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FIRE EXTINGUISHMENT AND CONTROL Fig. 34-2. Typical automatic sprinkler installation for a modern industrial plant Note sprinkler systems, yard mains, and water supplies Courtesy Factory Mutual Engineering Division "Handbook of Industrial Loss Prevention" expelling the water into the piping sup ply system 4 Elevated tanks or reservoirs that depend on gravity to force water through the system At least two of these independent sources must be available as primary and secondary sources of water to the Ere extinguishment equipment In case of fire, the primary source furnishes water to the system im mediately, it is reinforced by the secondary source that also supplies emergency protec tion if the primary source is out of service The preferred primary source is a connec tion from a reliable public water works system Connection should be made to two different mains to provide greater volume and flexibility in case of failure of one water mam The preferred secondary source is a fire pump that can deliver water at high pressure over an extended time This pump should be located where it will not be put out of service by a fire, and it should have an emergency power supply, independ ent of the plant system Care must be taken that the water con nections do not pollute drinking water, es pecially where emergency supplies are taken from a nver or other nonpotable source Stored water for private fire protection should not be removed for other purposes Everyday use of tank-stored water necessi tates constant refilling, hence the danger of accumulated sediment circulating mto the hydrant and sprinkler system, also the varying water level may shorten the life of a wooden tank or require frequent painting of a steel tank Construction and installation of water tanks are beyond the scope of this chapter, however, one basic consideration is men tioned--m freezing temperatures, the tanks should be heated In support of this con sideration, the heating system should be inspected daily during freezing weather, the control valves, weekly, and the entire sys tem (tank, supporting tower, pipmg, valves, heating system, and all components and ac cessories), annually a To facilitate inspec- National Fire Protechon Association, 60 Batterymarch St, Boston, Mass Water Tanks for Private Fire Protection. Stand ard No 22 Also -see '-NFPA. Foe Protec tion-Handbook 34-2