Original subtitles

[Narrator] Construction. Heavy machinery.

Tight schedules. Millions at stake.

What could go wrong? Everything.

Whether it's faulty equipment, poor design, human error...

or just bad luck...

...these are...

Construction fails.

In this episode...

Cantilevered buildings.

An architectural delight that defies gravity...

...until it doesn't.

G Forces:

When a ride comes to a sudden stop...

all that power can turn against us.

Chimneys.

We don't notice them... until they stop working.

High employment.

Whatever you do, don't look down.

They are some of the most exciting designs

in modern architecture.

Floating in the air.

Defying gravity.

Cantilevered structures are a visual delight,

especially for the architects who design them.

But for the structural engineers

who have to make these concepts concrete,

the cantilever design presents challenges

other buildings do not.

The cantilever is like a diving board.

It's meant to flex slightly as the load changes.

But if the load is too great, the cantilevered structure

will fail and fall.

Which is what happened at this mall in Mexico City.

The Artz Pedregal Mall opened its doors in March of 2018.

Less than four months later,

the cantilevered portion of the mall collapsed.

Luckily for everyone concerned,

the problem was detected early in the morning.

The overhang was noticeably sagging.

The building was evacuated and the nearby expressway

was closed to traffic...

All anyone could do was watch...

and wait.

So, what went wrong?

It may have been natural causes...

In fact, the root of the collapse

could stretch back 5000 years.

That's when a massive volcanic eruption

poured molten lava into the valley

where Mexico City now stands.

Volcanic rock makes an unpredictable base for building.

But what happened at the mall

may have more to do with corruption than eruptions.

Substandard building practices

have long haunted the Mexican capital.

Major earthquakes in 1985 and 2017

put the city's structures to the test...

And many failed badly.

The city also has notoriously poor subsoil conditions,

and developers often build on unstable land.

But whether the cause was natural, supernatural

or simply criminal,

the Artz Pedregal cantilever failed the stress test.

It all comes down to what structural engineers call

'the moment'.

The moment is the amount of stress on a joint

caused by weight along the length of the joint.

Think of an arm holding a five kilogram weight.

The moment is the force within the elbow...

The more the arm is outstretched

the more force on the moment.

In a cantilevered building,

the 'moment' is a crucial design metric.

On a short cantilever,

like the balconies on this tower,

the moment is low.

But the Artz Pedregal's moment was high.

Get the moment wrong and you'll need a new building.

Investigators of the Artz Pedregal incident

said a support beam failed in the upper floors

of the cantilevered section.

In other words, the moment changed

and the force of gravity

was transferred to other elements of the building.

Elements that were pushed past their limit.

According to news reports,

the cause of the collapsing cantilever

may have been hiding in plain sight.

Right here: The roof garden.

Investigators said the planters used in the roof garden

added excess weight that apparently contributed

to the collapse.

The solutions are simple: A deeper foundation

would have given more support to the building.

If they had built stronger weight-bearing

and structural beams, and had an accurate idea

of the appropriate amount of weight on the cantilever,

it's unlikely it would have failed.

With the development of new building techniques

and materials, the cantilever design

is increasingly popular.

But just so long as engineers remember

to stay in the moment.

Amusement parks.

Designed to thrill.

The long slow climb up to the top...

Then the sickening moment as gravity takes its grip

at the crest...

And then comes the drop...

We have an expectation that these rides will amuse us.

We strap ourselves in.

We trust in the machine to deliver us safely to earth.

It's a leap of faith.

But no matter where in the world you are,

amusement rides can fail.

This bone-chilling incident happened in western India.

This one in the Philippines.

This incident occurred in Thailand.

These people escaped serious injury.

Many of these failures are not investigated.

But this one was.

The Fireball.

The Ohio State Fair, July 2017.

The Fireball, a ride that spins a gondola at high angles,

breaks apart.

One person is killed.

Many are injured.

So, what went wrong?

Amusement parks have been thrilling us for centuries.

But the accent was on amusement not fear.

In fact, the original roller coaster

was intended as a wholesome distraction

from the sinful saloons of 19th century New York.

Designed by LaMarcus Thompson, the "switchback gravity railway"

opened in Coney Island in 1884.

That first roller coaster is quaint

compared to the monsters of today.

Higher.

Faster.

