Abstract: A hoist frame comprising a chain, a chain driving means and a chain blockage detecting device having a portion movable relative to the hoist frame and having a shaped opening for allowing the chain links to pass through and preventing the entangled chain links to pass through when the chain is driven. When the latter, occurs the movable portion is moved to the hoist frame causing a signal to be output to the chain driving means such that the chain is at least no longer driven in the same direction. A biasing means is provided to act against the movement of the movable portion by the entangled chain for delaying the signal to be output.