One important component of a stair pressurization system is achieving a balance between 1) preventing smoke from entering the stairwell and 2) making sure that the pressure differences between the stairwell / stair vestibule & the stair vestibule / corridor meet the code minimums (0.05 inches water column with stair vestibules or 0.10 inches water column without stair vestibules) but are not so high that the doors can’t be opened! The Code requirement is 30 lbs. of door opening force maximum, which translates to about 0.35 inches of water column. If there is also a corridor exhaust system for the floor in alarm, the pressure differences between stair vestibules and corridors increases further for that floor. For that reason, it is imperative that the stair pressurization system be modeled before building construction.
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