Automatic sprinkler system
An integrated arrangement of fixed facilities for protection from combustion by use of water extinguishment. The system comprises an adequate water supply, hydraulically designed internal piping, and sprinklers connected in a systematic pattern over the protected area; the system is activated by a fire to discharge a fine spray of water over the heat.
Essential features of a system are its self-detection of fire, prior installation, and built-in activation. In these respects, the automatic sprinkler system is among the earliest-used architectural features that contribute actively to maintenance of the internal environment (in contrast to the passive fire-resistant contribution of the static structure). Auxiliary to an automatic sprinkler system may be a fire alarm. See also Fire detector.
The principal component of the system is a thermally sensitive sprinkler with a linkage assembly that holds closed the discharge opening. In various designs the assembly is disrupted through a low-melting-point chemical, a frangible bulb filled with liquid, a bimetallic disk, or—usually—a low-melting-point alloy link. The sprinkler abruptly opens to discharge water against a deflector so that water falls in a hemispherical spray across the area below.
Water reaches the sprinklers variously in five basic setups. In the usual wet-pipe system, for heated buildings, all pipes contain water under pressure for immediate release through any sprinkler that opens. In a dry-pipe system—for unheated buildings in freezing climates or for cold-storage rooms—branch lines and other distribution pipes contain dry air or nitrogen under pressure. For occupancies where flash fires are possible, a deluge system is appropriate. All sprinklers are continuously open while the pipes are empty. In a preaction system, both heat-sensitive sprinklers and separate detectors guard the area; the separate detectors open a preaction valve and sound an alarm in the event of fire. Another adaptation is the recycling preaction system, applicable to unattended buildings, in which the water flow recycles if necessary to follow the fire cycle. See also Fire extinguisher; Fire technology.
