(January 19, 1990) There are two types of smoke detectors available for home use - ionizing and photoelectric.
(325.3256) WISE Stockholm - The photoelectric smoke detectors are an improved alternative to ionizing smoke detectors which contain the radioactive isotope americium-241 (the decay product of plutonium-241). Most detectors are of the ionizing variety.
Americium ionizes the air within a chamber of the smoke detector, enabling the air to actually carry an electrical current between two electrodes. When smoke particles enter the chamber, the current is interrupted, thus triggering the alarm. By contrast, photoelectric detectors contain a light source, and a light-sensitive photocell that is not directly in line with the light. When smoke particles enter the detector, they scatter the light beam, and the photocell detects the reflected light. This process triggers the alarm.
Americium-241 emits alpha and gamma radiation. Ionizing smoke detectors contain up to five micro-curies (185,000 becquerels) of americium 241. It has been estimated that one micro-curie (37,000 becquerels) of americium 241, if evenly distributed, has the potential to cause 78 lung cancers. The International Commission for Radiological Protection (ICRP) has set a maximum body burden for americium of 0.03 micro-curies (1,110 becquerels).
Photoelectric smoke detectors have other advantages over the radioactive model: they are better at detecting smoky fires. About 75% of home fires are smoldering fires and account for most fire deaths. However, ionizing detectors are faster at detecting the smaller smoke par- ticles of open flame fires. Further, photoelectric detectors last much longer than the estimated ten year life span of the radioactive type.
The Nuclear Awareness Project in Ontario, Canada is selling photoelectric smoke detectors for CDN $30.00 (best price in Ontario) plus postage and handling ($2.00 in Canada). The Nuclear Awareness Project has also published a short half-page "Consumer Guide To Smoke Detectors" containing information on producers and distributors in Canada.
Sources:
- The Anti-Nuclear Review (Canada), Summer/Fall 1989, pp. 7 and 8 (published by Nuclear Awareness Project)
- GreenNet, web.energy, topic 144, 14 Nov. 1989.
Contact: Nuclear Awareness Project, Box 2331 Oshawa, Ontario L1H 7V4, Canada, tel: 416-725-1565, e-mail: web:nucaware.