By David Shepardson
WASHINGTON (Reuters) - A U.S. safety board said on Tuesday it found anomalies in pressure relief devices (PRDs) of the freight train operated by Norfolk Southern Corp (NYSE:NSC) that derailed on Feb. 3 in East Palestine, Ohio.
The derailment of 38 cars including 11 carrying hazardous materials led to the release over 1 million gallons of hazardous materials, Ohio's attorney general said.
The National Transportation Safety Board (NTSB) said testing of the devices removed from five tank cars found anomalies with the function of some that may have compromised the capability of the valves to regulate internal pressure of the tank cars in a fire to lessen the risk of an explosion.
The derailment caused cars carrying toxic vinyl chloride and other hazardous chemicals to spill and catch fire.
Since the derailment, some of the town's 4,700 residents have reported ailments such as rashes and breathing difficulties and fear long-term health effects but no deaths or injuries were reported after the incident.
NTSB Chair Jennifer Homendy said in written testimony ahead of a Wednesday Senate Commerce hearing on rail safety that "investigators found that further metallurgical testing of the PRDs and valves, including valve stems, is warranted to evaluate their performance and compatibility with the vinyl chloride lading."
Earlier this month the NTSB found that aluminum parts on three tank cars may have melted and caused PRDs not to function, contributing to the release of toxic chemicals last month.
The NTSB said its preliminary examination suggested aluminum covers melted on protective housing for pressure-relief devices on three train cars. This could have prevented devices from performing as intended.
The NTSB said that according to the manufacturer’s part specifications, one internal spring of a pressure relief device was coated with aluminum, which is not compatible with vinyl chloride.
Homendy said investigators will now focus on issues including "tank car design and derailment damage; performance of PRDs and other valves; a review of the accident response, including the venting and burning of the vinyl chloride."