Series D01X4HY Hybrid Fire Dampers are designed for larger duct sizes that exceed the size limitations of dynamic curtain fire dampers and are a more economical solution than a multi-blade fire damper. The D01X4HY Hybrid Dynamic Fire Dampers are UL approved for use where local building codes require the protection of HVAC ductwork penetrations in walls and partitions that have a fire resistance rating of up to 2 hours. The D01X4HYs are classified for use in dynamic "fans on" systems where the HVAC system remains operative in the event of a fire and damper closure under airflow is assured. Integral sleeve fire dampers offer convenience and labor savings. The costly requirement to field or shop fabricate custom sleeves is eliminated and dampers ship directly from the manufacturer to the job site – saving time and money. Optional "Quick-Set" retaining angles complete the installation package. Factory fabricated, sized and shipped with damper, they install quickly, provide further labor savings and eliminate the need for any field fabrication.