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Notre-Dame de Paris, a treasured
icon of Gothic architecture
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and medieval engineering.
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Built from glass,
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stone
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and timber over the course
of two centuries,
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it's one of the world's
greatest cathedrals.
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Notre-Dame is one of
humanity's greatest
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artistic and architectural
achievements.
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This epic 90-metre-tall
symbol has stood
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at the heart of French culture
and society for 850 years.
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SPEAKS IN FRENCH
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But on 15th April 2019,
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disaster strikes.
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PEOPLE SCREAM AND SHOUT
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A massive fire rages out of control
and tears through the cathedral...
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..leaving it in ruins.
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Now, a team of master
craftspeople and elite engineers
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battle to save this
fragile structure
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from a catastrophic collapse.
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SHE SPEAKS IN FRENCH
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Out of tragedy is born
opportunity...
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Oh!
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..to solve archaeological mysteries
and understand the very fabric
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of this medieval megastructure
like never before.
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We can identify each
chemical element.
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Yes, it is important information.
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For the last year, our cameras
have had unique access
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to follow teams inside Notre-Dame.
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Can they decode clues from the past
and use pioneering technology
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to rebuild this historic landmark?
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This is the inside story
of the first year in the race
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to save Notre-Dame Cathedral.
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The Cathedral of
Notre-Dame de Paris,
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an 850-year-old Gothic wonder.
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It's the heart of France.
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Roads were traditionally measured
from this iconic structure.
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There was a continuation,
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a historical continuation from the
Middle Ages to nowadays.
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And it's very important
to build a kind of identity.
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Notre-Dame is one of the monuments
which achieved this identity.
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For Christians, it's a place
of worship, right?
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And for those of us
with different beliefs,
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it's one of...just this incredible
artistic and historical landmark.
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You've had coronations there,
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you've had the crowning of
Napoleon and King Henry
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and there's just so much
attached to the cathedral.
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But Notre-Dame
is much more than that.
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It's also the pinnacle
of medieval engineering.
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The cathedral can hold
9,000 worshippers
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and its 33-metre-tall walls
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contain more than 3,000 square
metres of stained glass.
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The ceiling is a series of
domed Gothic vaults
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that hold up the cathedral
from the inside.
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A complex 500-tonne web of timber
forms a cross-shaped roof
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topped with 1,300 lead tiles...
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..and a 90-metre-tall central spire.
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Wrapped around the church are
28 flying buttresses,
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limestone arches that brace the
walls from the outside...
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..and at the front,
two mighty towers,
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with ten massive
bronze bells inside,
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soar over 68 metres into
the sky over Paris.
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The construction took
many generations.
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Architecture was not
learned at the university.
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So, the architects and all
workers learned mostly onsite.
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Along the way, there
were many setbacks.
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In 1789, at the height of
the French Revolution,
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anti-Catholic forces
destroy parts of the cathedral.
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A newly secular France leaves
Notre-Dame in a state of neglect.
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But when Victor Hugo writes
The Hunchback Of Notre-Dame in 1831,
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it sparks a £170 million restoration
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that tops up the cathedral
with a new roof
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and a 750-tonne
timber and lead spire.
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And periodic renovations
continue to this day.
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On 15th April 2019, Notre-Dame is
wrapped in 500 tonnes of scaffolding
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as the cathedral begins
a £5 million operation
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to shore up the spire.
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THEY SPEAK IN FRENCH
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Notre-Dame's rector,
Monsignor Patrick Chauvet,
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has finished evening worship.
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His world is about to be
turned upside down.
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HE SPEAKS IN FRENCH
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At 6.18pm, a sensor detects smoke
in the medieval roof timbers.
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The system sends a coded fire
alert to the security team.
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Instead of heading
straight for the roof,
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a guard is dispatched to
the sacristy building nearby
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to check for a fire.
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But he finds nothing.
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He climbs up into the church attic.
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But by the time he gets
there, he's too late.
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The fire has been burning
for almost 30 minutes
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and spread across the roof.
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SIREN BLARES
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And there was this
horrifyingly huge plume of smoke
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billowing up out of it.
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It was surreal. I'd never seen
anything like that before.
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You saw the fire trucks come up
alongside the cathedral
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and ladders went up and the
hoses came out.
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You could see that the ladders
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were just too small for
a building of this size.
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And the hoses were not nearly big
enough for this kind of blaze.
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It was tragic.
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The resources that were available
were not going to be what was needed
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to bring this thing under control.
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A lot of us realised that this fire
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was just going to ravage
the cathedral.
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SPEAKS IN FRENCH
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A delay in responding to a
fire of this nature
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is absolutely critical.
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A small fire burning locally
is a very different thing
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than ten minutes later when all of
the timber elements are involved.
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So, in a situation like this,
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five, ten, 30 minutes can
make all the difference.
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This delay will have
huge repercussions.
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As firefighters arrive on scene,
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so does one of France's chief
architects of historic monuments,
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Remi Fromont.
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HE SPEAKS IN FRENCH
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As the inferno rages at
the top of the cathedral,
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Remi risks his life to venture
inside with the firefighters.
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Within minutes, the firefighters
are pumping tonnes of water
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into the attic space,
but it's not working.
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To the horror of the growing crowd,
the fire engulfs the famous spire.
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The world watches
helplessly
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as the 750-tonne oak and lead
masterpiece gives way.
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Oh, my God.
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Oh, my God, that is awful.
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When the spire fell into the roof,
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an additional ventilation
will have caused
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more oxygen-rich air to be sucked in
at the bottom of the compartment.
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That influx of oxygen could
have caused an increase
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in the severity of the fire
within Notre-Dame.
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It was just devastating to watch.
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We were suddenly really
aware that...of how easily
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this whole thing could come down.
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90 minutes after the fire begins,
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the entire roof of the
cathedral is ablaze.
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Inside, it's become even
more dangerous
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for Remi and the firefighters.
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Getting this fire under
control looks impossible.
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A south-easterly wind picks up
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and pushes the blaze towards
the famous bell towers.
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Inside the ingeniously engineered
13th-century north tower,
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a scaffold of wooden
beams holds eight bells,
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the biggest weighing
more than four tonnes.
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If the beams burn through,
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they'll trigger a
fatal chain reaction.
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The bells will fall
like wrecking balls
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and destroy the tower's
wooden backbone.
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If the tower falls, it
could trigger a deadly domino effect
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that brings down the
entire cathedral.
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To avert this catastrophic collapse,
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the firefighters have no option
but to venture deeper inside.
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REMI:
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To douse the fire on the roof,
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firefighters pump water
from the River Seine
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and feed it to fire trucks
around the cathedral.
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But to stop the towers collapsing,
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they must send a team into
the burning structure.
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Their mission -
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drop hoses in between the towers
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and fight the fire
spreading from the roof.
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But the steady wind doesn't let up.
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And despite their efforts,
the timber frame holding the bells
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has caught fire and could trigger
the destruction of the cathedral
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at any moment.
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So, the team must drag their hoses
to the top of the tower
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and soak the timber frame
to prevent the unthinkable.
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Throughout the night, the fate
of Notre-Dame hangs in the balance.
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Eventually, the firefighters
get the upper hand.
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The flames have been beaten back
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and only glowing embers
light up the night sky.
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Nobody knows how the fire started.
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An investigation begins.
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But for now, the urgent question -
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how damaged is the structure and
can it ever be rebuilt?
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President Macron pledges to restore
the cathedral in five years.
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HE SPEAKS IN FRENCH
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PEOPLE SING TOGETHER
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The world keeps vigil
for Notre-Dame.
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Daylight reveals the full extent
of the terrible destruction
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wrought by the fire.
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The oak roof and spire
are completely destroyed.
