All language subtitles for NOVA.S48E09.Hindenburg.The.New.Evidence.iNTERNAL.1080p.x265-ZMNT_track3_[eng]

♪

♪

NARRATOR:
The airship Hindenburg.

In 1937, the fastest way
to cross the Atlantic.

There was no other aircraft
at the time

that could do this type
of distance.

For the few who could afford

an airship trip,
the image is one of prestige.

NARRATOR:
Prestige also for the country
that built it.

The German government used
Hindenburg

as a propaganda symbol.

NARRATOR:
A revolutionary vision
of connecting the world

with a fleet of airships.

RICK ZITAROSA:
They were looking to have

40 to 50 airships

linking the cities of the globe
by 1945.

NARRATOR:
Then, disaster.

36 lives lost
in a horrifying instant,

an entire industry
essentially destroyed,

the precise cause never
conclusively proven.

Now, after more than 80 years,

new evidence.

Whoa, yeah.

No, I've never seen
this material.

NARRATOR:
And a new investigation.

That's the upwind pattern that
it was flying

as it's coming overhead
the hangar,

before it did its initial turn.

And you believe that the film
was shot

with this exact camera?
Yes, I do.

NARRATOR:
Can we still find answers?

KONSTANTINOS GIAPIS:
Initially, I thought it was
going to be relatively simple.

(loud sparking)
Whoa!

But very quickly, I realized

that there were a lot of
unanswered questions.

What is going on right now?

JASON HARRIS:
If one thing had been different
on that day,

we wouldn't have had the same
outcome.

NARRATOR:
"Hindenburg: The New Evidence,"
right now, on "NOVA."

♪

♪

NARRATOR:
In a nondescript building

in a Washington, D.C., suburb,

an investigation begins.

The focus is a cold case
over 80 years old

that was never definitively
solved.

An aviation accident.

The legendary crash of the
airship Hindenburg.

HERBERT MORRISON (archival):
It's burst into flames...
and it's crashing.

It's crashing, terrible.

Oh, my, get out of the way,
please, it's burning,

bursting into flames, and,
and it's falling

on the mooring mast...
oh, the humanity!

♪

NARRATOR:
Hindenburg.

Like Titanic,
synonymous with disaster.

The images seen countless times
by millions.

Despite two investigations
of the accident,

the precise cause...
The exact chain of events...

remains a mystery.

But now,
after more than 80 years,

there is new evidence.

This film.

Never seen by investigators
in 1937,

it has remained essentially
unknown.

Now, decades after the tragedy,

can this film shed new light

on one of the most notorious
aviation accidents in history?

Might it hold a clue to the
cause of the disaster?

This right here where we're
standing right now

is the actual crash site,
so you can sort of see

where we are
in relation to it.
Got it.

NARRATOR:
These men hope so.

The discovery of this
long-lost film

has prompted them to begin a new
investigation of Hindenburg.

♪

Lieutenant Colonel
Jason O. Harris,

an Air Force Academy graduate,
flew multiple combat tours

and has training in
accident investigation.

Today, he's a commercial airline
pilot.

When we look at aircraft
accidents,

whether it's an airship or an
airplane or even a helicopter,

you want to establish
a chain of events.

When we evaluate it,
we get to see

exactly where things begin
to break down.

And they were going to fly

basically toward the hangar
in this direction...

NARRATOR:
Harris's colleague in this
investigation

is aviation historian
Dan Grossman.

A bestselling author

and world-renowned authority
on airships,

Grossman has extensive knowledge
of Hindenburg

and the 1937 investigations.

No one's ever taken a fresh look

at the expert conclusions,
either based on testing

or based on the experience of
these experts,

and it's time to do that.

NARRATOR:
So, inspired by a newly found
reel of film,

Dan Grossman and Jason Harris

are re-examining the case
of the Hindenburg.

They'll work with specialists

who have expert knowledge

about vintage motion picture
film,

travel to Germany

to examine evidence

where the airship was built,

and observe specially designed
engineering tests

to see if anything new

can be learned about Hindenburg.

♪

It's May 3, 1937,
when the airship takes off

with 36 passengers

and 61 crew members.

GROSSMAN:
The ship left Germany on May 3,

intending to arrive at Lakehurst

early in the morning,
about 6:00 a.m., on May 6.

NARRATOR:
Lakehurst, New Jersey,

is a U.S. Naval Air Station

and hub with connections
to New York.

At Lakehurst,
Hindenburg will be serviced

for the return to Europe.

GROSSMAN:
They were hoping to have a day

to turn the ship around, refuel,
replenish.

And they were planning on
leaving that evening

with a full load of passengers
back to Germany.

NARRATOR:
Settling in for a comfortable
and scenic

two-and-a-half-day trip,

the 97 people onboard are
probably feeling quite safe.

In over 25 years of service,

no Zeppelin passenger airship
has ever

had a fatal accident.

And yet right over their heads
lurks potential danger.

What lifts Hindenburg into
the air is hydrogen gas.

Seven million cubic feet of it
are stored in 16 gas cells,

giant bags that fill the ship
from end to end.

Hydrogen is the lightest element
on the periodic table.

Because it's lighter than air,
it's buoyant.

It will go up if surrounded
by air.

