TOLEDO, Ohio (AP) — Officials in northeast Ohio said Friday that a chemical tank leak earlier in the week was caused by a chemical reaction resulting from an employee error and lifted all remaining evacuation orders.

Toledo Mayor Wade Kapszukiewicz said during a news conference that the venting of the tank that ruptured at MC Tank Terminal on Tuesday was finally completed late Thursday night, allowing a hazmat team to enter the site and test safety levels.

“At this time, we do feel confident that the site is safe," Toledo Fire and Rescue Battalion Chief Blake Molnar said.

The rupture happened late Tuesday night. MC Tank Transport, the owner of the site, said the tank contained glycidyl methacrylate, which it described as “an industrial chemical used to make certain plastics, paints and coatings perform better.” Hundreds of people were initially forced from their homes.

Dr. Brian Kaminski, vice president of medical affairs for ProMedica hospitals, said about 60 patients arrived at hospitals for treatment, most suffering relatively minor symptoms. A small number of patients who had underlying health conditions were admitted, and all patients were expected to recover, he said.

The chemical leak happened when an employee of the company “introduced a temperature level to the tank in the process of trying to transfer the liquid" that caused a chemical reaction, the mayor said. The company has “accepted responsibility” for what happened, the mayor said.

“There was no fire, there was no explosion. There was a very serious chemical reaction, which now happily has run its course, and we’re now finally able to return to some level of normalcy here in our community," he said.

Based on data that officials have seen so far, the amount of the chemical in the air didn't reach levels high enough to have “a long-term meaningful impact on human health,” the mayor said.

There are questions that remain unanswered, and the investigation is ongoing, he said.