OMAHA, Neb. (AP) — Federal investigators say a broken rail caused the fiery 2017 derailment in northwest Iowa that released 322,000 gallons of ethanol. The National Transportation Safety Board ruled Tuesday that Union Pacific’s maintenance was inadequate before the March 2017 derailment near Graettinger, Iowa, and Federal Railroad Administration inspectors didn’t do enough to identify flaws in the track.

No injuries were reported in connection with the derailment in a rural area about 160 miles northwest of Des Moines. Five of the 20 derailed tankers plunged into Jack Creek. The NTSB says the train in this derailment was carrying ethanol for export that had not been denatured by adding chemicals. The agency wants to study whether it’s safer to transport ethanol before it is denatured.