Too soon?

flammable isn't really an accurate word for hydrogen.

one of the first things they teach you in highschool chemistry is the "pop test" and that sure isn't a slow burn.

not only that, hydrogen cannot burn all at once like that without it already being in a pretty much precise ratio of 1:1 with oxygen, which isn't going to happen, and that means literally the hydrogen will mostly snuff itself out long before it gets a chain reaction starting, if the violence of the ignition of any part of it happens that's going to break a chain reaction by rapid dispersion

the hindenberg did not explode. its fire was not white, as it would have been if it were hydrogen. they literally used yellow iron oxide pigment and metallic aluminium turnings to make it all pretty and that is thermite, which caught on fire due to the nylon of the main body of the thing combined with some kind of natural fibre causing an electrostatic discharge that started the thermite and nylon burning.

you can see clearly in the film of the event that it was burning like thermite.

furthermore, the Mythbusters guys totally simulated it and proved it was not hydrogen burning but thermite.