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...

The Subway fire that changed fire safety...

Steam heat.

An explosive science lesson under the streets of New York.

How one Canadian shopping mall fell prey to weather.

Billboards. The highest form of advertising.

But when they come down...

...they come down hard.

In a perfect world, this building would be a museum...

And the red trucks inside them would be exhibits.

Fires would be used for positive purposes...

...like keeping our houses warm.

...or cooking our food.

...or campfires on the beach.

But the world isn't perfect...

and that's why we rely on these people.

Because no building is actually fireproof.

The key is to buy people time to get out of danger.

In November of 1987, a fire broke out in King's Cross,

one of the busiest stations of London's Underground.

It was a small fire...

The type easily snuffed out by an extinguisher.

But it was under an escalator.

Firefighters were on the scene in six minutes.

But within ten minutes of the alarm,

the blaze intensified.

A huge ball of fire raced up the escalator shaft

and exploded into the ticket hall

just beneath the street.

Thirty-one people were killed.

Dozens were injured.

What went wrong?

Investigation revealed that a single lit match

had dropped into the machinery beneath

the wooden escalator.

You heard that correctly: wooden escalators were common

throughout the London Underground.

The lit match found a perfect mix of machine oil,

grease and accumulated debris.

This explained the intensification

but not the fire ball.

With temperatures so intense the station clock

melted at 19:45.

Perhaps it was the wind.

Trains moving through the tunnels acted as bellows,

pumping air into the fire.

But even the strongest draught should not have caused

so quick a conflagration.

They looked at the paint in the escalator shaft.

Layer upon layer of paint along the ceiling

certainly burned in the fire.

But it wasn't enough of an accelerant

to explain the fireball.

Firefighters were on the scene in six minutes

and yet that was not enough time to save everyone.

Investigators created a computer simulation

of the escalator and ticket hall

to study the physics of the fire.

They built scale models.

They discovered a new phenomenon: the trench effect.

Researchers used wooden models with the same

exposed surface area, treated each with

one milliliter of kerosene.

...and set on the same 30 degree incline

of the escalator steps.

While gases curled over and over towards

each next step above...

...the metal walls of the escalator

contained the flames and directed them up

the 30 degree slope.

The airflow in the trench increased to such a point

that it created a flamethrower effect...

...in less than three minutes.

The investigation brought about massive change

in the London underground.

First to go were the wooden escalators.

Every wooden escalator in the entire underground network

was replaced with a steel escalator.

Automatic sprinklers and heat detection devices

were installed.

Fire-resistant paint was applied.

And, of course, smoking was banned throughout the network.

One hundred and eight Tube stations

were improved and upgraded.

It's all about buying time...

...something that the victims of the King's Cross fire

didn't have.

Fire-fighting is a science that has evolved with the fires

that occur in a changing urban landscape.

The King's Cross fire started with a wooden match...

...and ended in the discovery of a new fire phenomenon:

The Trench Effect.

As much as we try, the world of construction

can never be 100 percent fireproof.

We have to keep trying to keep it just safe enough

to make our escape...

...preferably before the fire fighters arrive

to get us out.

On a warm Manhattan morning in the summer of 2018,

commuters were making their way across Midtown

when 5th Avenue exploded.

The underground blast blew a 10-metre wide crater

in the street and shot a geyser of white hot vapour

into the sky.

Pedestrians scattered, dodging a hail of asphalt

and debris and chunks of toxic asbestos.

50 buildings in the area were evacuated.

Eight people were injured.

Something in the bowels of the city had erupted.

New Yorkers feared it might be a sewer explosion.

Or a gas leak.

Or even an attack.

Because it felt like a subterranean pipe bomb

had gone off.

And in a way it had.

A steam pipe bomb.

Through the day and through the night,

Manhattan runs on steam.

Heating it. Cooling it.

And using it for hundreds of applications...

from washing dishes...

to making cheese.

Over the last 100 years, thousands of buildings

have been powered by the New York steam system.

Making it the largest in the world ten times over.

Steam is what defines New York's iconic skyline.

These buildings get their heat delivered

from a central location so there are no chimneys

to blight that classic silhouette.

Steam is generated in gigantic boilers at plants

throughout the city, then fed through an underground maze

of steel pipes 174 kilometres long,

threading through the city just 2.5 metres below the surface.

