The American Society of Home Inspectors has concerns regarding ionization smoke detection. Ionization alarms have a small amount of radioactive material between two electrically charged plates that ionizes the air and causes current to flow between the plates.
When smoke enters a chamber, it disrupts the flow of ions, activating the alarm. The alarms respond best to “flaming fires.” Photoelectric smoke detection is more responsive to fires that begin with smoldering. Photoelectric-type alarms aim a light source into a sensing chamber. Smoke enters the chamber, reflecting light onto the sensor, triggering the alarm.
A fire-protection association study found that ionization alarms produced more nuisance alarms, making it more likely people will disable them. The inspectors’ group is advocating replacement of ionization alarms with photoelectric ones.
Skip Walker, the home-inspection group’s point person, said that in one UL study, “ionization alarms failed to trigger at all in 91 percent of tests for smoldering fires in synthetic materials such as mattress foam and nylon carpet.”
Regardless of which type you use, make sure your alarms work, experts say.