WATERLOO - A Waterloo couple is recovering after becoming ill from carbon monoxide gas that filled their west-side home, firefighters said.

The two called for an ambulance after they began vomiting sometime around 5 a.m. Monday, said Battalion Chief Virgil Powell of Waterloo Fire Rescue.

Paramedics and firefighters realized the couple was showing early signs of carbon monoxide poisoning and checked their house at 920 Wisner Drive, Powell said.

They found carbon monoxide levels at 295 parts per million and determined it was likely coming from a faulty furnace.

Normal background carbon monoxide is less than 10 parts per million.

Firefighters make recommendations about possible danger at 9 to 100 parts per million and have the authority to order people out of a building with more than 100 parts per million.

Colorless and odorless, carbon monoxide replaces oxygen in the blood stream and can be fatal, said Tammy Noble, education coordinator for the Iowa Statewide Poison Control Center.

"The symptoms are very similar to the flu," Noble said.

She said residents should be concerned about possible poisoning if multiple members of a household get sick at the same time.

Early signs include tiredness and headaches, Noble said. As the amount of exposure becomes more serious, the symptoms progress to nausea and vomiting and then lead to confusion, comas and finally death, she said.

Carbon monoxide poisoning is more common in the winter because more people are indoors, and more appliances that can leak the gas - furnaces and space heaters - are in use, Noble said.

Officials at the Poison Control Center recommend residents purchase carbon monoxide detectors, which track levels of the gas inside the home.

They are programmed to sound if there is a large level of carbon monoxide or if there is a low level sustained for a long period of time. They usually go off before the symptoms of poisoning show.

If the alarm sounds and the residents don't show symptoms, they can call the fire department or notify their utility company or a home heating specialist for further monitoring, Noble said.

If the alarm sounds and residents have symptoms, they should get fresh air and call authorities.

Jeff Reinitz can be contacted at (319) 291-1578 or jeff.reinitz@wcfcourier.com.