Authorities are continuing to look into the cause of Tuesday's incident. Robert Sumwalt, a member of the National Transportation Safety Board, said investigators were examining evidence on the scene and reviewing train video that might show the collision with a garbage truck that set off the incident. But he said they had not reached any conclusions.
Sumwalt said at a news conference Wednesday that the freight train was traveling 49 mph and that the engineer blew a whistle three times before it collided with the truck.
The train hit the right rear axle of the truck as it was crossing the tracks around 2 p.m. Tuesday, Sumwalt said. He added that the locomotive applied its emergency brakes and traveled nearly a mile before coming to a stop. Fifteen cars derailed, including three of the four cars that were carrying hazardous materials.
The chemical that exploded was sodium chlorate, which is highly volatile. Sumwalt said the explosion, which damaged nearby buildings and shook homes miles away, occurred 5 minutes and 23 seconds after the initial collision. The sodium chlorate was in powder form and was being hauled in a covered hopper car. Another chemical burned for nearly 10 hours after the crash.
CSX spokesman Gary Sease said the sodium chlorate in a derailed car near the front of the train exploded, igniting terephthalic acid in another derailed car.
Sodium chlorate is used mainly as a bleaching agent in paper production. Oklahoma State University chemist Nick Materer said it could make for a potentially explosive mixture when combined with an incompatible substance such as spilled fuel.
Another chemist, Darlene Lyudmirskiy, of Spectrum Chemical Manufacturing Corp. in Gardena, Calif., said such a mixture would be unstable and wouldn't need even a spark to cause a reaction.
"If it's not compatible, anything could set it off," she said.
The railroad said in a news release Wednesday that it continues to work with state and federal environmental officials to "clean up products released in the derailment." The company said it is conducting air, water and soil sampling and sharing that information with officials.
On Wednesday afternoon, workers were using heavy cranes to move the damaged rail cars, and an excavator was picking up broken pieces of track. The mangled truck lay on its side on the side of the railroad tracks, its contents littering the ground. Next to the track, the corrugated metal walls of a warehouse were bent and warped.
Among the buildings that sustained the most damage was a training facility for a plumbers and steamfitters union a few hundred yards away from the explosion site. Only a handful of employees were in the building at the time of the blast, and all but one rushed outside to see what had happened. They heard the crash first, followed by the derailment, then saw a plume of smoke.
Al Clinedinst, the training director for the facility, said he and a colleague drove closer to the derailment scene before the explosion to see if they could help, but they were turned back by the overwhelming heat.
"It was paint-bubbling hot," he said.
Then the explosion shook their truck.
"The blast, the force, it took the wheel out of my hands," Clinedinst said. "It really took a shot."
Sumwalt said late Tuesday that the collision occurred at a private crossing where the only marking was a stop sign, but he backtracked at a news conference Wednesday, saying the crossing was registered with the government and that the agency had to determine whether or not it was private. He said it wasn't clear why the truck driver was crossing the tracks or whether the vehicle was authorized to be there.
He also said Wednesday that the truck driver's business is on the other side of the tracks from the damaged warehouse and that the driver "uses that grade crossing quite frequently."
The truck driver, 50-year-old John J. Alban Jr., remained in serious condition Wednesday at Shock Trauma in Baltimore, a hospital spokeswoman said. Two CSX workers aboard weren't hurt.
In addition to the NTSB, the Federal Railroad Administration is investigating the crash of the 45-car train, which was en route from Selkirk, N.Y., to Waycross, Ga.
Baltimore County spokeswoman Elise Armacost said it wasn't clear whether the truck driver would face charges.
The county's Public Safety Department said that county, city and CSX hazmat experts did not believe the burning chemicals would produce toxic inhalants. But a National Institutes of Health website says oxidizers such as sodium chlorate may produce irritating, corrosive and/or toxic gases when burned.
Toxic inhalation hazards are a worry when trains carrying hazardous materials derail. They include chemicals such as chlorine, which killed nine people after a derailment of a Norfolk Southern train caused a release of the toxic gas in South Carolina in 2005.
In 2008, about six and half years after a CSX derailment and fire in Baltimore's Howard Street Tunnel, the railroad agreed to provide real-time information to Maryland State Police on shipments of certain chemicals called "toxic inhalation hazards." The federal Transportation Department maintains a list of about 150 of these chemicals, all gases or volatile liquids that meet certain toxicity thresholds if inhaled. Sodium chlorate is not on the list. It is usually shipped in powdered form, Materer said.
The fire was called under control late Tuesday just before midnight, and the fire department remained on scene only in a supporting role.
CSX said in the Wednesday news release that it was preparing to begin work on the tracks once the NTSB completes its work. The railroad said customers should expect a 24- to 36-hour delay in rail traffic passing through the area, with some freight trains being rerouted. CSX has also set up a community outreach center at a Rosedale hotel to work with affected residents.
AP writer David Dishneau reported from Hagerstown, Md.