BOSTON -- Boston School Transportation officials predicted that most buses would be on time Friday afternoon after a concrete plant malfunction in Charlestown delayed service.

NewsCenter 5's Jorge Quiroga reported that thousands of pounds of concrete dust spewed onto a school bus yard on Thursday, and several bus routes were delayed.

The Boston Public Health Commission said Friday there is no respiratory threat to the public in the area surrounding the plant.

"Air monitoring conducted at the site, and near residential areas of yesterday's cement factory incident, show results well below the acceptable exposures for the components that make up Slag set by the federal Occupational Safety and Health Administration," officials said in a statement.

Crews worked throughout the night to clean the dust off the buses, and officials said that everything should be back on schedule by the end of the day. Hazmat teams had to decontaminate nearly 200 school buses.

"(We've been working) all night long, and we are going home now, hopefully to take some rest," Marcor Environmental worker Johnny Vasquez said.

A malfunction at the Lafarge cement plant, which is adjacent to the bus yard, sent the dust spewing across the neighborhood. Sixty-one people were rushed to local hospitals, complaining of respiratory problems, and irritated eyes and throats.

School officials said that they had about 12 more buses left to clean.

"We are pretty confident that we are going to get most of our routes out on time this afternoon. There still will be some delays because we have some drivers who are doing some unfamiliar routes. So as I said earlier today, I want to reiterate to parents that when you are at your bus stop this afternoon, waiting for your student, there may be a delay," Boston School Transportation Chief Richard Jacobs said.

Parents were advised to call school hotline number 617-635-9520 for more information.