Carbon monoxide (CO) is a colorless, odorless, and tasteless gas, making it impossible to detect without specialized equipment. This invisibility makes it extremely dangerous, earning it the nickname “silent killer.” The gas is toxic because it binds to hemoglobin in the bloodstream, displacing the oxygen responsible for transport throughout the body. By displacing oxygen, carbon monoxide rapidly starves the body’s tissues and organs, leading to severe illness or death.
The Chemistry of Incomplete Combustion
Carbon monoxide is a byproduct of incomplete combustion, a chemical reaction that occurs when carbon-containing materials burn with a restricted supply of oxygen. Every fuel source, from natural gas to wood or gasoline, contains carbon atoms intended to combine with oxygen (\(\text{O}_2\)) during burning. When oxygen is plentiful, the fuel undergoes complete combustion, fully oxidizing the carbon atoms to form carbon dioxide (\(\text{CO}_2\)) and water vapor.
The formation of carbon monoxide occurs when the air-to-fuel ratio is unbalanced, meaning there is insufficient oxygen available to complete the reaction. In this oxygen-starved environment, carbon atoms are only partially oxidized, resulting in the creation of carbon monoxide (\(\text{CO}\)). This partial oxidation releases less energy than complete combustion and generates the toxic gas.
Everyday Sources of Carbon Monoxide
Any appliance or engine that burns fuel has the potential to produce carbon monoxide, making it a common residential hazard. Fuel-burning appliances, such as furnaces, boilers, and water heaters, are primary sources, especially if they are malfunctioning or improperly vented. Gas-powered cooking appliances, including stoves and ovens, can also emit CO if they are not maintained or are used incorrectly, such as using them to heat a room.
Internal combustion engines represent another major category of sources, including vehicles and portable power equipment. Running a car in an attached garage allows exhaust containing CO to seep into the home. Portable generators produce extremely high levels of the gas and must be operated far away from windows and doors.
Even seemingly benign sources contribute to indoor CO levels through incomplete burning:
- Fireplaces and wood-burning stoves produce carbon monoxide if their chimneys or flues are blocked.
- Items designed for outdoor use, such as charcoal grills and camping stoves, become dangerous when brought inside enclosed spaces like tents or cabins.
- Tobacco smoke contains significant levels of the gas, contributing to overall CO exposure for individuals in a confined space.
Conditions That Increase CO Formation
The factors that shift combustion from complete to incomplete revolve around limiting the oxygen supply or lowering the reaction temperature. Poor ventilation is the most common and direct cause, as it rapidly depletes the oxygen available near the appliance or engine. A blocked chimney, a damaged exhaust pipe, or operating a fuel-burning device in a sealed room quickly creates an oxygen-poor environment.
Lower operating temperatures also increase the production of CO, as the heat may be insufficient to fully sustain the oxidation reaction to form \(\text{CO}_2\). Equipment malfunction or lack of maintenance often leads to inefficient burning, which is signaled by a yellow or orange flame on a gas appliance that should normally burn blue.
Soot buildup on appliance surfaces or excessive moisture condensation on windows can also signal that the combustion process is not completing. These operational issues directly facilitate the partial oxidation of carbon atoms, pushing the chemical reaction toward the formation of the toxic gas.