Hydrogen was the fuel, there was plenty of oxygen too since it was out doors and I don't think that it was shot, more like detonated with some sort of an explosive charge.
Oh ya? http://www.youtube.com/watch?v=MMB2VR0087wNot a oxygen tank but uses the same elements,and sorry for double post.
I think I never posted this...
you should make it so when you throw it at people in elevators they fall through the floor