Building codes require fire dampers to maintain fire resistance ratings of walls, partitions, barriers, and floors when penetrated by ducts or other air transfer openings. Fire dampers are UL 555 classified with a fire resistance rating of 1½ or 3 hours. Fire dampers fall into two categories:

• Dynamic rated – used with HVAC systems that remain operational during a fire emergency
• Static rated – used with HVAC systems that shut down automatically during a fire emergency