Carbon Monoxide Exposure Risk Calculator

What this carbon monoxide exposure calculator does

This calculator estimates the percentage of carboxyhemoglobin (COHb%) in the blood based on an assumed constant carbon monoxide (CO) concentration and an exposure duration. It uses a simplified version of the Coburn‑Forster‑Kane (CFK) model to provide an approximate value for educational and planning purposes.

The tool is intended for homeowners, safety officers, industrial hygienists, and healthcare learners who want a rough sense of how sustained CO levels and time of exposure can influence blood COHb%. It is not designed to diagnose poisoning, guide treatment, or determine whether it is safe to stay in or re‑enter a space.

Emergency disclaimer: If you suspect carbon monoxide exposure or notice symptoms such as headache, dizziness, nausea, confusion, chest pain, shortness of breath, or collapse, leave the area immediately and call emergency services. Do not rely on this calculator to decide whether to seek urgent medical care.

Background: carbon monoxide and carboxyhemoglobin

Carbon monoxide is a colorless, odorless gas produced whenever fuels such as gasoline, natural gas, propane, wood, or charcoal burn without enough oxygen. Because it cannot be seen, smelled, or tasted, people may be exposed without realizing it, especially in enclosed or poorly ventilated spaces.

When inhaled, CO binds to hemoglobin in red blood cells with much higher affinity than oxygen does. The resulting compound is called carboxyhemoglobin (COHb). As the proportion of hemoglobin that is tied up as COHb increases, less is available to carry oxygen to tissues. This leads to tissue hypoxia and can damage the brain, heart, and other vital organs.

Even relatively modest CO levels can become dangerous over time if exposure continues. Higher concentrations can cause serious symptoms or death within minutes. Because carbon monoxide gives no sensory warning, properly installed and maintained CO alarms are essential in homes and workplaces that use fuel-burning appliances.

How the calculator estimates COHb%

Detailed toxicology models describe CO uptake and elimination using the Coburn‑Forster‑Kane (CFK) equation, which accounts for factors such as ventilation (breathing) rate, blood volume, and baseline COHb. For a simple risk-awareness tool, a linear approximation is often used for early exposure periods and moderate concentrations.

In this calculator, we treat the CO concentration as constant during the exposure and estimate the resulting COHb% using a proportional relationship between concentration and time. Let:

• C = carbon monoxide concentration in parts per million (ppm)
• t = exposure duration in hours
• COHb% = estimated percentage of hemoglobin bound to CO

The simplified formula can be written in standard mathematical notation as:

or, in plain text: COHb% = 0.16 × C × t

Key points about this simplified model:

• It assumes a non‑smoking adult at rest with normal lung function.
• It assumes the CO level is roughly constant over the exposure period.
• It treats COHb% as increasing approximately linearly with both concentration and time during the early phase of exposure.
• It does not model elimination (how COHb decreases after you leave the exposure) or repeated intermittent exposures.

The proportionality constant 0.16 is based on typical uptake rates observed in controlled studies and is meant to provide a rough, order‑of‑magnitude estimate rather than a personalized prediction.

Interpreting your estimated COHb%

Different organizations (such as the CDC, WHO, and national occupational safety agencies) describe somewhat varying symptom thresholds. The ranges below are approximate and assume a healthy, non‑smoking adult at rest. Children, pregnant people, older adults, and those with heart or lung disease may experience serious effects at lower COHb levels.

Important: Symptoms do not correspond perfectly to a single COHb number, and individuals vary widely. Some people become very ill at lower percentages, while others may appear relatively well even at higher levels. Do not wait for the calculator to show a specific threshold before seeking help if you feel unwell or suspect exposure.

Worked example

Suppose a person spends time in a poorly ventilated garage where a gasoline engine is running, and a CO monitor later shows that the average concentration was about 100 ppm for two hours.

Step 1: Convert the exposure time into hours (if necessary). In this example, the duration is already 2 hours, so t = 2.

Step 2: Plug the values into the simplified formula:

In plain text:

COHb% = 0.16 × 100 × 2 = 0.16 × 200 = 32%

An estimated COHb of around 32% falls into a range where serious neurological and cardiac symptoms are expected for many adults. This would be considered a medical emergency, even though the exact real‑world COHb value might be somewhat higher or lower than the estimate.

In practice, anyone exposed to that concentration for that length of time should leave the area immediately and seek urgent medical evaluation, regardless of what the calculator shows.

Model assumptions and limitations

Any calculator that condenses a complex physiological process into a single formula must make strong simplifying assumptions. Understanding these limitations is essential for safe use.

