Abstract: An actuator is usable in a damping system, which may be a component of an airside system, waterside system, building management system, or HVAC system. The actuator is coupled to a damper and may open and close the damper. The damper selectively seals a duct to prevent spreading of gas, smoke, or fire within a building. The actuator includes a gear that rotates as the damper is opened and closed. A cluster pinion is coupled to the gear and rotates with the gear. A locker is rotatably coupled to a stopper and has a range of motion limited by the stopper. The stopper includes a rib extending outwardly and limiting the range of motion of the locker. The rib is configured to deform at a temperature exceeding a threshold. A spring is coupled to the locker and biasing the locker against the rib.