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Do you have Photo-electric Alarms installed?

By Chris Barnes

Last updated: 2nd September 2016

It's a situation no one wants to have to face, but firefighters fight thousands of building fires every year and not everyone makes it out. To escape a house fire, early warning is vital. That's why every home in Australia needs a smoke alarm.

But with several different types of alarms out there, it can be confusing to know which ones you need in your house. Read on for information that will set you straight – and hopefully prevent you from having to wave the tea towel at a screaming alarm every time you burn your toast.

Types of smoke alarms

There are two main types of smoke alarm for home use: ionisation and photoelectric alarms.

Ionisation alarms

These contain a very small amount of radioactive material, which reacts to particles emitted in a fire and sets off the alarm. Ionisation alarms are best at detecting fast-flaming fires that don't emit much visible smoke. But most house fires tend to be smoky and smouldering long before they flare into flame, and ionisation alarms aren't as quick at detecting these. They can also be prone to nuisance alarms from cooking, so shouldn't be located near your kitchen. 

Photoelectric alarms

These contain a photo cell and a light beam shining away from the cell. When smoke enters the test chamber, some of the light is scattered by the smoke particles and hits the cell, triggering the alarm. Photoelectric alarms are best at detecting smoky and smouldering fires, which is the most typical type of house fire. Dust or insects entering the unit can cause false alarms, so they have to be cleaned occasionally.

Other types of alarms

There are two other types of home alarms that are generally used in special situations:

  • Carbon monoxide alarms – often used overseas to ensure safe operation of central heating systems.
  • Heat alarms – ideal for kitchens.

Even if you have one of these for a special purpose, you should still install a standard smoke alarm as well.

Which type is best?

Photoelectric alarms are the best type for homes, as shown by past CHOICE tests and as recommended by most fire authorities. Photoelectric smoke alarms are much faster at detecting smoke than ionisation alarms. In a typical house fire, burning material smoulders and smokes for a long time (possibly a few hours) before flaring into flames. It's crucial to detect the fire early in the smouldering phase so you can deal with the fire or escape the house; the longer the fire goes on, the more smoke can fill the home and become an inhalation and visibility risk. 

Studies have shown that photoelectric alarms typically respond to smoky fires within about three to five minutes. Most ionisation alarms take much longer – up to 20 minutes or more – by which time escape can be much more difficult. Ionisation alarms can be a useful additional level of fire protection, but should not be the only type you have in your home. 

Dual sensor alarms (which contain both ionisation and photoelectric sensors) are also worth considering, provided they aren't installed in a location (such as near a kitchen) where the ionisation sensor could be prone to nuisance alarms from cooking.

 

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