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The water supply for sprinkler systems shall be taken from one or more of the following sources:
(a) Gravity tanks. Having a capacity sufficient to supply not less than 25 percent of the total number of heads in the largest fire area served for a period of not less than 20 minutes. The bottom of the tank shall be not less than 35 feet above the highest sprinkler connected thereto and the discharge from each sprinkler shall be calculated as 22 gallons per minute; the minimum capacity of the tank shall be 10,000 gallons.
(b) Pressure tanks. Having a capacity of not less than 4,500 gallons and not more than 9,000 gallons each, designed to be two-thirds full of water and one- third full of air at a pressure of not less than 75 pounds per square inch. Total water capacity of tanks in gallons shall be calculated as given in the gravity tank capacity section. The drop from the gravity tank shall be arranged to enter the line from the pressure tank at a level at least 35 feet below the bottom of the gravity tank and the gravity tank check valve shall be at this level when both gravity tank and pressure tank are used.
(c) Fire pumps, connected to a city water main, having a capacity sufficient to supply not less than 25 percent of sprinklers in the largest fire area except that no fire pump supplying sprinklers only need be larger than 1,500 gallons. Capacity of a fire pump shall be not less than 500 gallons per minute; however, a 250 gallons per minute sprinkler fire pump supplied by not less than a four-inch connection to the city water may be used in a school, an institutional unit, or a building used only as a residential unit which does not exceed four stories or 55 feet in height and which has less than 100 sprinkler heads in any sprinkler area. The discharge from each sprinkler head shall be calculated as 22 gallons per minute. The pressure shall be sufficient to provide 18 pounds per square inch at the highest sprinkler for a system not utilizing hydraulic design.
A fire pump may supply both a sprinkler system and an inside standpipe system; provided, however, the capacity of the pump is equal to the required capacity for the automatic sprinkler system and one-half the required capacity for the standpipe system. It shall be designed to meet the pressure requirements prescribed for the more severe service. The city connection shall be increased two inches if used to supply both domestic service and fire protection demands when the domestic service exceeds two inches.
(d) City mains. City water mains having sufficient volume and residual pressure in the main to supply 25 percent of the total number of sprinklers in the largest fire area to a maximum of 1,500 gallons per minute at a residual pressure of 18 pounds per square inch at the level of the highest sprinkler for a system not utilizing hydraulic design. The discharge shall be calculated as 22 gallons per minute.
(Prior code § 91-11; Amend Coun. J. 10-30-96, p. 31216, § 1)