A boiler maker, 36, suffered fatal burns after an explosion occurred at a refinery. The victim and two injured co-workers were employed by a contractor at the facility. The three were hospitalized as a result of the explosion. The victim died four days later from burns over approximately 90% of his body. The events occurred in the area of the Flare and Knock-Out (KO) Drum. A 36-inch pipe delivers hydrocarbons from the refinery production area and collects them in the KO Drum. Another 36-inch pipe exits the top of the KO Drum and delivers vapors to be burned at the Flare to relieve pressure from the production area. The process leading up to the fatality began when, during a turnaround (shut down for maintenance), an environmental project was begun to capture flare gas and re-use it as fuel or feedstock rather than burn the gas in the flare.