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US Chemical Safety Board issues factual update on TPC Group explosion in November 2019

02 November 2020

On October 29, the US Chemical Safety Board (CSB) issued an interim factual update on its investigation into the November 2019 explosion at TPC Group’s facility in Port Neches, Texas. The blast caused $500 million of damage to the chemical plant and injured three workers.

TPC Group's Port Neches facility - Image: CSB
TPC Group's Port Neches facility - Image: CSB

On November 27, 2019, a major loss of containment event at TPC Group’s Port Neches facility, which manufactured 1,3-butadiene and raffinate-1, resulted in several fires and explosions. Two TPC employees and a security contractor suffered injuries while a four-mile radius evacuation order that impacted around 60,000 people was issued and remained in effect for two days.

According to the CSB, the incident has caused TPC to transition to a “terminal and services” operation while the company evaluates and plans to rebuild the facility. As part of this transition, TPC has terminated the employment of several workers and supervisors. The reported property damage loss from the incident is estimated to be around $500 million.

The CSB’s factual update provides background information, a preliminary incident timeline, and the path forward for its investigation.

The production and storage of 1,3-butadiene at TPC’s Port Neches facility meant the site was subject to the Occupational Safety and Health Administration’s (OSHA) Process Safety Management (PSM) standard, 29 CFR 1910.119, as well as the Environmental Protection Agency’s (EPA) Risk Management Plan (RMP) Rule.

The CSB’s investigation so far points to the explosion possibly being caused by a loss of containment event that led to the liquid level in the final fractionation phase to drop rapidly from its operating level. The CSB calculated the liquid volume at the time of the initial level drop to be approximately 6,000 gallons. The liquid, which was primarily butadiene, emptied from the fractionator in less than a minute and then vapourised upon release, forming a vapour cloud. Three workers were in the unit at the time, two of them facing toward the final fractionator. Both told the CSB after the incident that they saw a pipe rupture, with one of them also identifying a release point.

The workers’ observations are consistent with the unit’s recorded process data, the CSB says, although it has not yet visually confirmed the failure location due to the extensive damage and unstable structural conditions at the site. Shortly after the loss of containment, the vapour cloud ignited and caused an explosion that heavily damaged the site and many buildings offsite.

A key focus in the CSB’s investigation is the possible presence of a substance called “popcorn” polymer which can form in process vessels containing a high concentration of butadiene. It is a hard, porous, opaque material created when oxygen reacts with butadiene in various areas of a butadiene production plant. When oxygen reacts with butadiene, it forms peroxides which then react with butadiene to form popcorn polymer. This reaction can continue and increase the volume of the polymer to the point where it can crack steel equipment. The CSB says the build-up of popcorn polymer has historically caused equipment ruptures throughout the industry, leading to loss of containment.

The CSB goes on to note that a piping segment that is open to the process but that does not have flow through it, for example due to a closed valve in the segment preventing flow, is known as a “dead leg”. Dead legs are known by the industry to promote popcorn polymer formation. The CSB says it found that the butadiene fractionator at the Port Neches plant had a dead leg component from September 6, 2019, which may have contributed to the November explosion.

The CSB is continuing to conduct its investigation of the incident with investigators analysing a range of aspects. At the conclusion of the investigation, the CSB will publish a final investigation report discussing the facts, conditions, and circumstances of the event; the cause(s) or probable cause(s); and may issue safety recommendations to prevent the recurrence of similar incidents.

Read the CSB’s factual update in full here:

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