Economy

March 03, 2023 | Regulatory

East Palestine: NTSB Examining Tank Car Hatch Covers

Written by Carolina Worrell, Senior Editor

Following the completion of damage assessment inspections of the 11 Norfolk Southern (NS) hazardous materials (hazmat) tank cars, including the five carrying vinyl chloride, that derailed in East Palestine, Ohio, on Feb. 3, the National Transportation Safety Board (NTSB) says it is “concerned that aluminum protective housing covers on some tank cars melted or were consumed when pressure relief devices (PRDs) vented burning gas while functioning as designed to relieve tank pressure.”

The five derailed railcars carrying vinyl chloride were DOT-105J300W tank cars. Preliminary examination, which was completed Feb. 22 and released Feb. 23, suggests that melted aluminum may have dripped into some PRDs, possibly degrading their performance (see Figure 1, below), according to NTSB. The tank car wreckage was released to NS on Feb 24.



Figure 1. Tank car OCPX80235 with missing aluminum protective housing cover and metallic debris contained within the protective housing (left), and OCPX80370 with open steel protective housing cover (right) in East Palestine, Ohio. (Source: NTSB)

According to NTSB, when a tank car is exposed to fire conditions and its contents are heated, the pressure inside the tank rises. This, NTSB says, “can lead to loss of tank shell strength and eventually a breach. To protect emergency responders and the public from the possibility of catastrophic tank failure under fire conditions, the pressure inside tank cars must be controlled. PRDs are intended to regulate internal pressure by releasing small quantities of material and reclosing after normal conditions are restored. This reduces the probability of a breach in the tank shell and limits the amount of energy a breach can release if one occurs. Properly functioning PRDs thus reduce the potential for catastrophic tank failure.” Figure 2 (below) illustrates PRD function during the East Palestine derailment.​



Figure 2. Energetic pressure relief from a vinyl chloride tank car, East Palestine, Ohio, on Feb. 4. After releasing material, the PRD closed and remained closed. (Source: NTSB)

According to the preliminary investigation, NTSB discovered that three of the examined derailed vinyl chloride tank cars were manufactured in the 1990s with aluminum protective housing covers. Although the number of tank cars in flammable gas service with aluminum protective housing covers is presently unknown, NTSB has requested industry data to determine the size of the potentially affected fleet.

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PHMSA Safety Advisory Notice: Tank Cars Equipped with Aluminum Manway Covers

Thursday, March 2, 2023

PHMSA Safety Advisory - Tank Car Aluminum Manway Covers.pdf (197.92 KB)

This Safety Advisory alerts hazardous materials tank car owners and offerors of the potential harm to certain manway assemblies with aluminum protective housing covers when exposed to extreme heat. See Safety Advisory for more details.

DOT is committed to ensuring that information is available in appropriate alternative formats to meet the requirements of persons who have a disability. If you require an alternative version of files provided on this page, please contact PHMSA-Accessibility@dot.gov