What is CO poisoning?

Unsafe gas appliances can produce a highly poisonous gas called carbon monoxide. Carbon monoxide has no smell or taste and breathing it in can be very bad for your health. Exposure to high levels of CO can be deadly.

When carbon monoxide enters your bloodstream it mixes with haemoglobin, the part of red blood cells that carry oxygen around your body, to form carboxyhaemoglobin. When this happens, the blood is no longer capable of carrying oxygen, and it's this lack of oxygen that causes the body’s cells and tissue to fail and die. Every year there are around 25 deaths from accidental carbon monoxide poisoning in England and Wales.

Carbon monoxide poisoning isn't always obvious, especially from low-level exposure, which causes symptoms that are often compared to flu. But unlike flu, CO poisoning doesn't cause a high temperature (fever). The longer you inhale the gas, the worse the symptoms can be. You may lose balance, vision and memory and, eventually, you may lose consciousness. This can happen within just two hours if there's a lot of carbon monoxide in the air.

A headache is the most common symptom of mild carbon monoxide poisoning, but other symptoms include:

  • Dizziness
  • Nausea and vomiting
  • Tiredness and confusion
  • Stomach pain
  • Shortness of breath and difficulty breathing.

Breathing in high levels of carbon monoxide can cause more severe symptoms. These may include:

  • Impaired mental state and personality changes (intoxication)
  • Vertigo – the feeling that you or the environment around you is spinning
  • Ataxia – loss of co-ordination
  • Breathlessness and high heart rate
  • Chest pain
  • Seizures
  • Loss of consciousness – in cases where there are very high levels of carbon monoxide, death may occur within minutes.

Carbon monoxide is produced when fuels such as gas don't burn fully. The risk of exposure to carbon monoxide from portable devices may also be higher in caravans, boats and mobile homes.

It's important to be aware of the dangers and identify any appliances in your house that could potentially leak carbon monoxide. Boilers, cookers, heating systems and appliances should be installed and regularly serviced by a Gas Safe registered engineer. Do not attempt to install or service appliances yourself.

Install a carbon monoxide alarm in your home to alert you if there's a carbon monoxide leak. However, an alarm isn't a substitute for maintaining and regularly servicing household appliances. Make sure it's approved to the latest British or European Standard (BS Kitemark or EN50291). We recommend the Honeywell XC70-EN CO Alarm, available for roughly £20 with a 7 year warranty.

If your carbon monoxide alarm sounds or you suspect a leak:

  • Stop using all appliances, switch them off, and open doors and windows to ventilate the property
  • Evacuate the property immediately
  • Call the gas emergency number on 0800 111 999 to report the incident
  • Don't go back into the property – wait for advice from the emergency services
  • Seek immediate medical help – you may not realise you've been affected by the carbon monoxide, and going outside into fresh air won't treat any exposure by itself.


It's very important to be aware of the risk of carbon monoxide poisoning and to look out for warning signs - you should suspect carbon monoxide poisoning if:

  • Other people in your home or workplace fall ill with similar symptoms
  • Your symptoms disappear when you go away and return when you come back
  • Your symptoms tend to be seasonal – for example, if you get headaches more often during the winter when the central heating is on
  • Your pets also become ill - Pets are often the first to show signs of carbon monoxide poisoning. The smaller an animal or a person is, the faster they'll be affected.

Other possible clues of a carbon monoxide leak include:

  • Black, sooty marks on the front covers of gas fires
  • Sooty or yellow/brown stains around boilers, stoves or fires 
  • Yellow instead of blue flames coming from gas appliances
  • Pilot lights frequently blowing out.

More information as well as a directory of Gas Safe registered engineers can be found on the Gas Safe register website.


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