Environment & Energy

...because H2 is lighter than air and so it rises up and away, while heavier-than-air methane pools and puddles among the near environment making the explosions much more damaging when they ignite.

A far as the Hindenburg footage, most of the flaming of the vessel that is seen on film was actually the canvas shell burning off quickly, that canvas was painted in flammable gels to make the canvas "air" tight to contain the H2 within. The H2 within did indeed burn, but mostly it rose quickly up and away due to being lighter than air.