A B767 CREW WAS UNABLE TO SHUTDOWN THE R ENGINE WITH THE FUEL CTL CUTOFF SWITCH REQUIRING PULLING THE FIRE HANDLE INADVERTENTLY DISCHARGING THE FIRE BOTTLE.

Narrative

UPON ARRIVAL AT THE GATE AT ZZZ FROM ZZZ1 ALL NIGHTER; THE R ENGINE WAS OBSERVED TO NOT SHUT DOWN UPON THE PLACEMENT OF THE START LEVER IN THE CUTOFF POSITION. ALTHOUGH THE ENGINE DID INDICATE SOME; BUT NOT ENTIRE; EGT DECREASE AND SPOOL DOWN; CONCERN WAS FELT OVER THE 500 PPH FUEL INDICATION. THE CAPT AND I FELT THAT POSSIBLY THE FUEL CTLR WAS MALFUNCTIONING WITH THE POSSIBLE RESULT OF FUEL BEING PUMPED OUT UNBURNED INTO THE ENGINE. AFTER CONCURRENCE WITH THE CAPT; I PULLED THE R ENGINE FIRE HANDLE TO FULLY SHUT DOWN THE ENGINE AND CUT OFF THE FUEL. UPON PULLING THE FIRE HANDLE; WE NOTICED THAT THE FIRE EXTINGUISHER BOTTLE DISCHARGED INTO THE ENGINE. IT IS POSSIBLE THAT WHEN I PULLED THE FIRE HANDLE; I APPLIED SOME TWIST TO THE HANDLE ACCIDENTALLY; RESULTING IN THE FIRE BOTTLE FIRING. I AM NOT CERTAIN OF THIS HOWEVER; AS I FELT THAT I PULLED THE HANDLE STRAIGHT OUT. WHEN THE FIRE HANDLE WAS PULLED; THE ENGINE WAS OBSERVED TO COMPLETELY SHUT DOWN WITH FUEL FLOWS GOING ON DOWN TO ZERO PPH. AFTER PAX UNLOADING; I WENT DOWNSTAIRS TO FIND THE MECHANIC DOING THE WALK AROUND AND ADVISED HIM OF THE SIT. ADDITIONALLY; DURING THIS TIME DOWNSTAIRS I COULD SMELL THE ODOR OF UNBURNED FUEL AROUND THE R ENGINE; INDICATING TO ME THAT THE ENGINE INDEED DID NOT FULLY SHUT DOWN INITIALLY RESULTING IN FUEL PUMPING UNBURNED INTO IT.