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