[summa_tech]

While hydrogen-air mixes explode really readily (outstandingly wide flammability and pretty wide detonation range), and the energy released is considerable for the weight, the actual explosion does not produce a particularly high overpressure wave.

That's because the starting density of the hydrogen air mixes at near atmospheric pressure (such as in a balloon) is pretty low. Also, the balloon does not significantly contain the explosion, which reduces the danger a lot. I would not want to do it in a glass container.