The Photoelectric Smoke Detector

For an extra measure of fire safety, make an effort to locate and obtain a photoelectric smoke detector.

| May/June 1983

square white photoelectric smoke detector

An unidentified brand of photoelectric smoke detector.


In MOTHER EARTH NEWS' neck of the woods, a jaunt through neighborhood hardware and department stores would be enough to convince almost anyone that all smoke detectors contain radioactive material. In fact, not only were we unable to turn up a single alternative to the readily available ionization type of detector in a store-to-store survey, but we were amazed to find out that the owners of most of the firms were unaware that any other sort is even made.

As a result of our frustration, then, we were quite pleased when reader Robert Westcott sent us some information on the subject — including a long list of companies that reportedly sell or produce an alternative to the ionizing devices: a photoelectric smoke detector. We subsequently wrote to all the firms on that list, as well as to a few others we unearthed ourselves, and waited to see what was available. (Considering what we'd found — or, to be more accurate, not found — in our own region, we were quite prepared to learn that all such businesses had expired.)

Well, much to our surprise, we got four solid affirmative replies (we also received a few negative ones, while at least a dozen of the inquiries were neither answered nor returned). What's more, we learned a fair amount about both ionizing and photoelectric detectors, information that we think you'll find quite interesting.

Ion the Sky

The word radiation carries a whole lot of emotion with it these days. But as you're about to find out, there are more factors to be considered when choosing ionizing and photoelectric detectors than the presence of a substance that emits alpha radiation. In fact, the differences in performance of the two types of detectors could be far more important to your family's well-being.

To understand these differences, you'll need a general knowledge of how the two kinds of devices work. An ionization smoke detector uses a small amount of a radioactive substance — americium-241— to fill a detection chamber with ions. These particles support a very small charge of electricity, which passes between two poles and keeps the alarm circuit open (no sound). When smoke enters the chamber, however, the ions bond to the smoke particles and the current's path is disrupted, thereby triggering the alarm. Because these detectors depend on ion bonding, they react most quickly to the small, but numerous, particles typically given off by hot fires. (Burning paper in a wastebasket is one commonly cited example.)

Furthermore, ionizing detectors tend to give false alarms when exposed to the fumes produced by cooking or other household activities. Dual chamber models help alleviate the problem, but some studies have shown that, even at their best, ionization smoke detectors "cry wolf" almost twice as often as does the alternative type of device.

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