[Narrator] In a
high-rise building.
-There was no warning.
[Narrator] At sea.
-Innocent people died.
[Narrator] In a train.
-Everything was on fire.
Everything was burning.
[Narrator] Disasters can begin
with the smallest things.
-Changing the opening
hours of a restaurant.
-The bad glue job.
-A paperwork error.
[Narrator]
Now, combining the
latest research with every
available source of evidence,
experts will forensically
analyze three disasters
down to each tiny detail.
-You've really got to
think outside the box.
-You have to work your
way back and understand
each link in the chain.
[expl*si*n]
[Narrator] State-of-the-art
graphics reveal every critical
detail at every
critical moment.
-This whole disaster
could have been averted.
[Narrator]
We can dissect them.
Get inside.
Or underneath.
Freeze time.
And even reverse it.
To conduct a complete
Disaster Autopsy.
[Narrator] Europe, the Alps.
At 15,766 feet,
Mont Blanc is Western Europe's
highest mountain.
Deep inside the solid rock
runs a road tunnel more than
seven miles long,
connecting France with Italy.
When it opened in 1965,
it was the world's
longest road tunnel.
[reporter] There'll be two
carriageways about 12 feet wide,
and you'll be able to
drive under Mont Blanc
in less than a
quarter of an hour.
-By the late '90s about two
million vehicles were going
through the tunnel every year.
[Narrator] The tunnel is
carefully designed to
keep these drivers safe.
-There are smoke and heat
detectors throughout the
length of the tunnel.
Refuge rooms with their
own independent air supply.
We also have
emergency telephones and
fire extinguishers at
regular intervals.
-Even today, the
Mont Blanc Tunnel was an
extraordinary feat
of engineering.
[Narrator] But on
March 24th, 1999,
the safety systems fail.
A lethal fire breaks out
deep inside the tunnel.
-It took more than two
days for it to be put out.
[Narrator] 39 people die.
It is one of the deadliest road
tunnel disasters in history.
Now, by analyzing all the
available evidence,
we will digitally reconstruct
the Mont Blanc Tunnel disaster
to answer the question
What went wrong?
-We have a range of evidence
that we can look at to
understand this fire.
There's the remains of 36
vehicles that were left inside
the tunnel after the fire, we
have eyewitness accounts and
we also have data from an
array of sensors that were
located within the tunnel.
[Narrator] The first evidence
of the disaster comes from
one of these sensors.
At 10:52 a smoke detector
at rest area 18 triggers
an alarm in the control room
at the French end.
This matches eyewitness
testimony from truck driver
Gilbert DeGrave.
[Narrator] According to his
statement, DeGrave pulls over
into rest area 21.
Within minutes a fire
breaks out in his truck.
Video evidence reveals the
astonishing aftermath of
this small truck fire.
[Rory Hadden] So what
we see is the burnt-out shell
of the lorry
around rest area 21,
about halfway through the
tunnel towards the Italian side.
But we can see 35
destroyed vehicles
on either side of the truck.
22 lorries, ten cars,
two emergency vehicles,
and one motorcycle
spread over a distance
of around half a mile.
[Narrator] The
evidence is clear.
The disaster begins when
DeGrave's truck catches fire.
But records show there have
been at least 17 previous
vehicle fires in the tunnel
without a single loss of life.
Why is this one so deadly?
Using data from the
tunnel's control rooms,
we can piece together the
timeline of the disaster.
-DeGrave's truck is recorded
passing through the tolls and
entering the French portal of
the tunnel at about 10:46 a.m.
[Narrator] 6 minutes later,
at 10:52, the smoke detector
at rest area 18 is triggered,
the first warning
of the disaster.
-But it's not until about
10:55 a.m., 3 minutes later,
that operators stopped
vehicles entering the tunnel
on both sides.
[Narrator] Why isn't
access to the tunnel
stopped immediately?
-This tunnel was equipped
with two control rooms,
one on the French side and
one on the Italian side.
-We know from documentation
that the sensors in the French
side of the tunnel are routed
to the French control room and
the Italian side of the tunnel
to the Italian control room.
And that means when the alarms
start going off for area 18,
the Italians have no idea
because the sensors are
only going off on
the French side.
