A fire sprinkler system is a simple, but key, active component of a domestic or commercial building’s fire protection system.
Installed in ceilings or side walls, the system consists of a water supply, a water distribution piping system and sprinkler heads. The sprinkler discharges water automatically when a fire is detected, though it is not triggered by smoke. It controls or extinguishes the fire, so is both a fire detection and suppression system.
Sprinkler systems have been around since the late 19th century, when they were pioneered by Hiram Stevens Maxim. They are now extensively used worldwide, with over 40 million sprinkler heads fitted each year A system will generally involve water being held under pressure in a network of pipes running through a building.
Fire sprinkler types
There are four main types of fire sprinkler system:
- Wet pipe
- Dry pipe
In a wet pipe fire sprinkler system, the most common type in residential buildings, cold water is stored under pressure in the pipes and is released immediately by sprinkler heads when the predetermined heat level is reached.
Dry pipe sprinkler systems take slightly longer to activate and are used in unheated/unoccupied buildings where pipes may freeze and burst. Nitrogen gas or pressurised air is stored in the pipes, connected to a water storage tank or main. On activation by a fire, the air leaks out of the pipes, causing the water to flow through the pipes to the sprinkler heads.
Deluge sprinkler systems are typically used in areas where rapid fire damage is a major concern, such as warehouse loading bays and high-rise buildings. In these systems, the nozzle is always open. They are triggered by an alarm that opens a water release valve.
Pre-action sprinkler systems are a combination of wet and dry pipe systems, typically used in areas at high-risk of water damage. Water is not stored in the pipes until a fire is detected, when the water is released to the sprinkler heads. The response time is as fast as a standard wet pipe sprinkler system. Automatic fire sprinkler systems are also available and are effective in large areas such as offices and shopping centres.
Fire sprinkler heads
A fire sprinkler head is the component of a sprinkler system that discharges water when the fire has been detected. It comes in assorted designs.
Each sprinkler head contains a trigger mechanism, which opens to release water onto the fire.
With conventional heads, suitable for most residential fire sprinkler systems, some water is discharged onto the ceiling.
Upright or pendant spray sprinklers aim all the water straight down and are suited to rooms with high ceilings.
Heads need not be obtrusive and may be recessed in the ceiling or covered with resin caps to make them more aesthetically pleasing.
Side wall sprinklers attach to a high point on the wall. They usually give wider water coverage than conventional sprinkler heads.
The plug inside the head that holds back the water may be made of Wood’s metal, a mixture of bismuth, lead, tin, and cadmium that melts at a relatively low temperature, or a small glass bulb containing a glycerin-based liquid that expands and shatters when it gets hot, releasing the water.
Each sprinkler head activates independently. Only sprinklers above the fire will operate, maximising water pressure over the fire and reducing fire and water damage to the building. Sprinklers use far less water than fire hoses.