Abstract: Some employees were working on a chain-driven rotary car dumper, approximately 15 feet above floor level. They were heating and cutting away a section of a metal gear plate that had slipped loose and was causing the chain on the west side of the dumper to bind. When the piece snapped off, the dumper turned and threw Employee #1 to the ground. There were two gear plates at each end of the dumper. At least one gear plate was engaged with the drive chain at all times, to either turn the dumper or hold it in place. There was also a brake that, when set, was to hold the dumper in place. The brake, with new brake shoes, had been set before the employees began work on the dumper. After the accident, it was discovered that one gear plate on the east side of the dumper had slipped out of place and was not engaging the drive wheel at all. This allowed the dumper to turn when the bind was removed from the other end. The brakes apparently engaged the chains and, with the gear plates at both ends not engaged with the chains, there was nothing to hold the dumper in place.