NARRATOR:
But mixed with air,
it's also extremely flammable,

a bomb waiting to explode.

GROSSMAN:
Everyone knew that hydrogen
burned, and it burned furiously.

But the Germans had the feeling,
this overconfidence,

that after 37 years of working
with hydrogen,

"We got this, we know how to
deal with hydrogen safely."

♪

NARRATOR:
It's 1909

when the German Zeppelin company

starts the world's first
passenger airline.

Two decades later,

just after Charles Lindbergh
crosses the Atlantic,

their airship Graf Zeppelin

makes an international
publicity flight.

ZITAROSA:
In 1929,

the Hindenburg's predecessor,
the Graf Zeppelin,

flew from Germany here
to Lakehurst

with paying passengers,

and then did a circumnavigation
of the globe.

Their idea, their vision, was
that they were going to have

a fleet of these ships
crossing weekly in the same way

that there was a fleet of ocean
liners that crossed weekly.

NARRATOR:
Over the next several years,
the Graf Zeppelin

carries thousands of passengers

without a single mishap,
and proves the concept.

The next step:
expand to the U.S.

They had already established
service

with the Graf Zeppelin
to South America.

It was a tremendous
public relations

and investment opportunity

for German airship interests.

NARRATOR:
All they need now is more
and bigger ships.

The Hindenburg will be the first
of the new model.

♪

It's over three times longer
than a 747,

constructed around a lightweight
aluminum frame.

Hindenburg basically was
a metal framework

that was kind of
an engineering miracle

in that it had to be very big,
it had to be very strong,

and it had to be very, very
light.

NARRATOR:
Outside the frame,
a painted fabric skin.

GROSSMAN:
The fabric covering was there

to give it an aerodynamic shape

and to protect the gas cells
that were inside the covering.

NARRATOR:
Two diesel engines on each side
propel the ship

through the air.

A rudder steers it left and
right; elevators up and down.

The crew controls the ship
from a small car

mounted to the underside.

Above the control car,

inside the skin and beneath the
gas cells, are two decks.

The lower holds a few passenger
cabins, kitchen,

and crew's quarters.

The upper,
25 double-berth cabins,

a lounge, writing room,

dining room, and promenades.

It was definitely a, a rich
person's luxury way of travel,

sailing above the great sights
of ocean and Earth

with glasses of wine
in their hand,

eating gourmet meals,
looking down.

NARRATOR:
And it's fast.

GROSSMAN:
You could cross the Atlantic

in two-and-a-half days
on Hindenburg.

It took you five to six days
on an ocean liner.

ZITAROSA:
The Hindenburg was
the Concorde of its day.

It was a premium-priced service

particularly popular
with American businessmen

who were always in a hurry.

NARRATOR:
Starting in 1936,

the Hindenburg
makes propaganda flights

for Germany's Nazi government

at Nuremberg rallies
and the Berlin Olympics.

That year,

the ship crosses
the Atlantic 34 times.

Hindenburg has carried
over a thousand passengers

without a single mishap.

The 1936 service

was a testing period to see
if this thing

could be made to work.

And it worked very successfully.

NARRATOR:
For the 1937 season,

there is one overriding
priority.

ZITAROSA:
The key in the mind

of the Germans was to now
tighten up the schedule

and make for more
prompt arrivals and departures.

NARRATOR:
But on the very first flight,
the schedule slips.

The first problem is bad weather
all the way across,

which delays them.

GROSSMAN:
And so the ship was about
12 hours

behind schedule.

ZITAROSA:
They arrive over Manhattan

that afternoon

and they head directly to
Lakehurst.

Lakehurst cannot receive them,

and the weather conditions
are unsettled.

There were thunderstorms.

(thunder claps)

HARRIS:
You're trying to get
this airship

on the ground,

you're now under a lot more
stress

than you ordinarily would be.

NARRATOR:
Hindenburg circles over
New Jersey in a holding pattern,

waiting for Charles Rosendahl,
commander at Lakehurst,

to approve landing.

As 7:00 is approaching,

Commander Rosendahl signals
that conditions now suitable

for landing,
recommend landing now.

NARRATOR:
The ship begins
its final approach.

ZITAROSA:
The Hindenburg makes a wide
circle of the field

and approaches from the north.

MORRISON (archival):
Well, here it comes, ladies
and gentlemen, we're out now,

outside of the hangar...

NARRATOR:
Reporter Herbert Morrison
is recording a description

of Hindenburg's arrival
for later broadcast on radio.

MORRISON:
Thousands of people have come
out to witness

the landing of this great
airship.

The barometer is dropping,
the wind is shifting.

(wind blowing)

GROSSMAN:
It made a turn to realign
so its nose

was pointing into the wind.

They dropped two lines,
called trail lines.

NARRATOR:
The lines let the ground crew

pull the ship into position
and secure it.

In subsequent investigations,

these ropes will come under
intense scrutiny.

Roughly four minutes after
dropping these landing lines,

fire erupted.

(flames billowing,
panicked voices)

♪

(screams)

♪

NARRATOR:
In less than a minute,

there's nothing left
but smoking wreckage.

Of the 97 passengers
and crew, 35 are dead,

plus one ground crewman.

(speaking German):

NARRATOR:
What happened?

