NICET WBSL Level I cheat sheet

Water-Based Systems Layout

• Working pressure for layout: sprinkler discharge uses p = (Q/K)^2, where Q is flow in gpm, K is the sprinkler discharge coefficient, and p is pressure in psi; solve for Q as Q = K√p.

• Pipe schedule limits by size (Schedule 40 steel): 1 in. up to 2 sprinklers, 1¼ in. up to 3, 1½ in. up to 5, 2 in. up to 10, 2½ in. up to 30, 3 in. up to 60, 3½ in. up to 100, 4 in. and larger up to 100.

• Light hazard density starts at 0.10 gpm/ft² over 1,500 ft² design area; Ordinary Group 1 uses 0.15 gpm/ft² over 1,500 ft²; Ordinary Group 2 uses 0.20 gpm/ft² over 1,500 ft².

• Design area may be reduced by 25% (to a floor of 1,500 ft² for dry systems and 1,250 ft² where permitted) only when a listed quick-response sprinkler type is used and the ceiling is 10 ft or less; reduction applies only to the remote area, not to the density.

• Hazard classification drives spacing: light hazard maximum spacing 15 ft and 225 ft² per sprinkler; ordinary hazard maximum 15 ft and 130 ft² per sprinkler; extra hazard maximum 12 ft and 100 ft² per sprinkler.

• Hydraulic calculation formula: friction loss per foot in steel pipe = 4.52 Q^1.85 / (C^1.85 d^4.87) (Hazen-Williams), with Q in gpm, d in inches, C = 120 for steel and 150 for cement-lined ductile iron.

• Balancing: a branch line or head is balanced when its flow is increased until its pressure requirement equals the pressure at the junction; use Q_new = Q_old × √(p_new/p_old) for a single sprinkler.

• Flow test and supply: available pressure at the base of the riser equals static pressure plus (elevation loss/gain) minus friction loss from the source, and the supply curve must sit above the demand curve at the point of maximum demand.

• Alarm and control valves: a wet-pipe system requires a check valve, main control valve, and alarm check valve; a dry-pipe system requires a dry-pipe valve, air pressure (typically 20–40 psi above the trip point) and a quick-opening device where the system volume exceeds 500 gallons.