There is an important distinction in hydrogen fires from jet fuel ones: the moment it is released hydrogen escapes upwards, taking any fire with it. Jet fuel on

There is an important distinction in hydrogen fires from jet fuel ones: the moment it is released hydrogen escapes upwards, taking any fire with it. Jet fuel on the other hand tends to pool downward, while releasing its vapor (the part that actually burns) upwards. So it tends to spread fires in both directions. So a hypothetical of a zeppelin crashing into a building might light that building on fire, but most of the hydrogen from the vehicle would escape upwards into the atmosphere without having contributed to the building's fire.