Investigators have traced the cause of a $1.3 million fire that destroyed a hangar at the Ogden Hinckley Airport to hot slag inadvertently left by a welder.

The blaze Saturday morning consumed the hangar being used for equipment and materials storage by Levolor Lorentzen Inc., a window-covering manufacturer, said Fire Marshal Bob Wright.He said a worker doing some welding at the hangar Friday afternoon was concerned that hot slag had gotten into some insulation, and he used a fire extinguisher to douse the area before leaving about 5:30 p.m.

Workers at the airport reported the fire at 1:23 a.m.

Wright said the fire gutted the 90-by-125-foot hangar, valued at about $300,000. He said the building's contents, valued at an estimated $1 million, also were destroyed.