Flammable gasses are handled safely and put to use effectively all the time. Hydrogen is no exception, no need to fear, not much different from acetylene or propane. It could be done safely in an experimental environment. Obviously not a practical option.
And just imagine how bad ass it would be if you fitted a pilot light to the muzzle. Part airgun, part flamethrower. Test it the first time with a very long string tied to the trigger.
