Another possible reason for the fire was the coating of the ship. The Hindenburg was coated in a combination of iron oxide, cellulose acetate and aluminum powder to prevent it bursting as the hydrogen expanded. It was said by a professor of chemical engineering that "the total mixture might well serve as a respectable rocket propellant". This is known as 'doping', and was also used to reflect the sunlight off the surface of the ship, which would have caused it to heat up to an even greater extent. The aluminium was used for the is purpose.
Unfortunately the aluminium, a metal, could also caused a great static charge to build up on the ship surface while the ship flew through storm clouds, a precipitation charge. A precipitation charge causes lightening in clouds as the charge is neutralised by the lightening strike.
The designers of the Hindenburg thought this had been countered as they planned for the charge to be grounded by the mooring ropes when they touched the ground. There was a problem though as the charge was held on the different panels of surface material. Though all of the panels would have been charged in the storm, some might not have been discharged by the mooring ropes. This would mean that a spark could eventually be produced. The spark would then have ignited the material covering the ship and lead to the fire.
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