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Toxic lead that covered the roof
has been sprayed into the air,
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contaminating the site.
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Burned roof timbers
cover the vaulting.
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Three gaping holes in the stone
vaults weaken the entire structure.
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And the 500-tonne scorched
carcass of scaffolding
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could collapse at any moment...
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..something unthinkable to those
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tasked with preserving France's
rich cultural heritage.
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SPEAKS IN FRENCH
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Philippe Villeneuve is in charge
of historic monuments in France.
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This is the cathedral that
inspired him to become an architect.
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Since 2013, Philippe has been in
charge of conserving Notre-Dame.
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The stricken cathedral is
a giant house of cards.
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If the stone vaulting collapses,
the weight of the buttresses
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will push in the 33-metre-high walls
and Notre-Dame will be no more.
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So, Philippe assembles a
rapid response team,
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dozens of engineers,
architects and scientists.
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Their task is to prevent a total
collapse of the cathedral.
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It's not only a difficult job,
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it's also hazardous.
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The crumbling stone vaults
and twisted scaffolding
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make even venturing inside
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to investigate the
stability of the structure
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extremely dangerous.
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SHE SPEAKS IN FRENCH
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ALARM BLARES
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SHE SPEAKS IN ENGLISH
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Motion sensors are installed
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in the melted jumble
of scaffolding overhead.
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These can be triggered
by gusts of wind
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or signal a full-scale collapse.
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There are evacuations like this
each week that slow progress.
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To avert a catastrophic
collapse, engineers could build
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a steel skeleton inside the
nave to brace the walls.
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Then, even if the vaulting caves in,
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the walls of Notre-Dame
would stay standing.
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But it's far too dangerous
for workers to erect steelwork
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beneath the compromised structure.
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So, instead of bracing the
walls from the inside,
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the team will build timber frames
under the buttresses outside.
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Now, if the vaulting does fall in,
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the buttresses can't
push on the walls
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and they won't come tumbling down.
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THEY SPEAK IN FRENCH
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Workers at this specialised
factory race to cut and assemble
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around 225 tonnes of timber
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to create the massive supports
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Philippe's team needs to
prop up the vaults.
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It's critical each
support fits perfectly
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beneath each flying
buttress to hold its weight.
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Working around and inside this
space is a logistical nightmare.
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200 tonnes of lead cladding
covered the cathedral roof.
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This was mostly
melted during the fire
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and now toxic lead dust
covers every surface.
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The work site is
highly contaminated.
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Until the site is cleaned,
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team members must wear full
protective clothing
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to pass into the contaminated zone.
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When leaving site, they undress,
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discard all clothing, carefully wash
equipment, then shower themselves.
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Only then can they go back
to the clean area,
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even for a lunch break.
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But finally, five months later,
all 28 flying buttresses
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are locked in place and
the walls are safe.
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Now, they can turn to the
next challenge -
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secure the melted
massive scaffolding
249
00:18:38,960 --> 00:18:41,520
that hangs precariously
over the cathedral.
250
00:18:43,080 --> 00:18:46,320
The scaffold weighs more
than a jumbo jet
251
00:18:46,320 --> 00:18:49,400
and only rests on four spindly legs.
252
00:18:50,680 --> 00:18:54,480
The team plans to wrap three massive
steel lattice beams around it
253
00:18:54,480 --> 00:18:56,880
to tie the fragile
upper parts together.
254
00:19:00,160 --> 00:19:03,200
Then they'll build more
scaffolding either side
255
00:19:03,200 --> 00:19:05,040
and lay steel beams across it.
256
00:19:08,240 --> 00:19:12,080
This way, workers can get
inside the stricken scaffolding
257
00:19:12,080 --> 00:19:14,880
to help cut off its
50,000 steel poles.
258
00:19:16,000 --> 00:19:18,000
A truly herculean task.
259
00:19:22,040 --> 00:19:25,920
Only then can the team put
up a temporary roof
260
00:19:25,920 --> 00:19:29,400
to protect them from the elements
while they rebuild Notre-Dame.
261
00:19:39,800 --> 00:19:43,240
While engineers gear up
to remove the scaffolding,
262
00:19:43,240 --> 00:19:46,520
architect Remi Fromont
and Livio De Luca
263
00:19:46,520 --> 00:19:48,880
begin a ground-breaking project
264
00:19:48,880 --> 00:19:53,160
that will combine the investigative
work with new scientific analysis.
265
00:19:55,680 --> 00:19:59,520
Their ambition is to create a
data-rich model of Notre-Dame,
266
00:19:59,520 --> 00:20:01,840
a digital twin.
267
00:20:01,840 --> 00:20:07,600
The digital twin will embed not
only the geometric structure,
268
00:20:07,600 --> 00:20:10,400
or the visual appearance
of the cathedral,
269
00:20:10,400 --> 00:20:15,920
but also all the scientific
data coming from studies.
270
00:20:15,920 --> 00:20:19,360
For example, you can
click on a stone in the vault
271
00:20:19,360 --> 00:20:24,240
and access to all the information
about its physical properties
272
00:20:24,240 --> 00:20:26,040
such as the provenance,
273
00:20:26,040 --> 00:20:30,560
but also the mechanical behaviour
within the entire structure.
274
00:20:31,960 --> 00:20:38,080
This 3-D dynamic map will show
every stone, timber and iron nail
275
00:20:38,080 --> 00:20:42,920
in the structure across time
from the 12th century
276
00:20:42,920 --> 00:20:44,760
to the present day.
277
00:20:44,760 --> 00:20:48,400
This is an unprecedented project.
278
00:20:48,400 --> 00:20:52,080
The ambition is to collect
all the information
279
00:20:52,080 --> 00:20:54,720
from the past to pass it
to the future.
280
00:20:55,840 --> 00:20:57,760
There's very
little first-hand information
281
00:20:57,760 --> 00:20:59,400
about the construction
of Notre-Dame,
282
00:20:59,400 --> 00:21:01,160
or the craftspeople who built it.
283
00:21:03,520 --> 00:21:07,480
In the wake of the fire, new studies
of the cathedral's materials
284
00:21:07,480 --> 00:21:09,120
could unlock these secrets.
285
00:21:10,880 --> 00:21:14,200
This new data captured
in the digital twin
286
00:21:14,200 --> 00:21:17,920
will provide a blueprint for
the restoration and rebuild.
287
00:21:23,280 --> 00:21:27,400
Inside Notre-Dame,
scientists begin to gather data
288
00:21:27,400 --> 00:21:32,400
and investigate the damage to
treasured statues, murals and
windows.
289
00:21:37,360 --> 00:21:42,160
The cathedral's most fragile
wonder, its stained glass,
290
00:21:42,160 --> 00:21:44,360
dates back to the 13th century.
291
00:21:45,520 --> 00:21:50,360
36 windows circle the lower level,
42 around the middle level
292
00:21:50,360 --> 00:21:52,760
and 43 around the upper level.
293
00:21:55,120 --> 00:22:00,360
The three famous rose windows span
up to 13 metres in diameter
294
00:22:00,360 --> 00:22:05,200
and are made up of over 1,100
panels of beautiful stained glass.
295
00:22:06,560 --> 00:22:11,160
But the intense heat from the fire
that melted the cathedral's
lead-covered roof
296
00:22:11,160 --> 00:22:15,120
means that today, much of the
remaining glasswork
297
00:22:15,120 --> 00:22:17,800
is covered in a layer of
toxic lead powder.
298
00:22:19,360 --> 00:22:23,520
It was really painful to see
the catastrophe on TV.
299
00:22:23,520 --> 00:22:27,200
I was looking to see what's
up and around the windows.
300
00:22:28,440 --> 00:22:30,160
And it was, of course,
301
00:22:30,160 --> 00:22:33,440
totally difficult to have a
good idea of what's happened.
