Abstract: At approximately 10:00 p.m. on March 16, 1992, Employee #5, who worked in the millhouse of Building #12, noticed a strong sulfur dioxide odor coming from an unknown source. On the third floor of the building, Employee #3 had just turned on the main valve that controlled the sulfur dioxide addition in the grind mill operation. Employees #1 and #3 and their supervisor were in the control room when Employee #5 alerted them about the odor. The supervisor alerted the employees' general supervisor by phone. The supervisor and Employee #5 wore respirators. Employees #1 and #3, who were not wearing respirators, went to investigate the source of the sulfur dioxide. Employee #1 was able to access Building #4's third floor to turn off the main valve controlling the sulfur dioxide. Employees #1 through #5 suffered sulfur dioxide inhalation and were hospitalized.