BOULDER, Colo. – Several people were injured - one seriously - following a fiery, multi-vehicle crash involving an RTD bus near Boulder Monday morning.

A spokesperson with the Colorado State Patrol said an RTD bus collided with a van, which was parked in the lane behind a semi-tractor trailer in the 6600 block of Arapahoe Road. The collision pushed the van into the semi, immediately causing a fireball.

A man in the van had to be extracted and was rushed to the hospital with serious injuries. All three passengers on board the bus were injured. One passenger was taken to the hospital; two others were treated at the scene.

A fourth vehicle, a sedan, crashed into the rear of the bus. Two people in that car were transported to the hospital with moderate injuries.

One witness said he happened upon the crash and immediately set to work on saving victims.

"I saw fire, it didn't look terrible, but from here you can't really see the whole bus or anything like that," Sean Carpenter, said.

He said he realized the extent of the fire, which charred the exterior of the bus, when he turned the corner.

"The first thing I thought was just get in the bus and help whoever is in there out," Carpenter said. "I started breaking the window with thee fire extinguisher and it didn't work, and then I tried the door and the door opened up. I Got to the bus driver in the front and he was OK."

Although the driver was OK, the witness said he could still hear screaming.

"I doused the entire cab and just tried to put out as much as I could. He was screaming like crazy and I didn't think there was any way he was going to make it out," Carpenter said. "I don't know how he did it, but you can look at that, they pulled him out of there, it was wild."

Carpenter gave all credit to the fire department which responded, saying they saved the man's life.

Troopers also credited bystanders like Carpenter, saying they sprang into action at a critical time.

An investigation into what caused the collision is ongoing. Troopers say both the semi and van had their hazards on and may have been turning into a nearby business. Investigators will be talking to the bus driver to see what charges or citations may be issued.

Monday night, Colorado State Patrol identified the bus driver as Richard Castle, 73. CSP Trooper Nate Reid said he would be charged with careless driving causing injury.

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