The black substance left behind as a result of burning wood and coal is called soot. This substance is classified as a mixture of impure carbon particles that result when hydrocarbons are improperly burned.
While soot is often considered to be a harmless by-product of a fire, it is actually an airborne contaminant that is harmful to the human body when inhaled. Soot is also produced by many other processes, including waste incineration, steam boilers and internal combustion engines. In the case of gasoline and diesel engines, particle filters are generally used to reduce the amount of soot released into the air.