William Sweet is called "Bud" by the kids that ride his school bus, "Preacher" by his colleagues and now "hero" by thousands.

Sweet was driving Alcoa City Schools bus #47E on Monday morning when it caught fire.

"It's really unbelievable how fast the fire got started," Sweet told WBIR 10News.

Sweet said everyone on board heard a loud "pop," and shortly after that Sweet saw smoke in the rearview mirror.

"So, I just pulled over right away. I started getting the small kids who were right here off the bus, and everything went as smooth as it could," said Sweet.

It went smoothly, but it also went quickly. 

"By the time we pulled over you could see flames," he said.

Visible flames that were quickly spreading didn't deter Sweet from staying on the bus.

"I had to be the last one off. I made sure that none of the kids hadn't got frightened and crawled under the seat and was still back there," said Sweet.

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Sweet was the last one off, and not one of the students had a scratch on them. All 29 students on board made it off safely before it burst into flames. They included students from Alcoa Elementary, Intermediate, Middle and High School.

"I'm very thankful for Bud. Very grateful," said Amanda Cothren, whose son Damien rides Bud's bus.

"God bless you, Bud," said Damien.

Firefighters with the Alcoa Fire Department work to put out a school bus fire on Monday, Jan. 9, 2017.

The front seat Damien and his friend Cesar were sitting in is burnt to a crisp, as are all of the seats on the bus. The windows are blown out and the console is melted. The aftermath of what Bud calls the 'worst fire' he's ever seen.

"They (the flames) were shooting out of this hole here, going about as high as a telephone pole," said Sweet.
Fire investigators have determined a "mechanical failure of the brake system" sparked the flames that engulfed the bus.

A report from the Alcoa Fire Department cited overheated brakes as the cause of ignition in the Jan. 9 incident. 

Rocky Top Tours LLC, which is based in Maryville, owns the bus.  

The bus is inspected annually and was last checked in July of 2016, by the Tennessee Highway Patrol. It passed in all categories.