PAULSBORO, N.J. (December 2, 2012)--Heavy fog was delaying plans to start clearing a train derailment that caused a chemical spill and the evacuation of a 12-block area in Paulsboro, N.J.

Officials say they were waiting for a safe time to try to pump vinyl chloride out of a damaged tanker.

They planned to use a crane to remove the derailed cars.

Investigators say a signal may have malfunctioned on a southern New Jersey bridge where the train derailed over a creek, causing the hazardous chemical to spew into the air.

No serious injuries were reported, but more than 70 people went to a hospital.

An evacuation order remained in effect over several blocks.

National Transportation Safety Board Chairman Deborah Hersman was expected to provide updates at a Sunday morning news conference on the investigation of the Friday morning accident.