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...

a super-sized collapse at an under-construction supermarket.

Amusement parks deliver adrenaline-pumping attractions,

but these pyrotechnics aren’t part of the plan.

A brand-new light rail system goes off the rails.

Is there a light at the end of the tunnel?

It's a swing and a miss for the roof construction

of this baseball stadium.

Hurricane Milton: 1, Tropicana Field: 0.

41 construction workers trapped in a catastrophic collapse.

Their rescue requires tunnel vision.

Big construction projects mean big stakes.

The holes are deep.

Any sign of weakness in foundation

can fill them right back up.

The materials are heavy.

One swing and a miss can undo all the work that’s been done.

The cranes are tall.

So, it’s a longer way down when they fall.

And the risks can be at an all-time high.

When a big construction project goes down,

it makes a lot of noise.

That's what happened in Florence, Italy,

in February of 2024.

A sprawling construction site

spanning more than 100,000 square feet

was primed for a new beginning.

The site was a former bread factory,

like this one, abandoned in the 1970s.

The land was slated for redevelopment.

With plans to create green space, bike paths,

and a brand new 27,000-square-foot supermarket.

The project was well underway with the first three floors

of the supermarket under construction

when a giant concrete beam put a 15-ton wrench in the plans.

The heavy beam plunged down, destroying the floors below it,

claiming the lives of five construction workers

and leaving three injured.

So what went wrong?

The answer may be buried in the rubble.

A first look revealed a structural collapse

of the concrete beam.

The question is why did the beam collapse?

Investigators had three avenues to explore:

installation, manufacturing, and design.

Maneuvering a 15-ton beam in midair is no easy feat.

Did something go awry during installation?

To lift heavy stuff, you need heavy duty machinery,

like cranes and forklifts.

Specialized clutches, hooks or shackles

attach to the lifter of choice using chains and slings.

Larger elements are moved into place,

and beams are connected to columns

that are secured to foundations.

Whether you're working on a building or a bridge,

when big concrete beams are involved,

one wrong move, and the whole thing can go sideways.

The installation company that worked on

the supermarket construction in Florence

claims that the collapsed beam was anchored

and securely in place well before the catastrophic fall.

Yet, somehow, that beam gave way.

It's possible that the joint where the beam meets the column

didn’t hold properly.

But the analysis of the materials could not prove that.

Another theory suggests workers from a different company

began pouring concrete in the area directly above,

upping the weight that the beam had to support

before it was properly secured to handle the load.

Too many cooks in the kitchen can lead to chaos.

Way too many cooks in the kitchen

can lead to catastrophe.

Investigators uncovered that 61 subcontracted companies

were authorized to work on the construction project,

raising concerns about the impact of subcontracting

on workplace conditions and safety.

Big companies save big bucks by subcontracting

many small businesses

willing to do the same work for less pay.

But when you cut corners,

the quality of work may not be the same.

Following the collapse, labor unions went on strike

to protest the subcontracting system,

claiming shortcuts to work conditions,

safety and training are to blame for the tragedy.

As investigators looked into these allegations,

they also pursued the possibility

of another set of shortcuts--

manufacturing defects.

The collapsed 65-foot-long beam was made of concrete,

the most heavily used material on the planet,

second only to water.

Concrete can withstand a lot of compressive force

that squishes the material together.

But it's weaker under tensile stress,

which stretches the material.

This is why concrete beams are often reinforced

with steel rods.

Combining the two materials

makes one very strong structure.

Reinforced concrete beams, like the one that collapsed,

are commonplace in modern construction.

What’s newer in the industry is prefabrication.

Many of the elements in this construction project

were prefabricated.

In other words, a lot of the concrete pieces

that make up the building, like columns, beams and walls

were produced in an offsite factory.

These structural components are then transported

to the construction site where they are put together

like a jigsaw puzzle

to suit the architecture of the building.

This way of building has gained popularity in some countries.

Like Sweden, where prefabrication accounts

for about 80% of construction.

And Japan and New Zealand,

where it accounts for about 20%.

In fact, some of the most recognizable buildings

around the world are made of prefabricated concrete,

like the shell roofing of the Sydney Opera House

in Australia.

These prefabricated systems are said to expedite construction,

minimize waste, and reduce the risk of accidents onsite.

Well, maybe not the last one, at least not in this case.

Evidence initially pointed to a design error.

Investigators thought the shelf the beam rested on

might have been the wrong size,

therefore, couldn’t support the weight.

They were on the right track.

