Abstract: Employees #1 through #3 were working with drums A, B, C, D in a coker unit, which thermally cracks heavy residual feeds through a process called delayed coking. The employees were preparing to switch feed from the C drum to the D coke drum. This process involves opening and closing a number of valves. Employee #1 was on the 55 ft level where the switch valve was located. Employee #3 was also on the 55 ft level, approximately 50 ft away from Employee #1. Employee #2 was on the 40 ft level to prepare for the switch. Employee #1 told the controller over the radio to divert half of the feed flow to the D drum. At approximately the same time, they heard a noise and saw a vapor cloud rising from the vicinity of the feed pumps. The cloud ignited and fire went as high as the 141 ft level, fatally burning Employees #1, #2, and #3. Two other employees on the 40 ft level evacuated to safety. The leak was caused by a sudden failure of a 45 degree elbow in the 6 in. discharge line of the furnace feed pump(s).