CSB Investigation — Fatal Chemical Eruption
TS USA Molten Salt Eruption
Techniques Surfaces USA (TS USA) / HEF Groupe
📍 Chattanooga, TN
Incident Date: May 30, 2024  |  CSB Report Released: June 3, 2025
1
Fatalities
0
Injuries
Molten NaOH
Salt (~800°F)
Chemical / Hazard
7
CSB Recommendations
📋 Incident Summary

On May 30, 2024, a worker at the TS USA liquid nitriding facility in Chattanooga, Tennessee was fatally injured when a violent molten salt eruption occurred from a process vessel. Liquid nitriding is a metal surface hardening process in which metal parts are immersed into a bath of molten potassium nitrate and sodium nitrite salts at temperatures approaching 700–900°F (370–480°C). When a part with moisture, hollow cavities, or sealed features is introduced to the molten salt bath, water can flash to steam explosively, propelling molten salt at high velocity in a dangerous eruption.

The CSB found that TS USA had no formal safety management system. No hazard analysis of the nitriding process had ever been conducted. No written operating procedures existed. No training program with written materials had been developed. No physical barriers were installed around the molten salt baths to protect workers from eruptions. The corporate parent, HEF Groupe, had no governance program to audit its subsidiary facilities or share lessons learned across its global nitriding operations — even though similar incidents had occurred at other facilities.

The CSB's final report (released June 3, 2025) issued seven recommendations targeting physical barriers, safety management system development, corporate governance, and knowledge management. One recommendation — requiring a dedicated process safety professional at each TS USA facility — has been closed as accepted and implemented.

