Appeal 34910

2022 OSSC §404.5 Smoke Control – Atriums

A smoke control system shall be installed in accordance with §909.

Exceptions:

1. In other than Group I-2, and Group I-1, Condition 2, smoke control is not required for atriums that connect only two stories.
2. A smoke control system is not required for atriums connecting more than two stories when all of the following are met:

2.1 Only the two lowest stories shall be permitted to be open to the atrium.
2.2 All stories above the lowest two stories shall be separated from the atrium in accordance with the provisions for a shaft in §713.4.

Request to use a rated horizontal shutter to protect the atrium as a 2-story atrium following §404.5 Exception 1.

The James Beard Public Marketplace will include a 3 story atrium connecting all three stories of the building (see Attachment A). The proposed design is to follow §404.5 Exception 1 which omits smoke control requirements for atriums connecting only two stories.

The atrium will be equivalent to a 2-story opening because it is separated from Level 2 by a 2-hr rated horizontal shutter. The horizontal shutter will be activated by the fire alarm to create a two-story opening with a single story above, preventing smoke migration to the third story. The shutter will be supported by 1-hour rated construction and additional sprinklers around the floor opening will protect the floor of the atrium after the shutter has closed.

The building will include an atrium connecting all 3 stories of the market to allow daylight at all three stories via atrium skylights, to achieve a cohesive market presence between all 3 functional Market levels, and to meet energy conservation goals for reduced reliance on interior artificial lighting. Retrofitting a smoke control system into an existing building presents various technical challenges, including the difficulty in bringing sufficient make-up air to the lowest (basement) floor of the building. Instead, the proposed design is to protect the space as a two-story atrium during a fire event.

ACTIVATION:
The shutter will be installed to activate upon sprinkler waterflow or manual pull station initiated anywhere in the building. The selected McKeon H200 Series shutter features a fail-safe automatic self-closing mechanism which does not require power operation to self-close. Per NFPA 80 §8.4.1.3.1, the average closing speed of horizontal sliding doors must be not less than 6 inches/sec, not including any initial delay time for panel alarm communication. The manufacturer’s representative estimated that the proposed size of shutters for this project will close within approximately 20 seconds after activation. This closing speed limits the amount of smoke that is able to migrate to Level 2 above, minimizing tenability concerns for egress to the enclosed exit stairs from Level 2.

FIRE RATING:
The selected shutter provides 2 hour rated fire protection and is smoke/draft labeled per UL 1784 (see Attachment B). The rating exceeds the requirements of floor construction in a Type III-B building (0-hour rated per Table 601), and exceeds the requirements of atrium enclosure (1 hour rated per §404.6).

In following OSSC §711.2.3 requirements for rated horizontal assemblies, the supporting construction of the rated shutters will be protected to afford a minimum 1 hour fire-resistance rating as required for atrium separation. The rated supporting construction will include the beams around the floor opening and supporting columns to the foundation.

LISTINGS:
The OSSC includes prescriptive provisions for the use of fire shutters as part of vertical and horizontal fire door assemblies, but does not include or preclude the use of shutters in other applications. When used for fire door assemblies, OSSC §716.2.1.2 requires vertical applications to be tested per UL 10B / NFPA 252 and §712.1.13.1 requires load-bearing horizontal applications to be tested per NFPA 288. In this case, the opening is not an occupiable area and is surrounded by guardrails. Therefore, as a non-load bearing application, the shutter will meet equivalent test listings to UL 10B / NFPA 252. The shutter will be installed per NFPA 80 in accordance with §716.1.

OTHER VERTICAL OPENING:
The 3-story unenclosed stairway will be protected prescriptively as an exit access stairway using OSSC §1019 Exception 4, with sprinklered draft curtains. Though sprinklered draft curtains are not required at the top level as part of this Exception, the proposed design will provide sprinklered draft curtains at all 3 levels as an additional means of protection. The stairway is not used as a required means of egress. Because the opening is protected as an exit access stair, using the prescriptive code exception provided as equivalent protection to rated enclosure, the stair opening is not considered an atrium and has protections in place to prevent migration of smoke and toxic gases to other stories.

CONCLUSION:
The proposed design provides equivalent or greater fire/life safety protection to the prescriptive code requirements of §404.5. Though the shutter does require time for activation, this is similar to the activation time of a smoke control system installed in a 3-story atrium. When closed, the shutter provides greater fire separation protection than the baseline requirement of a non-rated floor per §404.5 Exception 1 and Table 601.

Therefore, we request that the proposed protection using a rated horizontal shutter be permitted to protect the atrium.

2022 OSSC §705.8

2022 OSSC Table 705.8 strictly prohibits openings less than 3 feet from any property line.

Sealing the proposed opening in each wall with an automatically closing fire rated assembly.

The property line walls between each building are considered exterior walls for the purposes of the code analysis. The reason for the opening restriction in an exterior wall is to prevent the spread of fire from building to building. Sealing the opening with an automatically closing fire rated assembly is an approvable solution (see Attachment A). The fire resistance rating for the proposed M occupancy is 2 hours based on OSSC Table 705.5. The minimum fire door assembly rating will be 1 ½ for exterior walls. OSSC Table 716.1(2). Each wall will be protected with an individual assembly. If both doors close a 3 hour protection will be provided . The doors will activate from a fusible link and local smoke detector.

The proposed opening creates the desired, open marketplace design. The occupants can freely traverse from market area to market area through the large opening. The separate fire doors maintain the structural independence and fire rating in the event of a single building collapse. Travel through the doors is not required for egress. Each building meets travel distance requirements separately.