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Radiation in the Home
In this section:
Microwave ovens
Should my microwave oven be tested regularly for microwave leaks?
No. Provided the oven door is undamaged and closes properly, there
is no need to have it checked for leaks.
The National Radiation Laboratory has tested leakage from many new and used microwave ovens. Any leakage has always been less than the maximum allowed by the Microwave Ovens Regulations 1982. Most ovens were ten to one hundred times better than are required by law. There is no evidence that old ovens leak more than new ones, or that leakage increases as the oven gets older.
Is radiation still present in food for several minutes after the
food has been cooked in a microwave oven?
Microwaves in a microwave oven are absorbed by polar molecules (that
is, molecules which have an uneven distribution of electric charge)
which makes them oscillate. One of the most important polar
molecules is water, which is present in almost all foods. Some
biological molecules, such as the amino acids which make up
proteins, are also polar. The increased oscillation of these polar
molecules is what is more familiarly called heat. Hence these
interactions convert the microwave energy into heat energy, which
cooks the food.
When some recipes call for the food to be left standing for a few minutes after you have finished cooking, this is merely to allow the heat to dissipate evenly through the food. When the microwave oven is turned off, there are no longer microwaves present in the oven, as absorption of microwaves in the food is instantaneous.
This is similar to what happens when the light is turned off in a windowless room. Any photons produced while the light was on are immediately absorbed by the walls and objects in the room. No more light energy is produced by the light bulb, so the room becomes dark immediately.
More information can be found in: IS 15 Safety of microwave ovens.
Radon
There is some concern overseas about the natural radioactive gas
radon, in houses. How serious is this problem in New Zealand?
A countrywide survey in 1986/87 measured natural radiation,
including radon concentrations, in New Zealand houses. The
concentrations found were typical of those found in most localities
overseas. The significant finding was that there was no evidence of
any "hot spots" with very high concentrations such as have been
found overseas. New Zealand soils only contain traces of uranium and
radium, the source of radon. Typically, the New Zealand population
gets about half its dose of natural radiation from radon. The rest
comes from cosmic radiation, and traces of other natural
radioactivity in the soil, building materials, and in our bodies.
Smoke detectors
Am I being exposed to excessive amounts of radiation from the
radioactive source in my domestic smoke detector?
No. The radiation emitted by the small radioactive source is almost
totally absorbed inside the detector and the plastic case. The
amount of external radiation from the source is extremely small and
residents in houses with alarms installed receive radiation exposure
of less than 0.01% of what a person receives from natural
sources (such as cosmic rays and naturally occurring radioactive
material).
Is there any risk that I can be poisoned by radioactive material
from my smoke detector?
No. The radioactive material is very securely bound in a metal foil,
which is enclosed in a tamper resistant metal chamber inside the
detector. Even if you removed the metal foil and swallowed it, you
will not absorb more than a tiny amount of radioactivity.
If I do have a house fire and my smoke detector is burnt, will there
be any danger from inhaling radioactive smoke?
No. The metal foil containing the radioactive source has been tested
to more than 800° Centigrade for at least 30 minutes, without
any release of radioactivity. This is a much more severe test than
most house fires.
When my smoke detector fails and I replace it, how do I dispose of
the old one?
Put it out in your normal rubbish disposal. Every cubic metre of New
Zealand soil, on average, contains naturally occurring radioactive
material equivalent to about thirteen smoke detectors. The
radioactivity in numerous smoke detectors dispersed in landfill
sites is not going to have a significant environmental impact
relative to the radioactivity that is there naturally. In fact, the
natural radioactivity of domestic rubbish is less than that of soil,
and even if every household throws out several smoke detectors per
year the average concentration of radioactivity in landfill sites
will still be significantly less than in most New Zealand soils.
How can I send a smoke detector to someone else?
The quantity of radioactive material involved is exempt from rules
relating to the transport of hazardous materials. Smoke detectors
can be transported in New Zealand by any means, private car,
commercial freight, or through the mail, either singly by a domestic
user, or in bulk by a trade dealer.
More information can be found in: IS 8 Domestic smoke alarms. 1998.