An insurance audit raised a red flag about combustible dust at the Hoeganaes Corp. Gallatin metal-powders plant all the way back in 2008. The end result is the company did nothing about it and five workers are dead and four others suffered injuries, said the U.S. Chemical Safety Board (CSB).

The latest accident, on May 27, which fatally burned three workers, started from a hydrogen explosion inside the plant that occurred because of a corroded pipe, and safety board investigators found the company had no inspection or maintenance program in place to keep pipes carrying the extremely flammable gas from leaking.

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Hydrogen works in the production of the metal powders Hoeganaes makes for the auto industry, which go into metal parts for engines and transmissions.

Safety board member John S. Bresland criticized Hoeganaes for lax corporate oversight of the known dangers in the plant that led to the accidents.

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“Something serious is missing here,” Bresland said, referring to the company’s failure to act before the accidents.

The board’s investigators, led by Johnnie Banks, said workers told them before the first fatal explosion in January, there had been numerous flash fires, with no injuries, caused by the highly combustible dust. The dust results from the metal-powder manufacturing process and accumulates on surfaces throughout the plant, the probe found.

Because there were no injuries from the earlier incidents, that possibly led the company and the workers to believe the dust was not a serious hazard, the investigators suggested.

“That certainly was the case for me,” said Dwight Terry, a 31-year worker at the plant who retired in September. He came to the safety board meeting to hear what the investigation found.

“We were aware there was some danger, but because there had been no serious accidents, we didn’t think the powder was that explosive,” he said. “We also were never told about the dangers of the hydrogen gas, but I did figure that sooner or later somebody was going to get hurt. I knew four of the five men who died, so it really hit me hard.”

Still, Terry said he doesn’t blame Hoeganaes for the deaths.

“They went for 30 years without a fatality, then they just had an unlucky year,” he said. “But I don’t know that there was anything they could have done to prevent this. I hope they can go another 30 years without another accident.”

The safety board investigators, though, said both of the fatal accidents were preventable and that changes in the way they collect dust and a program to maintain the pipes that carry the hydrogen could prevent future accidents.

Although the May 27 explosion was the result of a hydrogen leak, there was a secondary blast fueled by the metal dust that made the accident even worse, the investigators said.

They also questioned the plant’s practice of relying on protective clothing to prevent burns to workers in the event of fires and explosions. The probe found all of the workers killed by the January and May blasts were wearing fire-resistant clothing, but the fire was so hot that the protective gear just burned away.

The flame-resistant clothing “was not effective against the high heat of the explosions,” Banks said.

Investigator David Chicca said there was a general feeling throughout the metal-powder industry that “iron dust was not combustible.”

But after the insurance audit in 2008, Hoeganaes did its own tests in 2009 and again in 2010 on the explosive potential of the dust in the plant, and got the same results the safety board did in its tests of dust collected at Hoeganaes, the investigators said. Those tests showed the dust was highly explosive when it was in confined areas and ignited.

To prevent future dust and gas explosions, the investigators recommended that Hoeganaes conduct regular audits for compliance with fire-prevention standards, train employees and contractors on how to eliminate hazards, and implement preventive-maintenance and leak-detection procedures for all flammable gases inside the plant.

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