The National Transportation Safety Board (NTSB) released a preliminary report Thursday regarding the February 3 train derailment near East Palestine, OH, that pointed to an overheated bearing on one of the railcars, this one carrying polypropylene, as the likely cause of the derailment.

The Wall Street Journal reports:

A defect detector along the tracks alerted the train crew to the overheated bearing, which recorded a temperature of 253 degrees Fahrenheit above ambient temperature, according to a preliminary report from the National Transportation Safety Board. Upon hearing the alarm, a train engineer applied brakes to slow and stop the train, the NTSB said. The crew later observed fire and smoke and alerted authorities.

Two defect detectors, located 30 miles and 20 miles away from the one that sounded the alarm, didn’t record temperatures above Norfolk Southern’s established alarm thresholds.

The report also stated that the train was traveling 47 miles per hour, which is slower than the 50 mph maximum authorized speed. NTSB’s findings are subject to change based on additional information that may be gathered in its ongoing investigation.

Officials from the agency will hold a press conference later Thursday regarding the interim report’s release.