New Yorkers don't give the network underfoot

a second thought.

Until a pipe beneath them bursts like a blood vessel.

So, what happened to cause the rupture under 5th Avenue?

Steam is water as a gas.

When it cools, it contracts back to water.

But that concentration creates a vacuum,

like the plunger in a syringe...

On that day, cold water

from a leak in a nearby water line

leached into the steam pipe.

When that water met and cooled the superheated steam,

the vacuum was so powerful, it sucked even more cold water

into the pipe...

Resulting in a phenomenon called a water hammer.

A water hammer occurs when water under high pressure,

moving at high velocity is contained in an enclosed space -

like an underground steam pipe -

and slams into an obstruction.

It's like the banging on your home radiator.

But much, much more powerful.

It was a water hammer that exploded at the corner

of 5th Avenue and 21st Street.

While there were only a handful of minor injuries,

the primary concern was contamination

by air-born asbestos particles -

which is linked to lung disease and cancer.

Built in the 1930's, the exploded pipe

was insulated with asbestos to retain the heat.

Fortunately, the concentration was minimal

and passersby in the blast radius were hosed down

by fire fighters.

This wasn't the first time a water hammer had blown a hole

through the streets of Manhattan.

There have been a dozen incidents since the 1980s.

Scorching steam, debris and asbestos

have resulted in serious injury and death.

But it's unlikely they'll be replacing 174 kms

of underground pipeline in the near future

and of course New Yorkers remain unphased.

So it doesn't look like the Big Apple

will be running out of steam any time soon.

These days an alarming number of new homes are being destroyed

one drop at a time - in a very short time.

Drowning in water you can't even see.

Because all it takes is a steady trickle

to turn your house into a sodden disaster.

And it's not an act of God.

It's an act of negligence.

Many 21st century developers have responded

to the housing boom by building homes in a hurry,

based on blueprints that cut corners.

Shoddy construction and substandard materials

makes a building vulnerable to water damage.

Pretty soon that new coat of paint is peeling

and the drywall isn't so dry.

A few short years after moving in,

homeowners find themselves stuck in a half-million dollar sponge:

A giant petri dish for growing fungus

and feeding termites

that is literally crumbling around them.

Instead of spending time in their new houses,

homeowners are spending thousands in legal fees

trying to recoup the biggest investment

of their lives.

So why are these new developments

such construction fails?

Water is always looking for a way in.

And contractors use a variety of applications

designed to keep it at bay.

But waterproofing only works if applied with skill,

on structures and surfaces built to code.

Without proper drainage systems rainwater,

and groundwater seep into the foundation,

flooding basements,

causing sewer backups

and carving cracks in the walls.

Faulty downspouts and chimney flashings,

sloppy siding and window seals offer as much protection

from the elements as a sieve.

If pipes aren't insulated, condensation collects over time,

warping floors and collapsing ceilings.

Stucco is the preferred exterior for a lot of new construction.

The coating of lime and cement is sprayed and spackled

onto plywood or Styrofoam sheets.

Stucco is versatile, beautiful -

and a major problem.

Because when contractors cut corners

and don't apply the proper thickness,

the surface cracks, and water seeps in.

Trapped between layers, it rots the house

from the inside out.

But older homes, built of wood and stone

and brick tend to breathe more and dry out naturally.

Ironically, energy efficient construction is more vulnerable

to water damage.

Greener homes are closer to air tight and water tight.

So when moisture gets in - it stays in.

If you look for the early warning signs,

there's a chance you can staunch the flow before it's too late.

On the outside, check for cracks in the slab

and pavement tiles.

Patches of white salty deposits on bricks

called "efflorescence" are a clue

that water is breaking and entering.

On the inside check for spots on the rug

and stains on the walls and ceilings.

Because if you don't pinpoint the problem,

that invisible intruder will turn your house

into a soggy eyesore

long before you've paid off your mortgage.

Shopping malls.

The consumer destination of choice...

One location. Lots of stores.

And a controlled climate.

That's particularly important in cold places

like the city of Elliot Lake, Ontario, Canada.

In this community of 10 thousand along the northern shore

of Lake Huron, temperatures

between December and March are well-below

0 degrees Celsius.

When the Algo Centre Mall opened to the public in 1980,

it soon became a focus for the community,

with a branch of the city's public library.

