The Hindenburg Disaster
Prior to World War I, and during the early 1930s, Zeppelin Dirigibles represented the future of luxury travel. Whilst expensive, they were faster than trains or steam liners, presenting an attractive option for business travel and express mail service. When the Empire State Building was constructed in 1930, its spire and the 102nd floor were intended as an airship terminal.
On May 6, 1937, the age of the airship ended in flames. Three days earlier, LZ129, the Hindenburg, had department from Frankfurt headed for Lakehurst New Jersey. Delayed by adverse weather, and with a further storm brewing, the airship began a landing approach just after 7 pm. The tail was low, and repeated attempts were made to maintain level flight by dropping ballast and releasing hydrogen from the gas cells at the bow.. Eventually crew were even ordered to move to the front of the airship to add weight to the nose.
So, a storm brewing, a misbehaving airship, and a shifting wind. Captain Pruss, the commanding officer, ordered a tight turn to allow landing into the wind. At 7:21 the maneuver was completed, and landing ropes were dropped. At this stage the Hindenburg was 180 feet above the ground. Two of the ground crew would later report that they saw the outer covering flapping near the port rear of the airship. A few minutes later flames appeared at or near this spot, and crew on board the ship heard an explosion. Less than 30 seconds later the Hindenburg was on the ground engulfed in flames.
Despite the rapid destruction of LZ 129, 62 of the 91 people on board survived. Proximity to an exit was the main factor in survival – those who were killed were all deep within the airship or trapped on the starboard side when the ship rolled slightly as it hit the ground. Survivors also owed a debt to the Navy ground crew who ran towards the Hindenburg as it burned.
Whilst there were other airship disasters – most notably the British R101 and the USS Akron – this was only the second fatal crash of an actual Zeppelin in peacetime.
Two fatal accidents in 2000 flights is simply not enough data to tell us how dangerous the airships were. However, we can make a rough estimate by assuming that the underlying likelihood of accidents was somewhere between half and double the measured frequency. This gives us between 500 and 2000 accidents per million departures.
By contrast, early commercial aircraft such as the Boeing 707 and DC-8 experienced around 4 fatal accidents per million departures.
A fairer comparison though, might be the first commercial jet airliner, the De Havilland Comet 1, which began operations in 1952. There were 10 of these in operation, compared to 7 commercial passenger Zeppelins. In the two and a half years before the early Comets were grounded, there were around 2000 departures with four fatal crashes.
In other words, Zeppelins were very dangerous compared to mature jet airplane designs, but comparable to early jet flight. We’ll never really know if an improved understanding of airship safety would have led to low accident rates, or if the concept itself was inherently risky.
The main risk of hydrogen dirigibles was of course, hydrogen. More specifically, it was the very low energy required to ignite hydrogen, and the wide range of conditions under which hydrogen and oxygen mixtures are explosive.
There were two typical scenarios in which airships burned.
In the first scenario, an otherwise airworthy dirigible caught fire due to an uncontrolled ignition source. For example, LZ-6 burned when petrol was used to clean it, LZ-10 caught fire from static electricity, and the fire in LZ-18 started in the engines before spreading to the hydrogen cells.
In the second scenario, the dirigible suffered structural damage in a crash, and subsequently caught fire. This was the fate of R38 and R101.
Hindenburg apparently suffered both structural damage AND ignition, but the causes were undetermined. Two credible theories suggest that the storm or the tight landing manoeuvre fractured the rigid frame of the airship, ripping the hydrogen cells and eventually providing a spark.
Modern advocates of hydrogen-based technology such as hydrogen fuel cells often try to downplay the role that hydrogen played in airship accidents. They point to the materials used in covering and coating the Hindenburg as the real culprits. These arguments are contradicted by the available evidence, which despite the uncertain causes points clearly to a massive hydrogen fire playing the key role in all of the fatalities.
Finding alternative explanations for the Hindenburg disaster is futile and unnecessary. Fuel cells store and use hydrogen in a completely different fashion to airships, and have their own risks and benefits. Advocates would do better to point to the inherent danger and certain damage caused by fossil fuelled vehicles – the days of hydrogen being a scary word have, along with the grandeur and luxury of Zeppelins, passed into aviation history.
For modern safety engineers, the fate of the Hindenburg illustrates neatly the precedence of hazard mitigation. The first question you ask yourself about a hazard is whether it is necessarily present. For example, being a long way off the ground is dangerous, but it is probably necessary for efficient travel over long distances. On the other hand, a large bag of explosive gas is probably not so necessary, and replacing the gas with something else is a good idea.
