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Fire Sprinkler Systems: Understanding How and Why They Fail – Part 1
May 10, 2021 | By: Eduardo Mari
Sprinkler systems are designed to protect lives and property by suppressing or limiting the growth of fire in a building or structure. According to the NFPA, sprinklers were effective at controlling the fire in 96% of fires in which they operated. And the civilian fire death rate of 0.8 per 1,000 of reported fires was 87% lower in properties with sprinklers.[1]
These are highly effective and reliable systems; however, they are not infallible. And though instances of accidental activation are extremely rare (estimated at 1/16,000,000), if not properly manufactured, designed, installed and maintained, rather than preventing fire damage, sprinkler systems can be the cause of major water losses. Losses typically exceed $100,000 and can be upwards of $1,000,000 in many cases. It is therefore critical that these failures are investigated by a qualified forensic engineer to determine their root cause if insurers are to recover monies paid out in claims.
To understand how and why sprinkler systems fail, it is important to understand its main component parts and how they function; that will be the focus of this article, which will be followed by an examination of the most common causes of sprinkler system failures.
NFPA 13
The requirements for the design and installation of sprinkler systems are set forth in NFPA 13: Standard for the Installation of Sprinkler Systems. An important point of distinction, NFPA 13 does not specify which buildings or structures require a sprinkler system. That authority generally lies with the local, national or international building code. For example, until 2010, sprinkler systems in high-rise residences were not mandatory in Ontario despite being required in the rest of the country. And currently, British Columbia is the only province with fire sprinkler requirements for single-family homes. NFPA 13 is primarily concerned with how to properly design and install a sprinkler system and with which components and materials. It includes chapters on Classification of Occupancies and Commodities, System Components and Hardware, Sprinkler Location, System Types, and the Installation of Piping, Valves, and Appurtenances.
Types of Sprinkler Systems
There are two primary types of sprinkler systems, wet pipe systems and dry pipe systems. Both have inherent advantages and disadvantages.
Wet Pipe Sprinklers
Wet pipe sprinklers are the more common of the two by a wide margin. According to the NFPA, wet pipe sprinklers accounted for 87% of the sprinklers in reported structure fires.[2] In a wet pipe sprinkler system, the pipes are filled with pressurized water that discharges in the event of a fire. Wet pipe sprinkler systems are less complex than dry systems, less expensive to install, as well as easier to install and maintain. Which begs the question, why choose a dry pipe sprinkler system? Very often, the choice to install a dry system in a given location isn’t a choice at all, rather, a necessity. NFPA 13 regulations do not permit wet pipe systems to be installed unless the ambient temperature in the space remains reliably above 4°C.
Dry Pipe Sprinklers
Dry pipe sprinkler systems are used to protect areas that are exposed to low temperatures, such as parking garages, unconditioned areas of a building, and fridges/freezers. Dry pipe sprinkler systems are filled with pressurized air or nitrogen instead of water. The pressurized gas holds back the water supply at a dry pipe valve. When a fire is detected, the pressure drops and the valve opens to allow water to flow into the sprinkler pipes. The key advantage of a dry pipe system is it can be installed in areas of a building subject to sub-zero temperatures without the risk of pipes freezing and bursting. However, the additional control and air pressurization equipment make them more complex and therefore more expensive to install and more difficult to maintain. Critically, in the event of a fire, they also have a slower response time – as much as 60 seconds.
Sprinkler Piping
NFPA 13 lists both metallic and non-metallic materials appropriate for sprinkler pipe. Two of the most common of which are steel and chlorinated polyvinyl chloride (CPVC).
Steel
Steel has traditionally been the material of choice for fire sprinkler pipes because of its strength, durability, and high heat resistance. Steel has a melting point of 1,427°C – 1,538°C, meaning that even when subjected to intense heat inside a burning building it can still maintain the flow of water onto a fire. Furthermore, steel is not affected by exposure to ultraviolet light, nor is it easily damaged by mishandling. Steel is, however, the heaviest and least flexible of the materials listed, which can make installation more challenging and costly. Critically, it is also highly susceptible to corrosion.
Chlorinated polyvinyl chloride (CPVC)
CPVC has been used in sprinkler systems since the 1980s. Manufacturers of CPVC take PVC, which is a strong, durable product already used extensively for piping, and put it through a process called chlorination. The chlorination process allows it to withstand higher temperatures, making it suitable for fire sprinkler systems. When exposed to flame, the exterior of CPVC chars, creating a protective thermal barrier. And while its melting point (listed at 103°C) is far below that of steel, it is less expensive, lighter in weight, easier to install and resistant to corrosion – which explains its growing popularity. Among its drawbacks are susceptibility to damage from UV exposure and mishandling. Of course, it must be noted that whereas steel pipe is suitable for all fire protection systems, CPVC is limited to light hazard occupancies, one- and two-family dwellings and manufactured homes, and low-rise residential occupancies.
Sprinkler Heads
There are many misconceptions concerning the operation of fire sprinklers: That they are set off by smoke and/or alarms and that all sprinkler heads go off simultaneously. The reality is, in most systems, each sprinkler head activates independently and is triggered when the ambient temperature within its area of protection reaches a specific level (anywhere between 57°C and 343°C depending on the temperature rating). This not only minimizes water damage from the sprinkler discharge but also concentrates the water pressure over the area of origin.
When inactive, sprinkler heads are kept closed by either a heat-sensitive glass bulb or a two-part metal link held together with a fusible alloy. The bulb or link holds a plug in place which prevents the flow of water.
This is not an exhaustive list of sprinkler system components, but rather an overview of those most likely to fail or sustain damage that can lead to water losses. I feel it is important to restate these are very robust and reliable systems and this is in no way an indictment of their effectiveness. But, as with any critical piece of equipment, they require expert inspection and maintenance – which is governed by NFPA 25 – to maximize efficiency and prevent failures. In our next article, we will be covering the most common causes of failure in sprinkler systems.
Eduardo is a professional materials and metallurgical engineer with a Master’s Degree in Materials Science and Engineering from the State University of New York and over 15 years of experience in failure analysis, oil and gas industry and forensic engineering. He has led over 800 forensic and failure investigations and has specialized in the causes of failure of a wide variety of consumer and industrial products leading to property damage and liability claims arising from floods, plastic-polymer failures, mechanical and corrosion related failures as well as personal injury.
Eduardo has held leadership positions in technical groups for the materials engineering community as well as with the Canadian Standards Association where he is currently a member in one of the technical committees. He is currently a member of the Professional Engineers of Ontario (PEO), ASM International, National Association of Corrosion Engineers (NACE) and the National Association of Subrogation Professionals (NASP).
Eduardo has been a presenting author at several technical conferences and engagements for the insurance community.
[1] National Fire Protection Association, U.S. Experience with Sprinklers. Marty Ahrens. July 2017. https://www.nfpa.org/-/media/files/news-and-research/fire-statistics-and-reports/suppression/ossprinklers.pdf
[2] National Fire Protection Association, U.S. Experience with Sprinklers. Marty Ahrens. July 2017. https://www.nfpa.org/-/media/files/news-and-research/fire-statistics-and-reports/suppression/ossprinklers.pdf