Fire alarm systems have become increasingly sophisticated and functionally more capable and reliable in recent years. They are designed to fulfill two general requirements: protection of property and assets and protection of life.

All Fire Alarm Systems essentially operate on the same principle. If a detector detects smoke or heat, or someone operates a break glass unit, then alarm sounders operate to warn others in the building that there may be a fire and to evacuate. For the system protecting property, it is additionally likely that the Fire Alarm will incorporate remote signalling equipment which would alert the fire brigade via a central station.

A fire alarm system comprises a central Control and Indicating Equipment (CIE) with various types of detectors, manual call points (MCP), interface units and sounders connected to it.

Wired Fire Alarm Systems can be broken down into three categories:

a) Conventional,

b) Addressable

c) Analogue Addressable.

Choice of detectors for fire alarm alarm system

Smoke Detectors will generally detect a fire far sooner than heat detectors. It is therefore preferable to fit Smoke Detectors unless there is any possibility of false or unwanted alarms. It is not advisable for example to fit a Smoke Detector in a kitchen as anybody burning toast would cause an unwanted alarm.

Heat Detectors should be fitted in boiler rooms, generator rooms, garages and dusty areas. The products of combustion produced by a boiler, a leaky exhaust on a generator or exhaust fumes from a vehicle could all cause a smoke detector to operate and produce an unwanted alarm. Fixed Temperature Heat Detectors should be installed in areas where one would normally expect a sudden rise in temperature for instance kitchens and boiler rooms.

Rate of Rise Heat Detectors should be installed where Smoke Detectors would be unsuitable but one would not expect a sudden rise in temperature for instance, garages, car parks, dusty workshops etc.

There are two basic types of Point Smoke Detectors:

Ionisation chamber Smoke Detectors which are very sensitive to smoke with small particles ie: fresh cellulosic smoke and the source of almost invisible smoke one gets with burning paper and spirit. They are relatively insensitive to smoke with large particles for example, smoke produced by burning plastics or stale smoke.

Optical Smoke Detectors are sensitive to optically dense smoke i.e smoke with large particles and they are relatively insensitive to optically thin smoke.