Moore said the levels were within acceptable limits for prolonged exposure to the chemical, but the evacuation was ordered as a precaution.
More than 100 residents were put up in hotels overnight while others found shelter with friends or families.
Evacuees were advised to be prepared to remain away from home for three days.
Federal National Transportation Safety Board investigators in the meantime are waiting for the chemical to be removed from the tanker to begin their on site work.
In the meantime, they have interviewed the trains crew and are evaluating inspection reports for the low bridge over the Mantua Creek where the train derailed.
The bridge, which dates from the 19th century, was the scene of a less serious derailment in 2009.
A large barge carrying a large crane needed to remove the other tankers that fell into the creek is on its way from New York Harbor Moore said the barge could arrive by Sunday but added no other work will begin until the residual chemical is removed from the ruptured tanker.
While the initial threat passed within three hours of the 7 a.m. accident, removing the remaining vinyl chloride from a tanker car that ruptured, and pulling three others carrying the toxic chemical from the Mantua Creek, will require what several officials called a delicate operation.
"This is not something we look forward to," said Assemblyman John Burzichelli (D., Gloucester), a former mayor of Paulsboro.
"We'll be proceeding with caution," Deborah Hersman, chairwoman of the National Transportation Safety Board, said Friday afternoon as she arrived with 17 agency investigators who will look into the derailment's cause and oversee the cleanup.
Local officials said work at the site would occur within days and only during daylight hours. They plan to use Gloucester County's reverse-911 system to instruct residents about any actions they might need to take, including evacuating their homes if necessary.
The Red Cross will operate a temporary shelter at the Paulsboro Fire Department banquet hall during the procedure, Burzichelli said.
Eleven people, including workers near the bridge, were transported to Underwood-Memorial Hospital in Woodbury for treatment following the derailment and at least 60 others arrived on their own. As of Friday evening, all but three had been released.
Officials said the train, with two engines, 82 freight cars, and a caboose, was southbound when seven cars near the front derailed while crossing the low, A-frame swing bridge on wood pilings, the scene of a less serious derailment in 2009.
The bridge was rebuilt after that accident, but questions about its condition emerged Friday after State Senate President Stephen Sweeney (D., Gloucester), whose district includes Paulsboro, and other officials said Conrail inspectors had been out to check it repeatedly after nearby residents reported hearing strange noises from the span, including a loud bang when no train was on it.
Hersman said investigators would look at inspection reports for the bridge before and after the 2009 derailment and the span's rebuilding.
They also would examine the rails, check the train's electronic monitoring equipment, review mandatory drug and alcohol tests of crew, and inspect the derailed cars, she said.
"We have requested a great deal of information," Hersman said.
When the train derailed, the bridge collapsed, sending four tanker cars into the water. One dangled from the gap in the span and was only partly in the creek.
That car ruptured underneath and spewed about half its cargo of 25,000 gallons of vinyl chloride into the air in the form of gas, officials said. The other half "self-refrigerated" and remained in the tank car as an inert, slushy liquid, said Larry Hajna, a state Department of Environmental Protection spokesman.
The first step in the cleanup will involve removing the chemical in the ruptured tanker.
Burzichelli, spokesman for the incident command team, said that operation likely would involve pumping water into the tank. That would return the chemical to a gaseous state, and it would be neutralized by an umbrella mist of water sprayed at the same time, he said.
After that, work could begin on removing the remaining tankers, with a large crane on a barge that was expected to arrive on Saturday from New York.
Tom Butts, the county's emergency management coordinator, said removing the chemical while the cars were in the water did not appear to be an option because of fears that empty tankers might float away.
Engineers will draw up plans so the tankers do not rupture and leak as they are lifted, he said.
In the meantime, the U.S. Environmental Protection Agency is monitoring the air through a specially equipped bus that arrived Friday afternoon.
After the derailment, businesses and residents within a half-mile were evacuated or told to stay indoors, and police closed roads into Paulsboro.
Booms were set up in the water to prevent hydraulic fluid from the rail cars from spreading.
At room temperature, vinyl chloride is a flammable, colorless gas with a sweet odor. Short-term exposure can cause dizziness, drowsiness, and headaches, according to the EPA. Long-term exposure, not considered an issue in this case, has been linked to cancer.
Among those who went to the hospital was Tryphaena Cooper, 26, of Paulsboro.
She woke up Friday feeling light-headed and soon had diarrhea, she said. A thick fog had billowed in the sky above Cooper's house, where she lives with her mother and five children.
"You couldn't see the person next to you," she said.
Cooper said she received an emergency call instructing her to keep her windows shut and doors locked, but she did not immediately know why.
"It was like a horror movie out there," she said outside Underwood as she waited for doctors to evaluate her. "We thought we were going to die."
The industrial area along the Delaware River near the Mantua Creek has been the scene of other environmental accidents.
With two nearby refineries, accidental discharges of gases or chemicals are a recurring problem, and the air is often thick with the smell of petroleum.
In 2004, the mouth of the Mantua Creek was the scene of one of the Delaware River's worst oil spills when the hull of a Greek tanker, the Athos 1, was punctured by an abandoned anchor, spilling about 265,000 gallons of heavy crude destined for an asphalt refinery in West Deptford.
Terry Coney, a retired construction worker who has lived in Paulsboro since 1969, has a fatalistic view that others shared Friday.
"If it's going to happen, it's going to happen," he said.
Contact Joseph Gambardello at 856-779-3844 or firstname.lastname@example.org
Contributing to this article were Inquirer staff writers Andrew Seidman, Kathy Boccella, Jonathan Lai, and Robert Moran.