Ionizing vs photoelectric smoke detectors

PhotonWrangler

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Saw a report on the news today that claimed that ionizing smoke detectors are far less sensitive to fires that produce toxic gases than photoelectric detectors. They showed a demonstration using a simulated house fire where the room was filling with smoke, and the photoelectric detector sounded after about 17 minutes of light smoldering, where the ionizing units didn't sound until around 35 minutes. By that time the room was hazy with smoke and likely filled with invisible toxic fumes.

So from now on I'm only going to buy smoke detectors that use both detection technologies inside.

What puzzles me is this - up until today I had no idea that ionizing detectors were so much slower to reach than photoelectric ones. So why hasn't this been generally known by the public over the several decades that smoke detectors have been around?

:thinking:
 

Bullzeyebill

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Sounds like the photoelectric alarms are picking up the initial smoke of a fire, while the ionization alarms hold off till there are toxic fumes present, which would no doubt occur as a fire progressed. If that is the case, I would want the initial warning of smoke before there were toxic fumes present. However, if the ionization detectors can pick up toxic gas, say from a defective gas stove, heater, etc, then there is a place for them, but not to sense a fire.

Bill
 

SemiMan

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Other way around, but yes one is good for fast fires, and one is better for slow fires in general. I only buy dual type detectors now.
 

PhotonWrangler

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I have separate CO and combustible gas detectors, partly 'cause I want to easily differentiate the alarm sources if there's a problem. Also the combustible sensors generally need to be in different places than the CO detectors for my situation. But I'll be using dual sensor smoke detectors from now on.
 

yuandrew

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Ionization type detectors typically respond better to fast, flaming fires that would produce light smoke whereas a Photoelectric would be better at responding to thick smoke that a slower, smouldering fire would produce. Typically, ionization smoke alarms are more common due to their lower cost (less than $10 for a basic 9volt battery powered model) compared to the $25 a photoelectric model would start at. This issue had been known by some for a while but only until recently (last 4 years) has it been bought to news. Currently are two states that I know of (Iowa and Massachusetts) that now require photoelectric type alarms.

BTW, if you smoke alarms are 10 years or older, it's recommended to replace them with new units.
I'm using the Kidde Dual Sensor model PI2010
 
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