Hindenburg a few seconds after catching fire.
|Date||May 6, 1937|
|Site||Lakehurst Naval Air Station in Manchester Township, New Jersey, United States
|Fatalities||36 (13 passengers, 22 crew, 1 ground crew)|
|Aircraft type||Hindenburg-class airship|
|Flight origin||Frankfurt, Germany|
|Destination||Lakehurst Naval Air Station in Manchester Township, New Jersey, United States|
The Hindenburg disaster took place on Thursday, May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed as it was attempting to dock with its mooring mast at the Lakehurst Naval Air Station, which is located adjacent to the borough of Lakehurst, New Jersey. Of the 97 people on board, 35 people died in addition to one fatality on the ground. The disaster was the subject of spectacular newsreel coverage, photographs, and Herbert Morrison's recorded radio eyewitness report from the landing field, which was broadcast the next day. The actual cause of the fire remains unknown, although a variety of theories have been put forward for both the cause of ignition and the initial fuel for the ensuing fire.
The first of 10 scheduled round trips between Europe and the United States to be made by the Hindenburg in the 1937 season departed Frankfurt for Lakehurst on the evening of May 3 and except for strong headwinds which slowed the passage the crossing was uneventful. The airship was only half full with 36 passengers (capacity 70) and 61 crew members (including 21 training crew members), but the return flight was fully booked by people planning to attend the festivities for the coronation of King George VI in London the following week.
The airship was hours behind schedule when it passed over Boston on the morning of 6 May, and its landing at Lakehurst was expected to be further delayed because of afternoon thunderstorms. Advised of the poor weather conditions at Lakehurst, Captain Max Pruss charted a course over Manhattan, causing a public spectacle as people rushed out into the street to catch sight of the airship. After passing over the field at 4 p.m., Captain Max Pruss took passengers on a tour over the seasides of New Jersey while waiting for the weather to clear. After finally being notified at 6:22 p.m. that the storms had passed, the airship headed back to Lakehurst to make its landing almost half a day late. However, as this would leave much less time than anticipated to service and prepare the airship for its scheduled departure back to Europe, the public was informed that they could not be permitted at the mooring location or be able to visit aboard the "Hindenburg" during its stay in port.
Around 7:00 p.m. local daylight saving time, at an altitude of 650 feet (200 m), the Hindenburg approached the Lakehurst Naval Air Station. This was to be a high landing, known as a flying moor, because the airship would be moored to a high mooring point, and then winched down to ground level. This type of landing maneuver would reduce the number of ground crew, but would require more time.
7:09: The airship made a sharp full speed left turn to the west around the landing field because the ground crew was not ready.
7:11: The airship turned back toward the landing field and valved gas. All engines idled ahead and the airship began to slow.
7:14: At altitude 394 feet (120 m), Captain Pruss ordered all engines full astern to try to brake the airship.
7:17: The wind shifted direction to southwest, and Captain Pruss was forced to make a second, sweeping sharp turn, this time towards starboard.
7:19: The airship made another sharp turn and dropped 300, 300 and 500 kg of water ballast in successive drops because the airship was stern heavy. Six men (four were killed in the accident) were also sent to the bow to trim the airship. These methods worked and the airship was on even keel as it stopped.
7:21: At altitude 295 feet (90 m), the mooring lines were dropped from the bow, the starboard line being dropped first, followed by the port line. The port line was overtightened as it was connected to the post of the ground winch; the starboard line had still not been connected.
At 7:25, a few witnesses saw the fabric ahead of the upper fin flutter as if gas were leaking. Witnesses also reported seeing blue discharges, possibly static electricity, moments before the fire on top and in the back of the ship near the point where the flames first appeared. Several other eyewitness testimonies suggest that the first flame appeared on the port side just ahead of the port fin, and was followed by flames which burned on top. Commander Rosendahl testified to the flames being "mushroom-shaped" and knew at once that the airship was doomed. One witness on the starboard side reported a fire beginning lower and behind the rudder on that side. On board, people heard a muffled explosion and those in the front of the ship felt a shock as the port trail rope overtightened; the officers in the control car initially thought the shock was due to a broken rope.
At 7:25 p.m. local time, the Hindenburg caught fire and quickly became engulfed in flames. Where the fire started is controversial; several witnesses on the port side saw yellow-red flames first just forward of the top fin, around the vent of cell 4. Other witnesses on the port side noted the fire actually began just ahead of the horizontal port fin, only then followed by flames in front of the upper fin. One, with views of the starboard side, saw flames beginning lower and farther aft, near cell 1. No. 2 Helmsman Helmut Lau also testified seeing the flames spreading from cell 4 into starboard. Although there were four newsreel cameramen and at least one spectator known to be filming the landing, they were all recording the actions of the ground crew when the fire started and therefore there is no motion picture record of where it first broke out at the instant of ignition.
Wherever it started, the flames quickly spread forward. Almost instantly, a water tank and a fuel tank burst out of the hull due to the shock of the blast. This shock also caused a crack behind the passenger decks, and the rear of the structure imploded. The buoyancy was lost on the stern of the ship, and the bow lurched upwards as the falling stern stayed in trim.
As the Hindenburg's tail crashed into the ground, a burst of flame came out of the nose, killing nine of the 12 crew members in the bow. As the airship kept falling with the bow facing upwards (because there was more lifting gas still in the nose), part of the port side directly behind the passenger deck collapsed inward (where a crack formed during the initial blast), and the gas cell there exploded, erasing the scarlet lettering "Hindenburg" while the airship's bow lowered. The airship's gondola wheel touched the ground, causing the airship to bounce up once more. At this point, most of the fabric had burned away. At last, the airship went crashing on the ground, bow first. The ship was completely destroyed. Although the hydrogen had finished burning, the Hindenburg's diesel fuel burned for a few more hours.
