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00:00On October 23rd, 2018, thousands of football fans were making their way to the game in Rome.
00:06Excitement for the game was high, and the fans began to chant and sing.
00:10At 7.03pm, around 50 people were riding the long escalator down to the platform,
00:15but within 30 seconds the crowd had swelled to nearly double that.
00:19Everything seemed fine, but inside the escalator was a problem.
00:25The weight of the passengers was bearing down on the steps,
00:28and the load on the main motor was increasing.
00:31To try to slow the descent, the motor applied a counter torque,
00:35but as the force continued to increase, the stairs began to move faster.
00:39By 7.04pm, the crowd had tripled.
00:42The motor finally reached its limit, and under the massive strain, the drum began to slip.
00:47With the motor losing control, the escalator triggered its second line of defense.
00:52A safety relay tripped, immediately cutting power to the motor.
00:57The main brake clamped down on the metal drum to stop the descent of the stairs.
01:03But, it failed.
01:06The friction on the main drum wasn't enough to stop the motor from spinning, and the stairs continued to accelerate.
01:12Sensing the motor had lost control of the steps, the escalator engaged the last line of defense.
01:17In the event of an emergency, an auxiliary brake is designed to bypass the motor entirely and directly lock the drive shaft.
01:25Under normal circumstances, the chance that all three safety measures fail at the same time is vanishingly small.
01:32But these weren't normal circumstances.
01:35At 7.05pm, the third and final safety system failed, and the stairs began to plummet.
01:41Fans were flung forward and started streaming down the escalator.
01:45Some leapt over the central barrier in desperation, while others were swept into a crushing pileup.
01:51At the bottom, the landing became a dangerous choke point.
01:55Under the pressure, the steps twisted and buckled into jagged metal, leaving 24 people injured.
02:01Something like this shouldn't have been possible.
02:04And experts at the time knew that something had gone wrong, and they started to suspect foul play.
02:10In the aftermath, Rome's transit agency sealed off the accident site and closed the Republica station for several months.
02:17The authorities ordered both a technical and a criminal investigation, and the mayor even publicly vowed to discover the cause of the accident.
02:25So investigators began dismantling the wreck, tearing it down piece by piece to reconstruct what had happened.
02:34The ride people experienced on that escalator was one of the most terrifying rides of their lives.
02:39But maybe it's more similar to the origin of escalators than you might think.
02:44Like, what was the first escalator even used for?
02:47Do you want to have a guess?
02:49It was an attraction in a theme park all the way back in 1896.
02:55It had no steps, a 25-degree incline, and it was essentially just a slow conveyor belt made of metal and wooden parts.
03:03It brought people up a full seven feet before they would have to walk down stairs on the other side.
03:09And it was a huge success.
03:11Over 75,000 people enjoyed the attraction during its two-week stay at the Old Iron Pier on Coney Island.
03:18The ride was named the Continuous Elevator, and its inventor, Jesse Reno, had created it not just as an attraction,
03:25but as a proof of concept, because he saw it as the future of transportation.
03:33But as Reno watched people ride his invention, he began to notice a pattern.
03:38Nobody walked. Instead, they stood still, feet planted firmly sideways, with people gripping the handrail tightly.
03:46Two years later, the department store Harrods in England installed a similar device.
03:51But the ride was so unsettling that Harrods had to put staff at the top to offer brandy to men and smelling salts to women,
03:58just to calm their nerves.
04:00See, for both devices, the 25 degree conveyor belt was precarious to walk on, and unnerving to stand on.
04:07At around 12 degrees, walking on an incline becomes difficult, and 25 degrees is roughly the limit that our ankles can flex.
04:15If only there was a way to replace the conveyor belt with a moving set of stairs.
04:20Well, then the riders would always have a flat surface to stand on, and a staircase they could climb if they wanted to.
04:27One attempt at a solution had already been around for four decades, and it was called the revolving stairs.
04:33It consisted of a chain that went around a loop, then fixed stair-shaped blocks were attached to it,
04:39creating a flat surface to stand on during the main incline.
04:42But as soon as you'd reached the top, the steps tilted forward, making it treacherous to get off.
04:47And a similar problem plagued you at the bottom.
04:50Now, you might think if the top and bottom are causing problems, just extend each landing.
04:55But that also doesn't work.
04:57You just end up with a jagged mess for longer.
05:00So, how do modern escalators solve this problem?
05:03I mean, have you ever stopped to think what happens to the stairs at the top of the escalator when they disappear?
05:09Clearly, we have steps going around in some sort of loop.
05:12But how do they actually behave on the return journey?
05:16What if I give you two options?
05:18Do they stay right side up, like the cabins in a ferris wheel?
05:22Or do they flip upside down and then flip back again at the other side?
05:27I'm gonna go this one all day.
05:28Ferris wheel?
05:29This one makes more sense.
05:30Ferris wheel.
05:31Yeah, this one.
05:32I think they turn upside down.
05:34And they're actually right side up.
05:36I think I'm gonna go with this one.
05:37But wow, you're both, yeah.
05:39The solution to this problem came from another inventor named George Wheeler.
05:43His idea forms the basis of every escalator in use today.
05:47A modern version of it works something like this.
05:50A typical subway escalator has an electric motor at the top with a power output of around 50 kilowatts,
05:56smaller than most electric cars.
05:58This motor spins extremely fast at over a thousand RPM.
06:03But it's pretty weak.
