WASHINGTON, D.C. Jun 3, 2025 – The U.S. Chemical Safety and Hazard Investigation Board (CSB) today released its final report into the fatal explosion and eruption at the Techniques Surfaces USA (“TS USA”) liquid nitriding facility in Chattanooga, Tennessee, that fatally injured an employee on May 30, 2024. The incident also resulted in multiple fires, over $1 million in property damage, and the TS USA facility being shut down for approximately 8 months.
TS USA, a subsidiary of the French company HEF Groupe, treats metal parts in a liquid nitriding process, which involves a reaction to harden the surface of the metal. On the day of the incident, five hollow rollers were submerged in molten salt baths used in the nitriding process. Each roller was a large cylinder that had an empty cavity with drain holes on the top and bottom. When the rollers were submerged in the baths, molten salt entered the cavities through the drain holes. Due to the small size of the drain holes, when the rollers were lifted out of the salt bath, the salt was unable to fully drain from one of the rollers and created a thick, solidified plug at the bottom of the roller. All five rollers were submerged in a hot water rinse bath to remove residual salt, but when the rollers were lifted out of the water, the salt plug prevented water from draining out of the plugged roller.
When troubleshooting the plugged roller, the TS USA employees reintroduced all five rollers back into the salt bath to try to melt the solidified salt in the plugged roller so that it could drain out of the roller. However, the employees did not realize that there also was water in the cavity of the plugged roller. When the roller with the retained water was inserted into the 800°F salt bath, it began heating up. The boiling water inside the roller rapidly increased the pressure inside the roller’s cavity, ultimately releasing steam that caused the hot molten salt to erupt from the bath and engulf one of the TS USA employees. The employee suffered second- and third-degree chemical and thermal burns over 95 percent of his body. He was transported to a nearby hospital, where he died later that day. Three other TS USA employees suffered minor burns and were treated on-site.
“This terrible incident underscores how critically important it is for facilities like TS USA to have a comprehensive and effective safety management system in place,” said CSB Chairperson Steve Owens. “The absence of strong process safety protocols—and the failure to apply lessons from past similar events—put TS USA’s workers at serious risk, with one of them tragically being killed.”
The CSB's investigation identified critical process several safety failures at the TS USA Chattanooga facility, including the lack of a robust safety management system, the absence of hazard analyses, inadequate procedures and training, and failure to apply lessons from prior incidents across HEF Groupe (the parent company of TS USA) and HEF Groupe’s subsidiaries.
The CSB found that at least three prior incidents involving similar hazards had occurred at facilities that are part of the HEF Groupe organization. However, HEF Group failed to ensure that information about those incidents and lessons learned from them were shared and implemented organization-wide. The CSB also found that HEF Groupe failed to enforce corporate safety standards or ensure that its subsidiaries, including TS USA, adopted essential safety knowledge and practices.
The CSB is issuing a total of seven recommendations to TS USA and HEF Groupe. These include: (i) installation of physical barriers to protect employees from molten salt releases; (ii) development and implementation of a comprehensive safety management system incorporating industry standards; (iii) creation of a corporate governance and knowledge management program to ensure that safety information is effectively communicated and enforced across all HEF Groupe facilities; and (iv) establishment of a position with specific professional expertise and experience in and responsibility for safety management systems at each TS USA facility.
The CSB is an independent federal agency responsible for investigating industrial chemical incidents that result—or could result—in catastrophic releases of hazardous substances. The Board conducts thorough investigations, issues safety recommendations, and advocates for preventive measures to protect workers, communities, and the environment.
Board members are appointed by the President and confirmed by the Senate. The CSB does not issue fines or citations but makes non-binding safety recommendations to companies, labor organizations, regulatory bodies, and industry stakeholders.
For more information, visit www.csb.gov or contact Communications Manager Hillary Cohen at [email protected].