The recent Channel 4 documentary “What destroyed the Hindenburg” was a truly awful and dishonest bit of pseudo-science that insulted the viewer's intelligence and reduced our Science Correspondent to incandescent fury. It was hailed on television websites and the press as “Hindenburg mystery solved 76 years after historic catastrophe: static electricity caused the airship to explode” (Daily Mail headline) but in fact if did nothing to explain the 1937 disaster when the German flagship dirigible burst into flames and crashed at Lakehurst, New Jersey with tragic loss of life.
Of course it might be said that there is little mystery about enormous bags of hydrogen gas exploding. Hydrogen is dangerous stuff, and there was a long history of airships exploding before the Hindenburg disaster signalled the end of this particular form of air travel. In 1912 three went down, another four in 1915, and two a year in 1916, 1917 and 1918 – and that doesn't include any that were shot down by enemy action.
It was also well-known that lightning was a significant cause of such explosions. The 1915 crash of the airship L-10 near Cuxhaven was almost certainly caused by lightning, as was the 1917 crash of the SL-9 over the Baltic and the French airship Dixmude which exploded so violently on the Sicilian coast in 1923 that the flames were visible many miles away. And in 1937 there were thunderstorms looming over Lakehurst as the biggest of them all, Hindenburg, attempted to land.
Not such a mystery, then, although the programme said that several other theories had been advanced – among them a bomb, exploding paint, and St.Elmo's Fire.
The team from the Southwest Research Institute in San Antonio, Texas, fronted by broadcaster Jem Stansfield, made a televisual spectacle by building several 1/10th scale models of the Hindenburg and blowing them up in entertaining ways, though it has to be said that all the explosions looked remarkably similar to me. From this they drew conclusions – but they were conclusions that didn't hold water. Or hydrogen, come to that.
Firstly there is a problem over the use of models. A 1/10th scale model has linear dimensions that are 1/10th of the original, but physics dictates that its area dimensions will be 1/100 of the original, and that it will have only 1/1000 of the volume. This means the model only gives useful results if the variables are of the same dimension. For instance, models in wind tunnels work because the factors involved are distance and velocity so everything is linear. Burning buildings (or airships) don't work because the fuel is volume while the burned surface is area – for a given length there is a hundred times too much fuel compared to the real thing! The fire brigade have found that to see how fire behaves in buildings they have to build full-size buildings in one of the Cardington airship hangars, and burn them: models don't work.
The mass to surface area ratio is very important. Penguins who live near the equator are small, and the birds get bigger the further south you go. Biggest of all are the Emperor penguins who live closest to the South Pole. More mass for less surface area means less heat lost. How the “scientists” on this programme expected their models to prove anything is beyond comprehension.
The first experiment was to see what the pattern of destruction would be if someone had planted a bomb. To the untutored eye when the bomb was detonated the model crashed and burned in very much the same way as the Hindenburg did in 1937, but the “scientists” knew what they wanted to find so they dismissed it.
They considered lightning, which has to be favourite given the circumstances and the history. Lightning is a pretty common phenomenon and a lot is known about it – but not, apparently, to these programme makers. They did not seem to know that the first strike of lightning goes up, not down. It forms an ionised conducting path through the atmosphere and subsequent strikes go up and down this path. After flying for three days the Hindenburg would have picked up a strong static charge, most concentrated where the curvature is sharpest, probably at the tip of the tail. When mooring ropes are trailed under a thunderstorm this charge will build up rapidly even if the ropes don't actually touch the ground until it reaches a potential of about 1,000 volts per centimetre. Then there probably will be a strike upwards from the tail to the cloud base that could ignite any hydrogen that has leaked. But Jem Stansfield was convinced that this could only happen if the ship was earthed – if the ropes were touching the ground, in other words.
The third possibility considered was that the paint used to proof the fabric cover might have been inflammable. It has long been suggested that the paint contained thermite, a highly inflammable substance described by Stansfield as an ingredient of rocket fuel. However, thermite is not and never has been a rocket fuel. There is something else called nanothermite that has been used in rocket fuel, but it has nothing to do with thermite. Thermite has been used to weld locomotive chassis and railway lines, thermite grenades have been used in war – dropped down the barrel of a large gun it will burn so fiercely that barrel and breech are welded together, while incendiary bombs can be either phosphorus or thermite.
