Microwave Oven Safety

St. Lawrence University - Radiation Safety

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Guidelines for Safe Use of Microwave Ovens:

Hazard:

There are numerous microwave ovens on campus in lounges, dorm rooms, offices and science laboratories. Most microwave ovens available today in the US are manufactured to meet standards set by the FDA Center for Devices and Radiological Health (Title 21, CFR, Part1030.10). They are required to have microwave leakage less than 1 mW/cm2 at 5 cm distance from any surface of the oven. Most ovens will have a decal indicating that it meets the Underwriters Laboratory (UL) performance standards regarding fire and safety. Modern ovens use a magnetron tube to produce the microwaves at 2450 MHz frequency. The ovens have metal shielding and an interlock mechanism to shut off the magnetron tube if the door is opened. The magnetron tube is powered by high voltage, up to 4000 V DC and 300 mA of current. The ovens heat objects due to the energy of the microwaves being adsorbed and dissipated mostly by water molecules in the object. Most hazards pertaining to microwave ovens are associated with thermal expansion, irradiating metal objects placed in the oven, and misuse of or tampering with the oven. Microwave ovens do not emit substantial electromagnetic fields.

Safe Use Guidelines:

NEVER place any metal objects into a microwave oven (e.g., spoons, twist-ties, metal pie pans, etc.). This will create electrical (high voltage arcing) and fire hazards.

Regularly inspect the door seal. If worn, do not use the oven until the seal has been replaced.

ALWAYS be sure that containers are well vented when heating anything in the oven. Otherwise, thermal expansion could result in a container exploding. Plastic caps should not just be loosened, but should be completely removed from containers.

Regularly inspect the door for warping or bending, especially if the oven has been dropped, has had an explosion that caused the door to open violently, or has been otherwise abused.

Regularly inspect and test the door interlock to make sure that it is functioning properly.

Do NOT depend on store-bought leak detectors to test a microwave oven for leakage. They are usually unreliable.

NEVER use the same oven for science lab use and for preparing food.

Always clean any food contaminates from the oven. Otherwise, microbes (germs) could grow and promote illness.

Do NOT attempt to modify the oven for any reason, especially due to the hazards associated with the high voltage supply. Have repairs made by a qualified service technician or simply replace the oven with a new one.

Report any accidents involving microwave ovens to your immediate supervisor, department chair, or the campus Radiation Safety Officer (5645) as soon as possible.

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