Reliable ignition of hot oxygen generator

A stream of hot oxygen is formed by providing a duct (3) and a fuel lance (7) movable axially within the duct, flowing gaseous fuel out of the lance into the duct, mixing it in the duct with gaseous oxidant, flowing the mixture out of the duct into an atmosphere which is hot enough that it ignites the mixture without aid of an ignition source other than said atmosphere, and combusting said mixture in a flame that does not extend into said duct; then moving the lance so its fuel outlet (9) approaches the duct exit orifice (5) so that the base of said flame moves inside said duct to the fuel outlet; and then moving the lance to draw the fuel outlet and the flame attached thereto away from the exit orifice into the duct; and increasing the flow rate of gaseous oxidant in said duct, so that combustion of fuel within the duct heats uncombusted oxygen which emerges as a stream of hot oxidant.