Special Hazards
Special hazards covers the systems that put out a fire without water: clean agent, carbon dioxide, wet chemical kitchen protection, dry chemical, and foam. The exam wants to know how these systems are triggered, how they interface with the building fire alarm, and where human life changes the design.
Clean agent systems (NFPA 2001)
- Total flooding design concentration comes from the manufacturer's listing and the cup burner value. Halocarbon agents such as HFC-227ea and FK-5-1-12 typically land near 5-7 percent; inert gases such as IG-541 land in the mid-30s to 40 percent. Class C fires use the extinguishing concentration with no added safety margin.
- Occupied spaces need a pre-discharge time delay (commonly 30 seconds), a pre-discharge alarm, clearly marked exits, an abort switch at the exit, and a manual release.
- Discharge must close HVAC dampers, shut down air handling, and annunciate at the FACP. Hold time is normally specified at 10 minutes for Class A deep-seated hazards.
Carbon dioxide (NFPA 12)
CO2 works by oxygen displacement and is lethal at design concentration. It is for unoccupied spaces, with signage, pre-discharge alarm, and lockout. Local application is used for printing presses and similar equipment. Never design CO2 total flooding for an ordinarily occupied room.
Kitchen hood systems (NFPA 17A)
Wet chemical nozzles protect each cooking appliance and the plenum. Actuation is by a fusible link rated about 450 F, with a manual pull station on the path of egress. Actuation shuts off fuel and appliance power. The hood system must report to the building fire alarm as a supervisory/trouble or alarm condition per the AHJ, and a Class K extinguisher is required nearby.
Worked example
An 8 ft hood over a range and two fryers: you need one nozzle per appliance plus a plenum nozzle (four total), the 450 F link above the cooking surface, a manual pull near the exit door, and a gas shutoff valve. On the alarm side, hood actuation sends a supervisory signal to the FACP and shuts the gas valve. The FACP does not actuate the hood system; the hood system's own releasing panel does that.
Traps that cost marks
- Wiring the abort switch to the FACP instead of the releasing panel, which defeats its purpose.
- Using one detector plus the FACP alarm as the second cross-zone confirmation instead of an independent detector.
- Forgetting HVAC shutdown and damper closure on clean agent discharge.
- Assuming the hood suppression system needs FACP power to release.