The danger with using any sort of chuck key to release a chuck that has locked onto the spindle, is that it is engaged in a brittle, cast metal gear which is not desiged for taking the sharp knock that might be needed to release it. The safer way is to simply open the jaws sufficiently to put a length of flat-bar between the jaws, across the face of the chuck, and use it as a lever. The chuck has been designed to let the jaws take such rotational forces, but the keyways haven't!