22nd Oct 2020

What triggers fire sprinklers and can they go off accidentally?

What triggers fire sprinklers?

Fire sprinklers are triggered by the air around the sprinkler head in the room reaching a certain temperature. Usually the temperature to trigger a residential sprinkler is 56oC.  Heat of 63oC is required to trigger fire sprinklers in larger warehouses where lots of heat is generated and you wouldn’t wish the sprinkler to activate accidentally.

Inside each sprinkler head is a small frangible glass bulb containing a chemical liquid. When this liquid heats up it expands and pops the glass and this sets off the sprinkler.

How long do fire sprinklers stay on?

Domestic fire sprinklers are set to run for 10 minutes for pump and tank. If water mains fed then a home fire sprinkler system will usually run until the isolator – manual stop value is turned off. Residential sprinkler systems, ie care homes, larger blocks of flats, b&b have a 30 min run time. There are exceptions to this and it depends on fabric of the build and run time can be set accordingly. If the building is constructed with concrete between floors then in a care home the sprinkler run time can be set to run for 60 mins to allow additional time to for the residents to reach safety. Residential fire sprinkler systems are bespoke. (Source: AHJ (building control/fire officer/AHJ authority).

Can fire sprinklers go off accidentally?

Yes, it has been known. Where there is a room with fully glazed walls and no ventilation then the room can get hot in the sun – it’s rare. Records show that the chance of an accidental discharge from a fire sprinkler is in the region of 16 million to one. Can fire sprinklers go off accidentally? Of course is is possible, but you have more chance of winning the lottery!

Do fire sprinklers go off if you hit or touch them?

To trigger a fire sprinkler you would have to hit the bulb itself within the sprinkler head. This is virtually impossible to do accidentally. However some type of sprinklers could be triggered on purpose, say at a school or mental care home. In a vulnerable situation, we would suggest a different system without a bulb i.e. a dry pipe that is not liable to deliberate or melodious triggering.

What temp do fire sprinklers activate?

A residential sprinkler system is usually triggered when the temperature in the room reaches 56oC.  Heat of 63oC is required to trigger fire sprinklers in larger warehouses.

When there is a fire do all the fire sprinkler heads go off at once?

No. Only the fire sprinkler head closest to the heat source will activate, minimising damage to the building and ensuring that the water is directed to the fire.

Will burning incense or candles set off sprinklers?

An incense stick waved under a sprinkler head will not generate enough heat to activate the system. A candle will only activate a fire sprinkler if it is held close to the sprinkler head for long enough for the sprinkler head to reach the activation temperature. This would require some deliberate effort.

What is the liquid in fire sprinklers?

Within the sprinkler head is a trigger mechanism which contains a glass ampule filled with an organic liquid that expands when heated. Normal Residential Fire sprinklers use water to extinguish the fire. 

Can a laser pointer set off a sprinkler?

A standard laser pointer will not trigger a fire sprinkler as it will not heat the sprinkler head to the activation temperature. Ultrasafe are experienced at the installation of fire sprinklers into special use facilities such as X-ray rooms or special care facilities. Bespoke sprinklers systems can be designed to avoid accidental triggering of the sprinkler heads.

How sensitive are fire sprinklers?

Sprinklers are sensitive to the specific temperatures that would be reached if a fire was starting to damage the room or its contents. This means that they are very reliable. It is a mechanical trigger, no battery is required and failure is very unlikely. If deliberately tampered with or the activation temperature is reached the sprinkler head will trigger.

Do fire sprinklers detect smoke?

Smoke itself is not hot, so even dense smoke will not trigger a fire sprinkler.

Do fire sprinklers detect vape?

Fire sprinklers can not be triggered by vaping. Fire sprinklers are triggered by heat. Vaping does not create sufficient heat to activate a fire sprinkler.


If you would like more information on how fire sprinkler heads work and what activates them please take a look at the guide below.


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