A faulty alarm system helped cause the 2023 Norfolk Southern Corp. train derailment in East Palestine, Ohio, and the company may have compounded the disaster with an unnecessary burning of hazardous materials days after the incident, the National Transportation Safety Board said Tuesday.

The board met to review its final report on the catastrophe that sent volatile substances into the surrounding air, soil and water. A full report is expected within a few weeks.

“Unfortunately, some have sought to minimize the wide-ranging impacts of this derailment, pointing to the fact that there were no fatalities or injuries,” NTSB Chair Jennifer Homendy said at the Tuesday meeting. “For this, we are certainly grateful, but the absence of a fatality or injury doesn’t mean the presence of safety.”

Consistent with its preliminary report released last year, investigators concluded that an overheated wheel bearing on a rail car caused the derailment. However, the train passed over three bearing detectors that scan for temperature differences and other mechanical warnings prior to jumping the tracks without ultimately resulting in a warning that would’ve prevented the disaster.

Surveillance footage retrieved by the NTSB shows that by the time the train passed over the second detector, the suspected bearing was on fire but the detector only showed a reading of 103 degrees Farenheit above ambient temperature. Norfolk Southern’s guidelines say that a 200-degree difference between bearings on the same axle will trigger a critical alarm, warning engineers to “set out” the car for maintenance. NTSB staff said Tuesday that the presence of a fire indicates an alarm should have been triggered, meaning the detector was faulty.

By the third milepost, the suspect bearing measured 253 degrees Fahrenheit above the ambient temperature. Although all three bearing detectors showed above ambient temperature readings, the crew aboard the train were only alarmed by the third detector. And an off-site desk that monitors detector readings only received a non-critical alert at the second detector.

The detectors are not required or regulated by the federal government. Rather, the railroads voluntarily install them, with varying temperature alarm thresholds.

The NTSB recommended that the Federal Railroad Administration establish rules regulating railroads’ responses to bearing failure warnings, as well as standards for hot bearing detectors. Investigators added that failed bearings are the most common mechanical cause of train accidents.

Outdated cars, burn decision

The NTSB found that the train contained outdated tank cars, which investigators said typically lack safety systems that are now standard.

The train was also not labeled as a “high hazard flammable train” despite post-derailment fires at East Palestine that were “similar to scenarios the high hazard flammable train rules were intended to prevent,” investigators found.

The investigation also called into question the company’s decision to vent and burn tank cars carrying hazardous materials.

According to the investigation, Norfolk Southern and its contractors determined venting and burning some of the derailed tank cars was necessary due to increasing temperatures in one of the cars, which they said increased the danger of an explosion.

However, investigators found that such a conclusion ran contrary to those of the owner of the tank car, chemicals company Oxy Vinyls, which determined a low probability of dangerous polymerization that would lead to an explosion. Investigators said at the meeting that the car temperature was “not indicative” of polymerization.

Evaluation of the inside of tank cars prior to the vent and burn confirmed that a polymerization reaction did not occur, investigators said. Norfolk Southern and contractors also did not disclose the Oxy Vinyls assessment to the incident commander, who signed off on the vent and burn.

“The pattern of dismissing contradictory evidence while interpreting ambiguous evidence in support of Norfolk Southern and its contractors’ original belief was consistent with confirmation bias,” Paul Stancil, NTSB senior hazardous materials accident investigator, said at the meeting. “Whatever the underlying explanations were for the continued support of a current action, none justifies failing to communicate accurate and complete information, including dissenting expert opinions to the incident commander.”

The NTSB recommended that the federal government establish guidance on what circumstances and products warrant a vent and burn, as well as make the guidance more available to emergency responders.

The board also was critical of initial response efforts, which investigators said did not conform to the guidance for fires involving tank cars and unknown materials. The board attributed that to Ohio state volunteer firefighting training that does not cover hazardous materials.

First responders did not receive information on which hazardous materials were in the tank cars, which delayed response, officials said. Placards showing what was contained in the cars burned off during the blaze.

“Norfolk Southern, in this case, showed up on scene and without that information,” Homendy said. “In fact, they were asked for that information repeatedly after they showed up.”

The railroad industry has touted its safety actions following the derailment — including installing more hot bearing detectors, ramping up first responder training and reviewing programs to identify bearings that may become problematic. The industry has said that more than 99 percent of all hazmat moved by rail reaches its destination without a release caused by a train accident.