While an employee was attempting to change a leaking O-ring on an excavator's hydraulic line, a sudden release of hydraulic oil startled the employee. The employee fell back off the catwalk and down about 11 feet to the barge below. The employee hit a concrete ballast block, suffering several broken ribs, a broken pelvis (in three places), a concussion, a laceration of the ear, a fractured wrist, and a broken cheek bone.