FACT: Ionisation Smoke Alarms are very slow at detecting slow smouldering fires, but quick to detect flaming fires.
Flaming fires produce more small smoke particles and this type of fire will be more quickly detected by an Ionisation Smoke Alarm, when we say more quickly it is only a matter of seconds between the reaction time of a Photoelectric and an Ionisation Smoke Alarm. Unfortunately, most house fires begin as a smouldering fire with large smoke particles, so this type of fire will be more quickly detected by a Photoelectric Smoke Alarm.
A Photoelectric Smoke Alarm react up to 20 minutes earlier than an Ionisation Smoke Alarm and will warn occupants before the fire has become a fast flaming fire, most house fire fatalities occur because of smoke inhalation, not from the actual fire itself.
How a Photoelectric Smoke Alarm works
A photoelectric detector uses a special light source and a light sensor to measure smoke density. The light source is constantly on but the light beam is angled away from the light sensor. When smoke enters the chamber, the smoke particles scatter some of the light toward the sensor. As the smoke density increases, more light is scattered towards the sensor. When the amount of light scattered into the sensor reaches a predetermined threshold, the unit goes into alarm mode and the alarm will sound to alert occupants.
How a Ionisation Smoke Alarm works
Ionisation Smoke Alarms are sub-micron particle detectors that use a small amount of radioactive material to detect hot, invisible particles from cooking or an open flame. They do not detect visible smoke, even though they may appear to in some cases. Most people have experienced a nuisance alarm given out by Ionisation type Smoke Alarms, this type of Smoke Alarm is sensitive to small smoke particles, it will respond more quickly to particles typically given off during cooking, even where there may be no danger, this explains why over half of all installed Ionisation Smoke Alarms have had their battery removed due to the nuisance factor.
The worst part about Ionisation Smoke Alarms is they are also considered low level nuclear waste and contain a small amount of radioactive material Americium 241.
LINKS
Carbon Monoxide Safety