Abstract: Employees #1 and #2 , who worked for a nested maintenance contractor, were finishing the turnaround of the sulfur recovery complex at a refinery. They were removing a 14 in. isolation blind from the overhead inlet of a horizontal receiver vessel. The vessel was part of an amine treating unit that had been emptied, steamed out, and drained a few days before. After several attempts, the overhead piping had been replaced and the blinds had been removed and reinstalled. Employees #1 and #2 were working from a scaffold when they were exposed to strong hydrogen sulfide emissions from the vessel. Employee #1 staggered away, but within minutes had lapsed into unconsciousness and died. Employee #2 managed to escape and reach grade level. He was hospitalized for observation and released with no lasting effects. The vessel had accumulated sour gas from a connected overhead gas line, tied into nearby sulfur trains that were operating at relatively low pressure. The source was a single leaking 12 in. gate valve that had been closed and locked out. Employees #1 and #2 were working without respiratory protection or gas detection equipment. The valve inspection program, lockout/tagout program, and respiratory protections were found lacking. At the time of the accident, the foreman was also overseeing other crews at the site.