The time it took for the airship to be completely destroyed has been disputed. Some observers believe it took 34 seconds, others say it took 32 or 37 seconds. Since none of the newsreel cameras were filming the airship when the fire started, the time of the start of the fire can only be estimated from various eyewitness accounts, and will never be known accurately. One careful analysis of the flame spread, by Addison Bain of NASA, gives the flame front spread rate across the fabric skin as about 49 ft/s (15 m/s), which would have resulted in a total destruction time of about 16 seconds (245 m / 15 m/s = 16.3 s). The duralumin framework of the airship was salvaged and shipped back to Germany were it was recycled and used in the construction of military aircraft for the Luftwaffe as were the frames of the LZ 127 Graf Zeppelin and LZ 130 Graf Zeppelin II as well when both were scrapped in 1940.
The disaster is well recorded because of the significant extent of newsreel coverage and photographs, as well as Herbert Morrison's recorded, on-the-scene, eyewitness radio report being made from the landing field for station WLS in Chicago which was broadcast the next day. Heavy publicity about the first transatlantic passenger flight of the year by Zeppelin to the U.S. attracted a large number of journalists to the landing. (The airship had already made one round trip from Germany to Brazil that year.) Parts of the Morrison report were later dubbed onto the newsreel footage and this gave the impression to many modern viewers, more accustomed to live television reporting, that the words and film were recorded together intentionally. Morrison's broadcast remains one of the most famous in history. His plaintive words, "Oh, the humanity!" resonate with the impact of the disaster, and have been widely used in culture. Part of the poignancy of Morrison's commentary is due to its being recorded at a slightly slower speed to the disk, so when played back at normal speed seeming to be at a faster delivery and higher pitch; when corrected, his account is less frantic sounding, though still impassioned.
It's practically standing still now. They've dropped ropes out of the nose of the ship; and (uh) they've been taken ahold of down on the field by a number of men. It's starting to rain again; it's... the rain had (uh) slacked up a little bit. The back motors of the ship are just holding it (uh) just enough to keep it from...It's burst into flames! It burst into flames, and it's falling, it's crashing! Watch it! Watch it! Get out of the way! Get out of the way! Get this, Charlie; get this, Charlie! It's fire... and it's crashing! It's crashing terrible! Oh, my! Get out of the way, please! It's burning and bursting into flames and the... and it's falling on the mooring mast. And all the folks agree that this is terrible; this is the one of the worst catastrophes in the world. [indecipherable] its flames... Crashing, oh! Four- or five-hundred feet into the sky and it... it's a terrific crash, ladies and gentlemen. It's smoke, and it's in flames now; and the frame is crashing to the ground, not quite to the mooring mast. Oh, the humanity! And all the passengers screaming around here. I told you; it—I can't even talk to people, their friends are out there! Ah! It's... it... it's a... ah! I... I can't talk, ladies and gentlemen. Honest: it's just laying there, mass of smoking wreckage. Ah! And everybody can hardly breathe and talk and the screaming. Lady, I... I... I'm sorry. Honest: I... I can hardly breathe. I... I'm going to step inside, where I cannot see it. Charlie, that's terrible. Ah, ah... I can't. Listen, folks; I... I'm gonna have to stop for a minute because [indecipherable] I've lost my voice. This is the worst thing I've ever witnessed.
– Herbert Morrison, describing the events, as broadcasted to WLS radio.
Spectacular motion picture footage and Morrison's passionate recording of the Hindenburg fire shattered public and industry faith in airships and marked the end of the giant passenger-carrying airships. Also contributing to the Zeppelins' downfall was the arrival of international passenger air travel and Pan American Airlines. Aircraft regularly crossed the Atlantic and Pacific oceans much faster than the 130 km/h (80 mph) of the Hindenburg. The one advantage that the Hindenburg had over aircraft was the comfort it afforded its passengers, much like that of an ocean liner.
There had been a series of other airship accidents, none of them Zeppelins, prior to the Hindenburg fire. Many were caused by bad weather, and most of these accidents were dirigibles of British or U.S. manufacture. Zeppelins had an impeccable safety record. The Graf Zeppelin had flown safely for more than 1.6 million km (1 million miles), including the first circumnavigation of the globe by an airship. The Zeppelin company's promotions prominently featured the fact that no passenger had been injured on one of their airships.
Despite the violent fire, most of the crew and passengers survived. Of the 36 passengers and 61 crew, 13 passengers and 22 crew died. Also killed was one member of the ground crew, civilian linesman Allen Hagaman. The majority of the crew who died were up inside the ship's hull, where they either did not have a clear escape route or else were close to the bow of the ship, which hung burning in the air too long for most of them to escape the fire. Most of the passengers who died were trapped in the starboard side of the passenger deck. Not only was the wind blowing the fire toward the starboard side, but the ship also rolled slightly to starboard as it settled to the ground, with much of the upper hull on that part of the ship collapsing outboard of the starboard observation windows, thus cutting off the escape of many of the passengers on that side. To make matters worse, the sliding door leading from the starboard passenger area to the central foyer and the gangway stairs (through which rescuers led a number of passengers to safety) jammed shut during the crash, further trapping those passengers on the starboard side. Nonetheless, some did manage to escape from the starboard passenger decks. A number of others did not. By contrast, all but a few of the passengers on the port side of the ship survived the fire, with some of them escaping virtually unscathed. Although the most famous of airship disasters it was not the worst. Just over twice as many perished (73 of 76 on board) when the helium filled U.S. Navy scout airship USS Akron crashed at sea off the New Jersey coast four years earlier on April 4, 1933.
Some of the survivors were saved by luck. Werner Franz, the 14 year-old cabin boy, was initially dazed by the realization that the ship was on fire. As he stood near the officer's mess where he had been putting away dishes moments before, a water tank above him burst open, and he was suddenly soaked to the skin. Not only did this snap him back to his senses, as he would later tell interviewers, but it also put out the fire around him. He then made his way to a nearby hatch through which the kitchen had been provisioned before the flight, and dropped through it just as the forward part of the ship was briefly rebounding into the air. He began to run toward the starboard side, but stopped and turned around and ran the other way, because the flames were being pushed by the wind in that same direction. He made it clear of the wreck with little more than singed eyebrows and soaking wet clothes. Werner Franz is one of the two people aboard who are still alive as of 2008.
