Stair Pressurization – Pressurization of Exit Passageways

In accordance with the 9th edition of 780 CMR Massachusetts State Building Code, an interior exit stairway is defined as a means of egress component that “provides for a protected path of egress travel to the exit discharge or public way.” Where “land-locked” interior exit stairways do not have direct access to the building exterior, use of an exit passageway to connect the interior exit stairway to the building exterior is permitted by 780 CMR Chapter 10, and is a common approach to code-compliance. These exit passageways are designed to maintain the fire-resistance rating of the interior exit stairway(s) which they serve in accordance with the construction requirements of 780 CMR §1024.3.  In high-rise buildings, there is an added complication in that stairways are often pressurized as a means of satisfying the smokeproof enclosure requirements of 780 CMR §1023.11.  Where exit passageways are utilized to extend pressurized exit stairways, the exit passageway may require pressurization in the same fashion as the interior exit stairway, too, depending on its configuration.

Where interior exit stairways are pressurized, the termination of the pressurized exit stairways are subject to the requirements of 780 CMR §1023.11.1 ‘Termination and Extension.’  Exit passageways are specifically permitted to extend the smokeproof stair enclosure to the exit discharge, but are required to be “without openings” to adjacent building spaces.  In other words, the language of 780 CMR §1023.11.1 requires that exit passageways serving this function connect and communicate only with the interior exit stairway and the exterior of the building.  This configuration would not require the exit passageway to be pressurized; however, in practice it is often impractical or infeasible to avoid openings from adjacent building areas for egress purposes from those spaces.

In recognition of this practical challenge, Exception 1 to 780 CMR §1023.11.1 permits openings (from normally occupied spaces) into the exit passageway serving the smokeproof stair enclosure, when such openings are protected and the exit passageway is pressurized in the same manner as the smokeproof enclosure. The code requirement defining the performance criteria for stairway pressurization systems is 780 CMR §909.20.5, which requires 0.10 – 0.35 inches of water column be maintained throughout the interior exit stairway, relative to the building.  To qualify for Exception 1 to 780 CMR §1023.11.1, all doors communicating between the exit passageway and the adjacent building spaces would similarly need to meet the performance criteria of 780 CMR §909.20.5.

Pressurization of the exit passageway can be accomplished in a variety of ways such as the use of air transfer grille(s) in in the walls between the interior exit stairway and exit passageway, installation of ductwork connecting the two areas, or by installation of a separate fan for the exit passageway. In all cases, certain equipment and construction requirements will apply to ensure protection of the pressurization equipment and the integrity of the fire-resistance-rated enclosures are maintained.  Additionally, smoke detectors for the purposes of activating the pressurization systems are required outside of each exit passageway door in accordance with 780 CMR §909.20.6.

If you have any questions related to the requirements associated with pressurized exit passageways, please feel free to reach out to us and request additional information.