When a fire starts a plume of hot gases rise to the ceiling. If a sprinkler is installed, the glass bulb or solder link gets hot and at a specific temperature (typically 68 deg C) breaks, releasing the cap and allowing water to flow onto a specially designed diffuser.
The diffuser breaks up the water flow into carefully controlled droplets, which penetrate the fire plume and cool the burning material to below its ignition point, thus putting out the fire.
Only the sprinkler/s directly over the fire are operated - not all of them!
The sprinklers are connected to pipe work, which is supplied either from the water mains or from a storage tank via a pump.
When a sprinkler operates the flow of water in the pipe work operates a flow switch, which in turn operates an audible alarm system.
The flow of water is small, typically less than 1/100th the water used by the Fire Brigade.
Sprinklers do not go off accidentally and are only triggered by the heat from real fires.
Sprinklers are very reliable and less then 1:16,000,000 exhibit any form of manufacturing defect.
A sprinkler is similar to a hose nozzle because it breaks up the stream of water into a fine spray. A cap seals the waterway.
The cap is held in place by either a glass bulb or two thin pieces of metal that are soldered together.
A fire creates a narrow plume of hot air and gasses that rise to the ceiling and spread out. When the hot gases reach the nearest sprinkler they will heat the fusible element or glass bulb that holds the cap in place.
When hot enough the cap will fall away and the sprinkler will spray water on the fire.
Because the water immediately cools the hot fire gases, the other sprinklers usually won't open because there would not be enough heat to break the bulb or melt their fusible element.
If the fire is so hot that one sprinkler cannot handle it alone, hot gases will reach the next nearest sprinkler. Then that sprinkler would open to stop the fire
This design of opening only when there is enough heat limits the number of sprinklers to what is needed to stop the fire.
Fire records over the past century show that 93 percent of fires were handled by only one sprinkler. In the remaining cases, two sprinklers handled an additional four percent. and it took only three sprinklers to handle nearly all of the remaining 3 percent.
Keep in mind that these figures include large warehouses with high piles of combustible goods, some of them very combustible. In these cases, more than one sprinkler may be necessary to spray enough water to absorb the tremendous heat generated by the fire.
In residential settings, the likelihood of more than one sprinkler opening is very rare, and the number of fires controlled by one sprinkler is much closer to 100 percent.
The water spray from the sprinkler cools the fire gases over the fire. When the temperature of the burning material drops to below its combustion temperature, it can no longer burn and the fire goes out.
Responding firefighters will shut off the sprinkler only once they are sure that the fire is completely out.
