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Both Ion (Ionization) and Photo (Photoelectric) smoke alarms respond to
combustion particles given off by developing fires. Both have to pass
the SAME fire tests by Underwriters Laboratories Inc. (UL). Both are
designed to give adequate warning in case of fire, whether a fire starts
slowly and smolders, or bursts into flames quickly and spreads rapidly.
Ion and Photo sensing chambers use different methods to detect smoke.
The differences between them are pretty technical, so let's start with a
simple analogy: Think of wrist watches. Some are digital, some have
dials with hands. Both tell time, but they use different methods. Same
idea with ion and photo smoke alarms.
Ion smoke alarms
react to changes in ionized particles, and are somewhat better at
detecting flaming fires. Flaming fires spread quickly,
"consuming" or burning materials in their path rapidly.
Examples include paper burning in a wastebasket or stove-top grease
fires. According to a recent study released by the U.S. Consumer Product
Safety Commission, 94% of reported home fires were categorized as
flaming fires.
Photo smoke
alarms react to how smoke affects light, are somewhat better at
detecting smoldering fires. These fires can smolder for hours before
bursting into flames. Examples include cigarettes burning in couches or
bedding.
It's impossible to say one sensor -- photo or ion -- is universally
better at detecting all types of fires. Why? Because both sensors are
designed to respond to combustion particles produced by smoldering or
flaming fires, and because fires themselves are different. The
combustion particles produced will vary depending on what starts the
fire (matches, electrical fire, etc.) and what burns (paper, fabric,
wood).
If a lit cigarette drops directly onto a couch, it is more likely to
start a smoldering fire. If that same cigarette drops onto a newspaper
on the couch, the resulting fire may be more characterized by flames
than smoldering smoke.
Major testing under the National Bureau of Standards sponsorship
confirmed either type of smoke alarm will give adequate warning in
either type of fire. And remember, both have to pass the SAME fire tests
by Underwriters Laboratories Inc. (UL).
The most important factor in protecting your family is having the
recommended number of working smoke alarms installed in the proper
locations. It is recommended you install both photo and ion smoke alarms
in your home, or choose dual sensor smoke alarms which feature both
sensors in one unit.
A recent report by the Consumer Product Safety Commission (CPSC)
estimates that 94% of typical household fires are flaming fires.
However, since you can't be sure what type of fire might start in your
home, consider installing both ionization and photoelectric smoke alarms
on every level of your home, and near every sleeping area.
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