What Happens if a Metal Container Is Inadvertently Put in a Microwave Oven?

How Microwaves React

• The microwaves that heat up the items inside a microwave oven react in different ways to different types of materials. Fats, sugars and liquid absorb microwaves. This is what causes the food you cook to heat up. Microwaves pass through glass, ceramic and certain plastic containers, making these items optimal to use for heating up food. Microwaves aren't able to penetrate metal. The microwaves reflect off of the metal, meaning the food inside the container doesn't efficiently heat up. Metal in a microwave also can be dangerous.

Risks

• One risk associated with placing metal in a microwave is the risk of fire. Fire is an especially prominent risk when thin sheets or metal coverings are placed inside a microwave oven. For example, the thin metal layer that borders decorative plates can begin to spark and catch fire. The same is true when aluminum foil is placed inside a microwave, as well as thick pieces of metal. When microwaves reflect off the metal, they could bounce up and damage the oven's magnetron, which is what heats up the oven. A damaged magnetron is a costly repair.

Importance of Items Inside the Oven

• In addition to manufacturers recommending that you don't put metal in a microwave oven, it's also recommend that you never run the microwave when it's empty. When a microwave is empty, there's nothing inside of it to absorb the microwaves that are being created by the magnetron. Food or liquid in a microwave will absorb the heat and keep the air in the microwave at close to room temperature. When there's nothing to absorb this heat, the air in the microwave oven heats up and can cause damage to the magnetron and other parts of the appliance.

Metal Can Be Good

• Metal is not always a bad item to use. The exteriors of microwave ovens are made out of metal. The reason for this is because metal reflects the heat from microwaves. If the microwave oven were made from plastic or glass, the microwaves would escape from the oven and heat up the kitchen.