GARNER, N.C. (AP) – Investigators say a natural gas leak that ignited caused an explosion at a Slim Jim plant in North Carolina that killed three workers.

U.S. Bureau of Alcohol, Tobacco, Fireams and Explosives agent Earl Woodham said Saturday his agency has turned the case over to workplace investigators to determine the cause of the leak.

Woodham says electrical equipment is believed ignited the leak, but they haven’t norrowed down which piece of machinery it could have been.

The explosion Wednesday ripped through the 500,000-square-foot ConAgra Foods Inc. plant in Garner while 300 people were at work. Officials said 38 employees were injured, four of them critically.

Woodham says the ATF considers the blast an accident and has closed its criminal investigation.

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