When the control car crashed on the ground, most of the officers had leapt through the windows, but became separated. First Officer Captain Albert Sammt found Captain Max Pruss trying to re-enter the wreckage to look for survivors. Pruss's face was badly burned, and he required months of hospitalization and reconstructive surgery, but he survived.
Captain Ernst Lehmann escaped the crash with burns to his head and arms and severe burns across most of his back. Though his burns did not seem quite as severe as those of Pruss, he died at a nearby hospital the next day.
When passenger Joseph Späh, a vaudeville comic acrobat, saw the first sign of trouble he smashed the window with his movie camera, with which he had been filming the landing (the film survived the disaster.) As the ship neared the ground he lowered himself out the window and hung onto the window ledge, letting go when the ship was perhaps 20 feet above the ground. His acrobat's instincts kicked in, and Späh kept his feet under him and attempted to do a safety roll when he landed. He injured his ankle nonetheless, and was dazedly crawling away when a member of the ground crew came up, slung the diminutive Späh under one arm, and ran him clear of the fire.
Of the 12 crewmen in the bow of the airship, only three survived. Four of these 12 men were standing on the mooring shelf, a platform up at the very tip of the bow from which the forward-most landing ropes and the steel mooring cable were released to the ground crew, and which was directly at the forward end of the axial walkway and just ahead of gas cell #16. The rest were standing either along the lower keel walkway ahead of the control car, or else on platforms beside the stairway leading up the curve of the bow to the mooring shelf. During the fire, of course, the bow hung in the air at roughly a 45-degree angle and flames shot forward through the axial walkway, bursting through the bow (and the bow gas cells) like a blowtorch. The three men from the forward section who survived (elevatorman Kurt Bauer, cook Alfred Grözinger, and electrician Josef Leibrecht) were those furthest aft of the bow, and two of them (Bauer and Grözinger) happened to be standing near two large triangular air vents, through which cool air was being drawn by the fire. Neither of these men sustained more than superficial burns. Most of the men standing along the bow stairway either fell aft into the fire, or tried to leap from the ship when it was still too high in the air. Three of the four men standing on the mooring shelf inside the very tip of the bow were actually taken from the wreck alive, though one (Erich Spehl, a rigger) died shortly afterward in the Air Station's infirmary, and the other two (helmsman Alfred Bernhard and apprentice elevatorman Ludwig Felber) were reported by newspapers to have initially survived the fire, and then to subsequently have died at area hospitals during the night or early the following morning.
The four crew members in the tail fin all survived; they were closest to the origin of the fire but sheltered by the structure of the lower fin. They escaped by climbing out the fin's access hatch when the tail hit the ground.
Hydrogen fires are notable for being less destructive to immediate surroundings than gasoline explosions because of the buoyancy of H2, which causes heat of combustion to be released upwards more than circumferentially as the leaked mass ascends in the atmosphere; hydrogen fires are more survivable than fires of gasoline and of wood. The hydrogen in the Hindenburg burned out within about 90 seconds.
At the time of the disaster, sabotage was commonly put forward as the cause of the fire, initially by Hugo Eckener, former head of the Zeppelin company and the "old man" of German airships. (Eckener later publicly endorsed the static spark theory — see below.) Eckener, who was at the time on a lecture tour in Austria, was awakened at about 2:30 in the morning (8:30 PM Lakehurst time, or approximately an hour after the crash) by the ringing of his bedside telephone. It was a Berlin representative of the New York Times with news that the Hindenburg "exploded yesterday evening at 7 p.m [sic] above the airfield at Lakehurst." The newsman had no additional details for Dr. Eckener at that time, and Eckener spent a sleepless night trying to make sense of what he'd been told. By the time he left the hotel the next morning to travel to Berlin for a briefing on the disaster, the only answer that he had for the reporters waiting outside to question him was that based on what he knew, that the Hindenburg had "exploded over the airfield", sabotage might be a possibility. However, as he learned more about the disaster, particularly that the airship had burned rather than actually "exploding", he grew more and more convinced that static discharge, rather than sabotage, was the actual culprit. However there is also the theory that the hydrogen wasn't the initial source of the fire, seeing as hydrogen does not make visible flames. It is belived that the presence of aluminum and iron oxide in the airship's coating may have been a factor in the disaster as well.
Commander Charles Rosendahl, commander of the Naval Air Station at Lakehurst and the man in overall charge of the ground-based portion of the Hindenburg's landing maneuver, also came to believe that the Hindenburg had been sabotaged. He actually laid out a general case for sabotage in his 1938 book What About the Airship?, which was as much an extended argument for the further development of the rigid airship as it was an historical overview of the airship.
Another proponent of the sabotage hypothesis was Max Pruss, commander of the Hindenburg throughout the airship's career. Pruss flew on nearly every flight of the Graf Zeppelin until the Hindenburg was ready. In a 1960 interview conducted by Kenneth Leish for Columbia University's Oral History Research Office, Pruss said early dirigible travel was safe, and therefore he strongly believed that sabotage was to blame. He stated that on trips to South America, which was a popular destination for German tourists, both airships passed through thunderstorms and were struck by lightning but remained unharmed.
In 1962, A. Hoehling published Who Destroyed the Hindenburg?, a book that rejects all theories but sabotage. The book even names Eric Spehl, a rigger on the Hindenburg who died in the fire, as the saboteur.
Hoehling claimed the following in naming Spehl as the culprit:
Ten years later, Michael MacDonald Mooney's book, The Hindenburg, which was based heavily on Hoehling's sabotage theory, also identified Spehl as the saboteur. Mooney's book was made into the movie The Hindenburg, whose producers were sued by Hoehling for plagiarism, but Hoehling lost due to the fact that he had presented his sabotage theory as historical fact, and one cannot claim ownership of historical facts.
