Investigators are probing the cause of an explosion at a North Knoxville steel mill that critically burned one worker and injured five others Thursday night.

The blast was reported about 8:40 p.m. at the Gerdau Ameristeel facility, 1919 Tennessee Avenue, Knoxville Fire Department Capt. D.J. Corcoran said.

The most seriously injured victim suffered burns to more than 80% of his body, Corcoran said.

The explosion occurred in the area of a blast furnace where metal is melted down into molten liquid.

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