Three employees were a replacing an extruder header. The first employee went to acquire rigging equipment and prepare a hoist. The second employee detached the extruder supply/return lines and began loosening the side clamps. The third employee was preparing the header for removal by removing the eight mounting bolts. Upon removal of the eighth bolt, the header fell approximately 6 feet from its cradle and hit the third employee in the left arm and leg. The third employee fell to the ground and the drive side of the header was resting on the employee's left leg. The employee suffered a broken left tibia, fibula, and humerus as well as a sprained right ankle.