302
00:22:33,440 --> 00:22:38,280
There is a before and after 15th
April for historical monuments,
303
00:22:38,280 --> 00:22:39,520
that's for sure.
304
00:22:40,680 --> 00:22:45,760
Glass scientist Claudine Loisel
uses a hand-held digital microscope
305
00:22:45,760 --> 00:22:49,480
to investigate the levels of lead
powder on the stained glass.
306
00:22:49,480 --> 00:22:53,760
She must then formulate a strategy
to clean every single panel.
307
00:22:53,760 --> 00:22:56,520
It's a vast
decontamination programme
308
00:22:56,520 --> 00:23:00,160
that will make the glass safe for
restorers to begin work.
309
00:23:03,120 --> 00:23:07,120
This window is in the back of
the cathedral in the lower level,
310
00:23:07,120 --> 00:23:09,200
furthest from the inferno,
311
00:23:09,200 --> 00:23:12,520
but it's still badly contaminated.
312
00:23:12,520 --> 00:23:15,120
CLAUDINE SPEAKS IN FRENCH
313
00:23:15,120 --> 00:23:19,000
Fortunately, these windows have
not been cleaned for 100 years,
314
00:23:19,000 --> 00:23:22,000
so the lead has settled on
top of a dust layer,
315
00:23:22,000 --> 00:23:23,640
not on the glass itself.
316
00:23:25,080 --> 00:23:29,720
The first thick layer
of deposit was, we can say,
317
00:23:29,720 --> 00:23:32,120
as a small protection in one way.
318
00:23:32,120 --> 00:23:36,000
So, we have just to remove
all the deposit to clean
319
00:23:36,000 --> 00:23:38,480
these windows from the 19th century.
320
00:23:38,480 --> 00:23:42,120
Claudine examines deposits
from windows around the cathedral.
321
00:23:42,120 --> 00:23:44,080
The samples reveal vital clues
322
00:23:44,080 --> 00:23:46,960
about the spread of the
lead contamination.
323
00:23:46,960 --> 00:23:52,080
After the spire fell, the cloud
of dust, lead and different particle
324
00:23:52,080 --> 00:23:54,400
pushed in the other direction.
325
00:23:54,400 --> 00:23:57,520
So, we are a little bit more
protected in this area.
326
00:23:57,520 --> 00:24:00,560
The windows of the upper level
in the path of the lead cloud
327
00:24:00,560 --> 00:24:02,320
have been most contaminated.
328
00:24:05,080 --> 00:24:07,880
The team takes out and
transports these panels
329
00:24:07,880 --> 00:24:09,800
to this special laboratory,
330
00:24:09,800 --> 00:24:13,080
where they experiment with
ways to remove the lead.
331
00:24:15,920 --> 00:24:19,480
First, Claudine uses a
precision vacuum cleaner
332
00:24:19,480 --> 00:24:22,080
to hoover up the 100 years of dust
333
00:24:22,080 --> 00:24:25,600
and most of the lead
powder along with it.
334
00:24:25,600 --> 00:24:31,720
So, this is a good way to
protect the conservator.
335
00:24:31,720 --> 00:24:34,040
You can control the action,
336
00:24:34,040 --> 00:24:38,760
the pressure on the glass
and also on the painting.
337
00:24:38,760 --> 00:24:41,720
Then she uses water and cotton balls
338
00:24:41,720 --> 00:24:45,080
to meticulously remove the
last of the lead.
339
00:24:45,080 --> 00:24:49,720
Of course, you need scientific
evidence that it's working.
340
00:24:49,720 --> 00:24:54,360
Claudine uses X-ray spectroscopy
to measure exactly how many wipes
341
00:24:54,360 --> 00:24:57,240
it takes to bring the lead
down to normal levels.
342
00:24:57,240 --> 00:25:04,240
So, we can identify each chemical
element we have in the material.
343
00:25:04,240 --> 00:25:07,080
Too few wipes and the
lead will remain.
344
00:25:07,080 --> 00:25:10,920
Too many wipes and restoration
will take longer than necessary.
345
00:25:13,400 --> 00:25:17,560
OK, now, this analyses if
it's finished.
346
00:25:17,560 --> 00:25:21,120
After five wipes with
the distilled water,
347
00:25:21,120 --> 00:25:24,240
Claudine checks to see
if the glass is decontaminated.
348
00:25:26,960 --> 00:25:30,080
OK, we have different
chemical elements,
349
00:25:30,080 --> 00:25:32,480
calcium, iron.
350
00:25:32,480 --> 00:25:36,680
And if we want to see the lead,
there is no lead.
351
00:25:36,680 --> 00:25:38,720
CLAUDINE LAUGHS
352
00:25:38,720 --> 00:25:42,120
After nine months, we can
see a good solution,
353
00:25:42,120 --> 00:25:44,080
a good way to clean and to preserve
354
00:25:44,080 --> 00:25:46,840
the stained glass
windows from Notre-Dame.
355
00:25:51,960 --> 00:25:55,560
The upper-level windows were not
only in the path of the lead cloud,
356
00:25:55,560 --> 00:25:57,920
but also closest to the inferno.
357
00:26:00,520 --> 00:26:04,960
Claudine hunts for hairline
cracks caused by thermal shock,
358
00:26:04,960 --> 00:26:08,120
the rapid heating and
cooling of the glass.
359
00:26:08,120 --> 00:26:10,920
This is one window from the choir
360
00:26:10,920 --> 00:26:14,640
and we have two panels
from the middle of the...bay.
361
00:26:15,640 --> 00:26:17,240
But here we have a crack.
362
00:26:19,120 --> 00:26:21,360
The hand-held digital microscope
363
00:26:21,360 --> 00:26:24,000
helps Claudine see
deep into the crack.
364
00:26:24,000 --> 00:26:27,880
If it's caused by the fire,
it will be clean and fresh.
365
00:26:27,880 --> 00:26:31,400
If it's older, it will be
full of residue.
366
00:26:31,400 --> 00:26:35,440
We can see the well-defined
line of the crack.
367
00:26:35,440 --> 00:26:38,160
We have no residue,
368
00:26:38,160 --> 00:26:43,240
so, we can say this
crack is due to the fire.
369
00:26:43,240 --> 00:26:47,160
This is a recent crack and
this is typical thermal shock.
370
00:26:47,160 --> 00:26:50,000
It looks like the
upper-level stained glass
371
00:26:50,000 --> 00:26:52,760
will need to be painstakingly
glued back together.
372
00:26:54,800 --> 00:26:58,000
But inside Notre-Dame, the
lower-level stained glass
373
00:26:58,000 --> 00:27:01,160
appears to have survived unscathed.
374
00:27:01,160 --> 00:27:05,880
And, yeah, we can see we
have a good stability
375
00:27:05,880 --> 00:27:09,120
around of the painting.
376
00:27:09,120 --> 00:27:11,560
So, there is absolutely
no thermal shock.
377
00:27:11,560 --> 00:27:14,440
So, that's good news for us.
378
00:27:17,520 --> 00:27:22,080
On site, the teams of scientists
meet the engineers and architects
379
00:27:22,080 --> 00:27:23,840
to share their findings.
380
00:27:23,840 --> 00:27:26,760
CLAUDINE SPEAKS IN FRENCH
381
00:27:31,880 --> 00:27:34,760
Once Claudine's team has
restored Notre-Dame's glasswork
382
00:27:34,760 --> 00:27:36,400
to its former glory,
383
00:27:36,400 --> 00:27:40,000
they may use a radical
new preservation technique
384
00:27:40,000 --> 00:27:42,400
to safeguard it for
future generations.
