Abstract: EMPLOYEE#1 WAS STANDING BETWEEN THE MOUSE HOLE AND AN AIR HOIST. AN EASTMAN CIRCULATING HEAD HAD BEEN ATTACHED TO A SECTION OF DRILL PIPE AND THE ROTARY HOSE HAD BEEN MADE UP ON THE CIRCULATING HEAD. ACCORDING TO MANAGEMENT, A SAFETY CHAIN HAD BEEN INSTALLED CONNECTING THE ROTARY HOSE TO THE BAIL AND THE ASSEMBLY HOISTED. ANOTHER SECTION OF DRILL PIPE, RESTING IN THE MOUSEHOLE, WAS ATTACHED. THE TWO SECTIONS OF DRILL PIPE, ALONG WITH THE CIRCULATING HEAD AND THE ATTACHED ROTARY HEAD, WAS HOISTED AND ATTACHED TO THE HANGING PIPE IN THE HOLE. THE COMPLETE STRING WAS THEN HOISTED SOME 10 FEET. AFTER PUMPING APPROXIMATELY 5 MINUTES, THE PRESSURE GAUGE SHOWED A SUDDEN SURGE TO 500 PSI. THE CIRCULATING HEAD BECAME SEPARATED FROM THE DRILL PIPE. THE WEIGHT OF THE CIRCULATING HEAD (APPROXIMATELY 200 TO 300 POUNDS), ALONG WITH THE GREATER PORTION OF THE MUD-LOADED ROTARY HOSE WAS SUDDENLY THROWN ONTO THE SAFETY CHAIN (WHICH CONNECTED THE HOSE TO THE BAIL). THE CHAIN FAILED TO SUPPORT THE ENTIRE LOAD, ALLOWING THE CIRCULATING HEAD ON THE END OF THE ROTARY HEAD TO FALL TO THE DRILL FLOOR. AS THE HEAD & HOSE, STILL CONNECTED TO THE STANDPIPE, FELL, IT STRUCK EMPLOYEE #1 ON THE SIDE, THROWING HIM AGAINST AN AIR HOIST. EMPLOYEE #1'S INJURY WAS CAUSED BY HIS COLLISION WITH THE AIR HOIST.