Abstract: EMPLOYEE #3 ENTERED A FRAC TANK AT THE DRILLING SITE TO GET A KELLY HOSE. EMPLOYEE #2 WAS WAITING AT THE ENTRANCE ON TOP OF THE TANK. HE SAW EMPLOYEE #3 COLLAPSE. HE CALLED FOR HELP, THEN ENTERED THE TANK. EMPLOYEES #1 AND #4 WERE AT THE WELLHEAD. THEY RESPONDED BY ALSO ENTERING THE TANK. THE TANK HAD ABOUT 2 FEET OF WATER LEFT IN THE BOTTOM. BY THE TIME THE TANK HAD BEEN DRAINED AND THE EMPLOYEES REMOVED, EMPLOYEES #1 AND #2 HAD DROWNED. EMPLOYEES #3 AND #4 WERE HOSPITALIZED WITH VARIOUS SYMPTOMS, ATTRIBUTED TO OXYGEN DEFICIENCY AND EXPOSURE TO NATURAL GAS. THE ACCIDENT OCCURRED BECAUSE THE EMPLOYEES ENTERED A CONFINED SPACE WITHOUT TESTING THE ATMOSPHERE OR WEARING THE PROPER RESPIRATORY PROTECTION.