CLARKSVILLE, Tenn. (AP) — A fire at a Clarksville zinc plant was burning so hot Friday morning that the three-story building's metal walls glowed orange as firefighters struggled to smother highly combustible zinc dust with fire-retardant foam.

"It has been a long battle because you can't put water on the zinc dust because it reacts to that," Clarksville Fire Marshal Ray Williams told The Leaf-Chronicle ( "What we have been using is a foam without the water, and it has helped put it out, but it has not cooled down, so it rekindles back up."

No injuries were reported in the blaze at Purity Zinc Metals, which is located in an industrial park off Interstate 24.

Three workers were in the plant when the fire began around 12:30 a.m., but they all escaped unharmed.

The 40,000-square-foot structure was still burning at dawn and all of it had been damaged by either smoke or fire. Firefighters said they expected to be on the scene for most of the day.

"We haven't been able to make a good interior attack," Williams said. "It's a situation where it is almost better to let it burn itself out, but we are going to do our best to put the fire out."

According to the company's website, Purity Zinc Metals is a custom fabricator of zinc dust, zinc anodes, zinc alloys and other zinc products for worldwide markets. The Clarksville-based company also has a plant in Ontario, Canada.

The Clarksville plant, built in 2001, recently had much smaller fire inside one of its grinding machines.

Friday's fire comes less than a year after a series of deadly iron dust fires at the Hoeganaes metal powders factory in Gallatin, where five workers died last year.