Done in the lab at PSU at several thousand frames per second. Sounded like an explosion due to the 'higher' pressure of the H2 gas. The tissue, just below the balloon, bursts into flames (but only just gets started in this image--the burn rate of the tissue is much slower than the H2 burn).
This is the first nearly full size H2 Burn out on Rich's 'Smith Berry Barn' farm in Scholls (OR).
This is the second overfilled H2 Burn test.