Abstract: Employees #1 and #2 were instructed to record the pressure and depth of nitrogen and other acidifying chemicals flowing into a 500 BB1 fractionation tank from an oil well near completion. Employee #1 entered the tank to retrieve a gauge line that he had dropped into it through a manhole at the top. Employee #2 entered the tank after seeing Employee #1 unconscious inside the tank; he also lost consciousness. Crew members removed a manhole cover from the bottom of the tank and drained 2 1/2 ft of the chemical solution. A company representative wore an oxygen mask from the ambulance to enter the tank and remove both employees. Employee #1 was pronounced dead on arrival at the hospital. Employee #2 was hospitalized with acute respiratory failure due to noxious gas inhalation.