The decision to blow up five tanker cars loaded with toxic chemicals following the fiery derailment of a train in East Palestine, Ohio, last year was unjustified, federal investigators concluded Tuesday.

The freight train cars full of vinyl chloride, a cancer-causing chemical used to make plastic, were burned three days after the train careened off the tracks and released massive plumes of toxic smoke into the sky.

As incident commander, East Palestine fire chief Keith Drabick ultimately gave Norfolk Southern, the trains operator, the green light to torch the cars. He told federal investigators last year that Norfolk Southern and its contractors presented intentional burning as the only viable and safe option, and gave him 13 minutes to make the decision a request that he said left him blindsided.

Norfolk Southern has repeatedly defended the move, citing the purported risk of the tanker cars suddenly exploding.

But the National Transportation and Safety Board threw cold water on that narrative Tuesday during a hearing on the findings of the agencys lengthy investigation into the Feb. 3, 2023, derailment.

Investigators said there was no imminent sign of the chemical reaction, known as polymerization, that wouldve cause tank cars to explode. They said Norfolk Southern and its contractors misinterpreted and disregarded evidence in advocating for whats known as a vent and burn operation, which involved blasting holes in tanker cars, draining the vinyl chloride into pits in the ground and setting it on fire.

Norfolk Southern and its contractors continued to assert the necessity of a vent and burn, even though available evidence should have led them to re-evaluate their initial conclusions, Paul Stancil, a hazardous materials investigator at the NTSB, said Tuesday.