Why can't smoke detectors tell the difference between smoke and steam?

Baloo55th

Reading between the lines at http://en.wikipedia.org/wiki/Smoke_detector leads me to suspect that the non 'toast-proof' ionisation detector gets false positives from steam more than the (non-radioactive) optical type. They can both get false positives some of the time, but not all the time. So if yours goes off every kettle boiled, change it.... Sep 22 08, 8:25 AM

elburcher

It depends on the detector... This type of detector is cheaper than the optical detector; however, it is sometimes rejected for environmental reasons and because it is more prone to false alarms than photoelectric smoke detectors. It can detect particles of smoke that are too small to be visible. It includes less than a milligram of radioactive americium 241 (241Am). The radiation passes through an ionization chamber, an air-filled space between two electrodes, and permits a small, constant current between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and interrupts this current, setting off the alarm. 241Am, an alpha emitter, has a half-life of 432.2 years. This means that it does not have to be replaced during the useful life of the detector, and also makes it safer for people at home, as it is less radioactive. Alpha radiation, as opposed to beta and gamma, is used for two additional reasons: Alpha particles have high ionization, so sufficient air particles will be ionized for the current to exist, and they have low penetrative power, meaning they will be stopped by the plastic of the smoke detector and/or the air, reducing the risk of harm to people. To reduce false alarms caused by cooking fumes, use an optical or 'toast proof' alarm near the kitchen. http://en.wikipedia.org/wiki/Smoke_detector#cite_note-3 Sep 22 08, 8:40 AM