In important structures particularly in buildings, besides fire-resisting materials and method of construction, it is obligatory to make provision of fire detection and / fire extinguishing systems. These systems are described below:
1. Fire detection System
Also known as fire alarm system, it is installation provided with the aim of warning the occupants of the building of the out break of fire and to call for assistance at the same time. Fire alarm system can be either manual or automatic.
Manual Fire Alarm System
This consists of a hand bell or similar similar sounding device emitting distinctive sound when struck. Such devices are installed near all the main exists and passages. In the event of fire, the device is sounded by watch man and the occupants are thereby warned to have safe exit in shortest possible time.
Automatic Alarm System
This type of system on detection of fire starts sounding alarms or information to the nearest control point. Besides this, the system can also perform the function of sounding of evacuation gongs, hooters or siren and to transmit information of fire to a remote fire station.
2. Fire Extinguishing System
The commonly adopted fire extinguishing systems are described below:
Manual Fire-Extinguishing Equipment
Portable fire extinguisher is the equipment most commonly adopted in this category. Portable fire extinguisher can be of carbon dioxide type, large foam generation type and so on. Depending upon the capacity, the discharge from a fire extinguisher may last from 20 to 120 seconds. Sometimes buckets full of water and dry sand are also installed at convenient places for taking care of minor fires. These equipment are useful in extinguishing fire as soon as it starts.
This consists in providing a 150 mm diameter ring main outside in the ground around the periphery of the building. Fire hydrants are provided on the ring main. The ring main is fed from an underground water tank and it is ensured that the water pressure available at each fire hydrant is of the order of 3.5 kg/cm².
Wet Riser System
This consists in providing 100 to 150 mm. dia vertical ground level pipes at suitable locations within the building. The pipes are also known as risers and are fed from an underground water storage tank through a fire pump which ensures supply of water at 3 kg/cm³ at the topmost outlet. The wet risers have suitable connections at each floors from where constant supply of water can be drawn in the event of fire.
In this system a network of water supply pipes (normally 20 mm. dia)are fixed to the ceiling of the floor or roof slab. The center to center spacing of the pipes is normally 3 m. The pipes receive supply of water through header pipes is normally 40 mm. in dia which in turn are connected and fed from water storage tank. An installation known as sprinkler head is fitted to the pipes in ceiling at regular intervals normally at 3 m c/c. Each sprinkler head is provided with as fusible plug. In the event of fire the fusible plug in the sprinkler nearest to fire, melts by virtue of rise in temperature and water gushes out of the sprinkler head. The water spray falls on the fire and helps in extinguishing the same.