(CNN)The nation's railroads are facing federal pressure to take a closer look at how they use the detectors that investigators say may have been able to prevent the toxic train derailment in East Palestine, Ohio, earlier this month.
The Federal Railroad Administration is issuing a safety advisory Tuesday urging railroads to review the thresholds used on hot bearing detectors "in light of recent derailments," including the Norfolk Southern wreck, where 38 train cars, including 11 carrying hazardous materials, derailed.
Installed along the track, these wayside detectors measure temperatures as trains pass by or over them and issue alerts to crew and dispatchers if temperatures climb above threshold levels. Those thresholds are set by the railroad companies, investigators have said.
A preliminary National Transportation Safety Board report from the East Palestine derailment found detectors registered elevated temperatures twice before a third detector hit a high enough temperature to alert crew members to stop the train.
"Had there been a detector earlier, that derailment may not have occurred," said NTSB Chair Jennifer Homendy at a news conference last week.
Tuesday's notice says federal railroad investigators have identified four additional derailments since 2021 -- including two more Norfolk Southern trains -- where an overheating bearing was a factor.
The agency's recommendations, which railroads are not required to follow, also urge railroads to review training, inspection and maintenance of the devices and to be especially cautious with trains carrying hazardous materials.
"For trains containing hazardous materials, the potential consequence of a derailment is catastrophic, and allowing a train transporting a hazardous material to continue to operate, without restriction, after an HBD alert is likely not appropriate," the notice read.
The agency said it would also "continue to examine the potential for additional actions within our regulatory authority to ensure the highest level of safety on the Nation's railroads."
In response to the advisory, the Association of American Railroads noted that the detectors are "voluntary practices to boost safety."
"As we continue to learn more about the cause of the accident in East Palestine, the industry is reviewing its practices and procedures to determine next steps to further enhance safety and target the root cause of this accident," the group said in a statement to CNN.