Abstract: At approximately 10:45 p.m. on November 5, 1993, Employee #1 was on top of a frac tank that was being used to recover the backflow from an oil well. Employee #1 was measuring the fluid level of the frac tank using a tank gauge. The backflow from the oil well consisted of water, compressed nitrogen gas, and a little sand. Employee #1 was using a flashlight to peer into an opening that was approximately 2 ft by 2 ft. A coworker was assisting Employee #1 by opening the flow line at the oil well. Employee #1 apparently dropped the flashlight into the opening and climbed into the frac tank to retrieve it. The coworker, who was approximately 65 ft away, went over to the tank to see why Employee #1 was not on top of the tank. Employee #1 had been overcome by the gas in the frac tank. The coworker attempted to rescue Employee #1 from the frac tank but was not successful. Employee #1 died.