Chemical Board Still Probing Tennessee Nitriding Plant Blast That Killed Worker

Federal safety officials said that almost four months after a fatal explosion at a steel-hardening facility in Tennessee, teams are still trying to determine the exact cause of the incident.

One worker was killed in the explosion at the Techniques Surfaces USA (TS USA) liquid nitriding facility in Chattanooga, Tennessee, on May 30, and another worker was injured. The U.S. Chemical Safety and Hazard Investigation Board, known as the CSB, began investigating soon after.

“The CSB is issuing this update to keep the public informed on the agency’s ongoing investigation into the tragic incident at TS USA,” Board Chairman Steve Owens said in a statement Thursday. “Moving forward, the CSB will continue its analysis and of the cause of this incident in order to prevent similar events from occurring.”

The agency said that so far, the probe has determined that on the day before the incident, TS USA had completed a liquid nitriding process for five stainless steel rollers. The rollers were left in a hot water rinse bath overnight, a common practice at the facility.

The next morning, the plant manager found one roller still leaking water and suspected that it was clogged with solidified oxidizer salt, the CSB explained. After consulting with a process engineer remotely, the manager decided to reintroduce the rollers directly into the oxidizing bath without preheating.

At 8:58 a.m., an eruption of molten salt from the oxidizing bath occurred, fatally injuring one employee and igniting combustible materials in the area, leading to multiple fires.

The TS USA plant is part of HEF Durferrit USA, based in Springfield, Ohio. Among other processes, the facility uses salt baths to harden steel by nitriding, or causing the steel to absorb nitrogen.

Topics Tennessee Chemicals