Hoehling's (and later Mooney's) theory goes on to say that it is unlikely that Spehl wanted to kill people, and that he intended for the airship to burn after the landing instead. However, with the ship already over 12 hours late, Spehl was in the end unable to find an excuse to reset the timer on his bomb.
During the landing maneuver, rigger Hans Freund dropped a landing line in front of the lower fin. The line became caught in the bracing wires of the airship, so No. 2 helmsman Helmut Lau climbed up from the lower fin to release it. When both men looked up toward the front of the airship, they were surprised by what they saw.
Freund described a flash like a flashbulb's, and Lau said he saw a brilliant reflection between cells 4 and 5. They then heard a muffled detonation and a thud as the Hindenburg's back broke. Some believe that this is evidence for sabotage. Others believe Freund was actually looking rearward, away from cells 4 and 5, but that Rudolf Sauter, another crew member in the lower fin had seen the flash.
Since the publication of Hoehling's book, most airship historians, including Dr. Douglas Robinson, have dismissed Hoehling's sabotage theory because no solid evidence was ever presented to support it. No pieces of a bomb were ever discovered (and in fact there is no evidence in existing documentation that the sample collected from the wreckage, and determined to be residue from a dry cell battery, was found anywhere near the stern of the airship,) and on closer examination the evidence against Spehl and his girlfriend turned out to be largely circumstantial.
Another suspect favored by Commander Rosendahl, Captain Pruss, and several others among the Hindenburg's crew, was a passenger, a German acrobat named Joseph Späh, who survived the fire. He brought with him a dog, a German shepherd named Ulla, as a surprise for his children. (Ulla did not survive.) He reportedly made a number of unaccompanied visits to feed his dog, who was being kept in a freight room near the stern of the ship. Those who suspected Späh based their suspicions primarily on those trips into the ship's interior to feed his dog, that according to some of the stewards Späh had told anti-Nazi jokes during the flight, recollections by stewards that Späh had seemed agitated by the repeated delays in landing, and that he was an acrobat who could conceivably climb into the airship's rigging to plant a bomb. As with the allegations about Erich Spehl however, the evidence against Joseph Späh was entirely circumstantial.
However, opponents of the sabotage hypothesis argued that only speculation supported sabotage as a cause of the fire, and no credible evidence of sabotage was produced at any of the formal hearings.
Eric Spehl died in the fire and was therefore unable to refute the accusations that surfaced a quarter of a century later. The FBI investigated Joseph Späh and reported finding no evidence of Späh having any connection to a sabotage plot. According to his wife, Evelyn, Späh was quite upset over the accusations - she later recalled that her husband was outside their home cleaning windows when he first learned that he was suspected of sabotaging the Hindenburg, and was so shocked by the news that he almost fell off the ladder on which he was standing.
Neither the German nor the American investigation endorsed any of the sabotage theories. Proponents of the sabotage theory argue that any finding of sabotage would have been an embarrassment for the Nazi regime, and they speculate that such a finding by the German investigation was suppressed for political reasons.
Eckener believed that the reason why Pruss, Lehmann, and Rosendahl supported sabotage was because they may have felt guilty for their acts. Pruss made the sharp turn, Lehmann pressured Pruss to make it, and Rosendahl called the airship in.
Addison Bain and others posit that the fire was started by a spark caused by a build up of static electricity on the airship. The spark ignited hydrogen or the outer skin (see Incendiary paint theory below).
Proponents of the static spark theory point out that the airship's skin was not constructed in a way that allowed its charge to be distributed evenly throughout the craft. The skin was separated from the duralumin frame by non conductive ramie cords which had been lightly covered in metal to improve conductivity, however not very effectively, allowing a large difference in potential to form between them.
In order to make up for the delay of more than 12 hours in its transatlantic flight, the Hindenburg passed through a weather front of high humidity and high electrical charge. The storm could have made the airship's mooring lines wet and thus conductive, and may also have built up an electrical charge in its skin. The mooring lines also could have gotten wet as a light rain continued to fall at Lakehurst.
When the mooring lines, which were connected to the frame, touched the earth they would have grounded the frame but not the skin. This would have caused a sudden potential difference between skin and frame (and the airship itself with the overlying air masses) and would have set off an electrical discharge — a spark. The spark would have jumped from the skin onto the metal framework. At the same time, it’s also possible that hydrogen, either released during landing, or perhaps built up due to a leak, was in turn ignited by the spark.
In his 1964 book, LZ-129 Hindenburg, Zeppelin historian Dr. Douglas Robinson points out that although ignition of free hydrogen by static discharge had become a favored theory, no such discharge was seen by any of the witnesses who testified at the official investigation into the accident back in 1937. He goes on to write:
But within the past year, I have located an observer, Professor Mark Heald of Princeton, New Jersey, who undoubtedly saw St. Elmo's Fire flickering along the airship's back a good minute before the fire broke out. Standing outside the main gate to the Naval Air Station, he watched, together with his wife and son, as the Zeppelin approached the mast and dropped her bow lines. A minute thereafter, by Mr. Heald's estimation, he first noticed a dim "blue flame" flickering along the backbone girder about one-quarter the length abaft the bow to the tail. There was time for him to remark to his wife, "Oh, heavens, the thing is afire," for her to reply, "Where?" and for him to answer, "Up along the top ridge" - before there was a big burst of flaming hydrogen from a point he estimated to be about one-third the ship's length from the stern.
Unlike other witnesses to the fire whose view of the port side of the ship had the light of the setting sun behind the ship, Professor Heald's view of the starboard side of the ship against a backdrop of the darkening eastern sky would have made the dim blue light of a static discharge (or burning hydrogen) atop the ship more easily visible.