A design error was responsible for the collapse.

But the reason behind it was different.

The final report revealed the load that the beam

had to support was miscalculated.

As a result, there wasn't enough steel

reinforcing the beam, so it couldn’t handle the load.

This isn't the first supermarket to collapse

as a result of a design miscalculation.

In 2013, Riga, Latvia, experienced

one of its greatest tragedies

when the ceiling of a supermarket collapsed,

injuring dozens and claiming 54 lives.

The tragedy was a result of an error in calculating

the maximum load the roof of the building could withstand.

The roof had been weakened by a fire

during the building’s construction in 2011.

Five people were charged

for violating construction regulations

and criminal negligence in the 2013 tragedy.

In Florence, the government is planning stricter rules

around subcontracts in construction.

Up until the early 19th century,

the best equipment for cutting your grass was this.

Since then, lawn mowers have become a staple

in every DIYer’s garage.

The cutting-edge technology has really evolved.

People using that technology,

not so much.

Some people advise against cutting your grass too often

because lawn mowers can contribute to air pollution.

What could they possibly be talking about?

With the modern lawn mower, you can even go hands-free.

Or feet-free.

No reason to get grass stains on your new kicks.

You can tow it behind your scooter.

And why stop with just one of these babies

when you can have triplets?

And if you're inclined,

it doesn’t have to be a hill to die on.

This mowing method's called rope on a slope.

If you order now, this one comes

with this handy handle-extender option.

And for those harder-to-reach spots,

add this deluxe excavator option.

Allow six to eight weeks for delivery.

Some assembly required.

Excavator option not really included.

Not everybody’s cut out for cutting the grass.

This greener's first lesson took a left turn,

and then another left turn,

then a turn for the worse.

[laughter]

Good thing you don't need a license

to operate these things.

This guy would’ve totally flunked on parallel parking.

This moonwalker thinks he's auditioning

for "So You Think You Can Mow."

Everybody knows there's no grass on the moon,

so just beat it.

He couldn't cut it in the circus,

so instead, he cuts lawns for a living.

This lawnmower got tired of being pushed around and bolted,

heading for the open road.

This one would've gotten away, too,

if the owner hadn’t tied it up.

Lawn mowers come with all sorts of high-tech features.

But anti-gravity wheels isn’t one of them.

[slide whistle]

So buckle up.

And don’t forget that roll bar.

♪ Rolling, rolling ♪

♪ Rolling on the river ♪

Evel Knievel just called.

He wants his lawn mower back.

Gentlemen, start your mowers.

And they’re off!

The Lawn Ranger takes the lead, cutting through the pack.

Ooh, Sodbuster’s in the pit with a clogged carburetor.

And it's Bladerunner, mowing down the competition

and heading for the checkered flag!

[siren]

Sorry, Officer, was I speeding?

Any way you want to maintain lawn and order,

there’s a mower to do the job.

But if you can't cut it,

your field of dreams could become a nightmare.

Maybe we really were better off with this.

[baa]

[Narrator] Amusement parks are engineering marvels.

Super-sized dreamlands

jam-packed with thrills and spills

that’ll make your head spin and your jaw drop.

The phrase "emotional roller coaster"

exists for a reason.

Anxiety, fear,

relief, joy.

You can go through a whole arsenal of emotions in seconds.

But this dreamland can become a nightmare just as fast.

Sometimes, what goes up can come down.

Locomotives can go loco.

Mechanics can malfunction,

and human error can cost human lives.

That's what happened at Liseberg,

an amusement park in Gothenburg, Sweden.

The park opened its doors in 1923

and continues to draw big crowds

with 3 million visitors a year.

It’s one of Scandinavia’s biggest amusement parks,

and was about to make an even bigger splash

with a new water park extension.

Oceana was scheduled to open in summer of 2024

and deliver 14 thrilling water attractions,

including Europe's first six-person raft ride

and the world’s biggest mega drop.

But what happened next was more of a mega flop.

The plans for Oceana went up in smoke

the morning of February 12, 2024.

A water park catching fire

might sound like a contradiction,

but that's exactly what happened at Liseberg.

A waterslide was swallowed by flames.

22 people were injured and one person was killed.

So what went wrong?

Amusement parks are jam-packed with mechanical monsters

and mammoth machinery.

Fires can break out for all kinds of reasons.

In May of 2018, Germany’s gargantuan theme park Europa

went up in flames thanks to a technical malfunction

that began at a water attraction.

The fire broke out in a large building

and spread to nearby attractions.