Even before any investigation
starts,

Hindenburg's commander,
Max Pruss,

says what many are thinking.

My grandfather was in charge
as a captain

on the Hindenburg flight,

and he made no secret

of his opinion
that it was sabotage.

That someone must have placed
a bomb somewhere.

NARRATOR:
Pruss's boss, Ernst Lehmann,
agrees.

It had to be sabotage.

If you're one of the German
officers who made the decisions

that lead to that public
destruction

of this symbol of Nazi power,

you're going to be very careful
about what you say.

Lehmann had been mortally
injured.

He died within 24 hours.

He reportedly said on his
deathbed that he thought

it must have been sabotage,

that it could not have been
something else.

There were a lot of people,
even in 1937, who didn't like

the Hitler government.

It was perfectly natural
for people to ask,

"Did somebody bomb
this airship?"

♪

NARRATOR:
Two investigations begin,
one German, one American.

But no one finds any evidence
of foul play.

The reality is that all evidence
suggests

it could not have been sabotage.

NARRATOR:
If not sabotage, then what?

GROSSMAN:
They looked at a lot of things.

Diesel engine exhaust,

or a propeller breaking
and entering the airframe,

or someone from the ground
shooting at the airship,

but both agreed that it was
leaking hydrogen

ignited by some electrostatic
discharge.

(thunder rumbling)

NARRATOR:
Electrostatic discharge...
a sudden flow of electricity

between two electrically charged
objects.

In other words, a spark.

It can be tiny...
Like the spark you feel

when you walk across a carpet

and touch something.
(static)

Or enormous, like lightning.
(thunder rumbling)

Although investigators
eventually

conclude that leaking hydrogen
was ignited by a spark,

they never precisely demonstrate

the cause of the spark.

But the source of the hydrogen
is obvious:

a leak, somewhere in one of the
gas cells.

A surviving crewman reported
that he saw an orange glow

in gas cell four, near the tail.

Observers on the ground also saw
the first flames near the tail.

With so much of the physical
evidence destroyed,

investigators have to rely
on these eyewitness accounts.

But there is one other type
of evidence.

About a dozen press
and newsreel photographers

were covering the landing.

MORRISON (archival):
The landing crew of the airbase
here is superbly trained

to handle these massive ships
of the sky.

Safety comes first,
as it always should.

NARRATOR:
But for investigators,

every image of the accident
caught on film

has the same limitation: they're
all shot from the same angle.

All of the newsreel
photographers

were gathered in a small area

close to the mooring mast where
the ship was expected to land.

NARRATOR:
Not only are the films shot
from the same place and angle,

they all start at essentially
the same time:

after the fire is well underway.

There's no film capturing
the moment of ignition.

So for over 80 years,
the origin of the spark

that doomed Hindenburg
has remained elusive,

what exactly caused it

and where in the ship
it occurred

lost to history.

But now, a new piece of the
Hindenburg puzzle has surfaced.

Ironically, it was available
from the beginning,

but no one had been interested
at the time.

GROSSMAN:
I was here at Lakehurst for

the 75th anniversary,
and we had a memorial service,

and a guy comes up to me
and says,

"I've got some film on the
Hindenburg disaster.

"You probably don't really care,

"but this was taken by my uncle,
and if you want to see it,

I'll show it to you."

So this is right
where we met in...

This is right where we met.
In 2012.

Yeah.
Where you showed me this film
on your laptop.

Yeah.
And if you remember,
I was so excited,

I took my cellphone
and I took some photos...

I asked your permission...
And I took photos of the film

on your laptop.
Yup, yup.

Because it was, like,
this is special!
Yeah.

My dad had bought this nifty
Kodak camera,

a wind-up movie camera,
eight-millimeter.

And he couldn't come
because he worked.

So he asked my uncle and my mom

if they would take some shots
and see the Hindenburg land.

And as soon as I started looking
at it, I realize

it looked really different, and
it looked really interesting.

NARRATOR:
And yet, Harold Schenck's film...

which starts earlier and is shot

from a different angle than all
the other photographers...

is never seen by investigators.

SCHENCK:
It was, at the time,
publicly put out that he had it.

Nobody ever asked for it.

There was plenty of footage
taken by the newsreels.

And nobody really cared,
I guess, about angles.

NARRATOR:
But perhaps this new angle
will make a difference.

After 80-plus years, might this
footage show something new?

And what could a closer
inspection of the film reveal?

To learn more about
the film's history,

Dan Grossman brings it to
Colorlab,

a world-class facility
that restores historic film

for the Library of Congress,
National Archives,

and others.

PAT DOYEN:
I'm excited that you have
something

for me to look at, right?

I am excited for you
to look at it.

So, here is the film we've been
talking about.

Wow.
And I also brought you

the camera that
it was filmed on.
Oh, wow!

NARRATOR:
Film archivist Pat Doyen is an
expert in preserving

and restoring rare vintage film.

DOYEN:
Good provenance here.

And you believe that the film
was shot with this

exact camera?
Yes, I do!

I can see that this is
the kind of box

that this film
would have been packaged in.

I can see that you had it

processed by Kodak,
uh, there's an address,

there's a stamp from the time.

So this is all really good
information.

(reel creaking)

And when we look at it
over the light table,

there's a few things
we can tell.

