Hydrogen gets a bad rap. For the quantity that you’d have in a party balloon - even a dozen of them together - it’s safe, particularly as you aren’t going to ha

Hydrogen gets a bad rap. For the quantity that you’d have in a party balloon - even a dozen of them together - it’s safe, particularly as you aren’t going to have a stoichiometric mixture inside a balloon. If you managed to light one, you’d get a small implosion - much less than from a vacuum vessel. They’d also deflate more quickly, and wouldn’t travel anywhere near as far when inevitably released. You could even do instant balloons, which come pre-sealed and just require snapping a vessel within to generate hydrogen.