A B737-500 PARKED AT THE GATE DECLARED AN EMER AND EVACED THE ACFT DUE TO A PERCEIVED ENG FIRE CAUSED BY THE FUEL START LEVERS BEING MOVED FROM CUTOFF TO IDLE ALLOWING FUEL INTO THE HOT ENGS WITH RESULTING FUEL VAPOR AND SMOKE.

Narrative

NORMAL PROC IS TO HAVE THE APU RUNNING AND POWERING THE ELECTRICAL SYS; THEN UPON SETTING THE PARKING BRAKE; SHUT DOWN BOTH ENGS. THIS IS ALSO THE PROC ON SOME TERMINATING FLTS; BUT NOT THIS ONE. ON THIS FLT THE PROC IS TO SHUT DOWN ONLY 1 ENG UNTIL GND PWR IS AVAILABLE; THEN SHUT DOWN THE OTHER ENG. WHAT HAPPENED WAS I ACCIDENTALLY SHUT DOWN BOTH ENGS; WITH NO APU; THEREBY PUTTING THE ACFT ON ONLY BATTERY/EMER PWR. I REALIZED THIS IMMEDIATELY; BUT COULD ONLY WAIT FOR GND PWR. I DID; HOWEVER; INADVERTENTLY AND WITHOUT REALIZING IT REINTRODUCE FUEL TO THE ENGS. THIS CAUSED FUEL TO FLOW INTO THE HOT ENG AND WITH A TEMP OUTSIDE OF 32 DEGS F CREATED A BIG WHITE CLOUD OF FUEL STEAM/SMOKE. THIS WAS THOUGHT TO BE A FIRE BY GND PERSONNEL; WHO ADVISED ME OF A FIRE IN THE #2 ENG; PARTIALLY THROUGH PAX DEPLANING I ORDERED AN EVAC. I THEN BEGAN THE EVAC CHKLIST AND NOTICED THE FUEL LEVERS AT IDLE; NOT CUTOFF. I MOVED THEM QUICKLY TO CUTOFF AND THE SMOKE IMMEDIATELY STOPPED AND THE EVAC WAS CANCELED. PAX HAD ALREADY OPENED BOTH OVERWING EXITS AND WERE ON THE WINGS; AS WELL AS; A FLT ATTENDANT HAD BLOWN A SLIDE AT DOOR 2R AND PAX WERE EVACING DOWN IT. NO ONE WAS HURT AND NO DAMAGE WAS CAUSED; ONLY 1 SLIDE WAS USED. THIS MAY HAVE BEEN PREVENTED IF THE PROC WAS TO CALL FOR THE COPLT TO SHUT DOWN THE ENGS ON COMMAND. THAT WAY BOTH PLTS WOULD BE IN THE LOOP ABOUT WHICH ENGS WERE TO BE SHUT DOWN AND ONE PLT COULD QUESTION THE OTHER IF ONE OR BOTH WAS THE BEST/PROPER DECISION FOR THE SIT.