Vent and Burn of Tank Cars Following Derailment Unnecessary: NTSB
It was not necessary to vent and burn tank cars carrying vinyl chloride monomer following the February 2023 derailment of a Norfolk Southern train near East Palestine, Ohio, the National Transportation Safety Board concludes in a recent investigation report. According to NTSB, the derailment involved 38 mixed-freight railcars, including five tank cars carrying vinyl chloride monomer, a compressed liquified flammable gas. Those five cars were not mechanically breached during the derailment, but a fire ignited during the incident exposed four of them to heat as well as material released from pressure-relief devices. The vinyl chloride monomer in the derailed cars “remained in a stabilized environment…until those tank cars were deliberately breached with explosives,” the report’s abstract (PDF) explains, and the temperature trends observed at the scene “did not indicate that a polymerization reaction was occurring.” This means that the vent-and-burn procedure, which involved deliberately breaching tank cars, was not needed to prevent an explosion, NTSB says.
“Burning [vinyl chloride monomer] resulted in a column of black smoke that grew into a persistent cloud,” the NTSB report states. “According to the [Norfolk Southern] system manager for hazardous materials, the cloud likely contained soot particles, carbon dioxide, carbon monoxide, hydrogen chloride, and a trace of phosgene (a toxic gas).”
NTSB found that the local incident commander’s decision to vent and burn the tank cars “was based on incomplete and misleading information provided by Norfolk Southern officials and contractors,” the board’s news release states. According to the report, Norfolk Southern and its contractors did not communicate with the incident commander relevant expertise from the shipper of the cars carrying vinyl chloride monomer. The shipper, Oxy Vinyls, had shared with Norfolk Southern “dissenting opinions and evidence indicating that polymerization was not occurring.”
Other safety issues identified during NTSB’s investigation include inadequate training of volunteer first responders and concerns related to written guidance and information about chemical hazards.
For more information, see the full investigation report (PDF) and NTSB’s news release.
Related: Previous Synergist articles have focused on responsibilities for OEHS professionals in an incident command system (in two parts: one and two) as well as on the National Incident Management and Incident Command Systems.