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Carbon monoxide is a poisonous gas that has no smell or taste. Breathing it in can make you unwell, and it can kill if you're exposed to high levels.
Every year there are around 25 deaths from accidental carbon monoxide poisoning in England and Wales.
After carbon monoxide is breathed in, 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 fail and die.
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The symptoms of carbon monoxide poisoning aren't always obvious, particularly during low-level exposure.
A tension-type headache is the most common symptom of mild carbon monoxide poisoning. Other symptoms include:
The symptoms can gradually get worse with prolonged exposure to carbon monoxide, leading to a delay in diagnosis.
Your symptoms may be less severe when you're away from the source of the carbon monoxide. If this is the case you should investigate the possibility of a carbon monoxide leak, and ask a suitably qualified professional to check any appliances you think may be faulty and leaking gas.
The longer you inhale the gas, the worse your symptoms will be. You may lose balance, vision and memory and, eventually, you may lose consciousness. This can happen within two hours if there's a lot of carbon monoxide in the air.
Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, such as difficulty thinking or concentrating and frequent emotional changes – for example, becoming easily irritated, depressed or making impulsive or irrational decisions.
Breathing in high levels of carbon monoxide gas can cause more severe symptoms. These may include:
Carbon monoxide is produced when fuels such as gas, oil, coal and wood don't 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:
Incorrectly installed, poorly maintained or poorly ventilated household appliances – such as cookers, heaters and central heating boilers – are the most common causes of accidental exposure to carbon monoxide.
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:
Seek medical advice from your GP if you think you've been exposed to low levels of carbon monoxide. Go immediately to your local accident and emergency (A&E) department if you think you've been exposed to high levels.
Your symptoms will often indicate whether you have carbon monoxide poisoning, but a blood test will confirm the amount of carboxyhaemoglobin in your blood. A level of 30% indicates severe exposure.
People who smoke can often have higher than normal levels of carboxyhaemoglobin in their blood, which can sometimes make it difficult to interpret the results.
Mild carbon monoxide poisoning doesn't usually need hospital treatment, but it's 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 in hospital will be needed if you've been exposed to a high level of carbon monoxide, or you have symptoms that suggest exposure.
You'll be given 100% oxygen through a tight-fitting mask (normal air contains around 21% oxygen). Breathing in concentrated oxygen enables your body to quickly replace carboxyhaemoglobin. Therapy will continue until your carboxyhaemoglobin levels decrease to less than 10%.
Hyperbaric oxygen therapy (HBOT) floods the body with pure oxygen, helping it overcome the oxygen shortage caused by carbon monoxide poisoning.
There's currently insufficient evidence regarding the long-term effectiveness of HBOT for treating severe cases of carbon monoxide poisoning. Therefore, standard oxygen therapy is usually the recommended treatment option.
HBOT may be recommended in certain situations – for example, if there's 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 length of time it takes to recover from carbon monoxide poisoning will depend on how much carbon monoxide you've been exposed to and how long you've been exposed to it.
Prolonged significant 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 poisoning include:
Around 10-15% of people who have severe carbon monoxide poisoning develop long-term complications.
In rare cases, severe carbon monoxide poisoning can cause Parkinsonism, which is characterised by tremors, stiffness and slow movement.
Parkinsonism isn't the same as Parkinson's disease, which is a degenerative neurological condition linked to ageing.
Coronary heart disease is another serious condition that can develop as a result of long-term carbon monoxide exposure.
Coronary heart disease is where the heart's blood supply is blocked or interrupted by a build-up of fatty substances (atheroma) in the coronary arteries.
Long-term exposure to carbon monoxide gas can also damage an unborn baby. Babies exposed to carbon monoxide during pregnancy are at risk of:
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 reputable, registered engineer. Don't attempt to install or service appliances yourself.
Anyone carrying out work on installations and appliances in your home must be registered with a relevant association, such as the:
Make sure all chimneys and flues are swept regularly by a qualified sweep who's a member of the:
To protect you from carbon monoxide poisoning caused by exhaust fumes:
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.
You can buy a carbon monoxide alarm from a DIY or hardware store. Make sure it's approved to the latest British or European Standard (BS Kitemark or EN50291).
Follow the safety tips below to help protect yourself at home and in the workplace:
If your carbon monoxide alarm sounds or you suspect a leak:
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 possible clues of a carbon monoxide leak include: