Smoke Detector

Smoke detector is a device that senses smoke, typically as a indicator of fire.

Smoke detector consist of two part

1) A sensor to sense the smoke
2) Electronic horn to horn the people.
Two basic type of smoke detector are used today ionization and photo electronic.

1) Ionization smoke detector

Ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean- burning fires that produce small particle during combustion.

Advantages of ionization smoke detector

• Detect invisible product of combustion.it can detect fires that are in the incipient stage or detect other aerosol type smoke detector.
• Quick acting - provides for earlier detection than other type of smoke detector.

Disadvantages of ionization smoke detector

• Detect the presence of smoke only, not toxicity
• Has a potential for high false alarm rate

2) Photoelectric smoke detector

Photoelectric smoke detector utilize light as a detection mechanism. There are two type of photoelectrically smoke detector

Heat detectors in fire alarm system

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.

Heat Detectors should be sited so that the heat sensitive element is not less than 25mm, nor more than 150mm below the ceiling or the roof. The maximum horizontal distance between any point in the area being protected and the nearest detector should be as follows:

a) Under flat horizontal ceilings and corridors more than 5m wide then the maximum distance between any heat detector and any wall or partition should be 5.3m.

b) The maximum area of coverage per heat detector is 50 square metres.