385
00:27:45,400 --> 00:27:49,320
It's being used on a huge scale
here in northern England.
386
00:27:51,320 --> 00:27:53,920
This is York Minster,
387
00:27:53,920 --> 00:27:56,520
an 800-year-old Gothic masterpiece
388
00:27:56,520 --> 00:28:01,480
and home to the largest expanse
of medieval stained glass in the UK,
389
00:28:01,480 --> 00:28:03,360
the Great East Window.
390
00:28:04,960 --> 00:28:07,880
It is one of the largest
windows ever made anywhere
391
00:28:07,880 --> 00:28:09,440
in the medieval world.
392
00:28:09,440 --> 00:28:13,840
We've got glass from the 12th
right through to the 18th century
393
00:28:13,840 --> 00:28:16,160
in quite significant quantities.
394
00:28:16,160 --> 00:28:20,200
And it is really our national
treasure house of stained glass.
395
00:28:23,240 --> 00:28:27,280
Engineers here are
completing a £10 million project
396
00:28:27,280 --> 00:28:31,760
to protect York Minster's
stained glass from harmful UV rays
397
00:28:31,760 --> 00:28:34,160
and the corrosive effects
of moisture.
398
00:28:34,160 --> 00:28:36,360
In modern stained glass
conservation,
399
00:28:36,360 --> 00:28:38,720
we're really doing as much as we can
400
00:28:38,720 --> 00:28:43,680
to keep both surfaces of the
historic stained glass dry
and stable,
401
00:28:43,680 --> 00:28:46,160
and that's where our ventilated
402
00:28:46,160 --> 00:28:49,440
environmental protective
glazing comes into play.
403
00:28:52,080 --> 00:28:54,000
Right, I can see that I'm almost in.
404
00:28:57,760 --> 00:28:59,840
I think it's just this
last bit, here.
405
00:28:59,840 --> 00:29:03,520
Matt Nickels is installing
this new conservation system.
406
00:29:03,520 --> 00:29:08,040
He slots a protective clear
glass exterior frame
407
00:29:08,040 --> 00:29:09,640
into the window opening.
408
00:29:09,640 --> 00:29:12,920
And this goes into the
original glazing groove
409
00:29:12,920 --> 00:29:15,120
where the medieval glass
would have been.
410
00:29:15,120 --> 00:29:20,200
This protective glazing prevents
corrosive condensation from forming
411
00:29:20,200 --> 00:29:23,840
on the 800-year-old stained glass
that will sit behind it.
412
00:29:23,840 --> 00:29:27,960
The gap created means that there's
air circulation running through,
413
00:29:27,960 --> 00:29:32,160
and when you've got air circulation,
it's regulating the temperature,
414
00:29:32,160 --> 00:29:35,200
which means that there's
less moisture on the glass.
415
00:29:35,200 --> 00:29:39,800
Each frame is custom-made
and takes great skill to fit.
416
00:29:41,000 --> 00:29:42,800
You don't want to make it too small
417
00:29:42,800 --> 00:29:45,040
because it's going to
obviously slide through.
418
00:29:45,040 --> 00:29:47,600
No two windows are going
to be the same.
419
00:29:47,600 --> 00:29:50,080
With the outer panel installed,
420
00:29:50,080 --> 00:29:53,920
they can reinstate the
layer of medieval glass.
421
00:29:53,920 --> 00:29:56,080
They're actually in
fairly good condition
422
00:29:56,080 --> 00:29:59,520
considering that they're
early 13th century.
423
00:29:59,520 --> 00:30:02,920
There's always the worry whenever
you're handling glass like this,
424
00:30:02,920 --> 00:30:06,480
but you've just got to make sure
that you're really, really careful.
425
00:30:08,440 --> 00:30:12,000
There's nothing quite like seeing
it with sunlight behind it.
426
00:30:12,000 --> 00:30:14,840
When you put it up like this,
it's quite magical, isn't it?
427
00:30:17,800 --> 00:30:22,040
Techniques like this offer a glimpse
of how scientists like Claudine
428
00:30:22,040 --> 00:30:25,600
may eventually preserve
Notre-Dame's glass.
429
00:30:25,600 --> 00:30:29,960
This is the best way to
protect a stained glass window.
430
00:30:29,960 --> 00:30:31,880
So, it will be, for sure,
431
00:30:31,880 --> 00:30:34,640
an option to protect the
windows from Notre-Dame.
432
00:30:37,720 --> 00:30:39,960
By an incredible stroke of luck,
433
00:30:39,960 --> 00:30:43,400
the three spectacular rose
windows of Notre-Dame,
434
00:30:43,400 --> 00:30:45,640
that date from the 13th century,
435
00:30:45,640 --> 00:30:47,840
survived the fire intact.
436
00:30:47,840 --> 00:30:53,320
It was a great relief to see
all the panel in place,
437
00:30:53,320 --> 00:30:54,760
in good stability.
438
00:30:54,760 --> 00:30:58,400
So, it was really,
"Phew, everything is OK."
439
00:30:58,400 --> 00:31:00,960
Had the vaulting collapsed
next to the windows,
440
00:31:00,960 --> 00:31:03,960
the glass could have been
badly damaged.
441
00:31:03,960 --> 00:31:05,760
But luckily, the stone vaulting,
442
00:31:05,760 --> 00:31:08,840
which sits just under the
timber and lead roof,
443
00:31:08,840 --> 00:31:11,800
protected the windows
from the inferno above.
444
00:31:32,120 --> 00:31:35,200
The magnificent vaulting
was built to be resilient,
445
00:31:35,200 --> 00:31:38,720
thanks to precise
medieval craftsmanship
446
00:31:38,720 --> 00:31:42,400
using an estimated 800
cubic metres of limestone.
447
00:31:46,040 --> 00:31:48,760
The arches work together
to support the roof
448
00:31:48,760 --> 00:31:50,440
and stabilise the outer walls.
449
00:31:53,720 --> 00:31:58,280
But the intense heat from the
fire and the collapsing spire...
450
00:31:59,960 --> 00:32:02,560
..took out 15% of the
stone vaulting.
451
00:32:04,160 --> 00:32:08,560
Today, three 12-metre-wide
holes and several smaller gaps
452
00:32:08,560 --> 00:32:10,920
mean the vaults could
collapse at any moment.
453
00:32:14,400 --> 00:32:18,000
The team collects, stores
and catalogues the fallen stone
454
00:32:18,000 --> 00:32:21,040
in this tent located
alongside the cathedral.
455
00:32:22,920 --> 00:32:25,000
They may be able to use
some of this stone
456
00:32:25,000 --> 00:32:26,440
to reconstruct the vaults.
457
00:32:31,640 --> 00:32:35,080
But medieval masons never
intended the stone to be subject
458
00:32:35,080 --> 00:32:39,360
to an 800-degree inferno, then
soaked with tonnes of water.
459
00:32:40,960 --> 00:32:43,200
Now, without a roof to protect it,
460
00:32:43,200 --> 00:32:46,200
areas of the vaulting are
exposed to the elements.
461
00:32:47,200 --> 00:32:50,000
Stone scientist Jean-Didier Mertz
462
00:32:50,000 --> 00:32:54,400
forces mercury at high pressure
through samples of the damaged
vaulting
463
00:32:54,400 --> 00:32:57,040
to calculate the
porosity of the stones.
464
00:32:58,360 --> 00:33:01,360
This tells him how
sponge-like the stonework has become
465
00:33:01,360 --> 00:33:03,200
one year on from the fire.
466
00:33:03,200 --> 00:33:07,200
The damage produced some
cracks due to the fire.
467
00:33:07,200 --> 00:33:10,840
With these cracks, it
is possible to the water
468
00:33:10,840 --> 00:33:13,480
to go in and to fill all the cracks.
