Q. I had a bird's nest in my chimney and was told that we were probably getting some carbon monoxide in the house. He said that this is bad for your health. How bad?

Carbon monoxide (chemical symbol CO) is a colorless and odorless gas that can kill you. CO is a byproduct of combustion. It comes out of car tailpipes, gas ovens, fireplaces and heating systems.That bird's nest was blocking the evacuation of CO out of your chimney from your furnace and hot-water heater. The gas was backing up into your house.Red blood cells absorb CO more readily than they pick up oxygen. If there is a lot of CO in the air, the body may replace oxygen in blood with CO. This blocks oxygen from getting into the body, which can hurt you and eventually kill you.People with chronic heart disease, anemia or respiratory problems are more susceptible to the effects of CO. And many seniors fit into one or more of those categories.The most common symptoms of CO poisoning are headache, dizziness, weakness, irregular breathing, nausea, vomiting, chest pain, and confusion. You should go outdoors and breathe some fresh air immediately if you suspect CO poisoning. Then get medical attention right away.If you stay in the house, you could become unconscious and die.The proper operation and maintenance of all fuel-burning appliances is the most important way to reduce the risk of getting dangerous CO in your home. When appliances are kept in good working condition, they produce little CO. Also, having your chimney checked regularly is smart.Signs that might indicate improper appliance operation include:• Decreasing hot water supply• Furnace unable to heat house or runs constantly• Sooting, especially on appliances• Unfamiliar or burning odor• Increased condensation inside windowsHere are some no-nos: leaving a car running in a garage even with the door open, operating a gas generator in the house, burning charcoal indoors, using a gas oven or dryer to heat the house, and putting foil on the bottom of a gas oven because it interferes with combustion.And here's one that may surprise you. Do you have a car with a tailgate? If you drive with a tailgate open, you must open windows to make sure air is moving through your car. If only the tailgate is open, CO from the exhaust will be pulled into the car.Next to preventing the production of CO, the best defense against this lethal gas is a CO alarm. CO gas distributes evenly and quickly throughout the house. A CO detector should be installed outside bedrooms to alert sleeping residents.If you would like to ask a question, write to

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