​Creosote is a highly flammable tar-like substance that can easily start a chimney fire if it is not removed!

Creosote

Creosote and soot build-up in your chimney can be a fire hazard if your flue is not properly cleaned and maintained. 
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Creosote is a natural by-product of burning wood and its associated products; it can be defined as a combustible deposit which originates from condensed wood smoke. It includes tar vapours and other organic compounds. Tar droplets make up a major component of the smoke from smouldering wood.  These compounds are always present when the combustion process of wood is incomplete.
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There are three stages or degrees of creosote.

Stage 1 creosote is a fine black powder or dust.
Stage 2 creosote becomes a more rock-like formation.
Stage 3 creosote is like tar. It is sticky and viscous before hardening and having a glaze-like appearance. It is a highly concentrated fuel which hardens and can form a thick layer. As such it can easily catch fire resulting in a potentially devastating chimney fire. 

All three stages of creosote are combustible, but the longer you wait to have it cleaned, the greater your chance of a chimney fire.

Third degree creosote cannot be removed by conventional sweeping using a brush. It must be chemically treated.
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Third degree creosote is usually the result of one or more of the following:

• Incomplete combustion
• The chimney is not insulated or is cold 
• Burning unseasoned wood 
• Insufficient ventilation for the appliance
• An oversized flue for the appliance

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