Officials have stopped work at the site of last week's train derailment in Gloucester County after unsafe chemical levels were found in the air.
Officials ordered Paulsboro residents to stay inside and closed the schools when air quality monitoring detected unsafe levels of vinyl chloride at around 6 a.m. this morning. 
They dropped below unsafe levels by 9 a.m., but the shelter-in-place order remained.
More than 100 residents have already been evacuated as a precaution while workers tried to remove the hazardous chemical from a ruptured tanker car. Officials must remove the vinyl chloride before they can clear the track and examine what caused Friday's derailment.
Federal investigators said yesterday that Conrail crews had studied reported signal problems at the railroad bridge where the derailment occurred.
The NTSB is reviewing records with a focus on the reported signal problems and a 2009 train derailment on the same bridge.
The derailment sent dozens to a hospital, but no serious injuries have been reported.