Police estimate about 25,000 people were evacuated.

It took 250 firefighters to extinguish the fire.

No injuries,

but millions of euros went up in smoke.

But the Swedish fire involved a different malfunction.

The water park wasn’t even up and running yet.

It was still under construction.

Building a water park is no walk in the park.

It requires a lot of hydraulic and structural engineering

to bring these massive water attractions to life.

The slides are often made out of formed fiberglass pieces

that fasten together like sections of a toy racetrack.

These segments rest on a framework of steel girders.

To zip down a slide, you need a constant stream of water.

Most waterslides pump water from a collection pool

up a narrow pipe to the top of the slide.

The water runs down the slide

and the cycle continues

back up the pipe again.

It was these pipes that Oceana's construction workers

were installing when the slide set ablaze.

Preliminary findings suggested that the fire

could have started

when the water pipes were being put together.

Investigators believed the pipes were incorrectly mounted

causing them to overheat during welding.

The final report confirmed that the fire started

when the water pipes under one of the slides

were being welded together

using a process called electrofusion welding.

The method involves heating up and melting the plastic pipes

together using an electric current.

If done incorrectly, it can lead to overheating

and start a fire.

Investigators believe the fire spread

from the welding of the pipes to the waterslide,

then raged into the surrounding buildings.

Speaking of welding, in May of 2024,

just three months after the Gothenburg inferno,

flames erupted at this amusement park

in Gujarat, India.

The fire erupted on the ground floor.

CCTV footage shows a spark coming from welding work,

which then ignited flammable foam sheets stored nearby,

fueling the blaze.

The fire was off to the races when it came into contact

with 396 gallons of go-kart fuel.

Fun turned to fear fast, as more than 150 visitors

tried to escape the burning building from a single exit.

The uncontrolled fire engulfed the entire structure.

The tragic incident resulted in at least 27 deaths.

Ten people were arrested.

Improper storage of flammable materials,

insufficient firefighting equipment,

and inadequate evacuation routes

were just a few of the problems

officials uncovered in the investigation.

As for Gothenburg's giant new water park, Oceana,

the rebuild continues with new technology implemented

on the slides to ensure fire safety in the future.

[Narrator] Transit infrastructure is

one of the most important things a city can build.

It defines how its people move every day.

Get it right,

and you can get 11 million people where they need to go

on time 99.9% of the time,

as demonstrated by Hong Kong’s robust public transit.

But get it wrong,

and the whole thing can go off the rails,

as many cities around the world can attest to.

Canada's capital, Ottawa, joined that list

on September 14th of 2019.

When the city launched its new Light Rail Transit system,

LRT for short.

Nearly eight miles of electric rail line

servicing 13 stations.

A decade in the making

with a running tab of more than 9 billion Canadian dollars,

it was the most significant and the most pricey

infrastructure project Ottawa’s ever taken on.

The LRT was nearly 580 million dollars over budget

and 456 days late

when it finally opened its doors to the public.

Trouble is, the doors didn't seem to want to close back up.

But a few jammed doors were just the tip of the iceberg.

Deformed wheels, failing computers, derailment,

tracks that don't switch,

faulty overhead powerlines.

These trains just didn’t seem to want to leave the station.

Light rail? More like light fail.

So what went wrong?

In December of 2021, the Ontario government launched

a public inquiry to find an answer to that question.

For nearly a year, Ottawa's problem-plagued LRT

was under a microscope.

Millions of documents were combed through,

and 90 witnesses were interviewed.

Turns out the LRT’s had a bumpy ride from its very conception.

In its planning phase, instead of adapting existing vehicles--

the easier route-- new trains were designed,

using untested technology.

The construction phase wasn't exactly

full speed ahead either.

Sinkholes, tunnel collapses,

and numerous construction delays plagued the project.

When the LRT finally entered its testing phase,

that wasn’t a smooth ride either.

In fact, the trains performed so poorly,

the city had to lower its approval criteria.

But all this background information

was withheld from the public.

Commuters were learning about the LRT's problems

as they happened, via other passengers on social media.

The first month alone saw more than 15 delays

of half an hour or longer.

Some were a result of software quirks,

like automatic doors that jammed up,

requiring a system reboot,

which took trains offline for as long as an hour.

Other delays stemmed from bigger systemic issues,

like problems with power supply.

Electric trains move thanks to a suspended wire system

that powers the train through a pantograph,

an arm-like fixture on the roof,

connecting the train to the wires overhead.

