Chattanooga Fire Department received a call Monday evening that Unum was sending people home with headaches from their downtown campus on Walnut Street.
An employee who came by an area fire station had elevated carbon monoxide levels.
Then, CFD started receiving reports that other employees were showing up at hospitals with elevated CO levels.
Later, Unum called Station 1 and CFD crews responded. They found elevated CO levels in a construction area.
The HVAC system was purged to vent through the roof and the ventilation dropped the CO levels to well within normal range.