Earl Weener of the National Transportation Safety Board said an "event recorder" on the train -- similar to a black box on a plane -- indicated the train was traveling about 23 mph when it derailed on a curve, The Columbus Dispatch reported. The speed limit for that section of track is 25 mph, Weener said.
Norfolk Southern Corp. said 16 of the train's 98 cars left the tracks, including three that fire officials said had been carrying 90,000 gallons of ethanol, leading to a fire and explosion.
NTSB officials said Wednesday night they expect to be in Columbus investigating the derailment for at least a week and it could be a month before they determine the cause.
The derailment occurred just north of downtown Columbus near the state fair grounds.
The crew was not hurt. Two people suffered "very minor" injuries when they walked onto the tracks to see what happened when the explosion occurred, Battalion Chief Michael Fowler said.
The derailment occurred about 2 a.m. Wednesday. Fire officials and Columbus Mayor Michael Coleman noted the derailment occurred in a part of the city where few people were around at that time of night.
"It made a big difference that we didn't have it on top of people," Fowler said.