Overview

Sprinklers are the most effective way of fighting the spread of a fire in its early stages. And fighting a fire when it's small is the best way to prevent injury to people and damage to property.

According to the National Fire Protection Association (NFPA), when sprinklers are present, the chances of dying in a fire are reduced by one-half to three-fourths and the average property loss per fire is cut by one-half to two-thirds, compared to fires where sprinklers aren't present.

This quick course will:

  • Give you an overview of the kinds of sprinklers and how they work
  • Show you some conditions that can prevent sprinklers from working properly
  • Debunk some common myths about sprinklers

Automatic sprinklers definition

An automatic sprinkler is a fire-suppression or fire-control device with a heat-activated element. The sprinkler operates automatically when the air temperature rises to or above the device's specified temperature rating. When that happens, the sprinkler discharges water over a specified area.

Photo courtesy of Fire Sprinkler Association
1 – Heat from the fire causes the glass bulb to break
2 – Cap releases
3 – Water releases onto the diffuser
4 – Water puts out the fire

Automatic sprinkler temperature ratings

The National Fire Protection Association's Standard 13 (NFPA 13) contains a temperature rating system for sprinklers. The appropriate temperature rating for the sprinklers at a particular location depends on the maximum expected ceiling temperatures. Selection of the proper temperature rating will reduce the possibility of premature opening of sprinklers.


© 2006 FM Global. Used with permission. All rights reserved.

Fusible link sprinklers

A fusible link sprinkler has two levers held in place by a two-piece fusible link—solder that melts at a specified temperature. When the levers are in place, they hold a cap on the sprinkler orifice, preventing water flow. In case of a fire, when the air temperature gets hot enough to melt the solder, the link separates, allowing the levers to fly apart.

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Frangible bulb sprinklers

A frangible bulb sprinkler has a liquid-filled glass bulb that holds the cap on the sprinkler orifice, preventing water flow. In case of a fire, as the temperature begins to rise, the liquid in the bulb expands. When the air temperature gets hot enough, the liquid expands to the point of breaking the bulb.

That lets the water pressure push off the cap. Water flows out of the orifice and hits the deflector. The deflector creates a spray that covers the specified area.

Position of the automatic sprinklers

To operate properly, sprinklers have to be in the correct position or orientation. Otherwise, most of the water will bounce off the ceiling, creating a poor spray pattern at floor level and changing the size of the droplets.

 

Pendent sprinkler

A pendent sprinkler hangs down from the water pipe. The water stream flows downward against the deflector.

Upright sprinkler

An upright sprinkler extends up from the water pipe. The water stream flows upward against the deflector.

Sidewall sprinkler

A sidewall sprinkler is for installation where construction or other special considerations make it necessary to put sprinklers near a wall. A sidewall sprinkler has special deflectors that discharge most of the water away from the wall in a pattern resembling a quarter of a sphere, with a small amount of water aimed at the wall behind the sprinkler.

Automatic sprinkler guards

If a sprinkler is installed in a place where moving objects could strike and damage it, a sprinkler guard should protect it. For example, in a warehouse with rack storage, sprinkler guards can minimize damage from moving pallet loads.

Sprinkler guards can also protect people from injury in places with low clearance:

Photo courtesy of Schmidt Structural Products

Sprinkler guards minimize damage from moving pallet loads:

Automatic sprinklers storage cabinet

A building with sprinklers must keep a minimum supply of six spare sprinklers on the premises, so personnel can replace any sprinklers that have activated or that have been damaged in any way. The number of spares in supply corresponds to the number and types of sprinklers in the building.

Building managers should keep the spares in a cabinet located where the temperature will never exceed 100o F. The cabinet should also contain a special wrench used for removing and installing sprinklers. There must be one wrench for each type of sprinkler installed.

Impairments: Painted sprinklers

Painting a sprinkler can slow down the response to heat, interfere with free movement of the parts, and make the sprinkler inoperative.

Dried paint can seal the cap to the orifice, preventing the flow of water. Paint on a fusible link can prevent the solder from melting at the specified temperature. The only way to fix a painted sprinkler is to replace it with a new sprinkler with the same characteristics.

Painted sprinkler head:

Sprayed-over sprinkler:

Other impairments of automatic sprinklers

Inadequate clearance to storage

There must be at least 18 inches of clearance between the deflector and the top of anything stored below the sprinkler. Anything closer than 18 inches will block the flow of water to the fire and reduce the effectiveness of the sprinkler system.

 

Misuse of piping

Occupants of a sprinklered building must not use the piping for any other purpose, such as hanging objects from it. Hanging objects could block the flow of water or damage the piping.

Automatic sprinklers obstructions

When a sprinkler head activates, it's critical that the water reaches the burning material quickly. An obstruction not only impedes rapid water delivery—allowing a fire to grow—but also causes splashing and cooling that can prevent or delay additional sprinkler heads from opening.

A well-designed sprinkler system minimizes obstructions, such as:

  • Building structures
  • Bar joists
  • Bridge strapping
  • Electrical conduits
  • Lighting fixtures
  • Ventilation ductwork
  • Cable trays

An obstructed sprinkler:

Defractor is above styrofoam ceiling:

Common myths about automatic sprinklers

Myth: Heat from lighting a cigarette can activate the system.
Fact: Sprinklers operate only when the air temperature reaches the specified range. A small heat source, such as a match or a cigarette, will not cause a sprinkler to discharge.

Myth: When one "goes off", they all "go off".
Fact: In most systems, sprinklers operate independently when the heat at an individual sprinkler reaches the specified range. Generally, only one or two sprinklers open during a fire.

Myth: Sprinklers cause severe water damage.
Fact: A single sprinkler generates about 25 gallons per minute, depending on the water pressure and size of the sprinkler's orifice. That's not much compared with a fire hose, which can discharge 150 gallons per minute or more. And one or two sprinklers can usually control or extinguish a fire, preventing damage outside the immediate area.

Myth: Leaks and drips are common problems.
Fact: A properly designed and maintained sprinkler system does not leak.

Myth: Sprinkler systems are not cost-effective.
Fact: The cost of sprinkler systems is reasonable, especially considering how well they prevent property damage, injury, and death.

Automatic sprinklers summary

Simply installing a sprinkler system doesn't guarantee adequate fire protection. To be effective, a sprinkler system must be properly designed, installed, tested, and maintained.

For example:

  • Personnel must immediately replace any damaged sprinkler or any sprinkler that has discharged.
  • The system's designers must choose the appropriate type and temperature rating.
  • The system's installers must position the sprinklers properly.
  • No one should ever paint a sprinkler.
  • Nothing should block a sprinkler.
  • Nothing should hang from sprinkler pipes.

We have trained field staff to evaluate the design, installation, and condition of sprinkler systems anywhere in the country. Water supply should adequately supply all sprinklers that operate during a fire, and provide enough water for fire department operations.

Report: Sprinkler Assessment Report