NTSB Assesses Texas Hazmat Derailment

The National Transportation Safety Board recently issued an overview of its report on the Jan. 8, 2022 BNSF derailment in Texas where more than a half million gallons of denatured ethanol was released. Here’s the report.

What Happened

This is a synopsis from the NTSB’s report and does not include the Board’s rationale for the findings and safety recommendations. The final report and pertinent safety recommendation letters will be distributed to recommendation recipients as soon as possible.

On January 8, 2022, about 9:49 a.m. local time, an eastbound BNSF Railway Company train, U JOENYF7 07A, derailed 37 tank cars at milepost 156.2 on the BNSF Railway Company Red River Division in Oklaunion, Texas. The train had 2 crew members on board and was composed of 2 head-end locomotives, 1 distributed power locomotive at the rear of the train, 2 buffer railcars, and 96 loaded US Department of Transportation specification 117J (DOT-117J) tank cars carrying denatured ethanol, a flammable liquid. The BNSF Railway Company estimated that 601,819 gallons of denatured ethanol released from 28 of the 37 derailed tank cars. The ethanol ignited and burned uncontrolled for about 4 hours, resulting in a pool fire. No injuries or evacuations were reported.

What We Found

Because this was a hazardous materials investigation focused on the performance of the DOT-117J tank cars, we did not determine the probable cause of the derailment.

The majority of the ethanol released leaked from tank car service equipment (such as manway covers and bottom outlet valves) that remained intact during the derailment but sustained damage from the pool fire. We found that the gaskets used in the service equipment were made of materials that are vulnerable to damage when exposed to fire. Using gaskets made of more thermally resistant materials would likely increase the survival time of tank cars exposed to fire and reduce the severity of hazardous material releases.

Also Read: 3 Tips for Large Ethanol Spills

We also found that when the Pipeline and Hazardous Materials Administration created the DOT-117 specification (which includes the DOT-117J specification) for non-pressure tank cars, it expanded existing thermal protection regulations for pressure tank cars to non-pressure tank cars with different designs.

Further, we found that a mechanical (non-thermal) breach of a tank car involved in the derailment occurred because of loading between underframe components and tank head material—an outcome that a specific federal regulation and an industry standard, the 85 percent rules, are intended to prevent. This load scenario likely occurred because several of the tank car’s welds exceeded the sizes specified in the design, which led to the tank head material being the weakest point in the load path and fracturing, releasing lading. Further, because there is not an industry standard for rejecting an oversized weld, the design size for each weld is effectively a minimum size, and that as-built tank cars may have oversized welds that may lead to tank fractures. Relatedly, we found that a design that complies with the 85 percent rules does not prevent fabrication of tank cars that may violate the rules because of oversized welds that make the tank cars more vulnerable to tank fractures in a derailment.

Findings

Gaskets currently used in DOT 117J tank car service equipment may be made of materials vulnerable to thermal damage when exposed to fire, which can lead to the release of hazardous material.
Using gaskets with higher service and survival temperatures would likely increase the fire exposure survival time of DOT-117 tank car service equipment in flammable liquid service and reduce the severity of hazardous materials releases.
The Pipeline and Hazardous Materials Safety Administration’s 2016 expansion of existing thermal protection system regulations from pressure tank cars to non-pressure DOT-117 tank cars likely did not account for the design differences between these types of tank cars, thus a DOT 117 tank car certified as compliant with regulations may have deficient thermal protection because its service equipment may not be protected by its thermal blanket.
The mechanical breach of tank car TILX731751 between the tank head material and the front sill pad occurred because the window weld between the front sill pad and the tank continued to provide a load path between the tank head and the stub sill while the head brace remained attached to part of the front sill pad, leading to a local stress state that exceeded the strength of the tank head material.
Because welds between the head brace and front sill pad exceeded their design sizes, the strength of the head brace attachment weld for tank car TILX731751 likely exceeded the load carrying capability of the underlying front sill pad, reducing the probability of the weld failing as intended when placed under high loads, such as the ones that occur during a derailment, and resulting in the tank car being mechanically breached.
The weld size specified by a tank car design is effectively a minimum size for the weld on an as-built tank car because industry standards do not provide for the rejection of oversized welds that, if left unaddressed, may lead to tank fractures.
A tank car design that complies with the Association of American Railroads 85 percent rule does not prevent tank cars from being fabricated with oversized welds that make the as-built tank cars noncompliant with the rule and more vulnerable to mechanical breaches in a derailment.

What We Recommended

As a result of this investigation, we recommended that the Federal Railroad Administration and the Pipeline and Hazardous Materials Administration work together to develop and publish both benchmarks and thermal performance standards for gaskets used in tank cars transporting flammable liquids. We also recommended that the Pipeline and Hazardous Materials Administration revise the DOT-117 tank car specification to ensure that these tank cars use appropriate thermal protection systems, and that the Association of American Railroads update its certification process to ensure that tank cars comply with this revised specification.

We also recommended that the Association of American Railroads create an inspection standard in the Manual of Standards and Recommended Practices for rejecting oversized welds at key points on tank car underframes.

To the Federal Railroad Administration:

Work with the Pipeline and Hazardous Materials Safety Administration to develop and publish benchmark service and survival temperatures for gaskets to be used in tank cars used in flammable liquid service that reflect currently available gasket materials.
Work with the Pipeline and Hazardous Materials Safety Administration to develop and publish thermal performance standards for gaskets used in tank cars in flammable liquid service that address both accident and normal transportation conditions.

To the Pipeline and Hazardous Materials Safety Administration:

Work with the Federal Railroad Administration to develop and publish benchmark service and survival temperatures for gaskets to be used in tank cars used in flammable liquid service that reflect currently available gasket materials.
Work with the Federal Railroad Administration to develop and publish thermal performance standards for gaskets used in tank cars in flammable liquid service that address both accident and normal transportation conditions.
Revise the DOT-117 specification in 49 Code of Federal Regulations 179.202-6 to ensure that DOT-117 tank cars incorporate thermal protection systems appropriate to non-pressure tank cars so that service equipment is thermally protected.

To the Association of American Railroads:

After the Pipeline and Hazardous Materials Safety Administration revises the DOT-117 specification, revise your Certificate of Construction approval procedures for DOT-117 tank cars to ensure use of compliant thermal protection systems.
Revise the inspection requirements for welds associated with the 85 percent rule contained in the Manual of Standards and Recommended Practices to include a standard for rejecting oversized welds on as-built tank cars.