[amluto]

That’s not the same thing, though — your dad forgot the oxygen! A balloon full of approximately pure hydrogen makes a nice fireball but doesn’t really explode — the same group that made the exploding balloon I watched also did one of those.

The stoichiometric premixed balloon is only 2/3 H2 by volume, so it releases 1/3 less energy, but it’s a whole different experience when the energy is released essentially all at once. Interestingly, there was no noticeable fireball from the premixed balloon.

A premixed H2+air balloon probably makes a fine explosion, too :)

[sfink]

> That’s not the same thing, though — your dad forgot the oxygen!

Oh, I'm quite aware. The other fun game we played was with his acetylene welding torch and balloons. It has separately controlled tanks of acetylene and oxygen. Acetylene only = nice big fireball. Acetylene + oxygen = no fireball at all, instead a very loud boom + a bit of a shockwave.

[amluto]

A quick search for higher heating values suggests that acetylene and hydrogen gasses have fairly similar HHV per mole of oxidizer. (H2 needs 1/2 equivalent or O2; acetylene needs 5/2 equivalents, so H2 wins by a bit.)

But H2 takes up most of the space in the balloon, and acetylene is nice and compact, so considerably more total energy should be available with acetylene!

I don’t know whether oxyacetylene will detonate nicely, though, or whether a balloon-sized oxyacetylene mix will merely combust subsonically.