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Fire Sprinklers: FAQ

Last Updated: October 6, 2020 3:22:48 PM PDT
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The UC San Diego Fire Marshal answers the most frequently asked questions about fire sprinklers below.

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Expand section Frequently Asked Questions

How do fire sprinklers work?

The water in UC San Diego sprinkler system pipes is constantly under pressure. At each sprinkler head, the water is held back by a little plug. When sufficient heat reaches a sprinkler head, depending on the type of mechanism used, one of the following occurs:

  • The special solder that holds the sprinkler head together melts
    OR
  • The fluid in a glass vial in the sprinkler head expands enough to break the glass

In either case, the plug is released and the water begins to flow. Water will continue flowing until the system is mechanically turned off by an emergency responder.

Will smoke set off the sprinkler system?
Absolutely not. It takes actual heat, usually 165 degrees Fahrenheit, to set off a sprinkler.
What's the required clearance for sprinklers?

18 inches is the required clearance between a sprinkler and items stored on shelves.

Fire spreads when an obstructed sprinkler can't detect heat (fire) and is prevented from doing it's job.

Don't sprinklers sometimes go off by themselves?
Rarely. Fire sprinklers are extremely reliable. The odds against a sprinkler going off without cause are less than 1 in 3.3 million.
When one sprinkler goes off, won't they all go off?
Only in the movies! Each sprinkler is independent and must be subjected to direct heat to go off.
Why do we have sprinklers in some UC San Diegobuildings and not in others?
The building code requires fire sprinklers only in certain kinds of buildings — hospitals, for example. At UC San Diego, however, it is general policy to provide sprinklers for all new construction, and try to retrofit sprinklers into existing unsprinkled buildings.
Water is flowing from the sprinklers, but the alarms aren't going off. What's going on?
Each sprinkler system is equipped with a waterflow-sensing device connected to the building's fire alarm system. These devices incorporate a variable delay setting to prevent false alarms caused by changes in the campus water system supply pressure. Otherwise, every time the pressure surged, the detector would see a little water moving and activate the alarm. The waterflow-sensing devices at UC San Diego are set at a 30 – 45 second delay.

If you see a sprinkler operating, and the alarm hasn't yet gone off, it's probably because of this delay feature. However, you should immediately activate the nearest fire alarm or dial 911 to report the situation to the UC San Diego Police Department.

For more information, contact EH&S Fire & Life Safety, (858) 534-3659.
Notice: In case of fire, your first responsibility is to escape unharmed and sound the alarm. Use a fire extinguisher only if you have been trained to use one and you have a clear exit path behind you.