An oxy acetylene torch is a gas flame - mild or seriously hot, depending on settings.
I've removed quite a few stubborn or mangled bolts, that otherwise wouldn't budge, with a bit of heat.
If they get red hot for a moment, it usually frees them right off, no damage to anything or anyone...
A little gas flame from a propane etc torch may do the same job, I'd think that is the other one mentioned. May not be hot enough to get a red heat on the bolt though ?
hopethishelps.