[yuubi]

the story seems to be set in a world that uses gas to weld steel as part of a production process, making a blue flame. are there any torches that can weld steel and make a blue flame? does anyone use manual gas welding in automotive production‽

[anenefan]

The blue light is from a arc welding process be it stick rods or gas shielded continuous wire. A flame would not have the on and off as described as well as being hard to detect at any distance. The most common steel welding flame process, oxy acetylene flame has an inner blue hue but the welding pool is probably brighter, so I doubt even at 10 feet a person could notice any particular colour hue, for anything hand held.