COLUMBUS, Ohio — National Transportation Safety Board investigators have begun searching for clues to the train derailment that caused spectacular explosions in Ohio's capital, but a preliminary report is a month away.

NTSB board member Earl F. Weener said Wednesday night the agency has a 12-person team reviewing data from the early-morning derailment on the Norfolk Southern Corp. tracks, north of downtown. Three tank cars each carrying 30,000 gallons of ethanol exploded. Nobody aboard the train was injured.

Weener says the tankers are still burning and that they must cool down before the remaining ethanol can be removed.

Investigators are expected to be in Columbus for up to 10 days. Weener says a preliminary report will be issued in about a month but that the full investigation could take a year.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

Exploding freight cars full of ethanol made for a dramatic early morning scene in Ohio's capital on Wednesday, but officials said the train derailment that led to a hurried evacuation of an urban neighborhood could have been much worse.

The National Transportation Safety Board dispatched a 10-person team to investigate the derailment on the Norfolk Southern Corp. tracks, which led to spectacular explosions and the burning of three tank cars each carrying 30,000 gallons of ethanol. Nobody aboard the train was injured.

Officials said they don't know yet what caused the accident, which occurred at around 2 a.m. in an industrial area near Interstate 71, north of downtown. The explosions were felt for blocks and sent flames shooting high in the air.

Two people were injured while walking on the tracks to investigate when a second explosion occurred. Officials said they went to the hospital themselves with minor injuries.

Columbus Mayor Michael Coleman, who later Wednesday visited a temporary Red Cross shelter set up for evacuees, said the accident could have been worse if it had occurred in an area where more people lived.

"I'm grateful, in one respect as well, that this did not occur in a more populated area near more residents," he said. "It very well could have. A mile up or a mile south. North or south, east or west. It could have been tragic in other ways as well."

Assistant Chief David Whiting of the Columbus fire division said it was fortunate the accident occurred in the middle of the night.

"The time it occurred, where it occurred, were very good things for us," Whiting said. "Because we didn't have a whole lot of people around, businesses were closed, we were able to take care of getting our firefighters back and evacuating a small number of people."

About 100 residents who live within a 1-mile radius of the derailment were evacuated by firefighters, who decided to let the fire burn itself out, according to Whiting. Officials said the burning ethanol, an alcohol compound commonly used in fuel, posed no environmental or health concerns. Residents were back in their homes by mid-afternoon.

Nicholas Goodrich, a 35-year-old grocery store employee from Columbus, said he and two other people got as close as 100 feet from the explosion.

"Looking at it, I thought it was an atomic bomb or something," he said. "The heat was so excruciating that I had to ball up and cover my body."

Norfolk Southern spokesman Dave Pidgeon said the 98-car-freight train was traveling from Chicago to Linwood, N.C. Sixteen cars ended up going off the tracks, including the three hauling ethanol.

Two cars transporting wheat and corn syrup were breached and were leaking an undetermined amount, officials said. Crews were applying sand to stop the leaks before trying to recover what they can of the remaining cargo.

Joel Priester said he watched the blast from his home about two blocks away.

"I saw flames, then I heard a loud sound, like a boom, and saw the flames shooting higher," he said. "It looked like the sun exploded."

Patricia Reilly, a spokeswoman for the American Association of Railroads, said freight train accidents are uncommon, given the volume of freight that is transported around the country by trains.

Roughly 29.4 million carloads of freight are hauled every year across 140,000-plus miles of rail in the United States, she said. Of that, 1.8 million carloads are categorized as varying hazardous materials. Last year, about 325,000 carloads of ethanol were hauled over those lines.

Last year was one of the safest years ever for U.S. railroads, Reilly said.

"I think one accident is a horrible thing," she said. "But it's always a good education to understand in context what that represents in the big picture."

___

Associated Press writers Barbara Rodriguez in Columbus and Shelley Adler in Washington contributed to this report.

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  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

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    In this aerial photo, the charred lots of homes burned to the ground by the Waldo Canyon fire line the streets of the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

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  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

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  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

  • Some homes are left scorched by The Waldo Canyon Fire, while others survived, in the Mountain Shadows area of Colorado Springs, Colo., Wednesday, June 27, 2012. The wildfire doubled in size overnight to about 24 square miles (62 square kilometers), and has so far forced mandatory evacuations for more than 32,000 residents. (AP Photo/The Gazette, Christian Murdock)

  • This aerial photo shows the destructive path of the Waldo Canyon fire in the Mountain Shadows subdivision area of Colorado Springs, Colo., Thursday, June 28, 2012. Colorado Springs officials said Thursday that hundreds of homes have been destroyed by the raging wildfire. (AP Photo/Denver Post, RJ Sangosti)

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  • A helicopter flies over as the Waldo Canyon Fire continues to burn Wednesday, June 27, 2012, in Colorado Springs, Colo. The wildfire doubled in size overnight to about 24 square miles (62 square kilometers), and has so far forced mandatory evacuations for more than 32,000 residents.(AP Photo/Bryan Oller)

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  • Waldo Canyon Wildfire

  • Waldo Canyon Wildfire

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