NICET WBSL Level II cheat sheet

Water-Based Systems Layout

• Hazard classification drives design density and hose allowance: Light Hazard 0.10 gpm/ft² over 1,500 ft²; Ordinary Group 1 0.15 gpm/ft² over 1,500 ft²; Ordinary Group 2 0.20 gpm/ft² over 1,500 ft²; Extra Hazard Group 1 0.30 gpm/ft² over 2,500 ft²; Extra Hazard Group 2 0.40 gpm/ft² over 2,500 ft² (NFPA 13 density/area curves govern final values).

• Remote area size is adjusted by quick-response sprinkler credit (typically −25% for wet systems below 12 ft ceilings, with limits on reduction) and by slope: 1.5:1 slope adds 30% to the remote area in applicable occupancy classes.

• Minimum design pressure for a wet standpipe/hose outlet is 100 psi at the topmost outlet (65 psi residual with 100 psi flowing for combined systems); minimum sprinkler operating pressure is 7 psi per NFPA 13.

• Flow formula: Q = density × area (gpm). Friction loss via Hazen-Williams: p = 4.52 Q^1.85 / (C^1.85 × d^4.87), with C = 120 for black steel, 130 for galvanized, 150 for copper/cement-lined.

• Pipe sizing check: velocity = 4.05 Q / d² (Q in gpm, d in inches); keep velocities generally under 20 ft/s for supply mains and 15 ft/s in branch lines to limit noise and erosion.

• Sprinkler spacing: standard spray upright/pendent max 15 ft between sprinklers and 225 ft² per head for light hazard; 130 ft² per head for ordinary hazard; max 12 ft from a single sprinkler to any wall or 0.5 × spacing where greater.

• Hydraulic junction rule: at a split, flows divide so head loss is equal on both paths; balance by iterating branch flows, then add hose stream allowance and safety margin at the base of the riser.

• Pump curve selection: churn pressure must not exceed 140% of rated pressure; design point must fall on or below the pump curve, and the pump must satisfy the demand plus a 10-15 psi safety margin.