Clean Agent Hold-Time Failure in a Data Hall
A 6,000 ft³ data hall (30 ft by 20 ft by 10 ft) is protected by a pre-engineered FM-200 total-flooding system designed for 7.0 percent concentration and a 10-minute hold time. The room has a raised floor, a suspended ceiling, one double-leaf door with a 1.5-inch undercut, two 3-inch conduit sleeves that were added for new network cabling, and a return-air grille with no damper. During acceptance testing, a door-fan enclosure integrity test yields a measured hold time of 4.8 minutes. The owner's representative wants to add one 75-pound cylinder 'to make up for leakage' and sign off, arguing that the system still has spare capacity. The installing contractor says the door-fan test is optional because the system is pre-engineered and the room was already accepted. The AHJ has not yet issued final approval.
1. Evaluate the owner's proposal to add one cylinder. Would additional agent restore the required hold time? Explain the relationship between concentration, leakage, and retention.
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Additional agent does not fix a leakage problem. The design concentration is calculated from the enclosure volume, but hold time is a physical property of the enclosure: agent leaves through open paths and the concentration decays. Adding a cylinder raises the initial concentration and peak pressure, but the measured 4.8-minute retention time would still fail and the higher pressure could increase leakage. NFPA 2001 acceptance requires verification of enclosure integrity and the design concentration for the required duration. The correct conclusion is that the room must be tightened, not that the agent supply should be increased. Only after sealing and retesting should the agent quantity be recalculated to confirm it still matches the room volume and design concentration.
2. List the corrections you would require before a retest, and state the acceptance criteria for the enclosure integrity test.
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Require sealing of the two 3-inch conduit sleeves with a listed sealant or firestop system, installation of a damper or sealed closure on the return-air grille, and correction of the door undercut with a sweep and self-closer while maintaining required egress. Check ceiling tiles, raised-floor penetrations, and any other openings. Verify that the room pressure relief is adequate and does not itself bypass the enclosure. Retest with a door-fan enclosure integrity test per NFPA 2001 and the manufacturer. Acceptance should show a predicted hold time of at least 10 minutes with concentration remaining above the design concentration, dampers closed, HVAC shutdown verified, and no excessive pressure that would prevent door opening. If the enclosure cannot meet the hold time, revise the enclosure or the system design with the engineer.
3. What documentation should be provided to the AHJ to close the acceptance issue?
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Provide the pre-repair and post-repair door-fan test reports, details of sealed penetrations, damper and HVAC shutdown verification, door hardware checkout, agent cylinder weight records, and the manufacturer's design calculation confirming 7.0 percent concentration for the actual room volume. Include a statement that the enclosure integrity test was witnessed and accepted, update the system placard and as-built drawings, and record the final hold time and test conditions. The package should clearly show that the deficiency was physical leakage, not insufficient agent, and that the corrected enclosure meets the design basis.