Instabilities in the pyrogenic production of fumed silica caused by use of silanes having low ignition temperatures are caused by mixing the silanes, at a temperature above their dew point(s) with fuel gas in the absence of the use of a dynamic or static mixer, and then combining the resultant mixed stream with an oxygen containing gas and igniting. Self-ignition of the silanes and also the deposition of flammable or pyrophoric substances are avoided.