Fire causes carbon monoxide (CO), which is a serious safety hazard resulting from the chemical process of burning. Carbon monoxide is a colorless, odorless, and tasteless gas, meaning its presence cannot be detected by human senses. CO is a byproduct of combustion, the chemical reaction that occurs when any carbon-based fuel burns, making it a danger anytime a fire is present or a fuel-burning appliance is operating.
The Chemistry of Carbon Monoxide Formation
Carbon monoxide is specifically produced through a process called incomplete combustion, which occurs when there is a limited supply of oxygen available to fuel the fire. When a carbon-based fuel, such as wood, natural gas, or gasoline, burns with sufficient oxygen, the reaction is called complete combustion and produces primarily carbon dioxide ($\text{CO}_2$) and water ($\text{H}_2\text{O}$). When the air supply is restricted, the carbon atoms in the fuel do not fully oxidize.
Instead of forming a molecule with two oxygen atoms ($\text{CO}_2$), the carbon atoms bond with only one oxygen atom, resulting in carbon monoxide ($\text{CO}$). This incomplete reaction is inefficient and releases less energy than complete combustion. A yellow or sooty flame in an appliance is often a visual indicator that incomplete combustion is taking place and carbon monoxide is being generated.
Why Carbon Monoxide is a Silent Killer
Carbon monoxide starves the body of oxygen without providing any sensory warning. Once inhaled, CO rapidly passes through the lungs and enters the bloodstream, where it interferes with the function of red blood cells. The gas binds to hemoglobin, the protein responsible for transporting oxygen, with an affinity approximately 250 times greater than that of oxygen itself.
When CO binds to hemoglobin, it forms a compound called carboxyhemoglobin ($\text{COHb}$), effectively displacing the oxygen that should be carried to the body’s tissues and organs. This drastically reduces the blood’s capacity to deliver oxygen, leading to tissue hypoxia, or oxygen deprivation. Symptoms of mild to moderate CO poisoning can be mistaken for the flu, including headache, dizziness, and nausea. As exposure continues, a person may experience confusion, loss of consciousness, and eventually death due to the lack of oxygen reaching the brain and heart.
Common Household Sources of CO
While fire is the source of carbon monoxide, the gas is often generated by contained combustion in common household appliances. Any device that burns fuel, such as gas furnaces, water heaters, and gas stoves, has the potential to produce CO, especially if the appliance is malfunctioning or improperly vented. Blocked chimneys and flues prevent exhaust from escaping, forcing the gas back into the living space.
Other sources include portable kerosene or gas heaters, which can quickly deplete the oxygen in a room and cause incomplete combustion. Car exhaust also contains carbon monoxide, making it unsafe to run a vehicle inside an attached garage, even briefly. Portable generators pose a significant risk if they are not placed outdoors and at least 20 feet away from windows, doors, or vents.
Detection and Immediate Safety Measures
The only reliable way to detect CO is by installing carbon monoxide detectors. For maximum protection, a detector should be installed on every level of the home, including the basement, and near all sleeping areas. These devices should be regularly tested and replaced according to the manufacturer’s instructions, typically every five to ten years.
If a carbon monoxide alarm sounds, the immediate course of action is to evacuate the premises and move everyone, including pets, to fresh air outdoors. Opening windows and doors only provides temporary ventilation and should not be relied upon as a solution. Once safely outside, call the fire department or emergency services, and do not re-enter the building until emergency personnel have determined the air is safe. If anyone is experiencing symptoms of poisoning, they should seek immediate medical attention.