Kind: captions
Language: en
On October 23rd, 2018, thousands of
football fans were making their way to
the game in Rome. Excitement for the
game was high, and the fans began to
chant and sing. At 7:03 p.m., around 50
people were riding the long escalator
down to the platform. But within 30
seconds, the crowd had swelled to nearly
double that. Everything seemed fine, but
inside the escalator was a problem.
The weight of the passengers was bearing
down on the steps and the load on the
main motor was increasing. To try to
slow the descent, the motor applied a
counter torque. But as the force
continued to increase, the stairs began
to move faster. By 7:04 p.m., the crowd
had tripled. The motor finally reached
its limit, and under the massive strain,
the drum began to slip. With the motor
losing control, the escalator triggered
its second line of defense. A safety
relay tripped immediately, cutting power
to the motor. The main brake clamped
down on the metal drum to stop the
descent of the stairs,
but
it failed. The friction on the main drum
wasn't enough to stop the motor from
spinning, and the stairs continued to
accelerate.
Assensing the motor had lost control of
the steps, the escalator engaged the
last line of defense. In the event of an
emergency, an auxiliary brake is
designed to bypass the motor entirely
and directly lock the drive shaft.
Under normal circumstances, the chance
that all three safety measures fail at
the same time is vanishingly small. But
these weren't normal circumstances. At
7:05 p.m., the third and final safety
system failed, and the stairs began to
plummet. Fans were flung forward and
started streaming down the escalator.
Some leapt over the central barrier in
desperation, while others were swept
into a crushing pileup. At the bottom,
the landing became a dangerous choke
point. Under the pressure, the steps
twisted and buckled into jagged metal,
leaving 24 people injured. Something
like this shouldn't have been possible,
and experts at the time knew that
something had gone wrong, and they
started to suspect foul play. In the
aftermath, Rome's transit agency sealed
off the accident site and closed the
Republica station for several months.
The authorities ordered both a technical
and a criminal investigation, and the
mayor even publicly vowed to discover
the cause of the accident. So,
investigators began dismantling the
wreck, tearing it down piece by piece to
reconstruct what had happened.
The ride people experienced on that
escalator was one of the most terrifying
rides of their lives. But maybe it's
more similar to the origin of escalators
than you might think. Like what was the
first escalator even used for? Do you
want to have a guess?
[Music]
It was an attraction in a theme park all
the way back in 1896. It had no steps, a
25° incline, and it was essentially just
a slow conveyor belt made of metal and
wooden parts. It brought people up a
full 7 ft before they would have to walk
downstairs on the other side. And it was
a huge success. Over 75,000 people
enjoyed the attraction during its 2e
stay at the old Iron Pier on Coney
Island. The ride was named the
continuous elevator and its inventor,
Jesse Reno, had created it not just as
an attraction, but as a proof of concept
because he saw it as the future of
transportation.
[Music]
But as Reno watched people ride his
invention, he began to notice a pattern.
Nobody walked. Instead, they stood
still, feet planted firmly sideways with
people gripping the handrail tightly.
Two years later, the department store
Herods in England installed a similar
device. But the ride was so unsettling
that Herods had to put staff at the top
to offer brandy to men and smelling
salts to women just to calm their
nerves. You see, for both devices, the
25° conveyor belt was precarious to walk
on and unnerving to stand on. At around
12°, walking on an incline becomes
difficult, and 25° is roughly the limit
that our ankles can flex.
If only there was a way to replace the
conveyor belt with a moving set of
stairs. Well, then the riders would
always have a flat surface to stand on
and a staircase they could climb if they
wanted to.
One attempt at a solution had already
been around for four decades, and it was
called the revolving stairs. It
consisted of a chain that went around a
loop. Then fixed stair-shaped blocks
were attached to it, creating a flat
surface to stand on during the main
incline. But as soon as you'd reach the
top, the steps tilted forward, making it
treacherous to get off. And a similar
problem plagued you at the bottom. Now,
you might think, if the top and bottom
are causing problems, just extend each
landing. But that also doesn't work. You
just end up with a jagged mess for
longer. So, how do modern escalators
solve this problem? I mean, have you
ever stopped to think, what happens to
the stairs at the top of the escalator
when they disappear? Clearly, we have
steps going around in some sort of loop.
