Ohio train derailment investigation eyes hotboxes. What went wrong?

Jan 07, 2024

The investigation into the East Palestine, Ohio, derailment has put a spotlight on technology that railroads use to detect overheating wheel bearings before they fail — and the lack of federal regulations for how they are used.

As the Norfolk Southern train made its way toward the town on the evening of Feb. 3, it passed two detectors, according to a National Transportation Safety Board report released Thursday. Both detectors logged that a bearing was heating up but didn't sound an alarm because the temperature hadn't crossed safety thresholds set by the railroad.

At a third detector, the bearing registered 253 degrees above the surrounding temperature, which was enough to trigger a warning, but it didn't give the train crew enough time to stop before the bearing failed and the train derailed.

Crew tried to stop Ohio train after alert on overheating wheel bearing, NTSB says

The detectors are widely deployed across the United States, but their limitations have been highlighted in past safety investigations. Here's how they work and why there can be gaps in the system.

They work by detecting infrared emissions from bearings on the axles of train cars as they pass over, measuring their temperature and comparing it to the surrounding air. There are about 6,000 detectors along railroad tracks in North America, spaced roughly every 15 to 30 miles.

Norfolk Southern said in a statement it has invested $200 million in a network of about 1,000 detectors. In addition to warning crews as trains pass over, they also send data to a central help desk. The railroad's system carries out 2 billion readings a year, typically finding about 80 cars that need attention, according to Norfolk Southern.

Norfolk Southern's internal operating rules set thresholds for when the detector should send crews a warning message in their cab. The critical threshold is 200 degrees, at which point train crews are directed to stop and remove the problematic car from the train, according to the NTSB.

Before Ohio derailment, Norfolk Southern lobbied against safety rules

The railroad said its thresholds to trigger an alarm are among the lowest in the industry.

When a bearing is in the final stages of failing, it can heat up rapidly. Once it does, it can stop the wheels of the car from moving freely and even melt onto the axle, causing a derailment.

A study by the Federal Railroad Administration published last year concluded detectors have successfully reduced the number of derailments.

The NTSB and Norfolk Southern both say the detectors the train passed were functioning as intended, but the technology has limitations. They can report false positives — leading to costly delays — and also miss bearings at risk of failing that should be flagged. A 2020 study reported 151 misses that led to derailments between 2009 and 2018.

NTSB Chairwoman Jennifer Homendy said at a briefing Thursday that railroads set their own rules for where to place the detectors and the thresholds for triggering an alarm and action by the crew. She said those standards would be scrutinized as part of the board's investigation.

"The spacing and temperature are set by the railroads and vary considerably by railroad," Homendy said.

The first two detectors the train passed were spaced 10 miles apart. It didn't cross the third, near East Palestine, for another 20 miles. By that point, the bearing was failing. The NTSB said the crew reacted immediately to the warning and began trying to stop the train, but it was too late.

The bearing's temperature had increased 65 degrees between the first two detectors, according to the NTSB. Jared Cassity, alternate national legislative director for the SMART Transportation Division union, said that should have raised concerns.

"I cannot understand how that did not prompt someone monitoring the system to warn the train's crew," he said. "In other words, in my opinion, the thresholds are not good enough."

Homendy pointed to an investigation into a 2013 derailment in Canada in which hotbox detectors also failed to catch an overheating bearing in time. That study compared the strategies of Canadian Pacific, whose train derailed, and Canadian National, another major railroad. At the time, Canadian Pacific spaced its detectors 20 to 30 miles apart, while Canadian National's were 12 to 15 miles apart. The bearing on the Canadian Pacific train had failed 16 miles after passing a detector.

"If HBD [hot bearing detector] systems are not configured for maximum effectiveness, including the use of real-time monitoring and data trending, there is an increased risk that roller bearings that are beginning to fail will remain in service and will not be detected before they fail," investigators from the Transportation Safety Board of Canada wrote.

A 2017 study backed by a railroad industry research center concluded that 15 miles was the optimal spacing for detectors.

Homendy said it's possible that had the detectors on the line into East Palestine been closer, the derailment could have been avoided.

The NTSB doesn't have the power to impose regulations, but it does make safety recommendations. Those are likely a year to 18 months away in the Ohio case, but Homendy said investigators would examine the lack of federal regulations for detectors.

Christopher Hand, director of research at the Brotherhood of Railroad Signalmen, which represents about 10,000 workers, including more than 800 at Norfolk Southern, said there is a need for new rules.

"That's the problem with them being unregulated," he said. "They get to choose where they put them."

Toxic air pollutants in East Palestine could pose long-term risks, researchers say

He said the union has pushed for requirements to space sensors at least every 10 miles, and also more strategically so they are placed five miles outside of towns instead of in the middle of one.

"We do believe if they were regulated, maybe we could have more of them," he said. "They’ve proved to be a saving grace."

Others point to limitations in the system. Constantine M. Tarawneh, director of the university transportation center for railway safety at the University of Texas Rio Grande Valley, said the detectors are outdated and that measuring the health of bearings using temperature is ineffective because problems occur over the course of months. He compared it to trying to diagnose cancer with a thermometer.

"By the time you catch something, it's too late," he said. "You can only hope you stop the train in time before it derails."

Researchers have been experimenting with onboard sensors that would measure vibrations, potentially catching risks far earlier. Tarawneh is part of a team that has created and licensed a set of sensors, but while they have attracted attention from the FRA and the industry, they are not commercially deployed.

This article incorrectly described how hotbox detectors measure temperature. They detect infrared emissions from the bearings.

Post reporter Chris Dehghanpoor contributed to this report.

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