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What Makes Creosote?

"Creosote" refers both chemicals used to treat and preserve wood and residual deposits in chimney flues caused by incomplete wood or coal burning. Both are black, oily substances that can be dangerous in large quantities.

  1. The Preservative

    • Burning wood or coal at high temperatures yields ashes and deposits which are then distilled with other chemicals and oils to create wood tar or coal tar creosote. These creosotes, specifically coal tar creosote, are used to treat wood to keep it from sun or rain damage, especially on utility poles, bridges, log homes or railroad ties.

    The Flue Deposits

    • Burning wood or coal at low temperatures in residential fireplaces causes incomplete combustion of the products. Residue rises with the smoke and condenses inside the chimney flue, creating the black oily buildup called "creosote." This creosote is similar in composition to the preservative, but without all the process.

    The Dangers

    • When burned, wood treated with creosote releases harmful toxins into the air which, in large amounts for prolonged periods of time, can cause lung problems. The preservative creosote may also pollute groundwater via industrial runoff. Chimney-flue creosote primarily poses fire risks, as the accumulation may compound over time and provide a highly-combustible material should hot oxygen come in contact with it. This creosote causes chimney fires: 73-percent of heating fires and 25-percent of all residential fires can be tied to creosote.

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