What Triggers Fire Sprinklers and Can They Go Off Accidentally?

What Triggers Fire Sprinklers?

Fire sprinklers are activated by heat, not smoke. Each sprinkler head contains a small frangible glass bulb filled with a special liquid. When the surrounding air reaches a specific temperature, this liquid expands, causing the glass to break and releasing water to suppress the fire.

Typical activation temperatures:

Residential Sprinklers: Trigger at approximately 56°C.
Commercial & Warehouse Sprinklers: Activate at around 63°C, as these environments generate more heat and require a higher threshold to avoid accidental activation.

How Do Fire Sprinklers Go Off?

Fire sprinklers activate when the temperature around them reaches their pre-set activation threshold. Once the heat causes the liquid inside the glass bulb to expand and break the bulb, water is released to extinguish the fire.

How Long Do Fire Sprinklers Stay On?

Domestic Systems: If pump-and-tank fed, sprinklers run for 10 minutes. If connected to the mains, they continue until manually shut off via an isolator valve.
Residential Systems (e.g., care homes, apartment buildings, B&Bs): Typically designed to run for 30 minutes, but this varies depending on building materials and fire safety requirements. In buildings with concrete floors, care home sprinklers may be set to run for 60 minutes to provide extra evacuation time.

Can You Set Off a Fire Sprinkler by Touching It?

No, fire sprinklers do not activate from casual contact. The glass bulb inside must be directly and forcefully hit to break, which is almost impossible by accident. However, in high-risk environments like schools or mental health facilities, alternative systems such as dry pipe sprinklers (without a fragile glass bulb) can be installed to prevent deliberate tampering.

What Sets Off Fire Sprinklers?

Fire sprinklers are triggered by heat. They do not respond to smoke, steam, or dust. Only when the surrounding air reaches the sprinkler’s activation temperature will it discharge water.

Do All Fire Sprinkler Heads Activate Simultaneously?

No. Only the sprinkler head nearest to the heat source will activate. This minimizes water damage and ensures the fire is targeted directly.

Will Incense or Candles Set Off Fire Sprinklers?

No. Fire sprinklers require sustained heat to activate. Holding a candle directly under a sprinkler head for an extended period might trigger it, but normal use of candles or incense will not.

What Is the Liquid Inside Fire Sprinklers?

The glass bulb in a sprinkler head contains an organic liquid that expands when heated, causing the glass to break and the sprinkler to activate.

Can a Laser Pointer Set Off a Fire Sprinkler?

No. Laser pointers do not produce enough heat to trigger a sprinkler. Ultrasafe specializes in installing fire sprinklers in sensitive environments like X-ray rooms and special care facilities, designing bespoke systems to prevent accidental activation.

How Sensitive Are Fire Sprinklers?

Fire sprinklers are precisely calibrated to activate only when necessary. They do not rely on batteries or electrical components, making them highly reliable. Only heat at the activation temperature will set them off.

Do Fire Sprinklers Detect Smoke or Vape?

No. Fire sprinklers respond to heat, not smoke. Even thick smoke or vapor from vaping will not cause activation.

For more information on how fire sprinklers work, check out our Fire Sprinkler Activation Guide and these additional resources:

If you would like more information on how fire sprinkler heads work and what activates them please take a look at the guide . Or if you need to order or discuss a project get in touch with the team.