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How Fire Sprinkler Systems Work

Fire sprinkler systems are triggered by extreme heat and can quickly extinguish a fire in the room where it started.
Fire sprinkler systems are triggered by extreme heat and can quickly extinguish a fire in the room where it started.
©iStockphoto.com/Jimmi Larsen

You've probably seen a number of movies where a small amount of smoke triggers all of the sprinklers in a building, soaking everyone and everything inside. But did you know that sprinklers aren't even triggered by smoke, and they don't all go off at once? Fire sprinkler systems are actually heat activated, one sprinkler head at a time, and most fires usually require only one or two sprinklers to be extinguished. These are just two of the many misconceptions about fire sprinkler systems. In this article, we'll dispel other myths and learn the ins and outs of this important safety technology.

You might think installing a fire sprinkler system is like choosing water damage over fire damage. This belief is a spinoff from the myths we just mentioned -- that sprinklers are activated by smoke and every sprinkler head goes off at the same time. If that were the case, sprinkler systems could potentially cause more harm than good. After all, if you burned a piece of toast, every sprinkler would go off, soaking all of your belongings, even though there never was any real danger of fire. Fortunately, the clever engineers who developed these systems designed them to reduce the damage to your property from water, smoke and fire.

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Fire sprinkler systems have been around for more than two centuries and have seen significant improvements over the years. It's true that early versions weren't very reliable and caused significant water damage. But today, sprinkler systems are credited with reducing deaths and loss of property by more than 65 percent [source: Fleming]. Since each sprinkler head is automatically triggered by fire-specific temperature, just one or two sprinklers can quickly extinguish and/or contain a fire to the room where it started and cause little property damage. And because sprinklers use about six times less water than a fire hose, they're actually less harmful to your property than a visit from the fire department.

Still convinced you know everything you need to know about fire sprinklers? We'll address another common myth and discuss the details of how sprinklers work on the next page.

 

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You've heard about the importance of a properly maintained smoke detector. You've probably also heard the annoying beeping noise it makes when it needs some attention. Have you also heard that a smoke detector is all you need for fire protection? If so, you've heard another one of the most common myths regarding fire sprinkler systems: We don't need them if we have a smoke detector. Some even believe that smoke detectors can put out fires. They cannot. Smoke detectors are designed to alert us to a potential fire, and in cases where they're hooked up to an alarm system, alert the fire department. They're an important part of a fire prevention system, as are fire sprinklers. The presence of one does not cancel out the need for the other. They work together to save life and property from fire.

When a fire starts, the resulting smoke will eventually set off a smoke detector alerting residents to danger. This process can be quite slow depending on where the smoke detector is located. Meanwhile, the fire is growing. Alerting residents to the presence of fire is important. But, so is putting the fire out. When a fire starts, it quickly heats the air directly above it. This air rises and is pushed out to either side when it hits the ceiling. As this hot air reaches a sprinkler head, that sprinkler head is activated.

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Not just any heat source will trigger a sprinkler system to activate. The sprinkler heads must detect a high enough temperature -- usually between 135 and 165 degrees Fahrenheit (57 to 74 Celsius). Most sprinkler heads are equipped with a glass trigger filled with a glycerin-based liquid that expands at the appropriate temperature, breaking the glass and activating the sprinkler head. The sprinkler head is attached to a system of pipes that are hidden behind the walls or ceiling. These pipes wind through the building and outside to connect with a reliable water source. When the sprinkler head is triggered, a valve to the pipe system is opened, releasing the water that is kept under pressure from the pipes. The water is quickly pushed out of the pipes through the sprinkler head, spraying water downward and out to the sides. This carefully designed spray of water extinguishes the fire below and prevents it from spreading.

Fire sprinkler systems have revolutionized fire safety by automatically putting out fires in the room of origin and preventing fires from spreading or re-igniting. The amount of time this process requires depends on the type of fire sprinkler system. We'll learn more about the different types of fire sprinkler systems on the next few pages.

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Because fire sprinkler systems protect a variety of buildings and property, many different types have been developed over the years. These include wet, dry, deluge, pre-action and foam. Each has its own unique set of characteristics that protect the specific building and property for which it was installed.

As we learned on the previous page, sprinkler heads are connected to a system of pipes in the walls or ceiling of a room. These pipes are composed of steel, copper or fire-resistant plastic. The most commonly used system in commercial buildings is a wet pipe system, which is composed of steel pipes that are always filled with water (hence, the term "wet"). The water in the pipes is under a moderate amount of pressure. When the sprinkler head is activated, the pressurized water in the pipes is immediately released, providing a faster reaction time than any other type of system.