469
00:33:14,680 --> 00:33:17,560
Jean-Didier confirms
the surface of the vaulting stones
470
00:33:17,560 --> 00:33:19,640
are covered with micro cracks,
471
00:33:19,640 --> 00:33:22,120
dramatically
increasing the porosity.
472
00:33:26,560 --> 00:33:29,120
Greater porosity means the
vaulting can absorb more water
473
00:33:29,120 --> 00:33:33,320
than they thought, potentially
swelling the blocks.
474
00:33:33,320 --> 00:33:35,760
As the blocks dry,
they then shrink.
475
00:33:37,480 --> 00:33:40,760
Jean-Didier has dried this vaulting
stone under lab conditions.
476
00:33:42,120 --> 00:33:45,280
He knows the block
holds two kilos of water
477
00:33:45,280 --> 00:33:48,400
and takes six months
to fully dry.
478
00:33:48,400 --> 00:33:51,880
The vault of Notre-Dame,
it is not exactly the same
479
00:33:51,880 --> 00:33:56,400
because the cathedral is not
completely sealed.
480
00:33:56,400 --> 00:34:02,200
And with new rainwater
481
00:34:02,200 --> 00:34:05,240
and the repeated cycle
of swelling and shrinkage,
482
00:34:05,240 --> 00:34:07,640
it is a real decay...
483
00:34:08,960 --> 00:34:11,360
..the weathering of the material.
484
00:34:11,360 --> 00:34:15,160
Even if some fallen
vaulting stone can be reused,
485
00:34:15,160 --> 00:34:18,200
it's clear they'll also need
to source new stone.
486
00:34:31,080 --> 00:34:34,720
Notre-Dame is made up of many
different types of limestone.
487
00:34:36,040 --> 00:34:39,040
Medieval masons chose hard
limestone for the towers,
488
00:34:39,040 --> 00:34:43,320
pillars and outer walls to build
tall and hold up the roof.
489
00:34:46,520 --> 00:34:50,440
For the sculptures, they chose
dense, fine-grained limestone
490
00:34:50,440 --> 00:34:53,120
that can be carved
with great detail.
491
00:34:53,120 --> 00:34:57,640
And for the vaults, they selected
softer, more porous limestone
492
00:34:57,640 --> 00:34:59,280
that's light, but strong.
493
00:35:01,560 --> 00:35:06,040
If the team rebuilding the vaults
picks a limestone that is too heavy,
494
00:35:06,040 --> 00:35:09,240
the new vaults may not last
as long as they should.
495
00:35:11,880 --> 00:35:16,600
Geologist Lise Leroux investigates
what quarry this stone came from.
496
00:35:16,600 --> 00:35:23,280
We have some blocks coming from
the collapse of the vault for study.
497
00:35:23,280 --> 00:35:27,520
This detective work will help the
team source replacement stone
498
00:35:27,520 --> 00:35:30,720
that shares identical
mechanical properties.
499
00:35:30,720 --> 00:35:32,440
We have to verify...
500
00:35:32,440 --> 00:35:36,200
The fallen vaulting stone
contains a rare microfossil
501
00:35:36,200 --> 00:35:40,880
called Orbitolites complanatus,
a kind of plankton.
502
00:35:40,880 --> 00:35:45,440
Fossils like this are found
in just one layer of rock.
503
00:35:45,440 --> 00:35:50,480
This will make sourcing new stone
of the same type even trickier.
504
00:35:50,480 --> 00:35:53,200
Can they use this
geological fingerprint
505
00:35:53,200 --> 00:35:56,400
to discover the original
source of the vaulting stone?
506
00:36:00,200 --> 00:36:04,760
To find out, Lise and fellow
Notre-Dame scientist Claudine Loisel
507
00:36:04,760 --> 00:36:07,960
venture deep beneath Paris.
508
00:36:09,800 --> 00:36:14,080
Hidden under the city streets is a
rich source of limestone,
509
00:36:14,080 --> 00:36:17,680
a vast labyrinth of quarry tunnels.
510
00:36:17,680 --> 00:36:23,600
Lise and Claudine enter this maze,
two miles south of Notre-Dame
511
00:36:23,600 --> 00:36:25,440
in the famous Catacombs.
512
00:36:26,880 --> 00:36:28,280
Ah!
513
00:36:28,280 --> 00:36:30,160
Ah, oui!
514
00:36:49,720 --> 00:36:51,440
In the late 18th century,
515
00:36:51,440 --> 00:36:54,840
the quarries were given
a different purpose
516
00:36:54,840 --> 00:36:59,000
and they housed bones
from old cemeteries...
517
00:37:00,720 --> 00:37:02,960
..which were inside the towns,
518
00:37:02,960 --> 00:37:06,720
cemeteries which were closed
at the end of the 18th century
519
00:37:06,720 --> 00:37:07,960
for sanitary reasons.
520
00:37:09,360 --> 00:37:11,920
Amongst the bones, Lise and Claudine
521
00:37:11,920 --> 00:37:14,560
find traces left by
the medieval miners.
522
00:37:36,320 --> 00:37:37,640
D'accord.
523
00:37:43,040 --> 00:37:44,280
Mm.
524
00:37:47,440 --> 00:37:50,560
The upper level of the
quarry holds hard limestone
525
00:37:50,560 --> 00:37:53,720
with large, well-preserved fossils.
526
00:37:53,720 --> 00:37:59,760
These fossils are more
characteristic of limestones
527
00:37:59,760 --> 00:38:02,120
used for the pillars,
528
00:38:02,120 --> 00:38:04,280
the arch in Notre-Dame.
529
00:38:04,280 --> 00:38:05,640
But not for the vaults.
530
00:38:06,840 --> 00:38:10,600
Lise and Claudine hope to find a
match for the soft vaulting stone
531
00:38:10,600 --> 00:38:12,200
in the lower level of the quarry.
532
00:38:14,120 --> 00:38:21,040
We now...to look if we can find
the specific microfossils.
533
00:38:24,480 --> 00:38:29,680
I'm not sure because on the
surface it's very rough
534
00:38:29,680 --> 00:38:34,640
and it's not so clear because of
the state of the surface.
535
00:38:34,640 --> 00:38:36,960
The limestone here is softer,
536
00:38:36,960 --> 00:38:40,520
but Lise cannot see a match
for the rare microfossil
537
00:38:40,520 --> 00:38:43,240
found in the Notre-Dame
vaulting sample.
538
00:38:47,280 --> 00:38:50,960
So, back in the lab, she takes
a closer look at a sample
539
00:38:50,960 --> 00:38:53,360
of limestone from the lower
level of the quarry.
540
00:38:55,640 --> 00:38:57,560
These little fossils...
541
00:38:58,640 --> 00:39:01,760
..this one, this one, this one
542
00:39:01,760 --> 00:39:05,600
are, in fact,
some planktonic fossils
543
00:39:05,600 --> 00:39:08,920
which are called foraminifera.
544
00:39:08,920 --> 00:39:12,840
It's not the fossil signature
she's looking for.
545
00:39:12,840 --> 00:39:14,040
But then...
546
00:39:15,920 --> 00:39:17,160
Oh!
547
00:39:19,120 --> 00:39:23,880
This one here is
Orbitolites complanatus.
548
00:39:23,880 --> 00:39:30,000
This little planktonic
fossil is a dating fossil,
549
00:39:30,000 --> 00:39:35,760
which match with the stone
coming from the vault.
550
00:39:35,760 --> 00:39:38,640
It's a stratigraphic indicator,
551
00:39:38,640 --> 00:39:42,480
characteristic from the
middle Oligocene,
552
00:39:42,480 --> 00:39:46,120
which is a geological
age of deposit.
