Light smoke coming out the bay door at Designed Alloy Products is the only visible sign of a serious explosion that occurred there Friday morning.

Hours after an explosion at a small metal recycler in Alton Park injured six workers Friday, bulldozers were back to moving large piles of scrap metal, and office staff members were back to work.

Chattanooga police and firefighters went to Designed Alloy Products at 3033 Alton Park Blvd. just after 7:30 a.m. Friday in response to reports of a fire and explosion, fire department spokesman Bruce Garner said.

Once they arrived, firefighters found a large furnace within the building surrounded in flame. Workers had reportedly been melting stainless steel in the 3,000-degree furnace.

Because of the materials and heat involved, firefighters were warned not to use water to contain the blaze, so they had to use an extinguishing powder. Garner said it took 25 minutes to contain the fire.

Three of the six workers who were injured were treated for smoke inhalation at the foundry, but the other three were taken by ambulance to Erlanger hospital with burns. The names of those injured were not released.

Two suffered minor burns, according to Garner, but the third reportedly had second- and third-degree burns on almost 15 percent of his body.

Although the injuries were not reportedly life-threatening, the worker was taken to the burn center at Vanderbilt University Hospital in Nashville.

Garner said Erlanger spokeswoman Pat Charles reported that seven other "walk-in" patients showed up at the emergency department to be checked out, but all were expected to be treated and released.

Next door, at Tranco Logistics, owner Byron Trantham said his staff didn't realize anything was amiss until emergency responders arrived.

"The people upstairs heard a sort of rumble, but sometimes when the trucks back there hit the building it makes a boom. We didn't think anything was wrong until we heard sirens," Trantham said.

At that point Trantham went next door to see if his neighbors, or emergency workers, needed any help.

"They said everyone would be OK, and at about 8:30 a.m. they let all the office folks back in," he said. "I just asked if they needed anything, to get people out of the cold, or if there was anything we should be concerned about."

He said fire officials told him there was no immediate danger.

Mike Schroeder, president of Illinois-based Designed Alloys, said the company could not comment on the incident until the official and internal investigations are complete.

"As far as I know everything is OK, but we are not commenting at this time, because we haven't been able to get in and see what happened," Schroeder said.

Designed Alloys manufactures metal alloys for the foundry industry, Schroeder said.

Contact staff writer Louie Brogdon atlbrogdon@timesfreepress.com oe 323-757-6406.