But how do they actually behave on the
return journey? What if I give you two
options? Do they stay right side up like
the cabins in a ferris wheel? Or do they
flip upside down and then flip back
again at the other side?
>> I'm gonna go this one all day.
>> Ferris wheel.
>> This one makes more sense.
>> Ferris wheel.
>> Yeah, this one.
>> I think they turn upside down.
>> And they're actually right side up.
>> I think I'm going to go with
>> Wow, you're both.
>> The solution to this problem came from
another inventor named George Wheeler.
His idea forms the basis of every
escalator in use today. A modern version
of it works something like this. A
typical subway escalator has an electric
motor at the top with a power output of
around 50 kW, smaller than most electric
cars. This motor spins extremely fast at
over 1,000 RPM, but it's pretty weak.
So, to drive the steps, the escalator
needs to convert this into a slower
output with more force. To do this, it
uses a reduction gearbox and a gear
system, lowering the output to just a
few RPM and increasing the torque by a
factor of around 100.
The motor is connected with a large
sprocket to a reinforced steel chain
which pulls the stairs around a loop.
The so-called step chain is fitted with
wheels to allow it to roll smoothly
around curves. But unlike the design for
the revolving stairs, Wheeler proposed
attaching each step to this chain
through a single axle, giving it the
freedom to rotate.
Next, he added a second set of wheels to
each step that followed a different
track, allowing him to control the angle
of each step at any point. On the
incline, the two tracks overlap, just
like the revolving staircase, but then
at the top, the two tracks separate, and
this is what allows us to keep the steps
level throughout the entire ride. The
tracks then remain separated and curve
around. The steps flip upside down, tuck
into the loop, and start their return
journey. At the start of the incline,
the tracks rejoin and the whole process
repeats.
[Music]
>> So, the answer is you were both wrong.
>> Oh my god.
>> Oh,
>> yeah.
>> Wow. I never really thought about that.
>> Yeah. Like, like I would say it's like a
upside down elevator, bro.
>> Like,
>> guess what? You're right.
>> Yeah.
But despite all modern escalators
adopting Wheeler's design, at the time
it caught so little attention that he
was forced to shove the idea. It wasn't
until 8 years later that another
inventor, Charles Seabberger, bought his
patent and capitalized on the invention.
Seabberger partnered with the Otus
Elevator Company and together they built
a prototype.
A year later, in 1900, they showcased it
at the Paris Exposition Universal.
In total, 51 million people flocked to
the exposition to see the marvels of
modern technology. But one of the most
popular exhibitions was the world's
first true commercial escalator. The
machine drew huge crowds. French
historian Philipe Julianne described it
as the jolliest attraction at the
exhibition and wrote, "The escalator
caused many an incident worthy of the
vaudeville, separating families, sending
old men sprawling, delighting the
children, and reducing their nana to
despair." The escalator was even awarded
one of the grand prizes of the fair.
Shortly after, escalators started being
installed in different places across the
world.
But these escalators weren't perfect.
They had smooth, flat stairs, and when
they reached the top, these stairs would
disappear under a wooden board, leaving
a dangerous gap between them. Shoelaces,
coats, and especially the long skirts in
fashion at the time easily got caught in
the machinery. One incident even saw a
three-year-old girl getting her foot
pinched in the gap. And while the girl
luckily escaped with injured toes and a
missing shoe, something in the design
had to change. To solve this,
Seabburgger and Otis installed a
triangular shunt at the end of the
escalator, forcing riders to go off to
the left before they reached the
dangerous gap. This system worked, but
it was awkward because it meant people
had to put one foot onto solid ground
while the other was still moving, which
became especially tricky when some
people stood still and others walked.
So, to reduce the risk of people getting
in each other's way, operators asked
people to stand on the right and keep
the left lane clear for faster walkers.
It's a convention we still often follow
to this day. But, as it turns out,
there's a much better solution than the
shunt.
Modern escalator steps aren't smooth,
they're grooved. These grooves then
interlock perfectly with a comb plate at
the top of the escalator. So now, if a
small item approaches the end, the comb
plate lifts it up and out of harm's way.
This makes it much harder for things to
get stuck. And perhaps more importantly,
it allows people to safely step off
forwards.
But the comb plate doesn't entirely
solve the problem. We still have these
gaps on the side of the escalator that
can pinch and trap objects as the steps
move. So to address this, a new safety
feature called the skirt brush was added
to the escalator in 1982.
