Carbon Monoxide Poisoning

Symptoms

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". Every year in the UK, over 200 people go to hospital with suspected carbon monoxide poisoning, which leads to around 40 deaths.

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

• dizziness
• nausea (feeling sick) and vomiting
• 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).

The signs and symptoms of carbon monoxide poisoning are not always obvious, especially during low-level exposure. Some people may also have a pre-existing condition with similar symptoms.

Low levels of carbon monoxide

The symptoms of exposure to low levels of carbon monoxide (CO) can be similar to those of many other conditions, such as food poisoning and flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

The most common symptoms include:

• headache
• nausea (feeling sick) and vomiting
• dizziness
• 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.

The longer you inhale carbon monoxide, 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 carbon monoxide in the air.

Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, including:

• difficulty thinking or concentrating
• frequent emotional changes – for example, becoming easily irritated, depressed or making impulsive decisions

High levels of carbon monoxide

If you have breathed in high levels of carbon monoxide 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, caused by underlying damage to the brain and nervous system
• breathlessness and tachycardia (a heart rate of more than 100 beats per 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 carbon monoxide, 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 the gas. The smaller an animal or a person is, the faster this 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 carbon monoxide leak.

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 this 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 reach dangerous levels.

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

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.

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 cause of accidental exposure to carbon monoxide (CO) is household appliances, such as cooking and heating devices, which have been damaged, incorrectly installed or badly maintained.

The risk of exposure to carbon monoxide from portable devices may also be higher in caravans, boats and mobile homes. 

Other possible causes of carbon monoxide poisoning include:

• blocked flues and chimneys – this can stop carbon monoxide escaping, allowing it to reach dangerous levels
• burning fuel in an enclosed or unventilated space – for example, running a car engine, petrol-powered generator or barbecue inside a garage, or a faulty boiler in an enclosed kitchen
• faulty or blocked car exhausts – a leak or a blockage in the exhaust pipe, such as after heavy snowfall, could lead to a build-up of carbon monoxide
• paint fumes – some cleaning fluids and paint removers contain methylene chloride (dichloromethane), which can cause carbon monoxide poisoning if breathed in
• smoking shisha pipes indoors – shisha pipes burn charcoal and tobacco, which can lead to a build-up of carbon monoxide in enclosed or unventilated rooms

Being aware of the signs

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 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
• your pets also become ill

Other possible clues of a carbon monoxide 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 carbon monoxide 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 carbon monoxide
• call the Health and Safety Executive (HSE) Gas Safety Advice Line on 0800 300 363 for advice (freephone service)
• visit your GP as soon as possible

If you have a carbon monoxide 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, or have symptoms that suggest exposure.

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.

Seek immediate advice from your GP or local accident and emergency department if you think you have carbon monoxide poisoning.

Your symptoms will often indicate whether you have carbon monoxide (CO) poisoning, but a blood test 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.

Your house will also need to be checked for safety before anyone returns. Read more about what to do if you suspect a leak.

Standard oxygen therapy

Exposure to a high amount of carbon monoxide 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 quicker. 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.

Currently, there is 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 carbon monoxide, and nerve damage is suspected. The use of HBOT will be decided on a case-by-case basis.

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.

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

Complications

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

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

Around 10-15% of people who have severe carbon monoxide poisoning develop long-term complications.

Some of the possible complications of carbon monoxide poisoning are described below.

Brain damage

Prolonged exposure to carbon monoxide 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 carbon monoxide.

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

If the blood supply is restricted, it can cause 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 carbon monoxide gas can also damage an unborn child. Infants exposed to carbon monoxide 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 

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.

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