Ask around to find out if using metal in a microwave is okay, and the answer is often a no. A no is a safe answer, and that's for sure. There are instances where metal is absolutely to be avoided, and there are also times when a bit of foil greatly helps with things and can be used safely. But the situations will vary. With that in mind, let's look at, "Is it save to put metal in a microwave oven?"
It may be yes, or it may be no. Here's a suggestion. Let the manufacturer make the call on this one. Generally speaking, the magnetron (the component in the microwave that generates the microwave energy) won't be harmed by metal in the cavity (the cooking area). But any metal within the cavity might act like a microwave antenna, and this may create arcs, and even start a fire within the cooking area. This will melt and burn things within the cavity, and almost certainly damage the door, which will make the oven unsafe to use (if it doesn't actually disable the oven). But setting aside those issues, let's look more closely at the microwave and how it should be used.
No one on this board can tell for sure without the owners manual or the model number of the machine in question (so one could look at the owner's manual) whether metal can or cannot be used in a given machine. "No" is a safe answer, but it may not be correct. A microwave has some cooking capabilities that may not be obvious, and anyone who owns or uses one of these puppies should know whether or not something like foil can be used inside it. There are even some microwaveable "fast foods" that have a bit of foil in the microwaveable package. Additionally, some microwave ovens allow a bit of foil over a portion of a food item being cooked, like the ends of the drumsticks on a bird. If the manufacturer's manual is not handy, it may be possible to go to the manufacturer's web site and actually view it online. Certainly the pamphlet can be had by ordering it. Get the manual. Read it. There might be several things in there that weren't obvious. Like whether or not foil can be used in the oven. That's why the correct answer may be either yes, or no.
If you have any doubts or issues, or you are not familiar with the manufacturer's instructions for a given unit, the "no" is a safe default answer and should be applied. But further investigation and thinking is in order if a microwave user wants to get the maximum out of a unit and really develop insight into the truth in the answer.
A link is provided to the USDA page with microwave use and safety suggestions. Surf on over and scroll down to the section on the use of foil and see what they have to say. That's a good place to start, and you're a simple "click" away right now.
Actually, the right answer would be: good or at least average electrical conductor metals (meaning: all metals) would cause some electrical arcs and, eventually, if left inside while running, a fire. Still there are some exceptions: golden or silver lining of plates, foil and small amounts of average electric conductor metals would cause only small, or no sparks, arcs and are mostly harmless. The real threat actually are metallic containers (plates, cans, etc...) and metallic cutlery, especially gold- and silverware. My silver fork for example almost ignited our old microwave oven, but we use a gold lined plate (only on the edges, and really only a line) on a daily basis in it, and it hasn't produced a sparkle as to day. So quantity counts as well as quality :)
I have seen an entire door to a microwave oven explode off the oven denting the wall on the other side of the room from one metal handle on a Chinese food container.