Thermite needs exceptionally high temperatures to start the reaction – over 2,000 degrees C which is more than white hot. It's usually ignited using magnesium ribbon. It also needs a critical mass to keep it going. Do we know if any magnesium alloys were used in the structure of the Hindenburg, for instance? It does seem unlikely as the airship was built on a tight budget, and all the information we've been able to find is that it was made principally of aluminium.
Stansfield and his colleagues burned two pieces of canvas, one painted and one not. They both burned at pretty much the same speed and in the same manner, so they drew the conclusion that the paint with thermite could have played no part in the disaster. But the amount of material they burned was way below the critical mass required by thermite, and they started the fire with bunsen burners (800 – 900 degrees C). Both pieces of canvas burned with a yellow flame which indicates a temperature of 500 degrees C. This is like trying to make tea with melting ice and complaining that it doesn't work. They never gave the thermite a chance to ignite – so it didn't.
It's highly unlikely that thermite was a factor in the disaster, in any case – there's a detailed and authoritative discussion here - so why so much time was devoted to it is not clear, unless it was to give them the opportunity to burn some bits of canvas and pass it off as scientific experiment.
The final theory was that leaking hydrogen had been ignited by St.Elmo's Fire. Usually seen on ships at sea during thundery weather, St.Elmo's Fire is a concentration of static electrical charge at sharp corners of a structure. The electrons in the atoms jump to higher energy levels and back again, which makes them emit photons of light. Big jumps are seen at the blue end of the spectrum, smaller ones at the red.
It is true that there were reports from onlookers of blue flames on the tail of the airship as it manoeuvred to land. But – and here's the rub – photons aren't hot! Sailors can stand on the rigging of a ship and get St.Elmo's Fire playing from their outstretched fingers without harm. There are even reports of butterflies flying through a charge with St.Elmo's Fire flickering from their wings. St.Elmo's Fire couldn't light a fart in a bucket, let alone an 800 foot airship.
The programme made great play with the ventilation shafts which supposedly ran from the bottom to the top of the hull between the gas bags, though it has to be said that none of the pictures they used showed any shafts so whether they existed or not was a moot point. They claimed that the purpose of these shafts was to carry away escaped hydrogen, though as hydrogen is lighter than air (that's the point, isn't it?) it would only have to get out at the top of the envelope, not at the bottom. If these shafts existed it's more likely that they were to allow air to pass in and out of the envelope to equalise the air pressures inside and out as the ship went up and down.
However, the alleged scientists were delighted by an experiment that showed if they lit a fire at the top of a glass tube with hydrogen in it, after a while there would be a “pop!” and the fire would drop down and start burning at the foot of the tube. What this proved was not clear. Hydrogen rises, so if there were a leaky gas bag the gas would escape upwards and collect at the top of the envelope – the bottom of the shaft would probably have no hydrogen in it.
Indeed the famous film of the Hindenburg bursting into flame and subsiding stern-first to the ground does show just such a fire – a burn along the top of the envelope as each bag in turn ruptures from the heat and the ball of hydrogen it contains ignites at its surface.
A couple of facts that were not included in the programme were that the captain approached too fast in an attempt to make an impressive landing. When the wind dropped at the last minute he was forced to make a tight turn, which may have put a great strain on the 800 foot long framework. The aluminium framework was all tensioned by no less than 85 miles of steel wire, and there had been reports that much of this was rusty. It seems highly likely that under the strain one of these wires broke, and that the sharp end, whipping about, punctured a gas bag. A crewman claimed to have hear a bang before the crash, which Stansfield said was gas igniting – but it's more likely that this was the wire snapping.
As to what ignited the gas ... well, lightning had done it before. Or maybe there is something in the claims that there was a strong smell of diesel in the air – leaky diesel fuel tank ... drops of fuel landing on a hot diesel engine driving the propellors ... diesel is not a particularly inflammable liquid but it becomes much more volatile if it falls on something hot ...
What is absolutely certain is that the programme's main conclusion is entirely potty. St.Elmo's fire could not be to blame, and if you find me some I'll poke my grumpy finger in it to prove the point.
There may have been one or two actual scientists involved in this documentary, specifically staff from the American test facility. Surely they must have known that to draw conclusions solely on the basis of the “look” of a fire in a 1/10 scale model is very poor science indeed? And that not knowing the physical laws of length, area and volume and not understanding the nature of static electricity is just plain stupid? Assuming that they did, this programme was not just foolish and flawed, it was downright dishonest.
either on this site or on the World Wide Web.
Copyright © 2013 The GOS