Abstract: This invention relates to processes and apparatus for detecting the overall nature of combustion gases using a detector comprising a semi-conducting film of a metallic phthalocyanine which is deposited between two electrodes on an insulating wafer and which is placed in contact with the combustion gases and maintained at a temperature higher than a determined threshold, for example higher than 40.degree. C. for a monoclinic copper phthalocyanine, in order to render the phthalocyanine insensitive to the water vapour contained in the combustion gases.