DANVERS, Mass. (AP) – Residents driven from their homes by a chemical plant explosion were urged to contact town hall today or Saturday to learn whether it will be days, weeks or even longer before they can return.

Meanwhile, all 12 people hospitalized because of the blast at a building housing ink and paint companies had been released by Thursday, and refugees from the houses around the plant continued to marvel at the fact that no one was seriously injured.

“We’re all really thankful that we got out of there. It’s basically a Thanksgiving miracle,” said Michele Keith, as she returned briefly to her house to survey the damage and pick up some belongings.

Danvers Deputy Fire Chief Kevin Farrell said state fire investigators and federal officials, including members of the U.S. Chemical Safety Board, would begin to investigate the massive pile of rubble that was CAI Inc., an ink-making firm, and Arnel Co., a paint manufacturer, for clues to what caused the building along the Danvers River to blow up about 2:50 a.m. Wednesday. Farrell said the rubble from the explosion would not be moved until investigators begin their probe.

He said the chief concern on Thursday was the structural integrity of about six or seven businesses and homes closest to the plant. He said most probably would have to be razed.

Most of the other houses on the peninsula around Bates and Riverside streets appeared to be structurally sound, but their shattered windows have been boarded over and concerns remained about their electrical and natural gas connections.

Town Manager Wayne Marquis said all utilities in the blast area had been shut down and would remain off until electrical and natural gas experts could be certain all connections in the affected houses are safe.

Marquis said it was impossible to know Thursday how soon power would be restored.

He said town staffers would be available between 10 a.m. and 7 p.m. Friday and Saturday to try to answer questions from those forced out. Farrell said emergency crews worked until 1:30 a.m. Thursday sealing up about 80 houses and 20 businesses with plywood to keep out rain and human intruders.

Officers from Danvers and the state police patrolled the abandoned neighborhood.

Police Chief Neal Ouellette said the recovery from the blast would force the continued closure of Route 35, also known as Water Street, between Endicott and South Liberty streets until at least Monday.

“It’s going to be a very high traffic day with all the store sales,” Ouellette said, noting that Route 35 normally is a heavily traveled connection between Salem, Danvers and nearby shopping malls.

Mike Nalipinski, on-scene coordinator for the federal Environmental Protection Agency, said air quality tests of the area revealed no cause for concern. He said his chief worry at the blast site was chemical runoff from the plant into the waters around the Liberty Marina, and environmental workers placed booms just off the land’s edge to try to contain any solvents that may have leached into the water.

“The jury’s still out,” Nalipinski said about potential harm to the water. He said more tests would be run.

Farrell said a large number of 55-gallon drums of paints and inks at the plants would be encased in safety containers and moved off the site. He said the bulk of the chemicals at the site were contained in underground tanks that did not appear to be damaged. Farrell said the capacity of the tanks is roughly 6,000 gallons, but he could not say how full they were.

The violent explosion on the eve of the holiday did not deter townspeople from attending the traditional Thanksgiving Day football game between host Danvers High School and Gloucester High School.

“We have a lot of team spirit and town spirit. It’s a very spirited town,” Chuck Sterns said as he stood on the bleachers with his wife and daughter and watched the game through a wind-swept rain.

His wife, Sue, said she was glad town officials decided not to cancel the game. “These kids played hard all year. They deserve it. Plus, it’s Thanksgiving. It’s a tradition.”