How to Make an indoor hydrogen rocket
The picture may look like a mushroom cloud, but it is actually a can filled with hydrogen exploding. The can is fired into the ceiling. This demonstration still needs a little improvement in the area of safety (but it looks really cool). The problem is the partial pressure of hydrogen drops as the gas escapes and is replaced with air. This causes the reaction to be an explosion instead of a flame. Hydrogen is a tempermental element like that.