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Which Smoke Detector should I buy?

smoke detector

As a home inspector I am frequently identifying old smoke detectors (10+ years) and recommending new ones be installed. Many clients want to know which ones which ones they should buy. Something is better nothing...

As a firefighter I have been to numerous calls in the past 10 years where a working smoke detector could have prevented a tragedy. After the smoke clears one of the tasks is to see if there was a smoke detector present. Sometime we find it with no battery, in a drawer or sitting on a shelf or one time still in its box. Most adults have recieved some education about the value of smoke detectors but we continue to see preventable fire deaths from a lack of working smoke detectors.

Recently a old controversy has come back up which type of smoke detector is better: Ion (Ionization) or Photo (Photoelectric)? 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.

The Ion detector reacts faster and is more responsive to smoldering fires that put out small combustible particles of nearly invisible smoke. The Photo Electric detector is reacts slower than the ion and is more responsive to flaming fires which put out larger visual particles of black smoke. 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:

Ionization: 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.

Photoelectric: 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.

Is one better? 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.

U.S. Consumer Product Safety Commission recommends installing both ionization and photoelectric type smoke alarms throughout the home for the best warning of a fire. This recommendation is also supported by the United States Fire Administration, the National Fire Protection Association, Underwriters Laboratories, and by research conducted by the National Institute for Standards and Technology. There are also dual sensor smoke alarms that have both ionization and photoelectric sensors in one unit.

Personally I will add photoelectric sensors to each level of my home to enhance the safety of the 6 detectors already in place. I will also use lithium 9volt batteries that will last 10 years so I won't have to worry about season changes.

Rick Bunzel, CRI
Pacific Crest Inspections

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Posted by Rick Bunzel on 04/20/2008 11:57 AM

Comments (5)

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5 Comments on Which Smoke Detector should I buy?

APR

2008

Rick, I too like the idea of the 10 year batteries---when they go it is time to replace the whole unit---no more keeping track of how old the unit is. I don't think most people are aware that these things have a relatively short life expectancy.

SEP

2008

Helpful post! Since you can’t predict what kind of fire might happen, why not be as protected as you can with the duo, recommends the The U.S. Fire Administration. Get standard type battery powered smoke alarms, Batteries need to be replaced at least once per year and the whole unit should be replaced every 8-10 years. Your alternatives are: a. smoke alarms powered by long-lasting batteries, but you must replace the whole alarm when you need new batteries, or b. smoke alarms with hard-wired, battery back up. The batteries need to be checked monthly, and replaced at least once per year. The entire unit should be replaced every 8-10 years.

Also, for those hit with smoke from a wildfire fire, here’s an idea. When California had several wildfires this summer, homeowners who got an AspenAir Inside home air cleaning unit could quickly remove the smoke that came inside their home, reported Contra Costa Times journalist Janis Mara. In fact, the device got rid of up to 20 times more polluting particles than conventional home air cleaners systems. Most importantly, it removed, the tiny yet dangerous RSPs that irritate the lungs and worse.