What is the minimum fire damper rating for fire-resistance-rated assemblies that exceed 3 hours?

In fire-resistance-rated assemblies that exceed three hours, the minimum fire damper rating must match or exceed the fire resistance of the assembly itself. Fire dampers are critical in maintaining the integrity of fire-resistance-rated walls and floors, as they are designed to prevent the spread of fire and smoke through ducts.

By requiring a fire damper rating of three hours for assemblies that also have a three-hour fire resistance, the building code ensures that the damper can perform effectively for the same duration as the assembly. This alignment is essential for maintaining safety and compliance in the event of a fire.

The other options suggest ratings below this necessary threshold, which would not provide adequate protection and could lead to failure in preventing the passage of flames and smoke during a fire, undermining the effectiveness of the fire-resistance-rated assembly. Thus, it’s crucial that the fire damper's rating is at least equal to the fire-resistance rating of the assembly to ensure proper performance in maintaining safety standards.