A: The microwave oven probably is safe to use if there is no apparent damage (pitting of wall and ceiling surfaces).
Because microwave energy cannot penetrate metal, it's either reflected or absorbed, resulting in food that doesn't cook well. That's one reason why manufacturers told consumers not to use metal in microwave ovens.
The other reason has to do with the chance of arcing. Depending on the metal and other factors, a buildup of charged ions can occur, resulting in an electrical discharge, like tiny lightning. But, unlike lightning, it isn't over in a flash. The continuing discharge causes pitting or even holes in the walls of the microwave or the object being heated.
But metal isn't prohibited all the time. Newer microwave models are designed to be used with small amounts of metal. Be sure to check your manual before trying this, however.
In addition, some cookware containing metal can go into the microwave ovens. Look for "micro-wave safe" markings on the cookware or in the instructions that come with it.
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The underlying concern may be how microwave exposure affects one's health. Louis Bloomfield, a physics professor writing for howthingswork.virginia.edu, explains the potential health effects this way:
Escaping microwaves would flow out of the oven's cooking chamber like light streaming out of a brightly illuminated mirrored box.
If you are near a leaking microwave, some of those microwaves would pass through you and some would be absorbed by your body. If this were to continue, the absorption would heat your tissue to the point that you would feel warm.
In parts of your body that have rapid blood circulation, that heat would be distributed quickly to the rest of your body and you probably wouldn't suffer any instant injuries. But in areas that don't have good blood flow, such as the corneas of your eyes, tissue could heat quickly enough to be permanently damaged.
You'd probably feel the warmth and realize that something was wrong before you suffered any permanent injuries. However, exposure to micro-waves could have unpleasant effects on those with pacemakers.
If you are worried about microwave exposure, consider the cell phone. The cell phone's job is to emit microwaves, right next to your ear. The nonionizing radiation from those microwaves basically is dangerous only if it cooks you. At the intensities emitted by a cell phone, it's possible that some minor cooking is taking place. But the cancer risk is almost certainly nil.
