EE WAS SUPERVISING 2 EMPLOYEES DISASSEMBLE THE FEED PIPE TO 50750 FINE COAL CENTRIFUGE IN ORDER TO UNPLUG IT. THE PIPE IS CONSTRUCTED OF URETHANE & HELD TOGETHER WITH SLIP FIT COLLARS & CLAMPS. THE PIPE WAS BEING TAKEN APART AT A COLLAR. THE BLOCKED SECTION PULLED OUT OF THE COLLAR AFTER THE CLAMP WAS REMOVED. THE PIPE FELL STRIKING EE ON HIS RIGHT SHOULDER.