Carbon monoxide poisoning

Carbon monoxide is a poisonous gas that has no smell or taste. Breathing it in can make you unwell and it can kill.

Information written and reviewed by Certified Doctors.

Contents

Key Information

What should I do?

If you think you have this condition, you should call an ambulance or go to the hospital immediately.

How is it diagnosed?

Your doctor might suspect carbon monoxide poisoning based on your symptoms, physical examination findings and history of carbon monoxide exposure. A firm diagnosis can be made with a blood test.

What is the treatment?

If you are diagnosed with carbon monoxide poisoning, you will probably be treated with oxygen therapy. Oxygen is given via a mask until the levels of carboxyhaemoglobin in your blood decrease below 10%.

If your poisoning is mild, the doctor may decide that you do not need hospital treatment.

Introduction

Carbon monoxide is a poisonous gas that has no smell or taste. Breathing it in can make you unwell and it can kill.

Carbon monoxide (CO) is sometimes referred to as the 'silent killer'. In the UK, more than 50 people die from accidental carbon monoxide poisoning every year, and 200 people are left seriously ill.

A headache is the most common symptom of mild carbon monoxide poisoning. Other symptoms include:

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

Symptoms of carbon monoxide poisoning can be similar to those of food poisoning and the flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

Read more about the signs and symptoms of carbon monoxide poisoning.

Carbon monoxide

Carbon monoxide is difficult to detect because it has no smell, taste or colour. This means you can inhale it without realising.

Carbon monoxide is produced when fuels such as gas, oil, coal, or wood do not burn fully. When a fire burns in an enclosed space, such as a room, the oxygen is gradually used up and replaced with carbon dioxide. The fuel is unable to burn fully and releases carbon monoxide.

After breathing in carbon monoxide it enters your bloodstream and 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 able to carry oxygen and the lack of oxygen causes the body’s cells and tissue to die.

What causes carbon monoxide to leak?

Incorrectly installed, poorly maintained or poorly ventilated household appliances, such as cookers, heaters and central heating boilers, are the most common sources of carbon monoxide.

Blocked flues and chimneys can also prevent carbon monoxide escaping, allowing it to build up to dangerous levels.

The risk of carbon monoxide poisoning can occur at any time in any home or enclosed space.

Read more about the causes of carbon monoxide poisoning.

Being aware of the signs

It is 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 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

Other 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

What to do if you suspect a leak

If several people in the same building develop flu-like symptoms without a temperature, and you think it could be linked to a CO leak, you should:

  • immediately 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 the source of the CO gas
  • call the Health and Safety Executive (HSE) Gas Safety Advice Line on 0800 300 363 for advice (freephone service)
  • visit your doctor as soon as possible

If you have a CO leak, ask a suitably qualified engineer to inspect your cooking appliances, central heating and water heating appliances, to check they are safe.

Treating carbon monoxide poisoning

You will need oxygen therapy treatment in hospital if you have been exposed to a high level of carbon monoxide.

Oxygen therapy involves breathing in 100% oxygen through a tight fitting mask (normal air contains about 21% oxygen). Breathing in concentrated oxygen enables your body to quickly replace carboxyhaemoglobin.

Read more about how carbon monoxide poisoning is treated.

The time it takes to recover depends on how much carbon monoxide you have been exposed to and how long you have been exposed to it for.

Between 10-15% of people who have severe carbon monoxide poisoning develop long-term complications such as damage to the brain or heart.

Read more about the complications of carbon monoxide poisoning.

Risk groups

Carbon monoxide is a danger to everyone, but certain groups are more vulnerable. These include:

  • babies and young children
  • pregnant women
  • people with chronic heart disease
  • people with respiratory problems, such as asthma

Preventing carbon monoxide poisoning

The best way of protecting you and your family is to be aware of the dangers and identify any appliances in your house that could potentially leak carbon monoxide.

Installing a CO alarm will detect a carbon monoxide leak in your home and give out a high-pitched noise when levels of the gas are high. They are available from DIY and hardware stores. However, alarms are not a substitute for maintaining and regularly servicing household appliances.

Read more about preventing carbon monoxide poisoning.

Symptoms

A headache is the most common symptom of carbon monoxide poisoning.

Other common symptoms include:

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

Symptoms of carbon monoxide poisoning can be similar to those of food poisoning and flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

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

The longer you inhale CO gas, the worse your symptoms will be. You may lose balance, vision and memory. Eventually, you may lose consciousness. This can happen within two hours if there is a lot of CO gas in the air.

However, symptoms of carbon monoxide poisoning can sometimes occur days or months after breathing in carbon monoxide.

Symptoms of CO poisoning that develop later include:

  • confusion
  • memory loss
  • co-ordination problems

High levels of carbon monoxide

If you have breathed in high levels of CO gas, it is likely that you will experience 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 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

At risk groups

Certain people in your household may be affected by carbon monoxide poisoning more quickly than others. 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.

If your pet suddenly becomes ill or dies unexpectedly, and death is not related to old age or an existing health condition, you should investigate the possibility of a CO leak.

Causes

Carbon monoxide is produced when fuels such as gas, oil, coal and wood do not burn fully. Burning charcoal, running cars and the smoke from cigarettes also produce carbon monoxide.

Gas, oil, coal and wood are sources of fuel used in many household appliances including:

  • boilers
  • gas fires
  • central heating systems
  • water heaters
  • cookers
  • open fires

The main causes of carbon monoxide poisoning are outlined below.

Poorly installed or maintained appliances

Household appliances, such as cooking and heating devices, that are incorrectly installed and badly maintained are the main cause of accidental exposure to carbon monoxide. Correctly fitted and well mantained appliances should produce very little CO gas.

