The National Transportation Safety Board is investigating aluminum housing covers on three of the vinyl chloride monomer tank cars in a Norfolk Southern Corp. train that derailed Feb. 3 in East Palestine, Ohio.
Based on damage assessment inspections, NTSB officials are concerned that aluminum protective housing covers on some tank cars melted or were consumed when pressure relief devices (PRD) vented burning gas while functioning as designed to relieve tank pressure.
"Preliminary examination suggests that melted aluminum may have dripped into some PRDs, possibly degrading their performance," officials said March 2.
The derailment happened the night of Feb. 3. Almost 40 rail cars derailed, including five that contained VCM, which is a feedstock for PVC resin. No injuries were reported from the derailment.
Rising temperatures in one of the VCM cars led officials from both Ohio and Pennsylvania — very close to the derailment site — and the railroad on Feb. 6 to drain all five cars and burn off the VCM, resulting in thick black smoke and a chemical odor throughout the area. Officials said that decision was made because of the possibility of an explosion that could have sent shrapnel up to a mile away.
Government and railroad officials have said the air and water have tested safe in most of the area, but local residents — some of whom had been evacuated for three days — remain concerned about their health and the impact of the burnoff.
During the investigation, NTSB investigators discovered that three of the examined VCM 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," officials said.
PRD and valve assemblies recovered from the five VCM tank cars are being delivered to a testing facility. During the week of March 13, investigators will examine them to determine the conditions that might have affected their operation following the derailment.
Officials said NTSB is conducting the investigation to determine the probable cause of the derailment and issue any safety recommendations to prevent future derailments. NTSB also can issue urgent recommendations at any point during the investigation, they added.