[Narrator] And the French
sensor readings only show
some smoke.
That could just be from a
badly polluting vehicle engine.
-The Italians only become aware
of the unfolding disaster
when they receive
an emergency call.
[Narrator] The Italians
immediately tell the French
that there is a serious fire.
This means the tunnel isn't
closed to traffic until
nine minutes after
DeGrave's truck enters
and three minutes after the
smoke sensor is triggered.
-That might not sound like
very much time, but that is
an eternity when you
have a burning vehicle.
To give some context to that,
in that time, 18 trucks and
ten more cars
enter the tunnel.
[Narrator] Of the 39 people
who die in the fire,
37 enter the tunnel in
that nine-minute gap.
[sirens]
Why does the disaster get
out of control so fast?
-According to the truck's
manifest, it was carrying
12 tons of flour and
nine tons of margarine.
A load that most people would
imagine to be pretty innocuous.
[Narrator] But the
construction of the truck
reveals a hidden problem.
-Because it was carrying
margarine the trailer was
in fact refrigerated and
therefore it was insulated.
-The insulation is made from a
material called polyurethane,
which is highly flammable.
[Andrea Sella] Once the
fire had spread from the cab
to the trailer itself,
the shell would
have begun to burn.
[Narrator] When the
insulation ignites,
it creates a completely
unexpected new hazard.
[Andrea Sella] That would start
to warm up the margarine.
Now the margarine at that
point would begin to melt.
The result is it would
start to run and give off
a flammable vapor.
At this point, you've
really got problems.
[Narrator] It's not the burning
truck that leads to disaster,
it's the margarine.
-As the fire takes hold, and
the margarine and its packaging
begin to melt and pour out
of the back of the trailer
this whole horrible
burning mixture is going to be
gently sliding, pouring,
down the slope of the tunnel
towards the oncoming traffic.
[Narrator] The situation has
transformed from a small
truck fire into a
lethal disaster.
-After the fire, 27 victims were
found still in their vehicles.
[Narrator] Why don't these
victims simply drive away
from the spreading
margarine fire?
-Four of the passenger cars
that entered after DeGrave's
truck were found pointing at
an angle, suggesting they were
trying to make a U-turn
to escape from the smoke
and the heat.
[Narrator] Why don't
they manage to escape?
-As the fire burns,
it's going to be taking
oxygen from the air.
[Narrator] The problem is
that vehicle engines
need oxygen to work.
-It seems as though the smoke
didn't have enough oxygen
in it to allow the
engines to keep running.
[Narrator] Unable to escape,
the victims are k*lled by the
toxic smoke before the
flames even reach them.
But there is a curious
pattern to these fatalities.
Every single death is on the
French side of the truck fire.
Not one person dies
on the Italian side.
Why?
-Data from the smoke detectors
shows the smoke was traveling
at about four and a half miles
an hour in the region close to
DeGrave's truck, but it was
approaching 15 miles an hour
as it got close
to the French portal.
[Narrator] This evidence shows
the smoke accelerating away
from the Italian side.
What could cause the
smoke to behave like this?
Plans for the tunnel show
that it is designed with
five ventilation ducts
on the French side,
and five identical ones
on the Italian side.
-Whilst four of the
ventilation shafts could only
work in one direction,
ventilation shaft five
could be switched over
from exhaust to supply.
-Witness reports show the
Italians in the control center
saw people fleeing the tunnel
at the Italian side,
they turned on a supply of fresh
air through duct number five.
[Narrator] But according to
eyewitness reports, on the
French side the number five
fan remains set to exhaust.
The Italian side is
now blowing air in,
the French side
is sucking it out.
-By supplying air at
maximum flow rate
through duct number five,
this is creating a flow of
smoke towards the French side.
So the evidence suggests that
this fast-moving smoke
may have led to
unintended loss of life
on the French side.
[Narrator] One final
question remains.
What starts the fire
in DeGrave's truck?
[Narrator]
According to the statement of
truck driver DeGrave,
he first sees the
smoke in the Mont Blanc Tunnel
come from under the
cab of his truck.
-In DeGrave's truck, the
engine was positioned
below the cab.
So the fact that you could
see smoke coming out from
beneath him suggests
that an engine fire
is a potentially likely cause.
