ARE MICROWAVE OVENS SAFE?
When used according to manufacturers' instructions, microwave
ovens are safe and convenient for heating and cooking a
variety of foods. However, several precautions need to be
taken, specifically with regards to potential exposure to
microwaves, thermal burns and food handling.
Microwave safety: The design of microwave ovens
ensures that the microwaves are contained within the oven
and can only be present when the oven is switched on and
the door is shut. Leakage around and through the glass door
is limited by design to a level well below that recommended
by international standards. However, microwave leakage could
still occur around damaged, dirty or modified microwave
ovens. It is therefore important that the oven is maintained
in good condition. Users should check that the door closes
properly and that the safety interlock devices, fitted to the
door to prevent microwaves from being generated while it is
open, work correctly. The door seals should be kept clean
and there should be no visible signs of damage to the seals
or the outer casing of the oven. If any faults are found or
parts of the oven are damaged, it should not be used until
it has been repaired by an appropriately qualified service
engineer.
Microwave energy can be absorbed by the body and produce
heat in exposed tissues. Organs with a poor blood supply
and temperature control, such as the eye, or temperature-
sensitive tissue like the testes, have a higher risk of heat
damage. However, thermal damage would only occur from
long exposures to very high power levels, well in excess of
those measured around microwave ovens.
Thermal safety : Burn injuries can result from
handling hot items heated in a microwave oven, in the same
way as items heated using conventional ovens or cooking
surfaces. However, heating food in a microwave oven
presents some peculiarities. Boiling water on a conventional
stove allows steam to escape through bubbling action as the
water begins to boil. In a microwave oven there may be no
bubbles on the walls of the container and the water will
super-heat and may suddenly boil. This sudden boiling may be
triggered by a single bubble in the liquid or by the
introduction of a foreign element such as a spoon. People
have been severely burned by super-heated water.
Another peculiarity of microwave cooking relates to the
thermal response of specific foods. Certain items with non-
porous surfaces (e.g. hotdogs) or composed of materials that
heat at different rates (e.g. yolk and white of eggs) heat
unevenly and may explode. This can happen if eggs or
chestnuts are cooked in their shells.
Food safety : Food safety is an important health issue.
In a microwave oven, the rate of heating depends on the
power rating of the oven and on the water content, density
and amount of food being heated. Microwave energy does not
penetrate well in thicker pieces of food, and may produce
uneven cooking. This can lead to a health risk if parts of
the food are not heated sufficiently to kill potentially
dangerous micro-organisms. Because of the potential for
uneven distribution of cooking, food heated in a microwave
oven should rest for several minutes after cooking is
completed to allow the heat to distribute throughout the food.
Food cooked in a microwave oven is as safe, and has the
same nutrient value, as food cooked in a conventional oven.
The main difference between these two methods of cooking is
that microwave energy penetrates deeper into the food and
reduces the time for heat to be conducted throughout the
food, thus reducing the overall cooking time.
Only certain microwave ovens are designed to sterilize items
(for example baby’s milk bottles). The user should follow
the manufacturer's instructions for this type of application.
Misconceptions: To dispel some misconceptions, it
is important to realize that food cooked in a microwave oven
does not become "radioactive". Nor does any microwave
energy remain in the cavity or the food after the microwave
oven is switched off. In this respect, microwaves act just like
light; when the light bulb is turned off, no light remains.
HOW DO MICROWAVE OVENS WORK?
Domestic microwave ovens operate at a frequency of 2450
MHz with a power usually ranging from 500 to 1100 watts.
Microwaves are produced by an electronic tube called a
magnetron. Once the oven is switched on, the microwaves are
dispersed in the oven cavity and reflected by a stirrer fan
so the microwaves are propagated in all directions. They are
reflected by the metal sides of the oven cavity and absorbed
by the food. Uniformity of heating in the food is usually
assisted by having the food on a rotating turntable in the
oven. Water molecules vibrate when they absorb microwave
energy, and the friction between the molecules results in
heating which cooks the food.
Unlike conventional ovens, microwaves are absorbed only in
the food and not in the surrounding oven cavity. Only dishes
and containers specifically designed for microwave cooking
should be used. Certain materials, such as plastics not
suitable for microwave oven, may melt or burst into flames
if overheated. Microwaves do not directly heat food containers
which are designed for microwave cooking. These materials
usually get warm only from being in contact with the hot
food.
Oven manufacturers do not recommend operating an empty
oven. In the absence of food, the microwave energy can
reflect back into the magnetron and may damage it.
Microwave oven users should carefully read and comply with
the manufacturer’s instructions because new ovens vary widely
in design and performance. While most modern ovens can
tolerate some food packaging made of metal, oven
manufacturers generally recommend not placing metal in the
oven, particularly not close to the walls, as this could cause
electrical arcing and damage the oven walls. Also, because
metal reflects microwaves, food wrapped in metal foil will
not be cooked, while food not in metal wrap may receive
more energy than intended, causing uneven cooking.
Source :-http://www.who.int/peh-emf/publications/facts/info_microwaves/en/

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