Merseyside Fire & Rescue Service

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Carbon monoxide


What is carbon monoxide?

Carbon monoxide is a poisonous gas. It can be given off by appliances that burn fossil fuels such as gas, coal, wood or oil, if they're not working properly, if the flue is blocked in any way, or if the room is not properly ventilated.

Why is it so dangerous?

Carbon monoxide is odourless, colourless and tasteless, which makes it difficult to detect. However, its effects are deadly. On average, 50 people a year are killed by carbon monoxide poisoning due to faulty heating appliances.

What are the main causes of carbon monoxide poisoning?

Most cases of carbon monoxide poisoning are due to inadequate ventilation or poor maintenance of appliances, blocked or leaky flues and chimneys. Chimneys can become blocked for various reasons. It could be as a result of birds nesting on the chimney, or possible degradation of the flue. A blocked flue can lead to carbon monoxide leaking into your home.

Who is most at risk?

Some people mistakenly think that it is only gas-fuelled heating systems which can cause carbon monoxide poisoning - in fact, it can happen with any fossil fuel system if the system, which includes both the appliance and the flue, is faulty or the room is not properly ventilated. Also, some people associate carbon monoxide poisoning with rented accommodation - in fact, more people are killed in owner-occupied rather than rented properties.

Accident statistics


In the period 1989-1998 there were 533 deaths from carbon monoxide poisoning in the UK:

  • 438 in England and Wales
  • 46 in Scotland
  • 49 in Northern Ireland

Fuels involved in carbon monoxide poisoning accidents

Fatal accidents

Fatal accidents

Non-fatal accidents

Non-fatal accidents

Type of appliance involved (all accidents)

Type of appliance involved (all accidents)

Cause of fatal accidents

Age distribution of victims

Fatal accidents

Age distribution of victims

Non-fatal accidents

Non-fatal accidents

Carbon monoxide poisoning

A typical scenario is a living room with a solid fuel heater. The windows and doors have been draught-proofed and the permanent ventilation has been blocked up (by the victim) to prevent draughts. The chimney and flue have not been swept for years. The victim may not have carried out the regular maintenance of their appliance, like cleaning the throat plate monthly, let alone had the appliance serviced professionally. There may be soot deposits at the appliance outlet, or bits of the flue lining may have broken away and tumbled down to the appliance outlet. The weather is cold and the fire is not drawing well, so the victim opens the fire door to get more heat. This compounds the problem. The victim becomes drowsy, falls asleep, and doesn't wake up again.

Table 1 Regional variation of deaths from poisoning by carbon monoxide from domestic heating appliances (1989-1998)

  Total number of Cases 1989 to 1998 Average Death Rate per 100m Population per YearPopulation (m) Population (m)
  Gas Fired Non-Gas All Gas Fired Non-Gas All  
Greater London 39 6 45 55 8 63 7.1
South East 34 6 55 35 22 57 9.7
South West 22 21 39 43 33 76 5.1
Wales 33 17 63 114 103 217 2.9
West Midlands 41 30 69 60 41 101 6.8
East Midlands 35 28 57 59 37 97 5.9
North East 44 22 56 66 18 84 6.7
North West 36 12 45 57 14 71 6.3
Scotland 32 99 41 64 18 82 5.0
Northern Ireland 8 36 44 50 225 275 1.6
Total 324 190 514 57 33 90 57.1

Rates take no account of relative use of gas and non-gas appliances
Gas includes bottled gas
Source: Metra Martech
Note on interpretation of the figures
Northern Ireland has 275/90 times = 3.06 times national average death rate (roughly 3 times)
Wales has 217/90 times = 2.41 times national average death rate (roughly 21/2 times)
West Midlands has 101/90 times 8 approximately 10% higher than national average

Table 2 Seasonal fluctuation of fatal poisoning by carbon monoxide from malfunctioning domestic appliances

Table 2 Seasonal fluctuation of fatal poisoning by carbon monoxide from malfunctioning domestic appliances

Source: Metra Martech


  • General awareness of the danger of carbon monoxide is reasonably high among the general public, but practical and specific knowledge is low:
  • Awareness is largely limited to gas - very few people associate carbon monoxide with other fossil fuels. Over half (56 per cent) think that a coal fire cannot cause carbon monoxide poisoning, or simply do not know.
  • One in ten people cannot name any potential sources of carbon monoxide in their home.
  • Just one in four (27 per cent) is aware that poor ventilation can result in a build-up of carbon monoxide.
  • Over one in three do not know what colour a flame on a gas boiler will burn if there are traces of carbon monoxide (orange or yellow). One in twenty thinks that it actually should burn orange or yellow, rather than blue.

People do not necessarily take the recommended safety precautions to reduce the risk of carbon monoxide poisoning in their home:

  • Three in ten households with a gas boiler or heating system have not had it serviced in the last year. This is a particular problem among owner-occupiers.
  • Just one in five households (22 per cent) with a chimney in use has had it swept in the last year, and 58 per cent have not done so in the last four years, including 8 per cent who have never had it swept.

Source: MORI

Key safety messages: the danger signs

Carbon monoxide may be present if there are any of the following danger signs:

  • Gas flames that normally burn blue burn orange or yellow instead.
  • Sooty stains appear on or just above appliances, regardless of the fuel being burnt.
  • Coal or wood fires burn slowly or go out.
  • The fire is difficult to light.
  • The room is not properly ventilated.
  • The chimney or flue is blocked - watch out for smoke in the room. Look out for masonry debris in the grate or appliance.
  • You develop the following unexplained symptoms:
    • tiredness
    • drowsiness
    • headaches
    • dizziness
    • chest pains
    • nausea

Good practice guidelines

Given that accurate knowledge of the hazards of carbon monoxide is so low, it is important to communicate relevant information, so that people know the risks involved and the consequences of not taking the necessary safety precautions.

Key messages

  • Carbon monoxide can result from burning all fossil fuels - not just gas fires and boilers.
  • It is important to ensure rooms are ventilated - never block vents. If double-glazing or draught-proofing is fitted, make sure there is still enough air circulating for any heaters in the room.
  • Portable heaters do not need a flue, but they still need good ventilation.
  • Make sure that all chimneys and flues are regularly swept by a competent sweep_(i.e. a member of the National Association_of Chimney Sweeps), and kept clear. This includes chimneys being used as flues for gas fires, but it is particularly important for solid fuel appliances.
  • Boilers and heating systems and appliances should be installed, maintained and regularly serviced by a competent engineer (make sure they are CORGI-registered for gas appliances; HETAS-registered for solid fuel appliances; or OFTEC-registered for oil-burning appliances).
  • If you have recently moved, check when your boiler or heating appliances were last serviced.
  • Gas flames burning orange or yellow instead of blue may indicate the presence of carbon monoxide.
  • Carbon monoxide detectors should comply with British Standard BS 7860 - but remember they are only warning devices. Never rely on them entirely and do not use them as a substitute for regular servicing.
  • Never cook on a barbecue indoors - the charcoal gives off carbon monoxide.
  • If you develop any of the following unexplained symptoms - drowsiness, headaches, chest pains, giddiness, sickness, diarrhoea, stomach pains - you could be suffering from carbon monoxide poisoning. Switch off your appliances and see your doctor at once.
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