Hold time is how long a clean agent stays in the room at a concentration that still controls the fire. NFPA 2001 §5.6 requires at least 85% of the adjusted minimum design concentration at the highest level of protected content for 10 minutes, or until trained personnel respond. A room integrity test, also called a door fan test, checks this without discharging any gas.
The test measures how leaky the room is and predicts how fast the agent will drain out. If the predicted hold time is too short, the room fails and the leaks must be sealed. To get the agent quantity first, use the free FM-200, Novec 1230 and CO2 calculator.
Why Hold Time Matters
A clean agent system must discharge within 10 seconds to reach 95% of the minimum design concentration. Then the room must keep the agent long enough to stop the fire from starting again.
The agent and air mixture is heavier than normal air. It leaks out through low openings while fresh air comes in high. The line between the agent mixture and fresh air moves down over time.
If the line drops below the top of your protected equipment before 10 minutes, the top of the racks is no longer protected, and a hot component can re-ignite. That is why hold time is measured at the height of the highest protected content, not the floor.
How a Door Fan Test Works
The door fan test follows the enclosure integrity procedure in NFPA 2001. Here is what happens, in simple terms:
- The technician fits a temporary panel with a calibrated fan into an open doorway.
- The fan blows air into the room, then pulls air out of it.
- Gauges record the air flow and the pressure difference across the room boundary.
- Software works out the total leakage area of the room from these readings.
- Using the agent type, concentration, room height and protected height, the software predicts the hold time.
The result is a pass or fail against the §5.6 requirement. The report also shows the leakage area. Because no agent is discharged, you can repeat the test after each round of sealing.
Common Leakage Sources
Most failed tests come from the same few places.
| Location | Typical leak | Usual fix |
|---|---|---|
| Cable penetrations | Open sleeves, cable trays through walls, unsealed conduits | Seal with a fire-rated sealant or a listed penetration system |
| Ceiling tiles | Lay-in tiles that lift or are missing, with walls that stop at the false ceiling | Extend walls to the slab, or seal the ceiling void as its own protected volume |
| Doors | Gaps at the bottom and sides, damaged seals, missing closers | Fit drop seals and perimeter seals, repair closers |
| HVAC dampers | Dampers that do not close on discharge, leaky blades, open ducts | Fit tight-closing dampers interlocked with the suppression panel |
| Raised floor | Gaps at the perimeter, cable cut-outs, open floor grilles | Seal the perimeter and cut-outs, check floor void boundaries |
| Walls | Unpainted block walls, gaps at the slab, pipe sleeves | Seal or paint porous surfaces, fill gaps at the slab |
Low leaks let the heavy agent mixture drain out. High leaks let fresh air in. Treat both.
What to Check Before the Test
Before you book the tester for a clean agent room integrity test, confirm:
- All construction work in and around the room is finished.
- All doors close and latch, with seals in place.
- HVAC dampers close as they would on a real discharge.
- The ceiling void and raised floor boundaries are complete.
- You have the design data: agent, design concentration, room volume, room height and the height of the highest protected content.
- The facility team knows the test date and keeps the doors closed.
Design Factors, Voids and Hold Time
Hold time links back to the design. Three points cause confusion on site.
Voids are separate volumes. The ceiling void and the raised floor void are calculated as separate volumes, each with its own nozzles. Their boundaries affect leakage. A leaky floor void drains agent from the room above it.
Design factors do not fix leaks. NFPA 2001 §5.5.3.2 gives additional design factors for unclosable openings, acid gas control, re-ignition and obstructions. These add agent to cover a known condition. They do not replace good sealing.
More agent is not a free fix. Adding gas to a failed room also raises the peak concentration. The NOAEL is 9.0% for FM-200 and 10% for Novec 1230. In a normally occupied room, you cannot go above NOAEL without means to limit exposure. Seal the room first, then re-check the peak.
Also watch for the double safety factor error: 7.0 × 1.35 = 9.45% for FM-200 Class C is already above the 9.0% NOAEL.
For a clear walk-through of how the base FM-200 quantity is built, watch How to Calculate FM200 System Gas Quantity.
Practical Site Checklist
- Get the design concentration, net volume and protected height from the approved design.
- Walk the room, the ceiling void and the floor void with a torch.
- Mark every open penetration, gap and missing tile.
- Test each door: closer, latch, bottom seal and side seals.
- Confirm HVAC shutdown and damper closure with the BMS or HVAC contractor.
- Seal everything, then run the door fan test.
- If it fails, use the report's leakage area to find and seal the remaining leaks, then re-test.
- Keep the final report with the system records. Re-check the room after any building works, new cables or HVAC changes.
Clean Agent Hold Time FAQ
What is the required hold time for a clean agent system?
What is a room integrity test?
What are the most common reasons a room fails the door fan test?
Can I add more agent instead of sealing the room?
Are ceiling and floor voids included in the integrity test?
Related reading: Anti-Vortex Plate in Fire Pump Suction Tanks: What It Does
Sources: NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems and NFPA 12, Standard on Carbon Dioxide Extinguishing Systems. Values are from NFPA 2001 (2018 edition) and NFPA 12. Always check the edition adopted by your Authority Having Jurisdiction and the listed manufacturer's design manual.
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