Carbon Monoxide

Do you know anyone who smokes? Cigarettes release a colourless but dangerous gas called carbon monoxide. Or maybe you have seen a carbon monoxide detector in your house. Carbon monoxide poisoning kills approximately 30 people in England and Wales every year. Many other sufferers will experience chronic side effects. This poisoning is often caused by faulty engines, boilers, and cookers. How can a regular household appliance lead to long-term health problems? Read on to find out!

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Table of contents

    Carbon Monoxide Structure

    Let's start off with the basics. What is carbon monoxide?

    Carbon monoxide is a poisonous gas produced by incomplete combustion of carbon-based fuels.

    Carbon monoxide (CO) is an odourless, colourless, and tasteless gas. It's made of a carbon atom and an oxygen atom joined by a triple bond.

    Carbon monoxide is present in the Earth's atmosphere at very low concentrations. In the troposphere, the concentration ranges from 50 to 100 ppb (parts per billion). Natural sources of carbon monoxide in Earth's atmosphere include volcanic eruptions and bushfires. However, humans contribute vast quantities of carbon monoxide to the atmosphere, mostly as vehicle emissions.

    The carbon monoxide levels in urban areas are around 10 ppm (parts per million) - about 100 times greater than in Earth's atmosphere overall!

    Triple bonds (≡) are the strongest chemical bonds in existence; they have the highest bond dissociation energy.

    The bond dissociation energy is the amount of energy required to break the molecule apart.

    The CO bond in carbon monoxide is the strongest, with a bond dissociation energy of 1072 kJ/mol. In second place is the bond found in molecules of nitrogen gas (N≡N), at 946 kJ/mol. Their high bond dissociation energy is what makes these gases inert (unreactive).

    Carbon Monoxide vs Carbon Dioxide

    This table summarises the differences between carbon monoxide and carbon dioxide.

    PropertyCarbon MonoxideCarbon Dioxide
    Chemical FormulaCOCO2
    Structure1 carbon atom and 1 oxygen atom1 carbon atom and 2 oxygen atoms
    DensityLighter than airHeavier than air
    ToxicityExtremely toxic, can be fatalOnly at very high amounts

    Sources of Carbon Monoxide

    Carbon monoxide is produced by the incomplete combustion of carbon-based fuels. The formula equation is:

    CO2 + C ⇾ 2CO

    Common domestic sources of carbon monoxide pollutants include:

    • Gas ovens and cookers

    • Boilers

    • Fires (wood, gas, coal)

    • Heaters powered by paraffin or gas

    • Portable generators

    • Barbecues

    • Camping stoves

    • Engines (cars, lawnmowers, etc.)

    Effects of Carbon Monoxide

    To understand how carbon monoxide affects the body, you first need to know about red blood cells. These small, biconcave cells contain a red protein called haemoglobin. This protein combines with oxygen molecules to form oxyhaemoglobin, allowing easy transport of oxygen from the lungs to the tissues. An oxygen molecule has a choice of four specific binding sites on the haemoglobin molecule.

    If carbon monoxide is inhaled, it can rapidly accumulate in the bloodstream. The haemoglobin in red blood cells is up to 300 times more likely to take up carbon monoxide molecules than oxygen. As a result, it becomes very difficult for oxygen to bind to haemoglobin due to competition for the same binding sites. When haemoglobin binds to carbon monoxide, it creates carboxyhaemoglobin instead of oxyhaemoglobin.

    A pulse oximeter is a small device that clips over the fingertip. It indirectly measures the oxygen saturation of a patient's blood. However, it is unable to determine if somebody is suffering from carbon monoxide poisoning because it cannot detect the difference between carboxyhaemoglobin and oxyhaemoglobin.

    Symptoms of Carbon Monoxide Poisoning

    Carbon monoxide poisoning occurs when carboxyhaemoglobin is formed in red blood cells, reducing the body's ability to transport oxygen.

    Early symptoms of carbon monoxide poisoning are easily confused with food poisoning, viral infections, flu, or tiredness. The symptoms to be aware of are:

    • Headaches or dizziness

    • Nausea

    • Loss of consciousness

    • Breathlessness

    • Abdominal pains

    • Visual problems

    • Erratic behaviour

    • Tiredness

    Prolonged exposure can lead to long-term effects such as brain damage, coronary heart disease, incontinence, and Parkinsonism.

    Parkinsonism is an umbrella term used to describe symptoms of physical stiffness, tremors, and slow movements.

    In extreme cases, carbon monoxide poisoning can lead to death. Parts of the body experience oxygen starvation and tissue death. Furthermore, carbon monoxide can combine with proteins, damaging cells and organs.

    High-Risk Individuals

    Some people face a higher risk of developing carbon monoxide poisoning.

    Age: unborn babies, infants and older adults are most at risk.

    Altitude: those living at higher altitudes are more at risk due to a lower atmospheric concentration of oxygen.

    Pre-existing conditions: respiratory problems, coronary heart disease, anaemia increase the chances of developing carbon monoxide poisoning.

    Lifestyle: smokers face a high risk, and those with certain jobs may be exposed to high levels of carbon monoxide (e.g. firefighters, garage mechanics, welders).

