Likely static charge from a cloud causing hydrogen to ignite. Hydrogen burns freely at all concentrations both very low and very high and is therefore far, far more flammable even than natural gas, so I’m afraid hydrogen airships will always be a catastrophe waiting to happen.
https://en.m.wikipedia.org/wiki/Hindenburg_disaster
Likely static charge from a cloud causing hydrogen to ignite. Hydrogen burns freely at all concentrations both very low and very high and is therefore far, far more flammable even than natural gas, so I’m afraid hydrogen airships will always be a catastrophe waiting to happen.