Abstract: In the thermal purification of effluent gases charged with noxious substances by burning them with air at high temperatures, the improvement which comprises drawing the effluent gases charged with noxious substances through a zone established by a device which provides protection against back-firing and a combustion zone which is resistant to bursts of pressure of up to about 10 bars, and burning the effluent gases in the combustion zone at a temperature of about 800.degree. to 1000.degree. C. To carry out the process there is provided an apparatus comprising a back-firing safety device followed by a heat exchanger and then a combustion chamber. Components of the heat exchanger are made resistant to pressures of up to about 10 bars and the safety device prevents back-firing to the plant wherein the effluent gases are produced.