NE Fire Sprinkler cheat sheet
NE Fire Sprinkler · Keep the key ideas within reach.
Water-Based Fire Protection
NFPA 13 design approach: pipe schedules are limited to light and ordinary hazard occupancies up to specified sizes; hydraulic calculation is required for all other cases.
Density/area method: discharge density (gpm/ft²) is selected from the occupancy hazard curve and applied over the remote area; area may be reduced for dry systems (+30%), sloped ceilings, and high-temperature sprinklers per the standard.
Hazard classification drives everything: Light (e.g., offices, churches), Ordinary Group 1 (e.g., parking garages, laundries), Ordinary Group 2 (e.g., machine shops, mercantile), Extra Group 1 and 2 (flammable liquids, plastics).
Minimum operating pressure for a standard spray sprinkler is 7 psi (0.48 bar); the 7 psi floor is a common exam trap when computed pressure is lower.
K-factor relates flow to pressure: Q = K√P, where Q is gpm and P is psi. A K=5.6 sprinkler at 7 psi flows about 14.8 gpm.
Wet system: water in piping at all times; dry system: air or nitrogen under pressure with water held back by a dry pipe valve; preaction: detection must operate before water enters piping.
Deluge systems use open sprinklers or nozzles and a deluge valve; activation discharges water from all heads simultaneously in the protected area.
Sprinkler spacing and coverage: standard spray upright/pendent spacing maximums vary by hazard, commonly 15 ft (4.6 m) for light hazard and 12 ft (3.7 m) or less for higher hazards; check the applicable table.
Hydraulic calculation output must include the remote area flow, required supply pressure and flow at the base of the riser, plus hose stream allowance (e.g., 100-250 gpm depending on hazard).