08x42 - Flashover

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NARRATOR: In a crowded London Underground station,

a small routine fire suddenly erupts into a deadly inferno

and kills people.

Dozens more are injured.

A team of forensic experts searches for clues

to the cause of the blaze and finds

that the fire seems to defy the very laws of physics.

To unravel because of the mysterious fire,

investigators would need to recreate

the historic train station inside a modern computer.

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NARRATOR: The sprawling London Underground

is the largest and oldest subway rail system in the world.

But on the evening of November th, ,

commuters are unaware that disaster lurks beneath them.

At : PM, a passenger at the historic King's Cross Station

sees a flicker of flame underneath the heavily

varnished -year-old wooden escalator.

The London Fire Brigade is dispatched.

It seems to be a routine call.

ROGER KENDALL: An everyday call to a fire in an escalator

is something we were receiving probably or times

a month.

So it was no big deal.

NARRATOR: Fire captain Roger Kendall, one of the first

to reach the scene, waits above ground

for his supervisor to report.

ROGER KENDALL: We were waiting for message to come back

to say that we're all going home or we

may need a bit of equipment.

NARRATOR: Trains continue to come and go,

despite the minor commotion.

Musician Ron Lipsius arrives at the station

on one of those trains.

RON LIPSIUS: We noticed these two men.

I don't think they were in uniform,

but they were blocking, physically blocking,

the entrance to the wooden escalators on our left

which are the ones that directly go to big daily train.

So we thought, oh, that's strange.

And it was actually a tiny bit hazy in there, too.

We noticed that too.

Little bit smoky.

NARRATOR: Firemen see a small fire burning

about halfway up one of the escalators

bringing passengers from the tracks up to the ticket hall.

MICK HAMER: A very experienced fire officer looks down

the escalator and assessed the fire as being,

it was about the size of a cardboard box.

NARRATOR: But firefighter Colin Townsley spots something

he believes is dangerous.

He calls firefighters above ground

asking for more equipment and saying, people are in danger.

ROGER KENDALL: He, through his experience,

had seen something going on above the fire,

around the fire.

Whatever he could see, he knew that something

bad was about to happen.

NARRATOR: On the train platform below,

passengers are now being urged to get out.

The quickest escape route is up another bank

of escalators near the fire.

These two lead directly to the ticket hall.

RON LIPSIUS: As soon as we got near the top,

we noticed it was really dark and smoky.

At that time it was this policeman

with a flashlight saying, hurry up, don't just stand there.

NARRATOR: But the warning comes too late.

RON LIPSIUS: As soon as I went through that turnstyle,

some kind of expl*si*n happened.

When I was halfway up that escalator, a sheet of flame

erupted and sh*t across the top of the hole

at the top of the exit from that escalator,

so I was just moving up towards a wall of fire.

NARRATOR: Searing flames rip up the escalator

and into the ticket hall, incinerating

everything in their path.

RON LIPSIUS: There were like these

living things up in the corner by the ceiling,

and they were huge.

It was awesome.

And I just took one look at that thing

and I just, I felt like an ant.

And I felt like this thing is like a monster.

ROGER KENDALL: It was just a complete rush

of thick black smoke from the subways, right all

the subways leading out onto the main roads around the station.

And it was right at that moment we realized

that a flashover had occured.

NARRATOR: Flashover is a virtually

instantaneous spread of fire.

Everything flammable ignites simultaneously.

MICK HAMER: So for two minutes, it

had gone apparently the size of a cardboard box

to a major disaster.

NARRATOR: Firefighters tried desperately

to get inside the station but are driven back

by the intense heat and smoke.

ROGER KENDALL: The firefighters were collapsing

left, right, and center.

The heat down there had make some of them

urinate themselves with fear.

And when they came out onto the top,

they weren't capable of moving again.

A lot of them were collapsing in the heat.

NARRATOR: Ron Lipsius stumbles into the chaos outside

and for the first time realizes he is badly b*rned.

RON LIPSIUS: I looked at my hands

and there was this skin just handing down like when

a snake sheds its skin.

