A:Answer Operating the microwave oven empty or when the food is completely wrapped in aluminum foil can cause damage to the microwave oven and the food won't heat. Substantial pieces of metal, like the walls of a microwave oven, can usually tolerate these currents without any problems. However, thin pieces of metal, like aluminum foil, are overwhelmed by these currents and heat up very quickly. So quickly in fact, that they can cause a fire. Plus, if the foil is crinkled so that it forms any sharp edges, the electrical current running through the foil will cause sparks. If these sparks hit something else in the oven, perhaps a piece of wax paper, you'll probably be reaching for the fire extinguisher. While it's highly unlikely that a small piece of foil is going to cause your microwave oven to totally explode, it could cause a fire...^IFV
