Darien High School was forced into early dismissal on Monday because of an odor.
Police said an oil burner was not functioning properly and was behind the odor on the first floor of the building.
"We became aware of the issue first thing this morning," principal Ellen Dunn posted to the police department's Facebook page. "The system has been adjusted and the problem corrected but the ventilation system will take some time to refresh the building."
The air quality has been deemed safe by the fire and police departments.
Still, Dunn said they wanted to give the odor time to dissipate.
The school dismissed at 9:15 a.m.
However, after school practices and activities are still happening because police expect the building to be fine by then.
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