Fire Suppression Systems and Extinguishing Agents
Agent selection
Match agent to hazard: water for Class A; foam for Class B spills and tanks; dry chemical for B/C and pressure fires; wet chemical (saponification) for Class K cooking media; carbon dioxide for flammable liquids and energized equipment (no residue, but asphyxiation and re-ignition risk); clean agents (HFCs, fluorinated ketones, inert gases) for occupied electronics spaces. Design concentration must exceed the cup-burner/inerting value with a safety factor.
Automatic sprinklers
Know the four system types - wet pipe (fastest), dry pipe (adds water delivery delay and design-area increase), preaction (double interlock where water is damaging), and deluge (open nozzles, detection-triggered). Heads are defined by temperature rating, K-factor, response (quick vs standard), orientation, and application (control mode, suppression mode, ESFR, residential).
Demand calculation
Sprinkler demand = density × design area, plus hose allowance, plus inside/outside requirements. Density/area curves are not linear: lower density buys a larger remote area risk and vice versa. Dry systems increase the remote area; sloped ceilings and high-clearance storage drastically increase density (or mandate ESFR).
Supporting components
Risers, alarm valves, check valves, fire department connections, backflow preventers, fire pumps, and standpipes all affect achievable flow. Impairment procedures and NFPA 25 inspections keep systems reliable.
Worked example
A wet-pipe system with 0.20 gpm/ft² over a 1,500 ft² design area: 0.20 × 1,500 = 300 gpm, plus a 250 gpm hose allowance = 550 gpm total demand at the base of the riser. Compare against the supply curve at that pressure, not at city static pressure.
Traps
Confusing control-mode and suppression-mode sprinklers; forgetting hose allowance; forgetting that dry-pipe systems enlarge the design area; assuming halon remains available (production ended; replacements are HFC/inert/fluoroketone, and AFFF is being displaced by fluorine-free foams).