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00:01The Hindenburg, the largest aircraft ever built.
00:06An incredible feat of Nazi engineering.
00:10It was certainly the most advanced airship that had ever been built.
00:14But in 1937, disaster strikes.
00:20A raging fire tears through the giant airship.
00:24The cause of the crash is an ancient
00:2930-year-old mystery.
00:32In a matter of seconds, 245 meters of airship
00:35was reduced to just smoking wreckage.
00:3935 people lose their lives.
00:42What really happens that fateful night?
00:47Now, investigators use pioneering technology.
00:51I don't think the flight crew did the correct thing.
00:55And innovative forensic techniques to unearth new evidence.
01:00I can see the explosion immediately.
01:03We got a wolf, didn't we? You heard that chamber go?
01:08Using cutting-edge 3D graphics,
01:12We will resurrect the Hindenburg from the ashes.
01:18We'll reveal its inner workings.
01:21And the engineering that makes it fly.
01:25We'll reconstruct the Night of the Inferno.
01:28To reveal the mysteries of this incredible Nazi flying machine.
01:41May 6th, 1937.
01:45Adorned with Nazi swastikas,
01:47Germany's Hindenburg airship flies over New York
01:50after completing a three-day crossing of the Atlantic.
01:54It makes the journey twice as fast as the quickest ocean liner.
02:01The Hindenburg is the pride of the Nazi air fleet.
02:05At over 800 feet long,
02:07it's the largest aircraft ever to fly.
02:12Under its aluminum-coated skin,
02:14there's space for 61 crew and 70 passengers.
02:21It's a flying five-star hotel,
02:24with bedrooms,
02:26dining hall,
02:28piano bar,
02:29and smoking room.
02:35Gigantic cotton gas bags filled with hydrogen
02:37make this monster lighter than air.
02:50The Hindenburg approaches its final destination.
02:54Lakehurst Naval Base, New Jersey.
02:58But as it prepares to land...
03:01It burst into flames,
03:03and it's crashing.
03:03It's crashing,
03:04it's crashing terrible.
03:05Oh my, get out of the way, please.
03:07It's burning, bursting into flames,
03:09and it's falling on the mooring path.
03:11This is one of the worst catastrophes in the world.
03:13Oh, the humanity.
03:15I don't do it.
03:17Oh.
03:18I can't talk, ladies and gentlemen.
03:23You see this giant, beautiful airship float in,
03:27know that it's filled with people,
03:28and then all of a sudden,
03:30it just burst into flame.
03:33What causes one of the most notorious air disasters in history?
03:40The enormous Hangar 1 at Lakehurst
03:43is where the Hindenburg is stored when it flies to the U.S.
03:50In 1937, Hangar 1 is the largest single room in the world.
03:56It's 350 feet wide and nearly 1,000 feet in length,
04:01as long as the Chrysler Building is tall.
04:06It's here where airship historian Dan Grossman
04:10begins his search for the truth.
04:14This entire building would have been filled with airship.
04:18And it kind of gives you a sense of just how big the ship is.
04:22This building had Hindenburg from one end to the other end.
04:31The massive Hindenburg erupts into flames just overhead.
04:37Dan believes that the hangar contains clues to help solve this mystery.
04:42We are standing where the control car crashed.
04:46This entire area would have been covered with nothing but burning,
04:51smoldering wreckage of airship.
04:55To this day, Hangar 1 stores charred traces of the airship.
05:02Dan discovers evidence of the fire's intensity
05:04on these recovered pieces of silverware.
05:07We can take a look at some of the items that survived the fire.
05:10You can see where metal has melted and dripped onto these pieces.
05:16It was a horrific thing for people to go through.
05:19There was a lot of tragedy associated with this.
05:25In just 32 seconds, the fire consumes the entire Hindenburg,
05:30killing 35 of the 97 crew and passengers.
05:35But what can start a fire ferocious enough to melt metal?
05:43Within hours of the disaster,
05:45there are rumors that opponents of Hitler sabotage the ship.
05:51The Hindenburg is as large as the U.S. Capitol building.
05:56Plenty of room for foul play.
06:05Is there a bomb on board the airship?
