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What is carbon monoxide?

Carbon monoxide is an invisible, tasteless and odourless gas produced by the incomplete combustion of a fuel, for example when gas, oil, coal or wood do not burn properly.In the home this is most commonly caused by appliances and flues that have been incorrectly installed, not maintained or are poorly ventilated. Other locations which have claimed victims in recent years include boats, barbecues and vehicle exhausts. Possible signs of a CO leak include:

  • black, sooty marks on the front covers of gas fires
  • sooty marks on the walls around boilers, stoves or fires
  • smoke building up in rooms due to a faulty flue
  • yellow instead of blue flames coming from gas appliances

Carbon monoxide can kill quickly and without warning. CO reduces the oxygen transported by the circulating blood, and symptoms of poisoning can be similar to those of food poisoning and flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

Signs and Symptoms:

In the short-term, common symptoms include:

  • headache
  • dizziness and nausea (feeling sick)
  • vomiting (being sick)
  • tiredness and confusion
  • stomach pain
  • shortness of breath and difficulty breathing

Your symptoms may be less severe when you are away from the source of the carbon monoxide.

In cases of higher levels of exposure to CO, symptoms include: 

  • impaired mental state and personality changes (intoxication)
  • vertigo – the feeling that you or the environment around you is spinning
  • ataxia – loss of physical co-ordination due to underlying damage to the nervous system and brain
  • breathlessness and tachycardia (a heart rate of more than 100 beats a minute)
  • chest pain caused by angina or a heart attack
  • seizures – an uncontrollable burst of electrical activity in the brain that causes muscle spasms
  • loss of consciousness – in cases where there are very high levels of CO gas, death may occur within minutes

Those at particular risk include:

  • babies and young children
  • pregnant women
  • people with heart or breathing problems

Pets may be the first to show signs of carbon monoxide poisoning because they are vulnerable to the effects of CO gas. The smaller an animal or a person is, the faster CO gas will affect them.

Are you at risk?

You should suspect carbon monoxide poisoning if:

  • other people in your house, flat or workplace fall ill with similar symptoms
  • your symptoms disappear when you go away (for example on holiday) and return when you come back
  • your symptoms tend to be seasonal – for example, you get headaches more often during the winter when the central heating is used more frequently

If you suspect carbon monoxide poisoning:

  • if it's an emergency, immediately move outside or to a ventilated area and call 999
  • stop using all your cooking and heating appliances that use fuel other than electricity
  • open all of the windows in your house or building
  • move away from potential sources of the CO gas
  • report incidents to the National Gas Emergency Service line on 0800 111 999
  • call the Health and Safety Executive (HSE) Gas Safety Advice Line on 0800 300 363 for non-emergency advice
  • visit your GP


Frequently Asked Questions

A large part of the APPCOG's work is to help raise public and parliamentary awareness of carbon monoxide and threat it poses. On this page, we answer some of the most frequently-asked questions about CO and the threat it poses. If you have any questions, or if you are seeking further information not listed here, don't hesitate to contact us.

1. How do I tell which carbon monoxide alarm to buy? taken from Which? advice

An audible carbon monoxide alarm is a good way to ensure you're immediately alerted to any carbon monoxide in your home. A carbon monoxide alarm is cheap and easy to fit, and are widely available from DIY stores and supermarkets, usually found in the smoke alarm aisle, or through your energy supplier. But just as a smoke alarm doesn't detect carbon monoxide, your carbon monoxide alarm isn't a replacement for a standard smoke alarm - you'll need one of each. Prices on carbon monoxide alarms from brands like Kidde, FireAngel, Honeywell and Ei Electronics range between £15 and £35.Your carbon monoxide detector should:

  • have an audible alarm - rather just than a 'colour change' or 'back spot' indicator tool - which will sound an alarm when it detects CO
  • have a British Standard EN 50291 mark - also written as BSEN 50291 or shown with the CE mark
  • have a British or European Kitemark, Loss Prevention Certification Board (LPCB) or equivalent testing approval mark.

Watch out - cheap and uncertified alarms may not be tested to these rigorous standards and may not keep you safe

2. How many cases of CO poisoning are there annually in the UK?

According to a joint letter on CO from the Chief Medical Officer, Chief Nursing Officer and Director of Nursing at the Department of Health and Public Health England,

"Accidental (and therefore preventable) carbon monoxide poisoning still result in recorded cases of around 40 deaths and 200 hospitalisations each year in England & Wales. Recent figures from the Department of Health indicate that there are 4,000 attendances at accident and emergency departments for treatment for CO poisoning each year in England.  Whilst a considerable number of people die from accidental acute carbon monoxide poisoning, it is now confirmed many more are injured by sub-lethal exposure. It is likely that the true number exposed in this way is even greater than reported."

A study conducted by Liverpool John Moores University in 2011 measured CO levels in 109 homes over a number of weeks. It found that 24 homes (23%) had CO levels greater than 50 ppm (parts per million) – a level at which symptoms of poisoning such as headaches, tiredness and drowsiness can be experienced. A further 53 homes contained CO levels between 10 and 50 ppm. A further study conducted at UCL showed that 2% of 597 homes visited were assessed to have a “very high” risk of carbon monoxide exposure, and a further 4% were estimated as having a “high” risk of exposure to concentrations of CO above WHO guideline levels.

3. What other long-term effects does CO poisoning have?

People surviving carbon monoxide poisoning often have neurological damage and cognitive impairment that can mimic the symptoms of a stroke or some types of dementia. Furthermore, long-term, low-level exposure can also cause symptoms that are easily confused with chronic upper respiratory tract infection, asthma, non-specific headache, migraine, depression, angina, chronic fatigue syndrome and myalgia. These mean that the true cause – low-level carbon monoxide exposure – is often misdiagnosed. As a result the true incidence figures of low-level exposure to carbon monoxide remain unknown.

4. What can be done to protect against CO poisoning?

There are a number or important steps to take. Most importantly, have your domestic heating system, water heater and any other gas, oil or coal-burning appliances serviced by a qualified technician every year. Install an audible carbon monoxide detector in your home and remember to regularly check or replace the battery. Never burn anything in a stove or fireplace that isn’t vented.

5. Is CO poisoning only a threat in the winter?

No, not at all. Carbon monoxide is produced by the incomplete combustion of any fuel: including gas, oil, coal and wood. Summer BBQs and portable heaters can produce fatal levels of CO gas if poorly maintained or operated in non-ventilated area. Following a significant number of recent deadly cases, it has proved especially important to never take a used BBQ (even one that is cold to the touch) into a tent.


Please click here for the NHS website on carbon monoxide.