In the mid 1930’s a popular form of long-distance air travel was the rigid airship, or Zeppelin. Filled with lighter-than-air gasses, the airships could travel up to about eighty or ninety miles per hour and could stay aloft indefinitely crossing the Atlantic Ocean in about two or three days. But the glamour of airship travel came suddenly to a blazing end on May 6, 1937 in Lakehurst, New Jersey. Here’s what happened.
Background: The LZ 129 Hindenburg was a rigid airship designed and built in Germany by the Zeppelin Company, and launched for its first flight on March 4, 1936. It featured a duralumin structure with fifteen circular bulkheads along its length, and sixteen cotton gas bags fit in between the bulkheads. The bags were filled with highly flammable hydrogen instead of non-flammable helium, as helium was hard to obtain owing to a ban on export of the gas from its only industrial source—the United States. It was powered by specially designed diesel engines built for the Hindenburg by Daimler-Benz to provide the requisite thrusting power with the least possible weight. The outer skin of the airship was made of cotton doped with plasticized lacquer that also contained reflective materials designed to ward off damages from ultraviolet and infrared radiation. The Hindenburg was designed as a passenger aircraft, and made ten trans-Atlantic trips in 1936 from Germany to ports in the U.S. It began the 1937 travel season with a round trip from Germany to Rio de Janeiro, Brazil, in late March. It departed Frankfurt, Germany, on May 3, bound for Lakehurst, N.J. on its initial round trip to the U.S. for 1937. On May 6, it passed over Boston on its way south but needed to make slight course alterations owing to stormy weather at its destination. It arrived at Lakehurst Naval Air Station about 7 p.m. and made its initial approach to the docking tower. The stormy weather had subsided, but elements of wind and rain persisted in the area causing the crew to maneuver the ship somewhat so that the mooring lines could be tied up. At 7:25 p.m. the airship caught fire and was quickly engulfed in flames. After about 30 seconds the burnt skeleton crashed to the ground.
The Fire: It’s difficult to pinpoint where on the airship the fire started since it happened suddenly and spread so quickly. Witnesses have varying accounts of how it started, and even the news media with cameras at the ready did not capture the exact moment on film. The fire became most brilliant on top of the hull and toward the stern. One crewman heard a muffled detonation followed by bright reflection on the bulkhead at the beginning of the fire in the stern in the lower fin where he was stationed. Some observers on the port side saw the fire break out just in front of the horizontal port fin, followed by flames leaping up in front of the upper fin. On the starboard side witnesses observed the flames starting farther back behind the rudders. The fire raced rapidly throughout the stern and the ship fell stern first to the ground with the bow pointing up nearly forty-five degrees. This caused the fire to burn rapidly up toward the bow blowing like a blow torch through a hole in the nose. Seconds later the bow crashed to the ground as the hydrogen burned out and the fabric around the hull burned away. When the hydrogen was gone, the fire died down somewhat, but was not extinguished for several more hours as the diesel fuel supply continued to burn.
The Aftermath: Of the ninety-seven people on board at the time of the disaster, thirty-five were killed. Thirteen of the dead were passengers and twenty-two were crew members. One of the grounds crew also was killed making the total thirty-six. Most of the victims died from burns either still in the wreck or later in nearby hospitals. A few jumped or fell to their deaths attempting to escape the flames or smoke inhalation. Nearly all of the crew members in the bow were killed either by the flames or by attempting to jump when the ship was still too high in the air. Most of the passengers that were killed were trapped on the starboard side of the passenger deck with the wind blowing from the port side to the starboard side. Further, the ship rolled slightly to starboard when it crashed to the ground blocking the starboard side escape route with debris. A doorway jammed shut on the starboard side during the crash cutting off another escape route for those hapless passengers. Ironically, there was relatively little damage to the surrounding ground as the heat from combustion in a hydrogen-based fire has a tendency to rise quickly with the rising gas. This generally makes hydrogen-based fires easier to survive than wood, coal, or fuel-based fires.
The Cause: The actual cause of the blaze was never determined. There are numerous theories, however, and some of the more credible ones are described here.
Sabotage
The concept of sabotage became popular almost from the start as Hugo Eckener, a pioneer of rigid airships, received the news erroneous that the Hindenburg had exploded. He relayed this to the press thereby starting up the theory of a bomb of some kind on board. The theory gained support from the commander of the Naval Air Station at Lakehurst, Charles Rosendahl. Further, Max Pruss, the captain of the Hindenburg throughout its lifetime, believed the cause was sabotage also stating that the airship had flown through thunderstorms while operating in South America, and had been struck by lightning without any damage or consequences. Most of the surviving crew could not accept the idea that one of the crew members would have sabotaged the aircraft. A passenger, Joseph Spah, drew some attention as a potential saboteur as he made frequent trips into the interior of the aircraft to feed his dog. Further, he was an acrobat, and could have scaled the bulkheads to hide an explosive device. In the final analysis, neither the German nor the American investigations turned up any evidence that sabotage was in play, making the entire concept a matter of conjecture.
