Fire Suppression Systems
Design by density and area
NFPA 13 begins with the hazard classification: light hazard, ordinary hazard Groups 1 and 2, extra hazard Groups 1 and 2, plus the storage chapters. Read the density/area curve to obtain gpm/ft² and the design area (commonly 1,500 ft²), multiply to get the sprinkler demand, add the hose stream allowance, then run the hydraulic calculation against the available supply plus fire pump. Adjustment rules matter: quick-response sprinklers may permit a smaller design area; dry-pipe and preaction systems increase it by 30% because of water delivery delay; sloped ceilings and high-temperature sprinklers increase it too.
Hardware and interfaces
Fire pumps (NFPA 20) are evaluated at churn, rated flow, and 150% of rated flow, where residual pressure must remain at least 65% of rated while churn pressure is capped (roughly 140% of rated for most centrifugal pumps - confirm in the adopted edition). Standpipes (NFPA 14) come as Class I (2½ in for fire department use), Class II (1½ in for occupants), and Class III (both). ITM follows NFPA 25: periodic gauge and valve checks, annual main drain and flow tests, five-year internal pipe inspection.
Alternative agents
Clean agents (NFPA 2001) are designed above the extinguishing concentration but constrained by NOAEL/LOAEL so occupants can breathe the agent; enclosure integrity (door-fan test) and hold time are essential. CO2 (NFPA 12) is lethal at design concentrations and restricted to unoccupied spaces. Wet chemical (NFPA 17A) covers cooking; foam (NFPA 11) covers flammable liquids.
Worked example
Ordinary Hazard Group 2: 0.20 gpm/ft² over 1,500 ft² = 300 gpm, plus a 250 gpm hose allowance = 550 gpm required at the base of the riser, before any dry-system 30% increase (which would raise the design area to 1,950 ft² and the sprinkler demand to 390 gpm).
Traps
Omitting hose allowance; forgetting the 30% dry/preaction increase; confusing design concentration with NOAEL; applying 13R/13D allowances to a full NFPA 13 design.