[Luke Bisby] Other drivers say
that they saw smoke from
DeGrave's cab shortly after
he entered the tunnel.
This suggests that the fire
started either shortly after
DeGrave entered the tunnel,
or even before he entered it.
[Narrator] Is it possible for
DeGrave's engine to catch fire
on the approach to the tunnel?
The answer may be
simple geography.
The tunnel is in the Alps,
and the Alps are the highest
mountains in Europe.
-You have to climb a
two-and-a-half-mile
winding road and it takes you
up to 4,000 feet of altitude.
So imagine driving your truck,
pulling a heavy load,
particularly as the
air gets thinner,
as you reach higher altitude
and your engine's having to
work harder and harder.
In four of the five
last reported cases where
firefighters put
out truck fires,
engine overheating was listed as
the most probable
cause of those fires.
[Narrator] Because the
inferno is so destructive,
insufficient evidence survives
to definitively
prove how the fire starts.
But we can now identify the
key sequence of events
that leads to this disaster.
As Gilbert DeGrave's
truck enters the tunnel,
a small fire begins
inside the engine bay,
possibly from overheating.
The fire grows quickly and
DeGrave abandons his
burning truck at around
the halfway point.
The heat from the cab
fire ignites the flammable
insulation surrounding
the cargo of margarine.
[Andrea Sella] The heat of
the fire starts to melt and
vaporize the margarine,
and the entire flaming
mixture pours out of
the back of the truck.
-Burning fluids, including
margarine, fuel, and oil,
run down the bottom
of the tunnel,
spreading it more
than half a mile.
[Narrator] Italian operators
reverse the ventilation
to help people escape.
But this unintentionally blows
toxic smoke down the
French side of the tunnel.
Vehicles in the tunnel fail
from lack of oxygen and the
smoke moves too fast
to escape on foot.
39 people are k*lled.
After the fire, the tunnel is
closed for almost three years.
Its safety features
and operations
are completely overhauled.
-There are sensors installed
at the tolls that can detect
if trucks are overheating
even before they
get into the tunnel.
And there's now a new
underground escape tunnel
with a separate
supply of fresh air
that runs the length
of the tunnel.
-One of the key changes after
the fire is that there is now
one fire station
in the middle.
It's overseen by a
single authority.
[Narrator] Disaster can strike
in places we least expect.
On a car journey
through the Alps,
or something as
apparently mundane
as a shopping trip.
Seoul, South Korea,
1995.
The Sampoong Department Store
is a towering bright pink
symbol of South Korea's
commercial success.
It is located in the heart
of one of the city's
most desirable and
profitable locations.
People flock to it.
-The Sampoong shopping center
had been open for just under
six years, and it served
over 40,000 shoppers a day,
bringing in just
under $4 million a week.
[Narrator] June 29th, 1995,
is typically busy.
-There were over 1,000
shoppers in the center,
parking their cars
in the basement,
eating in the food court
on the upper floors
and just shopping in between.
[Narrator] At 5:57 p.m.,
the north wing collapses.
The packed store is
reduced to rubble
in less than
20 seconds.
[honking, sirens]
More than 900
people are injured.
502 are k*lled.
-This was the worst peacetime
disaster that South Korea
had ever experienced,
and it resulted in
police investigations,
multiple arrests,
and a revisit to
government policy.
[sirens]
[Narrator] Using detailed
analysis of the wreckage site,
photographic evidence,
and witness statements
we will digitally reconstruct
the Sampoong disaster
to answer the question
What went wrong?
What do we know about the doomed
wing of the department store?
-Sampoong department store is
a nine-story tall building,
four story in the basement
and five above the ground.
[Narrator] When a building
falls, the foundations that
underpin the entire structure
are always a prime suspect
and Sampoong building
records point to a
possible problem here.
-The Sampoong Department Store
was built on the landfill area.
So it's plausible to
think that the ground was
unconsolidated and
not stiff enough,
and that caused some
problems with the structure.
[Narrator] Is that theory
supported by the evidence?
[Yasmine Aktas] When you look
into the photographic evidence,
there's nothing that suggests
that there was problems
with the foundations.
[Narrator] In fact,
many people only survived
because they were
in the basement.
