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Over the past two decades, carbon monoxide (CO) has gained attention as a hazard to the public. Most firefighters associate CO with routine runs, as carbon monoxide detector activations are frequent responses.
Carbon monoxide is commonly associated as a hazard to citizens due to heating appliance malfunctions or poor ventilation. However, CO is a byproduct of combustion and present at every fire. Carbon monoxide should be considered as a possible hazard at all incidents where combustion is present. It should be always considered a hazard during actual firefighting operations. It is particularly hazardous at structure fires where enclosed spaces trap the byproducts of combustion and individuals breathe the ambient air.
Carbon monoxide is a colorless, odorless gas that is the result of incomplete combustion of carbon-based products such as wood, plastics, other petroleum-based products and synthetic materials. All residential occupancies today are loaded with carbon-based fuel. Many carbon-based fuels are also found in commercial and industrial occupancies. This means that carbon monoxide will be present at every structure fire.
Where CO Lingers
Since carbon monoxide is colorless, odorless and non-irritating, it is essentially undetectable by the human senses. This is important because even though smoke will be evacuated from a structure, significant levels of CO will still linger in the structure. This can occur during overhaul operations when masks are removed as soon as the smoke partially clears. Also, seemingly minor incidents may have the potential to create significant levels of CO. A smoke condition from a closed flue in a fireplace, a furnace backfire and a chimney fire are examples where hazards are minimal, but significant CO levels may exist with light or minimal smoke conditions. This also includes the use of power equipment in a structure during operations. Gas-powered appliances all produce carbon monoxide. Whenever gas-powered equipment is used in an enclosed structure, the atmosphere should be monitored for CO.
The severity of CO exposure is dependent on several different factors. Carbon monoxide poisoning is determined by the level of the CO in the ambient atmosphere, the length of exposure and the ventilation rate of the individual. The ventilation rate is the volume of air times the number of breaths per minute that an individual breathes over the course of a minute. A person at rest will have a lower respiratory rate and will move less air over a minute than a person who is working and breathing faster and deeper.
Firefighters doing strenuous physical activity are breathing faster and deeper and therefore will have a greater exposure to CO. They will suffer the toxic effects of CO quicker due to higher CO ingestion due to their respiratory rate. This is an important concept for firefighters because firefighting is extremely hard work. Firefighters will have a high ventilation rate while working at a structure fire. If firefighters are working without the protection of self-contained breathing apparatus (SCBA) in an environment with significant levels of CO in the air, they will be at greater risk for toxicity over a shorter period due to the physical nature of firefighting.
Toxicity of CO
Carbon monoxide exerts its toxicity on the body by reducing the amount of oxygen that red blood cells transport in the bloodstream. Oxygen is distributed to the body by the red blood cells. Normally oxygen is picked up in the lungs and delivered by the red blood cells to the peripheral tissues in the body. Carbon monoxide has a much higher affinity than oxygen for red blood cells, nearly 220 times that of oxygen. If CO is present, it will bind to the red blood cells and prevent oxygen from binding, effectively displacing oxygen being transported throughout the body.