Employees were waiting on a delivery truck to unstrap electrical panels and control panels for unloading. The driver of a tractor trailer unstrapped the electrical and control panels so the employees could unload them. An electrical panel slipped and hit a control panel, which then struck the injured employee, knocking him to the ground where he hit his head on the concrete. He was hospitalized with a contusion to the back of the head and ligament damage to his right knee.