AUBURN — Employees were back to work at the Pionite Decorative Surfaces plant Tuesday, one of the area’s largest manufacturers, after Monday’s fire.

Fire broke out in the ductwork at the plastics plant at around 6:30 p.m. Platoon Chief Scott Hunter with the Auburn Fire Department said that the State Fire Marshal’s Office returned to the scene Tuesday to continue its investigation into the blaze. Firefighters were at the scene until about midnight Monday. Hunter said investigators were not able to make much headway into a possible cause as of late that night.

Hunter said that he did not know an official estimate of damages, although some plant officials speculated Monday night that it could be upwards of $1 million. He said there were several representatives at the plant on Tuesday to survey the damages and prepare official estimates.

According to an employee at the plant, the 700-feet of ductwork on the roof of the building is used to move manufacturing emissions to a boiler house to be burned, reducing pollution from the plant as required by state law. The fire caused a lot of damage to the piping system, so the company is making alternate arrangements to deal with emissions.

Pionite Decorative Surfaces is a subsidiary of Panolam Industries International, based in Shelton, Conn.

Sharon Metz, returning a call Tuesday on behalf of Panolam general counsel Jeffrey Muller, said corporate officers had no comment on the fire, but “should be able to provide information tomorrow,” meaning Wednesday.

Panolam purchased the former Pioneer Plastics plant in 1999, paying $160 million. At the time, it was the largest manufacturing plant in Androscoggin County, employing about 700 workers. The following year, a large number of employees were laid off.

Last December, the company laid off 48 employees, about 16 percent of its remaining work force, bringing employment down to about 250 workers.

The recent layoffs were attributed to a downturn in the economy and a significant decrease in high pressure laminate sales, including laminate counter tops and bowling lanes, manufactured at the Auburn facility.

For the past several months, Panolam has been working with shareholders to restructure and shed about $151 million in debt, eliminating $16 million in annual credit payments. In addition to the Auburn site, Panolam operates plants in Wisconsin, Oregon, Georgia, Tennessee and Ontario, Canada.

According to the company’s most recent quarterly financial report, sales were down to $67 million between March and June 2009 compared to $99.3 million for the same period in 2008.

Last month, Auburn police responded to a report of significant vandalism at the Rodman Road facility, and spent a considerable amount of time interviewing employees about extensive damage done to cripple some of the manufacturing equipment. According to Auburn Police Chief Phil Crowell, that case is still under investigation.