NHTSA Engineering Analysis EA03001

IN SEPTEMBER 2002, A FUEL CYLINDER IN A NATURAL GAS POWERED VEHICLE (NGV) EXPLODED DURING A FIRE.FORD AND VRTC TEST ENGINEERS JOINTLY EXAMINED THE INCIDENT VEHICLE AND REVIEWED TESTING TO DETERMINE WHETHER THE PERFORMANCE OF THE PRESSURE RELIEF VALVE (PRD) WAS PROPER.THE PURPOSE OF A PRD IS TO PROTECT A COMPRESSED NATURAL GAS TANK FROM OVERPRESSURE BY ALLOWING THE CNG TO VENT WHEN THE TEMPERATURE REACHES A SPECIFIC POINT.THE PRD WAS REMOVED FROM THE FAILED TANK AND SUBJECTED TO A YIELD TEMPERATURE DETERMINATION TEST. IT WAS CONCLUDED THAT A DIRECT FLAME (FROM THE INTERIOR OF THE VEHICLE) ONTO THE CYLINDER (LOCATED BEHIND THE REAR SEAT IN THE TRUNK)COMPROMISED THE HOOP STRENGTH OF THE NATURAL GAS CYLINDER, THUS ALLOWING THE CYLINDER TO FAIL PRIOR TO THE PRD RELEASING AT ITSDESIGNED TEMPERATURE.AS A RESULT OF THIS TESTING AND REVIEW OF THE INVOLVED VEHICLE, FORD HAS DEVELOPED AN INSULATOR TO INSULATE THE NATURAL GAS FUEL TANK FROM A LOCALLY DIRECTED FLAME PROJECTING FROM THE INTERIOR OF THE VEHICLE.INSULATORS WILL BE INSTALLED BEHIND THE BACK SEAT ON SUBJECT VEHICLES TO PREVENT FUTURE FAILURES OF THIS TYPE. FORD'S ACTION ADDRESSES THE CONCERNS OF ODI.THEREFORE, THIS INVESTIGATION IS CLOSED.