06:09Fire and explosions expert Dr. Claire Benson
06:13puts the sabotage theory to the test.
06:16Eyewitness accounts at the time suggest there was quite a small fire
06:21towards the top and the back of the Hindenburg.
06:26Claire plans to detonate a bomb inside a model of the airship
06:30and analyze how quickly the fire spreads.
06:34She works with pyrotechnics expert Matthew Tosh.
06:39We are modeling now the individual reservoirs of hydrogen gas.
06:45So we've got our cylinder here and Claire is going to feed me some hydrogen gas.
06:51This replicates the Hindenburg's massive hydrogen-filled gas bags.
06:59Claire will analyze the explosion
07:01and compare it to footage of the fire that destroys the Hindenburg.
07:05The explosive we're using on our model is black powder, gunpowder.
07:09Okay, so this is the explosive going in.
07:14This is where tensions start to rise sometimes because we're now going into the firing system.
07:21Claire uses a slow motion camera to analyze the fire that the bomb sets off.
07:27Right, let's arm the system.
07:30We're armed.
07:31Okay, you ready?
07:32Here we go.
07:34In three, two, one.
07:40We got a wolf, didn't we? You heard that chamber go?
07:43Yeah.
07:51Okay.
07:53The camera footage is downloaded
07:55and Claire replays the explosion in super slow motion.
08:03I can see the explosion immediately and it seems to engulf the back third, I would say, of the model
08:10really quite rapidly.
08:12The Hindenburg fire lasts just 32 seconds.
08:17But Claire's experiment suggests an explosive would have engulfed the airship in half that time.
08:25An explosion happens really rapidly and then very quickly that fire propagates through the whole model and burns it up.
08:33Despite the apparent speed of the Hindenburg fire, Claire's experiment reveals in reality the airship burns too slowly for the
08:41cause to be a bomb.
08:43It's a breakthrough in the investigation.
08:46She's certain she can finally rule out the sabotage theory.
08:51I think we can conclude from the experiment that it's unlikely that the Hindenburg disaster was started by an explosive
09:00device.
09:03A bomb did not bring down the giant Nazi airship.
09:08So what else could it have been?
09:14Federal authorities discover that before the disaster, the Hindenburg's crew gets sent threatening letters.
09:26As they examine the airfield, investigators find suspicious tracks that lead away from the crash site.
09:36There are rumors of a gun in the wreckage.
09:41Fueling speculation of a shot from inside the airship.
09:47But even though investigators name two suspects, they eventually rule out sabotage.
09:57The explanation of this disaster remains a mystery.
10:03Today, in the search for answers, investigators turn to the design of the Hindenburg itself.
10:10What clues does it hold to the cause of the catastrophe?
10:27The Nazi-built Hindenburg airship bursts into flames as it arrives at Lakehurst, New Jersey.
10:35Sabotage is ruled out.
10:38But what else could cause this disaster?
10:42Now investigators look to the Hindenburg's design for answers.
10:52The Hindenburg skeleton is a complex web of aluminum struts and braces.
10:58It carries the ship's infrastructure as well as the engines, passengers, crew, and cargo.
11:08But its main job is to create a large empty space for the mission-critical components.
11:1516 gigantic cotton bags that hold 7 million cubic feet of hydrogen, the lightest element in the universe.
11:26The gas allows the Hindenburg to fly.
11:30But does it also cause its downfall?
11:36Hangar 1 at Lakehurst is the Hindenburg's American home.
11:41The giant airship fills the vast space.
11:45Today, it houses wreckage of the disaster.
11:50Airship historian Dan Grossman investigates one of the surviving pieces.
11:56This is an actual girder from the Hindenburg that was recovered after the wreckage.
12:00And you can see in the bends and the way this piece was designed and fabricated,
12:05that made it simultaneously very strong, but also very light.
12:09Because I can take this entire girder and I can hold it with one finger.
12:17The Hindenburg's designers make the frame as light as possible.
12:21A light frame allows the fuselage to be supersized.
12:25Key to carrying as much hydrogen as possible, keeping the Hindenburg airborne.
12:32But there's a problem.
12:34Hydrogen can be very explosive.
12:37Investigators want to know if that causes the fatal fire on board the Hindenburg.
