ROSEDALE, Maryland (AP) - A chemical-carrying freight train collided with a garbage truck, derailed and exploded at a rail crossing outside Baltimore, causing fires that were under control by Wednesday morning, authorities said.

In the third serious derailment in the United States this month, a dozen or so rail cars - at least one carrying hazardous materials - went off the tracks Tuesday afternoon in Rosedale, Maryland, a suburb east of Baltimore.

Several rail cars caught fire, sending a plume of black and gray smoke into the air that could be seen for kilometers, and an explosion rattled homes at least 800 meters away.

While local officials breathed a sigh of relief that only one person - the garbage truck driver - was seriously injured and that the chemical fire didn't pose a greater risk to nearby residents, some areas of inquiry for investigators were beginning to take shape.

Robert Sumwalt of the National Transportation Safety Board said late Tuesday that the collision occurred at a private crossing where the only marking was a stop sign. He said it wasn't clear why the truck was crossing the tracks or whether it was authorized to be there.

The truck driver, 50-year-old John J. Alban Jr., was in serious condition Tuesday night at Maryland Shock Trauma, a hospital spokeswoman said. Two CSX Transportation Inc. train workers for aboard weren't hurt.

Even hours after the blast, the thick plume of black smoke could be seen for kilometers and had drifted and covered the eastern part of Baltimore.

Later, the smoke that was left had lightened considerably, changing from black to gray, and Schultz announced early Wednesday that the fire was called under control late Tuesday just before midnight.

He said CSX had moved unaffected cars away from the derailed cars and fire department operations had been reduced to a fire watch.

A team of 15 NTSB investigators was on the scene and would likely remain there for up to a week, Sumwalt said.

Federal officials are also investigating Tuesday's crash of the 45-car train en route from New York state to Georgia. It contained a variety of products from lumber to printing paper.

Police also planned to investigate the circumstances that led to the track collision, but it was not clear what, if any, charges the truck driver or anyone would face, said Baltimore County spokeswoman Elise Armacost.

Gary Sease, a spokesman for CSX Transportation Inc., said four of the cars believed derailed carried terephthalic acid, which is used in the production of plastics and polyester, among other things. He said it is not listed as a hazardous material.

It was, however, the chemical that exploded as a result of the derailment, Sumwalt said.

A hazardous materials team responded, but Baltimore County Executive Kevin Kamenetz said at a news conference that no toxic inhalants were being released. Officials did not order an evacuation.

Toxic inhalation hazards are a worry when trains carrying hazardous materials derail. They include chemicals like 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.

Following a November 2007 derailment involving a freight train carrying hazardous materials near Baltimore's Camden Yards baseball stadium, CSX agreed the following year to provide Maryland officials with real-time information on shipments of toxic inhalation hazards. No such hazards were present Tuesday.

By nightfall Tuesday, the hazardous materials team had left, meaning there was no more danger posed from the chemicals in the rail car, Baltimore County police Capt. Bruce Schultz said.