And more dangerous.

The names say it all.

Leviathan.

Mindbender.

Fire Ball.

Some amusement park riders will experience over six Gs.

That's what an F-16 pilot will feel during a climb.

And double what an astronaut feels at lift-off.

With all the hurtling metal in action,

the risk to life and limb is sobering.

According to the US Consumer Product Safety Commission,

more than 42,000 people were injured at amusement parks

in the United States in 2018.

Most amusement parks are temporary.

It seems intuitive that a machine

that is constantly dismantled and moved

comes with added risk.

But in fact, according to the CPSC,

most deaths and injuries occur in permanent

or fixed-location amusement parks.

In the Ohio State Fair incident,

the Fire Ball ride had been in operation for 18 years.

Over those years, rainfall led to an accumulation

of water inside the support beam.

Weakened by prolonged corrosion,

the interior support beam of a gondola

failed under centrifugal force and broke off.

The company recommended detailed inspections

of gondola support beams and joints

on all similar rides.

It also developed a new support beam

that reduces water pooling

and the likelihood of corrosion.

In this incident, the left platform worked

as designed but the rope holding the right car snapped,

causing the platform to free fall

for the last six metres.

In Thailand, national police inspected the ride

the day after the accident.

The locking mechanism holding the safety bar

seemed to be defective.

But there was no conclusive evidence

as to what caused the failure.

Sometimes riders have to save themselves.

Forty people were stranded dangerously high on this ride.

One of the passengers pulled out his mobile phone

and called the fire department.

Everyone made it down safely.

42,000 injuries a year sounds like a lot.

But considering how many millions

visited amusement parks in the US,

the chances of being hurt are vanishingly small.

You're statistically more likely to be injured on the drive

to the amusement park than on any of the rides.

But that's cold comfort to terrified fair-goers.

Currently, accident statistics do not track

whether certain rides are more problematic than others.

Industry watchdogs have called for a database

that correlates injuries with specific rides

so that one day riders can make the call themselves.

If you're afraid of heights, you might want to turn away.

If high places make you dizzy,

you simply have a healthy respect for gravity.

Some people get high for a living.

Others do it for fun.

For some people there is no explanation...

Installing an air conditioner on the outside

of the building takes a special kind of cool.

No harness required.

Just a pair of slippery socks and a death wish.

Doesn't this guy realize how dangerous this situation is?

Every time his air conditioner breaks down

this high-flying handyman crawls out onto the ledge

to take his life in his hands.

Judging from his blasé attitude

the heat has already gotten to him.

It takes nerves of steel

to work without harnesses or safety gear.

And a very good sense of touch...

Especially in your feet.

How many city employees does it take to change a lightbulb?

When it's this streetlamp at least two -

and a few more safety precautions

might help them both make it to the end of their shift.

When this repair person's safety rope snapped,

he managed to hang on for dear life

until the firefighters dropped by and threw him a lifeline.

This 67 Kg man is using a 43 Kg bucket

as a counterweight.

Let's hope nobody does the math

until he's safely back on the ground.

These happy workmen look like kids in the playground

swinging on the monkey bars.

Except they're not kids.

And that scaffolding is 30 metres up.

Scaling these skyscrapers to keep them shiny takes guts

and a commitment to cleanliness.

Dangling from a single rope hundreds of metres in the air,

these window washers are squeegee-wielding superheroes.

But this wireless window washer

is putting cleanliness before common sense.

The risks of working at such heights is amplified

by the power of wind.

These window washers had a terrifying ride

when their platform turned into a kite

more than 200 metres in the air.

Luckily, the windows were not only clean but strong.

These workers confronted a different

but equally deadly force

when their platform touched a powerline.

Happily for them, a rescue team safely reconnected them

to a solid structure.

There are no bicycle lanes on this commute.

So when you're installing high-voltage power lines

in a remote area, the wire is the road.

This is an entirely different kind of commute.

It redefines the notion of strap-hanging.

But when there isn't a crane high enough

you need to hop on a chopper to get to the office.

This one's located at the top of a transmitter tower.

And when you work in the sky you can't just head

to the pub for a meal.

These electric techs are having a cold lunch

even though they're sitting on enough power to BBQ

a entire herd of cattle.

Up here there's no break room for a midday snooze.

