As long as the microwaves are enclosed, there should be no drastic effects. Never operate a microwave with the door open!
Microwaves—which flow randomly—interact most strongly with water. So you’ll have the best results if you microwave something that is uniformly moist. (That’s why halfway through heating up a frozen dish, you stop the microwave, stir, and zap it again.)
The inability to control the direction and flow of microwaves has made microwave heating most useful in small-scale heating. (Although the drying of pasta and potato chips is done partially by microwaves.)
Last year a company in North Carolina, Industrial Microwave Systems (IMS), announced that it had come up with a method of controlling microwaves. IMS says its patented microwave technology is a cost-effective solution to the industrial processes that require heating, drying, bonding, curing, reacting, pasteurizing, or sterilizing. In fact, it’s not limited to food, but can be used for fabric, paper, foam, chemicals, food, and other material. Even sewage!