Altoona, PA – Work returned to normalcy a few hours after a carbon monoxide incident at Chicago Rivet & Machine Co. near Tyrone led some to seek out medical evaluations Monday afternoon, officials said.

Larry Koch, a Chicago Rivet human resources manager, said carbon monoxide was released into the building because an exhaust fan was not turned on. Koch said multiple ovens remained on during the weekend, producing gas that was not properly dispersed.

“Over the weekend it built up, and it wasn’t noticed until later in the afternoon (Monday),” Koch said.

Koch said firefighters responded, and the building was evacuated until the issue was remedied.

Employees who were experiencing headaches or other illnesses were encouraged to seek medical attention, Koch sad.

“We wanted to err on the side of caution,” he said, adding that there were no employees who experienced serious medical issues.

Issues were resolved by about 5:30 p.m., Koch said. He said this was the first time carbon monoxide was a problem at the plant.

“Everybody is back to square one,” he said. “We are taking steps to make sure that it doesn’t happen again.”