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FIRE EXTINGUISHMENT AND CONTROL mechanical damage can be accomplished by connecting to the piping an automatic, lowpressure air supply that compensates for minor system leakage A rapid reduction m pressure resulting from, say, an acci dental breakage of the pipmg, sends a trou ble signal without tripping the water-con trol valve The preaction valve, which controls the water supply to the system pipmg, is actu ated by a separate automatic detection sys tem, which is located m the same area as the sprinkler, and not by the operation of a sprinkler Because the detection system is more heat sensitive than the sprinklers, the water-supply valve opens sooner than m a dry-pipe system The water-supply valve can also be operated manually Usually an alarm is sounded when the valve opens and starts filling the system with water There may then be tune to put out the fire with portable equipment before the sprinklers go into action and drench the area with water This system is espe cially effective where valuable merchan dise is handled or stored Deluge The deluge system wets down an entire area by admitting water to sprin klers that are opened at all times Deluge valves that control the water supply to the system are actuated by an automatic detec tion system located in the same area as the sprinklers The water supply valves can also be operated manually This type of system is primarily designed for extra-hazard occupancies where great quantities of water may have to be applied immediately over large areas Deluge sys tems are ordinarily used to best advantage where rapidly spreading or flash fires may be anticipated, such as m explosives plants, plants handling or processing nitrocellulose materials, lacquer plants, and buildings which contain large quantities of flamma ble materials Deluge systems are also used in aircraft hangars and large assemblv plants where ceilings are unusually high and where the possibility of drafts could cause sprinklers adjacent to the fire to op erate instead of those directly above the fire Another application of a deluge system is an open system of outside sprinklers for distributing water over the roof, extenor of a building, or at windows, cornices, etc, to protect it against fire from adjoining property This type is usually manually operated and is used where construction is inadequately protected by design or by dis tance from adjacent fire hazards. In special applications, open sprinklers and closed sprinklers may be combined m a single system where deluge protection is not needed over the entire area However, it must be remembered that separate auto matic detectors are also required m the area covered by the closed sprinklers, that operation of a closed sprinkler will not acti vate the entire system, and that a fire in the area of the closed sprinkler will also cause water to discharge bom all of the open sprinklers Automatic alarms, operated by the flow of water through the system, should be a part of every standard sprinkler installa tion. Such an alarm may be connected to a central-station fire alarm service or to the municipal fire department, or may be a local alarm signal Its purpose is to give prompt notice that the sprinkler system is operat ing It also signals water leakage or dis charge from causes other than fire The automatic alarm system must be tested and inspected frequendy and be maintained by persons thoroughly familiar with it Temperature rating of sprinklers Sprin klers should be selected on the basis of temperature rating and occupancy The proper rating is determined by the maxi mum temperature to which they will be subjected during normal (no fire) operat ing conditions Sprinklers are built with heat-actuated elements of solder that melt, or with special devices in which chemicals melt or expand to open them Table 34-A shows the ratings and distinguishing colors of sprinklers Quick operation of sprinklers--an advan tage when over a fire--may be a disadvan tage elsewhere, wasting water and wetting down materials that might otherwise be unaffected. Tests* conducted by the Fac- *"Temperahire Rating and Sprinkler Performance." NFPA Quarterly (July 1963) 34-6