Tara McDonald stood outside, filled with tears and disbelief, as three firefighters wearing gas masks and oxygen tanks inspected her home one Saturday afternoon.

After talking with one of the firefighters, all she could think about were the countless hours she had spent, completely oblivious to the potentially fatal carbon monoxide levels in her DeKalb home.

McDonald, a first-year early childhood education major, decided to buy a carbon monoxide detector Nov. 19, despite her friend and sister’s criticism that she was overreacting.

One day later, McDonald evacuated her house and called the fire department after the detector’s alarm had sounded.

“I don’t know why, but I just had this feeling that I needed a carbon monoxide detector,” McDonald said. “Now I know it was nothing but God who saved me.”

After a brief investigation, fire officials identified the source – a dirty furnace filter. The filter caused carbon monoxide levels in her home to rise to 92 parts per million (ppm), well above set danger levels of 35 ppm or more.

Carbon monoxide, a dangerous and nearly undetectable gas, comes from numerous sources including gas heaters and stoves, fireplaces, auto exhaust and tobacco smoke, according to the Environmental Protection Agency Web site. Symptoms of carbon monoxide poisoning include fatigue, impaired vision, dizziness, confusion, nausea and death in extreme cases.

Carbon monoxide alarms are fairly common. About 50 to 100 carbon monoxide alarms sound annually, most often during winter months, said Lt. Don Faulhaber of the DeKalb Fire Department.

There is always a small amount of carbon monoxide present in the home, Faulhaber said. But these levels increase significantly during colder months when there is less air circulation in homes.

“When we shut our house up to save on our heating bills, we also lock in carbon monoxide,” Faulhaber said.

Faulhaber said having gas furnaces checked professionally every one to two years, and good maintenance of natural gas and propane appliances such as clothes dryers and gas stoves, can help protect against carbon monoxide and fires.

Two weeks after the incident, McDonald said she makes sure to follow all of the firefighter’s guidelines. She checks her appliances regularly and tests her carbon monoxide detector to make sure it is working.

“Now I don’t let people tell me I’m overreacting,” McDonald said.

Carbon monoxide detectors cost between $14 and $170 and can be purchased at most hardware stores.

For more information on carbon monoxide, visit the EPA Web site at www.epa.gov.