Saw dust used to feed the boiler is off-loaded from specialized transport trailers to a drag chain conveyor trough. The trailers are equipped with a conveying system that is driven by a stationary motor and drive shaft at the facility. The trailers can be parked on opposite sides of the trough. The shafting from the motor connects to yokes on the trailer. There is a yoke on each side of the shaft to accommodate bi-directional parking. The injured employee was cleaning between the trailer and the trough on the side that was not connected to the shaft to the motor drive while the trailer was being unloaded. The employee's left arm was caught in the yoke on the trailer that was not connected and the upper arm was fractured.