Escalators are full of subtle safety
features like this. Some old and some
new, but almost all of them are designed
around people. All the way back in 1896,
Jesse Reno predicted that riders on his
attraction would need something to hold
on to. So he introduced a moving
handrail. In a modern escalator, the
motor has a separate connection to turn
a friction wheel that drives the
handrail. The only problem is that
friction wears things down. So over
time, the wheel gets smaller and as its
circumference decreases, each rotation
moves the rubber loop a slightly shorter
distance. So the handrail begins to move
more slowly. The effect is small, but it
builds up over time. So to compensate
for this, a new handrail is calibrated
to move around 2% faster than the steps.
You can actually try this yourself next
time you're standing on an escalator.
Just place your hand next to you as you
stand still, and you will watch as your
hand slowly drifts forward. This speed
difference stops the handrail from
lagging too far behind the steps over
time. Because I because I have
definitely noticed that that sometimes
I'm on an escalator and then it's going
faster than me. My hand is going faster
than my body.
But that means it's a new escalator.
>> Well, it's a it's a new frictional
wheel. That wheel that drives the hand
crater. So it's
we don't replace we don't replace the
entire escalator.
>> Oh wow. So So that's like a party trick
I can use to entertain my friends. I
mean I don't know when I'd have a party
on an escalator, but whatever. If I'm on
an escalator with my friends and I can
see it moving, I'd be like, "Hey, that's
because there's a new frictional wheel."
I can that's like I can tell them that
and impress them.
[Music]
But it's not just the handrail. The
speed of the steps themselves is also
something that needs to be carefully
controlled. Modern escalators use AC
induction motors, which are extremely
good at regulating their rotational
speed. And this has an unexpected
benefit on downward escalators.
With enough people riding, their weight
is enough that the motor no longer has
to power the ride. Instead, the weight
of the passengers themselves drives the
chain and causes the motor to spin. As
more people board, the force on the
motor increases and it's pushed to turn
faster. But modern AC induction motors
work by creating a rotating magnetic
field. When the motor tries to spin
faster than the field, electric currents
are induced inside it, which then create
their own magnetic field. This new field
pushes back in the opposite direction to
the spin, creating a breaking force
which resists the increase in speed.
But something interesting happens when
the motor resists like this. Rather than
consuming energy, the physics of the
motor flips and it uses the excess
mechanical energy to produce an electric
current. This is called regenerative
braking and it's the same trick that
electric vehicles use to recharge their
batteries. In effect, the motor turns
into a generator. The result is that on
a busy day, many modern downward
escalators aren't just moving people,
they're actually generating electricity.
Often, this is channeled back to the
building's internal grid and used to
power other devices, including the
upward escalators.
>> So, even the escalator that was uh like
invented by George Wheeler and was
installed in 1920
uh at the Paris exhibition, etc. I mean,
all these escalators were regenerated.
What?
>> Yeah. When there were people standing on
the escalator in down direction, these
escalators were feeding energy back into
the bridge.
>> No, it's like the down escalator is a
generator.
>> This regenerative braking makes
escalators extremely power efficient.
But more importantly, it makes them
inherently safe. But there is a point
where if you keep adding weight, then
eventually the force becomes so strong
that the motor can no longer resist it.
And if left unchecked, it would start
accelerating uncontrollably. The stairs
would go plummeting down, which is
exactly what happened in Rome. After a
nearly 2-year long investigation, the
investigators published this 86-page
report. Inside, it lists the exact
sequence of events that led to the
disaster. As fans crowded onto the
escalator, their combined weight
increased the load on the main motor.
The motor tried to resist this change,
but as more and more people funneled on,
the force got too high and eventually it
hit a tipping point and the motor
started accelerating uncontrollably.
Safety sensors in the machine noticed
this sudden change and triggered two
things in short succession. First, the
power to the motor was cut, and
immediately after that, the main brake
engaged. Two massive arms clamped down
on the drum to lock it in place and
avert a runaway.
This brake should have had enough
stopping power to bring the fully loaded
escalator to a halt, even under the
massive strain, but it didn't. Tests
after the incident showed that its
braking force was far too low, around
37% of the manufacturer's specification.
