Abstract: On January 16, 1996, Employee #1 was cleaning solid alumina catalyst from the shift converter, V-1284, unit 700, at a Texaco sulfur recovery plant. The catalyst was lying on a grating that went down the center of the vessel, dividing it into upper and lower halves. The vessel normally contained hydrogen sulfide and sulfur dioxide gases in a 2:1 ratio. A ventilation fan attached to the vessel drew in air from the open top hatch and exhausted it through the bottom manhole. The ventilation fan had been removed so that Employee #1 could enter the bottom of the vessel to vacuum out the catalyst that had fallen through the grate. The air was not tested before or during his entry or occupancy in the bottom half of the vessel. Employee #1 completed his work and was leaving the vessel when he was overcome and collapsed. He did not remember feeling any symptoms before his collapse. Medical tests indicated that he had been exposed to sulfur dioxide, which was not screened for by the air testing equipment at the plant . After the incident, Texaco used a Drager tube to test the air in the vessel and found 2 ppm sulfur dioxide. Texaco provided the air monitoring, stand-by personnel, and entry permit system at the work site.