In 2012, the three-level mall was still Elliot Lake's

principal retail destination.

Providing one-stop shopping ...

...and offering shoppers the convenience

of rooftop parking.

Until June 23, 2012 in the middle of the afternoon...

...when this happened.

A 288-square metre section of the rooftop parking deck

collapsed into the mall below.

The massive concrete slab and the vehicle on top of it

crashed through the upper level...

...and down to the food court, tearing out an escalator

as they fell.

Two people were killed.

Twenty were injured.

[Narrator] As rescue personnel leapt into action...

[Narator] Everyone in Elliot Lake had one question:

What went wrong?

Malls have all sorts of problems.

Some of them are minor.

Some of them are major.

And some are unbelievable.

Water was a problem at the Algo Centre.

Especially for the branch of the Elliot Lake Public Library.

Persistent leaking damaged many books.

Staff had to cover the stacks with tarpaulin.

One café had to close permanently

as customers needed umbrellas as they waited in line.

In 2012, over $120,000 in repair and maintenance work

was conducted.

An engineering report gave the Algo Centre

a clean bill of health.

But the mall tenants knew better.

The evidence was right over their heads.

Were there too many cars on the roof?

CCTV cameras show the roof was relatively empty

at the time of collapse.

Was the roof structure poorly engineered?

Architectural schematics show the structural steel

used in the mall was of the highest standard.

Ultimately, the roof failure was a failure on many fronts.

Winter is particularly harsh in northern Ontario.

It's not just the cold but the snow and the ice.

Streets and parking lots are ploughed

and then liberally doused with road salt

to improve vehicle traction.

But when the snow and ice melt into water,

the road salt drains with it, down to the surface

of the parking lot...

even when the parking lot is on the roof of a building.

The Algo's rooftop would have been plowed

and salted continuously through the snowy winter months.

In 2013, a forensic engineering investigation

found that the Algo Centre collapse was caused

by a two-stage failure.

The welding on a connection joining

structural steel failed due to extensive corrosion.

Three decades' worth of salt ate away at the steel beams.

According to the report, the amount of road salt

was so high it accelerated corrosion rates

to levels only found in marine environments.

But the salt and steel may never have mixed

if not for a disastrous construction decision.

Instead of covering the entire parking lot

with a waterproof membrane,

the mall owners chose an unproven, cheaper method.

The waterproofing company applied a sealant

and polyurethane membrane only at critical joints

in the concrete.

Water leaked through the hollow-core concrete slabs

from the time the mall opened.

By the time of the collapse, it was estimated

that more than 85 percent of the original weld capacity

had been lost to corrosion.

After a massive clean up, the Algo Centre Mall

was demolished in January of 2013.

The new mall that replaced it is just one level.

The public library is there.

Look up.

Look way up.

Since the dawn of the automobile,

the billboard has been there by the roadside,

selling things from high places.

Perched on a rooftop...

or parked on the curb...

Or spread over the side of a blimp.

Billboards can measure thousands of square metres.

High enough and wide enough to be readable from far away...

...and at high speed.

There are almost half a million billboards

lining US highways alone.

That's 19 for every kilometer of highway in the nation.

And there are millions more around the world.

Whether print...

...or digital ...or literal...

...the billboard is a free-standing,

omnipresent sign of the times.

And it's all about catching eyeballs.

But sometimes it is the billboard we cannot see

that quickly catches our attention...

and not in a good way.

This scooter driver had more than a close call...

but walked away...

although without his scooter.

Not everyone is so fortunate.

Fortunately, help was close by and quick to lend a hand.

This billboard fell on two pedestrians...

...everyone poured into street to help.

...even in the pouring rain.

Well-designed billboards are built to last.

Workers drop support poles 10-metres into the ground

and lock them down with poured concrete.

Much of the steel pipe frame

is bolted and welded together off-site,

then assembled on location -

stretching as high as 30-metres in the air.

But even a strong base can be overwhelmed by a strong wind.

A 70km/h gust can turn a billboard

into a destructive sail...

...a three-sided sail.

This wreckage was once a giant billboard...

This tower supporting this billboard stayed standing.

But the billboard itself became a warning

about the danger of wind.

The unspoken message on every billboard should read:

"Watch out".

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