January 1, 2005
There are two types of smoke detectors currently in use: the photoelectric detector and the ionization detector. The photoelectric detector responds to smoke, which deflects a small light beam inside of the detector and activates the photoelectric cell, setting up an alarm. This type is connected to an electrical outlet, and is subject to power failure if it does not have a battery backup.
The second type is called an ionizing detector, and it usually contains radioactive Americium 241 or Radium 226. These radionuclides continuously ionize the surrounding air within the detector, sending a small current of electricity through it. When a smoke particle impedes that current, the electric circuitry monitor sets off an alarm. This type of detector, which works best in a flaming fire, works on a battery and is subject to battery failure. A yearly vacuuming is often recommended for keeping them in good working condition. Some models require occasional cleaning with alcohol.
Photo-electric detectors are more sensitive to smoke than are the ionizing type detectors, and although they were originally slower to detect a flaming fire then were the ionizing type, they are now considered to be superior in both types of situation. According to tests performed by the US National Bureau of Standards, the improved photo-electric detectors provide 2 to 3 times more chance of escape than the ionizing type of detector containing Americium. According to an article by G. Blair, in the Journal: Politics and Other Human Interests, 31 January 1978, smouldering fires account for about 75% of all home fires. The photoelectric type detector is currently more expensive than the ionizing type, but affords broader and more realistic protection for common types of fires.
The main hazard of the ionizing type detector is the radioactive component, usually Americium 241, which has a half-life of 458 years. Radium 226 has a half-life of 1600 years. Americium is a waste product from nuclear reactors; it is encapsulated inside of the detector, but may become available for ingestion or inhalation through the gradual deterioration of its packaging when discarded in a landfill or after its release during an actual fire. It is easily absorbed into the body from the lungs or intestines, and can cause cancer and genetic injury or can have general negative effects on health. This will inevitably be a greater hazard to future generations rather than our own, since it is encapsulated on a ceiling fixture for our short period of use.
A typical Americium source contained in one ionizing detector intended for home use, would consist of 0.8 to 5.0 micro curies of Americium on a silver disc, coated with a very thin layer of gold. An industrial model may contain up to 15 micro curies. We usually speak of picoCuries of radiation, which are one millionth of a microCurie, as having biological significance for humans. According to Dr. Edward Martel, an expert on alpha particle emitters like Americium and Radium, one microCurie of Americium contains thousands of lethal doses if spread in a human population. Dr. Martel was a senior scientist at the US National Center for Atmospheric Research in Bolder, Colorado. Dr. Karl Morgan, Father of Health Physics and Emeritus Member of the International Commission on Radiological Protection, has stated that the risks are identical for Plutonium 239 and Americium 241. He adds that once in the environment, (after a fire or after having been discarded in a landfill), Americium is more of a risk than Plutonium because it is readily taken up by animals (including humans) and plants. (From the US Congressional Record House, page H521-H523, 1 February 1978 Legislation to Prohibit Sale of Smoke Detectors Containing Radioactive Isotopes)
Because Americium is soluble, it can accumulate in soil and water, and enter into drinking water, plants, fish and animals. In the human body, it moves into the blood stream and is stored in bone and liver. Friction, scratches, heat or other stress can easily damage the disc inside the smoke detector, which contains Americium or Radium. The alpha particles could escape from the metal foil while the detector is intact, if there is a leak of any kind or if the covering has been damaged. In a fire, incinerator, sanitary landfill (which is usually an aquifer recharging area), the radioactivity can be released. The gold foil covering the radioactive particle will melt at 1063 degrees Centigrade. In a one-hour fire test conducted by the US Atomic Energy Commission in 1969, a smoke detector reached 925 degrees Centigrade, almost the temperature of complete melt down. The foil, which contained 2.5 microCuries of Americium, lost 0.31% or 0.0074 micro Curies or, equivalently 7,400 picoCuries. Prior to 1990, the maximum permissible body burden of Americium for members of the public was 1,670 picoCuries. This limit has been proportionally lowered to 334 picoCuries, soon to be law in Canada. Many would argue that this is still 100 times too high a dose meaning that one domestic ionization fire detector contains between 2,400 – 15,000 times the maximum permissible body burden of Americium.
The British National Radiological Protection Board has also reported the release of an excessive amount of radioactive material when ionizing detectors were fire tested. (P. Burry, Detection Section, Fire Research Station, Borehamwood, England) There is really no way to test for a product defect or leakage in a home setting, since alpha particles cannot be detected even by an ordinary Geiger counter. There have been product recalls. For example, in the US, 110,000 were recalled because of an incorrectly rated resistor, which could cause the detector to self-ignite. Only 40,000 of these defective devices were retrieved.
It is my opinion that the ionizing type radiation detector should be eliminated from home use as soon as possible. Until then, these devices should be clearly labelled, tracked and returned to the manufacturer for the proper handling of radioactive waste. I believe that this type of detector was originally marketed in order to use some of the waste from nuclear reprocessing. I also heard ionizing detectors being used in a Nuclear Reactor Licensing Hearing as a defense against the deaths which would be caused by the radioactive waste and effluence of the nuclear reactor – in the hopes that saving lives would balance out lives lost. This debate could be best won by eliminating both nuclear power and ionizing fire detectors. We have ample benign technology to fulfill the functions of both technologies.
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