Dayton round fire/smoke dampers are designed for use in HVAC system applications where emergency fire/smoke control is required. Each damper comes standard with a 165ºF fusible link and factory installed actuator. Upon temperature elevation in emergency fire smoke situations, dynamic damper closes automatically to prevent the spread of fire and smoke. Includes factory installed actuator. Qualified to UL Standard 555 as a 11/2 hour fire damper and UL Standard 555S leakage class of II.