Building Construction, Utilities, and Fire Protection Systems
Construction types and fire resistance
NFPA 220 classifies buildings Type I through Type V. Type I is noncombustible with high fire-resistance ratings; Type II is noncombustible with lower or no ratings; Type III has noncombustible exterior walls and combustible interior elements; Type IV is heavy timber; Type V is wood frame. Legacy balloon framing spreads fire through stud channels from cellar to attic, while platform framing has fire stops at each floor. Lightweight engineered trusses and I-joists fail early under fire, creating a collapse hazard for investigators.
Utilities and suppression systems
Know the utility shutoffs: gas meter or riser valve, electric service disconnect, water main. Fire flow is the water rate needed for suppression and is not the same as sprinkler density (gpm/ft² over a design area). Standpipes are Class I (2.5-inch outlets for fire department use), Class II (1.5-inch for occupants), and Class III (both). Wet, dry, deluge, pre-action, and foam systems behave differently; the presence of sprinklers does not prove the fire was small - check the control valve, water supply, and operating records. Detection and alarm devices can preserve evidence of activation timing.
TRAP: Assuming an open sprinkler head proves it operated effectively, or that a burned-through roof means the system failed.
RULE OF THUMB: Before interpreting damage, identify the building type, the structural systems, and every utility and suppression system serving the area.