How long must a clean agent system hold its concentration?

NFPA 2001 requires the protected enclosure to retain at least 85% of the adjusted minimum design concentration at the highest level of combustibles for a minimum of 10 minutes. If the room leaks the agent out faster than that, the suppression system can discharge perfectly and still fail to extinguish — which is why enclosure integrity is verified, not assumed.

Two ways to demonstrate it:

• Enclosure integrity (door fan) test — a calibrated fan pressurises and depressurises the room to measure its equivalent leakage area, from which the predicted hold time is calculated. This is the standard approach because it doesn't discharge the (expensive) agent.
• Full discharge test — actually discharging and measuring the concentration decay, used where the AHJ requires it.

The integrity test is required at acceptance and should be repeated whenever the enclosure changes — new cable penetrations, removed partitions, altered HVAC — because every unsealed opening shortens the hold time. Many owners re-test annually alongside the suppression system inspection.

CertBox includes both a clean agent system inspection & test report and an enclosure integrity (door fan) test report recording measured leakage and predicted versus required hold time, with professional PDFs for the owner and AHJ.