NARRATOR: Firefighters battle the blaze for an hour.

When it is finally out, people are dead

and more than others are injured.

Among the dead is firefighter Colin Townsley.

ROGER KENDALL: Colin was found with two members of public

that he'd obviously pulled along the tunnel trying to get them

out to safety, two people that he'd obviously tried

desperately to get out of that inferno

and it cost him his life.

NARRATOR: The King's Cross Station is shut down.

The London Underground is crippled.

Thousands of commuters are stranded.

Through the smoky haze of the ruins, a mystery emerges.

Why did a fire the size of a cardboard box

explode into a deadly inferno in a matter of seconds?

In the hours following the deadly King's Cross fire,

investigators from England's Health and Safety Executive

sifted through the charred station looking for clues.

But finding them in the ruined ticket halls and tunnels

wasn't easy.

PROF.

DOUGAL DRYSDALE: There is nothing quite

like seeing a fire scene first hand

to give you a full appreciation of the devastation that has

taken place, and also to give you a feel for how

the fire may have developed.

NARRATOR: They needed to answer two critical questions-- what

sparked the fire, and how could it appears so suddenly

and erupt into a fatal blaze the claimed lives?

Nearly a million people relied on the underground each day.

They needed to know if the system was safe.

MICK HAMER: This is the stuff of nightmares, being

trapped by fire underground.

I mean, it really is something that tugged at the heart

strings of ordinary Londoners.

It was on the front pages of every newspaper,

obviously, for several days.

And there was enormous demand to find out why it had happened.

NARRATOR: Investigators started where the flames were

first spotted-- the escalator.

This was the lowest point of the fire,

indicating the fire had started there and b*rned upward.

No accelerants or other indications of arson

were found.

Underneath the escalator, investigators

found accumulated grease, litter, and debris--

ideal fuel for starting a fire.

They also found evidence of many previous small fires

started by smoldering matches and cigarettes.

PROF.

DOUGAL DRYSDALE: The actual source of ignition

is assumed to be a dropped match which

had not been extinguished.

And if that had come in contact with the grease on the running

track of the escalator, the grease would

have ignited very, very easily.

NARRATOR: Investigators speculated

that someone on the escalator lit a cigarette

and carelessly tossed away a burning match.

But could one match cause such a deadly fire?

MICK HAMER: They tried dropping matches from heights.

They found that a match would be able to,

in certain circumstances, to light

the grease on the escalator.

NARRATOR: But in the test, the fire was slow burning

and didn't explode up the escalator.

ROGER KENDALL: There was all sorts of theories

as to how this could have happened so fast.

And amongst those theories, everyone was desperately

searching for the truth.

NARRATOR: Meanwhile, journalists uncover

dozens of previous escalator fires

in the London Underground.

MICK HAMER: To some extent, the Undergrounds have been

extremely lucky for years.

They had a lot of these wooden escalators.

They all suffered from similar problems.

There had been a series of escalator fires.

It was reasonably predictable that there

was going to be a serious one.

NARRATOR: After a fire two years earlier at another station,

investigators said the system's aging wooden escalators were

a disaster waiting to happen.

But why did this fire turn into a deadly inferno?

ROGER KENDALL: There was a lot of thought about the trains

actually finding the flames, because it was extremely clear

whenever a train came into that station

that the smoke that was billowing out of the subways

[inaudible] would increase.

NARRATOR: But measurements of air flow in the escalator area

showed this would not affect a small fire on the steps.

Other theories blamed the varnish

on the wooden escalator and multiple layers of paint

on the ceiling.

PROF.

DOUGAL DRYSDALE: There are examples

of fires in old buildings in the UK

which have been painted regularly,

every three or four years.

And these buildings are a hundred years old.

And if the paint becomes involved,

it becomes an inferno very, very quickly

because paint delamintes, blisters, and burns rapidly.

SUZANNE SIMCOX: When they did some tests, when the agency did

some tests on ceiling paint, some of it that was not

damaged, they couldn't make the flames

spread fast enough along it.

And that's when they started to question what

else could be the main fuel.