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The wet pipe system is also the simplest and most reliable, boasting cost savings for easy installation and low maintenance. However, wet pipe systems are not always the best choice. Since the pipes are always filled with water, they're not recommended for locations where the pipes might freeze or in residential environments where accidental leaks could be detrimental.

As you might have guessed, in a dry pipe system, the pipes are not filled with water -- they're actually filled with compressed air. When the sprinkler head is activated, a valve releases the compressed air through the sprinkler head. Once all of the air is released, the pressure in the pipe changes, allowing water to fill the system. Dry pipe systems have a slower reaction time (up to a minute delay). To make up for this, dry pipe systems release a larger amount of extremely pressurized water, which requires larger pipes (and a larger budget). And, while a leaky pipe in a dry pipe system doesn't pose a flooding threat, maintenance to the system is more complicated and costly. So, this type of system isn't recommended unless specific conditions -- an unheated warehouse in Canada, for example -- exist. Read on to learn about the different types of dry pipe systems available.

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Pre-action and deluge systems are variations of the dry pipe system. Pre-action systems must be triggered twice before water is dispensed from the sprinkler head. The first trigger -- usually a smoke detector or a heat detector that is separate from the sprinkler head -- allows water into the pipes. Once this trigger occurs, the system acts like a wet pipe system. The second trigger, the individual sprinkler heads, releases the water, pushing it through the sprinkler head to extinguish the fire. This type of system provides added protection against false sprinkler head activation. If a sprinkler head is falsely triggered, an alarm will sound, but no water will be released, since the pipes remain dry until the second trigger has been activated. Although sprinkler heads are not likely to accidentally activate -- sprinkler heads have a one in 16 million false activation rate -- pre-action systems are very popular when dealing with sensitive property like in a museum or library [source: USFA].

In deluge systems, like the pre-action system, water enters the pipes when triggered by a heat or smoke detector, separate from the sprinkler heads. There may also be a manual function, where pushing a button or pulling a cord activates the system. The sprinkler heads in a deluge system are open, meaning they don't have a trigger function and are activated simultaneously. Deluge systems are usually installed in chemical plants or other areas where the spread of fire would be exceptionally hazardous.

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The widespread use of fire sprinkler systems and the resulting innovations are no doubt a result of laws, regulations and building codes that require their installation. We'll explore existing codes and the possible need for home regulations on the next few pages.

Fire sprinkler systems have been in use for more than 100 years. This is no doubt a result of codes and regulations, requiring the use of these systems in public buildings. Codes and regulations that require the installation of fire sprinkler systems were first put into place in the 1960s [source: Fleming]. Before then, builders mainly installed sprinklers to reduce property loss and insurance costs. After collecting staggering statistics comparing the fire death rate in sprinkler-protected buildings versus non-protected, the fire sprinkler industry began a push for updated building codes to require the installation of these systems.

Today, building codes in many countries require the installation of fire sprinkler systems, although the United States has the highest record of systems installed. These codes are usually based on generic code sets developed by building associations and other reputable organizations such as the International Code Council, the National Fire Protection Agency (NFPA) and the U.S. Fire Administration (USFA). Once adopted, these generic codes are locally amended. In the United States, building codes are set by city and state governments.

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Code sets usually require the installation of fire sprinkler systems across the board for new construction of high rises and commercial buildings. Retro-fit codes are becoming more popular. Some of the old, existing building types that now require sprinklers include hotels, nursing homes and dormitories. You can find out more about your area's codes for fire sprinkler systems by visiting your local government's Web site. Or visit www.nfpa.org for a free copy of the NFPA 5000 code set. The USFA Web site has many helpful resources as well, including a list of fire sprinkler protected hotels.

Unfortunately, even though most fire deaths occur in homes, codes have not yet been put into effect requiring fire sprinkler system installation in single-family homes. We'll discuss the advantages and disadvantages of installing home sprinkler systems on the next page.

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Despite the fact that a home fire occurs every 79 seconds, current building codes do not require automatic sprinkler systems in new-home construction.
Despite the fact that a home fire occurs every 79 seconds, current building codes do not require automatic sprinkler systems in new-home construction.
iStockphoto/Thinkstock

According to the American Fire Sprinkler Association, a home fire occurs every 79 seconds. A 2009 National Fire Protection Association study reports that 3,000 deaths a year can be attributed to fires in homes [source: Figueroa]. Given these startling statistics and what we've already learned about the life- and property-saving characteristics of fire sprinkler system installation, it's hard to believe that less than 2 percent of homes in the United States have fire sprinkler systems [source: Hall]. So why are homeowners hesitant to install a system that could save their lives and property?

