Nailor 1200 and 1200-3 Series Airfoil Multi-blade Fire Dampers are classified for use only in static "fans off" systems where the HVAC system is automatically shut down in the event of a fire alarm. Largest fire damper listing in the industry (exceeding curtain dampers) at 144" x 96" (3658 x 2438). Standard features include an innovative inter-locking double skin airfoil blade design that maintains a complete barrier throughout the fire test with absolutely no visible through-gaps. The airfoil blade design and elimination of blade sills, top and bottom, provide a low pressure drop design. The 1200 and 1200-3 Series dampers have been especially designed and tested to provide premium performance.