The difference between photoelectric smoke alarms and ionisation smoke alarms


Did you know that according to the Metropolitan Fire Brigade, in 2012, there were 3,800 house fires in Victoria alone that resulted in the loss of 12 lives and caused property damage in excess of $97 million.

These incidents, injuries and deaths could have been reduced or altogether prevented with awareness, prevention and the right fire safety system in those homes. Here in Australia, it’s no wonder that smoke alarms are mandatory in all Australian homes and buildings – in the event of a fire, they could make all the difference between life and death.

If you’ve ever shopped around for a smoke alarm, you would know that there are two main types of smoke alarm systems: ionisation smoke alarms and photoelectric smoke alarms. Fire departments and the Fire Protection Association prefer photoelectric smoke alarms; however because the two types of smoke alarms have different benefits and are suitable for different parts of the home, it is important to know the difference.

What are ionisation smoke alarms?
Ionisation smoke alarms detect smoke using ionisation sensing technology, which comprises of a manmade radioactive element called Americium 241. This ionises the air around it, and as a result, makes excellent conductivity possible.

With ionisation smoke alarms, current passes through the gaps in the air with ease without triggering the alarm. However, in the event of particles arising from combustion or dust particles, those particles encapsulate the ionising air, causing an increased resistance to conductivity, and therefore triggering the alarm.

Benefits of ionisation smoke alarms
Ionisation smoke alarms are most suitable for bedroom areas, as they are most efficient at detecting fast flaming fires, such as curtains that have caught fire. Compared to a photoelectric smoke alarm, an ionisation smoke alarm would trigger more quickly in that situation.

What are photoelectric smoke alarms?
Photoelectric smoke alarms detect smoke via the use of photoelectric sensing technology, which uses a light transmission source and a photosensitive receiver. When smoke or dust enters the light path, some light is scattered or absorbed, causing the photosensitive receiver to trigger and sound the alarm.

Benefits of photoelectric smoke alarms
Photoelectric smoke alarms are most efficient at detecting smouldering fires, such as those caused by a cigarette accidentally being left on a sofa. In that situation, the sofa will actually smoulder before it catches fire. With a photoelectric smoke alarm, the alarm will trigger once it detects the smouldering, giving the occupants plenty of warning before a fire actually breaks out.

Suitable for living areas and near kitchens, photoelectric smoke alarms are actually the smoke alarm preferred by most fire departments and the Fire Protection Association because they are much faster at detecting smoke.

What else do I need to know?
Last but not least, when buying a smoke alarm, it is also important to take note of the following:
  • Queensland (10 year phase out of Ionisation Smoke Alarms beginning 1 January 2017) and Northern Territory currently have legislation that only allows the use of photoelectric smoke alarms.
  • Any smoke alarm that you buy should comply with the Australian Standard AS3786.
  • Fire departments and Australian Standards recommend that you change your smoke alarm at least every 10 years.