A chimney fire is the combustion

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of residue deposits referred to as creosote, on the inner surfaces of chimney

Chimney

A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

 tiles, flue

Flue

A flue is a duct, pipe, or chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. In the United States, they are also known as vents and for boilers as breeching for water heaters and modern furnaces...

 liners, stove pipes

Chimney

A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

, etc. The process begins with the incomplete combustion (burning) of fuel

Fuel

Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

 in the attached appliance

Home appliance

Home appliances are electrical/mechanical machines which accomplish some household functions, such as cooking or cleaning. Home appliances can be classified into:*Major appliances, or White goods*Small appliances, or Brown goods...

, usually a wood or coal stove. The unburned volatiles are heated to the vapor

Vapor

A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 state but not consumed due to a lack of adequate heat

Heat

In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 within the appliance. These volatile distillates

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 escape into the chimney, where they contact cooler surfaces and condense into tar

Tar

Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

-like deposits. Successive layer

Layer

Layer may refer to:* A layer of archaeological deposits in an excavation* A layer hen, a hen raised to produce eggs* Stratum, a layer of rock or soil with internally consistent characteristics...

s accumulate until either the chimney plugs completely, or the chimney reaches a temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 and oxygen level at which the deposit will ignite

Combustion

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

. Due to the concentrated level of volatile material now present, these fires tend to burn very hot. The high temperatures stress the mechanical strength of the chimney causing distortion of metal structures, and failure of ceramic structures.

Causes of the deposits which lead to chimney fires include using green

Green wood

Green wood is a term used to describe wood products that have been recently cut and have therefore not had an opportunity to "season" by evaporation of the internal moisture. The term is used often in describing the relative moisture content of wood products such as firewood and lumber...

/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

Cold wave

A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24 hour period requiring substantially increased protection to agriculture, industry, commerce, and...

.

Steps to avoid this buildup of deposits include running appliances hot during initial ignition phase regularly, building short hotter fires, regular cleaning of flues

Modern chimney cleaning

Today, chimney sweeps still maintain a thriving new industry in many parts of the world. The industry has expanded from the maintenance of wood-burning fireplace and appliance venting systems to include venting for many types of heating appliances...

, and using interior chimney structures where possible versus chimneys attached to exterior walls. The latter tend to be cooler contributing to the problem as well as creating downdrafts which tend to introduce smoke

Smoke

Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

 into the structure as the fire subsides.

Control includes denial of oxygen, addition of extinguishing agents, and removing heat sources. Local fire authorities should be immediately notified due to the danger of failure of the chimney to maintain integrity, and spread of fire within adjoining partition

Room

A room is any distinguishable space within a structure.Room may also refer to:* Room , by Emma Donoghue* Room, Nepal* Room for PlayStation Portable, a social networking service* Thomas Gerald Room , Australian mathematician...

s of the structure.
Additional hazards include the possible buildup of toxic gases such as carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

within the structure due to restricted flues.