Hydrogen explosion or combustion process usually requires the following:
1)fuel
2)oxidizer
3)heat or spark or source of ignition.
In this case, hydrogen as the fuel and is oxidized by the oxygen as both molecules combined. When hydrogen and oxygen is mix it does not automatically explode. It still need a spark to ignite the combustion then the explosion-the bang.After that, water is form as a product of the combustion.
Here's the equation: 2H2 + O2 -> 2H2O.
The combustion process releases large amount of energy, in the form of heat that causes the water vapor to expand rapidly. This rapid expansion of gases is in fact, the basic principle of all explosives.
Watch this youtube video on hydrogen combustion/explosion.
The bubbles contained the hydrogen. So be careful with your experimentation.
If the hydrogen bubbles is contained and closed in a jar or bottle with no valve and using only a short nozzle, it would explode and shatters the jar or bottle.