Design and Installation Requirements
From hazard to hardware
Design starts with the enclosure. Compute the protected volume, deducting only solid, non-porous objects, then select a design concentration and a design temperature. Halocarbon quantity comes from the standard agent equation:
W = (V / s) × (C / (100 − C))
where V is enclosure volume (ft³), s is the specific vapor volume of the agent at design temperature (ft³/lb, from the manufacturer's table), C is design concentration (percent by volume), and W is agent weight (lb).
Worked example: 1,000 ft³ room, HFC-227ea, C = 7% (typical Class A/electronics value), s ≈ 1.9 ft³/lb at 70°F. W = (1000/1.9) × (7/93) = 526 × 0.0753 ≈ 40 lb. Round up to the nearest listed container size and add the manufacturer's piping/nozzle allowance.
Other requirements to know:
- The enclosure must retain the design concentration for the required hold time, proven by a door fan (enclosure integrity) test. Leaky rooms need their penetrations sealed and dampers made closable - not simply more agent.
- Pressure relief venting is sized for peak discharge flow, especially with inert gases.
- Halocarbon discharge must be complete within 10 seconds; inert gas systems get a longer window, up to 60 seconds.
- Halocarbon piping is two-phase and must be sized with listed software, not generic hydraulic formulas.
- Detection is cross-zoned so a single detector cannot discharge the system (NFPA 72).
- Kitchen systems need appliance, plenum, and duct nozzles, a manual pull, fuel/gas shutoff, and interlocks that stop the appliance on actuation (NFPA 17A, UL 300).
Trap: deducting volume for people or for doors that happen to be open, and signing off a room that was never integrity-tested.