04.Australian Standard for smoke alarms
The Australian standard for smoke alarms, AS 3786, covers both photoelectric and ionisation alarms. The CSIRO maintains the ActivFire register, which lists fire safety equipment that has been certified to the appropriate standards, including smoke alarms. Smoke alarm packaging will indicate if the product has been certified (alternatively, it might state the product is listed in the ActivFire register, which effectively means the same thing), but if you aren't sure if a particular alarm has been certified, you can look it up in the online ActivFire register.
All the alarms in this test are certified to the standard. Why then do they perform differently? It's because the Australian standard has different pass criteria for photoelectric and ionisation alarms.
- Photoelectric alarms must reliably activate, on average, when the smoke obscuration is between 3% and 20% per metre. 20% per metre is considered the maximum safe level of smoke. Therefore, a photoelectric alarm certified to the standard can be expected to give early warning of a smoky or smouldering fire. This is consistent with our test results.
- The pass criteria for ionisation alarms are not based on smoke obscuration. They are instead based on the MIC 'X" value, which is a measure of the level of small particles typically given off in a fast-flaming fire. An ionisation alarm certified to the standard can be expected to quickly detect flaming fire situations. However, these particular particles occur in comparatively low quantities in smoky, smouldering fires. So in a smouldering fire situation, by the time the MIC 'X" level has built up enough to activate an ionisation alarm, the level of actual smoke can be dangerously high.
In recent years there has been some debate whether the standard should be modified to require a uniform set of pass criteria for all types of alarm, regardless of their detector technology, based on smoke obscuration levels. A counter argument is that in certain special scenarios, such as in fuel storage depots where fast flaming fires are a particular hazard, ionisation alarms are the most appropriate type and the current standard is the best test for this type. Another argument is that the standard does not need changing, but that the Australian Building Code should mandate the use of photoelectric smoke alarms for homes.
Regardless of this, there is a broad consensus of opinion between fire authorities and industry experts that photoelectric alarms are a must-have item for homes. This is because toxic smoke and fumes are a major risk. In a house fire, it’s the flames that do the structural damage, but smoke is the main danger to people. The majority of deaths in fires come from smoke inhalation/poisoning. Modern homes contain a lot of materials — such as wood, wool, nylon and plastics — which, when burning, give out heavy smoke and toxic fumes such as carbon monoxide and cyanide gas. These materials can smoulder for a long time, putting out a lot of smoke and fumes before they burst into actual flames. If you’re asleep when the fire starts, you could suffer from smoke inhalation before you wake up; in fact, the combination of toxic smoke and reduced oxygen in the air can make waking up more difficult. So it’s important to have an alarm that rapidly detects smoke.
Photoelectric alarms are the best type for early detection of smouldering fires, and are fast enough at detecting flaming fires too. Ionisation alarms can be a useful additional line of fire protection, but should not be the only type you have in your home.