CSB Investigation — Explosion & Toxic Release
Dow Louisiana Operations Explosions
Dow Chemical Company
📍 Plaquemine, LA
Incident Date: July 14, 2023  |  CSB Report Released: February 26, 2026
0
Fatalities
0
Injuries
Ethylene Oxide
(EO)
Chemical / Hazard
4
CSB Recommendations
📋 Incident Summary

On July 14, 2023, at approximately 9:15 PM, multiple explosions and fires erupted in the Dow Louisiana Operations Glycol II Ethylene Oxide Finishing unit in Plaquemine, Louisiana. A toxic ethylene oxide (EO) release accompanied the blasts, causing substantial property damage. Fortunately, no injuries were reported — but the incident underscored the extreme hazards of ethylene oxide, a chemical that is simultaneously highly flammable (LEL 3%, UEL 100%), capable of detonation, and acutely toxic.

The CSB investigation found that flammable EO accumulated in a process line that was supposed to be inerted (blanketed with nitrogen to exclude oxygen) but was not continuously monitored during normal operation. The incident was linked to maintenance activities involving confined space entry — after the entry was completed, a vessel was not left in a clean, startup-ready condition, leaving flammable residues that ignited during restart.

The CSB's final report (released February 26, 2026) issued four recommendations targeting EO line monitoring practices and updates to confined space entry standards to address post-entry vessel cleanliness requirements — a gap not previously addressed in NFPA or ASSP standards.

🔎 Key Findings
Finding 1
Un-monitored Inerted EO Lines
Process lines in ethylene oxide service that should have been continuously monitored for inerting status were not. This created conditions where flammable EO could accumulate without detection.
Finding 2
Post-Confined Space Entry Gap
After confined space entry was performed on a process vessel, the vessel was not left clean and ready for startup. Flammable residues remained and were ignited when the process was restarted.
Finding 3
Industry Standard Gap
NFPA 350, NFPA 326, and ANSI/ASSP Z117.1 — the primary confined space entry standards — contained no specific guidance on ensuring vessels are clean and startup-ready after confined space entry completion.
Finding 4
Ethylene Oxide Severity
EO is classified as a PSM HHC with a threshold quantity of 5,000 lbs. It can detonate, not just deflagrate. Uncontrolled EO releases in process environments carry catastrophic potential.
Finding 5
No Injuries Due to Timing & Location
The incident occurred at night (9:15 PM) with reduced staffing in the unit area. The absence of injuries was fortunate circumstance, not the result of adequate safeguards.
Finding 6
Monitoring as a Safety Barrier
Continuous monitoring of inerted lines serves as a critical active safety barrier. When monitoring is absent, operators have no early warning of loss of inerting integrity.
🔍 Root Causes
1
Inadequate Inerting Monitoring
EO-containing lines designated for inerting were not continuously monitored during normal operations. Loss of inerting status went undetected, allowing flammable EO to accumulate.
2
Confined Space Entry Procedure Gap
No requirement existed to verify vessels were clean and startup-ready after confined space entry. The handoff between maintenance and operations lacked a critical verification step.
3
Industry Standard Deficiency
NFPA and ASSP confined space standards did not address post-entry cleanliness — a gap that allowed this practice deficit to exist undetected across industry.
☑ CSB Recommendations
→ Dow Chemical Company
At all Dow ethylene oxide facilities, identify all process lines in EO service that should be inerted but are not continuously monitored during normal operation. Eliminate lines where possible; establish inerting and continuous monitoring controls for those that remain.
→ National Fire Protection Association (NFPA)
Update NFPA 350 (Guide for Safe Confined Space Entry and Work) to provide guidance on ensuring vessels are left clean and startup-ready after confined space entry.
→ National Fire Protection Association (NFPA)
Update NFPA 326 (Standard for Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair) with requirements for post-confined-space-entry vessel cleanliness.
→ American Society of Safety Professionals (ASSP)
Update ANSI/ASSP Z117.1 (Safety Requirements for Entering Confined Spaces) to provide guidance on ensuring vessels are left clean and ready for startup after entry is completed.
💡 Lessons Learned
⚠ Inerting is a critical safety barrier for flammable process lines. Inerting without continuous monitoring is like having a lock without knowing whether it is actually locked.
⚠ Every confined space entry creates a transition point between maintenance and operations. That transition must include a formal verification that the vessel is clean and safe for restart.
⚠ Ethylene oxide is among the most hazardous chemicals in process industry — it can detonate and has an UEL of 100%. There are no minor EO incidents.
⚠ The absence of injuries does not mean the safeguards were adequate. This incident was one shift timing away from a potential fatality event.
⚠ Industry standards can have gaps. Just because a practice is not prohibited by a standard does not mean it is safe. Hazard analysis must go beyond standard compliance.
PSM Elements: PSI · MI · SOP · PHA
🔨 Safety Meeting Toolbox Talk
Topic: Ethylene Oxide Hazards, Inerting, and Confined Space Entry
💬Do we have any process lines that should be inerted but are not continuously monitored? How would we know if inerting integrity was lost?
💬After a confined space entry on a process vessel, what is our verification procedure to confirm the vessel is clean and ready for startup?
💬What monitoring equipment do we have for flammable atmospheres in EO or other highly flammable service? Is it functioning and calibrated?
💬Do our confined space entry permits require a post-entry cleanliness verification before restoration to service?
💬What are the specific hazards of ethylene oxide (or other flammable chemicals in our process)? Does everyone in the unit know the LEL, UEL, and TLV?
💬How are maintenance-to-operations handoffs documented when vessels are returned to service after maintenance? Is there a formal sign-off?
✎ Team Action Items
✓Review your unit's list of process lines in flammable service — confirm which are inerted and which have continuous inerting monitors
✓Review your confined space entry permit to verify it includes a post-entry cleanliness/readiness check before the vessel is returned to operations
✓Test your flammable gas monitors and verify calibration records are current
✓Discuss the EO (or facility-specific flammable HHC) specific emergency response with your team — what do you do if a release is detected?
🔗 PSM Failures Behind This Incident

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

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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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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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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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 →
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