Federal investigators are looking into why seven ethanol tanker cars derailed in South Dakota over the weekend. No one was injured in the derailment that occurred early Saturday morning, but at least one of the cars caught fire in the accident involving a 98-car Burlington Northern Santa Fe Railroad train.

Senate Transportation Committee chairman John Thune (R-SD) is watching the investigation closely and says they believe the derailment was caused by a broken rail or structural failure in the small bridge where the incident occurred. “Safety has got to be the highest priority,” said Thune. “These were some of the older model cars that actually derailed and started a fire there.” The Department of Transportation has required updates to fuel transportation cars, including the unjacketed DOT-111 cars which commonly carry ethanol.

“Ethanol should have some different treatment with respect to these cars compared to oil tank cars,” Thune said. “Most of the seven cars that derailed were older models that will require upgrades under these new safety standards.” Five of the seven cars were the DOT-111 models and two were newer jacketed models that will still be required to have some upgrades under the new standards.