Abstract: A fast, safe pyrogenic external torch assembly that provides pure steam for semiconductor processing in semiconductor processing furnaces includes a gas injection nozzle subassembly, a pulse heater subassembly and a compressed-air-cooled heat-exchanging jacket subassembly. The gas injection nozzle subassembly includes plural oxygen gas injection nozzles and a hydrogen gas injection nozzle that cooperate to provide a torch that is well-behaved over the practicable range of oxygen and hydrogen gas supply rates and ratios, that may be quickly ramped to any desired gas flow conditions and that is free from the possibility of unwanted explosion due to incomplete hydrogen gas consumption. The pulse heater subassembly includes one or more blackbodies and a radiant energy source that are cooperative to quickly and efficiently provide one or more hot spots at the industry safe-ignition temperature.