Chimney fires

Chimney fires occur when the deposits of combustion are left within the flueways. By definition, a chimney fire is the burning of soot or creosote within the appliance, outlet or flue system, which can result in improper function of the appliance, damage to the flue, house or surrounding structures and it can even start a house fire.

Chimney fires are usually started when high temperatures or flames from a very hot fire extend into the appliance outlet or flue and the combustible deposits catch light.

This type of chimney fire can be sometimes associated with:

• A loud roaring noise, which occurs as massive amounts of air are sucked through the appliance or fireplace opening and used to oxidize the combustible fuels within the system
•  Sparks and flames seen shooting from the chimney top, which can be firework like in appearance
•  A glowing or shimmering appliance outlet or connector
•  Vibrating appliance, outlet or connector
•  Flames visible through any tiny cracks in the outlet or connector
•  Smoke and odours noticeable in adjoining rooms or the loft space
•  The heating up of the chimney breast or flue pipe, in the same room as the appliance and also other rooms that the flue passes through

Important!  It should be noted that it is possible to experience a chimney fire without noticing any of the above characteristics; it is also possible that any combination of the above characteristics, will be noticed. As all chimney fires are different, the above characteristics are intended only as a useful guide.

All chimney fires are extremely dangerous even though their intensity and duration may vary. During a chimney fire, internal flue temperatures may reach a staggering 1,100 degrees Celsius. As a result, massive radiant heat is emitted through the chimney walls, and with the addition of possible thatched or wooden roofs, a devastating house fire can start quickly. Flames and sparks can leap from the chimney top or through cracks in the flue and ignite the roof and other parts of the house. The bricks of a chimney can become hot enough to combust nearby flammable materials such as thatch and wooden beams. Adjoining houses and nearby trees can also be affected.

If no apparent damage is visible on the exterior of the chimney breast or flue, it is still highly probable that damage may have occurred within the lining of the chimney. Chimney fires burn hot enough to damage liners, crack chimney walls and pots, and damage factory-built metal chimneys.

Unfortunately, with all methods of sweeping a chimney, you cannot remove tar and creosote that builds up internally within the flue if wet wood or some forms of coal are burnt in them. The tar and creosote that this creates can ingress into the fabric of the chimney. When the chimney is hot, this tar can melt and vaporise meaning it can combust if a spark rises into the vapour – resulting in a chimney fire.

Tar and creosote can only be removed by chemical means. However, if you burn smokeless fuel in the appliance, the sulphur that this produces can reverse the tar and creosote build up – but remember, smokeless fuel must only be burnt in appliances and flues designed for that purpose, and sweeping of the flue should be done by a chimney sweep until all deposits are removed and then should be monitored on a regular basis.

Heating and cooking appliances fuelled by coal, smokeless fuels, wood, oil and gas can cause CO poisoning if they are poorly installed, incorrectly used or if they are not properly and regularly maintained..

When fuel does not burn properly, it produces poisonous, and potentially deadly, CO gas. It can also damage your health permanently. The early symptoms of CO poisoning are: tiredness, drowsiness, dizziness, chest pains and nausea.

Householders can reduce the risk of CO poisoning by:

• Having appliances installed and properly checked by competent engineers
• Getting chimneys and flues inspected and swept
• Not overloading a fire and only burning the fuel it is designed for
• Fitting a carbon monoxide detector

The Health and Safety Executive has policy responsibility for carbon monoxide issues.

