More than 100 Paulsboro residents won't able to return to their homes in the 12-block evacuation zone until at least Saturday.
Officials must remove the vinyl chloride before they can clear the track and examine what caused Friday's derailment.
Federal investigators said Sunday that Conrail crews had studied reported signal problems at the railroad bridge where the derailment occurred.
The National Transportation Safety Board is reviewing records with a focus on both the reported signal problems and a 2009 train derailment on the same bridge.
Dozens of people went to a hospital with breathing and other issues after the derailment, but no serious injuries have been reported.
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