And that's when they came to talk to us to see if we

could do anything to help.

What do you think of these results, [inaudible]

NARRATOR: Investigators now turn to a team

of forensic mathematicians at the investigative firm of CFX.

Their goal was to create a computer

simulation of the deadly fire using computation fluid

dynamics, or CFD.

This was the first time it would be applied

to the behavior of fine.

But they believed it would work because heat and air flow

like fluids.

IAN JONES: The hot causes the fluid to expand

and it makes it lighter, and then

it tends to rise relative to the other ambient fluid around.

And so then you see smoke rising, smoke plumes.

And that's the kind of thing that we can simulate

with the software, because it really

is just simple fluid mechanics.

NARRATOR: But could it solve the mystery

of the King's Cross Fire?

To recreate the deadly King's Cross fire in a virtual world,

the station was measured and mapped onto a computer grid.

Then factors such as the fire's point of origin, air

flow, and types of wood and paint

we're added to the simulation.

But the results showed something unusual.

According to the computer model, the King's Cross fire

had literally defied the laws of physics.

This little bit of hot temperature--

NARRATOR: The hot air around the fire did not rise.

Instead, it clung to the steps.

SUZANNE SIMCOX: We saw that the hottest air seemed to be lying

down in the escalator trench.

Which was unexpected to me, anyway, and the other people

from HSE who came to look at those early simulations.

I think the initial reaction was it was possible

that I'd got gravity upside down, which

you can do in the computer.

So maybe I'd made things go the wrong way.

IAN JONES: Was it a human error?

Could we have input data incorrectly?

Could there be a bug in the program?

NARRATOR: Investigators entered all the data again.

The results were the same.

SUZANNE SIMCOX: We did all the checking and did more runs

and still found that the hottest air was lying down

in the trench, eventually spiraling

up over of the ceiling, but initially

lying down in the trench.

NARRATOR: It was a startling but significant clue.

The hot air and gases should have risen up to the ceiling.

But the escalator stairway appeared to channel

them into the ticket hall.

SUZANNE SIMCOX: And that made us stop to think about, maybe

they wood of the escalator could be the main feel.

If the flames are lying down in the trench,

they're preheating the wood ahead of the main flame front.

And therefore, once it gets going,

it could move very, very rapidly.

NARRATOR: They called what they saw the trend effect.

But it was merely a theory using untested computer simulations.

And it was inconsistent with typical fire behavior.

PROF.

DOUGAL DRYSDALE: If you have a fire burning in the open

on a flat surface, the fire feeds itself with air by

drawing it in from the outside.

It's created by the dynamics of the flame itself.

The buoyant gases rise, creating slight pressure

differences which draw air in at a low level.

NARRATOR: But on an incline, that airflow is

restricted on the uphill side.

To examine this, is a rough model,

/ of the size of the escalator shaft,

was placed flat on the ground.

The result was a slow vertical burn.

But at a degree angle, the angle of the King's Cross

escalator, the flames leaned into the shaft at an angle

and raced upwards.

In the confined trench, the fire can only draw air

from below, creating a draft.

SUZANNE SIMCOX: Because the air can't come around the fire.

It has to come, effectively, through the fire.

NARRATOR: Investigators then ran a bigger

test on a / size model of the complete King's Cross Station.

If the trench effect worked this time,

it would prove their theory was right.

IAN JONES: In the matter of three or four seconds,

the flames went from the upright to being,

lying, along the escalator trench.

And from then on, it was just as we'd predicted,

which was very gratifying.

NARRATOR: It was clear that the previously

unknown phenomenon called, "the trench effect" was real.

IAN JONES: People suddenly saw a fire and said,

now we understand.

We had an explanation of what it is.

It's now all obvious.

It fits together.

The jigsaw fits together perfectly.

NARRATOR: The investigative team now

had compelling evidence that would reveal

the deadly sequence of events.

For months, a government inquiry into the disaster the King's

Cross Station fire had struggled to find

out how a small fire had exploded so quickly

and k*lled people.

Now a team of forensic experts said new computer technology

provided the answers.