Now, there's a number here,
36814.

Oh, okay.
That was written on the box,
and you can see

it's also on this leader.
And who wrote that?

Would Kodak
have written that?
That... yes.

That would have been
for processing.
Okay.

So, right now, I'm going to look
for what they call a date code.

So Kodak put, um,
some symbols on the film

to tell us when
it was manufactured.

So I'm looking at the date code,
and I see a triangle square.

So how do you know what a
triangle and a square means?

So there's a reference
to check that out.

And we can see...

This film

was manufactured

between July to December 1936.

Ah.

NARRATOR:
1936,

the year before the accident.

When someone would buy
a film for 1937.
Great.

We can see the aperture plate,

the little cutout on
the left side.

NARRATOR:
The camera's aperture plate
defines the frame of the picture

where the image extends
in between the sprocket holes.

DOYEN:
This one here,
which matches our film,

has the square in between
the two perforations.

Is that, is it exactly

what we're seeing
right here?
Mm-hmm.

Oh, yeah, of course,
it looks just like your book.

It tells us that

it was shot with this
model of camera,

the Cine Kodak 8, model 20.

NARRATOR:
A year before the disaster,
in an eerily prophetic ad

featuring the Hindenburg,

Kodak suggested using
their cameras

to film
"moments that make history."

It also tells me that it was
camera-original.

NARRATOR:
Camera-original.

This film was exposed in
a camera... it's not a copy.

If it was a print,

you wouldn't see the circles
or the squares,

because the printer blocks
that off.

GROSSMAN: So what's your verdict
on the film?
So...

It's a little shrunken

and it's got some aging here,

it's got a little silver
mirroring,

which tells me that
it's an old film.

This doesn't happen right away,
overnight.

It takes years and years,

sometimes decades, so all
of this taken together,

I can't say with
a hundred percent certainty,

but everything points
to this film

being an authentic
film.
Wow.

DOYEN:
That it was shot
at that time.

This is a good day.

♪

NARRATOR:
After digitally scanning
the film,

Dan and Pat take a look
on a large screen.

This is the first time this
footage has been widely seen.

(film reel whirring)

Wow!

Look at how much detail
we get from this scan.

NARRATOR:
The roll of film will last
only two minutes.

To conserve it, Harold Schenck
shoots brief moments:

the ground crew assembling,

the giant ship passing
over the hangar.

The landing lines are the last
thing Harold Schenck records

before disaster strikes.

And as it exploded, he had the
camera at his side,

and it was a wind-up camera, so
he, he had the presence of mind

to switch the switch on
and pick it up at that moment.

♪

Thanks to that aperture plate,

you actually see the nose
and the tail at the same time.

Is that unusual?
Yes, it is.

NARRATOR:
The spring runs down.

After rewinding, he rolls again,
getting the aftermath.

GROSSMAN:
You can see details of the
girder structure.

Where the gas cells were would
be a lot of information for us

about how this flame progressed.

This is really great, thank you
for doing this for us.

NARRATOR:
Confident of the film's
provenance,

Dan now shares the new digital
transfer

with Jason.

GROSSMAN:
You can see
the mooring mast.

There's the ship,

it's flying over the building
we're in right now,

that's hangar one.

That's the upwind pattern
that it was flying

as it's coming overhead the
hangar

before it did its initial turn.

NARRATOR:
The sequence of events during

Hindenburg's landing approach
has clues about what went wrong.

Surviving crew members indicated

that they were having trouble
trimming the ship...

keeping it level.

The tail was heavy.

When an aircraft is out of trim,
it's not in balance.

And when you look at how massive
this aircraft was,

and then try to control it,
and it's out of trim,

it is not going to do what
you're asking.

NARRATOR:
To correct the problem,

they valve off gas from the bow,
making it heavier.

Depending on how heavy you
wanted to make the ship,

you held the gas valve open
for 15 seconds, 30 seconds.

NARRATOR:
They release gas multiple times.

They're still tail-heavy.

Then they drop weight,
water ballast, from the tail

to make it lighter.

ZITAROSA:
They've already dropped about
1,300 pounds of water ballast.

Now they've moved six men
into the nose.

That's another 1,200 pounds.

The ship is still tail-heavy.

NARRATOR:
Why might Hindenburg
be tail-heavy?

It seems most likely
that it was tail-heavy

because there was
a pre-existing hydrogen leak.

♪

NARRATOR:
They now have a choice: proceed
with the landing or stop

and diagnose the problem.

ZITAROSA:
It would have been
relatively simple

to send a few riggers back
to look into the condition

of whether the rear gas cells
were all intact.

If they needed to wait longer,

they could have just hung out
and waited longer.

It's not an issue of running
out of fuel.

It could stay up there for
an indeterminate amount of time

because it's an airship.

NARRATOR:
But who will make the decision?

The official commander of the
flight was Max Pruss,

but the director
of flight operations,

or the chief pilot, Ernst
Lehmann, was also onboard.

So Pruss was operating
under the eye of his boss.

Lehmann was very, very conscious
of the fact

that they were 12 hours behind
schedule,

and they had a full load
of passengers

that had to get onboard
and get back to Europe,

and this was now his ball game.

How do you tell your boss,
"Hey, boss, we're late,

and I actually want
to make us more late"?

