Welding students sparked a Tuesday afternoon fire at the Academies of Loudoun magnet school in Leesburg, evacuating the campus and leaving at least $1 million in damages, fire officials said.

911 dispatchers received a pull-station alarm from the school about 1 p.m., with the school resource officer reporting heavy smoke in the boiler room less than a minute later, Loudoun County Fire and Rescue said in a news release.

First responders from Leesburg, Ashburn, Lansdowne, Moorefield, Kincora, Philomont and Sterling, as well as the Metropolitan Washington Airports Authority and Fairfax County, were called to the scene. Meanwhile, students and staff safely evacuated.

“Arriving units found heavy smoke coming from the rear of the structure and made entry into the building in the area of the welding classroom, and determined the fire was located in the fume extraction system,” the release said.

Crews worked for nearly an hour to fully extinguish the fire.

The Loudoun County Fire Marshal’s Office determined students “had been welding and grinding earlier in the day, during which debris or a spark got into the hopper and started a fire,” the release said.

Damages are estimated at approximately $1 million. One firefighter and one adult civilian suffered minor injuries and were taken to area hospitals for treatment.

There were no reported student injuries and the fire alarm and sprinkler system functioned as designed, the release said.

The school remained closed Wednesday.