How Fire Detection Devices Work

by Steve on January 16, 2010

How Fire Detection Devices Work



Ionisation smoke detectors contain a small sealed ionising source which causes a small electrical current to flow through the air in the smoke chamber.

Smoke particles entering the chamber reduce the current, this is sensed by the electronics and when a pre-set threshold level is reached the alarm will sound.


Ionisation are best suited for detecting fast flaming fires and are better suited in rooms where there is a high risk of fire (except the kitchen).

Ionisation alarms are more prone to false alarms due to their sensitivity and therefore ideal locations for these alarms are living room and bedrooms.


Optical or Photoelectric

Optical or Photoelectric smoke detectors send a pulsed beam of infra red light through a smoke chamber.

If visible smoke is present, it scatters the light on to the photo-diode light receiver and this is detected by the electronics causing the alarm to sound.


Optical detectors are better on escape routes and designed to detect smouldering fires.

They less prone to false alarms.



Heat detectors only detect heat and not smoke.

There are two types of heat alarm fixed and rate of rise.


Fixed heat detects when the temprature reaches a certain level and then sounds.

Rate of Rise alarm detects a rapid rise in heat between two set temperatures.


Heat detectors are ideal for kitchen as they are not activated by cooking fumes as is common with smoke detectors.


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