"I know we're supposed to land,
but I don't think it's safe."

GROSSMAN:
There's no

cockpit voice recorder
from Hindenburg.

We don't know what they said
to each other.

NARRATOR:
All we know is what they did.

There's the line going down,
you see it hit the ground.

And the ship started to burn,

and look how quickly
this crashes, right?

In the time we have
just talked about this

for the past few seconds,

that is all the time these
people had to escape.

Wow.

That's totally different

than anything I've ever seen

from all the
other footage I've seen.
Right.

Because the person
with the eight-millimeter camera

was in a different location.

HARRIS:
So, so from what you've...

NARRATOR:
Where exactly was
Harold Schenck?

GROSSMAN:
Most of the press photographers

and all of the newsreel
film photographers

were over in that direction
where the mooring mast was.

♪

GROSSMAN:
It looks from
Schenck's photographs

that he was located around
hangar one.

HARRIS:
So he basically is seeing the
aircraft go from right to left

as it continues to go down
to this landing site.
Exactly.

And so, because he was
all the way over there,

he got a beautiful broadside
view of Hindenburg.

As opposed to the newsreel
photographers,

who were looking at the bow
of the aircraft

as it was flying toward them.

HARRIS:
Right.

♪

NARRATOR:
But for all it reveals,
Harold Schenck's film

does not show
what ignited the hydrogen,

the spark that doomed
Hindenburg.

GIAPIS:
How did the spark actually
find its way

to the location
in this enormous airship,

where actually hydrogen
was coming out,

mixing with air?

NARRATOR:
To try and learn more
about that spark,

Jason and Dan have turned to
Konstantinos Giapis,

professor of chemical
engineering at Caltech.

GIAPIS:
You see almost a mushroom cloud
right here.

And this is hydrogen being
released

massively from
the central airbags.

That hydrogen wants to rise up

because it's a very light gas,

and as it rises,
it takes a lot of heat with it.

When you look at this,

it's almost uncanny to think

that anyone actually was able
to walk away from this.

Well, you know,
if you happen to be

underneath the fire, you,

you don't suffer
as terrible consequences,

and I believe this is the reason

why so many people survived,
actually.

NARRATOR:
But the key question remains.

I see a few things,

but I don't see
the origin of the fire,

I don't see how
the fire started.

NARRATOR:
So Professor Giapis will design

experiments to learn more

about how the fire started.

GIAPIS:
The experiments
should include

addressing
the origin of the spark,

addressing the importance of

the rope falling
and becoming conductive,

and addressing the issue of,
how did a spark happen

close to where
the hydrogen was leaking?

(jet engine roaring)

NARRATOR:
To get more information
to help Professor Giapis

design historically relevant
experiments,

Jason and Dan travel to

Friedrichshafen, Germany,

home of the Zeppelin company
and Zeppelin Museum.

Hindenburg made its first
test flights over this lake.

The Zeppelin
and the industry that it set off

was a really important part
of the town's history.

HARRIS:
This is amazing.

Just walking in

and seeing
that airship hanging...

Isn't it incredible?
Yeah.

NARRATOR:
Dan has been coming here
for years;

this is Jason's first visit.

HARRIS:
I didn't know very much about

lighter-than-air aircraft.

I've read a few things,

but my background is
all fixed-wing aircraft.

And so I was looking to

fully understand
how the airships worked,

and even some of the
different concepts

in terms of how
the airship was constructed.

WAIBEL (in German):

GROSSMAN:
And you know,
this World War I exhibit

really gives you an
understanding

of just how experienced
the Germans were with Zeppelins.

And it actually explains
a lot about their confidence

and overconfidence
operating Hindenburg,

because they had flown these
hydrogen-filled Zeppelins

for 37 years.

They'd flown over 100 of them.

NARRATOR:
Nevertheless, Hindenburg is not
the first Zeppelin to burn.

There were a lot of hydrogen
airships that burned,

even outside of combat, as a
result of operating accidents.

NARRATOR:
In fact, the Zeppelin company

was hoping to abandon hydrogen,
because of the danger.

ZITAROSA:
The Hindenburg had
originally been designed

with the intention
of using helium gas.

However, helium was a strictly
American resource in those days.

Most of the world's
helium supply existed

within a 250-mile radius of
Amarillo, Texas.

NARRATOR:
In 1927, Congress passes
the Helium Control Act,

which forbids selling
helium to any foreign nation.

If Hindenburg's designers
want to use helium,

they'll need
Congressional approval.

(in German):

NARRATOR:
Of all the resources
in this museum,

Dan and Jason
are most interested

in the historical archive.

But first,
they show Harold Schenck's film

to Zeppelin Archive director
Barbara Waibel

and Zeppelin department
head Jürgen Bleibler.

Whoa, yeah, I've
never seen this material.

You can see it so clearly,

how, how the way of the fire is.

BLEIBLER:
This moment...
WAIBEL: Mm-hmm.

BLEIBLER:
Escaping for, of the passengers
is unbelievable.

GROSSMAN:
Yeah, isn't it?

They had so little time.

WAIBEL:
Mm-hmm.

I've never seen it
from this point of view.

So it's really
new material for me, yeah.

NARRATOR:
The fire started roughly
four minutes after

the landing ropes
hit the ground.