This suggests that the cause
of the collapse is not
in the foundations or basement.
That is supported by a
critical witness statement
from a security guard.
If the ceiling caves in, the
collapse must begin above.
The building collapses
onto the basement.
It's a miracle anyone
down there survives.
Could there be a flaw in the
design of the entire building?
[Narrator] The collapsed
Sampoong Department Store is
built using what's known
as a flat-slab structure.
-Now, a really common way to
design a multistory building
is to have flat concrete slabs
one on top of the other
that are supported by columns.
And these columns sit right on
top of each other in order to
funnel the loads from the top
of the building straight down
into the foundation
in a continuous way.
-Flat slab construction is
used all over the world.
If you abide by the rules and
if you are careful
with the detailing,
it works perfectly fine.
[Narrator] There's nothing
suspicious about the way
Sampoong is designed.
Could there be a problem
with the way it is built?
One clue could lie in
the evolution of the
building's purpose.
-Sampoong Departmental Store
wasn't initially conceived
as a departmental store,
but it was envisaged
as an office building.
Only after the first
set of approvals,
it was changed as a
commercial building.
[Narrator] The engineering
design of a department store
is fundamentally different
to that of an office block.
For a start, an office block
generally uses elevators,
but a department store
needs big escalators.
They need big holes in
the concrete floor slabs.
These not only weaken the
design, but they require
fire shutters to prevent
fire spreading upwards
through these holes.
These shutters are not
part of the original design.
Fitting them requires
further concerning changes.
-They not only had to take
large chunks of the slabs off,
but they also on
several levels,
they had to trim
some of the columns.
[Narrator] These are the
concrete columns that are
holding the building up.
-These types of alterations
will significantly weaken a
flat slab structure,
but in this case,
they were all
within the bounds of
what was permitted within
the building regulations.
They shouldn't cause the
structure to collapse,
so there must have been
something else going on.
[Narrator] There is another
clue in the history of the
building to what
that could be.
-When it was first designed,
it was a four-story building,
but when it finished, it had
five stories above the ground.
So you have this fifth
floor put on top of
an already weakened structure.
[Narrator]
An entire extra floor,
could this explain the collapse?
According to building records,
the new top floor is intended
to be lightly loaded.
This will reduce the
additional load on the
building beneath.
-In the initial
drawings for the fifth floor.
It shows a roller rink
at that location.
A roller rink, of course, is
a mostly open space with only
the weight of people
roller skating around on it.
[Narrator] But this lightly
loaded design is never built.
-After approval had been
granted, the use changed and
it was turned into
a restaurant floor.
And that's nothing
like a roller rink.
A restaurant, of course,
has tables and chairs,
the people who are eating,
and sometimes some
pretty heavy equipment
in order to provide
those services.
[Narrator] This fundamentally
changes things.
[Luke Bisby] The structural load
calculations for the roller rink
suggested that it would
need to support about one ton
for every square meter.
When it's changed to a
restaurant floor the load
goes up to about one and a half
tons per square meter,
but they don't recalculate,
and that's a very
significant increase in load.
[Narrator] And photographic
evidence from the site reveals
clues that this additional
floor was inherently weaker
than the floors below.
-A big divergence from the
original design was that
the columns were supposed to be
80 centimeters in diameter
with 16 rebars,
but the 4th and 5th-floor
columns weren't like that
when the building was finished.
[Narrator] Rebar is the steel
reinforcement buried inside
the concrete columns.
-Eight of the 16 columns
had been reduced from
80 centimeters diameter down
to 60 centimeters diameter,
and the amount of reinforcing
steel in the columns
had been cut in half.
[Narrator] That decision
has consequences.
-Reducing the column sizes
is going to make
the structure weaker.
[Narrator] The reduced diameter
also means the same load
is pressing on a
smaller ceiling area.
This increased pressure can
lead to the columns literally
punching through
the floor above.
It's known as a
punching shear failure.
And analysis of photographs of
the wreckage site clearly show
this has occurred.
Steel reinforcement was
originally in the floor slabs
that were at right
angles to the column.
But as the column punched
through the floor slab, it has
been twisted through
90 degrees and bent over
against the column.
This is unequivocally
punching shear failure.