Harold G. Dick was Goodyear Zeppelin's representative with Luftschiffbau Zeppelin during the mid-1930s. He flew on test flights of the Hindenburg and its sister ship, the Graf Zeppelin II. He also flew on numerous flights in the original Graf Zeppelin and 10 round trip crossings of the north and south Atlantic in the Hindenburg. In his book The Golden Age of the Great Passenger Airships Graf Zeppelin & Hindenburg, he observes:
There are two items not in common knowledge. When the outer cover of the LZ 130 [the Graf Zeppelin II] was to be applied, the lacing cord was prestretched and run through dope as before, but the dope for the LZ 130 contained graphite to make it conductive. This would hardly have been necessary if the static discharge theory were mere cover up. The use of graphite dope was not publicized and I doubt if its use was widely known at the Luftschiffbau Zeppelin.
In addition to Dick's observations is the fact that during the Graf Zeppelin II's early test flights, measurements were taken of the airship's static charge. It is clear that Dr. Ludwig Durr and the other engineers at Luftschiffbau Zeppelin took the static discharge theory seriously and considered the insulation of the fabric from the frame to be a design flaw in the Hindenburg. Thus, the German Inquiry concluded that the insulation of the outer covering caused a spark to jump onto a nearby piece of metal, therefore igniting the hydrogen. In lab experiments, using the Hindenburg's outer covering and a static ignition, hydrogen was able to be ignited, but with the covering of the LZ 127 Graf Zeppelin, nothing happened.
A variant of the static spark theory, presented by Addison Bain, is that a spark between inadequately grounded fabric cover segments of the Hindenburg itself started the fire, and that the spark had ignited the "highly flammable" outer skin. The Hindenburg had a cotton skin covered with a finish known as "dope". It is a common term for a plasticised lacquer that provides stiffness, protection, and a lightweight, airtight seal to woven fabrics. In its liquid forms, dope is highly flammable, but the flammability of dry dope depends upon its base constituents, with, for example, butyrate dope being far less flammable than cellulose nitrate. Proponents of this theory claim that when the mooring line touched the ground, a resulting spark could have ignited the dope in the skin.
A. J. Dessler, former director of the Space Science Laboratory at NASA's Marshall Space Flight Center and a critic of the incendiary paint theory (see below), favors a much simpler explanation for the conflagration: natural lightning. Like many other aircraft, the Hindenburg had been struck by lightning several times. This does not normally ignite a fire in hydrogen-filled airships, because the hydrogen is not mixed with oxygen. However, many fires started when lightning struck airships as they were venting hydrogen as ballast in preparation for landing, which the Hindenburg was doing at the time of the disaster. The vented hydrogen mixes with the air, making it readily combustible.
However, Dr. Eckener believed that the way the fire appeared was not consistent with that of a fire caused by lightning. Witnesses described the fire appearing in a wave motion. Eckener believed that the shape of the fire was consistent with that of a static spark.
On the 70th anniversary of the accident, The Philadelphia Inquirer carried an article with yet another theory, based on an interview of ground crew member Robert Buchanan. He had been a young man on the crew manning the mooring lines.
The excessively stormy day had not only delayed the dirigible's arrival but also soaked him and many of the other mooring crew. As the airship was approaching the mooring mast, he noted that one of the engines, thrown into reverse for a hard turn, backfired, and a shower of sparks was emitted. He and others think that this was the trigger that ignited the craft, not static electricity, as the official version goes.
When the Hindenburg ignited, instead of an explosion there were just three sequential plumes of flame on the outer shell. Another ground crewman named Robert Shaw saw what looked like a blue ring behind the tail fin. He too had seen sparks coming out of the engine. The cotton skin, depending on the exact makeup of its coating, may have been quite flammable, and therefore the heat and sparks from a backfiring engine could have ignited the skin, though this has not been proven beyond debate and it remains unknown if sparks did ignite the doping compound.
Dr. Eckener rejected the idea that hydrogen could have been ignited by an engine backfire when that theory was mentioned at an unofficial inquiry, which was a chat with crew members. Dr. Eckener believed that the hydrogen could not have been ignited by any exhaust because the temperature is too low to ignite the hydrogen. The ignition temperature for hydrogen is 700 °C, but the sparks from the exhaust only reach 250 °C. The Zeppelin Company also carried out extensive tests and hydrogen had never ignited. Additionally, the fire was first seen at the top of the airship, not near the bottom.
Most current analysis of the fire assumes ignition due to some form of electricity as the cause. However, there is still much controversy over whether the fabric skin of the airship, or rather the hydrogen used for buoyancy, was the initial fuel for the resulting fire.
The incendiary paint theory is limited to the source of ignition and to the flame front propagation, not to the source of most of the burning material, as once the fire started and spread the hydrogen clearly must have burned. Instead, for this topic the incendiary paint theory asserts that the major component in starting the fire and feeding its spread was the canvas skin because of the compound used on it.
Proponents of this theory point out that the coatings on the fabric contained both iron oxide and aluminum-impregnated cellulose acetate butyrate (CAB). These components remain potentially reactive even after fully setting. In fact, iron oxide and aluminum can be used as components of solid rocket fuel or thermite. For example, the propellant for the Space Shuttle solid rocket booster includes both "aluminum (fuel, 16%), (and) iron oxide (a catalyst, 0.4%)". However, the coating applied to Hindenburg's covering did not have a sufficient quantity of any material capable of acting as an oxidizer, which is a necessary component of rocket fuel.
Addison Bain received permission from the German government to search their archives and discovered evidence that, during the Nazi regime, German scientists concluded the dope on the Hindenburg's fabric skin was the cause of the conflagration. Bain interviewed the wife of the investigation's lead scientist, and she stated that her husband had told her about the conclusion and instructed her to tell no one, presumably because it would have embarrassed the Nazi government.
In television shows, Bain tried to prove the flammability of the fabric by igniting it with an electrical machine; critics claim it was not possible for the fabric to have been ignited by a static spark. Although the fabric ignited, critics point out that Bain had to correctly position the fabric so it would be ignited, and he used a Jacob's Ladder with a continuous electric current inconsistent to atmospheric conditions. Additionally, the German scientists at the time concluded that it was the poor conductivity, not the flammability of the doping compound, that lead to the ignition of hydrogen.