This strap 'n nap technique is safe enough -

as long as nobody sleep walks.

These guys are adding markers to the power cables

to make them more visible to low flying aircraft.

Just don't drop your wrench.

So the next time you plug in your toaster,

think of the heights workers go to getting power to your home.

It's a high wire act fraught with peril.

Early humans discovered fire over a million years ago.

It took another 999,000 years to come up with the smoke alarm.

[beeping]

And still, there are half a million urban fires

every year in the U.S. alone.

This office tower fire in China's Shanxi province

sent pillars of flame and plumes of black smoke into the air

before it was completely consumed.

This Chicago bakery blaze burnt more than the bread

in this four-alarm fire.

So what caused these buildings to go up in flames?

Common causes for fires include everything

from overloaded wiring to unattended candles.

But that's not why these buildings went up in smoke.

Ironically, the thing that torched

25,000 American homes last year

was the very thing that's supposed to prevent a fire.

The chimney.

Unless you're a fat man in a red suit,

most people don't spend too much time thinking

about their chimney.

But they should.

Their lives may depend on it.

Because where there's a fire, there's smoke...

and carbon monoxide.

Venting these toxic gasses is essential.

The first chimneys were made of wood and straw,

coated with clay...

Making them equal parts convenience

and fire hazard.

Trial and error led to the modern chimney,

built from fire-proof bricks and lined with a metal flue.

With all that fireproof material

why are there still so many chimney fires?

The flue that lines the chimney

acts like an exhaust pipe.

If it's installed properly - like this -

smoke will vent freely up and out the chimney top.

But if it is not fitted properly - like this -

the flue can get blocked,

hot gas can collect in the chimney

until it needs to escape.

It was a flue like this one

that lit up the Shanxi skyscraper.

A blocked chimney won't draw.

It creates an anti-draft.

Air flows the wrong way, venting smoke into the room,

tossing sparks that can quickly turn your flammable rugs

and furniture into kindling.

If wildlife, like racoons or pigeons

are nesting in your chimney

that can also cause obstructions and trigger a blaze.

And a chimney fire is no way cook squab.

The most common culprit behind a chimney fire

is also the most sinister.

Burning unseasoned wood in a poorly maintained chimney

can generate a buildup of creosote.

The tar like substance coats the chimney lining

and acts like high-combustion fuel when ignited.

But you won't know even know it's there until you hear

the low rumblings of a chimney fire.

Blocked and ill-fitting flues, fueled by creosote and neglect

add up to 25,000 chimney fires a year

in the US alone.

So when it comes to taking care of your chimney,

you can either do the maintenance

or keep the fire department on speed dial.

Because you don't want to heat your home

by burning it down.

In the construction world monster machines

do amazing things every day,

making light work of dredging rivers,

delicately demolishing towers,

and even saving sites from fire.

They are here to serve, and they know who's boss.

In fact, far from being frightening,

when constructions fail,

these monsters can be lifesavers.

This worker was investigating signs of smoke

in a half-finished apartment when the building erupted

into an inferno, trapping him

on a fifth floor balcony.

In a do-or-die decision, the man drops to the balcony below

as a rescue crane heads toward the building.

Reaching out, man and machine connect.

The crane retreats from the building with only seconds

and centimetres to spare.

A heart-stopping moment later the burning roof collapses

in a swirling firestorm.

[Voice] They got him! They got him!

[Narrator] When this home became engulfed in flames,

the only escape was out the window,

luckily this friendly neighbourhood crane

came to the rescue.

The crane arm boomed in, threw in a line,

and while the man hung on,

gently lowered him to safety like a giant metal bird.

He owes this guy a beer.

And his life.

When homes and businesses flood...

Machines take their rescue efforts out of town too.

This front-end loader carried a bucket-load of travellers

across a raging waterfall during Monsoon season.

Seems less like a rescue

and more like a water park attraction.

The seats are uncomfortable, but the view is stupendous.

Trapped on a bridge.

This excavator became an elevator

after a passenger pulled the alarm chain

in-between stations -

and automatically stopped the train.

Next stop, ground floor...

Actually, just the ground.

So, if you're ever in trouble you want to hope

there's a heavyweight construction hero nearby.

As they will go above, below, and beyond the call of duty

to come to your rescue.

[Voice] They got him.

♪ ♪