Static Electricity
After learning more about the disaster Eckener later changed his position on the source of the fire to static electricity that had built up on the ship’s hull. He pointed out that the ship’s outer skin was separated from the frame by non-conductive cords that may have caused a substantial imbalance of electrical charge to form between the skin and the frame. A professor at Princeton University, Mark Heald, witnessed the disaster and noted minutes beforehand to his wife that he could see St. Elmo’s Fires forming on the top of the aircraft. He then called out that “the thing is afire” just before a huge burst of flame from burning hydrogen erupted. An episode of Nova, the PBS series, points out that a hydrogen leak near the stern likely existed as the crew was having some difficulty bringing it into trim and the aft portion was too low. An electric charge may have climbed the mooring line up to the leak setting the hydrogen off. The researchers further pointed out that there may have been several such sparks that raced up and down the hull of the ship, and also that rain may have come into play, as the conductivity increased when the surface was wet.
Lightning
At the time of the disaster, the Hindenburg was venting hydrogen to even the ballast as it prepared to land. Hydrogen is not volatile until it mixes with oxygen when it is vented or released. The idea that a lightning flash occurred drew some backing, but witnesses all stated that there was no lightning strike during or just before the disaster.
Engine Failure
A ground crewman, Robert Buchanan, saw some sparks when one of the engines backfired having been thrusted into reverse to make a turn. Another ground crewman, Robert Shaw, also saw sparks shoot out of an engine at the time a blue ring occurred behind the tail. The blue ring could have been leaking hydrogen that was quickly ignited by the sparks. Eckener disputed this causal item as the sparks would not have been hot enough to ignite hydrogen that has an ignition point of 932 degrees Fahrenheit.
Static Spark Hypothesis
This is the most popular and widely accepted theory. Two members of the ground crew who were not near each other both witness a fluttering of the fabric cover in front of the upper fin that could indicate leaking hydrogen and could be the point of ignition. However, pictures indicate that the fire was not burning along the skin of the ship, but was burning in a pattern that coincided with the positioning of the gas cells inside the ship. This fact was confirmed by crew members in the stern who saw gas cells burning. No other disturbance was noted at the point where the skin fluttered.
Incendiary Paint
The fabric that covered the airship’s frame forming the outer skin had chemicals applied to it that could be combustible, raising the specter that this may have contributed to the cause of the fire. The proponents of this theory believe that these chemicals were contributable in starting the fire and aiding its spread. Although the chemicals were flammable, further research showed that they did not exist in a great enough quantity to impose a serious risk, and if they were present in enough quantity to start a fire, they would have weighted the airship to where it would be too heavy to take off. Further, these chemicals burn too slowly to have created the rapid conflagration that existed. Evidence from photographs, newsreel footage, and witnesses who saw a glow from inside the ship tend to indicate the fire starting somewhere inside the structure and not on the outer fabric.
Puncture
The Hindenburg executed several sharp turns in an effort to line up to the docking tower. Proponents of the puncture theory believe that during one or more of these turns a bracing wire in the stern broke and punctured a gas cell. This would have released hydrogen into the air, and the mix may have been set off by an electric spark. A ground crew member heard a sharp snapping sound that could have been one of the bracing wires breaking.
Fuel Leak
A 16-year-old boy said that he smelled gasoline near the tail of the airship while standing below the aft port engine indicating a possible diesel fuel leak. Vapor from the leak would be highly combustible and could have been the fire’s flashpoint. However, most witnesses observed the early stages of the fire coming from the top of the airship and not down near the keel where an engine may have been leaking. The only place for a diesel fuel combustion to take place outside the engine would have been someplace on the hot engine, and not anywhere else on the airship.
Conclusions: The suddenness of the fire and the rapid pace at which it destroyed the Hindenburg made reconstruction of what happened a difficult task. The shock waves it sent through the media along with the passionate reporting by Herbert Morrison for NBC’s Newsreel contributed to the loss of confidence in rigid airship transport. With the disaster the airship transport industry came abruptly to an end in conjunction with the development of fixed wing aircraft that could likewise fly across long distances.
Sources:
History.com, The Hindenburg Disaster.
Wikipedia, Hindenburg Disaster.
Photo by Sam Shere.