So, what was the real reason for the Hindenburg disaster? 

Well, it was thought for a long time that the reason was the hydrogen inside exploding, but this was recently proved incorrect. The eye witnesses saw coloured flames, but hydrogen burns with a colourless flame. 

From the films of the disaster it was seen that there was downward burning of the ship. Hydrogen only burns upwards, so the fire could not have been caused by the gas inside the ship. 

At the time after the disaster, the German engineers changed the coating of the Hindenburg's sister ship, the Graf Zeppelin. A common fire retardant, calcium sulfumate, was added to the mix and bronze replaced aliminium, which is far easier to burn. Bronze is heavier than aliminium but is also a better conductor, allowing the built up static charge to dissipate easier. Another change was to add graphite to the mooring ropes, making it more conducting and therefore allowing the charge to be grounded more efficiently.

So the real reason was a combination of the weather conditions and the skin of the ship. During the storm a large static charge built up which, as it discharged, ignited the highly combustible covering of the Hindenburg and led to the disaster.