Abstract: ON JULY 8, 1985, THE EMPLOYEES WERE PREPARING TO BACKFLOW AN OIL AND GAS WELL AFTER TREATING IT WITH 20% HYDROGEN CHLORIDE COMBINED WITH 700 STANDARD CUBIC FEET OF NITROGEN. A FLOW LINE CONSISTING OF A WACO MODEL DR 150 W PLUG VALVE, A HUBER-HERCULES 460 T JUNCTION, A WALWORTH 1796 (200 WOG) PLUG VALVE AND A THORNHILL CRAVER UNIBOLT ADJUSTABLE CHOKE WITH A ONE INCH ORIFICE. THE CHOKE VALVE WAS CONNECTED TO A HIGH PRESSURE HOSE LEADING TO A FRAC TANK. THE PRESSURE IN THE OIL AND GAS WELL WAS MEASURED AT 3150 PSIG WHEN THE FLOW LINE WAS INSTALLED. ALL VALVES WERE OPEN EXCEPT THE WACO PLUG VALVE, WHICH WAS LEAKING. THE CHOKE VALVE WAS OPEN TO A SCALE READING OF 12/64. BEFORE THE WACO VALVE COULD BE OPENED, APPROXIMATELY 600 PSI OF PRESSURE DEVELOPED IN THE PUMPING "T". THE WALWORTH PLUG VALVE RUPTURED, BREAKING THE CASING INTO AT LEAST TWO SECTIONS. ONE SECTION STRUCK EMPLOYEE #1 ON THE LEFT SIDE OF HIS HARD HAT, SMASHING THE HAT AND CAUSING SEVERE INJURIES TO HIS HEAD. HE WAS KILLED. TWO OTHER EMPLOYEES WERE INJURED.