553
00:39:47,480 --> 00:39:50,600
Lise confirms the origin
of the Notre-Dame vaulting stone.
554
00:39:51,720 --> 00:39:55,880
It's quarried from the deepest seams
of limestone beneath Paris.
555
00:39:55,880 --> 00:39:57,120
Conclusive.
556
00:39:57,120 --> 00:40:01,400
But what about the harder limestone
used by medieval masons to build
557
00:40:01,400 --> 00:40:04,640
Notre-Dame's load-bearing
pillars and arches?
558
00:40:04,640 --> 00:40:07,080
Another microfossil signature
559
00:40:07,080 --> 00:40:09,840
confirms the origin of
this type as well.
560
00:40:09,840 --> 00:40:13,360
The arches are built
with a hard stone,
561
00:40:13,360 --> 00:40:17,400
with a resistant stone
to support the vault.
562
00:40:17,400 --> 00:40:21,320
And the vault in itself is
logically constructed
563
00:40:21,320 --> 00:40:25,080
with a lighter, more porous stone.
564
00:40:25,080 --> 00:40:28,840
And in the quarry located in Paris,
565
00:40:28,840 --> 00:40:31,720
we have these two kinds of stone.
566
00:40:31,720 --> 00:40:36,120
Medieval masons knew exactly how
to exploit the varying mechanical
567
00:40:36,120 --> 00:40:38,960
properties of the
limestone for Notre-Dame,
568
00:40:38,960 --> 00:40:42,360
knowledge passed
down through the generations.
569
00:40:42,360 --> 00:40:46,840
Sourcing more of the correct
stone won't be easy.
570
00:40:46,840 --> 00:40:49,440
The old quarries are
no longer active,
571
00:40:49,440 --> 00:40:53,000
but engineers now know
what limestone to look for.
572
00:40:53,000 --> 00:40:57,320
This will help them find a
match in quarries outside Paris.
573
00:41:01,160 --> 00:41:05,320
Stone is not the only raw material
that will need to be replaced
574
00:41:05,320 --> 00:41:07,280
as engineers reconstruct Notre-Dame.
575
00:41:08,800 --> 00:41:11,880
The timber roof was also
a medieval wonder.
576
00:41:15,520 --> 00:41:19,240
It was constructed from
700 cubic metres of timber,
577
00:41:19,240 --> 00:41:21,600
cut from 52 acres of oak.
578
00:41:21,600 --> 00:41:24,640
That's approximately 1,300 trees.
579
00:41:28,840 --> 00:41:31,960
For this reason, it was
known as the "Forest".
580
00:41:31,960 --> 00:41:35,600
Every single oak in Notre-Dame's
Forest was hand-picked
581
00:41:35,600 --> 00:41:39,080
for the physical properties
needed in the roof structure,
582
00:41:39,080 --> 00:41:42,120
from dense straight
oak for pillars,
583
00:41:42,120 --> 00:41:44,600
to curved oak for support arches.
584
00:41:51,800 --> 00:41:54,920
But the fire consumed
every beam in the Forest.
585
00:41:56,760 --> 00:42:03,040
Today, this intricate 500-tonne
timber jigsaw lies in ruins.
586
00:42:03,040 --> 00:42:04,880
SPEAKS IN FRENCH
587
00:42:21,440 --> 00:42:26,160
Over 50 tonnes of the precious roof
timber lie precariously on top of
the vaults.
588
00:42:27,200 --> 00:42:29,440
Despite the destruction,
589
00:42:29,440 --> 00:42:32,800
every single beam holds
the history of Notre-Dame.
590
00:42:32,800 --> 00:42:35,160
It has deep archaeological value.
591
00:42:36,640 --> 00:42:39,520
It's vital that workers
forensically record the position
592
00:42:39,520 --> 00:42:42,680
where each beam fell
before they remove them.
593
00:42:43,720 --> 00:42:46,520
This helps them determine
where it originally sat
594
00:42:46,520 --> 00:42:48,160
in the roof structure.
595
00:42:49,320 --> 00:42:52,040
These highly trained rope
access technicians
596
00:42:52,040 --> 00:42:55,200
catalogue and clear the
charred timber on the vaults.
597
00:42:57,840 --> 00:43:00,160
THEY SPEAK IN FRENCH
598
00:43:01,840 --> 00:43:04,120
It's not possible to
walk on the vaults,
599
00:43:04,120 --> 00:43:06,560
because the structure
is very precarious.
600
00:43:06,560 --> 00:43:10,120
They needed to create a way
to access with ropes.
601
00:43:12,680 --> 00:43:14,960
We need to wear a special mask
602
00:43:14,960 --> 00:43:18,200
because of the lead dust
that we might inhale.
603
00:43:22,400 --> 00:43:26,640
We label the timbers and we
mark them with a code
604
00:43:26,640 --> 00:43:30,040
that the architects will
be able to identify.
605
00:43:35,480 --> 00:43:37,560
The team has their work cut out.
606
00:43:37,560 --> 00:43:41,080
There are thousands of separate
pieces of timber to catalogue.
607
00:43:41,080 --> 00:43:43,280
We have a lot of work to do.
608
00:43:43,280 --> 00:43:45,640
That's why we're
working day and night.
609
00:43:45,640 --> 00:43:49,080
They've already extracted
around 4,000 pieces.
610
00:43:55,320 --> 00:44:00,320
Timber scientist Catherine Lavier
begins painstaking detective work
611
00:44:00,320 --> 00:44:04,800
to reveal how Notre-Dame's vast
Forest was originally assembled
612
00:44:04,800 --> 00:44:07,200
and could be rebuilt today.
613
00:44:09,200 --> 00:44:12,240
Some pieces were very well preserved
614
00:44:12,240 --> 00:44:16,520
because, as you see
here, with different faces
615
00:44:16,520 --> 00:44:21,160
and another piece of wood is coming
here with a wooden joint here
616
00:44:21,160 --> 00:44:23,160
to assemble them.
617
00:44:23,160 --> 00:44:26,400
And it's rather typical
from the medieval period.
618
00:44:27,800 --> 00:44:30,960
And here you have a mark...
619
00:44:33,360 --> 00:44:35,280
..of carpenters.
620
00:44:35,280 --> 00:44:38,840
So, they are sure that this piece
with this piece are together.
621
00:44:40,280 --> 00:44:42,560
It's very important for carpenters.
622
00:44:42,560 --> 00:44:44,920
They prepare the wood on the ground.
623
00:44:44,920 --> 00:44:49,200
And after that, they go to the
roof and reassemble again.
624
00:44:50,640 --> 00:44:53,880
Every carpenter has his
own way to mark.
625
00:44:53,880 --> 00:44:59,040
But in general, it's based
on the Roman numbers.
626
00:44:59,040 --> 00:45:03,760
But we can find some differences
between teams of carpenters.
627
00:45:05,680 --> 00:45:09,000
We were very surprised to find
that, because I thought everything
628
00:45:09,000 --> 00:45:10,320
will be destroyed.
629
00:45:10,320 --> 00:45:12,200
And finally not.
630
00:45:12,200 --> 00:45:15,800
The tree rings of the
timbers conceal further clues.
631
00:45:15,800 --> 00:45:19,000
Each ring represents
one year of growth,
632
00:45:19,000 --> 00:45:23,840
a time capsule of information about
the life of the tree in that year.
633
00:45:23,840 --> 00:45:28,480
Catherine analyses core samples
from Notre-Dame's roof trusses.
634
00:45:30,280 --> 00:45:33,600
She measures each ring
to reveal the secret story
635
00:45:33,600 --> 00:45:37,280
of the very oak trees the
structure was made from.
