FORT VALLEY, Ga. — A fire on a Blue Bird propane school bus on Monday likely originated in a wheel end assembly and did not compromise the propane fuel tanks, an independent fire investigator found.

The fire occurred in East Ridge, Tenn. The bus was en route to be delivered to a dealership in another state. There was no one on the bus at the time of the fire, and the engine was off. There were no injuries.

Blue Bird immediately transported the bus to its facility in Fort Valley to complete a thorough investigation, company officials said in a statement. The preliminary review indicates that friction in the wheel end area likely caused the fire. Officials said that additional analysis will be conducted to confirm this theory. The company’s findings concluded that this was an isolated event.

Initial reports indicated that witnesses reported hearing two popping sounds at the scene. Those were confirmed to be the sound of the front tires rupturing from the heat of the fire.

The investigator confirmed that the multiple safety features in the engine, propane autogas system and fuel tanks performed as designed, and the propane fuel tanks were not compromised in the fire.

"This incident strongly reinforces the safety of the propane autogas system on our buses,” said Phil Horlock, president and CEO of Blue Bird Corp. “The safety record of Blue Bird propane autogas fueled engines in school buses is outstanding. There have been no propane-related fires or injuries with any of our school buses. All Blue Bird buses meet or exceed comprehensive federal and state safety specifications.”

“There are over 21 million propane-fueled vehicles on the road that travel hundreds of millions of miles a year, and propane has proven to be a safe and efficient fuel,” Horlock added. “At Blue Bird, safety is our top priority."