Chimney fire

A chimney fire is the combustion (burning) of residue deposits referred to as soot or creosote, on the inner surfaces of chimney tiles, flue liners, stove pipes, etc.

The process begins with the incomplete combustion of fuel in the attached appliance, usually a wood or coal stove, or open fire. The unburned volatiles are heated to the vapor state but not consumed due to a lack of adequate heat and oxygen within the appliance. These volatile distillates escape into the chimney, where they contact cooler surfaces and condense into tar-like deposits, and soot. Successive layers accumulate until either the chimney plugs completely, or the chimney reaches a temperature and oxygen level at which the deposit will ignite. Due to the concentrated level of volatile material now present, these fires tend to burn very hot.

Alternatively, a chimney fire may be caused by old bird's nests which have fallen into the chimney and lodged there. When a hot ember ignites the nests, the fire can be just as serious as one caused by ignition of soot. In very old houses, the chimney may also be very large and thick enough to withstand the fire.

The high temperatures may affect the strength of the chimney causing distortion of metal structures, and potential failure of ceramic structures.

Causes of the deposits which lead to chimney fires include using green/wet fuels, the operation of appliances with insufficient air intake, and low operating temperatures for prolonged periods followed by hot fires. Such practice typically occurs when mild weather periods are followed by cold snaps.

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