🔎 Key Findings
Finding 1
Molten Salt + Moisture = Violent Eruption
When moisture from a part flash-vaporizes in contact with molten salt at ~800°F, the steam explosion can propel molten salt at lethal velocity and distance. This hazard is documented in ASM International's Heat Treating Handbook — but had never been formally analyzed at TS USA.
Finding 2
No Safety Management System
TS USA had no Process Safety Management system or equivalent safety management framework. No structured hazard identification process had ever been applied to the liquid nitriding process.
Finding 3
No Written Operating Procedures
No documented operating procedures existed for the nitriding process — including no documented requirements for part inspection before nitriding, no moisture check protocol, and no sealed-cavity identification step.
Finding 4
No Worker Training Program
No training program with written materials existed for nitriding process operators. Workers were not trained on the specific hazards of moisture contact with molten salt, the mechanism of steam eruption, or the consequences.
Finding 5
No Physical Barriers
No physical barriers existed around the molten salt baths. Direct physical separation between workers and a 800°F molten salt eruption hazard is the most reliable safeguard available — and it was absent.
Finding 6
Corporate Governance Failure
HEF Groupe's corporate structure had no program to audit safety at subsidiary facilities or share incident learnings across its global network. Similar molten salt incidents at other HEF facilities were not communicated to TS USA.
🔍 Root Causes
1
Uncharacterized Thermal Eruption Hazard
The moisture/sealed-cavity eruption hazard in liquid nitriding was known in the broader industry but had never been formally analyzed at TS USA. Without a hazard analysis, the risk was invisible to management and workers.
2
No Written Procedures for Part Preparation
Without documented operating procedures, there was no standardized process for inspecting parts before nitriding — no moisture check requirement, no sealed-cavity identification step, no prohibition on reprocessing suspect parts without inspection.
3
No Worker Training on Thermal Hazard
Workers were not trained on the mechanism of steam eruption, warning signs of at-risk parts, or the consequences of introducing moisture-contaminated or hollow parts into the molten salt bath.
4
Absent Engineering Controls
Physical barriers between workers and the molten salt baths were not installed. A passive barrier that physically prevents workers from being in the projectile zone is the highest-reliability safeguard for this type of hazard.
5
No Corporate Safety Knowledge Sharing
HEF Groupe operated multiple nitriding facilities globally with historical incidents but had no mechanism to share those lessons across facilities. Knowledge that could have prevented the Chattanooga fatality existed within the parent organization.
☑ CSB Recommendations
→ TS USA
Implement physical protective barriers around all molten salt baths that isolate employees from hazardous releases.
→ TS USA
Develop a safety management system including: hazard analysis of the nitriding process; written operating procedures based on hazard analysis findings; a training program with written materials for all operators; and an incident investigation program with causal analysis and company-wide communication.
→ TS USA
Establish a position at each TS USA facility with expertise in safety management systems / process safety. [STATUS: CLOSED — Acceptable Action Taken]
→ HEF Groupe (Parent Company)
Include physical protective barriers around molten salt baths as part of standard facility design for all liquid nitriding processes.
→ HEF Groupe (Parent Company)
Develop a corporate safety management system incorporating CCPS risk-based process safety guidance, including hazard analysis, SOPs, training, and incident investigation programs applicable to all HEF nitriding facilities.
→ HEF Groupe (Parent Company)
Develop a Knowledge Management program for sharing findings from audits, hazard analyses, and incident investigations across the entire HEF Groupe organization.
→ HEF Groupe (Parent Company)
Develop a Corporate Governance program with regular audits of subsidiary facilities, tracking and accountability for all corrective actions, and documentation of findings and prompt responses to deficiencies.
💡 Lessons Learned
⚠ High-temperature thermal processes with potential for violent energetic reactions are process safety hazards, regardless of whether they meet OSHA PSM TQ thresholds. The principles apply universally.
⚠ A hazard that is documented in industry literature but has never been analyzed at your facility is still your hazard. Industry knowledge does not automatically translate into site-specific hazard controls.
⚠ Physical barriers are the highest-reliability safeguard for ejection hazards. Administrative controls (procedures, training) reduce human error; barriers work even when human error occurs.
⚠ Written operating procedures must cover non-routine tasks, not just routine operations. Part reprocessing, inspection criteria for borderline parts, and responses to abnormal conditions must be documented.
⚠ Corporate governance is a process safety requirement, not just a management best practice. If the parent company doesn't know what's happening at its facilities, it cannot prevent the next fatality.
PSM Elements: PHA · PSI · SOP · Training · MI · EP
🔨 Safety Meeting Toolbox Talk
Topic: Thermal Process Hazards, Barriers & Written Procedures
💬Does our process involve any materials at elevated temperatures that could react violently with water, air, or other contaminants introduced by a part or equipment?
💬Are there physical barriers between our workers and any high-energy thermal hazard (molten materials, high-pressure steam, hot oil, high-temperature reactors)?
💬What inspection steps are required before introducing material or equipment into any high-temperature process in our facility? Are these steps documented in writing?
💬When was the last time our process underwent a formal hazard analysis? Were non-routine tasks — reprocessing, off-spec conditions, abnormal operations — specifically evaluated?
💬If our facility has had incidents or near-misses with similar equipment at other sites, how do those lessons get communicated to us?
💬If a physical barrier were installed in front of a hazard in your work area, would it change the severity of the worst-case outcome? If yes, why isn't it there?
✎ Team Action Items
✓Identify all thermal hazards in your work area — any process material at elevated temperature that could cause severe burns or react energetically with moisture or contaminants
✓Verify that written operating procedures address part or material inspection before any high-temperature process — including moisture checks, cavity inspection, and prohibited conditions
✓Identify any physical barriers that separate you from a high-energy thermal hazard and confirm they are intact and in their designed position
✓Ask when your process last had a formal hazard analysis and whether non-routine tasks and reprocessing scenarios were included in that analysis
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 6 PSM elements (PHA · PSI · SOP · TRN · MI · EP). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Process Hazard Analysis (PHA)
A structured PHA or HAZOP study exists to identify exactly these scenarios before they occur. When PHA is absent, superficial, or overdue for revalidation, hazards operate unseen until they kill someone.
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Process Safety Information (PSI)
Accurate, complete Process Safety Information is the foundation every other PSM element depends on. When PSI is missing or wrong — chemistry data, equipment specs, P&IDs — the entire hazard analysis is built on a flawed base.
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Operating Procedures (SOPs)
Operators cannot reliably hold safe operating limits without clear, current, enforced procedures. Deviation from acceptable operating conditions — a root cause here — is a direct consequence of SOP failure.
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Training & Operator Competency
Workers must understand process hazards — not just the steps on the page. Training records, refresher frequency, and verified competency are all OSHA PSM requirements that gaps here violated.
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Mechanical Integrity (MI)
Equipment must be designed, inspected, and maintained to operate safely in its intended service. Mechanical integrity failures — degraded equipment, missed inspections, deferred repairs — contributed to loss of containment here.
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Employee Participation
OSHA PSM requires workers to be meaningfully involved in hazard analyses and procedure development — not just trained on the finished product. Active participation catches gaps that management alone misses.
Supporting documents in our library →
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