Currently, in Queensland, the smoke alarm market is dominated by two technical models, photoelectric and ionisation.
Each of these two types of smoke alarms are described in Part 3.7.2 of the BCA (NCC 2015) as follows:
- Photoelectric smoke alarms: This type of smoke alarm uses a light source and photocell. As the smoke enters the detection chamber it interferes with the light beam which in turn causes the alarm to sound.
- Ionisation smoke alarms: A small amount of radioactive material is used to create an electrical current travelling through ionised air. When smoke enters the detection chamber it impedes the flow of current and causes the alarm to sound.
Photoelectric smoke alarms are designed to detect and respond to the early, smouldering stage of a fire, as opposed to ionisation alarms which are only suitable for detecting fast flaming flares.
A typical residential, night-time fire tends to begin in a smouldering stage, where the smoke produced is visible, but cooler and less dense than the smoke produced from a flaming fire.
Ionisation alarms take significantly longer, even up to an hour more, to detect fire at the smouldering stage. By the time a fire of this type is in the flaming stage, the level of smoke in the air makes escape considerably more difficult.
In addition to this, ionisation devices are five times more likely to give off a false alarm. In practice, this means that residents are significantly more likely to disconnect their device to avoid the annoyance and inconvenience of a false alarm.
This is clearly contrary to the public interest because it leaves residents with no protection whatsoever against night-time fires.
We have sourced information about smoke alarms from the QLD Fire and Emergency Services website (qfes.qld.gov.au) and also the National Construction Code.