My Smoke Detector

I just recently learned something that I'm amazed I didn't know before about how smoke detectors work. I expect most of my readers don't know it either, so this post is my very first PSA (Public Service Announcement).

There are two kinds of smoke detectors: ion alarms and photoelectric alarms. Most smoke detectors manufactured and installed to date are ion alarms, because for a long time they were much cheaper, more efficient, portable and could operate on batteries (photoelectric alarms only recently became as flexible). Photoelectric alarms, however, are much better.

Ion detectors are essentially electric currents that are easily interrupted by smoke particles. When the current gets interrupted, the alarm goes off. Photoelectric detectors use an optical technique that involves bouncing light off of smoke particles and catching reflections in photo-detectors.

Ion alarms are more prevalent, but worse. Ion alarms more readily sound false alarms (such as in response to cooking steam). This often causes people to turn them off and forget to turn them back on again (or just disable them permanently around areas like the kitchen). But the worst part about ion alarms lies in the difference in response times between detectors depending on the type of fire. In a large blaze, an ion alarm will respond about thirty seconds faster than its photoelectric counterpart. But in a smoldering fire, photoelectric alarms can respond up to thirty MINUTES faster. This has to do with the types of particles created and how they're hurled into the air.

This difference was brought to my attention when an ion alarm's failure to activate in a smoldering fire resulted in the deaths of three Philadelphians. The article on philly.com contains the information I posted here, and is my primary source on the subject.

This concludes my first PSA.