So Professor Giapis is
interested in that rope.

Could it conduct electricity,

which might contribute
to a spark?

One of the things
we'd like to do

is test the electrical
conductivity of the trail rope,

the landing rope,
the Landestau.
Mm-hmm.

We'd like to get
a sample of that rope

and see what it looks like.

WAIBEL (in German):

Excellent.

HARRIS:
And is this one of the
actual ropes?

(in German):

Ah.

GROSSMAN:
So let's go ahead and see

how, how big the rope is,

what, what its circumference is,

so that we can either
acquire or recreate

something that matches.

14 centimeters.
Mm-hmm.

Mm-hmm.
Excellent.

And this is...
(speaking German)

14 centimeters,

and it's manila hemp rope,
right?

Yeah.
Yup.

NARRATOR:
Back at Caltech,

Professor Giapis
has immersed himself

in Hindenburg, focusing on how

the leaking hydrogen
may have been ignited.

GIAPIS:
I read the reports of
various committees.

They both agreed
that there was a hydrogen leak.

But there were certain things
that didn't make sense.

How did the spark happen,
where it happened,

and the time sequence,
the timeline of how it happened.

NARRATOR:
The German committee believed
the landing ropes

allowed a spark to happen,

because they
gave electricity a path

from the ship to the ground.

In a house, electricity flows
from one side of an outlet

through whatever
is plugged into it,

and back to
the other side of the outlet.

But it only flows
when it has a path.

Take away the path,
the flow stops.

Why this matters to
the Hindenburg

is because the airship
is carrying electricity

on its skin.

Any craft moving through the air

will accumulate a charge.

NARRATOR:
As long as Hindenburg's
electrical charge

has no path, it can't flow.

To find out if landing rope

could create an electrical path
to the ground,

Professor Giapis will test
a sample to see if it conducts.

Jason is back at Caltech
to observe.

So, what you were looking for
was, how did

the spark in
that particular place

connect with the hydrogen
in that explicit moment in time?

Yes.

The committees talked
about the skin charging up.

And the question is,
what happens to that charge?

I can try to find out
where the charge goes

and whether, in doing so,
it can create a spark.

NARRATOR:
Hindenburg approaches,

carrying a powerful
electrical charge on its skin.

But the charge has
no path to go anywhere.

Port and starboard trail lines
hit the ground.

NARRATOR:
But nothing happens.

From the moment the ropes
touch the ground,

it takes about four minutes
for the fire to start.

If the ropes created a path
for electricity to flow,

then why the delay?

What was important about
the rope and the four minutes?

So, the idea from both
investigative committees

was that the rope
was not conductive

to begin with.

It took four minutes or so
for it to get wet

to create the spark.

NARRATOR:
During the final landing
approach,

a light rain is falling.

The theory is that
as the rope got wet,

it became more conductive.

So I want to probe that.

I want to find out if the rope

was initially conductive at all,

and how quickly did it become
conductive when it became wet?

Where'd you acquire this rope
from and how is it similar

to what they had
80-plus years ago?

So, we had to search, uh,
quite a bit, actually,

to find this rope.

However, we found one

that is made of
the same material,

which is manila hemp.

And this one is
an eight-braid rope,

whereas the original one was
a 12-braid rope.

But it's approximately
the same diameter.

And it has
a lot of surface area,

which is important
for our experiment.

My first experiment was,

try to see if
any current flows through it

when you apply a voltage
across the,

the two ends of the rope.

I will increase the voltage

that I apply at the top.

NARRATOR:
Professor Giapis

applies almost 3,000 volts

to the top end of the rope.

GIAPIS:
What you see here is

something that I think
is pretty remarkable.

We see a current
flowing through the rope

when we apply...

It's almost three kilovolts.

GIAPIS:
To my immense surprise,

dry rope had some conductivity.

Now,
when I talk about conductivity,

what we're talking about
is the ability

to ground the airframe.

NARRATOR:
So even dry rope provides
an electrical path

from the ship to the ground,
which, theoretically,

could trigger a spark.

But the test isn't over.

Now we want to find out

what happens
when I make this wet.

So we have the same voltage
we have dialed before,

about three kilovolts,

and I will make this wet.

So I'm using deionized water

to try to simulate the
absorption of water by the rope.

Pay attention to this.

So it's increasing with

every bit of wetness.

With every bit of water,
you add to it, it's increasing.

And so you figure, for
four minutes,

it was constantly having
this done

with four minutes
of rain and moisture.

So it becomes

very conductive.

NARRATOR:
Over ten times more current

flows when the rope
is even slightly wet.

Now that it's wet,

let's look at what happens

as we come down.

You see that the voltage now,

two inches below,
is about the same.

As I come down,

that higher voltage
is communicated.

This thing is fully conductive.

NARRATOR:
So wet or dry,

the landing rope
does conduct electricity.

But how would that
cause a spark?

The Zeppelin is flying.

She's got an electrical charge
that she has picked up.

NARRATOR:
But the charge on

Hindenburg's skin
can't go anywhere... yet.

ZITAROSA:
The airship is isolated
from the ground.

The mooring ropes are dropped.

They become conductors.

NARRATOR:
But there's a problem.

