Carbon Monoxide Safety

What is carbon monoxide and who is at risk?

Carbon monoxide (CO) is a colorless, odorless deadly gas. Because you can't see, taste or smell it, carbon monoxide can kill you before you know it's there.

Everyone is at risk for carbon monoxide poisoning. Medical experts believe, however, that individuals with greater oxygen requirements such as unborn babies, infants, children, senior citizens and people with coronary or respiratory problems are at greater risk.

Why is carbon monoxide so dangerous?

The great danger of carbon monoxide is its attraction to hemoglobin in the bloodstream. When breathed in, carbon monoxide bonds with hemoglobin in the blood, displacing the oxygen which cells need to function. When CO is present in the air, it rapidly accumulates in the blood, forming a toxic compound known as carboxyhemoglobin (COHb).

Carboxyhemoglobin causes symptoms similar to the flu, such as headaches, fatigue, nausea, dizzy spells, confusion and irritability. As levels of COHb increase, vomiting, loss of consciousness and eventually brain damage or death can result.

Where does carbon monoxide come from?

Carbon monoxide is a by-product of incomplete combustion, present whenever fuel is burned. It is produced by common home appliances, such as gas or oil furnaces, clothes dryers, ranges, ovens, water heaters or unvented space heaters, fireplaces, charcoal grills and wood burning stoves. Fumes from automobiles also contain carbon monoxide and can enter a home trough walls or doorways if a car is left running in an attached garage.

All of these sources can contribute to a CO problem in the home. If a home is vented properly and is free from appliance malfunctions, air pressure fluctuations or airway, venting or chimney blockages, carbon monoxide will most likely be safely vented to the outside. But energy-efficient insulation meant to keep warm air in during winter months and cool air in during summer months could cause carbon monoxide to be trapped inside.

Furnace heat exchangers can crack, vents and chimneys can become blocked, disconnected or corroded; inadequate air supply for combustion appliances can cause conditions known as downdrafting or reverse stacking, which force CO contaminated air back into the home.

How can I protect myself and my family from carbon monoxide poisoning?

The Consumer Product Safety Commission (CPSC) recommends installing at least one carbon monoxide detector with an audible alarm near the sleeping area. A detector on every level and in every bedroom provides extra protection. Remember, a carbon monoxide detector is a purchase that could help save your life. Select an Underwriters Laboratories Inc. (UL) listed detector. For an extra margin of safety, chose a self powered, extra sensitive unit that responds to lower levels of carbon monoxide and protects even during a power outage. The manufacturers of First Alert Carbon Monoxide Detectors make such a model, as well as a plug-in detector and a hardwired AC model with battery back-up. In addition to installing carbon monoxide detectors, have a qualified professional check all fuel burning appliances, furnaces, venting and chimney systems at least once a year or as recommended by the manufacturer.

Checklist: Where to look for problem sources of carbon monoxide in the home

1. An improperly installed or malfunctioning forced air furnace could be the source of CO and should be carefully inspected by a professional.
2. Measure the concentration of CO in the flue gases.
3. Check furnace connections to flue pipes, chimneys and venting systems to outside of the home for signs of corrosion, blockages, rust, gaps or holes.
4. Check furnace filters and filtering systems for dirt or blockages.
5. Check forced air fans for proper installation and correct air flow of flue gases. Improper furnace blower installation can result in carbon monoxide build-up because toxic gas is blown into, rather than out of the house.
6. Check the combustion chamber and internal heat exchanger for cracks, metal fatigue or corrosion - be sure they are clean and free of debris.
7. Check burners and ignition system. A flame that is mostly yellow in color in natural gas-fired furnaces is often a sign fuel is not burning completely and higher levels of carbon monoxide are being released. Remember, you can't smell carbon monoxide. 
8. Check all venting systems to the outside, including flues and chimneys for cracks, corrosion, holes, debris or blockages. Animals and birds can build nests in chimneys, preventing gases from escaping.
9. Check all other appliances that use flammable fuels such as natural gas, oil, wood, propane, coal or kerosene.
10. Appliances include: gas water heaters, clothes dryers, kitchen ranges, ovens or cooktops, wood or coal burning stoves, gas refrigerators or pressure washing machines or generators.
11. Pilot lights can be a source of carbon monoxide because the by-products of combustion are released inside the home rather than vented to the outside. Gas ovens and ranges should be monitored closely and kept in good working order. Stove tops or ovens that operate on flammable fuels should never be used to heat a residence. 
12. Be sure space heaters are vented properly. Unvented space heaters that use flammable fuel can release carbon monoxide into the home.
13. Barbecue grills and hibachis should never be operated indoors or in an enclosed space such as a garage, even with the door open.
14. Check fireplaces for closed, blocked or bent flues, soot and debris. When operating a fireplace and a furnace at the same time, experts recommend opening a window a crack to equalize the pressure so the combustion gasses can flow freely up and out the chimney.
15. Check the clothes dryer vent opening outside the house to be sure it's free of any blockage such as lint or debris.

If initial testing does not confirm the presence of carbon monoxide, there may be several reasons:

• Testing equipment used to measure the presence of carbon monoxide in the air must be calibrated to sense low levels of CO concentration.
• Testing equipment should be capable of sensing levels as low as one part per million. For example, Underwriters Laboratories' standard for residential carbon monoxide detectors requires detectors to alarm before 90 minutes of exposure to 100 parts per million of carbon monoxide.
• If initial readings don't reveal sufficient concentration of carbon monoxide to set off the alarm, digital measurement testing equipment that produces a printed 24-hour record can be used to help identify.
• If doors or windows are left open or appliances are turned off and outside air enters the home, carbon monoxide can dissipate. This creates a lower reading than the level that triggered the alarm.
• To help assure proper measurement, carbon monoxide readings should be conducted as soon as possible after an alarm incident.
• If appliances, flues and chimneys are confirmed to be in good working order, the source of carbon monoxide leaks may be from a car left running in an attached garage or from downdrafting.

"Downdrafting" exists primarily in newer, more energy-efficient, "airtight" homes. Flue gases normally vent to the outside through flues and chimneys. When many exhaust fans are on, air pressure inside an airtight home may become lower than outside, causing flue gases that normally exit the house to turn around and flow back into the home.

Inadequate air supply in a room where two or more combustion-driven appliances share the same air source, such as: a water heater and furnace in an unvented utility closet, can create a more complicated form of downdrafting called reverse stacking.

This occurs when none appliance, such as the furnace, turns on and is unable to get adequate fresh air: When the furnace operates, it then draws CO contaminated air from the water heater exhaust and spreads polluted air throughout the house. 

A sticking thermostat can keep the furnace running continually, depleting the oxygen supply in the house.

In multiple family dwellings where living spaces share walls and pipes, carbon monoxide from one unit may enter a neighboring space through floor boards, cracks or underneath doors.

Car exhaust, which contains carbon monoxide, can enter the home when a car is left idling in an attached garage. . .even if the garage door is left open.