Critics point out that port side witnesses on the field, as well as crew members stationed in the stern, saw a glow inside Cell 4 before any fire broke out of the skin, indicating that the fire began inside the airship (or that it was a hydrogen fire feeding on the whole cell). Newsreel footage supports this.
Proponents of the paint theory claim that the glow can be explained. They claim that what witnesses saw was the fire on the starboard side (another proponent claims that a witness saw the fire start from the starboard side) through the structure, looking like a glow. However, photographs of the early stages of the fire show the gas cells of the Hindenburg's entire aft section fully aflame. Burning gas spewing upward from the top of the airship was causing low pressure inside, allowing atmospheric pressure to press the skin inwards. It should also be noted that not all fabric on the Hindenburg burned. The fabric on several of the tail structures was not completely consumed. That the fabric not near the hydrogen fire extinguished itself is not consistent with the "explosive" dope theory.
Occasionally the Hindenburg's varnish is incorrectly identified as, or stated being similar to, cellulose nitrate, which, like most nitrates burns very readily. Instead, the cellulose acetate butyrate (CAB) used to seal the zeppelin's skin is rated by the plastics industry as combustible but nonflammable. That is, it will burn if placed within a fire but is not readily ignited. In fact, it is considered self extinguishing without some kind of additional fuel. That many pieces of the Hindenburg's skin survived despite such a fierce fire is cited as proof.
Offering support for the theory that there was some sort of hydrogen leak prior to the fire is that the airship remained stern-heavy before landing. This could have been caused by a massive leak of the gas, which started mixing with air and filling up the space between the skin and the cells.
There are many theories about how that gas might have leaked, but the actual cause remains unknown. Many believe it was that a bracing wire cracked (see below), while others believe that a vent was stuck open and gas leaked through. During one trip to Rio, a gas cell was nearly emptied when a vent was stuck open, and gas had to be transferred from other cells to maintain an even keel..
The fire seemed to start near the top of the airship, far from any crew or passengers. Although proponents of the IPT claim that the hydrogen was odorized with garlic, it would have been detectable only in the area of a leak. Once the fire was underway, more powerful smells would have masked any garlic odor. There were no reports of anyone smelling garlic during the flight, but no official documents have been found to prove that the hydrogen even was odorized.
Pictures that show the fire burning along straight lines that coincide with the boundaries of gas cells suggest that the fire was not burning along the skin, which was continuous. Crew members stationed in the stern reported actually seeing the cells burning.
Opponents of this theory note that the fire was reported as burning bright red, while pure hydrogen burns blue if it's visible at all, although there were obviously many other materials that were consumed by the fire, possibly changing its hue.
Another problem is that most of the airshipmen at the time, including Captain Pruss, believed that stern heaviness was normal, since aerodynamic pressure would push rainwater towards the stern of the airship. However, reports of the amount of rain the ship had collected have been inconsistent. Several witnesses testified that there was no rain as the ship approached until a light rain fell minutes before the fire, while several crew members stated that before the approach the ship did encounter heavy rain.
The stern heaviness was also noticed minutes before the airship made its sharp turns for its approach, and crew members stated that it was corrected as the ship stopped (after sending six men into the bow section of the ship). Additionally, the gas cells of the ship were not pressurized, and a leak would not cause the fluttering of the outer cover, which wasn't seen until seconds before the fire. Instead, it has been suggested that such fluttering was caused by the initial blast wave of the hydrogen cells igniting.
While not issuing an opinion about whether it was the hydrogen or the treated skin of the airship that ignited first, the MythBusters explored the incendiary paint theory. Their findings indicated that the aluminum/iron oxide ratios in the Hindenburg's skin, while certainly flammable, were not enough on their own to destroy the zeppelin. Had the skin in fact contained enough metal to produce pure thermite, the Hindenburg would have been too heavy to fly. And even if it somehow did, a pure thermite reaction (at ~2500 degrees C) would have completely melted the airframe (assuming Aluminium 2024's melt point of ~630 degrees C for the duralumin of the day), whereas the real disaster left the spars and ribs recognizable. The MythBusters team also discovered that the Hindenburg's coated skin required a higher temperature to ignite than untreated material, but that after it was ignited the treated cloth reacted more violently. This led to their conclusion that the paint may have contributed to the disaster, but that it was not the sole reason for such rapid combustion.
An aspect of the hydrogen theory above claims that one of the many bracing wires within the airship snapped and punctured at least one of the internal gas cells. Advocates of this theory believe that the hydrogen began to leak approximately five minutes before the fire. Newsreels as well as the account of the landing approach show the Hindenburg made several sharp turns, first towards port and then starboard, just before the accident. Gauges found in the wreckage showed the tension of the wires was much too high, and some of the bracing wires may have even been substandard. One bracing wire tested after the crash, though possibly damaged by the fire, broke at a mere 70% of its rated load. A punctured cell would have freed hydrogen into the air and could have been ignited by a static discharge (see above). Or it is also possible that the broken bracing wire struck a girder causing sparks..
A ground crew member, R.H. Ward, reported seeing a piece of the airship fluttering, perhaps providing an opening for a spark to reach escaping hydrogen inside the airship, or vice versa. He said that the fire began there, but that no other disturbance occurred at the time when the fabric fluttered. Another man on the top of the mooring mast had also reported seeing a flutter in the fabric as well. People on board the airship reported hearing a muffled sound, and another ground crew member on the starboard side reported hearing a crack. Some speculate the sound was from a bracing wire snapping.
