Abstract: Employee #1 was working as a subcontractor for an oil and gas drilling company. He had been hired to monitor the water level of the frac tank by measuring it with a gauge tape. The frac tank is used to recover water that has been pumped into the gas well. The water is pumped into the ground with sand and potassium chloride. This mixture is allowed to escape from the well and flow into the frac tank. Employee #1, who was working alone, attempted to gain a more accurate measurement from a 2 ft by 2 1/2 ft hatch, which is open to allow the gases to escape and to alleviate pressure. Employee #1 was overcome by the vapor and fell into the tank , where he drowned.