GIAPIS:
My very first experiment
showed that the rope

had some conductivity,

and for the kinds of voltages

that I think were possible

on the airship,

that conductivity meant that...

(snaps)

The explosion
should have happened

the moment the rope
hit the ground.

NARRATOR:
So once the ropes
hit the ground,

what explains the four-minute
delay before the explosion?

Dan and Jason found a clue
in Germany.

In the Zeppelin Museum,

they got details of
Hindenburg's skin

and the paint that covered it,
called "dope."

Let's talk about the dope,

the Cellon that went
onto the fabric.

NARRATOR:
The Cellon dope paint

is what gave Hindenburg
its metallic sheen.

WAIBEL (in German):

NARRATOR:
But it's the electrical
properties

of Hindenburg's skin

that concern Professor Giapis.

GROSSMAN:
Barbara, one of the things
we care about

is whether there was
an electrical connection

between the, the fabric
and the metal.

WAIBEL (in German):

Right.

WAIBEL (in German):

Right.

WAIBEL (in German):

NARRATOR:
The wooden pegs, and the space
between skin and metal frame,

would theoretically prevent
a charge on the skin

from reaching the frame.

It's crucial information
for Professor Giapis.

It seems to be that

this wooden dowel
was actually put there

to separate the skin as a
protection/safety mechanism

in the building of the airship.

NARRATOR:
This design means there's
no electrical connection

between skin and frame.

As the ship comes in to land,

the skin
is electrically charged.

When the ropes drop,

the frame is electrically
connected to the ground.

So there's now a powerful charge
right next to a grounded frame,

with a small air gap in between.

It's like a person
who crossed a carpet

almost but not quite
touching the light switch.

A spark waiting to happen.

GIAPIS:
So there is electrical
communication

between the frame
and the ground.

So now we need to find out
what was happening

between the skin
and the airframe.

NARRATOR:
Professor Giapis wants to
better understand how

a charge that's
built up on the skin

could discharge in a spark

that jumps to the frame,

and why it took roughly
four minutes to happen.

GIAPIS:
The second test that I
developed,

tried to understand this
charging-discharging issue.

So I developed a scaffold

similar to the frame
of the original airship.

NARRATOR:
He'll use a reproduction of
a section of Hindenburg's skin

covered with dope,
stretched over

but not touching
an aluminum frame.

HARRIS:
So, what are we replicating here
in this experiment?

I'm trying to simulate

what was happening
in the top of the airship.

As this was

standing about 100 meters
away from Earth,

the top of it, at least,
collecting rain

and collecting also charge
from the ambient environment.

I need to figure out
a way to bring uniform charge

to these two panels
that we're seeing here.

And I have done this by
creating these electrodes,

and I will charge those

so that I can apply a voltage

that I think was existing
at that time on,

on the airship.

The airship is grounded.

It has the ability to, to
conduct,

but the surface
is actually just dry.

So, you're simulating

what it looks like,
or what happens

when the surface itself
is just dry.
Correct.

NARRATOR:
The electrodes apply a charge,

like that which would have built
up on the skin of Hindenburg.

I charged up the electrodes,

connected
the frame to the ground,

and I would observe no spark.

My dope was very

"dielectric,"
as we say in the jargon.

The charge
was not going anywhere.

NARRATOR:
With the skin dry, the charge
does not jump to the frame.

But these laboratory conditions
do not fully replicate

the situation at Lakehurst.

Now I want to find out

what happens if we actually,
you know, do this in the rain.

There was rain falling.

(thunder rumbling)

The ship had also
just crossed the ocean,

and there were salt particles
on its surface.

Now, rain and salt
make a conductive mixture.

All right.

So, let's see.

(spritzing)

Let's wait a little bit.

(sparking loudly)
Whoa!

(sparks)

What is going on right now?

(sparks)
Oh, wow, that was...

That's it.
Yes, that was significant!

That's the spark that matters.

GIAPIS:
Charging the top surfaces,

adding the rain to the mix,

you've got
the spark across the skin.

NARRATOR:
But why?

What changes
when the skin is wet?

Rain makes the top of the skin
conductive and allows

eventually for charges to move.

NARRATOR:
Making the skin more conductive

lets the charge move across it
more easily,

until it reaches
a spot over a frame member,

where it can
jump across the gap.

But there's still the question
of the four-minute delay.

Why didn't the spark happen

the instant
the ropes hit the ground?

So, then it occurred to me

that the moment
the airframe grounds,

you form a capacitor

capable of storing more charge

than what initially existed
on the surface of the airship.

And that means that
it will take time to charge up.

A capacitor
is a very simple device

that allows you to store energy.

NARRATOR:
A capacitor typically contains
two conductive plates

separated by
a non-conducting insulator.

Charge builds up on the plates,
positive and negative,

until it's strong enough
to jump across the gap.

On the Hindenburg, the skin
represents the top surface

and the grounded frame
represents

the bottom surface of
the capacitor.

NARRATOR:
Positive charge from
the air collects on the skin.

Negative charge from the ground
collects through the ropes

onto the frame.

With every passing second,

the electric field
between skin and frame

increases,

until finally it's strong enough
to jump across the gap,

making a spark.

