Officials say 21 freight cars hauling coal from Wyoming have derailed in South Texas as temperatures reached the triple digits.
Union Pacific spokesman Jeff DeGraff says authorities are investigating whether the searing heat played a role Sunday afternoon in the derailment in San Antonio. Temperatures reached 100 degrees (38 Celsius) that day.
DeGraff says heat can cause rails to buckle.
He says no one was hurt in the accident. The train was carrying two crew members. One locomotive also derailed.
DeGraff says no hazardous materials were aboard the 150-car train. DeGraff says some coal spilled as several cars piled into each other.
Some cars also overturned.
Cleanup continued Monday. DeGraff says the derailment happened on a section of track off the main line, so rail traffic wasn't impeded.