Abstract: At approximately 2:00 p.m. on December 8, 1990, Employees #1 and #2 drained a white liquor pressure filter and flushed it with cold water in preparation for acid washing. They then filled it with diluted 20 percent muriatic acid. At approximately 5:40 p.m., Employee #2 climbed onto the platform attached to the weak acid storage tank to open the dump valve, which would allow the spent acid in the filter to drain into the tank. From this vantage point, he could see Employees #1 and #5, who were at ground level, as they were about to climb a ladder affixed to a dike wall that surrounded the weak acid storage tank. Employee #1 disappeared from Employee #2's view; Employee #2 also saw Employee #5 stumbling around. Employee #2 went down to the ground level where he noticed the smell of hydrogen sulfide gas. He saw Employee #1 lying on the ground, went to help him, and passed out. He regained consciousness and made it to a phone to call for help. He went back to help Employee #1, who was on the ground by the dike wall ladder, but passed out again before he could rescue him. Employee #4 and other workers pulled Employee #1 to safety and administered CPR. A life-support CPR demand valve oxygen system with five suctions was brought to the scene by the plant nurse and used for 5 to 10 minutes until the air ran out.. After a 2 to 3 minute lapse, an SCBA was brought as a back-up; one had not been present at the work area. A witness later reported that a pulse could not be detected and that the SCBA was ineffective. Employees #1 through #5 were transported by ambulance to the hospital where Employee #1 was pronounced dead on arrival and Employees #2 through #5 were treated and released. Employee #3 was only a witness to the event but he was also exposed to hydrogen sulfide gas.