An electric train can’t move without power.

Seems like light rail construction 101.

Yet power problems took several trains out of commission

in the first few months of service.

What was supposed to be the crown jewel of Canada's capital

quickly became a capital pain in the [ding].

The system’s growing pains were more painful than expected.

And Ottawa's frustrated commuters

were forced to roll with the punches.

Until wintertime served up a knock-out.

Ottawa's temperature can dip down

to minus 27 degrees Fahrenheit in the winter months.

Electric switch heaters froze up,

preventing trains from switching tracks.

And the wheels of the train became deformed

under cold weather conditions and extensive braking.

Unfortunately, the trains,

designed specifically for North American winters,

were never tested in a North American winter.

Issues continued into summer with trains stalling, breaking,

and eventually derailing.

On August 8th of 2021, a train derailed

at Tunney's Pasture station,

shutting down service for five days.

Transportation safety investigators determined

that one of the wheels came off the axle

thanks to a faulty bearing.

The component meant to reduce friction

between the wheel and the axle did the opposite,

stressing the nut and causing it to unscrew.

As a result, the entire fleet was grounded for inspection

and reassembly of the parts involved.

But some bolts keeping the wheel components together

were not adequately torqued during refurbishment.

On September 19th,

after only about 500 miles of service,

another train derailed.

A gearbox from one of the wheels

was found near the tracks.

The gearbox runs power from the motor to the drive wheel.

It's usually connected to the wheel with this axle.

But that wasn’t the case.

The lack of torque during refurbishment

caused all 12 bolts to fail, resulting in derailment.

Years later, many kinks, like switch problems,

continue to get worked out.

And the expansion of Ottawa's LRT system is now on hold

for at least 25 years.

[Narrator] It’s one of the oldest metals,

believed to be in use for more than 6,000 years.

It’s an element on our periodic table.

Lead.

Malleable, durable,

resistant to leaks and corrosion.

In recent times, the versatile metal

has become a household name in construction.

It made our paint last longer,

weatherproofed our roofs,

protected our electrical power cables,

made up the piping of our plumbing systems,

and much more.

[Newsreel] Humble lead also plays its part

in preserving and protecting old and new buildings

in the form of white lead.

[Narrator] Its usefulness around the house seemed endless.

But so was its toxicity.

Ailments attributed to lead use

date as far back as ancient Rome.

Roman architect Vitruvius made the connection,

noting "Water should not be brought in lead pipes

if we desire it to be wholesome."

Yet lead became almost synonymous with plumbing.

The very word "plumbing" comes from the Latin term for lead--

plumbum.

Lead companies touted the benefits of using the metal

in plumbing, promising superior sanitation and better health.

And boy, did people buy in.

The same companies promised white-lead paint

would prolong the lives of their houses.

Little did we know, it may have been cutting lives short.

By 1980, reports estimated that the United States

was using more than a million tons of lead each year.

That’s 40% of the world’s supply.

The US may have been the leading producer

and consumer of refined lead,

but this metal was a staple in construction worldwide.

Some lead use was slowly phased out in the late 1900s

as its detrimental effects became more widely understood.

But most major bans on lead use didn't happen

until the late 20th century.

By the 21st century, its use in household items

like paint and pipes became limited or banned altogether

in at least 84 countries.

Deteriorating lead-based paint in older homes

across North America and Europe

is one of the leading causes of lead poisoning.

While in more than half of the world's countries,

leaded paint is still in use today.

Traces of lead in drinking water

is another leading cause of poisoning.

Many older homes have lead pipes.

It's impossible to see, taste, or smell lead

dissolved in water.

Testing is the only way to know

if the water in our home contains lead.

Lead can enter our water through in-home pipes,

lead solder at the joint,

faucets, fixtures, and fittings,

and lead service lines.

There are more than 9 million lead service lines

still providing water

to communities across the United States.

In 2020, up to 50% of European homes may have had lead pipes.

In other parts of the world,

including Africa, Asia, and South America,

little information on the use of lead pipes is available.

It'll take time and effort to replace lead

as a construction material

throughout our homes and businesses.

But it seems we're finally on the same page

as at least one ancient Roman.

Trucks are society’s workhorses.

We count on them to transport everything we need

to build our homes,

get things to the construction site

and make those deliveries.

Unless they don’t.

Because all it may take is a pothole,

or it could be pilot error,

and that precious cargo ends up scattered

on the highway to hell.

This right turn is about to go horribly wrong.

When this one takes a left turn, it left its load behind.