Despite all its many flaws,
Sampoong stays up for six years.
What triggers the
actual collapse?
An eyewitness statement from
a cook working in a 5th-floor
restaurant
provides a vital clue.
As he runs into the
emergency stairs,
the ceiling above him collapses.
There is only one thing above
the 5th-floor ceiling,
the roof.
This photograph taken on
the day of the collapse,
clearly shows the beginning
of punching shear failure.
What has made the
roof so vulnerable?
Analysis of aerial
images from 1989,
the year before
Sampoong is opened,
shows yet another unauthorized
change to the design,
AC units.
-They decided to install very
large air conditioning units
on the roof.
And there's no mention of
these in the original design.
[Narrator] The commercial AC
units at Sampoong weigh
15 tons each.
But when operating, they
are filled with water.
This doubles the
weight to 30 tons,
and there are three of them.
-Once the structural plans
were submitted and approved
these units were brought in,
which brought, of course,
considerable additional weight
on top of the structure.
[Narrator] This aerial image
shows the AC units are
originally placed on the
east side of the building.
But images from the wreckage
clearly show them
sitting on the west side.
These massive 15-ton
units have been moved.
Could this be the
trigger for the collapse?
[Narrator] Around
two years before the
Sampoong department
store collapses,
records confirm that the
giant AC units on the roof
are moved following
complaints about their noise.
-These are massive equipment
and they are very heavy.
What they should have done
is to bring a crane,
to lift it very gently and to
put it on the other side.
[Narrator] But that's
not what happens.
Instead, the company move the
AC units by loading them onto
wheels and rolling
them across the roof.
A roof supported on
undersized columns.
And eyewitness evidence
suggests they cannot bear
this concentrated load.
-Large cracks formed once the
AC units were moved from
one part of the
roof to the other.
[Narrator] According to
witnesses, one column under
the AC wheels, column 5-E,
appears to suffer most.
-You have growing
cracks over time,
particularly around
this column 5-E.
The fact that these cracks are
concentrated around one of the
columns could be signs of
imminent punching shear failure.
[honking, sirens]
[Narrator] We can now
piece together the evidence
to explain the
Sampoong disaster.
Around two years
before the collapse,
three 15-ton AC units
are wheeled across the roof.
This over-stresses
undersized columns
on the 4th and 5th floor.
Cracks appear in the roof
slab above these columns.
[Yasemin Aktas] These
cracks are unstable.
The crack width was increasing
with the vibration from these
air conditioning units.
[Narrator] The roof cracks
created by the AC units
continue to grow.
[Luke Bisby] There were multiple
warnings over the two years
following the movement of those
air conditioning units about
cracks in the fifth floor,
but all of these were ignored.
[Narrator] At 5:57 p.m. on
June 29th, the roof fails
by punching shear.
Probably
beginning at column 5-E.
-Then you've got the weight of
the roof, plus 90 tons of
air conditioning unit
that's all moving,
and impacts the floor below.
[Narrator] The main structure,
weakened by modifications for
escalators and fire shutters
fails under the avalanche of
collapsing floors above.
-That then falls down and
continues the pancake collapse
through the building.
[Narrator] It takes less
than 20 seconds for the
entire building to come down.
Thousands are inside.
502 of them are k*lled.
In the aftermath of the
disaster, the truth about
how the building ended
up so badly weakened
finally comes to light.
-A subsequent investigation
reveals that Joon Lee,
the owner of the building,
made these changes to the
construction against
the strong advice of
engineering firms that
were working on it.
Joon Lee is found guilty
of criminal negligence and
sentenced to ten and a
half years in prison.
His son, the CEO, is found
guilty of accidental homicide
and corruption and
sentenced to seven years.
And all told, 12 officials are
found guilty of corruption
as a result of this catastrophe.
[Narrator] The Sampoong
building collapse has a
profound effect
on Korean society.
-The public is shocked
by the catastrophe and
months of protest,
including street clashes,
follow the incident.
A countrywide program of
building investigation reveals
that hundreds of buildings
are in serious violation of
safety and engineering codes,
and several are on
the verge of collapse.
The ultimate conclusion of
the government inquiry is that
only 2% of the high rises
actually meet the safety codes.
