Carbon monoxide

Carbon Monoxide - the facts

  • Carbon Monoxide or CO is a natural gas created by the incomplete combustion of fossil fuels.
  • It has no smell, no taste and no colour, making it extremely hard to detect.
  • Despite being poisonous, our bodies will quickly and easily absorb carbon monoxide.
  • Approximately 40 people die each year in the UK from CO poisoning.

Fossil fuels are used extensively in our lives and are used every day in our homes. Gas, oil, coal and even wood burnt in boilers and engines can emit Carbon Monoxide, (CO), as can fossil fuels used in water heaters, oil burners, cookers, gas fires, open fires and solid fuel appliances. When these appliances are installed correctly, maintained and serviced regularly, the chances of CO building up are greatly reduced. Most victims of CO poisoning are exposed to gasses that are not vented adequately by heating equipment.

If you use an appliance that runs off any fossil fuel you should make sure:

  • There is adequate ventilation
  • The appliance has been installed correctly
  • It is serviced yearly
  • It is well maintained
  • You invest in a CO detector - it could save your life.

Carbon monoxide (CO) poisoning

Our bodies will quickly and easily absorb carbon monoxide. In fact, our bodies will actively seek to absorb CO over oxygen where it is present, even though the gas is fatal to us. If CO builds up in the air you breathe, you will begin to feel its effects. Once inhaled, carbon monoxide combines with oxygen carrying hemoglobin to form carboxyhemoglobin which then inhibits the transference of oxygen around the body, starving the organs of oxygen. This oxygen starvation particularly affects the heart, brain and central nervous system.

Carbon monoxide poisoning symptoms

Symptoms are often flu-like and their severity depends on the amount of carbon monoxide inhaled. The below guide shows symptoms experienced by an healthy adult at the relevant exposure level. The CO is measured in Parts Per Million (ppm) in relation to air.


ppm CO

Time Exposed


50 ppm


Safety level as specified by the Health and Safety Executive

200 ppm

2-3 hours

Slight headache, some may experience slight dizziness, nausea, chest tightness, fatigue, lack of concentration, memory loss.

400 ppm

1-2 hours

Headache, worsening to a severe headache with prolonged exposure, dizziness, nausea, fatigue, tightness across the chest, memory loss, lack of concentration.

800 ppm

45 minutes

Headache, dizziness, nausea, convulsions within 45 minutes. Unconscious within 2 hours. Death can occur within 2-3 hours.

1600 ppm

20 minutes

Headache, dizziness, nausea, convulsions, unconsciousness. Death can occur within 1 hour.

3200 ppm

5-10 minutes

Headache, dizziness, nausea, convulsions, unconsciousness. Death can occur within 1 hour.

6400 ppm

1-2 minutes

Headache, dizziness, nausea, convulsions, unconsciousness. Death in approximately 30 minutes.

12,800 ppm

1-3 minutes


People who are poisoned over a length of time will often display symptoms ranging from:

  • Headache
  • Dizziness
  • Nausea
  • Fatigue
  • Lack of concentration
  • Memory loss
  • Disorientation
  • Irritability
  • Tightness across the chest.

As the level of CO in the body increases the symptoms will develop to include:

  • Confusion
  • Weakness
  • Lack of co-ordination
  • Lack of balance
  • Heart problems
  • Cerebral edema
  • Convulsions
  • Coma
  • Death.

Effects on the heart include rapid and irregular heartbeat, decreasing blood pressure, cardiac arrhythmias, heart blocks, ventricular ectopic beats, heat attack and death. When subject to CO poisoning the brain can develop cerebral edema (swelling). Cerebral edema causes brain cells to crush into each other through swelling, thus killing the compacted cells. Carbon monoxide related cerebral edema can cause irreversible damage to the brain which in turn can effect the nervous system.

CO poisoning can be mis-diagnosed as flu or gastroenteritis through its symptoms. Due to its effects on the brain and nervous system it can also be mis-diagnosed as a neurological or psychiatric disorder.

Who is at risk of CO poisoning?

Although anyone who inhales an unsafe level of CO gas will suffer poisoning to some degree (depending on the amount of CO in the air) children, the elderly and pregnant women succumb quicker to the effects of Carbon Monoxide poisoning. It is also suggested that acute CO exposure can give an expectant mother a non-lethal dose of CO, but can harm an unborn child and lead to miscarriage. Pets display symptoms at a faster rate and will show the same kind of effects as humans (dizziness, nausea, fatigue, disorientation, irritability, weakness, lack of co-ordination, convulsions, coma, death).

People already suffering from a heart condition can succumb more rapidly to carbon monoxide, as can those with respiratory health problems. Smokers are at a higher risk as they will already have elevated levels of Carboxyhemoglobin in their blood.



CO poisoning and gas appliances

A lot of people assume "it will never happen to me". The chances are that it won't, but it does pay to take precautions to make that risk even less likely. If you know the facts surrounding Carbon Monoxide poisoning, you can act to reduce your risk.

According to figures from the Health and Safety Executive (HSE):

  • Poisoning incidents involving piped natural gas and LPG are the highest in November, December and January.
  • The heating season (starting from the first cold days of autumn when the central heating system is first put into use, to the time when it is turned off in the spring) is the period where most poisonings happen.
  • Most gas related CO poisoning happen in homes where the owner is the occupier.
  • It is reported that the most common faults causing appliances to produce CO gas is a lack of servicing and flue/terminal faults. Next most common is poisoning caused by a lack of ventilation.
  • People are most likely to be poisoned in their bedroom or living room.

Avoiding carbon monoxide poisoning

Everyone who owns an appliance that uses fossil fuels (gas, oil, coal, wood) should:

  • Check the flame colour of the appliance (if it is burning orange it is not operating properly and could be emitting CO gas).
  • Service appliance(s) every year by someone qualified to work on them. All people working with gas have to be Gas Safe Registered by law.
  • Maintain all appliances adequately - check in the case of boilers that the flue is not blocked, remove any debris, obstructions or plants from the flue area.
  • Ensure there is adequate ventilation in your home, not only to vent out any noxious gasses but also to allow oxygen and fresh air into the home.
  • Invest in a CO detector which can recognise low CO levels and warn you of any change.
  • Just like a smoke alarm, remember to test your Carbon Monoxide detector regularly and replace batteries when required.
  • If you are a tenant you should have a gas safety certificate. Your landlord has to by law have appliances checked yearly. Check if your landlord has fitted a CO detector.
  • If you suffer from headache, dizziness, nausea, fatigue, lack of concentration, memory loss, disorientation, irritability and tightness across the chest you may be suffering from CO poisoning. Ask your doctor for a CohB test.
  • In mild cases of CO poisoning, victims recover when administered oxygen or simply brought into fresh air. If you start feeling the effects of CO poisoning, get outside of the premises immediately.
  • Don't use open flames, ovens etc to heat your home - use appliances only for the purpose they are intended.
  • Remember it is not just your boilers that are at risk, anything that goes through the process of combustion can produce carbon monoxide. Cookers, water heaters, oil burners, gas fires, log burners, open fires, barbecues, engines and solid fuel appliances can all produce CO.

Finding an installer

Heating Engineers working on gas boilers should all be Gas Safe registered. For oil-fuelled appliances turn to OFTEC registered engineers, or a HETAS registered engineer for bio and solid fuel. You can ensure your engineer also works to the highest of standards by employing CIPHE registered heating professional. Use our find a plumber online service to find the best tradesperson for you.

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Gas Safe Registered installers

You can also use the Gas Safe Register website to search for Registered installers.

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