Chicago fire officials say several people are lucky they didn't die when carbon monoxide levels reached lethal levels in their Chicago apartment building Thursday morning.

Fire department spokesman Larry Langford says seven people were taken to hospitals in serious condition, including at least two children. But he says all were conscious when they left the scene and they were expected to recover.

He says a broken furnace caused carbon monoxide levels to rise in the northwest side building and carbon monoxide detectors failed to alert residents because their batteries were dead.

Five other people were treated on the scene.

Langford says one resident woke to find members of their family unconscious or acting strangely. He says if that person hadn't called 911, there may have been fatalities.