Abstract: At about 8:30 p.m. on April 27, 1993, Employees #1 and #2, waterproofing technicians, ages 30 and 25, were overcome by chemical vapors while applying basecoat material inside a 17-foot by 26-foot by 8-foot fire protection water storage tank. The wife of one of the workers contacted a company superintendent after her husband failed to come home after work. The superintendent drove to the work site and found Employees #1 and #2 incapacitated in the tank. After an attempted rescue, 911 was called and they were removed from the tank by local firemen. Employees #1 and #2 were transported to a local hospital emergency room. Employee #2 was released after a 7 hour observation period, but Employee #1 was not released until 2 days later. Employee #2 was found overcome at about 2:00 p.m. by Employee #1. While attempting a rescue, Employee #1 fell into a 5-foot by 5-foot by 5-foot sump pit in the middle of the tank and was also overcome by the vapors. The respirator that Employee #2 was wearing had foreign material stuck in the exhalation valve. This allowed air to pass through the exhalation valve during inhalation. Employee #1's respirator was most likely dislodged from his face when he fell into the sump pit while attempting to rescue his partner from the tank.