Sprinkler system
|
|
- The term "sprinkler system" may also refer to a type of irrigation system.
Sprinkler.jpg
Sprinkler systems for fire protection consist of overhead pipes fitted with sprinkler heads. Each head is held closed independently by heat-sensitive seals. These seals prevent water flow until a design temperature is exceeded by the individual sprinkler heads. Seals may be broken by melting (fusing) of metals with a low melting point (often bismuth alloys), or may be glass bulbs that break from pressure differences when heated.
Sprinklers have been in use in the United States since 1874, and were used in factory applications where fire losses at the turn of the century were often catastrophic in terms of both human and property losses. In the US, sprinklers are today required in all high rise and underground buildings generally 75 feet (23 m) above of below fire department access, where the ability of fire fighters to provide adequate hose streams to fires is limited. Sprinklers may also be required in hazardous storage spaces by building codes, or may be required by insurance companies where liability due to potential property losses or business interruptions can be reduced by adequate automatic fire protection. Building codes in the United States 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.
Typical sprinkler head activation temperatures are 135 °F (57 °C), 155 °F (68 °C), 200 °F (93 °C), and 286 °F (141 °C), which correspond to the type of hazard the sprinkler system protects against. Life safety hazards, such as residential occupancies, use a lower (therefore quicker) activation temperature. Each sprinkler activates independently. The design intention is to limit the total number of sprinklers that operate, thereby providing the maximum water supply available from the water source to the point of fire origin. Standard wet sprinkler systems are designed for 1500 square feet (140 m²), and maximum water supplies of about 300 US gallons per minute (20 L/s).
Typical "wet" systems are simple and passive, requiring no manual controls to activate, so long as adequate water supplies are provided. Specialty systems called "dry" systems, designed for small unheated spaces, have a low "maintenance" air pressure in the pipes, which can be displaced by water in the event that a sprinkler "fuses" allowing the maintenance air pressure to reach a minimum pressure point. "Pre-action" systems are highly specialized for locations where accidental activation is unacceptable such as museums with rare art works, manuscripts, or books. Pre-action valves are connected to fire alarm initiating devices such as smoke or heat detectors and virtually eliminate the possibility of accidental water flow. In the event that there is a fire, the fire, and the fire department's hose streams which provide around 250 US gallons per minute (15 L/s), will do more damage than sprinkler activation, generally around 14 US gallons per minute (1 L/s), per sprinkler.
Other specialty systems may have foam instead of water suppression agents for fire protection in occupancies with flammable liquids, such as airport hangars. "Clean agent" gaseous systems, such as Argon/CO2/Nitrogen mixtures can be used in very small spaces where water cannot be used for suppression, such as magnesium storage spaces.
Cost of sprinkler systems run from US$2 - $5 per square foot ($50/m²), depending on type and location, however specialty systems may cost as much as $10/square foot ($100/m²). Systems can be installed during construction or retrofitted. Some communities have laws requiring residential sprinkler systems, where large municipal hydrant water supplies ("fire flows") are not available. Nationwide in the United States, one and two-family homes generally do not require fire sprinkler systems, although the overwhelming loss of life due to fires occurs in these spaces. Residential sprinkler systems are relatively inexpensive (about the same per square foot as carpeting or floor tiling), but require larger water supply piping than is normally installed in homes, so retrofitting is usually cost prohibitive.
According to the National Fire Protection Association, fires in hotels with sprinklers averaged 78% less damage than fires in hotels without them (1983-1987). The NFPA says the average loss per fire in buildings with sprinklers was $2,300, compared to an average loss of $10,300 in unsprinklered buildings. The NFPA adds that there is no record of a fatality in a fully sprinklered building outside the point of fire origin. However, in a purely economic comparison, this is not a complete picture; the total costs of fitting, and the costs arising from non-fire triggered release must be factored.
The NFPA states that it "has no record of a fire killing more than two people in a completely sprinklered building where a sprinkler system was properly operating, except in an explosion or flash fire or where industrial fire brigade members or employees were killed during fire suppression operations."
The world's largest fire sprinkler manufacturer is the Grinnell division of Tyco International, other manufacturers are Viking Sprinkler Co. and Reliable Sprinkler Company.
See also
External links
- American Fire Sprinkler Association SprinklerNet (http://www.sprinklernet.org/)
- National Fire Protection Association (http://www.nfpa.org/)
- British Automatic Sprinkler Association (http://www.basa.org.uk/)de:Sprinkleranlage