A Williston man who died in a camper fire at a truck stop near the city was overcome by smoke and gas fumes while trying to rescue a pet, according to authorities.

A Williston man who died in a camper fire at a truck stop near the city was overcome by smoke and gas fumes while trying to rescue a pet, according to authorities.

Phillip Unnerstall Jr., 23, died March 21 in the fire behind the Pilot truck stop. The state medical examiner's office determined that he died of smoke inhalation, and authorities ruled the death accidental.

The Williams County Sheriff's Office believes the fire was caused by a small propane heater being operated inside the camper.

Instead of rushing to safety, Unnerstall went to the back of the camper to try to save his pet dog, County Fire Marshal Chris Nelson told the Williston Herald.

"I think it was a heroic effort. Unfortunately it was a foolish effort," Nelson said.

A woman inside the camper broke a window to escape, and oxygen in the air that rushed in intensified the flames, Nelson said. Items inside the camper caught fire, and the camper's low ceiling trapped "superheated" gases and smoke, he said.

"It was really tragic. I think it was just a series of errors," Nelson said.

The fire happened around dawn at the truck stop on U.S. Highway 2 north of Williston.

"By the time we got there it was way too late to try to save anybody," Sheriff's Capt. Verlan Kvande said.

The woman who escaped, Patty Fouse, 57, of Williston, suffered minor injuries.