Heavy fog is delaying plans to start clearing a train derailment that caused a chemical spill and the evacuation of a 12-block area in Paulsboro.

Train derailment in Paulsboro (KYW TV)

Officials say they are waiting for a safe time to try to pump vinyl chloride out of a damaged tanker. They plan to use a crane to remove the derailed cars.

Investigators are looking at a signal on the bridge where the train derailed over a creek, causing the hazardous chemical to spew into the air. No serious injuries have been reported, but more than 70 people went to a hospital. An evacuation order remains in effect over several blocks.

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