These are fires whose fuel is flammable or combustible liquid or gas. SnO is used in sensors of combustible gases including carbon monoxide detectors. Catalytic heaters generate flameless heat from a supply of combustible fuel. The predominant use of hydrocarbons is as a combustible fuel source. These eddies can contract a tornado-like vortex that sucks in debris and combustible gases. Flammability of combustible liquids are defined by their flash-point. It should not be stored near combustible substances. Acetic anhydride is an irritant and combustible liquid. Oxygen is a highly reactive substance and must be segregated from combustible materials. Special precautions are usually required for substances that are easily combustible. There are at least a 140 known substances that produce combustible dust. It is usually applied to a combustible fuel mixture. GFRPs hinder incineration and are not combustible. Eyewitness reports confirmed the use of a combustible chemical in addition to kerosene. It is also important in processes that produce combustible substances as a by-product.