Microwave Oven - Hazards

Hazards

Homogeneous liquids can superheat when heated in a microwave oven in a container with a smooth surface. That is, the liquid reaches a temperature slightly above its normal boiling point without bubbles of vapour forming inside the liquid. The boiling process can start explosively when the liquid is disturbed, such as when the user takes hold of the container to remove it from the oven or while adding solid ingredients such as powdered creamer or sugar. This can result in spontaneous boiling (nucleation) which may be violent enough to eject the boiling liquid from the container and cause severe scalding.

Closed containers, such as eggs, can explode when heated in a microwave oven due to the increased pressure from steam. Insulating plastic foams of all types generally contain closed air pockets, and are usually microwave-unsafe, as the air pockets explode and the foam (which can be toxic if consumed) may melt. Not all plastics are microwave-safe, and some plastics absorb microwaves to the point that they become dangerously hot.

Products that are heated for too long can catch fire. Though this is inherent to any form of cooking, the rapid cooking and unattended nature of microwave oven use results in additional hazard.

Some magnetrons have ceramic insulators with beryllium oxide (beryllia) added. The beryllium in such oxides is a serious chemical hazard if crushed and ingested (for example, by inhaling dust). In addition, beryllia is listed as a confirmed human carcinogen by the IARC; therefore, broken ceramic insulators or magnetrons should not be handled. This is obviously a danger only if the microwave oven becomes physically damaged, such as if the insulator cracks, or when the magnetron is opened and handled directly, and as such should not be a concern during normal usage.