Thursday, the owner of an OHV called our Assistant Chief to report that their vehicle was on fire. The Chief told them to hang up and immediately call 9-1-1. The Chief went directly to the scene via POV. About the time he hit the driveway the tones dropped. The Chief found the Ranger to be fully involved, and already a total write-off. When the first engine arrived (about 1 ½ miles from the station) a few minutes later, only the tires needed to be extinguished. After the fire, the owner reported that a 20 lb. portable propane cylinder in the back of the Ranger had exploded. The cylinder was found about 150 feet away. The safety valve on the propane cylinder did not operate as designed.