Types of fire alarm systems

Written by britt barclay
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Types of fire alarm systems
A manual fire alarm. (Fire alarm button image by TekinT from Fotolia.com)

Fire alarms, if used correctly, can save lives and valuable tangible assets. Different types of buildings have different requirements for fire alarm systems. In homes they are usually simple smoke detectors. Commercial properties and larger buildings will often have hard-wired fire alarms attached to an alarm panel in addition to manual fire alarm boxes. The three main types of fire alarms are thermal alarms, photoelectric alarms and ionisation alarms.

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Thermal fire alarms detect heat within a room. They work through a sensor. At room temperature, the sensor will have a certain amount of conductivity. When the sensor is heated, the conductivity of the sensor changes. This conductivity change will trigger the alarm.


Photoelectric alarm systems are slightly more complex than ionisation systems. They rely on the visible particles created by flames. Photoelectric alarms are battery powered. They work through a small chamber that monitors solid particle concentration. When enough particles are in the chamber to reflect and block waves transmitted to a receiver, the receiver will set off a switch. This switch will route electricity to the beeping alarm; the beeping will notify the building occupants of a fire.


Smoke detectors are the simplest type of fire alarm system; they are also the most commonly used. Ionisation detectors don’t detect the fire itself, just the particles in the smoke from the fire. Due to the fact that smoke occurs in the early stages of a fire, this method of detection is highly effective. The ionisation detector uses a small amount of radioactive material and relies on an incomplete circuit through the material. When smoke particles come into contact with the radioactive material, they create conductive ions. The ions then complete the circuit, allowing electricity to reach the alarm. The alarm then sounds, notifying that there is a fire. The radioactive material is quantity that is harmless to humans.


Manual alarms must be pulled by a human. In larger buildings they are found mounted to the walls, and are wired to a building-wide alarm system. If someone in the building sees a fire or large quantities of smoke, all they have to do is pull the handle to sound the alarm. Some manual alarm systems release a staining liquid when pulled. This allows authorities to determine the culprit if a prankster pulls the alarm.

Interconnected Fire Alarms

Interconnected fire alarms are an essential safety measure. They connect all fire alarms within a building so that when one alarm goes off, they all go off. This gives additional safety because those in a location not yet endangered by flames are still warned; if the fire alarms weren’t interconnected, the building occupants would not be notified of a fire until it was near enough to set the local fire alarm off. It also prevents people from endangering themselves to warn others of the flames.

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