WASHINGTON (CNN) -- A CSX freight train derailed on a bridge over the Anacostia River on Friday, dumping 10 rail cars carrying coal into the chilly water.
Officials say 10 of the train's 90 cars fell into the water, dumping coal into the river.
No one was hurt in the incident in southeast Washington, but a witness called it "very frightening."
"It was a loud noise, a big thump," Alice Spann said.
"And then, the train just started going up in the air. The wheels separated from the train. Then the track went over, the rails went up in the air. I never saw anything like it before," she said.
"I thought the world was coming to an end." Watch her describe how the train split in half »
Several fireboats and other emergency vehicles responded, including some engine companies with hazardous materials units that came to the scene as a precaution.
Ten of the train's 90 cars were in the water.
The crash dumped coal into the river, along with hydraulic fluid and oil from the train cars, District of Columbia Fire Department spokesman Alan Etter said.
"The environmental impact, we're hoping, will be minimal," he said.
Booms were in place to prevent any hazardous materials from moving downriver, said Assistant Fire Chief Lawrence Schultz. He said the water had a "sheen," indicating some petroleum products, but pH tests have been neutral.
"It could be something as simple as brake fluid from the train," he said.
The train was parked with no one on board when another freight train rear-ended it, said Gene Maestas of the U.S. Coast Guard.
But the Fire Department said the cause was unknown, and federal agencies were being called to investigate.
"The National Transportation Safety Board is en route, and we expect them to be here shortly," Schultz said. "We're just not sure what happened. When the investigators get here, they'll do a full investigation."
Structural engineers were assessing the bridge and eventually wanted undamaged rail cars removed "to try to get some weight off the bridge," Schultz said Friday.
"We believe there is some structural damage to it," he said.
Bob Sullivan, a spokesman for CSX, said the train was carrying no hazardous materials.
Maestas, however, said that coal qualifies as a hazardous material. E-mail to a friend
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