Automatic sprinkler systems are used more than any other fixed fire protection system and over 40 million sprinklers are fitted world-wide each year. Sprinkler systems have been proven in use for well over 100 years. Possibly the oldest in Britain was fitted in 1812 at the Theatre Royal Drury Lane and an updated form is still in use today.
A fire sprinkler system is a network of fixed water pipes supplied by a constant water supply. Water can be supplied from a tank via pumps or from the town mains, providing the flow is sufficient and fills the pipes.
Detector heads are nozzles that direct a jet of water on to a deflector plate which defuses over a large area. The water is held back by a glass bulb or soldered strut which holds a plug in place. When heat is applied from a fire below, the glass bulb will burst, due to expansion of the liquid in the bulb, or the solder will melt, which then releases the plug and water flows through the sprinkler head.
The hot gases from a fire will raise the temperature at ceiling level and when the area adjacent to the head reaches a specific temperature that sprinkler head will actuate and spray water on to a fire. Only the sprinklers over the fire will open and the others will remain closed. This limits any damage to areas where there is no fire and reduces the amount of water needed.
Sprinkler heads can be placed in enclosed roof spaces and into floor ducts to protect areas where a fire can start without being noticed. In a large warehouse sprinklers may be placed in the storage racks as well as the roof.
At the point where the water enters the sprinkler system there is a valve. This can be used to shut off the system for maintenance. For safety reasons it is kept locked open and only authorised persons should be able to close it.
All sprinkler systems will have present and mains water shut off valves which allows the system to be closed down when the fire has been extinguished.
Dry risers are often called dry rising mains. They are intended for the use of the Fire Service to provide a readily available means of delivering considerable quantities of water, this is achieved through a fire hose connected to the outlet valve on each floor of the building to extinguish or prevent the event of a fire.
Before installation of a dry/wet riser, the local Fire Service must be consulted to ascertain their exact requirements.
If, having completed your risk assessment, you conclude that the Fire Service would need to use this equipment during a fire, you are responsible for maintaining it.
Dry risers will generally be found:
In buildings over 18 metres above ground level or, in Scotland, buildings over 7 metres.
In low level buildings where there are excessive distances from entrances.
Typical dry risers contain the following components:
- Large vertical pipe of 100mm or 150 metres diameter that can run internally or externally to the building.
- Twin/four way inlet connection at street level boxed in a steel cabinet with glazed door for the dry riser only.
- Outlet valves at each landing.
- Automatic air release valve at the highest point to provide bleeding of air from the system when it is filled with water.