BOULDER, Colo. (CBS4) – Residents of an apartment building in Boulder remain evacuated due to a carbon monoxide leak.

At about 9 a.m. on Friday Boulder Fire-Rescue responded to the Canyon Apartments after a woman reported she was feeling extremely sick.

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When firefighters arrived, the level of carbon monoxide was 449 parts per million. Normally fresh air contains 0 ppm molecules.

Everyone in the building, which has 24 occupied units along with three dogs and two cats, were evacuated safely.

“Medical personnel are still checking the vitals of everyone exposed to the CO,” Boulder Fire-Rescue said in a statement. “So far no one has been transported for further medical treatment.”

The carbon monoxide leak was traced to the boiler room.

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The building is being ventilated, and will remain evacuated until the boiler is repaired. There is no word on how long that should take.