Sunday, January 29, 2023

A smoky subject

| November 28, 2010 8:00 PM

Question of the Month: (November 2010)

"How do smoke detectors work? Which type is better?"

The fact that you're reading this month's article is encouraging. It means you must have finally finished my last, rather lengthy article on emergency call centers in Kootenai County and are ready for more! OK, so I get a little long-winded now and then when discussing information on emergency services, mostly because I'm afraid I might miss sharing something important. So this month I promise to keep it shorter, but equally as valuable.

This month's question is a common one, especially at this time of year. People are frequently reminded to change the batteries in their smoke detectors when they change their clocks in the many public service announcements during October, which is Fire Prevention Month each year. The weather is also getting colder and people are lighting their wood stoves and turning on furnaces which also prompts fire awareness.

By now, I'm sure each of you have recently tested your smoke detectors and changed the batteries. Right? Did you notice which type of detector you had? Is it time to replace them? Is yours the type more sensitive to high heat - low smoke or is it more responsive to smoldering fires?

Are you asking yourself, "How the heck do I know?" If this is you, please keep reading!

There are two main types of smoke detectors: Photoelectric and Ionization. Both are effective in alerting occupants of smoke and fire to provide enough time to exit the home safely and both kinds last approximately 10 years before the recommendation for replacement.

The ionization detector is perhaps the most common because it is generally cheaper, sometimes costing only $7 to $10 each. This type uses a very minute amount of ionizing radioactive material called americium-241. This material emits alpha radiation between two metal plates within the "ionization chamber." Through activity at the atomic level, it creates a very slight electrical current between the positive and negative charged metal plates. When heat and smoke enter into the chamber, the smoke particles attach to the ions and neutralize them which in turn reduce the electrical current, triggering the alarm.

Photoelectric alarms work quite differently and are more sensitive to smoky and smoldering fires. A light emitting diode (LED) is placed in the top, horizontal portion of a "T" shaped chamber. It "shoots" the light across the top. Placed at the bottom of the chamber (base of the "T") is a photo (light) detector. When smoke enters the chamber, light is reflected off the smoke particles and is scattered about the chamber. When the reflected light hits the photo detector at the bottom it sounds the alarm.

Which type is better? Both. Or I should say, to have both or "dual" smoke detectors so they can quickly alert you to both smoldering and high heat situations. Upon checking with the National Fire Protection Association (NFPA), they currently do not have a strong recommendation as to which type of detector is safer in case of fire. Both types can provide occupants invaluable time needed to exit a home fire and both flaming and smoldering types of fires can be equally as dangerous.

The critical factor is that homeowners have working smoke detectors in each bedroom, on each level of the home and at the top of stairwells. For more information on placement, readers can visit or call your local fire department.

In closing, since I still have your attention, I want to stress that cold weather is upon us and homeowners across Kootenai County will be turning on their furnaces and cranking up wood stoves to stave off the chill. If you have a forced air system with oil or gas fuel or use a wood stove for heat, an invaluable tool for your home fire safety is a carbon monoxide detector. These detectors should be placed in all sleeping areas to alert us to dangerous levels of carbon monoxide in the air due to the incomplete combustion of fuels.

Also, stay vigilant with home fire safety. Keep flammables at least three feet from heat sources such as space heaters and stoves and keep candles in non-flammable containers and away from holiday decorations. Let's work together at keeping this a safe and enjoyable holiday season, free of fire related injuries or fatalities.

Stay safe out there!

Jim Lyon is the public education specialist/information officer with Kootenai County Fire and Rescue (KCFR). If you have a question about emergency services in your area, please submit your question to "Ask Firefighter Jim" at Visit our Web page at for additional information and to read archives of previously answered questions under the link, "Prevention."

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