Abstract: At approximately 8:00 a.m. on September 9, 1988, Employee #1, a part-time foreman, was sent to the top of a 146 foot high vessel to visually check the level of blown-in perlite insulation. A coworker, a laborer who had worked for the company for approximately 30 days, went with him. Two supervisors remained at ground level. Employee #1 and the coworker removed the manhole cover and were unable to see the perlite level. Employee #1 told the coworker not to tell anyone and then proceeded down into the vessel. The normal atmosphere had been displaced with 77 percent nitrogen. Employee #1 made it back to within four feet of the entrance point before he lost consciousness and fell back into the vessel. He was killed.