[Narrator] The Sampoong
building collapsed
in front of people's eyes.
But some disasters happen
without anyone noticing.
Susquehanna River,
Pennsylvania.
Three Mile Island's giant
nuclear power plant
produces enough energy
to supply 900,000
American homes.
-Since the 1950s, nuclear
energy had been sold to the
American public as this
great source of energy
that would be clean,
and it would be cheap,
and it would be efficient.
Life in the
young and growing nuclear age
will become richer and
more meaningful.
-Nuclear power was going
to revolutionize America.
[Narrator] On March 28th, 1979,
at 4:00 a.m.,
that dream dies.
[reporter] Serious trouble
today at the Three Mile Island
nuclear plant in Pennsylvania.
[Narrator] Operators at the
massive nuclear power plant
lose control of reactor 2.
[Nadia El-Awady]
Three Mile Island is
heading towards disaster.
It's at risk of
entering into core meltdown.
[Narrator] And we know just
how deadly that could be.
[Sascha Auerbach]
Three Mile Island is going
through a process very similar
to what eventually caused
the cataclysm at Chernobyl.
[Andrew Steele] Look at
the area around Chernobyl,
uninhabitable for
decades to come,
and imagine this happening
in central Pennsylvania.
[Narrator] Directly across
the river, are close to 5,000
people living in
Londonderry Township.
[firefighter] Attention please
there has been a state of
emergency declared
on Three Mile Island.
[Narrator] Using
eyewitness statements,
data from the control room,
and the remains
of the damaged reactor,
we will digitally
reconstruct the disaster.
How do things go so
catastrophically wrong?
[Narrator] No one spots the
first signs of disaster at the
nuclear plant on
Three Mile Island.
-Three Mile Island's
problems begin with
something relatively minor.
[Narrator] According to plant
operation logs, it begins in
the unit housing
reactor number 2.
Using data from the accident,
we can digitally dissect
what happens in this
part of the plant.
Operators initially report
a fault with the
feed water pump.
This is part of the system
that generates steam for the
electricity generators by
extracting the incredible
volumes of nuclear heat
from water surrounding
the reactor's core.
According to the logs,
at 4:00 a.m.,
the feed water
pump stops working.
The problem is, cooling water
is absolutely essential
to keep the reactor safe.
-A nuclear reactor is a
little bit like Goldilocks.
It has to be just right.
If you produce too little
heat, then you're not going to
produce steam and you're not
going to drive the turbines.
But if you produce too
much heat, that's even worse
because then you
get a meltdown.
So as long as you keep
extracting the heat as fast as
it's being produced,
everything's fine.
[Narrator] With no cooling
water flowing, the huge
quantity of heat continuously
generated inside the reactor
is no longer being removed.
-Now, by itself, the cooling
water pumps failing shouldn't
have been a big problem.
There are backup pumps.
[Andrew Steele] In the control
room, they could see that
lights had come on saying that
the backup pumps were working,
which sounds like great news.
But unfortunately, although
the backup pumps were running,
the water wasn't
actually flowing.
[Narrator] What goes
wrong with the backup pumps?
-Maintenance records show that
a few days earlier there'd
been some testing carried out
and those test required
the pumps' valves be shut,
and they simply
weren't opened again.
[Narrator] As far as the
control room is concerned
the backup pumps are working.
They have no idea that
the reactor isn't being
cooled down anymore.
-That delicate balance
that's so essential for
a nuclear power station to work,
it's still producing
all that heat,
but it's not being taken away.
This is a disaster
waiting to happen.
[Narrato But there are
multiple layers of
safety systems in the
Three Mile Island reactor.
Why don't those
protect the plant?
According to the plant's logs,
just three seconds after
the pump failure,
pressure and temperature within
the reactor start to climb,
because of the
vast heat being generated
by the nuclear core.
-As the temperature inside
the reactor increases,
the water inside
starts to expand,
and that increases the
pressure inside the reactor.
[Narrator] Excess pressure
is dangerous, so this event
triggers another
automatic safety system.
The plant logs record that eight
seconds after the pump stops,
a safety valve responds to the
rising pressure by opening.
This extracts reactor coolant,
to reduce the pressure
to safe levels.
The log shows that five seconds
after the valve opens
another safety
system is triggered.
