The couple has been tired and sluggish all week. e couple has been tired and sluggish all week. They thought it was just a case of the flu. Or perhaps it was the odor from the new wallpaper they'd just hung.

Then one night two new carbon monoxide detectors they just received --- both still under the Christmas tree --- went off.

The cause of their illness was carbon monoxide poisoning. The source --- a malfunctioning furnace.

An estimated 10,000 people are affected by carbon monoxide poisoning each year in the United States. Eight hundred to 1,000 die.

However, a few simple measures can often prevent poisoning.

Symptoms easily dismissed

Carbon monoxide is a poisonous gas produced by incomplete combustion of fuel. It has no color, taste or odor. Pretty easy to see how it could go undetected.

Carbon monoxide poisoning is like a form of slow suffocation. When you breathe in the gas, it attaches itself to hemoglobin, the oxygen-carrying protein in your blood. This reduces the oxygen-carrying capacity of your blood, starving your body of oxygen.

Signs and symptoms of carbon monoxide poisoning may include headache, fever, skin rashes, dizziness, weakness, fatigue, nausea, vomiting, shortness of breath, chest pain and trouble thinking. If your blood has too much carbon monoxide, you may lose consciousness and even die.

Carbon monoxide poisoning often sneaks up on people because signs and symptoms often come on slowly and may be mistly and may be mistaken for a cold or the flu.

One clue that you may be affected by carbon monoxide is if everyone in the same building -- including pets -- experiences similar symptoms. Another clue is if your symptoms improve when you leave the building for a day or more, then come back when you return.

In addition to getting away from the poisonous air, treatment may involve supplemental oxygen to help restore your body's normal oxygen supply. If treatment is started soon enough, most people recover completely. However, if poisoning is severe it can lead to permanent memory loss or brain damage.

Be aware of possible sources

The most common sources of carbon monoxide are gas and oil furnaces, wood stoves, gas appliances, pool heaters and engine exhaust fumes. Others include cigarette smoke and paint removers containing methylene chloride.

Cracked heat exchangers on furnaces, blocked chimneys or flues, and disconnected or blocked appliance vents can allow carbon monoxide to reach living areas. Inadequate fresh air supply to a furnace can also allow carbon monoxide to be drawn from the furnace into living spaces when you turn on an exhaust fan or clothes dryer.

Tight home construction may also increase your risk for carbon monoxide poisoning by reducing fresh air infiltration into your home.

Get a detector

Carbon monoxide detectors come in both ps come in both plug-in and battery-powered models and generally cost between $35 and $80.

Inexpensive detectors that simply change color if carbon monoxide is present aren't recommended because they don't sound an alarm.

The U.S. Consumer Product Safety Commission recommends detectors that meet the newest (1992) standards of Underwriter Laboratories Inc. The detectors sound a warning when carbon monoxide builds up slowly or quickly. Look for UL 2034 on the package.

If the alarm does sound, ventilate the area by opening doors and windows. If anyone is experiencing poisoning symptoms, evacuate immediately and call 911 or your fire department from a nearby phone. If no one is experiencing symptoms, continue to ventilate, turn off all fuel-burning appliances and have a qualified technician inspect your home.