DANVERS, Mass. (AP) – Investigators on Friday got their first close-up look at a chemical plant leveled by an explosion that also damaged or destroyed dozens of nearby homes.

A team of local, state and federal officials briefly examined the charred wreckage on Friday afternoon after a hazardous materials team checked the site to ensure it was safe for investigators, who nevertheless wore respirators as a precaution.

The lengthy probe into the cause of Wednesday’s blast was expected to continue through the weekend, but work at the site will be limited to daylight hours.

State Fire Marshal Steve Coan said the damage was so extensive that investigators don’t know the precise point where the explosion started.

“It will take quite some time to just get in and document the scene,” Coan said. “It’s nothing more than a pile of rubble.”

Meanwhile, residents Friday waited to see if they would be permitted to permanently return to their houses for the first time since the explosion.

“I just want to see what the damage is and get back to normal. A good night’s sleep would be good,” said Susan Tropeano, 45, who fled her house with her husband and 16-year-old son after the explosion.

Gov.-elect Deval Patrick on Friday visited the site of the former CAI Inc. chemical plant and Arnel Co., a paint manufacturer, which was obliterated early Wednesday morning in an explosion that destroyed about 10 houses.

After meeting with safety and local officials on the site, Patrick released a statement that said “We are blessed” that no one was killed or seriously hurt.

“I will continue to monitor developments in Danvers closely to assure that the affected families are given the help they need and that the Danvers community remains strong despite this calamity,” Patrick said.

All 12 people who were hospitalized because of the blast were released by Thursday. The explosion woke people sleeping in communities miles away and was felt in New Hampshire.

Fire Chief James Tutko released revised numbers of the damage caused by the blast, which were lower than initial estimates.

Tutko said about 70 houses in the areas suffered some damage in the explosion, with 10 of those destroyed. Another dozen homes were extensively damaged and will require some reconstruction, he said. On Friday, the 50 remaining houses were being evaluated to determine if it was safe for families to return, Tutko said. For those residents, Tutko said it would likely be “a matter of days, not weeks” before they can go back.

“We want to make sure they can move back into a safe environment,” Tutko said.

Tropeano was among the Danvers residents who visited Town Hall on Friday to learn more about when she and her family can return to their house. Her house suffered cracks in the walls and foundation – damage she said was relatively minor compared with neighbors’ homes.

Tropeano and her family have been staying with her mother, who also lives in Danvers.

“We really have the best-case scenario here,” she said.