PAULSBORO, N.J. (CBSNewYork/AP) — Officials said Saturday that there may have been a problem with a signal at a South Jersey bridge just before a trail derailed there, spewing a hazardous chemical into the air that sickened dozens of people.

National Transportation Safety Board chairman Deborah Hersman said Saturday that train crewmembers have told investigators that a radio code used to change a light from red to green failed to work just before Friday’s accident.

KYW Newsradio Philadelphia’s Cherri Gregg reports for 1010 WINS |titles=NTSB: Signal Problem May Have Preceded South Jersey Derailment|artists=Cherri Gregg]

“They had a red signal, and the bridge was in the closed position,” Hersman said.

The conductor got out of the train and visually inspected the bridge in Paulsboro, she said. The crew then called for and received permission to cross, she said.

“Two locomotives, several cars had cleared the bridge when the crews stated they saw the bridge collapse,” Hersman said.

It was unclear if the malfunctioning signal had anything to do with the accident, she said. Hersman said the train was moving 8 mph just before seven cars derailed on the bridge — below the 10 mph speed limit.

The derailment happened just before 7 a.m. Friday, as a train with two locomotives, 82 freight cars and a caboose made its way from Camden to the industrial town of Paulsboro, just across the Delaware River from Philadelphia International Airport.

Seven of the train cars detailed. One tanker containing 25,000 gallons of vinyl chloride was sliced open in the accident and some of the gas spewed into the air, while the rest turned into a solid and settled into the bottom of the tanker.

More than 70 people were hospitalized for minor breathing problems. Officials initially thought the air quality was safe, but then at 6 p.m. Friday, officials ordered an evacuation of a 12-block radius surrounding the accident site because of an increase in the level of the vinyl chloride gas.

U.S. Coast Guard officials said about 500 residents were told to pack bags good for three days, and were taken to area hotels. More than 100 people remained out of their homes Saturday.

Members of the National Transportation Safety Board arrived in New Jersey on Friday afternoon to investigate the incident. They will try to determine whether it was a problem with the bridge that caused the derailment or if the derailment is to blame for the partial bridge collapse.

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 2009.

The Federal Railroad Administration last inspected the bridge in January 2010 and found no defects. Railroads are required by law to conduct their own inspections. The FRA does not know when Conrail last did one.

Nine cars on a coal train derailed at the moveable bridge on Aug. 23, 2009, in an accident that was attributed to a bridge misalignment.

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