Results of application of the technology of vapor-air burn-out of coke from the quenching-vaporizing units (QVU) in an EP-300 ethylene plant operated by the JSC Tomskneftekhin (Tomsk Petrochemical LTD), which improves the operational efficiency of pyrolysis oven trains by reducing QVU decoking time, and, consequently, raises the yield of target products are reported. The efficiencies of conventional mechanical cleaning of QVU tubes vis-a-vis the vapor-air decoking process are indicated.