Mayor Richard M. Daley on Wednesday praised the survivors of an underground train derailment for keeping their heads as they helped each other through a darkened, smoke-filled tunnel to an emergency exit.

"I'd like to commend the passengers on this train for their calm and orderly response," Daley said. "This had to be a very frightening experience, especially in the light of the train bombings in India that happened several hours earlier."

A day after the derailment and fire injured more than 150 people during the evening rush hour, wary riders headed back into the Blue Line's reopened downtown subway stations Wednesday morning.

The soot-covered train cars had been removed and officials with the National Transportation Safety Board were trying to determine what had caused the last car's wheels to jump the track and ignite debris below. The train was old enough that it did not have data recorders required of newer models, NTSB board member Kitty Higgins said.

Law enforcement officials have said they found no indication of foul play or terrorism.

As many as 1,000 people were aboard the eight-car train heading toward O'Hare Airport when it derailed under the city's downtown business Loop and sparked the fire, said Chicago Transit Authority President Frank Kruesi.

City Fire Commissioner Raymond Orozco said 152 passengers were taken to 12 hospitals, primarily to be treated for smoke inhalation. At least two remained hospitalized Wednesday in critical condition.

Kruesi and other city officials praised the train operator for getting the passengers off the train quickly.

"He followed the procedures precisely right," Kruesi said. "The key was to get people out of the train and up the exits, and that's what he did."

The train operator led passengers out through the smoky subway tunnel to the nearest emergency exit, where they climbed out through a grate in the sidewalk above.

"It felt like it jumped the line, and a fire started in the car behind me," said Joel Johnson, 24, whose face and white shirt were covered in soot when he emerged Tuesday. "I saw the orange flames but I didn't hear it. I could barely breathe."

The train was on a downtown stretch of the Blue Line — which takes travelers from one of the nation's busiest airports to the business district, its Amtrak stations and then Chicago's West Side. It had just left the busy Clark/Lake station Tuesday when the operator realized there was a problem, stopped the train and called for power to be cut, Kruesi said.

Rita Bacon, 25, who was on the train, said she felt much safer after commuters were able to open the train cars' doors using the emergency release.

"Everyone was just holding out their hands, holding each other's hands, feeling their way along," she said. "It was pitch black in places, but there were signs in the tunnel that said, '500 feet to the exit, 250 feet to the exit,' so I felt much better."