Abstract: On August 13, 2010, Employee #1 and a coworker were replacing valves on a natural gas heater-treater. A tank battery to the north of the equipment being repaired had a vent line that was sagging. The tank battery belonged to the same lease owner as the heater-treater they were repairing. After they finished with the repairs to the heater-treater, Employee #1 decided to repair the vent line. He backed the truck up to the tank and threw the welding leads on top of the tank. He climbed the stairs to the catwalk and crawled on top of the tank and started welding a piece of metal bar under the vent line. He was up wind from an access hatch, approximately 8 ft, were vapors were escaping. The vapors ignited, creating a flash fire that knocked him off the tank. He fell approximately 20 ft onto a guard rail around the tank battery. He was transported to a hospital, where he later died.