To see how long it would take to
fully charge Hindenburg's skin,

Professor Giapis calculates

how much charge
the ship can hold

based on its surface area

and compares that with the rate
of atmospheric electricity

flowing in
the stormy conditions that day.

So then I wrote down the numbers

of how long it would take
for it to charge,

and I ended up with

four minutes.

And then it all clicked,

because nobody
has been able to explain

the four minutes
it took for it to explode.

NARRATOR:
Rope hits the ground,

turning Hindenburg into
a giant capacitor.

Charge is building up.

It will take about four minutes
to fully charge the ship.

Rain is accumulating
on the skin,

making it easier for
the charge to move

to locations of
underlying frame members.

♪

For his final test,
Professor Giapis

repeats the experiment,
adding the rope.

GIAPIS:
The rope to the ground

as if it's just thrown down.

And then we're going to
make the rope wet

in the correct sequence.

So we're going to
try to find out

what happens when
all of this is together.

I have zero volts down here.

HARRIS:
Yeah.

I have one volt up here.

What is that telling us
at this point in time?

It's telling us that
it's a perfect conductor.

The frame is connected to
the ground very efficiently.

So that allows for
a maximum charge

to accumulate up there.

So, I will go now
and try to recreate the spark.

Ready?

(spritzing)

(spark buzzing)
HARRIS:
Oh! Whoa!

GIAPIS:
That was it!

Tell us, what did we just
experience right there?

There is a capacitor forming
between the skin and the frame.

The capacitor is fully charged.

But the charge cannot move

through the rope to the ground.

Despite the fact that

the rope is wet, fully wet.

However, when I

drop a little bit of rain
on top,

magic happens.

NARRATOR:
Professor Giapis has shown that

rain did contribute
to the disaster.

Wetting the skin made it
easier...

Whoa!
NARRATOR:
for the charge

to flow to where frame members
were located.

That's the spark.

That's how you get the spark
to occur under the skin.

So, it happens underneath,
only after

all of these series of events

have taken place.
Yes.

The rope hits the ground.
Yes.

The rope then gets wet.

There's a charge on the top of
the surface of the airship,

and there's rain on top of
the airship.

Correct.
So, all of those things
have to happen,

and we pretty much
just walked through...
Yes.

That one without
the other means nothing.

Yes.

But once you put
the rain in there,

that's where we get
the magic of the spark.

The magic ingredient, yes.
Wow.

NARRATOR:
But another mystery remains.

Why did the spark
happen where it did?

What were the chances

in this enormous ship

that the spark, the tiny spark,

happened right there
where the hydrogen was leaking

or in the vicinity of
where it was mixing with air?

How was it possible to get
the spark right there, where,

you know, things were happening?

NARRATOR:
Professor Giapis believes

Hindenburg's frame,
horizontal girders,

and vertical rings

in effect formed
individual panels.

I realized that each panel,
each crossing of these girders,

is a separate capacitor.

NARRATOR:
There didn't have to be one
spark in just the right place.

Why?

Because there were
multiple sparks!

One of them was
bound to happen near it,

because it was
happening everywhere!

♪

NARRATOR:
Ironically,

the design
keeping skin and frame

electrically separate,

possibly intended
as a safety feature,

actually
made this spark possible.

MORRISON (archival, crying):
"I, I can't talk,

"ladies and gentlemen.

"Honest, it's just laying there,
a mass of smoking wreckage.

"I'm going to have to
stop for a minute

"because I've lost my voice;

this is the worst thing
I've ever witnessed."

NARRATOR:
Ultimately, although a spark

almost certainly
caused the fire,

it was something else
that caused the tragedy.

ZITAROSA:
The story of the Hindenburg

is a story very familiar,
even today,

of human error

compounded by some very
unfortunate circumstances.

The Hindenburg had been put
by her command

into a great deal of jeopardy.

NARRATOR:
After the accident,

the Zeppelin company
made some design changes

in the skin-to-frame attachment,
but it didn't matter.

After the Hindenburg disaster,

no rigid airship ever carried
a paying passenger again.

By the time Hindenburg
actually left its hangar,

there were airplanes
that could do things better.

NARRATOR:
Although Harold Schenck's film
did not show

how the hydrogen ignited,

it did inspire
a new examination of Hindenburg,

new experiments,
and new results.

Wait a little bit...
(sparking)

Whoa!

So the science gave us an answer

to a previously
unsolved question

that was 80-plus-years-old

that we thought
we'd never be able to answer.

GIAPIS:
There is an opportunity here
to use science

to answer an unsolved mystery.

We come up with a new theory,
we break it apart into pieces,

we go to the lab,
and we try to validate

every one of these pieces.

NARRATOR:
Yet no matter how many
questions we answer

about the details of
what happened,

it's the image of Hindenburg

that never loses its grip
on our imagination.

Today, we're used to seeing
horrible stuff on television.

People in 1937 were not
used to seeing a disaster

with their own eyes.

And to see this airship
filled with people

burn and be destroyed
in a matter of seconds

was really
shocking and dramatic.

I think the fact that
this disaster was caught on film

is why we still think of it
today.

♪

♪

ANNOUNCER:
To order this program on DVD,
visit ShopPBS

or call 1-800-PLAY-PBS.

Episodes of "NOVA" are available
with Passport.

"NOVA" is also available on
Amazon Prime Video.

♪