ON 9/30/2016, A THERMAL EVENT OCCURRED WHILE THE BUS WAS IN THE SHOP FOR ROUTINE MAINTENANCE. AS THE BUS WAS BEING MOVED (BACKED-OUT) OF THE SERVICE BAY AND SMOKE WAS SEEN ESCAPING FROM THE CNG TANK STORAGE COMPARTMENT AT THE REAR OF THE BUS. LOCATION: 4127 ELM ST., DALLAS, TX 75226 A DALLAS AREA RAPID TRANSIT (DART) EMPLOYEE QUICKLY OPENED THE COMPARTMENT AND EXTINGUISHED THE SMALL FLAME. DAMAGE WAS LIMITED TO THE CNG FUEL TANK SOLENOID (MELTED) AND THE CONNECTING HARNESS (MELTED). THIS VEHICLE HAS A HIGH PRESSURE ELECTRONIC SHUT-OFF SOLENOID VALVE MOUNTED DIRECTLY TO THE ON-BOARD CNG FUEL TANK(S). NOTE: IF THERE IS A FUEL LEAK OR OTHER COMBUSTIBLE MATERIAL IN THE VICINITY, THERE IS A RISK OF IGNITION. DART HAS A TOTAL OF 123 EA., 2012 MODEL YEAR GM 6.0L CHEV EXPRESS SHUTTLE BUSES WHICH WERE PURCHASED FROM NATIONAL BUS SALES & LEASING BY DART. PRIOR TO DELIVERY, THE BUSES WERE MODIFIED BY ARBOC AND CONVERTED TO DEDICATED CNG OPERATION BY IMPCO AUTOMOTIVE IN UNION CITY, IN. EACH VEHICLE IS CONFIGURED WITH (2 EA.) LINCOLN 21' X 80' CNG CYLINDERS FITTED WITH OMB SOLENOID VALVES MOUNTED INSIDE AN ENCLOSED STORAGE COMPARTMENT BEHIND THE PASSENGER AREA. THERE WERE SIMILAR OCCURRENCES DOCUMENTED UNDER OTHER RECALL NOTIFICATIONS (GM BULLETIN #: 13139 AND IMPCO AUTOMOTIVE #: 13V-225); WHERE THE OEM IDENTIFIED ROOT CAUSES AND CORRECTIVE ACTIONS. UNDER THOSE GM AND/OR IMPCO REPORTS AND/OR DEFECT RECALLS REPORTED TO NHTSA, SIMILARLY, THE CONNECTOR TO THE CNG FUEL TANK EXPE