What are Safe Levels of Microwave Oven Radiation?
Microwave ovens are sealed enclosures that heat food or liquids by means of exciting the water molecules in them to such an extent that they heat up. Power in a microwave oven can often exceed several thousand watts. Very little of this microwave radiation escapes to the external surfaces and areas in close proximity to the oven, because these ovens are shielded adequately.
The amount of power density in air is defined by the power produced, divided by the volume in which that power exists; For example, watts/cubic inch, or watts per cubic centimeter. The U.S. Food and Drug Administration (FDA) defines the external safe limits in terms of milliwatts per cubic centimeter. They also define the frequency of microwave radiation in these appliances, to be in the range of 890-6000 Megahertz. This frequency band is sometimes called the ISM band, and is the same band used by cell phones , portable phones, and computer Wi-Fi equipment.
The FDA defines the safe level of microwave energy (at the time of customer purchase) to be less than one (1) milliwatt per square centimeter at a any point distant from the the external surface of the oven. This limit is increased to a maximum of five (5) milliwatts per square centimeter over the lifetime of the oven.
All microwave ovens are required to be designed with safety interlocks that will shut off the microwave energy if the door is opened while the oven is in operation. If the oven ever operates with the oven door open, unplug it, discontinue its use, and then take it to a repair center as soon as possible.
How Do I Know if My Microwave Oven is within the Safety Limits?
Since unsafe levels of microwaves can only be measured by means of power devices that are designed for this purpose. A microwave oven tester can be obtained to measure these values. When using the tester the oven should be filled with a glass of water. Put into the glass about 300 milliliters of water. Turn the microwave oven up to its maximum heating setting (if this is possible), and run it while you make your measurements.
The water acts as a load, and simulates food or other liquids that you typically would be heating. Microwave ovens should not be operated without some food or beverage in them. If they have nothing to heat, the emissions out of the oven will typically be quite a bit higher, and it will not be good for the longevity of the oven.
Moderately priced instruments for oven radiation testing are available for the consumer market. A Microwave Oven Radiation Tester will determine if your oven is leaking too much microwave energy. The maximum “safe level” as mentioned above is five milliwatts/cubic centimeter. This is a Power per Volume measurement, (milliwatts per centimeter-squared) and these instruments will measure this power density during test. Some testers will sound an alarm, or flash a signal LED, if the tested value is over the recommended limit.