No one was injured in the derailment as both crewmembers escaped unharmed.
The train was carrying ethanol from the Superior Ethanol Plant and was bound for Texas City, Texas. The fire occasionally sent explosions and fireballs high into the sky as highly flammable ethanol fumes poured from the ruptured tanks. NTSB officials said that some of the tankers, which carry about 25,000 gallons each, had spilled ethanol into the creek, but environmental officials don't believe it's enough to be toxic to wildlife or fish.
The department says creek water checks downstream found no obvious signs of a spill.
"Twenty cars derailed and 15 evolved with fire", he said, adding that two cars were still burning at the time of the conference.
The derailment occurred around 1 a.m. (0700 GMT), on a Union Pacific Corp rail line near Graettinger and along Jake Creek, about 160 miles northwest of Des Moines, the NTSB said in a press release. The ends are especially vulnerable to tears from couplers that can fly up after ripping off between cars.
"But meanwhile, people have forgotten about the potential hazard of transporting ethanol using these cars", he said. "The NTSB has identified many vulnerabilities in the DOT-111 tank auto design that create the risk of the release of hazardous materials or flammable liquids when those tank cars are involved in an accident", the release said.
There have been at least seven significant accidents involving trains hauling ethanol since 2006 that released a combined 2 million gallons of the fuel. "It's not like we haven't seen that kind of tragedy before", said Karen Darch, co-chair of an Illinois-based coalition of local officials, called TRAC, that has pushed for rail safety enhancements.
Sumwalt said the crews of both the accident train and the preceding train were interviewed. The NTSB has called for replacing DOT-111 tank cars with DOT-117 cars as soon as possible. Those that carry ethanol would have to be replaced by 2023.