Where there's combustion, there's carbon monoxide. It could be from a woodstove, fireplace, gas range or even a car in the garage.

Burning any fuel produces carbon monoxide. When combustion appliances operate properly, there's little risk. However, poor maintenance, improper installation, damaged equipment or improper construction practices can allow flue gases containing CO (and other hazardous gases) to spill into the building.

CO has been called the "silent killer." You can't see it, smell it or taste it. The symptoms of low level exposure (headache, dizziness, nausea and fatigue) are easily mistaken for the flu. Children, pregnant women, elderly people and cardiac patients can be especially sensitive. According to the U.S. Consumer Product Safety Commission (CPSC), carbon monoxide (CO) poisoning kills between 200 and 300 people each year in their own homes. Some health experts fear that CO poisoning has been under reported and is more serious than statistics indicate.

The current workplace standard set by the Occupational Health and Safety Administration says that CO concentration can't average more than 50 parts per million (ppm) over eight hours. Standards set by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) say CO shouldn't exceed 9 ppm.

CO in a home without combustion appliances is typically 0.5 to 5 ppm, which is the same as the outdoor air. Cooking over a gas range can add 5 to 10 ppm. Unvented space heaters have been shown to raise the concentration to as much as 39 ppm. Even vented appliances can release CO into the home if they malfunction due to improper installation or maintenance.

The only sure way to avoid problems would be not to install combustion devices. That would mean no fireplaces, wood stoves, gas ranges, gas or oil furnaces, etc. Isolating the water heater and furnace in a garage that's sealed off from the living spaces is another possibility.

CO Detectors

Properly working carbon monoxide detectors can provide an early warning to occupants before the gas builds up to a dangerous level. They look like smoke detectors and warn occupants when the CO concentration reaches a certain level. The CPSC believes that CO detectors are as important to home safety as smoke detectors.

When shopping for a CO detector, be sure to select one with a label showing it meets the Underwriters Laboratories Standard 2034.

Six companies make detectors meeting UL 2034 . The detectors range in price from $40 to $100.

The UL Standard targets high concentration exposures. The health effect of long-term exposure to low concentrations isn't clear. However, one indication that lower concentrations should cause concern is the much lower level listed in Occupational Safety and Health Administration and ASHRAE standards.

Detector manufacturers can exceed the UL standard by making their products more sensitive. For example, Nighthawk makes a monitor with a numeric display that shows CO concentration down to about 5 ppm. Also, the alarm sounds if 30 ppm last for two hours.

Like smoke alarms, a CO detector should be mounted to the ceiling in a hallway near bedrooms. For additional safety, it's a good idea to place another detector near the combustion equipment. When the alarm sounds everyone in the building should leave immediately.

For recorded messages on CO, call the CPSC at 800-638-2772. Message 802 describes the dangers of CO and message 168 lists CO detectors that meet UL 2034.

Codes

In September 1993, the City of Chicago became one of the first jurisdictions to pass an ordinance requiring CO detectors. All new single-family homes and existing single-family homes with new oil- or gas-fired furnaces must have CO detectors.

A CO detector is cheap insurance for homes that are known to have a greater risk.