According to the Chimney Safety Institute of America (CSIA) indications of a chimney fire can be described as creating: loud cracking and popping noise, a lot of dense smoke, and an intense, hot smell

The majority of chimney fires go undetected and the homeowner may not know they had a fire until a later chimney inspection. However, the high temperature of the fire can cause damage to the chimney structure.

Creosote is the resulting residue of the by-products  of combustion and it sticks to the inner chimney walls. Creosote is a brown or black residue that can be flaky and crusty, tar-like, shiny, or hardened. All forms of creosote are highly combustible and a build-up can cause a chimney fire when the internal flue temperature reaches high enough temperatures.

The best way to prevent a chimney fire is to have an annual inspection of the chimney

Example of creosote build-up and a creosote plug 

Cap showing damage from previously undetected chimney fire