The driver of a refrigerated truck was in critical condition Saturday night after leaping from his vehicle when an explosion started a "propane-related" fire in the truck's cab, officials said.

Scott Wolt, age unavailable, Sandy, was being treated for burns over an estimated 60 percent of his body after being flown by helicopter to the Intermountain Burn Center at the University of Utah, a spokeswoman said.Wolt was southbound on 1-15 near the Woods Cross exit about 5:20 p.m. when the explosion occurred, causing the vehicle to go off the road, said Utah State Trooper Betty Bajorek.

"The driver bailed out and ran and then there was another large explosion," she said, adding that smoke could be seen for some distance by motorists backed up behind the accident scene.

One witness said the man was in flames when he jumped from the truck.

Fire crews extinguished the blaze, which was considered hazardous because of the toxic fumes associated with the coolant in the refrigerated truck, the trooper said.

The blaze possibly started as a result of a break in a propane gas line, she said.