Smoke generally refers to a visible mixture of products given off by the incomplete combustion of an organic substance such as wood, coal, fuel oil etc.. This airborne mixture general contains small particles (dusts) of carbon, hydrocarbons, ash etc. as well as vapors such as carbon monoxide, carbon dioxide, and water vapor. Liquid droplets may also be present in the mixture. The term "smoke" is closely related to "fumes". Smoke is generally reserved for products of combustion, however the two are sometimes used interchangeably. In general use, any cloud of fine particles can be referred to as a smoke. Soot refers specifically to the fine, black, carbonaceous (carbon-containing) particles produced by incomplete combustion of an organic material. Soot can be airborne or collect on a surface such as a chimney or flue liner. Soot can contain carcinogenic compounds such as polycyclic aromatic hydrocarbons and is a flammable material, so treat it with respect!