"There was a problem with an air compressor in Room 201 which overheated or malfunctioned and that set off a smoke detector and sounded an alarm," Washington Fire Chief Bill Halmich said.

The alarm sounded around 1:45 p.m. Monday. Nobody was in the room at the time. Minor smoke damage was reported.

School officials called 911 and evacuated the students, including those in the practical nursing classes and East Central College classes, while firefighters responded to the scene.

"School officials did not know the cause of the alarm," Halmich said. "When we arrived, we observed smoke coming out the cracks of the door to the compressor room."

After finding that the door was not hot, fire crews opened the door and saw smoke had filled the room but no flames.

"The room was so full of smoke, you couldn't see past your nose," said Randy Kosark, director of the vocational school.

Kosark said a ladder truck was brought in and was prepared to be put into use if a fire broke out.

The fire chief said crews removed all combustible products from the area and performed air quality checks before reoccupying the building.

School maintenance staff were looking into the cause of the problem Monday afternoon and Tuesday morning.

"We had the maintenance staff look at the sensor in that room and try to trace the cause back down to the source," Kosark said.

"We found a broken intake valve that could have sucked in some oil," said Kevin Hunewell, director of buildings and grounds at Four Rivers Career Center.

"There's a pop off valve on the cylinder head for the air compressor and it could have come off and heated up thin tubes along there which caused the white-colored smoke. Basically, you have a bad cylinder head," Hunewell said.

Hunewell said the school is getting estimates to repair the compressor. He added that a second compressor in the same room is being used at the school in the mean time.

Students, faculty and staff waited about 45 minutes before returning to classes.

"The school did very well," Halmich noted. "They followed their fire drill protocol and everything went very well."

Kosark said the entire building was evacuated in under three minutes.

"Everyone was very fortunate and the staff did a great job of getting the kids out of the building," the school director said.

He complimented the fire crews for their work and for routinely performing fire drills at the school.

"I want to thank them for observing fire week earlier in October," Kosark said. "We had some recent practice because of that."

Kosark said there have been no major fires during his time as director.

"In the past, we have had sensors that were bad," he said. "One time, we had fumes coming from a classroom that drafted down a freight elevator, but we've had no incidents with a real fire."

He noted that sometimes smoke from welding classes may set off an alarm, but said proper ventilation is always used.