A B737 WAS HIT IN THE ENG BY A BELT LOADER AT THE GATE.

Narrative

LANDED RWY 12R AND TAXIED TO GATE X. CAPT AND FO BOTH RESPONDED THAT SAFETY ZONE WAS CLR PRIOR TO PARKING AT GATE. WE ARRIVED ON TIME AND DAYLIGHT CONDITIONS. I LEFT ACFT FOR FOOD. RAMP SUPVR INFORMED FO THAT A BELT LOADER HAD BACKED INTO AND STRUCK THE L ENG COWLING. I RETURNED TO GATE AND INSPECTED DAMAGE TO ACFT. I CALLED DISPATCH AND TALKED TO ACR MAINT. I ALSO TALKED TO CHIEF PLT ON CALL. BECAUSE NO RAMP PERSONNEL WOULD ADMIT TO DRIVING THE BELT LOADER; I TALKED TO GND MARSHALER AND AN ASSISTANT AND BOTH INDICATED TO ME THAT BELT LOADER WAS NOT IN SAFETY ZONE PRIOR TO ACFT ARRIVING AT GATE. I ALSO RECALL THAT THERE WAS NOT AN ACFT AT GATE Y OR RAMP PERSONNEL AT GATE Y WHEN WE ARRIVED AT X. HOWEVER; A FLT DID ARRIVE AT GATE Y APPROX 8 MINS AFTER OUR ARR. I ALSO ASKED THE RAMP SUPVR TO TRY TO OBTAIN THE SECURITY CAMERA VIDEO OF THE RAMP AREA. EVEN THOUGH THE DAMAGE TO THE ENG COWLING APPEARED TO BE MINOR; DISPATCH GAVE US ANOTHER ACFT AND WE LEFT SJC AND PROCEEDED. YYY MAINT REPLACED THE PAN COWLING ON THE ACFT AND IT WAS RETURNED TO SVC THE NEXT DAY. LESSONS LEARNED: I HAVE ALWAYS BEEN EXTREMELY VIGILANT ABOUT GND EQUIP IN THE SAFETY ZONE. I HAVE NOTICED THAT SOME RAMP PERSONNEL APPEAR TO BE ANNOYED IF YOU MAKE THEM MOVE EQUIP THAT IS JUST SLIGHTLY OVER THE LINE. HOWEVER; THIS EXPERIENCE REINFORCES THE NEED TO NOT ALLOW RAMP PERSONNEL TO BECOME COMPLACENT.