Hardware that improves the safety of operating sectional doors that use torsional coil springs to facilitate door movement. A rotor assembly with centrifugally activated throw-out latches is affixed to the rotating shaft that bears the torsional coil springs. When a spring breaks, the shaft rotates rapidly as cables supporting the door unwind. Rapid rotation causes centrifugal force to bias the latches to an outer position in which they strike a trigger plate, allowing a pawl to move into a position in which the pawl blocks further rotation of the rotor, thus halting the descent of the sectional door. Raising the sectional door manually moves the latches, trigger plate, and pawl to their original position, disengaging the present invention and permitting the door to be lowered slowly without danger of injury.