LGT PARKED AT GATE WHEN MECH COMES ABOARD TO INFORM OF ENG FIRE.

Narrative

UPON ARRIVING AT THE GATE IN BOS AT THE TERMINATION OF THE FLT; THE FLC WAS IN THE PROCESS OF DEPLANING APPROX 8 PAX. APPROX 3 TO 5 MINS AFTER ALL ENGS HAD BEEN SHUT DOWN; A MECH RAN ONTO THE FLT DECK AND ADVISED US THAT THE #2 ENG WAS ON FIRE WITH HVY SMOKE. THE SECOND OFFICER PULLED THE #2 FIRE SHUTOFF HANDLE AND I ASKED THE MECH IF HE WOULD LIKE US TO DISCHARGE THE FIRE BOTTLE INTO THE ENG; AND HE AGREED THAT WE SHOULD; SO I DISCHARGED THE L FIRE BOTTLE AND THE R FIRE BOTTLE INTO THE ENG. THE CAPT WAS AT THE BACK OF THE COCKPIT BY THE COCKPIT DOOR WHEN THIS OCCURRED AND HE CONFIRMED THAT WE DISCHARGE THE BOTTLES INTO THE #2 ENG. THE LEAD FLT ATTENDANT PROCEEDED TO COMMAND PAX TO GET OUT OF THE ACFT IMMEDIATELY. SOME PAX WERE DIRECTED OUT THE AFT AIRSTAIRS BY THE FLT ATTENDANT PERSONNEL. SINCE THIS WAS THE AREA WHERE FIRE WAS SUSPECTED; THE LEAD FLT ATTENDANT IN THE FORWARD CABIN INSTRUCTED PAX TO 'COME THIS WAY!' WHILE MOTIONING THEM TO COME FORWARD. WHEN I REALIZED THAT THERE WERE PAX EXITING THE ACFT THROUGH THE AFT AIRSTAIR AREA; I ASKED THE CAPT IF I COULD USE THE PA SYS TO ADVISE PAX TO EXIT ONLY THROUGH THE FORWARD EXIT. THE CAPT AGREED AND I MADE THE ANNOUNCEMENT. AFTER THE ANNOUNCEMENT; TO THE KNOWLEDGE OF THE FLC; NO FURTHER DEPLANING OCCURRED THROUGH THE AFT AIRSTAIR AREA OF THE ACFT WHERE MECHS AND FIRE-FIGHTING PERSONNEL WERE LOCATED. FOLLOWING THIS INCIDENT; WE CREWMEMBERS WERE ADVISED THAT ONE OF THE PAX THAT EXITED THE ACFT THROUGH THE AFT AIRSTAIRS RAN IN FRONT OF AN APCHING FIRE TRUCK. WE ALSO LATER LEARNED THAT COMPANY MAINT REPLACED THE ENG #2 STARTER AND START VALVE.