Gerdau SA, a steel manufacturer with operations in 14 countries, was trying to determine the cause of the explosion Thursday night, and production was shut down while the investigation is underway, spokeswoman Kimberly Selph said.
The blast occurred at the plant's melt shop, where scrap metal is melted in a furnace and poured into molds, Selph said.
The product from the melt shop is milled into long-steel products, generally rebar, she said. All six workers suffered burns, either from steam or from drops of molten metal, Knoxville Fire Department Captain D.J. Corcoran said.
The most severely injured worker, who had burns over 80 percent of his body, was being treated at a regional burn center, Corcoran said.
The five other workers were treated and released from a Knoxville medical center, he said.
Many workers live within five miles of the mill, Corcoran said. They reported feeling their houses shake at the time of the blast Thursday night, he said.
Selph refuted the fire department's report about the extent of the mostly seriously injured worker's burns, but didn't provide details.