636
00:45:37,280 --> 00:45:39,360
SHE SPEAKS IN FRENCH
637
00:46:08,400 --> 00:46:10,640
Catherine is gaining new insight
638
00:46:10,640 --> 00:46:13,120
into the types of trees best suited
639
00:46:13,120 --> 00:46:16,760
to rebuild the complex
Forest of Notre-Dame.
640
00:46:16,760 --> 00:46:21,360
This extraordinary challenge will
require around 1,300 oak trees...
641
00:46:22,760 --> 00:46:27,520
..craftspeople versed in the lost
art of medieval carpentry practices
642
00:46:27,520 --> 00:46:32,800
and a blueprint for possibly the
most complex timber structure in
Europe.
643
00:46:34,440 --> 00:46:37,400
The one person who may
possess the key to unlock
644
00:46:37,400 --> 00:46:42,320
the lost Forest's geometrical
secrets is architect Remi Fromont.
645
00:46:43,360 --> 00:46:48,840
In 2014, Remi spent the entire year
mapping every inch of the timber.
646
00:47:02,320 --> 00:47:04,640
We are collecting photographs...
647
00:47:12,720 --> 00:47:16,040
The fire at Notre-Dame
triggers a race across France
648
00:47:16,040 --> 00:47:20,240
to 3D-scan historical
monuments inside and out.
649
00:47:22,000 --> 00:47:26,640
These represent a digital insurance
policy to preserve French heritage.
650
00:47:30,440 --> 00:47:33,560
The laser bounces off each
contour in the room.
651
00:47:33,560 --> 00:47:38,440
The machine then measures the time
it takes for the laser to return.
652
00:47:38,440 --> 00:47:43,360
Millions of measurements form a
cloud of data called a point cloud.
653
00:47:45,640 --> 00:47:49,520
In 2016, researchers used
this same technology
654
00:47:49,520 --> 00:47:52,960
to create a full
point cloud of Notre-Dame's
655
00:47:52,960 --> 00:47:55,000
lost timber roof structure.
656
00:47:55,000 --> 00:48:00,440
This remarkable 3D scan will combine
with Remi's 2014 survey
657
00:48:00,440 --> 00:48:03,720
in Livio's digital
twin for Notre-Dame.
658
00:48:03,720 --> 00:48:08,960
What we are producing today
will be probably the information
659
00:48:08,960 --> 00:48:11,120
usable for the next generations.
660
00:48:11,120 --> 00:48:15,160
The team now has the data
they need to rebuild the timber roof
661
00:48:15,160 --> 00:48:17,640
with the exact same geometry.
662
00:48:17,640 --> 00:48:20,240
And the 500 tonnes of new oak needed
663
00:48:20,240 --> 00:48:22,920
could come from forests like this.
664
00:48:25,120 --> 00:48:28,360
Almost a third of France
is covered with forest.
665
00:48:28,360 --> 00:48:30,800
Oak was a vital strategic resource
666
00:48:30,800 --> 00:48:33,320
throughout the Middle Ages
and the Renaissance.
667
00:48:35,680 --> 00:48:39,760
Vast forests were needed to
build cities and expand navies.
668
00:48:42,400 --> 00:48:45,400
Felling and carving oak
for Notre-Dame's roof
669
00:48:45,400 --> 00:48:49,920
requires carpenters skilled in
using medieval tools and techniques
670
00:48:49,920 --> 00:48:53,560
like this team who keep the
old ways alive to this day.
671
00:48:53,560 --> 00:48:56,960
We rebuild buildings
using only hand tools
672
00:48:56,960 --> 00:48:58,600
and no power tools at all.
673
00:49:00,120 --> 00:49:04,400
Using this kind of tool, you don't
apply your vision on the tree.
674
00:49:04,400 --> 00:49:09,600
You...you have your work influenced
by the shape of the tree itself.
675
00:49:09,600 --> 00:49:15,280
Today, carpenter Leo Rousseau has
the honour of felling his first tree
676
00:49:15,280 --> 00:49:17,200
using techniques
from the Middle Ages.
677
00:49:18,960 --> 00:49:23,840
Ah, yeah, it's like
everything, it takes practice.
678
00:49:23,840 --> 00:49:27,480
You don't have to go to the
sports room at night.
679
00:49:28,920 --> 00:49:31,480
You don't want your tree to
fall into another trees,
680
00:49:31,480 --> 00:49:35,120
because you want to use the other
trees for the next generations.
681
00:49:35,120 --> 00:49:39,280
So, the idea is to create
here a hinge that gives you
682
00:49:39,280 --> 00:49:41,920
the direction where you want
the tree to fall.
683
00:49:41,920 --> 00:49:44,640
And then you cut from the back
for the tree to fall.
684
00:49:50,960 --> 00:49:52,880
THEY SPEAK IN FRENCH
685
00:50:01,240 --> 00:50:06,800
Leo now has a taste of what it took
for the Notre-Dame carpenters
686
00:50:06,800 --> 00:50:10,200
to source the 1,300 oaks
for the roof timbers.
687
00:50:14,240 --> 00:50:18,960
I like the feeling that you have to
put so much effort into one tree.
688
00:50:18,960 --> 00:50:21,600
It gives you a little bit of respect
689
00:50:21,600 --> 00:50:25,840
on what you're going to do
with that particular beam or...
690
00:50:25,840 --> 00:50:28,160
Yeah, it's a different feeling.
691
00:50:29,960 --> 00:50:32,000
Carpenters are using the
old ways to restore
692
00:50:32,000 --> 00:50:35,160
the Chateau de Beaumesnil
in Normandy.
693
00:50:35,160 --> 00:50:37,360
It's a national historic monument
694
00:50:37,360 --> 00:50:40,920
built on the site of an
1,100-year-old castle.
695
00:50:40,920 --> 00:50:43,360
SPEAKS IN FRENCH
696
00:50:48,560 --> 00:50:50,960
The chateau has seen better days.
697
00:50:50,960 --> 00:50:54,520
The curved beams that hold up
the roof are close to collapse
698
00:50:54,520 --> 00:50:56,040
and must be replaced.
699
00:50:58,760 --> 00:51:01,280
SHE SPEAKS IN FRENCH
700
00:51:15,920 --> 00:51:19,480
The carpenters here face many
of the same challenges
701
00:51:19,480 --> 00:51:22,680
that Notre-Dame restorers
will need to overcome
702
00:51:22,680 --> 00:51:25,880
when they rebuild
the cathedral's lost Forest.
703
00:51:27,320 --> 00:51:29,080
The timber has been chosen
704
00:51:29,080 --> 00:51:33,440
so the curve of the grain perfectly
matches the curve of the new beam.
705
00:51:33,440 --> 00:51:37,920
If you get a straight tree
which has a straight grain
706
00:51:37,920 --> 00:51:44,080
and then you get a curved piece
of wood inside of this...
707
00:51:45,440 --> 00:51:49,080
So, here is the fibre so it
can break right there.
708
00:51:49,080 --> 00:51:52,920
But if you take the tree
that's curved,
709
00:51:52,920 --> 00:51:57,400
the fibre is like this,
so it cannot break.
710
00:51:57,400 --> 00:52:01,560
You keep all of the structural
strength of the...of the tree.
711
00:52:05,640 --> 00:52:08,280
They use an original beam
to produce a template
712
00:52:08,280 --> 00:52:10,600
and mark out the new
beam on the oak.
713
00:52:13,000 --> 00:52:17,000
The carpenters who built Notre-Dame
would be familiar with the tools
714
00:52:17,000 --> 00:52:20,120
this team uses to
hew the raw timber.
715
00:52:23,400 --> 00:52:25,960
So, we would start with these axes.
716
00:52:27,880 --> 00:52:31,640
You know, it's a long handle,
which gives you a long swing.
