HEAT EXCHANGER OVERPRESSURE — REBOILER EXPLOSION — 2 FATALITIES
Williams Olefins Geismar Reactor Explosion
Williams Olefins, LLC
📍 Geismar, LA
Incident: June 13, 2013  •  CSB Report: June 2015
2
Fatalities
Propylene / Butylene (Process Reboiler Overpressurization — Heat Exchanger Failure)
Chemical Involved
12
CSB Recommendations
📋 Incident Summary

On June 13, 2013, an explosion and fire at the Williams Olefins plant in Geismar, Louisiana, killed two workers and injured 167 others. The explosion originated in a process reboiler — a heat exchanger used to supply heat to a distillation column in the propylene/butylene separation unit.

A reboiler that had been taken out of service was inadvertently returned to heating service while still isolated from the process. With no flow path through the exchanger and with the process-side liquid trapped, the heat from the steam side rapidly vaporized the trapped liquid, creating pressure that exceeded the vessel's design limits and caused catastrophic failure.

The CSB found that the sequence of events that led to the explosion was set in motion by a management of change failure. A modification to the reboiler configuration had been made years earlier without a formal MOC review. This change created the precondition for the trapped-liquid overpressurization scenario, which was then triggered when operators returned the reboiler to service in its isolated state.

🔎 Key Findings
Finding 01
Reboiler Returned to Service While Isolated — Trapped Liquid Overpressurized
A reboiler isolated from process flow was inadvertently returned to steam service. With the process-side liquid trapped and no flow path, rapid vaporization built pressure beyond vessel design limits, causing catastrophic failure.
Finding 02
Management of Change Failure Created Precondition for Incident
A change to the reboiler configuration made years before the incident was implemented without a formal MOC review. This undocumented change created the process configuration that made the trapped-liquid overpressurization scenario possible.
Finding 03
167 Workers Injured — Largest Injury Count in Recent CSB Investigation History
The explosion injured 167 workers — one of the largest injury counts in any single CSB-investigated incident. The scale of injuries reflected the number of workers present at the facility on a normal working day and the extent of the explosion.
Finding 04
No PHA Identified the Overpressurization Hazard
The process hazard analysis for the propylene/butylene separation unit had not identified the trapped-liquid overpressurization scenario for the isolated reboiler configuration. The hazard was not recognized until the explosion occurred.
Finding 05
Operating Procedure Did Not Prevent Reboiler Startup While Isolated
Operating procedures for the unit did not include steps to verify that the reboiler was in service (not isolated) before returning it to steam heating service. The procedural gap allowed the hazardous condition to develop without recognition.
🔍 Root Causes
1
Undocumented MOC Created Hazardous Reboiler Configuration
A change to the reboiler configuration, implemented without MOC review, created a process configuration in which the reboiler could be placed in steam service while isolated from process flow — a direct overpressurization hazard.
2
Reboiler Activated in Isolated Condition — Operators Unaware of Hazard
Operators activated the reboiler steam supply without recognizing that the reboiler was isolated from process flow. The hazardous condition was not identified because the undocumented configuration change had not been communicated or analyzed.
3
PHA Did Not Capture the Trapped-Liquid Scenario
The facility's PHA had not identified the trapped-liquid overpressurization scenario for the reboiler. The hazard was latent in the process configuration but unrecognized because no systematic hazard analysis had been applied to the specific reboiler configuration.
☑ CSB Recommendations
→ Williams Olefins / Chemical Processors
Review all process modifications to identify any changes implemented without MOC review; conduct retroactive hazard analysis for undocumented changes; update PSI, PHAs, and operating procedures to reflect as-built configurations.
→ OSHA
Emphasize MOC program adequacy in PSM enforcement; conduct targeted inspections of facilities' MOC programs to identify undocumented process changes that may have created unanalyzed hazards.
→ Chemical Industry
Apply MOC review to all process configuration changes, including temporary changes, maintenance reconfigurations, and changes made "in-kind" that alter the process flow path or isolation capability.
→ CCPS / AIChE
Update guidance on MOC to specifically address heat exchanger bypass and isolation configuration changes; include heat exchanger configuration as a standard scope item in facility-wide MOC audits.
💡 Lessons Learned
