Firefighter Health & Wellness: Carbon Monoxide: A Silent Hazard

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.

The effects of decreased oxygenation within the body are profound. Carbon monoxide toxicity results in a range of symptoms, depending on the actual concentration of CO in the blood. Low levels of CO in the blood result in generalized symptoms that are non-specific and may be misinterpreted as common cold or flu-like symptoms. This includes nausea, vomiting, headache, malaise (the sensation of feeling ill), dizziness, muscle aches and mild confusion.

Higher levels of CO in the blood will lead to more profound neurologic symptoms as a result of decreased oxygenation to the central nervous system. This includes more pronounced confusion, decreased level of consciousness, coma, seizures and death. Again, since CO levels in the blood will rise more rapidly in physically active individuals, firefighters working at a structure fire may experience symptoms within a shorter period. Firefighters exposed to the byproducts of combustion and who exhibit signs or symptoms of CO toxicity they should be transferred to an emergency department immediately for assessment. Personnel assigned to the rehab sector at incidents should be aware of the signs and symptoms of CO poisoning to be able to identify these symptomatic firefighters.

To prevent CO toxicity, firefighters must first be knowledgeable about the condition and consider it whenever a smoke condition or combustion exists in a structure. Fire departments should also have standard operating procedures (SOPs) or standard operating guidelines (SOGs) concerning removal of SCBA during interior operations at structure fires. All structures with smoke conditions should be monitored for CO to ensure toxic levels of CO do not exist. This includes smoke conditions due to fireplace issues, heating appliance malfunctions, burning wires, food on the stove, chimney fires and similar hazardous conditions.

This procedure should identify the CO level that is deemed safe to remove SCBA. The permissible occupational exposure level (PEL) for CO according to the Occupational Safety and Health Administration (OSHA) is 25 PPM. The PEL is maximum exposure to a chemical a worker can have over an eight-hour period without ill effects. The PEL established by OSHA is a reasonable limit to adopt as the safe level to remove SCBA during interior operations.

The guideline should also clearly identify who is responsible to give the “all clear” to remove SCBA. Some departments designate this responsibility to the incident safety officer, other departments make this the responsibility of the interior operations officer. As with all responsibilities on the fireground, if this responsibility is not formally delegated through standard guidelines, the incident commander assumes the responsibility of giving the “all clear” to remove SCBA. Having a formal policy concerning SCBA removal at structure fire allows the incident commander to focus attention on other, more variable operational issues. The policy will also help prevent unnecessary firefighter exposure to CO operating at the scene if SCBA is not allowed to be removed unless the “all clear” is given.



CO is an odorless, colorless gas that is present during all structure fires and is present when combustion is occurring. Structures should be monitored for CO whenever a smoke condition is present in a structure as high levels of CO may exist even with light smoke conditions.

Departments should adopt guidelines regarding CO monitoring at structure fires. Personnel should remain on SCBA until the “all clear” to remove SCBA is given based on CO monitoring. Rehab personal should be aware of the signs and symptoms of CO poisoning to be able to identify firefighters who might have suffered CO poisoning. Firefighters with signs or symptoms of CO poisoning should be transferred to emergency departments for further evaluation.

Preventing CO poisoning requires awareness that CO could be present when any smoke condition or fire condition is present. To accomplish this, CO must always be suspected when smoke or fire is present in a structure.