12:43Today, fire and explosions expert Dr. Claire Benson is taking a new look at how hydrogen behaves when ignited.
12:51This is a bag filled with pure hydrogen and inside is an electrical igniter and we're going to see what
12:58happens when we try to ignite pure hydrogen.
13:04Arming.
13:06And three, two, one.
13:10It won't set on fire.
13:13A spark cannot ignite the hydrogen.
13:16The igniter went off, but there was no combustion reaction inside with the hydrogen because it's just pure hydrogen.
13:23But in certain circumstances, hydrogen will ignite.
13:27Claire fills a second bag with hydrogen mixed with another gas that's all around us.
13:33Oxygen.
13:35Okay, arming.
13:37Three, two, one.
13:41Together, hydrogen and oxygen create an explosive cocktail.
13:46But if they are kept separate, then hydrogen is perfectly safe.
13:50We have to manage it.
13:51We have to make sure that we can contain it and that we can keep it away from oxygen that
13:55it could react with and from ignition sources.
14:02In the First World War, German airship designers used membranes from cows' intestines to make bags that safely contain hydrogen.
14:14In the 1930s, they changed to helium.
14:18A gas with less lifting power, but also less risk.
14:26But the only place in the world that produces helium is America, and the US won't sell helium to the
14:34Nazis.
14:36The Hindenburg must use hydrogen, but can now afford to have nine extra cabins, as hydrogen has more lifting power.
14:47The Hindenburg's designers also create a new way to safely contain the gas.
14:53They make airtight cotton gas bags to hold the hydrogen.
14:58They are so confident their plan is foolproof, they even allow passengers to smoke on board the airship.
15:08So why does the Hindenburg catch fire?
15:12Claire believes there can only be one answer.
15:16On the Hindenburg, if there was a leak or some kind of mixing of the hydrogen with the air, it's
15:22the mixing that would enable the ignition of that reaction.
15:27Could a deadly leak of hydrogen play a part in bringing down the Hindenburg?
15:31What sparks the catastrophic fire?
15:46The massive Nazi airship Hindenburg erupts in a raging fire.
15:51Seven million cubic feet of hydrogen are set aflame.
15:55Within moments, 35 people are dead.
15:59But hydrogen will only burn when mixed with oxygen.
16:03It should be completely safe within the airship's giant airtight gas bags.
16:08Now investigators want to know, how does this hydrogen escape?
16:15Seconds before the disaster, a witness sees the ship's skin fluttering.
16:22Possible evidence of a gas leak.
16:27Right beneath this spot are gas bags number four and five.
16:32Each filled with half a million cubic feet of hydrogen.
16:37Could something inside the airship snap and tear the gas bags?
16:45Now hydrogen can escape and mix with oxygen, turning Hindenburg into a gigantic flying bomb.
16:57But how could a section of the Hindenburg structure break?
17:02Dr. Praskovia Milova is an aeronautical engineer from the Universite Libre in Brussels.
17:10She examines the Hindenburg's design for clues.
17:14We can see that the main structure of the Hindenburg was supported everywhere by steel bracing wires.
17:23Thousands of feet of steel wire braces Hindenburg's innovative lightweight frame.
17:29Steel wires surround all 16 gas bags, securing them in place.
17:35From this view, you can imagine that the gas bag would be filling this whole space and even pressing against
17:44the wires.
17:46But steel is prone to rust.
17:51Steel is a corrosive material just by nature and rust then has a significant impact on the strength of the
17:59material.
18:05Before the disaster, the Hindenburg makes 17 round trips across the Atlantic, with each crossing taking an average of 55
18:14hours.
18:17It flies at a cruising altitude of only 650 feet, exposing it to moisture and salt from the ocean.
18:27To shield the skeleton under the Hindenburg's skin from corrosion.
18:32It is covered with protective paint.
18:38But the steel bracing wires are unprotected.
18:41And when exposed to salt and moisture, they can rust.
18:49Praskovia thinks there's another threat to the steel wires.
18:54The airship's aluminum frame bends and stretches to cope with the challenging weather conditions crossing the Atlantic.
19:01Corrosion eats the material, so it creates little cracks on the surface.
