If the downward speed is too high, the claw has no time to move back into the housing. The claw is driven against the catch and blocks movement. The claw is additionally pressed into the rail by the downward motion of the anchorage point. The anchorage point is not directly connected to the claw. Therefore, the claw can not be disengaged if the person climbs. The design of the blocking system guarantees that the block function is not impaired by spring breakage or contamination.