Residents of Paulsboro, N.J., were ordered to stay in their homes with their windows closed for most of Monday morning. Heightened concentrations of vinyl chloride were measured in the air there, three days after a derailed train fell from a bridge over Mantua Creek and spilled the chemical.

 Public schools were cancelled Monday as well.

By the afternoon, after the shelter order had been lifted, traffic in tiny Paulsboro was humming again. But a helicopter circling overhead and frequent police car passes downtown signaled all was not quite right in Paulsboro.

Local baker Doug Ricotta said the whole community is nervous about air quality after the derailment.

"Nobody wants to come to a town when they're constantly watching TV and see 'Breaking news, Paulsboro, chemical spill, the air is no good,'" Ricotta said. "They start panicking and they get scared, and you can see, nobody comes down here, so all the businesses are hurting."

National Transportation Safety Board chair Deborah Hersman said the investigation into the cause of the derailment is focusing on the mechanisms that allow the bridge to open and close to allow boat traffic to pass on the creek underneath. But with cleanup efforts ongoing, the NTSB have not been able to investigate on the scene.

"We are in the preliminary phases, we're still gathering factual information, evidence, conducting interviews," Hersman said. "We still have a lot of work to do. Nothing has been ruled out."

Records show there were problems with the locking mechanism on the bridge in the days leading up to the accident.

Meanwhile, more than 100 evacuated residents will be barred from returning to their homes until at least Saturday.

"It's frustrating because (of) the comfortability of my home, and also it's holidays," said Edward Veney. He was walking his white pit bull with his stepson Monday morning outside a Motel 6 where they were staying.

"We just put up the Christmas tree," Veney said. "We want to look at our Christmas tree, we don't want to look out the window and see Rite Aid and all this parking lot stuff."

Exposure to vinyl chloride, which spilled after one tanker on the derailed train was gashed, can cause respiratory problems and dizziness. It is used to manufacture PVC plastic.