Answer to Question #2088 Submitted to "Ask the Experts"

Q

I was at work the other day and the microwave remained on after the door had opened. No one really thought anything of it until later that day when we all had headaches. The next day the microwave did the same and our headaches returned. I determined that we probably shouldn't use the microwave anymore. What risk am I and my coworkers at because of constant exposure to microwaves? Are the headaches a symptom or mere coincidence?

A

Commercial microwave ovens are doubly interlocked, making it highly unlikely that the microwaves could be ON when the door is open. U.S. Food and Drug Administration (FDA) regulations limit the microwave power intensity outside a microwave oven to no more than 5 mW per sq cm throughout useful life under conditions of allowable door positions and primary interlock failure. So the first thing you might consider is what evidence was there that the microwave power was actually ON when the door was open? The main effect of the microwaves of course would have been to heat. The heating power inside the oven is sufficient that if the power remained ON when the door was open then there would be a substantial tissue heating effect outside the open door. Unless you felt or observed heating outside the oven door, then it is unlikely that the oven power was actually ON. The same is true for harmful health effects: the first indication of documented harmful health effect is the heat sensation.

I do concur with your solution of not operating this unit until you are sure its interlocks are working right. If it were in my home I would call the manufacturer for specific advice on what might be causing interlock failure and how to get it diagnosed and repaired. I would be curious to know what you find out as I have not previously heard of any cases of interlock failure causing significant external microwave fields on commercial microwave ovens.

Gary Zeman, ScD, CHP
Lawrence Berkeley National Laboratory