An employee was using a ladder to take a nitrogen purge line off of a unit that was being decommissioned. He lost his balance on the ladder and fell backwards onto his backside. This is not the fall that caused the injury, but was a precursory fall. He gathered himself and headed back toward the control unit when he then tripped over his feet and landed on an approximately 12-inch high dike on his right side, causing the injury. He was hospitalized for a fractured pelvis.