What are the fire-stopping requirements for a multi-story curtain wall?

Fire-stopping requirements are a critical life-safety component in the design and installation of a multi-story curtain wall. Because a curtain wall is installed on the exterior of the building structure, a gap is created between the edge of the floor slab and the back of the curtain wall on every level. If left unprotected, this gap would act as a chimney, allowing fire, smoke, and hot gases to travel rapidly from one floor to the next, bypassing the fire-rated floor assemblies. Building codes, including the Saudi Building Code (SBC), mandate that this void be sealed with a tested and listed fire-stopping system. This system must meet a specific fire-resistance rating, typically equal to that of the floor slab itself (e.g., two hours). The most common type of fire-stopping system used in this application is known as a "safing" and "smoke seal" system. It consists of two main components. First, a fire-resistant mineral wool insulation (safing insulation) is compressed and installed tightly into the gap between the floor slab and the curtain wall. This material is non-combustible and designed to withstand high temperatures. Second, a fire-resistant smoke sealant is applied over the top of the mineral wool. This flexible sealant prevents the passage of smoke and hot gases. The entire assembly must be installed according to the manufacturer's specifications and tested industry standards (like ASTM E2307) to ensure it can effectively contain a fire to the floor of origin for a specified duration, allowing occupants time to evacuate safely.