Special Hazards Systems
Domain scope
Special Hazards Systems III tests design and plan-review competence for systems outside ordinary sprinkler protection: foam, clean agent, carbon dioxide, dry/wet chemical, water mist, and explosion suppression. You must match the hazard to the standard - NFPA 11 for foam, NFPA 12 for CO2, NFPA 17/17A for chemical, NFPA 2001 for clean agent, NFPA 750 for water mist - and defend quantities, flow rates, and hardware from the listed design basis.
Core rules
- Define the hazard first: flammable liquid class, electrical energization, occupied vs unoccupied, enclosure integrity. Each drives agent choice and egress timing.
- Total flooding clean agent design depends on enclosure volume, minimum design concentration, and holding time; leakage area and enclosure integrity are as important as agent weight.
- CO2 total flooding requires life-safety safeguards because the design concentration is lethal; review pre-discharge alarms, lockout, and signage.
- Foam systems are sized by application rate, discharge duration, and foam concentrate inventory, not by sprinkler density alone.
- Wet chemical systems for cooking media rely on appliance-specific listings, plenum protection, and fuel shutoff interlocks.
- Water mist design is pressure- and nozzle-dependent; the listed spacing, K-factor, and minimum operating pressure cannot be swapped between manufacturers.
- Explosion suppression systems require a hazard analysis of the vessel, deflagration index, and detection response time before hardware selection.
Worked example
A print shop asks for clean agent protection of a 12 m × 8 m × 3 m room (288 m³) with a design concentration of 7% and a 10-minute hold. From the manufacturer's flow calculation, agent quantity is based on volume and concentration; the reviewer must also check that the enclosure leakage does not prevent the hold time. If the room has an unsealed door, the correct response is not to add agent - it is to require enclosure repair and a door fan test, then recalculate.
Traps
Using sprinkler density logic for foam; accepting agent weight without holding-time verification; omitting CO2 pre-discharge alarm; confusing wet chemical with dry chemical for cooking hoods.