The weakened brake struggled to slow the
spinning motor and the escalator's
downhill acceleration continued.
This is when the last line of defense
kicked in. When the escalator's speed
rose by more than 20%, the auxiliary
brake triggered, driving steel wedges
into a disc on the drive shaft. But when
investigators opened up this brake, they
were shocked. The final mechanical back
stop had been partially disabled.
Someone had physically tied plastic
straps around one of the two brake
wedges and rendered it useless.
With half the system unable to engage,
its stopping power was cut by 50%, just
enough for the weight of all those
passengers to overpower the brake and
render the last line of defense useless.
Investigators knew that these failures
should have been automatically recorded
in the error logs, but when they went to
check, they found nothing. The error
codes had been turned off, meaning
critical malfunctions could occur
without leaving a trace. The only way
this could happen was if they had been
disabled on purpose, meaning someone
must have reprogrammed the system to
stop recording fault codes.
Next, investigators turned to the
maintenance records.
But they found these similarly
incomplete and evidence of major work on
the escalator was nowhere to be found at
all.
With all the main safety systems
compromised and critical alerts turned
off, the escalator had been a ticking
time bomb. All findings from the
technical investigation pointed not to a
manufacturing defect, but to a pattern
of neglect and falsification by those in
charge of keeping the machine safe. This
left the prosecution with one clear
question. Who was responsible?
The trail of evidence led back to June
2017 when maintenance responsibilities
for Rome's escalators shifted to a new
contractor, Metro Roma. The transit
authority at severed its contract with
Metro in an attempt to wash its hands of
the situation. But as the criminal
inquest continued, it became clear the
problem went far deeper. The
investigators discovered that Metro Roma
had been working handinhand with the
transit authority, ATAC, and together
they presided over negligent maintenance
and falsified records all across the
network. By September 2019, 11 suspects
were named and the courts had suspended
three ATAC managers along with the chief
of Metro Roma.
The prosecution's findings were grave.
In many cases, safety devices had been
deliberately sabotaged to avoid
escalator shutdowns, and those in charge
had covered their tracks through a
pattern of fraud and obstruction. In the
midst of the public outrage, prosecutors
recorded a chilling wiretap of ATC
manager Renato Demo. The translation, if
you run the numbers, out of 700
escalators, there'd be like three or
four more dropping. Come on. The
prosecutors note in their report that
Demo appeared uninterested in the
possibility there might have been people
on those three or four escalators. It
was simply a matter of numbers and
percentages to him. It was a callous
remark, and it painted a clear picture
of the incident. This wasn't an
engineering failure. It was a human one.
But that brings us to a more fundamental
question. I mean, how safe are
escalators really? The truth is, when
they're properly maintained, the safety
margins on escalators are enormous. Each
system is engineered to handle forces
far beyond what they'll ever see in
service.
>> So, the braking load of our step is like
greater 15 kon, so 1.5 tons. So, you can
put an elephant on the step and it won't
break. Well, I've never I've never seen
a step break in my whole career. Never
seen a step chain break either. I mean,
that's that's just not happening. I
mean, I'm not here to say that there are
no accidents on an escalator, but the
estate the accidents I know.
I mean, it's critical like that you that
you ensure the right maintenance. That's
the important thing because in the end,
it's all it's all about maintenance.
When this is done right, the chances of
a catastrophic failure are vanishingly
small. And with around 1.5 million
escalators worldwide, that really is how
it should be. In the US and Canada
alone, over 100 billion escalator trips
are happening every year, making the
escalator one of the most widely used
forms of transport on the planet. On a
scale that large, it's sometimes easy to
point the finger at our technology when
things go wrong. But the truth is, no
matter how well-designed our systems
are, they all rely on people to maintain
them. And perhaps that's the lesson
here. As humans, we have a duty of care,
not just to ourselves, but to everyone
around us. And sometimes that means
taking responsibility for keeping each
other safe.
In a way, that's how the escalator's
story began, with one person deciding to
take responsibility for a problem that
everyone else ignored. Back when Jesse
Reno was at university, every day he had
to climb more than 300 steps to get to
his frat house. But while everyone else
complained about this, Reno did
something about it. He had the math, the
science, and most importantly, the
problem solving skills to create the
world's very first escalator, which he
took to Coney Island. So, how do you go
from a frustrating everyday problem to
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