I just finished viewing on PBS a doco on the Hindenburg airship disaster (Lakeland, New Jersey, USA).
The initial findings attributed the accident to static electricity accumulated as the airship and gone between bad weather cells, which discharged and lit off the hydrogen.
Using modern forensic methods, a NASA scientist, whose specialty is hydrogen (fuels specialist) started investigating the disaster.
The first suspicion was that eyewitness accounts indicated that the fire was red in color, not the blue of hydrogen. Also, that even as the fire was spreading from the rear towards the front, the airship maintained buoyancy for a longer time than burning off of the rear hydrogen cells would have supposed.
In the end, inspecting and researching with pieces of Hindenburg covering surviving to this day, he discovered that the fabric covering the airship was doped with a concoction of chemicals containing a significant concentration of iron oxide and powdered aluminium. As a side note, iron oxide and powdered aluminium are key components of the solid fuel in the Shuttle's boosters.
Further support for this theory came out in the Zeppelin Company's official inquiry into the disaster. Samples of the covering from the Graf Zeppelin and the Hindenburg were tested, under similar electrostatic discharges, and while the G. Zeppelin's covering did not burn, that of the Hindenburg, went up immediately. This testing was done barely two months after the disaster and the report was never made public.
Essentially, the Hindenburg would have burned whether it had had helium or hydrogen ... it was doped in rocket fuel..!!