While aesthetics shouldn't outweigh life safety, one reason many single-family homeowners don't want to install sprinkler systems is that they believe sprinkler heads are an eye sore. Fortunately, new designs for residential systems are actually quite undetectable, and many can be installed flush to the ceiling. Flush sprinkler heads are hidden behind a metal panel that hides the sprinkler head, but still allows it to spray normally.

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And residential sprinklers are smaller than commercial ones and require less water. They're typically dry pipe systems, providing added protection against potential water damage that could occur during home improvements or other home accidents. Additionally, since the development of residential systems is a newer concept, their designs include many new innovations (like improved sensitivity), making them faster than commercial sprinklers.

Perhaps the most common myth about home sprinkler systems is that they're expensive. Not only is the installation of a home fire sprinkler system affordable, it can drastically decrease your home owner's insurance premium. Considering installation costs, reduced insurance rates and potential property destruction costs, a 2007 National Institute of Standards and Technology found the addition of a home sprinkler system could produce up to $4,800 in savings. Home systems will only continue to become more cost-effective as they become more common. Don't be surprised if you're required to install sprinkler systems in your home at some point in the future.

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Sources

  • USFA. "Residential Sprinkler Myths and Facts." April 15, 2009. (March 7, 2010)http://www.snohomishfire.org/Community%20Information/Residentail%20Fire%20Sprinklers/Basic%20Information/Myths%20and%20Facts%20FEMA.pdf
  • Fleming, Russell. "The Fire Sprinkler Situation in the United States." National Fire Sprinkler Association. 2002. (March 15, 2010)www.sprinklerworld.org/vds.doc
  • Rollins Fire Sprinklers, Inc. "Learn About Fire Sprinklers." (March 15, 2010)http://www.rollinsfire.com/learn.html
  • Faith, Nicholas. "How Fire Sprinklers Work." The Providence Journal. (March 15, 2010)http://www.projo.com/extra/2003/stationfire/pdf/sprinkler.pdf
  • Fleming, Russell. "Anniversary Time: Recalling three big years in the development of automatic sprinklers." NFPA Journal. November/December 2009. (March 15, 2010)http://www.nfpa.org/publicColumn.asp?categoryID=1920&itemID=45069&src=NFPAJournal&cookie%5Ftest=1
  • Rodgers, Harlold. "Patent Application Publication." USPTO. September 20, 2007. (March 7, 2010)http://www.google.com/patents?id=lKeBAAAAEBAJ&printsec=description&zoom=4#v=onepage&q=&f=false
  • Fire Protection Group. "Fire Protection Systems." (March 15, 2010)http://www.apifiregroup.com/index.php
  • NFPA. "Residential Fire Sprinkler Information Kit." (March 7, 2010).http://docs.google.com/viewer?a=v&q=cache:II0GNdavoA4J:www.firesprinkler.org/downloads/AFSA-8060.pdf+fire+sprinkler+stats&hl=en&gl=us&pid=bl&srcid=ADGEEShD2Ldb_sWCeg3oGBhdeAU_xuT6jPHjHeOs77539boosZt9Z8evjlPeTeLBKjnOyGuNt-d9T5NZvKjlQUVudUkZK0l2QtRh8DrhVexbza2Fk-DJAYQLws_dcDd2nuhtX93C1UUV&sig=AHIEtbRtb-ge58UqgGoUM3wyY8o6wMmHGg
  • NFPA. "U.S. Experience with Sprinklers." February 2010. (March 7, 2010)http://www.nfpa.org/assets/files//PDF/Sprinkler_Fact_Sheet.pdf
  • NFPA. "The deadliest fires and explosions in U.S. history by property class." February 2010. (Dec., 2002)http://www.nfpa.org/assets/files/PDF/Research/Winecoff.pdf
  • Hall, John, Jr. "U.S. Experience with Sprinklers and Other Automatic Fire Extinguishing Equipment." NFPA. February, 2010. (March 7, 2010).http://www.nfpa.org/assets/files//PDF/OSsprinklers.pdf
  • National Institute of Standards and Technology. "Home Fire Sprinklers Score 'A' In Cost-Benefit Study." ScienceDaily. October 15, 2007. (March 15, 2010)http://www.sciencedaily.com/releases/2007/10/071011154124.htm
  • Figueroa, Maria. "Re: Fire sprinkler requirement public commentary." Fire Prevention Field Office. July 16, 2009. (March 15, 2010)http://www.bragannarbor.com/ezefiles/NFPA_Letter_-_Maria_Figueroa.pdf

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