19:07And then, because the whole structure is flexible, the steel wire would be repetitively tensioned and relaxed, tensioned and relaxed,
19:18and eventually breaks.
19:22Each cotton gas bag is reinforced and sealed by a thin layer of rubber.
19:28Could a snapping steel wire puncture one of the bags?
19:36This is the fabric that was used for Hindenburg, which is a kind of sandwich material of two layers of
19:43cotton joined with latex.
19:46The cause of the leaking hydrogen is a mystery.
19:50Today, Praskovia is finally putting the suspect gas bag material to the test.
19:56She prepares samples of the rubberized cotton with lab technician Inga Dismet.
20:04We chose the pointed needle because if the wire broke, it would have had the sharp edges, and the pointed
20:13needle would be the best to simulate that broken wire.
20:20The machine ramps up the force.
20:26The sample was punctured.
20:29We can see the hole.
20:32The puncture resistance is around 40 newtons.
20:37Praskovia's test reveals how little it takes to pierce the material.
20:42The gas bag material could have been pretty much easily broken by a broken wire.
20:49All the vital forensic evidence is destroyed in the intense fire.
20:54But with the results of her test, Praskovia is now certain a tiny piece of metal is the most likely
21:00culprit.
21:01The cause of the Hindenburg disaster is finally getting clearer.
21:10But the leak still needs a spark.
21:13What starts the mighty fire?
21:26May 1937.
21:28The wreckage of the airship Hindenburg lies burning on a New Jersey airfield.
21:34Now investigators believe a broken steel wire has ripped open a gas bag.
21:40And half a million cubic feet of hydrogen leaks out.
21:45But the highly flammable mix of hydrogen and oxygen needs to be ignited.
21:50So what sparks the deadly fire?
21:55The Hindenburg lands at Lakehurst during a thunderstorm.
22:00Eyewitnesses report dim blue lights rippling across its aluminum coated skin.
22:06Are these the sparks that ignite the hydrogen?
22:10And bring down the Hindenburg?
22:17Dr. Chris Gould is an electrical engineer from Staffordshire University in England.
22:25He investigates if a thunderstorm can produce a spark powerful enough to start a fire.
22:30What we're trying to test here is how can a spark be created within the Hindenburg structure.
22:39Thunderstorms produce millions of volts of electricity.
22:43The Hindenburg is electrically charged flying through the stormy conditions.
22:50But dropping its mooring ropes for landing should safely discharge the airship.
22:57The mooring ropes should channel any electrical charge to Earth.
23:02Eliminating the risk of potentially lethal sparks.
23:08How is a spark created on the Hindenburg?
23:13Chris and technical assistant Suhill want to find out.
23:18They use a replica of the Hindenburg skin to investigate.
23:22This model represents the main components of the Hindenburg.
23:27The airframe and the outer skin.
23:29Which is a woven fabric painted with aluminum powder.
23:35And we have this aluminum bar which represents the metal structure of the airship airframe.
23:45The mooring ropes are only attached to the airship's aluminum alloy frame.
23:52The skin is separated from it by wooden dowels.
23:56Chris suspects this separation means the skin keeps its electrical charge when the airship drops its mooring ropes.
24:05The electrical current then flows across the gap in the form of a spark.
24:10If we can create the spark in that gap, then potentially that can lead to ignition.
24:18Flying through the storm, the Hindenburg's outer skin gets covered in water.
24:24Chris and Suhill recreate the same conditions on their model.
24:28The water that we poured onto the fabric of the airship is replicating the pools of water that are formed
24:35as the airship has been traveling through the poor weather conditions.
24:41Suhill connects the high voltage generator to the wet skin.
24:46And grounds the inner frame exactly like the Hindenburg moments before the disaster.
24:51I think we're ready to go.
24:54Chris's equipment can produce up to 50,000 volts.
24:58The experiment must be done inside a cage for safety.
25:041,000.
25:06One and a half.
25:082,000 volts.
25:10We can see a spark. We've got a spark.
25:14Chris creates a spark in the exact conditions the Hindenburg faces.
25:19His findings are conclusive.
25:23Chris believes it's a discovery to finally solve an 82-year-old mystery.
25:29The test reveals a fatal design flaw in the Hindenburg.
