Merseyside Fire & Rescue Service

Our Mission: Safer Stronger Communities - Safe Effective Firefighters.

How Sprinklers Work

Sprinklers detect a fire in the early stages of development and will operate before the fire develops and becomes life-threatening. The system is heat-activated at a temperate of 57 degrees Celsius (domestic property) when the concealed lid drops off. At 65 - 70 degrees Celsius, the glass bulb of the sprinkler head smashes, allowing the plug to drop and water to be released. Water from the activated sprinkler will cool the atmosphere around the fire, which will reduce the rate of burning, the production of smoke and will protect the surrounding materials limiting fire spread.

Research illustrates that the vast majority of fires controlled by a sprinkler system have involved just one sprinkler head activating.

The following information and original artwork were kindly provided by the Residential Sprinklers Association (RSA). You can find more information about the RSA, residential sprinklers and accredited installers by visiting .

Sprinkler 1

The typical sprinkler head consists of a plug held in place by a trigger mechanism. The most common type of trigger is a glass ampule filled with a glycerin-based liquid that expands when heated.

Sprinkler 2

This liquid is designed to expand and break the tube at a certain temperature. The most common are designed to break at 155 degrees. In the average sized room, a 5mm diameter ampule will usually break in about one to one and a half minutes from contact with a heat source. Ampules as thin as 1mm are manufactured for a faster response time.

Sprinkler 3

The plug is forced out by the pressurized water behind it and deflected away by a beveled edge. The water sprays over the deflector plate which is designed to distribute it in an even pattern. Water will continue to flow until the main valve is shut off.

How an uncontrolled fire spreads

Smoke and toxic gases rise from the source of the fire. They spread quickly along the ceiling and heat the air in the room.

Sprinkler 5

The current of hot 2 air forces a curtain of deadly gases down the walls, making escape more difficult. In a few minutes the air will become so hot that the entire contents of the room will ignite spontaneously. This is known as flashover and usually occurs between 1,000 and 1,500 degrees.

Sprinkler 5

How a sprinkler system puts the fire out.

Even a small smoldering fire acts like a heat engine as it steadily increases the air temperature directly above it. The hot air fans out across the ceiling, heating up the nearest sprinkler head.

Sprinkler 6

As soon as the trigger mechanism is heated to the required temperature, it trips and the water is released. The immediate cooling of the heat source usually prevents other sprinkler heads from activating. Often, one or two sprinkler heads are enough to control a fire.

Sprinkler 6
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