-The reactor's control systems
noticed this increase in heat
and decided to
lower the control rods.
And what that means is they're
absorbing some of the neutrons
damping down that nuclear
reaction and removing the
main source of heat
inside the reactor.
[Narrator] These safety systems
are triggered automatically,
exactly as designed, and exactly
as the control room operators
expect in the rapidly
escalating situation.
After 13 seconds, pressure
in the reactor chamber
drops back to safe levels.
The safety valve
has done its job,
and the light indicating
that it is open goes out.
-What we know from the
operators in the control room
was that there was a light on
the control board that they
thought meant that the
safety valve was shut.
[Narrator] But that doesn't
fit with plant records.
They show that the pressure in
the reactor continues to drop.
Yet the indicator light is
telling the operators that
the safety valve that
initiates the pressure drop
is now closed.
But plant schematics tell a
different story about
this indicator light.
-The command has been
sent to the safety valve.
But that light doesn't give
any indication whether the
valve has actually obeyed
that command that's been sent.
[Narrator] The indicator light
tells them nothing about
what the valve itself is doing.
-And that means there's a very
simple explanation for the
fall in pressure.
The safety valve
isn't closed at all.
It's stuck open.
-Three Mile Island is designed
to operate under pressure.
But with the safety valve
stuck open, the coolant was
just gonna boil off.
It's gonna disappear.
[Narrator] Even though the
reactor has shut itself down,
it still needs coolant.
-The reactor's still
producing a residual heat.
It's called decay heat,
and that's gonna
continue for a while
and as long as it continues,
you still need cooling water.
[Narrat The temperature of
the nuclear core is continuing
to rise towards meltdown,
and no one in the plant
or in the nearby town
has any idea that a
nuclear disaster is looming.
-The risk of a meltdown in a
nuclear reactor is so serious
that they created a system
called the emergency
core cooling system
as a backup system that
floods the nuclear reactor
in an emergency
with high-pressure water.
[Narrator] Logs show that as
coolant levels in the reactor
continue to fall, the
emergency cooling system
does start automatically.
But according to eyewitness
testimony, a minute later,
the operators shut it down.
-Shutting down the emergency
cooling system is probably
the single most dangerous
mistake of this whole crisis.
[Narrator] Why do they
turn off such a vital system?
[Narrator] Three Mile Island
is heading towards
nuclear meltdown and
nobody can see it.
-You can't look directly
into a reactor chamber,
and so for the operators in
the control room to kind of
figure out what's
happening inside the reactor,
they have to look at all these
switches and dials and gauges
that they have on
their control board
and put the pieces of
the picture together.
[Narrator] And this
time they get it wrong.
-What they think is happening
is that the water level in
another part of the water
system is rising, and they've
been told never to let
that water rise too high.
So what they do is
they shut down the
emergency core
cooling system
before it pumps in
too much water.
[Narrator] This is, in effect,
the last line of defense
against meltdown and they
have just turned it off.
Eyewitness statements
suggest they then
make the situation even worse.
-Still thinking the problem
was too much water
inside the reactor,
they opened something
called the let-down system,
draining even more coolant
from the overheating core.
[Narrator] Nearly 80 minutes
after the crisis begins,
the control room operators
report loud vibrations
coming from the reactor.
-Banging and crashing noises
are really not what you want
to hear from a
nuclear reactor.
And what's going
on here is that
the reactor coolant
levels have gotten so low
that the pumps are
trying to circulate steam
as well as water and they're
just not designed to do that.
This is now a rapidly
deteriorating situation.
The coolant waters are
catastrophically low,
but the operators just
don't realize it.
[Narrator] Instead, concerned
that the pumps are being
damaged, the
operators shut them down.
-This is terrible because
it means there's actually
no cooling water whatsoever
now getting to the core.
[Narrator] And throughout
this whole crisis,
precious cooling water
continues to escape
from the stuck safety valve.
-Based on the rate of
coolant loss, we think that
sometime around 6:00 am,
so that's two hours after
the disaster started,
the water was getting
so low that it begins to dip
below the top of
the reactor rods,
and now things are
getting really serious.
[Narrator] This is the
beginning of a core meltdown,
exactly what causes
the Chernobyl disaster.
