Situation shown on attached drawing. Issue is:
Given: 1995 CBC was code; non-rated floor separating two levels of a Type II-N building sprinklered and unlimited; open stairway between two floors is allowed; there are ducts from roof equipment down through 2d floor and distributing air to open ceiling at 1st floor; unenclosed ducts are allowed: for cosmetic purposes and to avoid damage to the duct drops, the duct drops were surrounded by walls of steel studs and drywall.
Question: Section 711.3 appears to require fire-stopping around the duct where it penetrates the 2d floor. Given that open stairs are allowed, with free air flow between two floors, what would be the purpose of the fire-barrier at that annular opening, and is it in fact required? Am I missing something?
ANY HELP APPRECIATED