A hazardous materials situation prompted the evacuation of a Near North Side office building early Thursday afternoon.
The Chicago Fire Department responded to a Level One HazMat situation at 770 N. LaSalle, Fire Media Affairs tweeted at 12:14 p.m.
The carbon monoxide was initially measured at 200 ppm and the HazMat was elevated to a Level Two, according to Fire Media.
The building was evacuated, according to Fire Media. The source of the carbon monoxide was a gasoline-operated air-conditioning generator being used on the first floor of the building by a construction crew.
About 12:50 p.m., air quality returned to normal and crews were released from the scene.
CTA buses were also temporarily rerouted in the area.