How Exactly Did the Explosion Occur
The Germans put up specific guidelines and clear instructions when dealing with an airship landing. As the Hindenberg was running a few minutes late, the crew lowered the ropes from a higher altitude in haste to be on time, resulting in a high landing.
Source: Wikimedia Commons
The people investigating the explosion agree that a spark of static discharge triggered the explosion by interacting with a hydrogen tank. The sudden lowering of the ropes and the presence of a thunderstorm at that moment increased the risk of the static discharge, in turn leading to the explosion.