Oxy / Acetylene welding?
Extremely slim chance of a tank exploding without " help" from an outside source.
There are inexpensive ,one way safety valves to prevent "backflash" on gas lines that go between the regulator & fuel gas hose.
Only other dangers are to unprotected eyes & skin as well as fire because of combustible material in the work area.
Low pressure , unregulated fuel tanks ( Bernzomatic & plumbers type sweating torches) are not a problem.
Any welding supplier can set you up w/ necessary safety equipment & advice.