Balloons and Airships Main Index

Hydrogen, Helium, the Hindenburg, Airship Safety and the Future

At first sight it is obvious that a thin rubber bag containing 1000 m3, or even 1 000 000 m3, of a very flammable gas is Very Dangerous. So today helium, which is non-flammable, has almost completely replaced hydrogen for filling balloons and airships.

However, just because something is obvious does not mean that it is true. For example, if you had lived six hundred years ago it would have been obvious that ships could not be made out of iron. Wood floats, iron sinks: ships have to be made out of wood. If you had said you could make a ship out of iron you would probably have been locked up as a lunatic; if you had succeeded in making a ship out of iron it would have been obvious that you had used witchcraft and you would probably have been burnt at the stake.

Hydrogen is very much cheaper than helium, and also very easily manufactured in every part of the world, while most of the world's helium comes from underground rocks in the United States of America. Today there is a growing interest in the use of hydrogen as a totally non-polluting fuel, and so there is a renewed interest in hydrogen-filled airships.

If you let a flammable gas out of a pipe and light it where it is escaping the gas will burn and you will get a flame. This is not dangerous provided you do not burn yourself with it or allow it to set fire to other things near it - it is after all what you do every time you turn on the gas on your hob or oven. Even where a workman has put a pneumatic drill through a gas main and the escaping gas has become ignited, the 10 m high flame might be terrifying but it is not usually dangerous. The danger with flammable gases is not fire but explosion, where the gas has first escaped to mix with the air and then the mixture of gas and air has become ignited. This is very likely to happen where the gas is escaping into a confined space, for example a room in a house, or the gas is heavier than air and can collect in a cellar or drain - this is more fully discussed in the Page on the Storage of gases - to link to it please click here Link to storage of gases

But hydrogen is very much lighter than air, and hydrogen escaping from an airborne balloon will disperse very rapidly indeed and never build up around the balloon to form an explosive concentration. Not only that, there are most unlikely to be any sources of ignition around the area of any leak. Almost all balloon accidents involving hydrogen fires have taken place on the ground at the time the balloon was being filled - in fact they have really involved cylinders containing hydrogen rather than balloons filled with it.

Of course, if a balloon develops a leak it will start to lose height - not crash straight into the ground - whatever it is filled with, but this does not usually lead to the death of everyone on board, any more than if a ship springs a leak it will immediately sink drowning everyone on board.

As described on another page, a Zeppelin airship was not just a single huge sausage-shaped balloon filled with hydrogen. It was actually a number of smaller gas bags fixed to a metal framework, the whole being covered with a fabric cover.

During the early part of the First World War the Germans used hydrogen-filled Zeppelin airships to bomb Britain and for many other military purposes. You would have thought that these were so large and moved so slowly that they would have been easy to shoot down, but this was not the case at all. You could shell or machine-gun them but very few of the shells or bullets would hit a gas bag, and even if several gas bags were punctured the escaping hydrogen would not catch fire and the airship would remain airworthy - unlike an aeroplane, every part of an airship is accessible in flight for the crew to make repairs. Only after a direct hit on a gas bag with an incendiary shell, which not only punctured the gas bag but also immediately set fire to the escaping hydrogen, would the airship be in any danger.

From about 1916 British fighters were equipped with machine guns firing incendiary shells and after several airships were shot down in this way the Germans discontinued their use as bombers.

By far the best known accident involving a hydrogen-filled airship is the destruction of the German Zeppelin Hindenburg at New York on 6th May 1937. This visit of the Hindenburg to New York was very important for many reasons and so lots of people were filming it, even some in colour. As it came into land it caught fire and within thirty five seconds had been completely destroyed. Thirteen of the thirty six passengers and twenty three of the sixty one crew were killed.

Helium is non-flammable and is “considered” to be safer than hydrogen. Because helium has very slightly less lift that hydrogen, a balloon or airship designed to be filled with hydrogen cannot be filled with helium, although one designed to be filled with helium can be filled with hydrogen. The Hindenburg was designed to be filled with helium but was actually filled with hydrogen, for one reason only: the United States had a monopoly of helium production and would not grant an export licence to Nazi Germany. This visit of the Hindenburg to New York was part of a vast propaganda exercise by the Third Reich to persuade the United States to lift its export ban on helium. This is more fully discussed in another Page of this Web Site - to link to it please click here To hydrogen and helium

Very recently, re-examination of all the cine-films and eye-witness reports, particularly the colour cine-films, has established the cause of the accident beyond all doubt. A small group of engineers and scientists has built a number of scale models of the Hindenburg and tested each one with a different theory, to see which one most accurately produced the video footage of the destruction of the real Hindenburg.

Count von Zeppelin had been a military man and before the First World War had been able to pursuade the Kaiser of the advantages of airships as bombers. The German military did not want them but were over-ruled. After the War and the death of Count von Zeppelin the Zeppelin Airship Company continued to develop airships for purely peaceful purposes. When they were building their largest airship Adolf Hitler told them he would like it named after the greatest German of all time, so they called it the Hindenburg, an incredibly courageous decision. Hitler saw very clearly the propaganda value of German airships flying all over the World.

In Zeppelin airships the hydrogen was contained in bags inside an aluminium framework, and then this framework was covered with a fabric covering. This covering was then painted with a very special kind of paint. It had to conduct electricity so that any static electricity could be conducted away safely without causing any sparks, and it had to reflect sunlight so that the hydrogen inside did not get warm and expand, so changing its buoyancy.

