Abstract: ON SEPTEMBER 9, 1986, A WELL SERVICE RIG CREW FROM THE TRIAD DRILLING AND SUPPLY COMPANY FINISHED SERVICING A WELL PUMP LOCATED 8 1/2 MILES SOUTH OF HIGHWAY 290, OFF HIGHWAY 1291 NEAR WALLDECK, TEXAS. DOWN-RIGGING HAD BEGUN AND ALL GUYWIRES WERE DISCONNECTED. THE OPERATOR ATTEMPTED TO PULL THE DERRICK LOCKING PINS HYDRAULICALLY AND WAS SUCESSFUL WITH ONE OF THE TWO. THE OTHER PIN WOULD NOT BUDGE, PROBABLY DUE TO AN UNLEVELED RIG OR A LACK OF ADEQUATE HYDRAULIC PRESSURE, OR A COMBINATION OF THE TWO. A DERRICKMAN WAS SENT UP THE MAST TO DISLODGE THE PIN BY HAND, BUT WAS UNABLE TO DO SO. ANOTHER DERRICKMAN (EMPLOYEE #1) WAS SENT UP THE MAST WITH A HAMMER. HE WAS ABLE TO DISLODGE THE PIN. UNFORTUNATELY, DUE TO A LACK OF HYDRAULIC PRESSURE, THE UPPER PART OF THE MAST DROPPED, SEVERING THE MAN'S LEG AND CAUSING HIM TO FALL APPROXIMATELY 50 FEET TO THE GROUND. HE RECEIVED A FATAL HEAD INJURY.