radiation because they are smaller than the wavelength used. Visible light, however, easily passes through the holes, so you can watch what you are cooking through the window. (Microwave wavelength is about 12 cm, compared to 400-700 nanometers for visible light.)

But, what about pacemakers? Here is an excerpt from a 1992 article in the Journal of Occupational Medicine:

"In the early days of microwave ovens and cardiac pacemakers, there was a real possibility that a leaky oven with a significant electromagnetic field being emitted could interfere with operation of a pacemaker with an unshielded lead. Both problems have since been corrected."

Indeed, implanted pacemakers are not easily susceptible to interference from microwave ovens. They have shielded circuitry, highly selective filters, and the ability to recognize and reject interference and continue to operate. Tests have demonstrated that a normally functioning microwave oven will not affect an implanted pacemaker.

That's why most authorities, including the FDA, do not recommend the posting of warning signs near microwave ovens to alert persons with pacemakers. Certainly, patients with pacemakers are encouraged to consult their physicians if they have concerns.

With the 1971 regulations in place, we are left with bizarre incidents to report:

In a 1983 non-microwave incident, an engineer working at a 275,000-volt electrical substation in the UK felt a thumping sensation in his chest when he was near high voltage conductors. It was established that the electromagnetic field generated by the high voltage was interfering with the man's pacemaker. Let us stipulate that a 275,000-volt substation will generate a much stronger electrical field than a microwave oven. The man was unharmed.
In a 1984 non-pacemaker incident, a man wearing a transdermal patch (used to deliver drugs through the skin) was sitting near an operating microwave oven. The patch became hot, and gave him a second-degree burn. This accident was the result of an improperly repaired oven that leaked microwave energy, which was absorbed by an adhesive strip of aluminized plastic on the patch. It is quite doubtful that a pacemaker patient would have been affected at all in this scenario.

The take-away here is to rest easy about having a pacemaker and using a microwave oven.