Fire Sprinkler System Design and Layout
Domain 1 checks whether you can turn an occupancy description into a workable layout: hazard classification, density/area selection, sprinkler type and K-factor, spacing and coverage limits, and the obstruction rules that decide where an extra head is needed. Questions are short scenarios - a room, a ceiling height, a commodity - with four plausible layouts, and usually only one survives the standard.
Hazard classification comes first
Light, Ordinary Group 1, Ordinary Group 2, Extra Hazard Group 1 and Group 2 are the five occupancy classes. Storage is handled differently, through commodity Class I–IV and plastics groups, using the storage chapters rather than the occupancy curves. A misclassification moves density, remote area, hose allowance and duration simultaneously, which is why it is the most expensive error on a set of drawings.
Density, area and the demand point
Base curve points you should know cold: light hazard 0.10 gpm/ft² over 1,500 ft²; Ordinary Group 1 0.15 over 1,500; Ordinary Group 2 0.20 over 1,500; Extra Hazard Group 1 0.30 over 2,500; Extra Hazard Group 2 0.40 over 2,500. The curves trade density against area, but you must stay on the curve for the correct hazard - sliding to a neighbouring curve to make the numbers work is a classic exam trap.
Spacing and coverage limits
Standard spray sprinklers: maximum 15 ft between sprinklers on a branch line, 15 ft between branch lines, protection area capped at 225 ft² per sprinkler in light hazard and 130 ft² in ordinary hazard, and no sprinkler more than half the allowable spacing from a wall. Deflectors sit not less than 1 in and not more than 12 in below the ceiling (6 in below combustible ceilings).
Worked example
A light-hazard office area is protected at 15 ft × 15 ft spacing with K 5.6 pendents. Remote area demand = 0.10 × 1,500 = 150 gpm. Hose allowance for light hazard adds 100 gpm, so the supply must satisfy 250 gpm. Flow per sprinkler = 0.10 × 225 ft² = 22.5 gpm; required pressure = (22.5 ÷ 5.6)² = 16.1 psi. That pressure is the starting node for the hydraulic calculation.
Traps that cost marks
Using occupancy hazard where commodity classification is required; forgetting the hose allowance; specifying 225 ft² coverage at a spacing wider than 15 ft; applying NFPA 13R or 13D relaxations to a full NFPA 13 building; and ignoring the obstruction rule for ducts or beams within 18 in of the deflector.