Washington, Feb 24 : The National Transportation Security Board (NTSB), a US federal agency, has released a preliminary report on the derailment of a train carrying hazardous chemicals in East Palestine, Ohio, earlier this month.

The initial fire started February 3 when a Norfolk Southern rail car carrying plastic pellets was heated by a hot axle, said Jennifer Homendy, chair of the National Transportation Safety Board.

The temperature of the bearing increased as the train passed two wayside defect detectors – but it wasn’t high enough to trigger an audible alarm message until it passed a third detector, Homendy said.

She said the threshold for those detectors is set by the railroad. Investigators have not identified any track defects nor issues with the wayside defect detectors, Homendy said.

But “had there been a detector earlier … that derailment may not have occurred,” Homendy said.

The NTSB will investigate Norfolk Southern’s use of wayside defect detectors, including the spacing of the detectors and set temperature thresholds, she added.