IAN JONES: The computer graphics helped us to understand what

had taken place, and also to present the results to people

who were maybe not as familiar with the technology

that we were using.

So we could explain the results to them very simply.

NARRATOR: Sometime around : PM,

a smoker at King's Cross carelessly

dropped a match on the wooden escalator.

The match fell between the steps and the side of the escalator

into the gear bead, below.

It was lined with years of grease and debris.

A slow burning fire began.

At : PM, the flames became visible

and underground staff called the Fire Brigade.

At : PM, two firemen saw the low lying flames

and at first assumed it could be easily extinguished.

PROF.

DOUGAL DRYSDALE: The fireman who was walking down the escalator

number six and looked across to escalator number four,

approximately one minute before flashover,

and described the fire as being a relatively small.

NARRATOR: But then the fire spread across the steps,

the bottom of the trench.

It can only draw oxygen from one direction, from below.

This was the trench effect.

PROF.

DOUGAL DRYSDALE: And once you'd established a fire

across the width of the escalator it meant

that the flames were deflected into the trench

and began to flow up the treads, the risers,

and exposing the balustrades to very high levels of heat flux.

IAN JONES: Then it just switched and flips over

to stick to the floor of the escalator trench.

From there it's preheats the wood,

the hot gases are-- go up the escalator

trench ahead of the flame.

They're heating the wood quite considerably,

gets quite hot even though there's no flame there.

SUZANNE SIMCOX: It's sucking up the air

from below like a chimney wood, which is what it needs to do.

And that would tend to flatten the flames down

in the early stages as well, which would start this effect

off, of the trench effect.

NARRATOR: The escalator trench acted

as a chimney made not of brick, but of highly flammable world.

At :, a torrent of superheated gas

rushed up the escalator, priming everything in its path to burn.

SUZANNE SIMCOX: It was called a flashover.

The sudden movement of the fire up the escalator

was called the flashover that burst into the booking hall

at the top.

NARRATOR: The hot gasses and flames exploded into the ticket

hall, feeding off years of thick paint on the walls

and three tons of varnished wood on the escalator below.

The cavernous room was a death trap.

ROGER KENDALL: Those people would

have d*ed extremely quickly.

And if there's anything-- if there's any comfort there,

it is the comfort that they didn't

suffer very, very long at all.

They were taken extremely quickly.

NARRATOR: The government's board of inquiry

accepted the new science of the trench effect

and found it had caused the disaster.

MICK HAMER: There was a general sense amongst people

that really, the Underground should

and could have prevented this.

I mean, there were resignations, of course.

But I think there was a sense that the Underground

hadn't really been on top of the problem of fire underground.

NARRATOR: To ensure such a tragedy would never happen

again, all wooden escalators were eventually

removed from the system.

Flammable, grease, and debris are regularly removed

from beneath escalators.

And the Underground staff is now required to be trained

in fire evacuation procedures.

Those directly affected by the fire

can take some comfort that science explained the mystery

that changed their lives.

RON LIPSIUS: It ruined the life that I was having.

My life was going a certain way, I was perfectly happy with it.

And it totally ruined that life.

But I-- I got on to a different life.

ROGER KENDALL: I-- I don't use the Underground.

I haven't used the Underground since that night

at King's Cross.

I'm not saying it's not safe, because I believe it's

far safer now than it ever was.

But for me, personally, I'm happy to avoid it.

NARRATOR: Those who solved the mystery of the King's

Cross fire know their intensive efforts will help save lives.

IAN JONES: There's also a plaque in the booking hall to memory

of the people that d*ed then.

I often just stop there and stand

and read it and just spend a quiet moment in reflection.

Because there was a human tragedy

there, which is sometimes is-- can easily be forgotten.

So I feel strange going back there.

And a little shiver.

SUZANNE SIMCOX: I enjoyed seeing the computer model be used

in a way that was good, so people could understand

what had happened and therefore try

and prevent it happening again.

PROF.

DOUGAL DRYSDALE: It's opened a whole new line of study

on flame spread that perhaps we've

taken much longer to achieve if we haven't had

the experience of King's Cross.

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