Abstract: An employee was operating a Rotochopper, Model Wood Chopper to aid in the recycling of wooden construction debris. After approximately 30 minutes, the machine jammed. He called the supervisor to assist him with the problem, since the supervisor had been to the manufacturer's facility for training. When they opened up the machine to inspect the mechanism, they found the shear pin at the junction of the hydraulic cylinder and the screen control arm was broken. The hydraulic cylinder when fully extended, forces the control arm to push the screen away from the grinder. When fully retracted, the cylinder causes the control arm to bring the screen in close to the grinder. The employee noticed the cylinder was extended 5 inches. He placed lock out rings on the cylinder to prevent retraction. At this time, the screen was still in next to the grinder. He preceded to pound out the broken piece of shear pin while the supervisor stuck his head inside the access panel of the grinding compartment to examine the wedged screen. The machine accidentally restarted allowing the cylinder to further extend out to its maximum 8 inches forcing the wedged screen abruptly out towards the supervisor. He was hospitalized for his injuries.