Automatic Fire Sprinkler Systems
System types and design basis
Wet-pipe systems are the default where freezing is not a risk. Dry-pipe systems use air or nitrogen and require a larger design area and faster water delivery; pre-action systems add detection and are used where accidental discharge is unacceptable; deluge systems open all heads on a signal. Design begins with hazard classification and a density/area curve: density in gpm/ft² (or mm/min) applied over the remote area. Hydraulic calculation proves that the water supply meets the most remote demand plus a safety margin. K-factor relates flow to pressure: Q = K√P.
Layout and traps
Candidates must know maximum sprinkler spacing and coverage area by hazard, minimum clearance below deflectors, obstruction rules, and the treatment of sloped ceilings and beams. ESFR heads are for high-challenge storage; they are not a general substitute for control-mode design. Dry-pipe and pre-action systems attract remote-area increases, and antifreeze systems have limited concentrations. Traps: assuming the design density applies to the whole floor; confusing K-factor with flow; taking pressure at the wrong reference point; and forgetting that a larger K-factor lowers pressure but increases flow demand.
Worked example: a sprinkler with K = 8.0 gpm/psi^0.5 at 15 psi flows Q = 8.0 × √15 = 31 gpm (about 117 L/min). If the design density is 0.20 gpm/ft² over a 1500 ft² remote area, demand is 300 gpm. At 31 gpm per head, at least 10 heads must be included in the calculation, unless the chosen density/area point or head spacing changes the number. Confirm the supply curve gives adequate residual pressure at the base of the riser.