Series D0100 (steel) and D0100SS (stainless steel), Curtain Fire Dampers, designed for use in dynamic "fans on" systems where the HVAC system remains operational in the event of a fire, are UL approved for use where building codes require protection of HVAC ductwork penetrations in walls, partitions or floors that have a fire resistance rating of 2 hours or less. The D0100 Series features stainless steel closure springs for assured damper closure under airflow.