Temperatures in the reactor
are becoming so high that
the nuclear fuel
rods are melting.
-And that means that they
form this sort of horrible
radioactive slag
known as corium,
which starts to
make its way down
to the bottom of
the pressure vessel.
[Narrator] If the white-hot
corium melts through the
steel reactor container,
huge quantities
of radiation could
pour from the plant for years.
-The corium created at the
Chernobyl disaster is still
lethally radioactive 40
years after the incident.
[Narrator] Pennsylvania
is on the brink
of nuclear catastrophe.
At 6:18, two hours and 18
minutes into the crisis,
the control room
finally realizes
the safety valve is stuck open.
By this point, half the
nuclear fuel has melted.
[Sascha Auerbach] Radiation
alarms are going off
all across the site.
The plant operators are
starting to get some inkling
of how serious an
incident this is.
They declare an emergency.
[Narrator] Three Mile Island
is now just 30 minutes
from total core meltdown.
[alarms]
-It's only at this point that
folks in the outside world
start to realize
just how dangerous
the situation is becoming.
[Narrator] There is just one
option left, get water back
into the superheated
reactor at any cost.
The operators finally begin
emergency cooling protocols.
It avoids nuclear catastrophe
by the narrowest of margins.
But restoring a reliable
continuous flow of coolant
takes almost 16 hours.
Finally, the temperatures
in the core start to drop.
-By this time, the interior of
the reactor has been reduced
to 20 tons of radioactive slag
that are resting at the bottom
of the containment vessel.
[Narrator] Reactor 2
has been destroyed.
It will never
generate electricity again.
-We're really lucky it didn't
melt through the pressure vessel
and get out into
the environment.
If it had, it would
have irradiated
hundreds of square miles
of Pennsylvania.
Three Mile Island came
so close to being a
really serious nuclear disaster.
[Narrator] We can now piece
together the evidence
and explain the
Three Mile Island meltdown.
At 4:00 a.m. on the
28th of March,
a pump circulating water from
the turbines stops working.
-The valves on the backup
pumps are closed so they
don't kick in.
The reactor coolant instantly
begins to heat up and
the pressure shoots up.
[Narrator] The rising pressure
automatically triggers a
safety valve to open and
the control rods drop to
shut down the core.
-With the nuclear
reactor shut down,
and the pressure dropping,
the safety valve should shut.
The indicator light is
saying that it's shut,
but in reality,
it's still stuck open.
[Narrator] Cooling water pours
out of the reactor through
the stuck valve.
This triggers the
emergency cooling system.
[Sascha Auerbach] Because the
operators can't make sense of
the indications they're getting,
they shut off the
emergency cooling system.
They think they're
just following protocol.
[Narrator] They then drain
even more reactor coolant.
It a disastrous call.
-Two hours after the crisis
begins, the core starts to melt.
[Narrator] Three Mile Island
very nearly becomes
America's Chernobyl.
-I don't even know whether
it's right to call this lucky,
but this disaster could
have been so much worse.
[Narrator] On the 1st of April,
four days after the
feed water pump stopped,
the crisis is officially
declared over.
The cleanup operation begins.
140,000 people
have fled the area.
[reporter] People who fled
their homes are returning,
and there are even jokes now
including a T-shirt printed
"I'm from Harrisburg
and I glow in the dark."
-The cost of the
cleanup is over $1 billion.
It takes 14 years,
and reactor number two
is a total write-off.
[Sascha Auerbach] The
real consequences that follow
are the disastrous
public confidence hit that
Three Mile Island causes
with regards to nuclear power.
[Narrator] The American public
never views nuclear energy
the same way again.
[Sascha Auerbach] Even though
no one was harmed
in the incident and
no radioactive material
was released, over
100 nuclear power stations are
canceled before
the first brick is even laid.
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01x03 - 3 Mile Island, Mont Blanc Tunnel, Sampoong Mall
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Expert analysis recreates real-world disasters in 3D graphics to uncover hidden causes like paperwork errors, bad glue jobs, or changed restaurant hours.
Expert analysis recreates real-world disasters in 3D graphics to uncover hidden causes like paperwork errors, bad glue jobs, or changed restaurant hours.