By Tim Ghianni
NASHVILLE, April 19 (Reuters) - An explosion at a central Tennessee ammunition plant that killed one man and injured three other people this week resulted from an industrial accident, a federal official said on Saturday.
The blast on Wednesday at Rio Ammunition plant in McEwen occurred in an area of the plant that fed smokeless powder into a hopper, said Michael Knight, spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).
ATF investigators have deemed the incident as non-criminal in nature and called it "an industrial accidental explosion," Knight said.
"Human factors played a role in the explosion," said Knight, who could not provide additional details.
One man died on Wednesday after being airlifted to Vanderbilt University Medical Center in Nashville, which is about 50 miles (80 km) east of McEwen.
Another man also airlifted from the plant to the hospital has been upgraded to stable condition from critical, said hospital spokesman Paul Govern. A man and a woman who were injured in the blast have been released from the medical center.
The cause of the blast will be further investigated by the Tennessee Occupational Safety and Health Administration. (Editing by Alex Dobuzinskis and Sandra Maler)