GARNER, N.C. (AP) -- Federal investigators plan to enter the ruins of a sprawling Slim Jim snack plant Friday to look for the cause of an explosion that killed three workers and injured scores of others, a spokesman said.
Investigators are interested in the "dead center" of the damaged building in Garner, said Earl Woodham of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives. He said he didn't know what was at that spot.
Woodham said propane gas is not a focus of the investigation despite reports that employees smelled it before the time of the blast.
"There's a propane system but propane is not the main culprit," he said, adding that the investigators had looked into that. "That's not a focus."
Structural engineers from the federal agency got into the partially collapsed ConAgra Foods Inc. building through the less-damaged back side on Thursday, Woodham said.
"It took hours and hours," he said. "We're going to get inside today. We expect today for ATF special agents to be able to enter the same way and make it to an area of interest."
The next step is to work out from the center of the damaged south portion of the 500,000-square-foot plant.
"They're going to look for the blast effect and trace it back to a point of origin and then they can look for a cause," he said.
Officials said at least half of the plant was damaged in the Tuesday explosion. About 300 people were working in the factory at the time and at least 38 were injured.
Doctors are treating four people with critical burns covering between 40 percent and 60 percent of their bodies.
The company has 25,000 employees worldwide and makes brands such as Chef Boyardee, Hunt's tomato sauce, ACT II popcorn and Hebrew National hot dogs.