Atomic hydrogen welding is basically taking a COTS plasma cutter and blowing H2 thru it and welding with it, not welding with H2 but with hydrogen ions. On a scale of hazardous welding technologies, its up there. Possibly the only thing I'd less enjoy doing by hand would be explosive welding or some of the thermite processes. Its not "is there going to be a fire" but "how much damage will the inevitable fire cause vs the cost of alternative fabrication"
On the bright side (oh the pun) during the welding its pretty efficient at preventing weld pool oxidation. On the bad side, if long term hydrogen embrittlement is an issue with the base metal, this is an interesting way to find out. Also you can get some gas porosity problems as the weld bubbles while cooling, exactly CO2 in soda water, although hydrogen is better than the noble gasses (like argon in a plasma cutter)
Burning homemade H2 in a modified acetylene torch like you're talking about is comparatively harmless with the exception that H2 can find leaks that acetylene can't find, although its not that much worse. Oh and the regulator is different because acetylene comes out of a coke bottle solution like CO2 out of soda, but hydrogen comes out of a tank like O2 so the pressures are a bit higher.
On the bright side (oh the pun) during the welding its pretty efficient at preventing weld pool oxidation. On the bad side, if long term hydrogen embrittlement is an issue with the base metal, this is an interesting way to find out. Also you can get some gas porosity problems as the weld bubbles while cooling, exactly CO2 in soda water, although hydrogen is better than the noble gasses (like argon in a plasma cutter)
Burning homemade H2 in a modified acetylene torch like you're talking about is comparatively harmless with the exception that H2 can find leaks that acetylene can't find, although its not that much worse. Oh and the regulator is different because acetylene comes out of a coke bottle solution like CO2 out of soda, but hydrogen comes out of a tank like O2 so the pressures are a bit higher.