Carbon Monoxide - The Silent Killer!

Carbon monoxide is known as the 'silent killer' in that carbon monoxide is odourless and can not be seen but can kill. In the UK around 30 people die from carbon monoxide poisoning each year and hundreds of people suffer as a direct result of carbon monoxide inhalation. It is important to understand the causes, prevention and signs of carbon monoxide poisoning.

What is Carbon Monoxide (CO)?

what is carbon monoxide








Carbon monoxide is a product of incomplete burning of carbon based fuels and can be emitted from many sources such as boilers, fires, flues, water heaters and stoves. Carbon monoxide can not be seen, tasted or smelt and so inevitably poses an extremely dangerous threat. Carbon monoxide is in fact one of the most toxic substances that the average person will come into contact with.


Carbon monoxide is one part oxygen and three parts carbon with the symbol 'CO', and in humans when the carbon monoxide enters through the lungs it prevents the blood from bringing oxygen to the cells and organs.

Symptoms of Carbon Monoxide

One of the biggest issues with carbon monoxide poisoning is actually not diagnosing it quick enough and in many cases people are being poisoned without even realising it! Many of the symptoms of carbon monoxide poisoning may be incorrectly diagnosed as a viral infection or flu, as they both share similar symptoms. However unlike the flu carbon monoxide poisoning does not normally increase your body temperature, so if there are a number of people in your home suffering from flu like symptoms but with no increase in temperature get yourself and your appliance checked immediately.

One of the biggest signs that the symptoms point towards carbon monoxide poisoning would be if you notice your symptoms reduce significantly when you are away from your home. Many people who may have been feeling ill go on holiday and start to feel better, then return where the symptoms continue but wrongly put this down to the 'holiday blues'.

symptoms of carbon monoxideSome common symptoms include:

  • headache
  • nausea
  • vomiting
  • stomach upset
  • sore throat
  • dizziness
  • weakness
  • fatigue
  • confusion
  • disorientation
  • irregular heart rate
  • hyperventilation
  • difficultly in breathing
  • seizures
  • drowsiness
  • loss of consciousness

Since carbon monoxide poisoning stops the blood transporting oxygen to the cells and organs, serious illness, long term effects and even death can occur in severe cases. Carbon monoxide poisoning can be confirmed by a blood test which will show the level within your body. If you believe that you have been exposed to carbon monoxide poisoning contact your GP or hospital immediately, seek fresh air and turn off all fuel burning appliances and boilers.

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  • Causes and warning signs

    The physical signs of carbon monoxide poisoning have been discussed above. However even though carbon monoxide is odourless and can not be seen there are a few signs that can be seen on an appliance or boiler than can suggest poor combustion which may result in carbon monoxide, these include:

    • yellow or orange flameYellow or orange rather than blue flames (apart from fuel effect fires or flueless appliances which display this colour flame)
    • Soot or yellow/brown staining around or on appliances
    • Pilot lights that frequently blow out
    • Increased condensation inside windows

    If you think that your appliance or boiler is showing any of these signs or you have any other doubts, switch off you appliance immediately and contact a Gas Safe registered engineer for further assistance.


    Carbon monoxide is produced as a result of incomplete combustion of carbon based fuels and as such arises from poorly maintained, serviced or installed appliances or boilers. This is by in large the most likely cause however other causes such as blocked flues can also be accountable for causing carbon monoxide poisoning. It is important to make sure that your flue or chimney is not obstructed in any way by, plants, dead animals, leaves or any other obstructions.

    Another possible cause could be ventilation, many gas appliances and some boilers require a natural supply of fresh air to create the correct air ratio. If your air bricks or other means of ventilation is restricted or even not supplied this could starve the appliance of the correct oxygen ratio and result in poor combustion within the appliance burner.


    Prevention is better than cure, this is especially relevant to carbon monoxide poisoning, as sometimes when carbon monoxide is detected it is often too late. There are a number of measures that can help prevent carbon monoxide poisoning from actually happening, these include:

    • Ensure that all work carried out on your gas or oil appliance is completed by a Gas Safe(gas) or Oftec (oil) registered engineer.
    • Ensure that all appliances or boilers are checked (legally required for Landlords) and serviced yearly with out fail.
    • Always make regular checks on your flue, chimney and other ventilation to make sure that they are not blocked in any way.
    • Install a carbon monoxide detector

    Carbon Monoxide Detector

    If you always follow a regular service plan for your appliance(s) and take all the appropriate measures you gas or oil appliance / boiler are inherently safe and many never pose a carbon monoxide threat. However for extra piece of mind and assurances for your family installing a carbon monoxide detector is always one of the best ways in which you can prevent carbon monoxide poisoning.

    It must be noted that a carbon monoxide detector should not be used as a replacement for proper maintenance and servicing on your gas or oil appliance, but should be used as a back up measure. There are many different types of carbon monoxide detectors available, some built into fire alarms and others housed in their own units. It is important to look closely at the features and ensure that you buy a detector that suits your requirements.

