Answer to Question #6514 Submitted to "Ask the Experts"

I have heard that americium in a smoke detector is very dangerous if inhaled, but if it is ingested it passes through the digestive tract without much retention. I can't find much information about americium being inhaled except in a fire. If somehow the americium disk was punctured by a sharp pin or lightly scratched, would there be a release of any dangerous amount of inhalable americium?

My question is on a personal note. I had an incident about six months ago when I was renovating a room and inadvertently left an old ionization smoke detector from the late '70s-early '80s on my desk. These units had close to 3 microcuries. The unit said "Sears" on the back, worked by 9-volt battery, and had a detachable cover (which was off at the time). I wasn't paying attention and one of my five-year-old twin brothers started sticking brads—miniature finishing nails—into the slots of the ionization chamber. One apparently went in. After noticing what they were doing I tried to turn the unit upside down and back many times trying to get the brad out. After an hour I gave up and threw the unit in the garbage.

A week later I was reading an article about the americium in these detectors and how it is very dangerous if inhaled, but was insoluble and would pass through the digestive tract without much harm. However, I became very worried about the matter. The future threat of this incident may be causing cancer, etc. I understand that a fire will vaporize some of the source, but I don't know what will happen if the source was hit by one of these brads. I appreciate any information you can give me. Everyone tells me to stop worrying.

I can understand your concern about your twin brothers, but neither they nor you would be at risk at all. It is very difficult to damage a smoke detector containing americium-241 in such a way that the americium would be released and present a hazard to people. Damaging the radioactive source severely enough to release some americium would require considerable effort and is not easily accomplished. The source is very stoutly constructed and resistant to damage; the small brads would likely have no effect on source integrity. In short, there is very little likelihood that the actions you described damaged or breached the integrity of the source or produced any radiological health concerns.

However, the fact that you threw the unit in the garbage is of some concern. Since the americium used in these smoke detectors is radioactive, it is regulated by the Nuclear Regulatory Commission (NRC). NRC regulations require that such smoke detectors be returned to the manufacturer for proper disposal as radioactive waste. So next time you want to dispose of a smoke detector containing amercium, please return it to the manufacturer (the address should be on the device) or to the place from which you purchased it.

For further information, you may wish to consult the NUREG-1717 report prepared by the NRC. This report provides an estimate of the radiation dose received both during normal use of smoke detectors as well as from accidents and misuse. Of interest in this report is the evaluation of the radiation dose to a hypothetical teacher who removed the source from a smoke detector for classroom demonstrations. The dose was estimated to be less than 0.01 mrem—a trivial exposure. Similarly, NUREG-1717 has evaluated other accident scenarios.

Ron Kathren, CHP