Fatal Metal Treatment Facility Explosion: CSB Final Report

The US Chemical Safety and Hazard Investigation Board (CSB) issued its final report following an investigation of an incident that occurred May 30, 2024, at a metal treatment facility in Tennessee.

Three employees suffered minor burns. A fourth employee suffered major chemical and thermal burns on 95% of his body and died later the same day.

The incident also resulted in multiple fires, over $1 million in property damage, and the…facility being shut down for approximately 8 months.

What Caused the Chattanooga Explosion?

On the day of the incident, five rollers were placed in 800ºF 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 lifted out of the salt bath, the salt did not fully drain from one of the rollers and created a solid plug at the roller’s bottom.

The rollers were resubmerged to remove residual salt, but the salt plug prevented water from properly draining out of the plugged roller. The water in the roller quickly heated up, released steam, and caused the salt bath to erupt.

US CSB Made Three Recommendations

Implement Physical Barriers

Implement physical, protective barriers around the molten salt baths that isolate employees from hazardous releases at all locations that perform liquid nitriding.

Develop a Safety Management System

Develop a safety management system that incorporates industry guidance and includes, but is not limited to:

• A hazard analysis program for assessing the nitriding process.
• Written operating procedures for the nitriding process.
• A training program, including written materials, for the employees involved in the nitriding process.
• An incident investigation program.

Hire a Process Safety Manager

For each facility, establish a position with specific professional expertise and experience in safety management systems, such as risk-based process safety.