WASHINGTON - Devices that should have regulated internal pressure of rail tank cars involved in the East Palestine train derailment may have failed, according to investigators with the National Transportation Safety Board.

The NTSB examined and tested pressure relief devices removed from the five vinyl chloride monomer tank cars involved in the Feb. 3? derailment of a Norfolk Southern train, and found anomalies with the function of some devices that may have compromised their pressure relieving capability.

Pressure inside the tank rises when a tank car is exposed to fire conditions. This can lead to loss of tank shell strength and eventually a breach.

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.

The concern is for the safety of emergency responders and the public from the possibility of catastrophic tank failure under fire conditions.

According to the manufacturer's part specifications, one of the devices internal spring was coated with aluminum, which is not compatible with vinyl chloride.

While aluminum debris from melted protective housing covers entered the devices discharge areas, there was no evidence that melted aluminum entered the tank.

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  NTSB

 Concerns that the leaking tankers were in danger of exploding caused authorities to conduct what they called a "controlled burn", that sent a plume of toxic smoke over East Palestine and into Pennsylvania.

The NTSB says further testing and evaluation are needed to assess the impact on the operation of the devices.

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

The investigative update is available online.