Damaged appliances can also produce higher levels of CO gas than normal and become dangerous.

Blocked flues and chimneys

Blocked flues and chimneys are another potential cause of carbon monoxide poisoning because they can stop CO gas escaping, allowing it to build up to dangerous levels in a room.

Enclosed or unventilated spaces

Burning fuel in an enclosed or unventilated space increases the risk of CO poisoning. For example, a car engine left running inside a garage or a faulty heating boiler in a poorly ventilated kitchen can emit potentially lethal levels of CO gas.

A car left running in a closed garage will take around 10 minutes to build up a lethal level of CO gas.

Faulty or blocked car exhausts

A leak in your car exhaust could lead to a build up of CO over time. A blocked exhaust pipe, such as after a heavy snowfall, could also lead to a build up of CO.

Paint fumes

Fumes from cleaning fluids and paint removers that contain methylene chloride (dichloromethane) can also cause carbon monoxide poisoning. When breathed in, methylene chloride is converted into CO gas.

Treatment

Seek immediate advice from your doctor if you think you have carbon monoxide poisoning.

Your symptoms will often indicate whether you have carbon monoxide poisoning, but a blood sample will confirm the amount of carboxyhaemoglobin in your blood. A level of 30% indicates severe exposure.

Mild carbon monoxide poisoning doesn't usually need hospital treatment, but it is still important that you seek medical advice.

Standard oxygen therapy

Exposure to a high amount of CO gas is treated with oxygen therapy. You will be given 100% oxygen through a tight fitting mask (normal air contains around 21% oxygen).

Breathing in concentrated oxygen enables your body to replace carboxyhaemoglobin more quickly. You will continue to receive oxygen therapy until your carboxyhaemoglobin levels decrease to less than 10%.

Hyperbaric oxygen therapy

Hyperbaric oxygen therapy (HBOT) floods the body with pure oxygen, helping it to overcome the oxygen shortage caused by carbon monoxide poisoning.

There is currently insufficient evidence regarding the long-term effectiveness of HBOT for treating severe cases of carbon monoxide poisoning. Therefore, standard oxygen therapy (as described above) is usually the recommended treatment option.

However, HBOT may be recommended in certain situations, such as where there has been extensive exposure to CO gas and nerve damage is suspected. The use of HBOT will be decided on a case-by-case basis.

Prevention

The best way to protect against carbon monoxide poisoning is to be aware of the dangers and to identify appliances that could emit CO gas.

It is important to be aware of the signs and symptoms of carbon monoxide poisoning.

Follow the guidelines below to protect yourself in your home and workplace.

  • Make sure home appliances are safe and well maintained.
  • Boilers, cookers, heating systems and appliances should be installed and regularly serviced by a reputable, registered engineer.
  • Never use ovens or gas ranges to heat your home.
  • Make sure rooms are well-ventilated and do not block air vents. If your home is double-glazed or draught-proofed, make sure there is still enough air circulating for any heaters that are in the room.
  • Make sure that all chimneys and flues are swept regularly by a qualified sweep.
  • Do not use gas-powered equipment and tools inside your home if you can avoid it. Only use them in a well-ventilated area and put the engine unit and exhaust outside.
  • Always use a safety mask when using chemicals that contain methylene chloride.
  • Do not burn charcoal in an enclosed space, such as on an indoor barbecue.
  • Do not sleep in a room that has an unflued gas fire or a paraffin heater.
  • Fit an extractor fan in your kitchen (if it does not already have one).

Engine exhaust fumes

The following precautions can help to protect you from carbon monoxide poisoning caused by exhaust fumes.

  • Do not leave petrol-fuelled lawnmowers or cars running in the garage.
  • Make sure the exhaust of your car is checked every year for leaks.
  • Make sure your exhaust is not blocked before turning the engine on – for example, after heavy snowfall.

CO alarms

Installing an audible CO alarm will provide an early warning system in case there is a carbon monoxide leak in your home. You can buy one from a DIY or hardware store.

CO alarms give out a high-pitched noise when levels of CO are high. However, a CO alarm is not a substitute for maintaining and regularly servicing household appliances.

When buying a CO alarm, you should make sure that it is approved to the latest British or European Standard (BS Kitemark or EN50291).

Complications

Prolonged exposure to carbon monoxide can cause serious complications including brain damage, heart problems and death in very severe cases.

Effects of severe carbon monoxide poisoning include breathlessness, chest pains, seizures (fits) and a loss of consciousness. The severity depends on the amount of CO gas you have been exposed to and how long you have been exposed to it for.

Between 10-15% of people who have severe carbon monoxide poisoning develop long-term complications.
Some of which are described below.

Brain damage

Prolonged exposure to CO gas can cause memory problems and difficulty concentrating. It can also cause vision loss and hearing loss.

In rare cases, it can cause Parkinsonism, which is characterised by tremors (shaking), stiffness and slow movement.

(Parkinsonism is not the same as Parkinson's disease, which is a degenerative neurological (brain) condition linked to ageing.)

Heart disease

Coronary heart disease is another serious condition that can develop as a result of long-term exposure to CO gas.

Coronary heart disease is where the blood supply to your heart is blocked or interrupted by a build-up of fatty substances (atheroma) in the coronary arteries.

If your blood supply is restricted, you may get angina (chest pains). If the coronary arteries become completely blocked, it can cause a heart attack.

Read more about coronary heart disease.

Harm to unborn babies

Prolonged exposure to CO gas can also damage an unborn child. Infants exposed to CO gas during pregnancy are at risk of:

  • low birth weight
  • perinatal death (stillbirth and death that occurs within the first four weeks of birth)
  • behavioural problems
Content supplied by NHS Choices