Stair Pressurization Test Fails on Pressure and Door Force
A newly constructed 12-story office building has a stair pressurization system serving two egress stairs and an atrium smoke exhaust system. During acceptance testing, the contractor reports the following: with all stair doors closed, the pressure difference at the top stair is 0.05 inches of water column; with the required test doors open, it drops to 0.02 inches; the force to open one stair door is 32 pounds at the handle; one atrium exhaust fan shows 80 percent design airflow; and a smoke detector in the return-air plenum alarms 90 seconds after test smoke is introduced. The design documents specify a minimum closed-door pressure of 0.10 inches and a maximum door-opening force of 30 pounds. The contractor proposes increasing the supply fan speed and disabling the door closer on the worst door to “make the test pass.” The building owner wants to occupy the first six floors immediately. The fire code official must evaluate the acceptance test and the proposed fix.
1. Interpret the test results. Is the stair pressurization and smoke exhaust system acceptable as tested?
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The system is not acceptable as tested. The design requires at least 0.10 inches w.c. with all stair doors closed; the measured 0.05 is half that. With test doors open, 0.02 is also below the design basis. The 32-pound door-opening force exceeds the 30-pound maximum, so simply adding fan pressure would make the door problem worse. The atrium exhaust fan at 80 percent of design airflow is another deficiency. The return-plenum detector alarmed at 90 seconds; that may or may not meet the design intent, but it must be compared with the approved sequence and detector spacing. I would document each failure separately and reject the acceptance test rather than treat it as a single fan-speed issue.
2. Evaluate the contractor’s proposed fix of increasing fan speed and disabling a door closer. What diagnostic steps are appropriate?
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The contractor’s proposed fix is not acceptable. Increasing supply fan speed can raise closed-door pressure but also raises door-opening force; disabling a door closer violates the egress and fire-door function and cannot be used to make a test pass. The correct approach is to diagnose the cause: stair leakage through doors, penetrations and roof hatch; relief-air path; fan balance; duct leakage; and whether the test was run with the required doors open. A balancing report and leakage survey should precede any fan change. The door force should be rechecked after adjustment at the worst-case door. If the fan cannot meet both pressure and force limits, the design may need relief dampers or a revised fan/relief strategy.
3. What re-testing and inspection sequence would you require before allowing occupancy of the first six floors?
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Before any occupancy, I would require a re-test by an independent agency or the design engineer: all stair doors closed and open in the required combinations; pressure differentials at top, middle and bottom; door-opening force at each stair door; atrium exhaust airflow and make-up air; fan status and feedback; smoke detector response; and the full integrated sequence with the fire alarm. The first six floors cannot be occupied on a failed system unless an approved temporary alternative provides equivalent tenability and egress. A fire watch is not equivalent to stair pressurization in a 12-story building. The owner may occupy only after the system passes and the inspection record is complete.