High carbon monoxide levels forced the evacuation of 150 seniors from a Northwest Side nursing home Thursday, fire officials said.

The Chicago Fire Department secured the 4-story Norwood Crossing facility at 6020 N. Nina Ave, within two hours of the 9:16 a.m. 911 call, spokeswoman Eve Rodriguez said.

The problem was discovered when carbon monoxide detectors in the hallways of the building's upper floors went off, according to Marcia Mahood, chief operating officer for the Norwood Life Care Foundation, which operates the home.

There were no reported injuries. "They're all fine," Mahood said. "It was sort of an adventure for them."

The residents were taken by wheelchairs to the lobby where they waited while firefighters opened windows to ventilate the building.

Officials are still investigating the source of the high readings of carbon monoxide.