Sprinkler System Demand and Water Supply (NFPA 13)
From the discharge density on the floor to the water supply the system is designed around: sprinkler demand = density x design area, plus the inside/outside hose-stream allowance, held for the required duration to give the stored volume. An Ordinary Hazard Group 2 space at 0.20 gpm/ft^2 over 1,500 ft^2 plus 250 gpm of hose for 90 minutes needs 550 gpm and 49,500 gallons, the numbers that size the fire pump and the tank. The area/density screening demand; the full most-remote-area hydraulic calculation is a separate analysis. A design aid, not a stamped hydraulic submittal; a qualified fire-protection engineer and the AHJ govern.
Formula and source
sprinkler_gpm = density x design_area; total_gpm = sprinkler_gpm + hose_gpm; volume_gal = total_gpm x duration_min.
NFPA 13 (Standard for the Installation of Sprinkler Systems), 2022, by name; the density / design-area / hose / duration levers come from the hazard classification and the density-area curves.
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