Firefighters Matthew Cetin, left and Russell Ashe hold smoke detectors in a smoke room in Barre, Vt., Feb. 6, 2008. (Toby Talbot/Associated Press)
In Depth
Consumers
Smoke detectors
Two types: which one's for you?
Last Updated March 3, 2008
CBC News
You're about to move, and you want to make sure your new home is going to be as safe as possible.
If it's a brand new home, you're probably feeling pretty complacent. You know there will be smoke detectors and — most likely — they will be hard-wired. The national building code requires that smoke alarms be hard-wired in new homes. There has to be one smoke alarm on every level, and where there are bedrooms, installed near their doorways.
They will work — as long as there is electricity in your home and you replace the batteries that provide back-up power should a power blackout hit your neighbourhood.
The National Fire Safety Code calls for approved smoke alarms that can be powered by batteries in existing one and two-family dwellings.
While smoke alarms are required in virtually every home across the country, actual regulations can vary from province to province as well as on the municipal level. The national building and fire codes are not mandatory, although most provinces do follow them.
Preventable deaths
In the first two months of 2008, 24 people died in house fires in Ontario — almost half the average for the entire year for the province. Most of those deaths could have been prevented if smoke alarms were present and in working order, according to Ontario Fire Marshal Pat Burke.
Five people died when flames engulfed a home in Hamilton, Ont., in the early morning hours of Mar. 1, 2008. Fire investigators say there was no sign of a smoke detector in the house.
On Dec. 6, 2007, four people died in a house fire in an old farm house near Sussex, N.B., that fire officials say was not equipped with smoke alarms. That fire was caused by a lit cigarette.
One thing the building and fire codes won't tell you is what kind of smoke alarm you should have in your home.
There are two types of smoke detectors, and each is better at detecting certain types of fires.
Ionization alarms more sensitive to steam
The ionization type of detector is your key line of defence should your house be hit by one of those fast, flaming fires that feeds on combustible materials. These fires spread quickly. The fire could be sparked by such things as paper burning in a garbage pail or a grease fire in the kitchen. This type of fire accounts for 70 per cent of home fires.
Photoelectric smoke detectors are more sensitive to slow-burning fires that may smoulder for hours before they erupt in flames. These are normally the "careless smoking" fires caused by cigarettes burning in couches or bedding. They account for 30 per cent of home fires.
Ionization detectors are generally cheaper than photoelectric detectors, and they're not very environmentally friendly. They contain small amounts of radioactive americium-241, which is used as a source of alpha radiation.
The heart of the detector is an ionization chamber, which is an air-filled space between two electrodes. The radioactive material passes through the chamber, allowing a constant current to pass between the electrodes. Introduce smoke to the chamber, and some of the alpha particles are absorbed, which interrupts the current and sets off the alarm.
This works well when heat and flames break out quickly in your home. But this type of detector can also be set off when someone's spent a lot of time in a hot shower, sending clouds of moisture into the hallway. It can also be set off when the toast has been in the toaster a little too long.
Photoelectric smoke detectors will cost you a little more but are less likely to be set off by kitchen or bathroom steam.
Photoelectric detectors sense light. They are made up of an optical chamber consisting of an infrared light-emitting diode (LED), a lens that adjusts the light into a beam and a photoelectric sensor set at right angles to the beam acting as a light detector. If there's no smoke in the room, the light passes in front of the detector in a straight line. If there is smoke, some of the light is scattered activating the sensor, which sets off the alarm.
Which one is better for you?
In March 2005, the Ontario Fire Marshal's office released a report that asked the same question. Its conclusion?
"Within the fire protection and prevention industry, it is recognized that neither sensor type, photoelectric nor ionization, is universally better at detecting all types of fires," the document states. "Why? Each sensor operates on a different principle and therefore may respond differently to various conditions."
The fire marshal recommends that to adequately protect yourself, you should have both types installed in your home. If they are hard-wired, you should replace photoelectric and ionization detectors every 10 years. And regularly check those back-up batteries to make sure they'll keep your detector working during a power failure.
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