25:34Wooden dowels insulate its skin from the metal frame and the mooring rope.
25:40The frame loses its charge when the mooring rope drops down.
25:44But the skin remains charged and can still trigger sparks.
25:51Chris is convinced this is the cause of the deadly fire.
25:56That spark would be enough to be able to ignite a leaking hydrogen mixture from the Hindenburg.
26:04Investigators discover that an electric spark ignites the Hindenburg.
26:0962 of the 97 onboard survive the resulting fire.
26:13How can so many people escape the inferno?
26:27The Hindenburg airship, leaking hydrogen and electrically charged by a huge thunderstorm, approaches Lakehurst, New Jersey.
26:40During the landing, most passengers are in the lounge.
26:43They have no idea what's happening 400 feet behind them.
26:49A spark ignites a gas bag in the tail and turns it into a fireball.
26:56A huge flame blasts through the central walkway.
27:01Fire engulfs five crew in the central control rooms and traps nine crew in the bow.
27:08The nose becomes a giant blow torch and the ship starts to crash.
27:15How can 62 of the 97 people on board survive this inferno?
27:25Airship historian Barbara Weibel hunts for answers in the town where the Hindenburg is built.
27:32Friedrichshafen, Germany.
27:34The Zeppelin Museum houses a full-scale replica of the Hindenburg's interior.
27:48The trip across the Atlantic takes three days.
27:54A round trip costs $720.
28:01Not much today, but in 1937, it's half the average US worker's annual salary.
28:17The need to save weight is the biggest priority.
28:22Each cabin only contains what is absolutely essential.
28:31The Hindenburg makes its final approach towards Lakehurst, New Jersey.
28:36Most passengers are in one of the two lounges, enjoying the dramatic views of New York City.
28:41The Hindenburg is designed with vast windows along the length of each lounge.
28:47Reconstructed here at the museum.
28:55As the Hindenburg descends to the airfield at Lakehurst Naval Base, the large windows in the lounges are the most
29:02popular place to be.
29:05But the passengers here are the first to notice the disaster.
29:22The windows not only help alert passengers to the unfolding disaster, they help with a hasty escape.
29:42The Hindenburg catches fire 200 feet in the air before it crashes to the ground.
29:49People escaping must wait for exactly the right moment to jump.
30:16But not all passengers are in the lounges during landing.
30:21Many are in their cabins preparing to disembark.
30:26They face greater danger.
30:38The cabin's modern minimalist design lacks one crucial feature.
30:43A window.
30:47All the cabins are situated in the center of the airship with no views to the outside.
30:54Passengers in their cabins are unaware of the disaster unfolding around them.
31:12It takes just 32 seconds from the first flames being spotted to the giant airship hitting the ground.
31:21Passengers still in their cabins have no time to escape.
31:31No one in their cabins survives the disaster.
31:3723 passengers do escape.
31:40Every one of them are in the lounges.
31:44However, the crew are spread throughout the airship.
31:5014 of the 61 crew on board are killed almost instantly in the fire.
31:55The rest have a chance to make their escape.
32:06At the time of the disaster, the captain is overseeing the landing from the Hindenburg's control car.
32:20The control car is far away from the start of the fire at the tail.
32:24The captain and 11 of the crew here escape when the airship crashes to the ground.
32:46But this is not the end of their ordeal.
32:51Now on the ground, they must find their way through the burning wreckage.
33:08Two of the crew in the control car die trying to escape.
33:13The captain survives, but is severely burnt fleeing the wreckage.
33:18Other members of the crew are luckier.
33:25The engine cars are far away from where the fire starts, and 9 of the 11 crew there escape.
33:35With the tail virtually touching the ground, all four crew in the rear also walk away virtually unscathed.
33:46In total, 39 of the 61 crew survived the disaster.
33:52But could the entire catastrophe have been averted?
33:57What can the captain do differently to stop the disaster?
34:11Lakehurst, New Jersey, May 1937.
34:15The wreckage of the Hindenburg lies scattered on the airfield.
34:2035 people are dead.
34:24Can the captain of the airship do anything to stop the disaster?
34:33Mats Backlund is a retired airship pilot.
