Abstract: At 10:00 a.m. on January 23, 2021, an employee working for a crane manufacturer was assisting in the preparation of a 310T overhead crane for installation at a steel mill. The crane was outside resting on stands and being prepped for sheaving. A coworker was working from an aerial lift removing bolts with an impact wrench. The bolts were located in a sheave cover on the right side of the crane. The employee helped remove a few bolts that the coworker could not reach from the lift. The employee then went back down to the ground and was standing off to the left of the cover as the coworker removed a bolt on the far-right bottom corner. Once the coworker had removed the bolt, the cover shot off the crane and struck the employee on the ground, knocking him unconscious. The incident happened outdoors; however, it is not believed that the weather played a factor. Employees install a variety of cranes, and each installation is unique. It is thought that during shipment, the cover may have shifted, resulting in unexpected, stored energy. The employee was hospitalized to treat a fractured vertebrae, a dislocated hip, and an unspecified knee injury.