What is the minimum damper rating per hour for a less than 3-hour fire resistance rated assembly?

The minimum damper rating for a less than 3-hour fire resistance rated assembly is 1-1/2 hours. This rating is established to ensure that fire dampers can effectively maintain the integrity of fire-resistance-rated assemblies by preventing the spread of fire and smoke. Fire dampers are an essential component in HVAC systems, designed to automatically close in the event of a fire, and their rating must correspond with the fire-resistance rating of the assemblies they are installed in.

In the context of a fire resistance rating of less than 3 hours, a 1-1/2 hour rating is sufficient to meet the safety standards set forth by building codes, which require that a damper can withstand the effects of a fire for a specific duration. This effectively allows for adequate time for occupants to evacuate and ensures that the fire does not compromise adjacent areas or building sections.

The higher ratings such as 2 hours or 2-1/2 hours, while appropriate for assemblies with longer fire resistance ratings, exceed what is necessary for those rated less than 3 hours. Therefore, the 1-1/2 hour minimum rating strikes the right balance, providing safety and compliance without unnecessary over-specification.