This dedicated driver does not take his work lying down.

Oh. Wait.

While the neighborhood's sleeping,

this garbage truck drops off the trash,

so it can pick it up later.

It’s the perfect business model.

This probably isn’t the best spot for a comfy couch.

That mattress is made of memory foam.

So it’s never going to get over this trauma.

This parking lot has a steep incline

and a built-in learning curve.

So what have we learned?

Always strap in the cargo-ho-ho! There it goes.

[Narrator] Tropicana Field,

a one million-square-foot stadium in Florida

opened its doors to the public in 1990,

becoming best known as the home

of the Tampa Bay Rays baseball team.

But in October of 2024,

the stadium was being transformed into an area

of refuge for thousands of emergency workers.

Another major hurricane was on its way: Hurricane Milton.

Residents prepared their homes against flooding,

securing sandbags in entryways.

Businesses boarded up doors and windows to prevent destruction.

This wasn’t their first rodeo.

Just weeks prior, Hurricane Helene touched down

in Florida, devastating several coastal communities.

Florida is often hit during hurricane season.

And Hurricane Milton was anticipated to be a big one.

The system was predicted to hit the Gulf coast,

including the Tampa Bay area, home to more than 3 million,

an area that's evaded a direct hit from a major hurricane

for more than a century.

Officials prepared for the worst,

opening shelters,

stocking up on food and supplies

in community centers,

and lining Tropicana Field with cots

for first responders and clean-up crews.

♪ ♪

No one anticipated the stadium

would become a major part of the cleanup.

So what went wrong?

Originally named the Florida Suncoast Dome,

the stadium structure was built completely

from precast, prestressed concrete,

a stronger concrete, formed under stress,

cast in reusable molds,

then transported to the construction site.

The building was made up of more than 7,000

of these concrete components weighing over 50,000 tons.

The stadium was sheltered by a fabric roof

made of Teflon-coated fiberglass,

kept taut with cables connected by struts.

Opposing forces from a tension ring in the center

and a compression ring around the perimeter

kept the roof in an arc.

It was the first cable-supported dome

of its kind in the United States,

and the largest in the world.

It took six acres of Teflon-coated fiberglass fabric

and 180 miles of cable to construct the roof,

and minutes for Hurricane Milton

to nearly tear the whole thing down.

Yet the dome was built to withstand hurricanes.

Along with reducing construction and cooling costs,

its slanted roof was intended

to protect the stadium from hurricanes

and withstand winds of up to 115 miles per hour.

Hurricane Milton made landfall on Florida's west coast

with 120-mile-per-hour winds,

qualifying it as a category 3 hurricane.

There are five categories based on windspeed.

Category 3 and higher are considered major hurricanes.

Reports estimated winds at 100 miles per hour

by the time Hurricane Milton reached St. Petersburg.

Tropicana Field was built to withstand this kind of wind.

[Onlooker] The whole roof is coming off the Trop.

[Narrator] So why didn’t it?

It appeared a smaller tear in the roof may have formed

and the wind made its way under the dome.

Once that happened, the material didn’t stand a chance.

The high wind combined with the damaged fabric

are the likely reasons the roof fell apart.

The fabric was 34 years old.

Turns out Teflon fabric has a service life of about 25 years.

So this roof was nearly a decade past

its best-before date.

The oversight isn’t exactly a home run for the Rays.

With no drainage system in place,

the bases were loaded with rainwater.

The storm dumped down as much as 18 inches of rain.

Much of the city was ravaged with damage to buildings,

downed trees, even a downed tower crane.

The construction crane broke apart and struck the building

across the street, home to the Tampa Bay News.

The newspaper broke their own story.

Luckily no one was injured.

Across Florida, many weren’t so lucky.

The hurricane claimed at least 42 lives

and an estimated 34 billion US dollars in damage.

The stadium sustained substantial water damage.

But both the building and the dome's supports

remained structurally sound.

The price tag for repairs

sits just under 56 million US dollars.

The Tampa Bay Rays plan to play ball here again in 2026,

under a new roof.

[Narrator] Tunnels come in all shapes and sizes.

Some are used for mining, some carry water and sewage,

others provide passage for transportation.

The blueprints may look different,

but the dangers of constructing these complex infrastructures

are similar.

If these tunnels come crashing down,

there may be nowhere to run.

That's what happened in Uttarkashi, India,

in November of 2023,

when the Silkyara tunnel collapsed,

trapping 41 workers inside.

