NEWPORT, Maine — Discarded sawdust and solvents from the refinishing of the gymnasium floor sparked a fire Sunday morning that heavily damaged the northern exterior of the gym at Nokomis Regional High School.

“The fire doors held and did exactly what they were supposed to do,” Lt. Ricky Turner of the Newport Fire Department said. The fire, which began outside the double doors to the gym, damaged a section of the floor inside, the exterior wall and portions of the roof directly above the doors.

The fire was reported about 7:45 a.m. by a passerby, and when Lt. Randy Wing of the Newport Fire Department arrived he could see black smoke pouring from the school. The call for full fire department mutual aid went out, and firefighters from Newport, St. Albans, Pittsfield, Plymouth, Corinna and Dexter fire departments responded.

The school parking lots were jammed with firetrucks and emergency vehicles as well as dozens of school staff members and alumni who came to watch. Within an hour, the fire was extinguished.

Firefighters’ quick actions were credited with saving the rest of the school from damage.

“They were incredible, unbelievable,” Principal Arnold Shorey said shortly after arriving at the school. Shorey said the floor refinishers had been working Saturday, using hoses to fill buckets outside the doors with sawdust from the project.

Looking at the damage, SAD 48 Superintendent William Braun said, “Boy, it could have been worse.” He said the area above the fire doors used to contain windows and it was the wood and siding that had replaced them that burned so heavily.

Braun said classes at the 42-year-old high school, which serves Etna, Dixmont, Newport, Palmyra, Plymouth, St. Albans, Hartland and Corinna, began last Wednesday.

He said the refinishing of the floor had been complete and the work crew was planning to paint it Tuesday. He said that only physical education classes were using the gym and that repairs to the wall, floor and rubberized roof over the door area will begin immediately. The light smoke odor inside the main building will be cleared when classes resume Tuesday, he said.

Braun said the school was insured with either a $500 or $1,000 deductible.

School board member Tim York, who also is an investigator with the State Fire Marshal’s Office, arrived at the scene and called in other investigators to avoid any appearance of a conflict of interest.

By 11 a.m., fire marshal’s investigator Sgt. Ken Grimes was surveying the scene.

“The fire departments did a wonderful job both putting out the fire and leaving the scene intact,” Grimes said. He confirmed that the sawdust waste had self-combusted and caused the fire.

The investigation is continuing, and Grimes said he would be interviewing several witnesses over the next few days.