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(Source: National Transportation Safety Board press release, March 21, 2023)

WASHINGTON, D.C. — ​​​Investigators with the National Transportation Safety Board examined and tested pressure relief devices removed from the five vinyl chloride monomer (VCM) tank cars involved in the Feb. 3​ derailment of a Norfolk Southern train in East Palestine, Ohio.

Pressure relief devices, or PRDs, regulate the internal pressure of rail tank cars by releasing material when under pressure, reducing the potential for a catastrophic tank failure. NTSB investigators recovered the PRDs and tested them at a Texas facility.

The examination and testing revealed:

  • NTSB testing found anomalies with the function of some PRDs that may have compromised their pressure relieving capability. This will require further testing and evaluation to assess the impact on the operation of the PRDs.
  • ​According to the manufacturer’s part specifications, one of the installed PRD’s internal spring was coated with aluminum, which is not compatible with vinyl chloride.
  • While aluminum debris from melted protective housing covers entered the PRD discharge areas, there was no evidence that melted aluminum entered the tank. The NTSB continues to assess if the debris impacted the PRD operation.

The NTSB is continuing to conduct a safety investigation to determine the probable cause of the derailment. Additional actions may be recommended to prevent future derailments as the investigation proceeds.

The investigative update is available online.

Additional information is available on the investigation webpage.