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Automatic Sprinklers

Sprinkler Systems Quick Courses


Sprinklers are a very reliable and effective way of fighting the spread of a fire in its early stages. And fighting a fire when it is small is the best way to prevent injury to people and damage to property.  Put simply, sprinklers reduce the impact of fires, in both preventing injury and death to civilians and firefighters and are effective at controlling and mitigating the effects of fire, significantly reducing property damage. Sprinkler statistics are available from the National Fire Protection Association (NFPA) in their statistical reports entitled, “US Experience with Sprinklers.”  

This quick course will: 

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

Learn how to evaluate the sprinklered properties in your portfolio

Fighting Fire

The Verisk Sprinkler Assessment Report (SAR) is an analytical tool that can help quantify whether a sprinkler system will be effective in mitigating loss for a building in the event of a fire, making it an important resource for commercial property underwriting.

Our white paper, Fighting fire where it starts, explains how the SAR can help insurers identify hazards from gaps in required maintenance, changes in occupancy, inadequate water supply, and human error.

Download the white paper

What is an automatic sprinkler?

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What is an automatic sprinkler?

An automatic sprinkler is a fire-suppression or fire-control device that operates automatically when the heat-activated element reaches its operating temperature. This occurs when the ambient air temperature rises to or above the sprinkler’s specific temperature rating. When that happens, the operating parts clear the waterway, allowing the water to discharge below the sprinkler.

Photo courtesy of Fire Sprinkler Association

  1. Sprinkler in its normal condition.
  2. Heat from a fire causes the fluid within the glass bulb’s thermal element to expand, shattering the glass bulb, and allowing the sprinkler to operate.
  3. Water begins to flow at the available pressure, clearing the waterway of all operating parts.
  4. Water flows freely through the open sprinkler and onto the sprinkler’s deflector, which evenly distributes it over the protected area below.

Types of sprinkler thermal operating elements

Sprinkler thermal operating elements come in two types: Fusible solder link and frangible glass bulb. Both types of thermal operating elements are designed to maintain a mechanical compressive force down on the orifice cap to keep the sprinkler sealed.

Fusible link sprinklers

Fusible link sprinklers utilize two levers held in place by two link halves fused together by a eutectic-type solder mechanically designed to keep the cap sealed on the sprinkler orifice, preventing water flow.  Upon reaching its rated temperature during a fire, the solder goes directly from solid to liquid, causing the link halves to separate, allowing the operating parts to clear the waterway. 

Fusible Link Sprinkler

Fusbile Link

Frangible glass bulb sprinklers

Frangible glass bulb sprinklers have a liquid-filled glass bulb that contains a fluid that expands at its rated temperature. The glass bulb is strong enough to provide an axial compressive force to hold the cup assembly and washer seal against the sprinkler orifice, preventing water flow. Upon reaching its operating rated temperature, the liquid in the bulb expands to the point of shattering the glass bulb, allowing the operating parts to clear the waterway. 

Sprinkler Class2

Sprinkler Class5

Sprinkler sensitivity

Sprinkler sensitivity measures how quickly the thermal operating element reaches its rated temperature and operates. This is determined by laboratory-based operating parameters. Sprinkler sensitivity is then categorized into fast response or standard response. Types of fast response sprinklers include commercial quick response, quick response and extended coverage sprinklers, residential sprinklers and Early Suppression, Fast Response (ESFR) storage sprinklers. Certain applications and designs within NFPA 13 require specific types of thermal sensitivity as well as temperature ratings. Thermal elements of fast response sprinklers usually have a smaller mass relative to their construction. For example, in the case of frangible glass bulb sprinklers, standard response sprinklers use a 5 mm glass bulb, while quick response sprinklers use a 3 mm glass bulb.

Standard Response

Standard Response -
5 mm bulb

Quick Response

Quick Response –
3 mm bulb

Automatic sprinkler temperature ratings

A sprinkler’s thermal operating element, whether glass bulb or solder link, operates at a predetermined temperature called its temperature rating. Sprinkler temperature ratings, classifications, and color coding can be found in the National Fire Protection Association's Standard 13 (NFPA 13), Standard for the Installation of Sprinkler Systems. Each temperature rating has an associated maximum ceiling temperature specified to safeguard against accidental operation due to excessive ambient temperatures in a particular location, such as unconditioned attics or warehouses. Temperature ratings can also be specified as part of specific NFPA 13 design requirements.

To distinguish between different temperature ratings, sprinklers with fusible solder link-type thermal elements will have the appropriate temperature rating color-coded on either the frame arms of the sprinkler or the operating element itself. Sprinklers with glass bulb thermal elements will be color-coded based on the color of the fluid within the bulb.

