The Spark

LXXIV

The Hindenburg Memorial at Lakehurst New Jersey is an outline of the gondola where it crashed to earth, killing Ernst Lehmann. The Hindenburg's hangar still stands (right)

 

So if Erich Spehl or Joseph Spah did not destroy the Hindenburg, what did?

It is universally agreed that the ship burned because hydrogen and oxygen interacted elementally. It is also universally agreed that the chemical reaction of the two gases was catalyzed by an electrical spark. These facts answer the "why" of the fire. But beyond this lies of host of questions about the precise "how" of the fire.

There are several theories, none completely convincing:

>>> Dr. Eckener testified that the accident occurred because the Hindenburg had been put through structural stress during its approach to the mooring; specifically, he criticized Captain Pruss' tight "Hard-a-Port, Hard-a-Starboard" S-turn near the mooring. Eckener felt that the wiggle-waggle of the ship caused a bracing wire on one of the ship's frames to snap. The free end then buried itself in a gas cell, causing a hydrogen leak. Dr. Eckener further theorized that the leaking hydrogen gas then rose up through the hull (causing the fluttering of the fabric that had been observed); this also, according to Eckener, caused the ship's tail-heaviness. When the mooring lines were dropped, the ship, which was carrying an electrical charge because of friction with the surrounding stormy air, grounded, and a spark jumped somewhere within the hull, igniting the hydrogen. Eckener concluded by saying that the accident was caused primarily by pilot error --- Pruss, who was more interested in keeping to a schedule for political reasons, should have circled the field instead of forcing the ship to make a tight turn.

Until the day he died, Pruss insisted that the ship had been sabotaged. Pruss never forgave Eckener for his public shaming, and Pruss always denied that he was watching the clock while on the Bridge, or that he was under orders to rush the landing in order to reach London on time. However, there is no question that Pruss felt he was under a time constraint to reach London for the Coronation (regardless of propaganda he had a full flight booked) and that he cut corners to make the landing at Lakehurst.

Despite the fact that modern forensic accident investigators have proven that Dr. Eckener's theory holds true when tested, there is a problem with the time course of events.

For one thing, the Hindenburg did not turn on a dime. The ship turned sharply to Port at 7:09 and sharply to Starboard at 7:18, a full nine minutes apart. The ship was not wrenched around in a manner that would cause a bracing wire to snap.

If a bracing wire had snapped or its shackle failed, the tense wire, thick as a finger, would have let go with a whipcrack report that would have definitely attracted attention. Yet none of the survivors from inside the envelope remember hearing any such sound though they do remember the more subtle sound of the gas igniting.

If the gas cell had been breached at 7:09 at the time of the first turn, the ship would have likely have become tail heavy sooner than 7:18, and if the cell had been breached at 7:18, the tail-heaviness would have become apparent much later, not immediately.

Likewise, Dr. Eckener's theory regarding the grounding of the ship works when tested, but the problem again is time. The heavy hemp mooring lines were dropped at 7:21. The ship blew up at 7:25. Hemp is not a great conductor, but the ropes were wet from the rain and hit wet ground. It's most likely that the static electricity built up in the ship did not take four minutes to discharge.

Thus, some other mechanism was in play. Given the chain of events the gas leak began in response to some order from the Bridge. That can be said. Where the spark originated from is far less certain.

This diagram of the Graf Zeppelin (LZ-127) shows the internal construction of the ship, including the gas shafts

>>> It should be remembered that the Hindenburg was not inert between 7:21 and 7:25. It was raining. The atmosphere was unsettled. The mooring lines had been picked up by the ground crew and one had been attached to a metal winch. She was being reeled in toward the mooring mast, however slowly, allowing the very wet outer envelope to pick up additional static charge. A static discharge on the outer envelope would have ignited the leaking hydrogen.

A blue aura was seen along the top of the ship just before the fire. It is possible, though less than likely, that St. Elmo's Fire along the hull could have caused the fire to ignite. However, St. Elmo's Fire has a very weak electrical charge, and no one and nothing ever exposed to it has been harmed. It would be a trillionth chance, even in the presence of hydrogen, that St. Elmo's Fire, which seemingly has never ignited anything, could have ignited the fire that destroyed the Hindenburg.

However, under less rare conditions, hydrogen gas and ordinary air can interact and spontaneously combust, causing fire. It is possible that the blue aura mistaken for St. Elmo's Fire was just a hot blue flame caused by this combustion in the roiled air.

>>> The Hindenburg's outer envelope had been redoped in preparation for the 1937 season. The new dope mixture was much lighter than the old dope, removing some tons of deadweight from the ship, lightening her. The cover was also extremely watertight. However, there was a tendency for water to pool in certain areas, rather than bead and run. Water is an excellent electrical conductor that would have helped propagate sparking.

It was discovered in testing after the accident that among the various materials in the new dope were aluminum and iron oxide, two compounds that together create thermite, a highly combustible material. Pure thermite can ignite spontaneously when exposed to a spark or even to water being poured upon it. Although the other materials in the dope should have precluded such a reaction in the absence of extreme heat or fire, the ignition of the hydrogen by a spark would have set the thermite compound ablaze. Thermite burns violently, with extreme heat, and with a distinct orange color --- the exact conditions of the Hindenburg fire. DZR had unwittingly wrapped an oceanliner-sized aircraft full of explosive gas in flash-fire packaging.

As an aside, it was also found that the older dope mixture used on the old Graf Zeppelin refused to burn, even at high temperatures. It would char, but not burn. A new variant of the older dope was used on the Graf Zeppelin II.

 

The Hindenburg aflame

A Thermite fire

>>> There is a possibility that Dr. Eckener was mistaken about the snapping of the bracing wire as the cause of the gas leak. A crewman testified that he had seen the center of Gas Cell Four ignite first. A ground observer claimed to see a light within Gas Cell Five. The two cells were adjacent to each other.

The Hindenburg's gas cells were doughnut-shaped or bagel-shaped affairs stood side-by-side on their edges. An axial walkway like a second keel ran down their centers from bow to stern. A number of gas shafts stood between the gas cells just adjacent to the ship's rings. These shafts rose from the keel to topsides where they ended in the ship's gas vents. Each shaft had gas valves and controls, some automatic.

The Hindenburg had had a problem with a gas valve in 1936. It was found and corrected. However, there is always the possibility that a gas shaft control failed within the ship on the day it died, allowing hydrogen to escape. That would explain the fire at the center of Cell Four (near where the controls were located) and the possible involvement of Cell Five.

Whatever the cause of the fire, the result remains inscribed in memory.

The Hindenburg and a Douglas airplane. The past and the future meet