Management of change is the process safety element specifically designed to prevent the introduction of new hazards through modifications. The Williams explosion illustrates what happens when MOC fails: a configuration change that creates a new, unanalyzed hazard persists indefinitely, invisible to operators and PHAs, until the conditions that trigger it are reached. MOC is not optional for any process configuration change — even changes that seem routine or temporary.
Heat exchanger and reboiler isolation configurations are a known, documented source of overpressurization hazards. The scenario of heat input to a blocked-in, liquid-filled exchanger is a textbook overpressurization failure mode. This scenario must be a standard PHA node for any heat exchanger that can be isolated from process flow while remaining connected to a heat source. The hazard was foreseeable — it simply was not analyzed.
Operating procedures for returning equipment to service must include verification steps for the process configuration, not just the equipment condition. Before activating steam or heat to a heat exchanger, a procedure must require verification that the process side is unblocked and in flow service. A simple verification step in the startup procedure could have prevented this explosion.
When 167 workers are injured in a single explosion, the scale of consequence illustrates that facility siting and occupancy management are themselves process safety issues. The number of workers present in a facility during normal operations, and their proximity to high-hazard process units, determines the consequence of a catastrophic failure. Reducing occupancy near high-hazard units and reviewing siting of work areas are process safety decisions.
MOC: Management of ChangePHA: Process Hazard AnalysisSOP: Operating ProceduresPSSR: Pre-Startup Safety Review
🔨 Safety Meeting Toolbox Talk
►Does your MOC program capture all process configuration changes — including heat exchanger bypass/isolation configurations, temporary changes, and maintenance reconfigurations? When was the last MOC program audit conducted?
►Has your PHA included a specific node for trapped-liquid overpressurization in heat exchangers that can be isolated from process flow while remaining connected to a heat source?
►Do operating procedures for returning heat exchangers or reboilers to service require an explicit verification that the process side is unblocked and in flow service before heat or steam is applied?
►Has your facility conducted a retroactive review for any process modifications that may have been implemented without MOC review? Are there undocumented configuration changes that create unanalyzed hazards?
Immediate Action Items
✓Conduct an audit of your MOC program records for all heat exchangers and reboilers; identify any configuration changes implemented without MOC review and perform retroactive hazard analysis.
✓Add trapped-liquid overpressurization as a standard PHA node for heat exchangers that can be isolated from process flow while remaining connected to a heating medium.
✓Update operating procedures for returning heat exchangers to service to include a mandatory verification step confirming process-side flow path is open before heat is applied.
✓Conduct a facility-wide MOC compliance audit to identify any process changes — in any unit — that may have been implemented without formal MOC review and hazard analysis.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 4 PSM elements (MOC · PHA · SOP · PSSR). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Management of Change (MOC)
Changes to equipment, chemistry, operating limits, or procedures that bypass formal review create new hazard pathways your PHA never evaluated. MOC failures open the door to incidents like this one.
Supporting documents in our library →
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.
Supporting documents in our library →
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.
Supporting documents in our library →
Pre-Startup Safety Review (PSSR)
PSSR is the final checkpoint before hazardous chemicals are introduced into a new or modified system. When PSSR fails or is bypassed, unresolved hazards go live with the process.
Supporting documents in our library →
Process Safety Management Consulting & Document Library
📂
PSM Document Library
32 ready-to-deploy PSM documents covering all 14 OSHA elements — procedures, checklists, and audit templates built for facilities operating under 29 CFR 1910.119.
Browse the Library →
📊
Free PSM Health Score
Find out where your PSM program stands across all 14 OSHA elements. Our free health score surfaces your biggest gaps in under 10 minutes — no account required.
Check Your Score →
📞
Consulting Services
PHA facilitation, PSM program builds, compliance audits, and OSHA inspection support. Transparent flat-fee pricing — no retainer required to get started.
View Pricing →
📋 Explore the full incident library: All 132 CSB Case Studies →