A chemical command is still probing an explosion at a nitriding plant in Tennessee that killed one worker

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

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

“CSB is issuing this update to keep the public informed of the agency’s ongoing investigation into the tragic incident at TS USA,” board chairman Steve Owens said in a statement Thursday. “Going forward, CSB will continue its investigation and cause of this incident to prevent similar occurrences.”

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

The next morning, the plant manager found a roll still leaking water and suspected it was clogged with solidified oxidizing salt, CSB explained. After remote consultation with a process engineer, the manager decided to reinsert the rolls directly into the oxidation bath without preheating.

At 8:58 a.m., molten salt erupted from the oxidation bath, fatally injuring an employee and igniting combustible materials in the area, resulting in 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 the steel by nitriding, or for the steel to absorb nitrogen.

TOPICS
Tennessee Chemicals