An incident occurred when the rig crew was in the process of loading a skid (3rd party modified shale bin) to a truck for removal from the rig site. To give the crane operator the signal to slack off the load the injured person (IP) positioned himself in between the rear of the load and a pipe tub (3 foot space), just as the load was positioned onto the truck. As the crane operator slacked off the load, a 500+ pound ramp (225kg) slid from the position it was in on the skid and fell to the ground. In the process it struck and pinned the IP under the ramp. The IP was removed from beneath the ramp and stabilized on site and Medivaced from location for medical treatment.