Dr. Eckener concluded that the puncture theory was the most likely cause of the disaster. Because of this, he felt that Captains Pruss and Lehmann, and Charles Rosendahl were to blame for the whole disaster. He believed that Lehmann told Pruss to make the sharp turn, and that Pruss and Rosendahl were concerned more about the time delay than the weather, because an unobserved storm front occurred just when the Hindenburg approached. But in his heart, Dr. Eckener knew that he was to blame as much as anyone else, for a decision eight years earlier, which he kept a close secret.
Eckener concluded that the fire was caused by the ignition of hydrogen by a static spark:
I believe that the fire was not caused by an electrical spark, but by a static spark. A thunderstorm front had passed before the landing maneuver. However if one observes more closely one can see that this was followed by a smaller storm front. This created conditions suitable for static sparks to occur. I believe spark had ignited gas in the rear of the ship.
It may seem strange that the fire did not occur the moment the landing ropes had touched the ground, because that is when the airship would have been earthed. I believe there is an explanation for this. When the ropes were first dropped they were very dry, and poor conductors. Slowly however they got dampened by the rain that was falling and the charge was slowly equalized. Thus the potential difference between the airship and the overlying air masses would have been sufficient enough to generate static electricity. The Hindenburg would have acted as a giant kite, close to the storm clouds, collecting a static spark.
I am convinced, that a leak must have occurred in the upper rear section of the ship. My assumption is confirmed by the remarkable observations by one of the witnesses. He described seeing a peculiar flutter as if gas were rising and escaping. If I were to be asked to explain what had caused this abnormal build up of gas, I could only make to myself one explanation.
The ship proceeded in a sharp turn during its landing maneuver. This would have generated extremely high tension in the sections close to the stabilizing fins, which are braced by shear wires. I suspect that under such tension one of these wires may have broken and caused a rip in one of the gas cells. The gas then filled up the space between the cell and the outer cover, which is why the airship sank at the rear. This accumulated amount of gas was then ignited by a static spark. This was not lightning but a small static spark, enough to ignite free gas in the rear.
Captain Pruss believed that the Hindenburg could withstand tight turns without significant damage. Other engineers and scientists believe that the airship would have been weakened by being repeatedly stressed. Even a 10-meter, scale replica of the Hindenburg's passenger quarters, displayed in the Zeppelin Museum in Friedrichshafen, has developed some metal fatigue.
The airship's landing approach actually proceeded in two sharp turns. The first turn was towards port at full speed as the airship circled the landing field. After it had circled the landing field, the wind shifted direction towards the southwest, and a sharper turn to starboard was ordered near the end of the landing maneuver. After the last turn the airship seemed to drop even more at the stern, though a slight stern heaviness had already been noticed before this turn. One or both of these turns in opposite directions could have weakened the structure.
However, evidence against this theory is the fact that the first sharp turn was too wide and circular to cause any damage, and that the final turn, while considered sharp, was far too slow for any structural failure to occur.
The airship did not receive much in the way of routine inspections even though there was evidence of at least some damage on previous flights. It is not known whether that damage was properly repaired or even whether all the failures had been found. The Hindenburg had once lost an engine and almost drifted over Africa, where it could have crashed. Dr. Eckener was furious and ordered all section chiefs to inspect the airship during flight.
In March 1936, the Graf Zeppelin and the Hindenburg made three-day flights to drop leaflets and broadcast speeches via loudspeaker. Before the airship's takeoff on March 26, 1936, Captain Lehmann chose to launch the Hindenburg with the wind blowing from behind the airship, instead of into the wind as per standard procedure. During the takeoff, the airship's tail struck the ground, and part of the lower fin was broken. Many spectators' cameras were confiscated to prevent negative publicity, but Harold G. Dick concealed his camera and took pictures of the damaged fin. Dr. Eckener was very upset and rebuked Captain Lehmann:
How could you, Herr Lehmann, order the ship to be brought out in such wind conditions. You had the best excuse in the world for postponing this idiotic flight; instead, you risk the ship, merely to avoid annoying Herr Goebbels. Do you call this showing a sense of responsibility towards our enterprise?
Though that damage was repaired, the force of the crash may have caused internal damage.
Only six days before the disaster, there was a plan assisted by the U.S. Navy to make the Hindenburg have a hook on her hull to carry aircraft in a similar way to what the Navy did with the USS Akron and the USS Macon. However, the trials were unsuccessful; the biplane had bashed the hook several times. This could have also caused damage and weakening of the structure.
Photographs and newsreels of the initial stages of the fire show that the stern section of the airship collapsed inward in a similar way to an eggshell, as well as a "crack" directly behind the passenger decks. When the stern of the ship hit the ground and collapsed, this part collapsed inward, causing another plume of fire to start. Some experts have suggested that the collapsing of the structure in this manner suggests problems within the cell bulkheads and the bracing wires.
This theory has not been very popular because it is not so much about what caused the fire as an element of support for the puncture theory.
The 2001 documentary Hindenburg Disaster: Probable Cause suggested that 16-year-old Bobby Rutan, who claimed that he had smelled "gasoline" when he was standing below the Hindenburg's aft port engine, had detected a diesel fuel leak. During the investigation, Commander Charles Rosendahl dismissed the boy's report. The day before the disaster, a fuel pump had broken during the flight. A crew member said this was fixed but it may not have been done properly. The resulting vapor would have been highly flammable and could have self combusted. The film also suggested that overheating engines may have played a role.
Critics say the documentary is misleading because it misconstrued the statements by the crewmen in the Hindenburg's lower fin. The crewmen said they saw a flash in the axial catwalk, but the film placed the flash in the keel catwalk closer to the passenger areas.
Some more sensational newspapers at the time said that a person on board committed suicide because a Luger pistol with one shell fired was found among the wreckage. Yet, there is no such evidence suggesting an attempted suicide. One thing to consider was that the Luger pistol ejected each empty round after firing, and that some owners would keep an empty shell in the gun for safety reasons.
Regardless of the source of ignition or the initial fuel for the fire, there remains the question of what caused the rapid spread of flames along the length of the airship. Here again the debate has centered on the fabric covering of the airship and the hydrogen used for buoyancy.
