In certain occupancies, a duct that penetrates a fire-resistance rated floor/ceiling assembly may connect how many stories without requiring shaft enclosure protection?

In certain occupancies, a duct that penetrates a fire-resistance rated floor/ceiling assembly can connect two stories without requiring shaft enclosure protection. This is in accordance with the building codes and standards that aim to ensure fire safety and restrict the spread of fire and smoke between different levels of a building.

The rationale behind allowing ducts to connect two stories is based on the understanding that the risk of fire spread is relatively manageable over this distance, particularly in specific occupancy classifications where the nature of the assembly can mitigate hazard concerns. By not requiring shaft enclosures for ductwork spanning two stories, the code strikes a balance between safety and practicality in design and construction, facilitating installation while still adhering to fire safety provisions.

In contrast, connecting three or four stories without shaft enclosure protection raises significant fire safety risks. As the number of stories increases, the potential for smoke and fire spread also escalates, necessitating the use of additional protective measures such as shaft enclosures to ensure that fire and smoke are contained within a particular area of the building and do not compromise the safety of occupants on other levels. Therefore, the choice of allowing connections up to two stories aligns with comprehensive fire and safety strategies employed in building design.