Abstract: Employee #1, a welder working alone in a clean room for fabrication of vessels and related components, entered the interior of a flat-bottomed, titanium vessel that was 16 ft high and positioned vertically. He entered without benefit of ppe and/or engineering controls and was overcome. The interior of the vessel contained argon which was being employed as a back purge for exterior welding. Employee #2, a welder who was not familiar with clean room fabrication processes, entered the vessel, also without ppe and/or engineering controls, in a rescue attempt of Employee #1 and was overcome. A third employee was about to enter the vessel but stopped when he saw Employee #2 fall to the floor of the vessel. Employees #1 and #2 died of asphyxiation. It was discovered that the employer had developed a tank entry procedure in 1978 after two other workers were overcome by inert gas inside a vessel. The procedure had not been implemented.