A fire sprinkler system is an active fire protection method, consisting of a water supply system providing adequate pressure and flowrate to a water distribution piping system, to which fire sprinklers are connected. Although initially used only in factories and large commercial buildings, systems for homes and small buildings are now in use.
Fire sprinkler systems are extensively used worldwide, with over 40 million sprinkler heads fitted each year. Fire sprinkler systems are generally designed as a life saving system, but are not necessarily designed to protect the building. Of buildings completely protected by fire sprinkler systems, if a fire did initiate, it was controlled by the fire sprinklers alone in 96% of these cases.
History
Leonardo da Vinci designed a sprinkler system in the 15th century. He automated his patron's kitchen with a super-oven and a system of conveyor belts. During a large banquet, a fire broke out. It was concluded that, "The sprinkler system worked all too well, causing a flood that washed away all the food and a good part of the kitchen."
Ambrose Godfrey created the first successful automated sprinkler system in 1723."History of Sprinkler Systems". Associated Fire Protection. He used gunpowder to release a tank of extinguishing fluid.
Frederick Grinnell improved Henry S. Parmalee's design and in 1881 patented the automatic sprinkler that bears his name. He continued to improve the device and in 1890 invented the glass disc sprinkler, essentially the same as that in use today.Casey Cavanaugh Grant, PE "The Birth of NFPA" NFPA, 1996
Until the 1940s, sprinklers were installed almost exclusively for the protection of commercial buildings, whose owners were generally able to recoup their expenses with savings in insurance costs. Over the years, fire sprinklers have become mandatory safety equipment" in some parts of North America, in certain occupancies, including, but not limited to newly constructed "hospitals, schools, hotels and other public buildings", subject to the local building codes and enforcement. However, outside of the US and Canada, sprinklers have rarely been mandated by building codes for normal hazard occupancies which do not have large numbers of occupants (e.g. factories, process lines, retail outlets, petrol stations, etc.)
Sprinklers are now commonly installed in non-industrial buildings, including schools and residential premises. This is largely as a result of lobbying by the National Fire Sprinkler Network, the European Fire Sprinkler Network, and the British Automatic Fire Sprinkler Association.
Usage Sprinklers have been in use in the United States since 1874, and were installed in factory applications where fires at the turn of the century were often catastrophic in terms of both human and property losses.
Sprinklers may be required to be installed by building codes, or may be recommended by insurance companies to reduce potential property losses or business interruption. US building codes for places of assembly (generally over 100 persons) and places with overnight sleeping accommodation such as hotels, nursing homes, dormitories, and hospitals, usually require sprinklers either under local building codes, as a condition of receiving State and Federal funding, or as a requirement to obtain certification (essential for institutions who wish to train medical staff).
Regulations
United States The primary fire code writing organization is the private National Fire Protection Association (NFPA). NFPA sets the standards for technical aspects of sprinklers installed in the US. Building codes, which specify which buildings require sprinklers are generally left to local jurisdictions. However, there are some exceptions:
In 1990 the US passed PL-101-391, better known as the Hotel and Motel Fire Safety Act of 1990. National Fire Protection Association (NFPA) This law requires that any hotel, meeting hall, or similar institution that receives federal funds (i.e. for overnight stay, or a conference, etc.), must meet fire and other safety requirements. The most visible of these conditions is the implementation of sprinklers. As more and more hotels and other public accommodations upgraded their facilities to enable business with government visitors, this type of construction became the de facto industry norm – even when not directly mandated by any local building codes.
If building codes do not explicitly mandate the use of fire sprinklers, the code often makes it highly advantageous to install them as an optional system. Most US building codes allow for less-expensive construction materials, larger floor area limitations, longer egress paths, and fewer requirements for fire-rated construction in structures which are protected by fire sprinklers. Consequently, the total building cost is often decreased by installing a sprinkler system and saving money in the other aspects of the project, as compared to building a non-sprinklered structure.
In 2011, Pennsylvania and California became the first US states to require sprinkler systems in all new residential construction. However, Pennsylvania repealed the law later that same year. Many municipalities now require residential sprinklers, even if they are not required at the state level.
Europe Renewed interest in and support for sprinkler systems in the UK has resulted in sprinkler systems being more widely installed. In schools, for example, the government has issued recommendations through Building Bulletin 100, a design guide for fire safety in schools, that most new schools, except for a few low risk schools, should be constructed with sprinkler protection.Department for Children, Schools and Families, Building Bulletin 100, accessed 1 June 2021 In 2011, Wales became the first country in the world where sprinklers are compulsory in all new homes. The law applies to newly built houses and blocks of flats, as well as care homes and university halls of residence. In Scotland, all new schools are sprinklered, as are new care homes, sheltered housing and high rise flats.