Proponents of both the incendiary paint theory and the hydrogen theory agree that the fabric coatings were probably responsible for the rapid spread of the fire. The combustion of hydrogen is not usually visible to the human eye in daylight, because most of its radiation is not in the visible portion of the spectrum but rather infrared. Thus what can be seen burning in the photographs cannot be hydrogen. However, black and white photographic film of the era had a different light sensitivity spectrum than the human eye, and was sensitive farther out into the infrared and ultraviolet region than the human eye. And while hydrogen tends to burn invisibly, the materials around it, if combustible, would change the color of the fire.
The motion picture films show the fire spreading downward along the skin of the airship. While fires generally tend to burn upward, especially including hydrogen fires, the enormous radiant heat from the blaze would have quickly spread fire over the entire surface of the airship, thus apparently explaining the downward propagation of the flames. Falling, burning debris would also appear as downward streaks of fire.
Of note is that in 1935 a helium filled blimp with an acetate aluminium skin burned near Point Sur in California with equal ferocity. Even the USS Macon, a U.S. Navy airship, burned after crashing into the Pacific off Monterey Bay. Those who disagree with these claims insist these two incidents had nothing to do with the dope, instead the small blimp burned because of a fuel leak, and the Macon burned because it was firing flares.
Those skeptical of the incendiary paint theory cite recent technical papers which claim that even if the airship had been coated with actual rocket fuel, it would have taken many hours to burn — not the 32 to 37 seconds that it actually took.
Modern experiments that recreated the fabric and coating materials of the Hindenburg seem to discredit the incendiary fabric theory. They conclude that it would have taken about 40 hours for the Hindenburg to burn if the fire had been driven by combustible fabric. Two additional scientific papers also strongly reject the fabric theory.
However these claims do not agree with the results the Mythbusters achieved on their Hindenburg special of their TV show and others feel the criticisms does not take into account the conditions that lead to firestorms, such as convection and ignition from radiant energy.
The most conclusive proof against the fabric theory is in the photographs of the actual accident as well as the many airships which were not doped with aluminum powder and still exploded violently. When a single gas cell explodes, it creates a shock wave and heat. The shock wave tends to rip nearby bags which then explode themselves. In the case of the Ahlhorn disaster on January 5, 1918, explosions of airships in one hangar caused the explosions of others in three adjoining hangars, wiping out all five Zeppelins at the base.
The photos of the Hindenburg disaster clearly show that after the cells in the aft section of the airship exploded and the combustion products were vented out the top of the airship, the fabric on the rear section was still largely intact, and air pressure from the outside was acting upon it, caving the sides of the airship inward due to the reduction of pressure caused by the venting of combustion gases out the top.
The loss of lift at the rear caused the airship to nose up suddenly and the back to break in half (the airship was still in one piece), at that time the primary mode for the fire to spread was along the axial gangway which acted as a chimney, conducting fire which burst out the nose as the airship's tail touched the ground, and as seen in one of the most famous pictures of the disaster.
As mentioned previously, the Discovery Channel series MythBusters explored the incendiary paint theory (IPT) and the hydrogen theory in an episode that aired January 10, 2007. While their experiments didn't concern what actually started the fire, the show's hosts, Adam Savage and Jamie Hyneman, demonstrated that when set alight with a blowtorch a 1:50 scale model of the Hindenburg burnt twice as fast in the presence of diffused hydrogen as without it. Combustion was observed in the burning skin, which would have accelerated the fire, but their experiments showed that hydrogen was the main fuel. The hydrogen filled model produced a fire with flames that came out of the nose and resembled the newsreel footage of the Hindenburg disaster. That program concluded that the IPT myth was "Busted".
The MythBusters constructed three 1/50 scale models made out of welded steel wire and covered in cotton fabric. They were suspended from a hangar ceiling and stayed horizontal the entire time. The first model was painted with iron-oxide and then aluminum powder dopes, closely replicating the actual skin of the Hindenburg. Ignited with a blowtorch, it took about 2 minutes to burn, with thermite-like events (sparkling blazes) noted in a few places. The second model had the same skin, but a water trough inside diffused hydrogen gas at sub-explosive concentrations. This one burned about twice as fast, with more thermite burning. The third model, done more for spectacle than anything else, had the skin painted with a thermite-like iron-oxide and aluminum powder enriched dope. It was noted that it would probably be far too heavy to fly. With model 2's hydrogen enrichment, it took 30 seconds to completely consume the skin. The conclusion was that neither the hydrogen gas nor the flammable skin bore sole responsibility for the speed of the fire, but both contributed.
The National Geographic program Seconds From Disaster had veteran air crash investigator Greg Feith study all of the available evidence, including eyewitness accounts, interviews with the last two living survivors, newsreel footage, weather reports, and the Hindenburg blueprints. Feith burned a sample of doped cloth and it took one minute to consume the whole piece, ruling out the skin as the primary accelerant. Feith's investigations concluded that a gas bag was punctured, probably by a bracing wire broken from the two sharp turns, and that electrostatic discharge from the skin to the ship's skeleton ignited the leaked hydrogen.
In Search of..., a show mainly focused on paranormal investigations and conspiracy theories, made an episode based on this tragic accident, and immediately raised the question of whether it was really an accident or instead sabotage by then-Nazi Germany.
The actual site of the Hindenburg crash at Lakehurst Naval Air Station (reestablished as Naval Air Systems Command (NAVAIR) at Naval Air Engineering Station (NAES) Lakehurst, or "Navy Lakehurst" for short) is marked with a chain outlined pad and bronze plaque where the airship's gondola landed. It was dedicated on May 6, 1987, the 50th anniversary of the disaster. Hangar #1, which still stands, is where the airship was to be housed after landing. It was designated a Registered National Historic Landmark in 1968. Pre-registered tours are held through the Navy Lakehurst Historical Society . Due to security concerns, no foreign nationals are permitted on the tours.