Moore Township, PA – Six people were hospitalized after a buildup of carbon monoxide in their home Monday morning, fire officials said.

The residents at 505 Helen Circle were awoken by their carbon monoxide alarm, Moore Township Assistant Fire Chief Bill Knitter Jr. said.

Knitter said the residents were able to get out on their own, but one collapsed before being taken to a hospital. All six were breathing on their own, Knitter said.

Carbon monoxide gas, or CO, built up inside the home because a stove was not properly venting through the chimney. Knitter said firefighters were called to the home about 5:30 a.m. and went inside wearing breathing apparatus to make sure everyone was out.

“People need to get their chimneys cleaned,” Knitter said.

There were high readings inside, he said, between 45 and 50 parts per million. People can begin to feel the initial effects of high CO levels, such as headaches and nausea, in the 35 parts-per-million range.