The man killed Thursday afternoon in a four-vehicle crash on Montana 82 near Somers has been identified as 24-year-old Trenton James Thornton of Kalispell.

The crash - a head-on collision between Thornton's 1988 Chevrolet van and a tractor-trailer carrying apples - sparked a fire that mostly consumed the truck and scorched a nearby field.

Thornton, who was on his way home from work when the crash occurred, was pronounced dead at the scene, according to Flathead County Sheriff's Sgt. and Deputy Coroner Lance Norman.

According to the Montana Highway Patrol, the tractor-trailer was eastbound on Montana 82 at 4:07 p.m. when Thornton's van drifted across the center line and struck the truck head-on.

After the initial impact, the tractor-trailer crossed into the oncoming lane of traffic and hit a small sport-utility vehicle traveling west behind Thornton's van.

Debris from the initial collision struck a fourth vehicle, a Ford Taurus also traveling westbound. The Taurus did not collide with any vehicles.

The 68-year-old driver of the tractor-trailer was taken to Kalispell Regional Medical Center with a possible broken leg and other minor injuries. The 23-year-old driver of the SUV, along with her 2-year-old and 5-month-old children, were not injured but taken to the hospital as a precautionary measure.

An older couple from Great Falls in the Taurus also were not injured.

It was unknown Friday what caused Thornton to drift into oncoming traffic, Montana Highway Patrol Trooper Lacie Alby said. Excessive speed did not contribute to the crash, but whether alcohol was a factor has not been determined, she said.

It is standard procedure in fatal crashes to take blood samples from all the drivers involved. The blood samples will be sent to the state crime lab in Missoula.

Thornton was not wearing his seat belt, but the other drivers were, Alby said.

The tractor-trailer eventually stopped in the ditch on the highway's north side - about 150 yards east of where the van came to rest - and caught fire.

"When we arrived on scene, the tractor-trailer was fully engulfed," said Somers Fire Department Chief Rich Boon. "We concentrated on that part of the fire because it was spewing ash … and the wind was pretty heavy."

Flames from the burning tractor-trailer spread into a field, jumping Montana 82 and igniting a second field on the other side of the highway.

Boon estimated the grass fire grew to between 2 and 3 acres before it was put out.

Three hours after the crash, firefighters brought in an excavator to pull the charred load of apples off the destroyed tractor-trailer, allowing them to extinguish the freighter's hot spots.

"Mainly the boxes were still in there smoking," Boon said.

Thornton was the 18th traffic-related fatality in Flathead County this year. Twenty-six people were killed on Flathead County highways in 2007.