Ionization Vs Photoelectric Smoke Alarms:
In most fires, the difference is deadly. What type of smoke alarm do you have?
Imagine your car air bags deploying randomly when you hit a pothole, but failing over half the time in a collision. As unthinkable as this seems, that is the harsh reality with the smoke alarms found in most homes. Like most, I always assumed that a smoke alarm was a smoke alarm. What I now know is that there are two basic types of smoke alarms; Ionization and Photoelectric. In real-world fatal fires, these alarms behave very differently. In this case – different is not good. Knowing the difference could very well save your life.
When was your alarm last checked or replaced?
“A smoke detector that sounds approximately nineteen minutes after smoke reached its sensing chamber is like an airbag that does not deploy until nineteen minutes after a car accident.”
Over 90% of homes have ionization smoke alarms installed, around 5% of have photoelectric alarms installed and the rest have no alarm of any kind. The number of homes with smoke alarms has risen dramatically in the last 30 years. Yet after installing smoke alarms in millions of homes, the risk of dying in a fire has remained roughly the same. Does that make sense to you?
No, here is why.
Smoke alarm testing typically use two test scenarios. One is a “fast flame” fire, the other is for smouldering fires. A “fast flame” fire is a fire that is based on accelerants, such as gasoline, cooking oils, grease, and paper fire. A smouldering fire is the early stages before open flames develop and is characterized as slow moving with significant smoke.
In tests, ionization alarms will typically respond about 30 to 90 seconds faster to “fast-flame” fires than photoelectric smoke alarms. However, in smouldering fires ionization alarms respond an average of 15 to 50 minutes slower than photoelectric alarms. Several testing studies indicate that ionization alarms will outright fail to activate up to 20-25% of the time. In the same tests, photoelectric alarms activated 100% of the time.
The vast majority of residential fire fatalities are due to smoke inhalation, not from the actual flames and almost two-thirds of fire fatalities occur at night while we sleep.
Ionization alarms are also notorious for nuisance tripping, i.e.; going off when you cook, burn toast, shower, etc. When alarms nuisance trip, people become frustrated and intentionally disable the alarms. This leaves the family completely unprotected. According to several studies, ionization alarms are 8 times more likely to be intentionally disabled. Ionization alarms account for the vast majority of disabled alarms.