Recently, the New Zealand media including The NZ Herald and Stuff, have paid a lot of attention to the risk of using ionisation smoke alarms and the benefits of using photoelectric smoke alarms. This comes from a recent article released by Consumer NZ and their strong recommendation to stop selling ionisation smoke alarms. A fair statement considering many states in Australia have in fact already made a move to ban ionisation all together.
COMPARISON OF TECHNOLOGIES
A photoelectric smoke alarm’s sensing chamber contains a light emitting diode and a light sensitive receiver. When smoke, or other by-products of combustion, fills this chamber the light beam is scattered and sets off the alarm. Photoelectric smoke alarms are suitable for living rooms, dining rooms, hallways and bedrooms. This is because these rooms often contain large pieces of furniture such as sofas, chairs, and mattresses, which, while burning, will create more smouldering smoke than intense flame and heat. However photoelectric smoke alarms will recognise both fire stages. This type of smoke alarm is now the internationally recommended solution for household use.
An ionisation type smoke alarm uses radioactive material to ionize air in the sensing chamber. As a result, the air chamber becomes conductive, permitting current to flow between two charged electrodes. When smoke, or other by-products of combustion enter the chamber, the conductivity of the air within the chamber decreases. When this reduction in conductivity is reduced to a predetermined level, the alarm is set off.
For the past decade, it has been recognised around the world – from conducting laboratory and field testing – that Photoelectric alarms respond significantly faster to smouldering fires (more common).
In several countries ionisation alarms have been removed from their Building Code. In Australia, photoelectric smoke alarms are mandated in most states and Queensland have put into legislation that all houses must have interconnected photoelectric smoke alarms by 2027.