What Is The Difference Between An Ionisation & A Photoelectric Smoke Alarm?
Ionisation smoke detectors were one of the most common types of smoke alarms used, but are now being replaced with photoelectric smoke detectors in many states across Australia.
What is ionisation?
Ionisation is a process in which a neutral atom gains or loses electrons and is converted into either a negative or positive electrically charged atom known as an ion.
How do these smoke detectors work?
An ionisation smoke detector uses the process of ionisation to detect a fire with an ionization sensor. Inside the alarm there is a sensing chamber that contains a small amount of radioactive material which ionizes the air between differently charged electric plates. When smoke enters the chamber it interrupts the flow of ions between these plates and activates the smoke alarm.
An ionization smoke detector is classified as a spot-type detector which means that it responds to the number of smoke particles in the chamber. This is effective for quickly detecting flash fires yet less effective at detecting smouldering fires and smoke.
What is the difference between an ionization smoke detector and a photoelectric smoke detector?
Photoelectric smoke detectors use an LED light sensor and a photodetector to track the fluctuation of light within the room. When a significant fluctuation has been detected, the sensor will trigger an alarm that is connected by an electric circuit.
The benefit of a photoelectric smoke detector in comparison to an ionization smoke detector is that the light sensor has greater sensitivity to smaller smouldering fires and smoke.
In fact, a report by the US Government's National Institute for Standards and Technology in 2018, found ionisation alarms took on average 30 to 33 minutes longer than photoelectric alarms to respond to smouldering fires.
Why did the Queensland legislation change from Ionization smoke detectors to photoelectric smoke detectors?
The photoelectric smoke detector is recommended by fire authorities and is now compulsory to use in many Australian states. This type of smoke alarm is faster at detecting smouldering fires and smoke which is a more likely fire danger to occur in your home. While flash fires are dangerous, they mostly occur in the kitchen when you are cooking and can already see the danger present.
What types of smoke alarms comply with government legislation?
- All smoke alarms must comply with the Australian Standard for smoke alarms — AS 3786:1993, which recommends a photoelectric smoke detector
- The legislation in Queensland has changed and now legally requires a photoelectric smoke detector that is no older than 10 years and complies with AS 3786:2014 — like our interconnected photoelectric smoke alarm with a lithium battery
- The legislation in Victoria has changed and now legally requires homes before 1997 to install a 9 volt battery powered smoke alarm and homes built after 1997 to install a 240 volt hard-wired smoke alarm — like our photoelectric smoke alarm with a lithium battery.