In the handling and charging of pre-heated coal, the coal is transported from a coal storage container to the oven chambers by an enclosed continuous conveyor system. The coke oven chambers are charged individually in a continual manner by transporting a measured amount of coal from the container, sufficient to fill a respective chamber. If coal, due to a malfunction, passes beyond the intended charging hole, it can jam the drive area causing extensive damage. To prevent this, a safety device is provided which includes a sensing device, e.g. a pivotally mounted switch for determining the presence of coal on the conveyor and associated therewith, a time delay system for determining if a particular amount of coal, to which the sensor is responding, is of sufficient volume to cause jamming of the conveyor drive system.