Abstract: Molecular chlorine level in flue gases from incineration of chlorinated organic materials is reduced by injecting into the incinerator's quench zone an amount of a C.sub.1 -C.sub.4 hydrocarbon which depends on the amount of air fed into the combustion zone, the amount of air being such that there is a 1-40 % excess of oxygen. When the wall temperature of the combustion zone is about 800.degree.-1500.degree. C., the temperature at which the hydrocarbon is added to the quench zone is about 450.degree.-1000.degree. C. Hydrogen chloride, which is formed from molecular chlorine and hydrocarbon, is more readily water-scrubbed than chlorine, so that less polluting flue gases are obtained.