The town of Uttarkashi

sits at an altitude of 3,800 feet above sea level,

surrounded by the Himalayas.

Tunneling in this geographically complex area

is a tough job,

made tougher by the scale of this project.

The tunnel in Uttarkashi

is part of an ambitious 1.5 billion-dollar construction

of a Hindu pilgrimage route to better connect

northern India's four sacred towns

via 550 miles of road.

The 43-foot-wide tunnel was designed

to accommodate two lanes of bi-directional traffic

along nearly three miles of road.

The construction was moving along well.

The tunnel was only 1,400 feet from completion

when it suddenly collapsed,

putting 200 feet of debris in front of the only way out.

With no emergency escape, the 41 workers were trapped.

So what went wrong?

A drill-and-blast method was used in the construction

of the Silkyara tunnel.

It's exactly what it sounds like.

Holes are drilled and explosives are placed inside

to blast away the rock.

It’s a centuries-old, tried-and-true mining method.

Once the rock is blasted away,

a ventilation pipe rids the tunnel of dust.

Loose rocks are dislodged using excavators,

and the rubble is removed.

With the area cleared out, workers assess the tunnel.

Sometimes a technique called reprofiling is required.

This work involves repairing any cavities

created by drilling and blasting.

The reprofiling process commonly backfills

and reinforces those areas using wire meshing.

Reprofiling work was happening

on the day of the catastrophic collapse.

Underground tunnel collapses like this one

in India's district of Himachal Pradesh,

pose an immediate threat to the workers inside.

From flooding...

to oxygen shortage,

a lot can go wrong.

India's government agencies combined resources

launching an immediate operation

to get the 41 workers out as soon as possible.

200 rescuers were involved.

An expert called it the toughest tunnel rescue

he’s ever encountered.

Choosing the right strategy

for this geologically fragile area took time.

Options included drilling through the debris

to insert a horizontal evacuation pipe,

vertical boring for an exit route from the top,

or tunneling through the remaining 1,400 feet

on the other side.

But first, several smaller lifeline pipes were installed

to transfer essentials

like food, water, and cell phones

while the 41 men waited.

Rescuers decided to go through

the collapsed part of the tunnel.

Excavators cleared the way.

On day five, a powerful horizontal boring machine

called the auger was used to expedite the process.

The auger can drill at a rate of up to 16 feet an hour.

After numerous setbacks,

mere hours from reaching the trapped workers,

on day 14, the auger drill broke down 39 feet short

of breaking through to the workers.

On day 16, the rescue team decided to use

a controversial method called rat-hole mining

to get through the mining debris.

The technique involves digging through narrow tunnels

that typically fit just one person.

Hence the name, rat hole.

Though the method was deemed unsafe and banned in 2014,

the practice is still employed in some areas of India.

In 2018, 15 miners were trapped in an illegal rat-hole mine

in Meghalaya in northeastern India and had to be rescued.

Ironically, rat-hole miners were the rescuers

in the Silkyara tunnel incident.

Due to the fragility of the tunnel,

experts felt a manual approach was best suited.

When the rat-hole miners finally dug their way

through the rubble,

an evacuation pipe was inserted to get the men out.

On November 28th, day 17, all 41 men were rescued.

The workers and their rescuers were greeted

with flower garlands as they emerged from the tunnel

one by one.

But the focus soon shifted to the cause of the collapse.

It's no secret that this region of northern India

is deeply impacted by the fragile geology

of the Himalayas.

Flash floods and landslides

plague the area’s road infrastructure.

Initially, investigators attributed

the Uttarkashi tunnel collapse to the area’s geology.

The rock here varies in strength.

In some pockets, there's hardened rock,

while in others, the rock is soft enough to crumble.

It's possible there was a section of weak rock

that water seeped into, eroding away that area

undetected during the construction of the tunnel,

ultimately leading to its collapse.

Further investigation confirms that the tunnel was being built

in an unstable area, with weaker rock,

prone to crumbling.

It also reveals negligence in the tunnel's design

and execution, highlighting a disregard

for the area's fragile geology

and compromising workers' safety

by not providing an escape route.

Before construction continued, the Silkyara tunnel underwent

an assessment to ensure standards were met.

The relationship between India's infrastructure

and its geology is a complex one.

Conservationists have long advised against

major construction in the ecologically fragile Himalayas.

It seems the Silkyara tunnel collapse may have prompted

the highway ministry to listen.

India's highway authorities plan to embark

on a nationwide inspection

of all tunnel construction projects across the country.