An explosion that killed three workers at a North Carolina Slim Jim plant was caused by a natural gas leak that ignited in a room housing vacuum pumps for sealing the snacks, authorities said Saturday.
It will now be up to state and federal workplace investigators to determine how the leak happened and what caused it to ignite in Tuesday's blast at the ConAgra Foods Inc. plant in Garner, said Earl Woodham, an agent with the U.S. Bureau of Alcohol, Tobacco, Fireams and Explosives.
ATF agents believe the gas was sparked by a piece of equipment such as a fan motor or thermostat, but Woodham said another cause, like static electricity, couldn't be ruled out. Such electrical equipment would be capable of catching natural gas on fire even if it were operating normally, he said.
"It could have been anything that could have created a spark," Woodham said. "By the very nature of the fact that whatever caused it is no longer there due the destructive explosion, we're never going to be able to say, 'yes this motor' or 'yes this thermostat' did that."
The ATF concluded the explosion was an accident and closed its criminal investigation.
Gas smell hours before blast
The explosion ripped through the 500,000-square-foot plant in Garner while 300 people were at work. Officials said 38 employees were injured, four of them suffering critical burns. Three firefighters were treated after inhaling fumes from ammonia, which is used in the plant as a refrigerant.
Some workers in and near the pump room reported smelling gas in the hours before the blast, Woodham said.
On the day of the explosion, workers were installing a new piece of equipment in the room, but it's not clear if that played a role, Woodham said.
Omaha, Neb.-based ConAgra plans to assist the state Department of Labor, Occupational Safety and Health Administration and the U.S. Chemical Safety Board as they take over the investigation, company spokesman Dave Jackson said.
The company has no timetable on when the plant could be reopened, Jackson said.
"Our resources are devoted to assisting the investigation," Jackson said. "Based on the investigation, we'll then see what needs to be done next."
Killed in the explosion were Barbara McLean Spears, 43, of Dunn, and two Clayton residents: Rachel Mae Poston Pulley, 67, and Lewis Junior Watson, 33.
Officials in Garner said they will do whatever it takes to help reopen the plant, which employees 900 in the town of 25,000, just south of Raleigh.
ConAgra has 25,000 employees worldwide and makes brands such as Chef Boyardee, Hunt's tomato sauce, ACT II popcorn and Hebrew National hot dogs.