34:38Mats programs this state-of-the-art simulator to exactly replicate the conditions on the day of the disaster.
34:46In the search for clues, he's recreated the Hindenburg's precise flight path.
34:54There are major differences between airships and planes.
34:58But the trickiest part of any operation is the landing.
35:04The ground can be very unforgiving if you hit it the wrong way.
35:08The Hindenburg is flying through a thunderstorm.
35:13It charges the airship with lethal electricity.
35:18And puts it hours behind schedule.
35:22The captain decides to land fast.
35:25He uses a quick and efficient method called a flying moor.
35:30In a flying moor, the Hindenburg drops its ropes at a high altitude and is winched to the ground.
35:37But only the airship's frame is safely discharged of electricity while it's 200 feet in the air.
35:44The height of the airship increases the electrical charge of the skin, causing the catastrophic spark.
35:52The captain's choice to land using a flying moor is the catalyst for the disaster.
35:58Mats thinks there's a safer way to land.
36:01We're going to try to do the approach at a lower level.
36:06Airships can also land like conventional aircraft, slowly reducing speed and altitude until coming to rest on the ground.
36:19A low landing is much slower and harder for a pilot to do.
36:25But it dramatically reduces the risk of a disastrous spark.
36:31Mats attempts to land like an aircraft to see if the captain can do it and avert the catastrophe.
36:40The flight crew has more tasks, more conditions to deal with.
36:45If you're very low, you can easily force the tail to strike a tree or even the ground.
36:53Mats approaches Lakehurst Airfield and begins the critical stage of the landing.
37:00We're coming into the final approach.
37:04Try to avoid hitting partly on the right here.
37:09Mats safely brings down the massive airship onto the airfield.
37:15We're now going to be settling down to the ground.
37:24Mats's new experiment proves the disaster is not inevitable.
37:28The captain could have chosen the slower but safer option.
37:36The Hindenburg disaster is seen around the globe and shocks the entire world.
37:43The catastrophe brings an abrupt end to the airship era.
37:49Astonishingly, Dr. Praskovia Milova believes that despite the tragedy,
37:55hydrogen-filled airships could grace our skies once again.
38:00Hydrogen's amazing lifting power means it could be the perfect green alternative for moving cargo.
38:07Praskovia and her team are building a brand new airship they hope will avoid the mistakes of the past.
38:14We've spent so much time by now designing and researching all the components of the airship model due to the
38:23disasters that happened in the past with the hydrogen airships.
38:28They develop a 50-foot prototype model to test their technology.
38:34The airship is built from carbon fiber tubes that are corrosion-resistant.
38:39We are using carbon tubes, which are light, which are strong, and they are also electrically conductive, which is very
38:48important for a hydrogen airship.
38:52Praskovia needs to test the most critical component of her design.
38:56The material that makes up the hydrogen gas bags.
39:01She's discovered a brand new fabric she thinks will prevent any possible leak.
39:07The solution is to have two layers of plastic film for even more gas-tightness, plus a carbon fiber, which
39:17is a synthetic material to make it even more strong.
39:21Praskovia tests her new material.
39:24Will it be stronger than the Hindenburg's original fabrics?
39:29She's using a machine that will test them to destruction.
39:34Basically, it pulls away until the sample is broken, and then the force is measured.
39:41Lab technician Inga Dismet loads the tension machine with the material used in the Hindenburg and sets the test running.
39:53The force ramps up and rips apart the cotton.
40:00It gives us around 200 newtons of force to break it.
40:08Praskovia runs the same test on her brand new material.
40:17It doesn't rip until 700 newtons.
40:21Her modern fabric is much stronger.
40:25Compared to the cotton-based material used in Hindenburg, this is three and a half times more strong.
40:34Praskovia is confident she's found a material to safely contain hydrogen.
40:41And our skies could soon be filled by a fleet of brand new hydrogen airships.
40:52The crash of the Hindenburg is one of the most spectacular aviation disasters in history.
40:58Modern investigations reveal a punctured hydrogen bag creates an explosive gas.
41:04And a spark of electricity that ignites it.
41:1135 people die in the catastrophic fire.
41:18But new discoveries from the tragedy may mean a new age of hydrogen airships is dawning.
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