B737 CREW REPORTS APU DISINTEGRATION WITH RESULTANT FIRE AND PASSENGER EVACUATION WHILE PARKED AT THE GATE.

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AT THE GATE IN ZZZZ; FORWARD ENTRY DOOR OPEN AND JETWAY ATTACHED; THE APU DROPPED OFF LINE. GND CREW MEN ANNOUNCED THAT THERE WAS AN APU FIRE. IT TOOK THE THIRD WARNING FOR US TO UNDERSTAND BECAUSE OF THEIR HVY ACCENT. WE RAN THE APU FIRE CHKLIST. AFTER ACHIEVING THE NECESSARY ITEMS ON THE PAX EVAC CHKLIST; WE STARTED TO COMMAND AN EVAC OUT THE FORWARD ENTRY DOOR BUT NOTICED THE FLT ATTENDANTS HAD ALREADY DONE SO BECAUSE AN OPS AGENT IN THE JETWAY TOLD THEM THAT HE SAW A FIRE ON THE REAR OF THE PLANE. WE ASSISTED; AND SAW AFTER THE PLANE WAS EMPTY THAT AN OVERWING EXIT DOOR WAS OPEN. I LEARNED LATER THAT A DOZEN OR SO PAX SELF-INITIATED AN EVAC OUT THE R WING AND DOWN A BELT LOADER. CFR PERSONNEL CHKED THE PLANE OVER. THE FIRE WAS OUT. THE MECH DETERMINED THAT THE APU FAILED INTERNALLY AND BLEW METAL JUNK OUT ITS EXHAUST. THERE WERE NO INJURIES. AFTER THE LOGBOOK WAS SIGNED OFF AND AUTH WAS RECEIVED FROM THE COMPANY AND LCL CAA; THE FLT PROCEEDED TO ZZZ. LANGUAGE BARRIER WAS AN OBSTACLE TO UNDERSTANDING THE GND PERSONNEL THE FIRST TIME.