Key assumptions

• Non‑smoking adult at rest: The model assumes an average adult who is not smoking and is sitting or performing only light activity. Smokers often have elevated baseline COHb levels, and exercise can increase CO uptake.
• Stable CO concentration: The formula treats the CO level (in ppm) as constant over the entire exposure period. Real environments may have rapidly changing CO levels (for example, engines turning on and off).
• Single continuous exposure: It assumes one uninterrupted exposure interval rather than multiple shorter exposures separated by time in clean air.
• Normal cardiopulmonary function: It does not adjust for chronic lung disease, anemia, heart disease, pregnancy, childhood, or advanced age, all of which can change both susceptibility and CO kinetics.
• Short to moderate exposure duration: The linear approximation best fits early exposure periods. At longer durations or higher concentrations, the relationship between COHb%, concentration, and time becomes nonlinear.

What the calculator does not do

• It does not measure COHb levels in your blood; only a blood test or certain medical devices can do that.
• It does not incorporate multiple different concentrations over time (for example, varying readings from a data-logging monitor).
• It does not reflect the effect of treatment, such as breathing 100% oxygen or using hyperbaric oxygen therapy.
• It does not provide personalized medical advice or determine whether it is safe to stay in a location.

Because of these limitations, the estimated COHb% should be treated only as a rough educational indicator. In real incidents, safety professionals and clinicians rely on direct CO measurements, patient symptoms, exposure history, and laboratory tests rather than a single model output.

When to seek emergency care

Carbon monoxide poisoning can progress quickly and may be fatal. You should seek immediate emergency help (such as calling your local emergency number) if:

• A CO alarm sounds and you feel unwell.
• You notice headaches, dizziness, nausea, confusion, or chest pain in a setting where CO exposure is possible (for example, near running engines, fuel-burning heaters, or during a fire).
• Multiple people or pets in the same environment develop similar symptoms at the same time.
• You lose consciousness or witness someone collapse in a potentially contaminated area.

Leave the building or area immediately, move to fresh air, and call emergency services from a safe location. Do not re‑enter until qualified responders say it is safe, even if you feel better or the calculator suggests a low or moderate estimated COHb%.

Practical use tips

If you are using a CO monitor, you can enter the approximate average concentration during the exposure window, together with the total time spent in that environment. Some examples:

• Home heating malfunction: An indoor monitor records 30–50 ppm over several hours near a gas furnace. You might enter a midpoint (for example, 40 ppm) and the total time you were in that space.
• Garage or workshop: A vehicle or generator is running indoors with partial ventilation, and a handheld meter shows sustained readings around 80 ppm while you work there for 1.5 hours.
• Occupational exposure: In a workplace, you may compare the calculator's rough estimate with applicable occupational exposure limits, always deferring to official guidelines and professional industrial hygiene assessments.

Treat the output as a prompt to improve ventilation, check equipment, or consult safety professionals—never as a guarantee that current conditions are safe.

FAQ

Can you smell or see carbon monoxide?

No. Carbon monoxide is colorless and odorless. You cannot rely on your senses to detect it. Only CO alarms and measurement devices can reliably detect elevated levels indoors.

What CO level is dangerous indoors?

Guidance varies by organization, but prolonged exposure to levels above about 9 ppm is generally considered undesirable for residential indoor air. Short-term exposures above 35 ppm are a concern, and sustained levels of 100 ppm or more are considered hazardous. However, susceptibility varies, and symptoms can occur at lower levels in vulnerable individuals.

How quickly can carbon monoxide poisoning develop?

At high concentrations (for example, from running engines in enclosed spaces), serious poisoning can develop within minutes. At lower levels, symptoms may build over hours. Because of this, any suspected exposure should be taken seriously, regardless of duration.

Does exercise or heavy work change CO risk?

Yes. Exercise increases breathing rate and cardiac output, which can speed the rate at which CO enters the bloodstream. The simplified calculator does not adjust for this, so it may underestimate COHb% for people doing heavy physical work during exposure.

Where can I learn more about CO safety?

For detailed guidance on carbon monoxide prevention, symptoms, and treatment, consult reputable sources such as your national public health agency, fire safety authorities, or occupational safety organizations. Many of these organizations publish accessible CO safety fact sheets and recommendations for alarm placement and maintenance.

Summary and responsible use

This carbon monoxide exposure risk calculator provides a simplified, model-based estimate of carboxyhemoglobin percentage as a function of CO concentration and exposure duration. It is useful as an educational tool to illustrate how both concentration and time drive risk, but it is inherently limited and cannot replace professional assessment, direct measurements, or medical testing.

Always prioritize real-world safety actions—ventilation, equipment maintenance, CO alarms, and rapid medical evaluation if exposure is suspected—over any numerical estimate. When in doubt, act as though the risk is higher than the calculator suggests.