German hydrogen-filled Zeppelin airships had been carrying fare-paying passengers since 1909 without a single accident to a passenger, but for purely political reasons a different type of finish was ordered to be used on the fabric covering on the Hindenburg, and the people who gave this order did not heed the warning that the new paint to be used was very flammable.

Any airship or aeroplane builds up a static charge in flight, but this is not dangerous. However, when the airship or aeroplane lands this charge must be totally discharged to the earth. Aeroplanes have tyres made of a special type of synthetic rubber which conducts electricity; the Hindenburg was equipped with special ropes which were dropped as it came in to land. These ropes served as landing ropes which the ground crew could use to manouevre the airship on the ground, and also to discharge static electricity. Every part of the airship should have been electrically bonded (earthed) to the main metal framework to ensure that every part was fully discharged as it came into land, but one of the skin panels at the back of the Hindenburg was incorrectly bonded and so was not fully discharged.

As the Hindenburg came into land and the earthing ropes were dropped a spark passed from this panel to the metal framework and a small fire started - this first fire can clearly be seen on several different films. The fire then very quickly spread to the paint on the skin panels and within a few seconds the skin panels along almost the entire length of the ship were on fire. This fire damaged the gas bags and the hydrogen very quickly began to burn - burn note not explode.

You can see a video of the disaster by clicking here Link to video of Hindenburg disaster You can clearly see that the flames are yellow: hydrogen burns with an almost invisible blue flame.

There have been many attempts to reconstruct these thirty five seconds for the cinema and television, not all based upon the evidence. If you are watching a tv documentary on the Hindenburg accident take care to notice whether what you are seeing is cine film taken at the time or reconstructed afterwards: in particular any shots of the fire taken from the air are reconstructions.

One more thing needs to be explained however: tests on samples of fabric and paint similar to those used on the Hindenburg have shown that the flames from the burning fabric could not have spread from one end of the airship to the other in only a few seconds without some sort of help.

The Germans had been using Zeppelin airships to make regular passenger flights between Europe and South America (via West Africa to take advantage of the shortest ocean crossing) for many years, but the Hindenburg's visit to New York was part of an attempt by Nazi Germany to set up a scheduled direct passenger airship service between Germany and the United States. (There were no direct scheduled aeroplane passenger services between Europe and North America until after the Second World War.) The outward flight of the Hindenburg to New York was not fully booked, but the return flight was, mainly by passengers travelling on to London for the Coronation of King George 6th. It was very important for purely political reasons that the return flight left on time, otherwise the passengers would not be able to get to London in time for the Coronation.

The Hindenburg's flight to New York had been slowed down by stronger than usual head winds. It was already several hours late when it reached New York, but when it approached the landing area the winds were too strong for it to land safely straight away, and this caused further delays. Eventually the wind dropped enough for the Captain to decide to attempt a landing, but then the wind direction changed. The correct procedure at this point would have been for the Captain to abort the landing, but this would have delayed things even further, making it impossible for the Hindenburg to take off again on the return journey on time. In the Control Room with the Captain was a very senior member of the Nazi Government, and a decision was taken to complete the landing. The Captain ordered a very sharp turn to the left followed immediately by a very sharp turn to the right, manoeuvres which the Hindenburg had never been designed to perform - it was after all nearly 250 m long! The most likely explanation for what happened next is that as a result of this manoeuvre one of the bracing wires which kept the frame in shape, like the spokes on a bicycle wheel, at the back of the airship snapped, and the whiplash of one of the broken ends of the wire tore a hole in one of the gas bags, allowing a small amount of hydrogen to escape. Eye witnesses reported seeing a rippling of the surface of the envelope at the rear of the airship just after these manoeuvres such as might have been caused by escaping hydrogen, and the airship developed a slight tail-heavy trim which the Captain corrected by releasing water ballast. The leaking hydrogen did not catch fire, but it spread out inside the covering along the length of the ship. Then when the fire at the rear of the ship started, some time later, this hydrogen caught fire and carried the fire from one end of the ship to the other in just a few seconds, setting fire not to the hydrogen bags directly but to the skin panels, and the heat from the burning skin panels damaged the remaining gas bags and so allowed the hydrogen to escape and catch fire.

All, or most, of this was known to the German accident investigation team within a few days of the accident, but the visit of the Hindenburg to New York had been an important part of Hitler's propaganda machinery for the Third Reich, and Hitler would not allow it to be thought that German scientists or engineers or members of his Government were at fault, so refused permission for their report to be published. Instead all sorts of other explanations, including of course sabotage, were allowed to circulate.

Sabotage was a very attractive explanation to the German government as it meant that people would not come to doubt the safety of hydrogen-filled airships, while to both the German Government and the rest of the world sabotage was by far the most obvious cause: the Nazi regime was hugely unpopular throughout the world and such an iconic symbol of its power was an obvious target for its enemies.

The World’s first hydrogen-filled airship made its first flight in 1852. More than a hundred and fifty years later the Hindenburg disaster is still the only accident to any airship involving the death of a passenger. The facts simply do not support the idea that hydrogen-filled balloons and airships are Very Dangerous, but today, as in 1937 and probably at every other time in history, what matters is not whether something is true but whether people believe, or can be led to believe, that it is true.

© Barry Gray March 2013

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