The NTSB (National Transportation Safety Board) is “looking closely” at how aluminum protective housing covers on three tank cars carrying vinyl chloride performed after a Norfolk Southern train derailed near East Palestine, Ohio, on February 3.
Eleven tank cars carrying hazardous materials, including five containing vinyl chloride, derailed. NS conducted a controlled release of the vehicles carrying vinyl chloride on February 6 to prevent them from exploding due to chemical reactions inside the tank cars.
In a Thursday update, the NTSB expressed concern that aluminum protective housing covers on some of the tank cars may have melted or been consumed when pressure relief devices vented burning gas while functioning as intended to release tank pressure.
Potential Impact of Melted Aluminum on Pressure Relief Devices
According to the agency, melted aluminum may have dripped into some of the pressure relief devices (PRDs), potentially degrading their performance.
“When a tank car exposes itself to fire and its contents heat up, the pressure inside the tank rises.” This can result in a loss of tank shell strength and, eventually, a breach,” according to the NTSB. “To protect emergency responders and the public from the possibility of catastrophic tank failure under fire conditions, operators must control the pressure inside tank cars. PRDs control internal pressure by releasing small amounts of material and then reclosing when normal conditions return. This reduces the likelihood of a tank shell breach and limits the amount of energy released if one occurs. Properly working PRDs reduce the possibility of catastrophic tank failure.”
The NTSB is concentrating on the aluminum protective housing covers used on three vinyl chloride tank cars. The protective housing covers were made of aluminum in the 1990s.
The agency will look for industry data to determine how many tank cars are in use.
The tank cars were DOT-105J300W models.
The PRDs and valve assemblies from the five vinyl chloride tank cars will be tested further.
The NTSB reiterated that it could issue urgent recommendations at any time during the investigation.
The EPA has ordered Norfolk Southern to conduct dioxin testing in East Palestine.
Meanwhile, the EPA has directed NS (NYSE: NSC) to conduct dioxin testing in the area surrounding the derailment.
The tests are being conducted in response to residents of East Palestine’s concerns.
The EPA said Thursday that if the level of dioxins is unacceptable for human health and the environment, it will immediately clean up the area. The EPA has also ordered NS to conduct a background study comparing dioxin levels in East Palestine to levels in areas not affected by the derailment. According to the EPA, common activities such as burning wood and coal release dioxins into urban and rural environments.
The agency stated that it would continue to sample for “indicator chemicals” as well. Test results suggest a low probability of the release of dioxin from the derailment.
The agency is reviewing a draft plan developed by NS that would create a dioxin “fingerprint” for soil sampling so that scientists and the EPA can determine whether any dioxin from the derailment or the controlled release impacted the local environment, according to the EPA.
