It's a common danger each winter: carbon monoxide poisoning. Each year thousands of Americans are sickened by the silent killer, and about 200 people die from it.
Many people mistake their symptoms of CO poisoning for the flu. Because CO replaces oxygen in the blood, it makes people feel sleepy. If they already are asleep, it can prevent them from waking up.
When it comes to protecting yourself and your loved ones, the key is prevention.
Susan Thomas with the American Red Cross says this time of year, many people are starting to use alternative heat sources, especially with a slow economy. She advises people to learn how to use fuels safely.
Symptoms of CO poisoning include nausea, dizziness, headache, fatigue. Thomas says if you feel like you have the flu but aren't sure, try getting fresh air.
The steps to preventing CO poisoning include having your chimney and appliances -- such as the furnace -- checked. Using alternate fuels in your house or garage is not recommended.
CO detectors in your home can help, also. "If you're sleeping when this happens, you won't wake up. That's why the CO detectors are important," Thomas said.