Runaway Polymerization — Dead Leg Popcorn Polymer Accumulation
TPC Port Neches Butadiene Explosions and Fire
TPC Group
📍 Port Neches, TX
Incident: November 27, 2019  •  CSB Report: December 19, 2022
0
Fatalities
1,3-Butadiene — Popcorn Polymer
Chemical Involved
5
CSB Recommendations
📋 Incident Summary

On November 27, 2019, a series of explosions and fire at the TPC Group butadiene production facility in Port Neches, Texas, injured 3 workers, caused ~$450M in on-site damage and $153M in off-site property damage, and required approximately 60,000 residents to shelter-in-place. Additional explosions followed over several days.

The CSB determined that popcorn polymer — an autocatalytic solid formed by spontaneous polymerization of 1,3-butadiene — accumulated in a dead leg created when a spare pump was taken out of service and isolated. The stagnant butadiene provided extended residence time for popcorn polymer initiation and growth until it ruptured the pipe.

The December 2022 CSB report issued 5 recommendations: 3 to TPC Group and 2 to the American Chemistry Council (ACC), all closed, focused on dead leg management programs and industry-wide reactive hazard guidance.

🔎 Key Findings
Finding 01
Dead Leg Created by Isolating Spare Pump
When TPC took a spare pump out of service, the isolation created a dead-end piping section containing stagnant high-purity butadiene — stagnant conditions provided the residence time required for popcorn polymer initiation.
Finding 02
Popcorn Polymer Accumulated and Ruptured Pipe
Popcorn polymer — an autocatalytic solid that grows rapidly once initiated — accumulated in the dead leg over time, exerting increasing pressure on the pipe wall until it failed and released butadiene.
Finding 03
Hazard Not Recognized in PHA or PSI
The facility's PSI and PHAs did not recognize the popcorn polymer accumulation hazard associated with dead legs in butadiene service — a known industry hazard for high-purity diene systems was not identified.
Finding 04
No Dead Leg Management Program
TPC Group had no formal program to identify, track, and mitigate dead legs in butadiene service — the hazardous stagnant section was not identified or monitored after the pump was isolated.
Finding 05
$603M Total Damage; 60,000 Residents Sheltered
On-site damage of ~$450M and off-site damage of ~$153M, plus a multi-day shelter-in-place order for ~60,000 residents, illustrate the catastrophic community consequences of the event.
🔍 Root Causes
1
Popcorn Polymer Hazard Not Recognized for Dead Leg
TPC Group did not have adequate PSI or PHA hazard recognition for popcorn polymer formation in dead legs — the decision to isolate the spare pump was not evaluated for the resulting dead leg hazard.
2
No MOC Review for Dead Leg Creation
Isolating the spare pump was not processed through the MOC system, so no hazard review was triggered that might have identified the popcorn polymer accumulation risk.
3
Absence of Dead Leg Identification and Mitigation Program
The facility lacked a systematic program to identify dead legs in diene service, assess them for popcorn polymer risk, and implement monitoring or elimination measures.
☑ CSB Recommendations
→ TPC Group (all closed)
Develop and implement a formal dead leg management program for all butadiene and diene-service piping, including identification of all existing dead legs, risk assessment, and elimination or active monitoring protocols.
→ TPC Group
Update PSI and PHAs to specifically address the popcorn polymer formation hazard in high-purity butadiene and diene systems, including dead leg creation scenarios.
→ TPC Group
Revise MOC procedures to ensure that any change resulting in isolation or stagnation of diene-service piping is evaluated for dead leg and popcorn polymer accumulation hazards.
→ American Chemistry Council (all closed)
Develop and publish industry guidance for dead leg management in butadiene and diene-service systems, including hazard recognition criteria and mitigation options.
→ American Chemistry Council
Update ACC process safety resources to include popcorn polymer as a reactive hazard requiring specific PSI, PHA methodology, and MI management in butadiene facilities.
💡 Lessons Learned
Popcorn polymer initiates spontaneously in stagnant, high-purity butadiene and grows autocatalytically. Process safety information must explicitly capture this reactive hazard — it is a well-known but underappreciated diene system risk.
Dead legs in reactive chemical service are inherently high-risk. Every dead leg in butadiene or diene service requires a formal risk assessment and mitigation program — not just identification.
Management of Change must cover operational changes that create or modify dead legs. Taking a pump out of service and isolating it is a change that can inadvertently create conditions for hazardous polymer accumulation.
The scale of community impact from this incident ($153M off-site damage, 60,000 sheltered) illustrates that process safety at butadiene facilities is a community safety imperative.
Reactive chemical hazards like popcorn polymer are often not listed as standard HAZOP deviation scenarios. PHA methodologies for diene processes must include node-specific review of reactive polymerization hazards in stagnant flow conditions.
PSI: Process Safety InformationPHA: Process Hazard AnalysisMI: Mechanical IntegrityMOC: Management of Change
🔨 Safety Meeting Toolbox Talk
►Does your facility have a formal dead leg management program? When was the last time dead legs in hazardous chemical service were inventoried and assessed?
►If you took a pump or valve out of service and isolated it, would your MOC process evaluate whether a dead leg was created?
►Are there reactive chemical hazards at your facility — like polymerization or autocatalytic reactions — that could accumulate in stagnant piping sections?
►How does your PHA process address reactive chemical hazards that only manifest under stagnant or low-flow conditions?
►What would you do if you discovered an unidentified dead leg in a reactive chemical service line during a routine inspection?
Immediate Action Items
✓Initiate a dead leg identification walk-down for your highest-risk process units — document all isolated sections, spare equipment connections, and blind flanges in hazardous chemical service.
✓Review your MOC procedure to confirm it triggers a hazard review when equipment is isolated and stagnant conditions may result in reactive chemical accumulation.
✓Pull PHA reports for diene, monomer, or other reactive chemical processes and verify that popcorn polymer or analogous reactive hazards are specifically addressed.
✓Confirm that PSI for reactive chemical processes includes documentation of reactive polymerization hazards and the conditions that initiate them.
✓Brief your maintenance and operations teams on the TPC Port Neches incident and ask them to identify any analogous reactive chemical dead leg risks at your facility.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 4 PSM elements (PSI · PHA · MI · MOC). 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.
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.
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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.
Supporting documents in our library →
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 →
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