The higher readings also complicated things for investigators. Hersman said railroad officials, their contractors and other environmental experts were trying to determine the best way to get the rest of the vinyl chloride out of the ruptured tanker before further inspections could be done or the train cars could be moved.
She said her team of investigators would be focused first on reviewing records and interviewing witnesses — things that can be done away from the accident site.
Tom Butts, the chief of emergency management for Gloucester County, said it would take at least a day to get the large crane to the site to pick up the damaged cars. The recovery work was expected to take place only during daylight hours and it was not clear how long it would take.
The bridge usually supports at least three major trains each day serving refineries and other customers in an industrial area along the Delaware River. It was rebuilt after it buckled in August 2009 and when nine cars on a coal train detailed. Officials attributed that accident to bridge misalignment.
State Senate President Stephen Sweeney, whose district includes Paulsboro, said he had been told that complaints had been made in recent weeks about noise coming from the bridge and that Conrail was looking into it. But he said he didn't have any details.
At a news conference, Conrail spokesman John Enright said that the company is concerned with safety and cooperating with authorities, but he would not take any questions.
Early in the day, State Assemblyman John Burzichelli, a former mayor of Paulsboro who was serving as spokesman for the town, said he believed that it was a problem with the bridge that caused the accident. But he later backed off that, saying he did not know the cause.
The Federal Railroad Administration doesn't routinely inspect the structural safety of bridges owned by freight railroads, although it does inspect the tracks and can do an inspection if it receives a complaint or if track inspectors notice a problem. The agency last inspected the Paulsboro bridge in January 2010 and found no defects.
The railroads themselves are responsible by law for inspecting their own bridges. The FRA does not know when Conrail last did one.
The NTSB's Hersman says her agency will review bridge safety records and other details, including the mechanical systems on the train and the structural integrity of the bridge. She said inspectors will seek to interview crew on the train and to give them drug and alcohol tests.
Burzichelli said that as long as the bridge is out, factories and refineries in the area will have to rely on shipping materials by barge and truck.
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