Is my household smoke detector emitting radioactive rays?

Cecil replies:

Your hair may well fall out some day, but if it does you’ll have nothing to blame but Ma Nature and your balding forebears. The additional exposure you receive from a smoke detector is considerably less than the normal background radiation in most parts of the country. Most detectors make use of about two microcuries of americium-241, which is used to make the air in the detector’s “ionization chamber” electrically conductive. If smoke enters the chamber, it inhibits the flow of electricity, which causes the alarm to sound. At a distance of one foot — which, needless to say, is much closer than you normally get — you’d receive a radiation dosage of about a half-microrem per hour. Normal background radiation in Chicago is about two millirems per hour (i.e., a whole lot more than a half-microrem). One consumer organization estimates that if ionization-type smoke detectors were placed in every U.S. home, they’d result in one additional cancer death every seven years. On the other hand, they’d save the lives of perhaps 4,500 of the 7,000 people who die in fires every year. From the cost-benefit point of view, that’s a pretty good trade-off.

A related safety tip: when your smoke detector begins to beep every few seconds, that means it’s time to change the battery, lest your longsuffering neighbor downstairs come up and brain you with an axe.

The Teeming Millions beg to differ

Dear Cecil:

I know you’re not in the habit of admitting you were wrong, but for the sake of your readers’ health and safety you should at least publish all the facts on an issue. Ionizing smoke detectors are indeed dangerous — the Health Research Group, a unit of Ralph Nader’s Public Citizen organization, said so in 1976. The detectors are so radioactive that defective or “used” detectors are supposed to be shipped to the NRC. However, nobody does this so the darn things get crushed and burnt in city incinerators. Even if they did it wouldn’t matter because in reality the NRC has no disposal plan. The thin foil surrounding the americium is able to be punctured and detectors can be destroyed by fire or vandalism while still in their boxes or in use. Imagine a whole shelf full of them destroyed in a hardware store fire or roof collapse, and leaking radioactivity into the environment. What’s more, safe detectors are available. Any Sears store can order the photoelectric type, which is no more costly than the radioactive type — and they are very effective. I know because several friends of mine were saved by one in their apartment last winter.

— C.A.S., Baltimore

Cecil replies:

I’m not in the habit of admitting I’m wrong for the simple reason it’s not often I am wrong. The Ralph Nader charges you refer to were examined by Consumers Union, a respected research organization not known for its proindustry bias, and found to be largely without merit. CU’s full report appeared in the January 1977 issue of Consumer Reports. Here I’ll simply respond to the claims you make in your letter.

It’s generally recommended that used detectors be returned not to the NRC but to their manufacturers, which are required to dispose of them at approved low-level waste facilities. Americium-241, the substance used in smoke detectors, mainly emits alpha and gamma particles. The principal danger comes from the alpha particles, which are indeed toxic, but only within a range of a few centimeters. Moreover, the particles are readily blocked by almost any material. The tiny quantities of americium used in smoke detectors would become a hazard only if they became lodged in the body, where they would be able to irradiate tissue for an extended period of time. Experiments indicate that the chances of this happening as a result of fire, vandalism, or general carelessness are remote. The NRC tested various scenarios and calculated that only in the most extreme — firemen fighting a blaze in a warehouse containing 25,000 smoke detectors under numerous unfavorable conditions — would there be a significant radiation danger.

Photoelectric alarms aren’t as effective as the ionizing kind for detecting certain kinds of fires, notably fast-burning, smokeless ones, although they’re better for smoky blazes. To provide double protection, some smoke alarms use both kinds of detector. There’s unquestionably some risk involved in the use of a radioactive substance, but it’s small compared to the risk of fire deaths that ionizing detectors are meant to prevent. I don’t suggest the Teeming Millions shouldn’t be concerned about such things, but I sure wish they could learn to think rationally about them.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.