Smoke alarms in homes – better than nothing
By Alex Wood
By Danielle Warfe
02 August 2018
You may have been hearing conversation in the news about smoke alarms and their effectiveness. There are two types of smoke alarms that can be installed in Australian homes: photoelectric and ionisation. Photoelectric and ionisation smoke alarms are sensitive to different types of combustion products and so respond to different types of fires.
|Rely on light sensitivity, where smoke particles scatter light and a light receiver triggers the alarm. These types of smoke alarms respond well to slow, smouldering fires that produce larger visible combustion particles.
|Use an electric current produced by radioactive material, where smoke particles interrupt the current and trigger the alarm. Ionisation alarms respond well to fast, flaming fires that produce smaller, invisible combustion particles.
Other fire detection alarms include dual-sensor (both photoelectric and ionisation) alarms, heat alarms that detect heat rather than smoke, multi-criteria (photoelectric and heat) alarms, and carbon monoxide alarms that trigger when carbon monoxide concentrations increase.
The National Construction Code (NCC) specifies that smoke alarms must be
- installed in homes,
- appropriately located (between bedrooms and living areas, and on each storey),
- hardwired, and
- interconnected if there’s more than one.
The NCC is the minimum standard and does not specify which type of alarm must be installed. Ionisation alarms are installed in the majority of Australian homes with smoke alarms, largely because they’ve been around a lot longer than other alarms and are more readily available and cheaper.
Modern house furnishings are resulting in quicker fires compared to previous decades, as vividly demonstrated on Catalyst, making the presence of smoke alarms even more important. But fires in bedrooms and living areas more commonly begin as smouldering fires, and for this reason, most of Australia’s fire authorities (including Tasmania’s) recommend installing photoelectric alarms. In fact, Queensland and the Northern Territory are transitioning to compulsory photoelectric alarms in homes.
Recent research by Fire & Rescue New South Wales (FRNSW) and co-funded by the Australian Building Codes Board tested the performance of photoelectric, ionisation, dual-sensor and multi-criteria alarms in responding to fire tests (10 smouldering, 13 flaming, and 4 nuisance tests). The research (available here) found the following results:
|Dual-sensor alarms responded most quickly overall.
|In smouldering fire tests, dual-sensor alarms activated more quickly than all other alarm types, and photoelectric alarms activated faster than ionisation alarms.
|In flaming fire tests, dual-sensor and ionisation alarms were equivalent and responded more quickly than both photoelectric and multi-criteria alarms.
|In false alarm tests (which tested activation to burnt toast, steam, cigarettes or candles), false alarms were triggered in 10% of cases and were more commonly triggered by ionisation and dual-sensor alarms.
|Concerningly, smoke alarms of all types only provided sufficient time for evacuation from bedrooms before conditions became untenable (i.e. too toxic) in 35% of smouldering fires, and this was reduced to near zero for flaming fires.
It is clear from this and other research that housefires are highly variable, making it difficult to characterise them and define the “best” detection method for all scenarios. But based on these findings, we support the recommendations of the Tasmania Fire Service.
The best thing you can do right now to maximise your protection from a housefire is
- install a hardwired smoke alarm with battery backup in each bedroom, hallway and living area,
- make sure they’re interconnected so when one goes off, they all do, and
- prepare a home fire escape plan, and practice it, so you know exactly what do if there’s a fire.
Together, these measures will give you and your family more time to get out safely.