Robert Sumwalt from the National Transportation Safety Board talks about the investigation into Tuesday's train derailment in Rosedale. (Jenn Marshall/Baltimore Sun video)

As Rosedale residents and business owners began to clean up after the fiery train derailment, federal officials said Wednesday that a chemical, sodium chlorate, had likely exploded in one of the train cars.

Investigators with the National Transportation Safety Board said Tuesday afternoon's explosion occurred 5 minutes and 23 seconds after the train collided with a truck at an unprotected crossing. Officials will inspect the truck – a 2003 Mack Granite operated by Alban Waste LLC — including an examination of the brakes, board member Robert Sumwalt said at a news briefing.

Sumwalt said the train — two locomotives and 45 cars — was traveling at 49 mph and sounded its horn three times in the 17 seconds before the collision. Fifteen rail cars derailed, including three that carried hazardous materials.

"Although we've made tremendous progress today, I do want to emphasize that we are still very early in the investigation," Sumwalt said as the agency began what will be a months-long investigation, retrieving video footage from the train and examining a timeline of the incident.

Meanwhile, those who live and work in the area dealt with the widespread damage — including blown-out windows, cracked foundations and a loss of structural integrity in some nearby buildings. Throughout the area, massive metal garage doors buckled like accordions and, in one nearby building, a piece of window glass stuck about an inch into a solid wooden door.

Some residents expressed frustration over mixed messages from CSX Corp. regarding how the company planned to assess damage, and owners of some businesses along Lake Drive, which runs parallel to the tracks, weren't able to get to their buildings — leaving them unsure of the extent of damage and when they'd be able to start cleaning up.

"You can't even get back there to get a game plan together. We don't even have a time frame," said Mike Brown, operations manager for the Baltimore Windustrial warehouse just yards from the track. "Basically the whole front of our building is completely leveled."

Brown had made a split-second decision to tell all his employees at the industrial pipe-valve-fitting distributor to evacuate — to run to their cars after the derailment, jump in and drive off down the street.

"It's the best thing I ever did," he said Wednesday. "From that point, it only took about three and a half minutes for that thing to blow up and decimate our building. I'm just so glad I got everyone out."

As police and fire personnel blocked off the area around the tracks Wednesday, crews with CSX and the NTSB analyzed the crash scene and the most heavily damaged areas. Insurance adjusters and structural engineers made their way to nearby homes and businesses in the wider area. A group of men in yellow hazmat suits and white hard hats crisscrossed the tracks just south of the mangled train cars, going into marshy woods on either side with oil-absorbent booms.

Mike Tobias, owner of Eastern Truck and Trailer, a truck repair and fleet maintenance business on the street, stood a block away Wednesday awaiting word that he could return to his shop, where the disruption to business will mean lost time and money.

"We have insurance, but the main thing is getting down there and getting going," he said. "We've got a lot of stuff going on, a lot of commitments. It hurts."

Still, Tobias said, more important to him was that no one was killed.

According to George Ferguson Jr., John Alban Jr., the injured driver whose trash truck collided with the train, said shortly after the crash that he "didn't hear the train until he got on the track."

The result was all around him as he spoke, said Ferguson, one of Tobias' employees.

"I was jumping over trash, you see the engine of the truck, the guy laying there," Ferguson said. "I mean, you've gotta believe in miracles yesterday, because I don't know how he survived it."

Alban was still listed in serious condition Thursday afternoon at Maryland Shock Trauma Center, a hospital spokeswoman said.

Tobias took a dramatic video from the side of the train just as his crew was locating Alban, but stopped recording to call 911 just before the explosion.

"It looked like the sun. A big white-orange ball came out of the center of it. It was unbelievable," Tobias said of the blast. "My ears were numb last night, like you'd been at a concert all night."

On Wednesday, a police helicopter hovered above the crash scene. Repairmen at nearby businesses boarded up windows that had shattered and overhead garage openings, the doors of which had buckled.