Carbon monoxide is a known, silent killer. Carbon monoxide poisoning produces symptoms that are easily blamed on something else: headaches, fatigue, and dizzy spells.

Keep this killer at bay by knowing its sources, knowing its signs and knowing how to stay safe, says a North Dakota State University safety specialist. Headaches caused by carbon monoxide in the air result from a lack of oxygen in the blood going to the brain. Bluish fingernails are a result of oxygen-deprived blood. Carbon monoxide reduces the ability of the blood to carry oxygen. This blood does not have the bright red color of healthy blood but has a bluish tint which can be seen through the fingernails.

"Carbon monoxide can affect you at very low levels, as little as one tenth of a percent, causing chronic headaches, fatigue, dizzy spells, and confusion," says George Maher of the NDSU Extension Service. "It affects everyone; senior citizens, youngsters, the unborn, and average people, too." The oxygen-carrying capacity of hemoglobin in the blood is reduced by carbon monoxide producing these symptoms. Carbon monoxide accumulates in the blood, and the level of can be determined by a doctor with a carboxyhemoglobin test.

With furnaces and space heaters coming into use, the dangers of carbon monoxide become more common. "If combustion gases are present in the air, carbon monoxide will be there too," Maher says. "But, carbon monoxide can be present without the presence of other gases of combustion. It is a by- product of the combustion of flammable fuels."

Common producers of carbon monoxide are gas or oil furnaces, gas or oil water heaters, fuel burning space heaters, wood stoves, gas ranges, charcoal grills, and gas grills. "If you have any of these appliances that burn a fuel then you really can’t afford not to have a carbon monoxide detector. It is essential to monitor the safety of your home," he says.

"A furnace with a cracked or burned-through heat exchanger can produce all of the above mentioned symptoms," Maher notes. "The end result can be fatal." If a heat exchanger is defective it can allow combustion gases, carbon monoxide for one, to enter your home from the burning fuel. The gases are distributed throughout the house by your hot air vents. It can be a deadly situation.

Homes with attached garages have been found to have much higher levels of carbon monoxide than homes with un-attached garages due to automobile engines running while parked in the attached garage.

"Carbon monoxide is produced by automobile engines, gasoline and diesel, in very dangerous quantities and is drawn into the house through doorways connecting the garage to the house," Maher notes. "Even small engines such as those on snow blowers and lawn mowers should never be run in a garage with the doors closed. Always open the garage door before starting any engine in the garage, and wait to close the door a few minutes after stopping the engine."

Likewise, it is never safe to operate any kind of grill, charcoal or gas, in the attached garage of your home, even if the doors are open, he says.

Very dangerous levels of carbon monoxide will be produced by the burning fuel. Always do the grill cooking outdoors to minimize the levels of carbon monoxide in your home.

Even using a wood stove in an attached garage, either for heating or disposing of waste paper, is a dangerous practice that can produce dangerous carbon monoxide levels. "Only an approved and properly installed heating system should be used in a garage attached to your home," Maher says.

A smoke detector may not alert you to low levels of carbon monoxide in the air, but a carbon monoxide detector will. If it goes off, producing the warning signal, get out of the house immediately. Call the fire department from a neighbor’s house or a cell phone, but do not enter the house until the firemen determine it is safe to do so.

"Regardless of which detector is selected for use in your home, maintain it with care. Replace the battery when it is needed, and test on a regular, weekly basis," Maher says. "Know that it is operating the way it is supposed to, and then live and sleep a little more securely."