    Diagnosis and Treatment

    If somebody is suspected to have carbon monoxide poisoning, they will be given a blood test to detect unusually high levels of carboxyhaemoglobin.

    For non-smokers, a carboxyhaemoglobin level of 3-4% is outside normal limits.

    Medical professionals may require an electrocardiogram (ECG) to check for ischaemia, irregular heart rhythms, and to assess overall heart function.

    Ischaemia is a lack of blood supply to the heart. This condition is serious and often fatal.

    To treat carbon monoxide poisoning, the affected person will be removed from the area of exposure. In hospital, they will then be given an oxygen mask to breathe through or provided with hyperbaric oxygen therapy (HBOT).

    During HBOT, the patient breathes pure oxygen in a pressurised environment. This therapy is commonly used to treat decompression sickness, infections, and radiation injuries.

    Poison Prevention: Carbon Monoxide Detectors and Controls

    To prevent carbon monoxide poisoning in the home, it's important to:

    • Make sure that any appliances are properly installed and maintained regularly

    • Ensure boilers are serviced regularly

    • Chimneys are kept clean and well-maintained

    • Don't use barbecues or camping stoves indoors or inside a tent, or leave engines running inside garages

    • Install carbon monoxide detectors

    Carbon Monoxide car exhaust combustion engine carbon monoxide StudySmarterRunning car engines inside can lead to a dangerous build-up of carbon monoxide. Unsplash

    Carbon monoxide detectors give out a loud, high-pitched alarm when the carbon monoxide levels of a room exceed a certain limit. Carbon monoxide is lighter than air, so it rises. As a result, detectors should be placed at least five feet above the floor.

    Catalytic Converters

    Catalytic converters are devices used to reduce emissions from an internal combustion engine (such as those found in cars). Internal combustion engines often don't have enough oxygen available to completely oxidise the fuel, so toxic by-products are produced.

    Toxic by-products found in combustion engines include nitrogen oxides, hydrocarbons, and carbon monoxide.

    Catalytic converters provide a site for the oxidation and reduction of these toxic by-products into less hazardous substances. For carbon monoxide, the formula equation is:

    CO + O2 ⇾ CO2

    Thin layers of platinum and rhodium are used in the catalysts. These are expensive metals, so catalytic converters are often targeted by thieves and cut out from the underside of cars.

    Improved Combustion Efficiency

    Combustion efficiency is a measure of how effectively a fuel is transferred into usable heat.

    To maximise the combustion efficiency of a boiler, it should be operated with excess air. This increases the amount of oxygen available to the combustion of fuel, minimising carbon monoxide emissions. A high combustion efficiency also saves money – it minimises heat loss and fuel requirements.

    I hope that this article has explained carbon monoxide for you. It's formed by incomplete combustion of carbon-based fuels. If inhaled, it binds to haemoglobin, preventing the effective transport of oxygen around the bloodstream.

    Carbon Monoxide - Key takeaways

    • Carbon monoxide (CO) is a poisonous gas. The carbon atom and oxygen atom are joined by a triple bond. Carbon monoxide is produced by the incomplete combustion of carbon-based fuels.
    • If inhaled, carbon monoxide molecules bind to haemoglobin instead of oxygen. This prevents oxygen from being transported around the body.
    • Symptoms of carbon monoxide poisoning include headaches, dizziness, nausea, and loss of consciousness. Prolonged exposure can cause long-term effects and even death. Some people are more susceptible to carbon monoxide poisoning than others.
    • Carbon monoxide poisoning can be detected using a blood test or an electrocardiogram. Treatment involves removing the patient from the area of exposure, oxygen masks and hyperbaric oxygen therapy.
    • Methods of preventing carbon monoxide poisoning include installing detectors and catalytic converters, and improving combustion efficiency of appliances like boilers.

    1. Robert Kalescky, Identification of the Strongest Bonds in Chemistry, The Journal of Physical Chemistry A, 2013

    2. Sagar Patel, Physiology, Oxygen Transport And Carbon Dioxide Dissociation Curve, StatPearls, 2022

    3. UCAR, Carbon Monoxide, 2022

    4. Welsh Government, Recognising Carbon Monoxide Poisoning, 2019

    5. Yvette Brazier, What does carbon monoxide poisoning feel like, and how to treat it, Medical News Today, 2022

    Frequently Asked Questions about Carbon Monoxide

    What is carbon monoxide?

    Carbon monoxide (CO) is a poisonous gas.

    How is carbon monoxide produced?

    Carbon monoxide is produced by the incomplete combustion of carbon-based fuels.

    Why is carbon monoxide dangerous?

    If carbon monoxide is inhaled, it binds to haemoglobin in red blood cells. This reduces the body's ability to transport oxygen. 

    What are the main effects of carbon monoxide poisoning?

    The main effects of carbon monoxide poisoning are headaches, dizziness, nausea, and loss of consciousness.

    Is carbon monoxide heavier than air?

    Carbon monoxide is lighter than air, so it rises. Detectors should be placed at least five feet above the floor.

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    What are some symptoms of carbon monoxide poisoning?

    What are some long-term effects of carbon monoxide poisoning?

    Those living in high altitudes are at lower risk for carbon monoxide poisoning.


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