The most common causes of chimney fires are:

• Infrequent sweeping and cleaning
• Burning unseasoned wet wood
• Improper appliance sizing
• Overnight burning or smouldering wood for long periods in wood stoves

It is recommended that these measures are taken to help reduce the risk of chimney fire:

• Chimneys must be swept on a regular basis this can be as much as three times in the burning season (winter) but at least once per season regardless of fuel type.
• All wood burned must have a moisture content of no more than 25 percent. Moisture meters are available to provide consumers with information about moisture content – Visit the HETAS website for more information about fuel quality.
• It is important to purchase the correct size appliance for your room, an appliance which is too large will never be used hot enough to volatilise all of the fuel within the wood and unburned fuel will pass up the chimney as smoke and condense within the flue as extremely flammable creosote.
• To minimize creosote production in a wood stove these steps can be followed:
  
  
  • Once the fuel load has been ignited and the flue has been heated to its operating temperature, the stoves air supply should be adjusted to limit the amount of air to avoid over firing and excessive heat loss up the chimney. They should, however, be open enough to maintain moderate flaming combustion in the fire box (the flames should fill the entire window or fire box without being sucked up the chimney).
  • To determine if this is maintained the condition of the fire should be checked through any glass panels and the density of the smoke as it exits the flue at the top should also be checked.
  • An internal probe type thermometer located within the flue can be used to ascertain if flue temperatures are of a sufficient temperature, or if they are excessive, magnetic flue temperature thermometers can also be utilised to this end
  • It is important when using a multi fuel stove that you control the burning of the appliance by the air inlets provided for this purpose not using any dampers which could obstruct the safe passage of exhaust from being able to exit the appliance

Remember a blocked flue can kill and the exclusion of air will put out a fire.

These types of terminals are designed to give ventilation to unused chimneys only. They should not be fitted to chimneys that have working gas, oil or solid fuel fires or boilers, as they slow the escape of the fumes from the chimney and could cause smoke and carbon monoxide to enter occupied rooms. If you have one of these fitted to your chimney ensure it is removed if you wish to use the chimney.

Any person that uses flued appliances has a responsibility to maintain the appliance and flue. It is often stated that people should take reasonable care within the terms of household insurance policies and in the instance of thatched properties, the frequency of sweeping required is often specified by the insurers.

Landlords have a duty of care to their tenants and are required:

• To repair and keep in working order, any room heater and water heating equipment

Visit the NACS website for further technical information on chimney safety.

Chimney sweeping is important. The function of sweeping the flue/chimney is to remove the deposits that build up when the burning of carbon based fuels occur. By sweeping the flue/chimney it ensures that there is a clear and safe passage for the safe exit of combustion products, which are caused by the burning process. This lessens the chances of the chimney catching fire.

It is important to remember that all fuels contain carbon – including oil, gas, wood, charcoal, coal and smokeless fuel – and care should be taken with all flues at all times to ensure its safe use. If you do not get complete combustion then carbon monoxide will be produced.

Sweeping will also ensure the safe removal of obstructions that may have lodged inside the flue:

• Nests
• Cobwebs
• Flue collapse (loose brickwork), which could prevent the safe exit of products of combustion

The other function of a chimney sweep is to help and advise people in the safe use of the appliance or intended appliance they may be called out to sweep.

Sweeping frequency recommendations:

• Smokeless coals - at least once a year
• Wood - up to four times a year
• Bituminous coal - twice a year
• Oil - once a year
• Gas - once a year

After a chimney fire has occurred and been extinguished, the chimney must be inspected as soon as possible. A certified sweep should perform a thorough inspection before the chimney is used again to ascertain if the rapid and dramatic changes of temperature, which would have occurred within the chimney, have caused any damage and also to determine the need for any remedial measures. It is imperative that the chimney is not used prior to inspection.

If any damage is present and there is another chimney fire then it is quite likely the fire will spread to other parts of the building. If cracks are present within the flue then poisonous fumes can either filter through these cracks or damage. This may effect and dilute an effective warm air up draught and cause the fire to smoke. After a chimney fire, it is extremely important to sweep the burned "expanded" creosote residue from the flue, as this will cause obstructions and blockages within the flue. It is likely that, after a chimney fire, some damage will have occurred and remedial work will be necessary.

It is essential that a smoke test is carried out in accordance with the current Document J Standards.

You can search for a Chimney Sweep on the NACS website.

Alternatively, you can search for a chimney sweep on the HETAS website.

Download a leaflet about heating your home safely.

Contact us if you require further information, or have another community safety enquiry.