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On May 6, 1937, at 19:25 the German zeppelin Hindenburg caught fire and was utterly destroyed within a minute while attempting to dock with its mooring mast at Lakehurst Naval Air Station in New Jersey. Of the 97 people on board, 13 passengers and 22 crew-members were killed. One member of the ground crew also died, bringing the death toll to 36.
The LZ-129 Hindenburg and her sister-ship LZ-130 "Graf Zeppelin II" were the two largest aircraft ever built. The Hindenburg was named after the President of Germany, Paul von Hindenburg. It was a brand-new all aluminium design: 245 m long (804 feet), 41 m in diameter (135 ft), containing 211,890 m³ of gas in 16 bags or cells, with a useful lift of 112 tons, powered by four 1100 horsepower (820 kW) engines giving it a maximum speed of 135 km/h (83 mph). It could carry 72 passengers (50 transatlantic) and had a crew of 61. For aerodynamic reasons the passenger quarters were contained within the body rather than in gondolas. It was skinned in cotton, doped with iron oxide and cellulose acetate butyrate impregnated with aluminium powder. Constructed by Luftschiffbau Zeppelin in 1935 at a cost of £500,000, it made its first flight in March 1936 and completed a record double-crossing in five days, 19 hours, 51 minutes in July.
The Hindenburg was intended to be filled with helium but a United States military embargo on helium forced the Germans to use highly flammable hydrogen as the lift gas. Knowing the risks of hydrogen gas, the engineers used various safety measures to keep the hydrogen from causing any fire when it leaked, and they also treated the airship's coating to prevent electric sparks that could cause fires.
The disaster is remembered because of extraordinary newsreel coverage, photographs, and Herbert Morrison's recorded radio eyewitness report from the landing field. Morrison's words were not broadcast until the next day. Parts of his report were later dubbed onto the newsreel footage (giving an incorrect impression to some modern eyes accustomed to live television that the words and film had always been together). Morrison's broadcast remains one of the most famous in history – his plaintive words "Oh, the humanity!" resonate with the memory of the disaster.
Herbert Morrison's famous words should be understood in the context of the broadcast, in which he had repeatedly referred to the large team of people on the field, engaged in landing the airship, as a "mass of humanity." He used the phrase when it became clear that the burning wreckage was going to settle onto the ground, and that the people underneath would probably not have time to escape it. It is not clear from the recording whether his actual words were "Oh, the humanity" or "all the humanity."
There had been a series of other airship accidents (none of them Zeppelins) prior to the Hindenburg fire, most due to bad weather. However, Zeppelins had accumulated an impressive safety record. For instance, the Graf Zeppelin had flown safely for more than 1.6 million km (1 million miles) including making the first complete circumnavigation of the globe. The Zeppelin company was very proud of the fact that no passenger had ever been injured on one of their airships.
But the Hindenburg accident changed all that. Public faith in airships was completely shattered by the spectacular movie footage and impassioned live voice recording from the scene. Because of this vivid publicity, Zeppelin transport came to an end. It marked the end of the giant, passenger-carrying rigid airships.
Questions and controversy surround the accident to this day. As with many historic events, interpretations of the causes are often colored by politics and polemics.
On the one hand, some speculate that the German government of that era placed the blame on flammable hydrogen in order to cast the U.S. helium embargo in a bad light. suggest that present-day proponents of hydrogen as a transportation fuel have forwarded a revisionist "flammable fabric" analysis of the fire in order to deflect public concern about the safety of hydrogen.
Nonetheless, there remain three major points of contention: 1) How the fire started, 2) Which material (fabric or gas) started to burn first and 3) Which material (fabric or gas) caused the rapid spread of the fire.
At the time, sabotage was commonly put forward as the cause of the fire, in particular by Hugo Eckener, former head of the Zeppelin company and the "old man" of the German airships. The Zeppelin airships were widely seen as symbols of German and Nazi power. As such, they would have made tempting targets for opponents of the Nazis. However, no firm evidence supporting this theory was produced at the formal hearings on the matter.
Although the evidence is by no means conclusive, a reasonably strong case can be made for an alternative theory that the fire was started by a spark caused by static buildup. Proponents of the "static spark" theory point to the following:
The airship's skin was not constructed in a way that allowed its charge to be evenly distributed and the skin was separated from the aluminium frame by nonconductive ramie cords. The ship passed through a moist weather front. The mooring lines were wet and therefore conductive. As the ship moved through the moist air the skin became charged. When the wet mooring lines connected to the aluminium frame touched the ground they grounded the aluminium frame. The grounding of the frame caused an electrical discharge to jump from the skin to the grounded frame. Witnesses reported seeing a glow consistent with a St. Elmo's fire.
Most current analysis of the accidents assumes that the static spark theory is correct. However, as discussed above, there are two schools of thought as to whether it was the hydrogen gas used for buoyancy or the coating on the fabric envelope that provided either the initial fuel for the fire and/or served as the primary means for the rapid spread of the flames.
of the "flammable fabric" theory point out that the coatings on the fabric contained both iron oxide and aluminium impregnated cellulose acetate butyrate. Cellulose acetate butyrate is well known to be flammable and iron oxide is well known to react with aluminium powder. In fact, iron oxide and aluminium are sometimes used as components of solid rocket fuel or thermite. (However, the oft-cited claim that the ship was "coated in rocket fuel" is a significant overstatement.) While the coating compenents were potentially reactive, they were separated by a layer of material that should have inhibited the reaction from starting.
After the disaster the Zeppelin company's engineers determined this skin material, used only on the Hindenburg, was more flammable than the skin used on previous craft. Nonetheless, the Hindenburg had flown for over a year (and through several lightning storms) with no reports of adverse chemical reactions much less fires on the fabric.
The proponents of the "flammable fabric" theory also point to fact that the naturally odorless hydrogen gas in the Hindenburg was 'odorised' with garlic so that any leaks could be detected, and that there were no reports of garlic during the flight or prior to the fire.
The proponents of the "flammable fabric" theory also contend that the fabric coatings were responsible for the rapid spread of the flames. They point out that hydrogen burns invisibly (emitting light in the UV range) so the visible flames (see photo) of the fire could not have been caused by the hydrogen gas. Also motion picture films show downward burning. Hydrogen, being less dense than air, burns upward.
Opponents of the "flammable fabric" theory point out that once the fire started, all of the components of the ship (fabric, gas, metal, etc) burned. So, while it may be that the combustion of the metal and fabric changed the color of the flame, the presence of color does not imply that hydrogen did not burn as well. Further, while all fires generally tend to burn upward, including hydrogen fires, the enormous radiant heat from the burning of all of the materials of the ship would have quickly led to ignition over the entire surface of the ship, thus explaining the downward propogation of the flames.
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