Soot & Creosote
Every time wood is burned in a fireplace, soot is created.
Regular soot results if exclusively dry, split and not too big pieces of wood are used. Soot is wood that has been
completely burned. The soot is transported through the
chimney to the outside together with the smoke.
Regular soot is either brownish, grey or matt black, and it is always of very fine and of dusty consistency.
Highly Combustible Creosote
Creosote is wood that has not been burned completely. Creosote is caused if wet, humid, poorly seasoned, or large pieces of wood are burned in the fireplace. Creosote is vapourous wood that is transported through the chimney to the outside together with the smoke. During this process, the vapourous creosote sticks to the inner walls of the chimney. The creosote dries out and remains as a persistent deposit inside the chimney.
Creosote is highly combustible and consits of almost 100% incompletely burned wood.
Why Is Creosote Dangerous?
Once there is sufficient creosote buildup, the highly combustible creosote inside the chimney can be ignited by a regular fire in the fireplace and cause a chimney fire. The temperature of a chimney fire is at least 2000 °F and higher. A regular chimney cannot withstand this high temperature, therefore the outside wall of the chimney will be hot enough to ignite combustible materials around the chimney. In most cases, the walls of the chimney will break from the inside out, and while many chimney fires stay contained inside the chimney liner, it is not uncommon for a chimney fire to become a structural fire as well.
Chimney sweeping is the primary defense against chimney fires.