717
00:52:33,200 --> 00:52:38,240
Because if you want to make
notches cutting deep in the wood,
718
00:52:38,240 --> 00:52:43,720
so you want a long handle to give
you momentum and use the weight
719
00:52:43,720 --> 00:52:46,760
of the tool itself to
basically do the job.
720
00:52:48,600 --> 00:52:51,600
And after you've split
most of the wood,
721
00:52:51,600 --> 00:52:56,080
you use a second type of axe,
which is called a broad axe.
722
00:52:56,080 --> 00:52:59,920
They have a single bevel,
long cutting edge
723
00:52:59,920 --> 00:53:03,440
and the handle is offset.
724
00:53:04,680 --> 00:53:09,040
So, if you're working
as you go down,
725
00:53:09,040 --> 00:53:13,720
your hand here, you see I'm not
hitting the...this sharp edge.
726
00:53:16,320 --> 00:53:21,000
For skilled carpenters, cutting
Notre-Dame's roof timbers with axes
727
00:53:21,000 --> 00:53:24,880
compared to a modern sawmill
would take roughly twice the time.
728
00:53:26,800 --> 00:53:29,200
This curved oak will be one of ten
729
00:53:29,200 --> 00:53:33,640
the team needs to install as part
of the chateau roof restoration.
730
00:53:33,640 --> 00:53:38,080
It sits alongside this 400-year-old
original beam.
731
00:53:38,080 --> 00:53:40,200
HE SPEAKS IN FRENCH
732
00:53:52,720 --> 00:53:56,600
Just like the Notre-Dame beams,
the chateau's original beam
733
00:53:56,600 --> 00:53:59,800
holds messages from the
old carpenters.
734
00:54:09,400 --> 00:54:11,800
French carpenters have the oak,
735
00:54:11,800 --> 00:54:13,520
they have the skills
736
00:54:13,520 --> 00:54:16,760
and they have the plans
required to reconstruct
737
00:54:16,760 --> 00:54:19,800
Notre-Dame's vast Forest
of roof timbers.
738
00:54:27,200 --> 00:54:30,960
While the architects consider
options for rebuilding the roof,
739
00:54:30,960 --> 00:54:34,320
they must also work out
what innovations to engineer
740
00:54:34,320 --> 00:54:38,040
into the structure to safeguard
it against future fires.
741
00:54:40,520 --> 00:54:44,840
Scientists here at the University
of Edinburgh School of Engineering
742
00:54:44,840 --> 00:54:47,000
use scale models to investigate
743
00:54:47,000 --> 00:54:49,760
how fires spread through
timber structures
744
00:54:49,760 --> 00:54:52,120
like the Forest of Notre-Dame.
745
00:54:52,120 --> 00:54:55,120
Our job is to understand
the underlying physics
746
00:54:55,120 --> 00:54:58,800
and then to use our understanding
of the physics to create strategies
747
00:54:58,800 --> 00:55:00,720
by which people can be more safe
748
00:55:00,720 --> 00:55:02,840
and assets can be more
safe from fire.
749
00:55:04,120 --> 00:55:06,120
As Luke ignites a single beam
750
00:55:06,120 --> 00:55:08,920
in this model of a timber
roof structure...
751
00:55:08,920 --> 00:55:10,680
Ignition.
752
00:55:10,680 --> 00:55:14,400
..it becomes clear
how quickly the energy radiates
753
00:55:14,400 --> 00:55:19,000
to the timber beam alongside
until it too catches fire.
754
00:55:20,360 --> 00:55:23,320
This phenomenon is called
reradiation.
755
00:55:23,320 --> 00:55:25,640
In a structure like a
roof at Notre-Dame,
756
00:55:25,640 --> 00:55:29,120
what we had is a collection of
timber members in a nice pattern,
757
00:55:29,120 --> 00:55:31,760
all kind of looking at each
other as they burn.
758
00:55:31,760 --> 00:55:33,840
And that fact that they're
looking at each other,
759
00:55:33,840 --> 00:55:35,360
they're radiating at each other,
760
00:55:35,360 --> 00:55:37,400
is what causes the
fire to grow and escalate
761
00:55:37,400 --> 00:55:39,200
in such a dramatic way.
762
00:55:39,200 --> 00:55:40,800
If you create a gap or a firebreak
763
00:55:40,800 --> 00:55:42,880
within your network
of timber elements,
764
00:55:42,880 --> 00:55:45,720
you can prevent the
combustion from occurring
765
00:55:45,720 --> 00:55:48,120
on the far side of the firebreak.
766
00:55:49,600 --> 00:55:51,840
To stop the spread of
fires like this,
767
00:55:51,840 --> 00:55:55,560
today, engineers build
fire-separating partitions
768
00:55:55,560 --> 00:55:57,520
into the roofs of
historic buildings.
769
00:56:01,200 --> 00:56:05,880
These firewalls are erected
inside the roof of York Minster.
770
00:56:05,880 --> 00:56:07,480
In the event of a fire,
771
00:56:07,480 --> 00:56:11,520
they should prevent the
reradiation and transfer of energy.
772
00:56:11,520 --> 00:56:16,560
Innovations like this could help
safeguard Notre-Dame's new roof
773
00:56:16,560 --> 00:56:18,440
against future threats.
774
00:56:25,360 --> 00:56:29,840
One year after the fire that
ravaged Notre-Dame Cathedral,
775
00:56:29,840 --> 00:56:34,280
investigators have still not
pinpointed the cause of the blaze.
776
00:56:34,280 --> 00:56:38,760
And immense challenges and
uncertainties still lie ahead.
777
00:56:38,760 --> 00:56:41,800
The building is not yet
out of danger.
778
00:56:41,800 --> 00:56:46,680
Over the next 12 months, engineers
must remove the melted scaffolding
779
00:56:46,680 --> 00:56:50,360
and seal the cathedral roof
to make it watertight.
780
00:56:50,360 --> 00:56:52,760
Then they can stabilise
the weakened vaulting.
781
00:56:53,960 --> 00:56:58,640
It's a monumental feat, and
rebuilding the entire cathedral
782
00:56:58,640 --> 00:57:02,920
could take much longer than the five
years decreed by President Macron.
783
00:57:21,000 --> 00:57:24,960
Architects around the world
have unleashed their imagination
784
00:57:24,960 --> 00:57:28,920
to submit grand plans for what
the new spire above Notre-Dame
785
00:57:28,920 --> 00:57:30,600
could look like...
786
00:57:30,600 --> 00:57:33,840
..from mirrored roofs
with kaleidoscopic pinnacles
787
00:57:33,840 --> 00:57:37,600
and vast solar panels powering
nearby buildings,
788
00:57:37,600 --> 00:57:42,520
to stained glass edifices that will
light up the Paris skyline.
789
00:57:44,320 --> 00:57:46,560
However Notre-Dame is rebuilt,
790
00:57:46,560 --> 00:57:49,680
the unique collaboration
of architects and scientists
791
00:57:49,680 --> 00:57:53,240
is rewriting how we
understand the very fabric
792
00:57:53,240 --> 00:57:55,520
of this magnificent cathedral.
793
00:57:55,520 --> 00:57:59,240
I think the fire in some ways
helped remind a lot of people
794
00:57:59,240 --> 00:58:01,800
what an important part of our
sort of shared history
795
00:58:01,800 --> 00:58:03,440
and shared culture this is.
796
00:58:03,440 --> 00:58:07,520
Soon, a complete digital
twin of Notre-Dame
797
00:58:07,520 --> 00:58:11,960
should allow future generations of
craftspeople to maintain,
798
00:58:11,960 --> 00:58:15,640
protect and faithfully
rebuild Notre-Dame...
799
00:58:16,840 --> 00:58:18,960
..as many times as necessary.
67476
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