Carbon monoxide, a colorless, odorless and tasteless gas, is responsible for more than 200 accidental deaths each year, according to the Consumer Product Safety Commission. Thousands more are stricken with its symptoms — mild headaches, dizziness, flu-like symptom and tiredness — and are unaware of the cause.

 

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The usual culprit is a faulty fuel-burning appliance, such as gas or oil furnaces and hot-water heaters, fireplaces, gas stoves, and unvented gas or kerosene heaters. Car exhaust fumes that filter indoors from attached garages and become trapped are another common source, especially in homes where the garage is below the living space.

Young children, pregnant women and people with asthma, anemia or heart or lung disease are especially vulnerable to the toxic effects of carbon monoxide, even in small doses, according to the EPA.

Proper appliance maintenance is the best way to reduce the risk of carbon monoxide poisoning, but a device that constantly monitors the air is a crucial backup, says Edward Groth, an environmental health expert for Consumer Reports magazine.

Carbon monoxide poses the biggest health threat in most homes, says David Kibbey, an environmental building consultant in Berkeley.

"Most people are familiar with the idea of an auto in a closed garage, but they don't realize (carbon monoxide) is a byproduct of any combustion appliance,'' he says. "It is a common problem here where you have a garage below a living space, usually a bedroom. It is very hard to seal, and it is where you spend the most amount of time, making it quite dangerous.''

Rebecca Fall and her husband, Scott Kauffman, count their family among the lucky few who were able to identify — and solve — a carbon monoxide problem before it became a tragedy.

"I just noticed that one morning Caleb got up and his cheeks were just bright, bright red,'' says Fall of the couple's son, now 6. It was the winter of 1992 and the family (including son Emmett, now 4) had just moved into a San Francisco duplex.

She had noticed a peculiar exhaust smell and felt dizzy in the mornings after turning on the heater, but she couldn't determine its origin. Caleb's condition that morning was the final straw. Seeking the help of an environmental consultant, she called Kibbey.

Kibbey found that a large hole had been unwittingly carved out by a plumber doing work in the area between the garage and Caleb's bedroom above. When the heat was turned on in the mornings and the other owner warmed up his car in the garage, the exhaust was sucked inside the home.

The hole was fixed for about $1,000.

"We were fortunate we could detect the smell,'' says Fall, whose family later moved to a nearby single-family home. "It could have been a disaster.''