A method for starting up a pressurized partial oxidation gas generation system comprising a gas generator and gas purification train without atmospheric pollution. The method comprises isolating and prepressuring the gas purification train to a pressure of at least 50 percent of normal operating pressure, starting the gas generator and autogenously increasing the pressure in the gas generator to the pressure of the gas purification train before establishing communication with the gas purification train to permit flow of gas through the gas purification train. Purified gases discharged from the gas purification train may be burned in a flare without atmospheric pollution.