The Flathead County Sheriff’s Office is investigating a suspected arson fire that occurred at a Montana Department of Transportation gravel pit north of Kalispell along U.S. 93.

According to Kalispell Fire Chief Dave Dedman, it appears a welding torch attached to a three-quarter ton flatbed utility truck was left in the driver’s seat. The welder was on and running when fire crews responded at around 5 a.m. Tuesday.

The truck was fully engulfed in flames when firefighters arrived on the scene, Dedman said.

The truck had been stolen from the U.S. 93 bypass construction site in Kalispell.

The construction boss told investigators that he had the keys to the truck. Upon further investigation, it was determined that the thief had broken a window to a building on the job site and may have been able to get a spare set of keys that way.

The damage to the truck was estimated to be $30,000, although that did not factor in the cost of tools that were in the vehicle, Dedman said.

Reporter Megan Strickland can be reached at 758-4459 or [email protected].