Debris from a Norfolk Southern freight train lies scattered and burning along the tracks on Feb. 4, 2023, the day after it derailed in East Palestine, Ohio. As the NTSB found in its preliminary report, the derailment was likely caused when a bearing on the left front wheel of the 23rd train car failed, investigators said. Gene J. Puskar/Associated Press

Norfolk Southern’s decision to release and burn toxic chemicals from five derailed train cars last year in East Palestine, Ohio, was not necessary and stemmed from a misinterpretation of the risk by the railway and its contractors, National Transportation Safety Board investigators said Tuesday at the board’s final meeting on the derailment.

The agency’s findings offer the most authoritative timeline yet on the decisions that caused a giant toxic plume to rise above the Ohio town in early 2023, alarming residents and triggering a national debate about rail safety and the government’s response.

After a fire following the derailment heated up five tank cars, the railway and its contractors – concerned that one of the cars could explode – disregarded the fact that the car’s temperature began dropping, which should have signaled that the danger was waning, NTSB investigator Paul L. Stancil said.

They also failed to provide the local fire chief and other officials with a key report from the chemicals’ manufacturer, who had inspected the train cars and determined that the probability of the worst-case scenario was low, investigators found.

In addition, investigators found that firefighters and emergency responders stayed at the fiery derailment scene longer than they should have immediately after the crash because Norfolk Southern didn’t share information about what hazardous materials were on the train until an hour after firefighters arrived.

“This resulted in greater exposure of emergency responders and to the public to post-derailment hazards,” said NTSB investigator Troy Lloyd.

The board’s meeting Tuesday, held in East Palestine, examined aspects of the crash, the emergency response and the actions of Norfolk Southern.

After hearing from investigators, board members will vote Tuesday on their final findings and recommendations, including the probable cause of the derailment; the NTSB’s full final report will follow several weeks later.

The Feb. 3, 2023 derailment roiled East Palestine – a town near the Pennsylvania border of roughly 4,600 people – drawing national attention to freight railroad safety and leaving residents with lingering fears of contamination. A year and a half later, cleanup by the Environmental Protection Agency is ongoing – one of many ways the derailment’s effects are still being felt.

The disaster has already prompted industry changes and legislative and regulatory efforts. On Monday, the Department of Transportation announced a new requirement that railroads provide local emergency agencies with information about all hazardous materials being carried through their areas. The NTSB’s recommendations will likely spur more changes in how railroads and other carriers can prevent and respond to chemical releases.

Former NTSB chair Robert L. Sumwalt said he expected the NTSB to make an array of recommendations aiming “to improve rail safety when it comes to transporting hazardous materials.”

“This derailment will be another one of these watershed accidents that really will change the way that the industry does business,” said Sumwalt, the executive director of the Boeing Center for Aviation & Aerospace Safety at Embry-Riddle Aeronautical University.

As the NTSB found in its preliminary report, the derailment was likely caused when a bearing on the left front wheel of the 23rd train car failed, investigators said. After overheating, the high temperatures twisted the part and it fell off, allowing the car to drop to the ground.

The crew wasn’t notified the first time the bearing’s high temperature was detected by a trackside device, investigators said, because the alert, categorized as noncritical, went to back-office personnel. The device likely measured the temperature lower than it really was.

Investigators laid out several other factors that contributed to the derailment and its effects, including the use of a type of tank car that was easily punctured to carry flammable butyl acrylate, which started the initial fire.

That type of car is being phased out for such use and won’t be eligible to carry butyl acrylate after May 2029, investigators said. Its failure likely led to the fire, and the fire caused the concern about whether the cars carrying vinyl chloride were heating up.

“The events that eventually led to the vent-and-burn could’ve been avoided had there been no DOT-111 tank cars carrying combustible and flammable liquids on this train,” Stancil said.

The emergency responders’ struggle to get information about what hazardous materials were in the train cars also affected the response, investigators said. When one called Norfolk Southern to ask for the information, known as the train consist, the person who answered said she would call them back and never did. Meanwhile, diamond-shaped placards on the train cars that show what they’re carrying burned in the fire, making them illegible.

The first responders had so little information that a volunteer firefighter who was a chemistry teacher was the one trying to evaluate some of the hazards, said Jennifer Homendy, chair of the NTSB.

“The deputy chief was asking for what was on that train for quite some time,” Homendy said. “Norfolk Southern … showed up on the scene without that information. They were asked for that information repeatedly after they showed up.”

The investigators suggested the NTSB members make recommendations to address the factors that caused the derailment and fire and led to the vent-and-burn, along with other factors that influenced what unfolded, from Ohio’s volunteer firefighter training standards to regulatory definitions.

Much of the NTSB’s investigation has centered around the decision by Norfolk Southern contractors and officials to release vinyl chloride, an odorless carcinogenic chemical, from the five train cars. On Tuesday, investigators provided new details about the decision, saying the railway and its contractors exhibited “confirmation bias” in assessing the likelihood of whether the vinyl chloride was undergoing polymerization and could cause the train car to explode.

At a Senate hearing in March, Homendy testified that the burn-off could have been avoided and that the decision had been based on flawed information.

Norfolk Southern has defended the vent-and-burn decision as an attempt to protect the community from potential disaster and has said they received conflicting information from the vinyl chloride manufacturer, Oxy Vinyls.

Ahead of Tuesday’s meeting, Norfolk Southern announced it would lead an industry working group to examine the vent-and-burn practice. It also released a report summarizing the company’s steps to increase safety, including new equipment, a system for communicating what trains are carrying to first responders and a reported reduction in accidents and employee injuries.

The company has also pledged millions for community and environmental initiatives in East Palestine. It will pay millions in lawsuit settlements with the federal government and residents.

“There is no finish line when it comes to improving safety,” Norfolk Southern chief safety officer John Fleps said in a statement Monday. “We will continue looking for improvements in all that we do.”

The train derailed on the night of Feb. 3, 2023, after the bearing overheated and the crew couldn’t stop the train in time. Thirty-eight cars went off the tracks, including 11 that held hazardous materials, and a fire ignited.