Abstract: A PETROCHEMICAL REFINERY WAS UNDERGOING TURNAROUND. A CONTRACTOR CREW HAD BEEN ASSIGNED THE JOB OF SANDBLASTING THE INSIDE SURFACES OF A REACTOR VESSEL (CONFINED SPACE). ALTHOUGH UNWRITTEN COMPANY POLICY CALLED FOR THE USE OF AIR COMPRESSORS FOR SUPPLYING RESPIRATOR AIR, THIS CREW, WITH THE SUPERVISOR'S KNOWLEDGE, HAD PREVIOUSLY USED PLANT AIR TO SUPPLY BREATHING AIR. THE CREW MISTAKENLY HOOKED UP AN AIR FILTER TO AN UNLABELED NITROGEN LINE (ONLY THE SHUTOFF VALVE WAS LABELED) USED BY THE REFINEREY FOR PURGING CONFINED SPACES. PLANT NITROGEN LINES AND AIR LINES WERE IDENTICAL AND BOTH HAVE CROW'S FOOT COUPLINGS COMPATIBLE WITH THE COUPLING ON THE AIR FILTER. EMPLOYEE #1 CLIMBED TO THE BOTTOM OF THE VESSEL, PLACED THE SANDBLAST RESPIRATOR HOOD ON HIS HEAD AND BEGAN SANDBLASTING. HE WAS ASPHYXIATED WITHIN FIVE MINUTE'S TIME. ATTEMPTS TO REVIVE EMPLOYEE # WITH OXYGEN FAILED.