Federal investigators say a broken rail in the track was the probable cause of a fiery 2017 train derailment in northwest Iowa.

The derailment happened March 10th of last year, southeast of Graettinger, near a bridge over Jack Creek. Fourteen tanker cars spilled 322,000 gallons of ethanol.

The National Transportation Safety Board report cited Union Pacific for an “inadequate track maintenance and inspection program.” The report also said the Federal Railroad Administration’s oversight of track safety standards was “inadequate.”

The board’s report listed another contributing factor: the continued use of tanker cars that have been flagged as “vulnerable” to releasing hazardous or flammable materials in an accident.

The train wreck destroyed a 152-foot-long railroad bridge and about 400 feet of track. No one was injured in the derailment.