In Canada, microwave ovens must conform to the Radiation Emitting Devices ACT, also known as the RED ACT. In order to sell a new oven, manufacturers must contact Health Canada and submit a statement of conformance to the RED ACT.
A used oven can be imported as long as it meets the regulations of the RED ACT. Selling an oven that is in non-conformance is punishable by law and can result in a fine and/or imprisonment.
Are microwave ovens dangerous? On newer ovens we have tested, even by warping the doors extensively, the leakage observed was minimal. A peak measurement of 4 times higher than that allowed by the RED act (20mW per square cm , the limit being 5mW per square cm) was observed 1cm from the top of the oven, at the centre, with the door slightly ajar. At 10cm from the oven, the readings were well below the limit. Further opening the door only resulted in a complete shutdown of the oven. Considering these measurements, it is extremely unlikely than any injury could occur from exposure to electromagnetic fields (EMFs) from the oven. The only confirmed health effect from the exposure to EMFs is overheating of the tissues, resulting in a burn. It is unlikely than members of the general public can be exposed to such high fields. Finally, as long as there is no visible damage to the oven (holes, cracked door seal, etc.) there is no reason to believe that the oven will leak in excess of the limit.
Can I make measurements myself? There are companies promoting products that claim to be able to measure leakage from your oven. However, to date, out of every type of device available to us for testing, not one was capable of doing so, adequately. The only capability of these devices is to measure the presence of a field. Unless equipped with a meter worth hundreds to thousands of dollars from a reputable manufacturer, the readings will not provide a proper radiofrequency field strength reading.
Perhaps the greatest risk of injury to a person by the use of a microwave oven is as a result of liquid super heating. There have been reports of serious burns after a person stirred a cup of hot liquid heated in a microwave. The oven can heat a cup of water to over 100 degrees Celsius without the water starting to boil. Once the liquid is agitated by either removing it from the oven or stirring, it then begins to boil, sometimes explosively. This is thought by some individuals to be caused by radiation remaining in the liquid, which is utterly incorrect. Once the magnetron ceases to operate, all microwaves in the oven cavity, and in the food disappear. Though super heating seems to be a rare occurrence (we have never been able to obtain it ourselves), one should exercise caution in removing hot liquids from the oven.
Another concern is whether or not there is a change in the food. Some believe vitamins are lost, others are convinced that the food is contaminated in one way or another. The fundamental difference between the conventional oven and the microwave oven is in the way the food molecules are agitated. (The end result of adding heat energy to a substance is to increase the amount of motion of the molecules, which are always in motion as long as the substance is above absolute zero in temperature.) In a conventional oven, the molecules are agitated in a random fashion, while the microwave oven will agitate all the molecules in unison. With either form of cooking there will be a chemical change in the food, however this is the desired effect. This chemical change is what distinguishes cooked food from raw food. Perhaps the only downfall of cooking with a microwave oven is that the water molecules in the food are preferentially agitated, resulting in their being boiled and evaporated. This sometimes leaves a rubbery feel and taste to the food (especially bread). Though there are many Internet sites suggesting health effects from consuming food products in the microwave oven, these claims are unfounded. Some sites simply thrive on generating public fear.