In the UK, since the 1990s sprinklers have gained recognition within the Building Regulations (England and Wales) and Scottish Building Standards and under certain circumstances, the presence of sprinkler systems is deemed to provide a form of alternative compliance to some parts of the codes. For example, the presence of a sprinkler system will usually permit doubling of compartment sizes and increases in travel distances (to fire exits) as well as allowing a reduction in the fire rating of internal compartment walls.
Operation
Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb or a two-part metal link held together with fusible alloy. The glass bulb or link hold in place a "pip cap" which acts as a plug to prevent water from flowing, unless the ambient temperature around the sprinkler reaches the design activation temperature of the individual sprinkler head. In a standard wet-pipe sprinkler system, each sprinkler activates independently when the predetermined heat level is reached. Thus, only the sprinklers sufficiently heated from the fire will operate. This maximizes water pressure over the point of fire origin, and minimizes water damage to the building.
Many systems have a water flow alarm near the fire department connection pipe This is used to guide the fire department to the fire department connection pipe, as well as alert those who are not in the building that a sprinkler has been activated, and there is a possibility of a fire in the building. Although interior fire alarm notification appliances in modern systems are electronic horns, bells are regularly used for water flow alarms, as they can be powered purely by water flowing through the pipe rather than an electronic signal.
A sprinkler activation will usually do less water damage than a fire department hose stream (which provide approximately 900 litres/min (250 US gallons/min). A typical sprinkler used for industrial manufacturing occupancies discharges about 75–150 litres/min (20–40 US gallons/min). However, a typical Early Suppression Fast Response (ESFR) sprinkler at a pressure of will discharge approximately .
In addition, a sprinkler will usually activate within one to four minutes of the fire's start, whereas it typically takes at least five minutes for a fire department to register an alarm and drive to the fire site, and an additional ten minutes to set up equipment and apply hose streams to the fire. This additional time can result in a much larger fire, requiring much more water to extinguish.
Types
Wet pipe Wet pipe sprinkler systems are installed more often than other types of fire sprinkler systems. They also are the most reliable, because they are simple, with the only operating components being the automatic sprinklers and (commonly, but not always) the automatic alarm check valve. An automatic water supply provides water under pressure to the system piping.
Wet systems have optionally been charged with an antifreeze chemical, for use where pipes cannot reliably be kept above .
While such systems were once common in cold areas, after several fires which were not controlled because of sprinkler systems filled with too high a percentage of antifreeze, the regulatory authority in the United States effectively banned new antifreeze installations. A sunset date of 2022 applies to older antifreeze systems in the US. This regulatory action has greatly increased costs and reduced options for cold weather tolerant sprinkler systems.
Dry pipe
Dry pipe systems are the second most common sprinkler system type. Dry pipe systems are installed in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, which would make the system inoperable. Dry pipe systems are most often used in unheated buildings, in parking garages, in outside canopies attached to heated buildings (within which a wet pipe system would also be provided), or in refrigerated coolers. In regions using NFPA regulations, wet pipe systems cannot be installed unless the range of ambient temperatures remains above .NFPA 13 2007 ed. Sections 7-2 and A7-2
Water is not present in the piping until the system operates; instead, the piping is filled with dry air at a pressure below the water supply pressure. To prevent the larger water supply pressure from prematurely forcing water into the piping, the design of the dry pipe valve (a specialized type of check valve) results in a greater force on top of the check valve clapper by the use of a larger valve clapper area exposed to the piping air pressure, as compared to the higher water pressure but smaller clapper surface area.
When one or more of the automatic sprinkler heads is triggered, it opens, allowing the air in the piping to vent from that sprinkler. Each sprinkler operates independently, as its temperature rises above its triggering threshold. As the air pressure in the piping drops, the pressure differential across the dry pipe valve changes, allowing water to enter the piping system. Water flow from sprinklers, needed to control the fire, is delayed until the air is vented from the sprinklers. In regions using NFPA 13 regulations, the time it takes water to reach the hydraulically remote sprinkler from the time that sprinkler is activated is limited to a maximum of 60 seconds. In industry practice, this is known as the "Maximum Time of Water Delivery". The maximum time of water delivery may be required to be reduced, depending on the hazard classification of the area protected by the sprinkler system.NFPA 13 2010 ed. Table 7.2.3.6.1
Disadvantages of using dry pipe fire sprinkler systems include: