CO2 Total Flooding in a Room With a Conveyor Opening
A high-pressure CO2 total flooding system protects a 500 ft² dip-tank room in a metal finishing plant. The design concentration is 34%. The room is normally unoccupied, but an operator loads parts through a manual door, and a conveyor passes through two unsealed wall openings into a packaging area where several people work all shift. The system has a manual pull station outside the door, no predischarge alarm, no time delay, and no warning signage. Room ventilation is tied into the packaging area's air handler and the return is in the packaging area. The owner wants to add a conveyor lockout switch and otherwise leave the system alone.
1. Rank the life-safety deficiencies you would cite and explain why each matters.
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- No predischarge alarm or time delay in a space that can be occupied. CO2 at 34% is far above the level that is immediately dangerous to life; a person inside has seconds, not minutes. The standard requires an alarm and a delay before discharge where a space can be occupied, precisely so the space can be evacuated.
- Open conveyor penetrations into an occupied area. This is both a design failure (the enclosure cannot hold concentration) and a life-safety failure - the agent that leaks out goes where people are working.
- Shared ventilation. If the return is in the packaging area and the room is on the same air handler, a discharge or a leak can be distributed to occupied space.
- No warning signage at entrances warning of the CO2 hazard and prohibiting entry after discharge.
- The proposed conveyor lockout is worthwhile but insufficient - stopping the belt does not close the opening or warn anyone.
2. Can the enclosure hold 34% with the conveyor openings as they are? What are the realistic options?
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No. CO2 total flooding depends on a reasonably tight enclosure; two permanent open conveyor slots are a direct discharge path into the packaging area. Options, in order of preference:
- Interlocked closure: listed shutters or dampers on the conveyor openings that close on alarm and before discharge, interlocked so the conveyor stops and the closure proves closed before agent releases. This preserves total flooding and protects the adjacent area.
- Convert to local application over the dip tank itself, designed to the applicable local-application criteria. For open dip tanks this is often the technically correct hazard approach, since the tank - not the room - is the fire.
- Enclose the tank in a purpose-built, tight enclosure that is designed and tested to hold concentration.
The wrong answer is to increase agent quantity to compensate for permanent openings. Get the engineer of record and AHJ involved before any of these; the system's documented design basis must be revised.
3. What is the appropriate action on the shared HVAC, and what else must be verified before the owner's change is accepted?
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HVAC: the room must be isolated from the occupied area. Provide interlocked shutdown of the room's supply and return on alarm, with dampers that close, and confirm that no return air path exists from the protected room to the packaging area. If ducts are shared, that is a design deficiency to be corrected, not merely an alarm interface.
Also verify:
- Detection arrangement is cross-zoned or otherwise not prone to a single-device false discharge, since a discharge into a partially occupied room is itself a hazard.
- Manual discharge station location, accessibility, and signage.
- Discharge nozzle layout still suits the current tank and enclosure arrangement.
- The gas shutoff/process shutdown sequence for the dip tank.
- The conveyor lockout is tied into the same pre-discharge sequence and is functionally tested, not just installed.
- Employee training and the post-discharge re-entry procedure are documented.