Automatic sprinkler K-Factors

A sprinkler’s orifice is the opening through which water flows, and its size determines how much water will flow through it at a given pressure. Sprinkler orifices are typically tapered and are characterized by their discharge coefficient or K-factor. As the sprinkler orifice size increases, so does the K-factor; the larger the K-factor, the larger the orifice and the larger the flow. It takes less pressure to push the same amount of water through a larger orifice. 

Traditional sprinklers typically had an orifice size of ½" or 5.6. K-factors are specified in sprinkler manufacturer’s data sheets for a specific model sprinkler. Sprinklers of several types are available with nominal K-factors as specified in the manufacturer’s data sheet and identified in NFPA 13. 

Location, orientation, and position of automatic sprinklers

To operate in a timely and effective manner, sprinklers must be located and appropriately spaced, oriented, and positioned based on the requirements of NFPA 13 and/or the manufacturer’s requirements based on the sprinkler’s UL Listing. This includes:

  • Proper location relative to sprinkler spacing and minimum distances to obstructions for effective water distribution.
  • Properly orientated so they distribute the water in the direction as intended. These orientations include:
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Upright sprinkler

An upright sprinkler is designed and listed to be installed in a manner that the water discharges in an upward direction against the sprinkler deflector, and then redirected downward.

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Pendent sprinkler

A pendent sprinkler is designed and listed to be installed in a manner where the water discharge is directed downward against the deflector.

Sidewall Sprinkler

Sidewall sprinkler

A sidewall sprinkler is designed and listed with special deflectors to discharge most of the water away from a wall in a quarter of a sphere pattern, with a small portion of the discharge directed at the wall behind the sprinkler.  Sidewall sprinklers can be identified as vertical sidewalls or horizontal sidewalls.

Automatic sprinkler guards

Sprinkler Guard1

For sprinklers installed in areas subject to mechanical damage, where moving objects could strike and damage the sprinkler causing inadvertent operation, sprinkler guards are installed to encase and help protect the sprinkler. These sprinkler guards must be listed and approved for use with a specific sprinkler to ensure proper water distribution. Sprinkler guards can also minimize damage from moving pallet loads and help protect people from injury in places with low clearance. 

Sprinkler Water Shield

Sprinklers installed within rack structures in warehouses or under metal grading mezzanines or catwalks may require to be installed with a combination sprinkler guard and water shield. The water shield helps to protect the thermal operating element from water spray impingement caused by sprinklers located at a higher elevation. 

Automatic sprinklers storage cabinet

Sprinkler Class5

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 spare sprinklers required corresponds to the number and types of sprinklers in the building as specified by NFPA 13.

Building managers should keep the spares in a cabinet located where the temperature will never exceed 100 degrees F. The cabinet should also contain a specific sprinkler wrench used for removing and installing sprinklers. There must be one sprinkler wrench for each specific 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 sprinkler thermal operating element can insulate and prevent the sprinkler from operating at the specified temperature rating. The only way to fix a painted sprinkler is to replace it with a new sprinkler having the same characteristics. 



Other impairments of automatic sprinklers

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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 obstruct the flow of water to the fire and reduce the effectiveness of the sprinkler system.  This clearance increases for storage sprinklers, which is typically 36 inches.

Misuse Of Piping

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, damage the piping, or cause unnecessary stress on mechanical fittings.

Obstruction to automatic sprinkler discharge

When a sprinkler 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 sprinklers from operating. This is especially critical when the sprinkler system is an Early Suppression, Fast Response (ESFR) sprinkler system.

A well-designed sprinkler system minimizes distances to obstructions in accordance with the obstruction criteria in NFPA 13 for specific sprinklers. Such obstructions include:

  • Building structural members such as beams and columns
  • Bar joists
  • Bridge strapping
  • Electrical conduits
  • Lighting fixtures
  • Ventilation ductwork
  • Cable trays
  • High Volume ceiling fans

ESFR sprinkler obstructed by bar joist
Styrofoam Ceiling

Sprinkler deflector above plane of ceiling:
Styrofoam Ceiling

Common myths about automatic sprinklers

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

Myth: When one "goes off", they all "go off".
Fact: Sprinklers operate independently, and only when the ambient air temperature from a fire rises to meet or exceed the sprinkler’s temperature rating. In fires of most occupancy types, only one or two sprinklers operate during a fire. The only time water discharges from all sprinklers simultaneously is with a deluge sprinkler system. Deluge systems use open sprinklers (they have no fusible thermal element) or specially designed nozzles. Water is prevented from entering a deluge system by a closed deluge valve that is controlled by a detection system specific to the occupancy being protected.

Myth: Sprinklers cause severe water damage.
Fact: A single sprinkler generates about 25 gallons per minute, depending on the water pressure and the size of the sprinkler's orifice. That's not much compared to 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 of the immediate area.

Myth: Leaks and drips are common problems.
Fact: A properly designed and maintained sprinkler system does not leak. Part of the sprinkler’s listing criteria contains several leakage tests to ensure sprinkler seal integrity.

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

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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 piping.

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.

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