No injuries were reported Thursday morning after high levels of carbon monoxide were detected in a Chinatown apartment building.

Shortly after 5 a.m., firefighters were going door-to-door in approximately 100 units in the seven-story building in the 2200 block of South Princeton, trying to confirm the source of the high carbon monoxide reading, according to the Chicago Fire Department.

Fire officials said the leak may have happened because of a new heating unit.

Peak carbon monoxide readings were reported at 130 parts per million and a Level 2 HazMat response was called, fire officials said. The department’s Mobile Ventilation Unit worked to vent the building and all heating in the unit was shut down.

By 6 a.m., all readings were showing zero parts per million and the building was deemed safe, fire officials said. There were no evacuations and no one was taken to the hospital. Peoples Gas responded to the scene.