    If your carbon monoxide detector does go off, you should:

    • Make sure it is the CO detector and not the smoke alarm.
    • Check to see if any member of your household is experiencing symptoms.
    • If they are, get them out of the house immediately and seek medical attention.
    • If no one is feeling symptoms, ventilate the home with fresh air and turn off all potential sources of CO.
    • Have a qualified engineer (Gas Safe or Oftec) inspect your fuel-burning appliances, boilers, chimneys or flues to make sure they are operating correctly.

    Useful Links

  • CO Awareness -  Carbon monoxide awareness website
  • CO Gas safety - Carbon monoxide awareness website
  • NHS Direct -Health care advice from the NHS
  • Gas Safe Register - Gas safety advice from Gas Safe
  • HSE - Health and safety on carbon monoxide

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    You can’t see it, taste it or smell it but it can kill quickly and with no warning.

    Student poster imageUnsafe
    Gas appliances produce a highly poisonous gas called carbon monoxide (CO). It can cause death as well as serious long term health problems such as brain damage.

    Remember the six main symptoms to look out for:

    1. headaches
    2. dizziness 
    3. nausea 
    4. breathlessness 
    5. collapse 
    6. loss of consciousness 

    Being aware of the symptoms could save your life.

    Carbon monoxide symptoms are similar to flu, food poisoning, viral infections and simply tiredness. That’s why it’s quite common for people to mistake this very dangerous poisoning for something else.

    Other signs that could point to carbon monoxide poisoning:
    • Your symptoms only occur when you are at home
    • Your symptoms disappear or get better when you leave home and come back when you return 
    • Others in your household are experiencing symptoms (including your pets) and they appear at a similar time 

    What should I do if I experience any symptoms of carbon monoxide poisoning?

    • Get fresh air immediately. Open doors and windows, turn off gas appliances and leave the house
    • See your doctor immediately or go to hospital - let them know that you suspect carbon monoxide poisoning. They can do a blood or breath test to check 
    • If you think there is immediate danger, call the Gas Emergency Helpline 
    • Get a Gas Safe registered engineer to inspect your gas appliances and flues to see if there is a dangerous problem 
    Don’t assume your gas appliances are safe: get a Gas Safe registered gas engineer to do a check. This is the only safe way to prevent yourself and those around you from incurring serious illness or death due to carbon monoxide exposure.

    What is carbon monoxide?

    Carbon monoxide (CO) is a highly poisonous substance produced by the incomplete burning of gas and Liquid Petroleum Gas (LPG).

    This happens when a gas appliance has been incorrectly fitted, badly repaired or poorly maintained. It can also occur if flues, chimneys or vents are blocked.

    Oil and solid fuels such as coal, wood, petrol and oil can also produce carbon monoxide.

    What is carbon monoxide poisoning?

    Carbon monoxide poisoning occurs when you breathe in even small amounts of the gas.
    When you breathe in carbon monoxide, it gets into your blood stream and prevents your red blood cells from carrying oxygen. Without oxygen, your body tissue and cells die.
    Levels that do not kill can cause serious harm to health when breathed in over a long period of time. Long term effects of carbon monoxide poisoning include Paralysis and brain damage. Such long term effects occur because many people are unaware of unsafe gas appliances and subsequent gas leaks.

    How do I avoid a carbon monoxide leak in my home?

    Your home may show signs of carbon monoxide. Any one of the following could be a sign that there is carbon monoxide in your home.
    • The flame on your cooker should be crisp and blue. Lazy yellow or orange flames mean you need to get your cooker checked
    • Dark staining around or on appliances 
    • Pilot lights that frequently blow out 
    • Increased condensation inside windows 
    If you have a faulty appliance in your home, it could lead to carbon monoxide poisoning.Get your gas appliances checked to avoid carbon monoxide poisoning.

    Why should I get a carbon monoxide alarm?

    Because carbon monoxide has no taste, smell or colour. Gas Safe Register strongly recommends you fit an audible carbon monoxide alarm in your home.

    While an alarm will alert you to carbon monoxide in your home, it is no substitute for having an annual gas safety cehck and regular servicing by a Gas Safe registered engineer.

    A carbon monoxide alarm looks similar to a smoke alarm and is very easy to fit by following the manufacturer’s instructions. You can purchase a carbon monoxide alarm from £22 at your local DIY store, supermarket or from your energy supplier.

    Before purchasing a carbon monoxide alarm, always make sure it is marked to EN 50291. It should also have the British Standards' Kitemark or another European approval organisation's mark on it. Follow the alarm manufacturer’s instructions on siting, testing and replacing the alarm.

    You are particularly at risk from carbon monoxide poisoning while sleeping, as you may not be aware of early carbon monoxide symptoms until it’s too late. Do not use the ‘black spot’ detectors that change colour when carbon monoxide is present. These will not make a sound to wake you up if the poisonous gas is present while you are sleeping