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Failed wheel bearing caused train derailment and subsequent chemical spill

28 June 2024

The US National Transportation Safety Board (NTSB) confirmed on 25 June that a rail car’s defective wheel bearing caused the derailment and subsequent hazardous material release in East Palestine, Ohio on 3 February 2023. Investigators said that the derailment occurred when a bearing on a hopper car failed and overheated, leading to the fiery derailment in the centre of the small town.

Image: NTSB
Image: NTSB

NTSB investigators, speaking at an NTSB board meeting held on 25 June at East Palestine High School, said the decision by the local incident commander three days later to conduct a vent and burn of the contents of the tank cars carrying vinyl chloride monomer was based on incomplete and misleading information provided by Norfolk Southern officials and contractors. The vent and burn was not necessary to prevent a tank car failure, NTSB investigators found.

According to the Federal Railroad Administration, a vent and burn procedure should be a last resort, used when a tank car is about to fail. Norfolk Southern rejected three other removal methods and began planning for a vent and burn shortly after the derailment, investigators found.

Contributing to the severity of the hazardous materials release was the continued use of DOT-111 tank cars to transport flammable liquids and other hazardous materials. During the derailment, three DOT-111 cars were mechanically breached, releasing flammable and combustible liquids that ignited. The fire spread and exposed other tank cars to heat, leading to a decision to conduct vent-and-burn action on five tank cars carrying vinyl chloride. The vent and burn resulted in a mushroom cloud that towered over the town and surrounding area.

The DOT-111 tank car is being phased out of flammable liquids service because of its long record of inadequate mechanical and thermal crashworthiness and propensity to release lading in a derailment. This unacceptable safety record is why the NTSB is calling for an accelerated phaseout of DOT-111 tank cars in hazmat service, the agency said.

Overheated wheel bearings are a common cause of rail accidents. Hot bearing detectors are part of system intended to warn crews to stop the train before the hot bearing can cause a derailment. The crew did not receive a hot bearing warning until the train passed over a detector in East Palestine, when the overheated bearing was about to cause its axle to fail. The crew began to slow the train using dynamic braking, but it was too late. A total of 38 rail cars derailed, including 11 rail tank cars carrying hazardous materials.

The difficulty of accurately measuring temperature inside the bearing, combined with Norfolk Southern’s standard operating procedures and the spacing between detectors, meant the crew did not receive adequate warning to stop the train before the derailment, NTSB investigators said.

“Unfortunately, some have sought to minimize the wide-ranging impacts of this derailment, pointing to the fact that there were no fatalities or injuries. For this, we are certainly grateful, but the absence of a fatality or injury doesn’t mean the presence of safety,” said NTSB Chair Jennifer Homendy. “Our agency doesn’t wait for death or injury to occur. Instead, we objectively analyze the facts and evidence to make recommendations that, if implemented, will ensure this never happens again. Thanks to the hard work of our world-class investigators, we now have a roadmap to do just that.”

As a result of this investigation, the NTSB issued new safety recommendations to the Secretary of Transportation, FRA, PHMSA, the state of Ohio, the Association of American Railroads, Columbiana County Emergency Management Agency, the Chlorine Institute, Norfolk Southern Railway, the International Association of Fire Chiefs, the International Association of Fire Fighters, the American Chemistry Council, Oxy Vinyls, LP and the National Volunteer Fire Council. The recommendations address safety issues including:

- Failure of wayside monitoring systems to diagnose a hot wheel bearing in time for mitigation to prevent a derailment.
- Inadequate emergency response training for volunteer first responders.
- Hazardous materials placards that burned away, preventing emergency responders from immediately identifying hazards.
- A lack of accurate, timely and comprehensive information passed to local incident commanders and state officials.
- The continued use of DOT-111 tank cars in hazmat service.

An abstract of the final report, which includes the findings, probable cause, and all safety recommendations, is available by clicking here. The full final report will be publish in the next few weeks.

Norfolk Southern says safety enhancements align with NTSB recommendations

Following the NTSB’s findings, Norfolk Southern said it appreciates the NTSB's investigation, recommendations for enhancing rail safety and the acknowledgement of the steps Norfolk Southern has taken to improve safety. The company said it shared the commitment and over the last 16 months had implemented many enhancements and technologies to make its railroad even safer.

In relation to the vent and burn recommendation, Norfolk Southern said its only motivation in recommending the vent and burn to the Unified Command was the health and safety of the community and first responders.

After carefully considering all alternatives, Norfolk Southern and its specialist contractors recommended a controlled vent and burn to the Unified Command as the only option to protect the community from a potential catastrophic explosion. This recommendation was developed under guidance from two of only three specialized firms in the US certified by the Chlorine Institute to respond to vinyl chloride emergencies.

Several key factors indicated the strong possibility of a catastrophic, uncontrolled explosion including:

- The tank cars had been damaged in a high-speed derailment and were exposed to extensive pool fires.

- The pressure relief devices were not working – the behaviour of the pressure relief devices on the affected tank cars indicated that dangerous pressure was building inside the tank cars without being properly released.

- The manufacturer's safety guidance warned that vinyl chloride monomer may polymerize when exposed to the conditions present at the derailment.

- Other options for safely removing the vinyl chloride monomer cars from the derailment site (such as rerailing them) were not possible, due to damage sustained in the derailment and dangerous conditions on-site.

In a statement, Norfolk Southern said it had received conflicting information from Oxy Vinyls' personnel as to whether polymerization was or could be occurring and that Oxy Vinyls' safety data sheet was clear that polymerization was possible in the circumstances observed at the derailment.

The statement said: “Norfolk Southern does not agree with the conclusion that it "withheld" Oxy Vinyls' views from the Unified Command. Oxy Vinyls had every opportunity to participate in the Unified Command. They were on scene in the building where the Unified Command was operating. There was no obstacle to Oxy Vinyls making their views known to the ultimate decision-makers.

“Unified Command was advised that a vent and burn procedure might be necessary approximately 20 hours before the Unified Command made the final decision to proceed with the operation. Expert contractors began necessary preparations in the event a vent and burn recommendation was adopted.

“The vent and burn effectively avoided a potential uncontrolled explosion. There was no loss of life and contractors took steps to manage environmental impact.”

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