06:04So to drive the steps, the escalator needs to convert this into a slower output with more force.
06:10To do this, it uses a reduction gearbox and a gear system.
06:13Lowering the output to just a few RPM and increasing the torque by a factor of around 100.
06:19The motor is connected with a large sprocket to a reinforced steel chain, which pulls the stairs around a loop.
06:26The so-called step chain is fitted with wheels to allow it to roll smoothly around curves.
06:31But unlike the design for the revolving stairs,
06:34Wheeler proposed attaching each step to this chain through a single axle, giving it the freedom to rotate.
06:40Next, he added a second set of wheels to each step that followed a different track,
06:45allowing him to control the angle of each step at any point.
06:49On the incline, the two tracks overlap, just like the revolving staircase.
06:53But then at the top, the two tracks separate,
06:56and this is what allows us to keep the steps level throughout the entire ride.
07:00The tracks then remain separated and curve around.
07:03The steps flip upside down, tuck into the loop, and start their return journey.
07:08At the start of the incline, the tracks rejoin, and the whole process repeats.
07:14So the answer is, you are both wrong.
07:16Oh my god!
07:17I don't want me to do that.
07:20Yeah.
07:21Yeah, I never really thought about that.
07:23Yeah, like, I would say it's like an upside down elevator, bro.
07:27Like, guess what?
07:29You're right!
07:30Yeah?
07:31Yeah!
07:32But despite all modern escalators adopting Wheeler's design,
07:36at the time it caught so little attention that he was forced to shelve the idea.
07:40It wasn't until eight years later that another inventor, Charles Seberger,
07:44bought his patent and capitalized on the invention.
07:47Seberger partnered with the Otis Elevator Company,
07:50and together they built a prototype.
07:52A year later, in 1900, they showcased it at the Paris Exposition Universale.
07:59In total, 51 million people flocked to the exposition to see the marvels of modern technology.
08:04But one of the most popular exhibitions was the world's first true commercial escalator.
08:09The machine drew huge crowds.
08:11French historian Philippe Julien described it as the jolliest attraction at the exhibition,
08:16and wrote,
08:17The escalator caused many an incident worthy of the vaudeville,
08:20separating families, sending old men sprawling, delighting the children, and reducing their nanas to despair.
08:26The escalator was even awarded one of the grand prizes of the fair.
08:30Shortly after, escalators started being installed in different places across the world.
08:35But these escalators weren't perfect.
08:38They had smooth, flat stairs.
08:40And when they reached the top, these stairs would disappear under a wooden board,
08:44leaving a dangerous gap between them.
08:47Shoelaces, coats, and especially the long skirts in fashion at the time,
08:50easily got caught in the machinery.
08:53One incident even saw a three-year-old girl getting her foot pinched in the gap.
08:57And while the girl luckily escaped with injured toes and a missing shoe,
09:01something in the design had to change.
09:04To solve this, Seaburger and Otis installed a triangular shunt at the end of the escalator,
09:09forcing riders to go off to the left before they reached the dangerous gap.
09:14This system worked, but it was awkward,
09:16because it meant people had to put one foot onto solid ground while the other was still moving,
09:21which became especially tricky when some people stood still and others walked.
09:25So to reduce the risk of people getting in each other's way,
09:28operators asked people to stand on the right and keep the left lane clear for faster walkers.
09:33It's a convention we still often follow to this day.
09:38But as it turns out, there's a much better solution than the shunt.
09:43Modern escalator steps aren't smooth, they're grooved.
09:46These grooves then interlock perfectly with a comb plate at the top of the escalator.
09:51So now, if a small item approaches the end, the comb plate lifts it up and out of harm's way.
09:57This makes it much harder for things to get stuck.
09:59And perhaps more importantly, it allows people to safely step off forwards.
10:03But the comb plate doesn't entirely solve the problem.
10:08We still have these gaps on the side of the escalator that can pinch and trap objects as the steps move.
10:13So to address this, a new safety feature called the skirt brush was added to the escalator in 1982.
10:21Escalators are full of subtle safety features like this.
10:24Some old and some new, but almost all of them are designed around people.
10:28All the way back in 1896, Jesse Reno predicted that riders on his attraction would need something to hold onto.
10:34So he introduced a moving handrail.
10:37In a modern escalator, the motor has a separate connection to turn a friction wheel that drives the handrail.
10:43The only problem is that friction wears things down.
10:46So over time, the wheel gets smaller.
10:49And as its circumference decreases, each rotation moves the rubber loop a slightly shorter distance.
10:55So the handrail begins to move more slowly.
10:58The effect is small, but it builds up over time.
11:01So to compensate for this, a new handrail is calibrated to move around 2% faster than the steps.
11:07You can actually try this yourself.
11:09Next time you're standing on an escalator, just place your hand next to you as you stand still.
11:14And you will watch as your hand slowly drifts forward.
11:18This speed difference stops the handrail from lagging too far behind the steps over time.
11:23Because I have definitely noticed that, that sometimes I'm on an escalator and then it's going faster than me.
11:31My hand is going faster than my body.
11:34But that means it's a new escalator.
11:36Well, it's a new frictional wheel.
11:39That wheel that drives the handrail.
11:42We don't replace the entire escalator.
11:46Oh, wow.
11:47So that's like a party trick I can use to entertain my friends.
11:50I mean, I don't know when I'd have a party on an escalator, but whatever.
11:53If 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.
11:59I can, that's like, I can tell them that and impress them.
12:02But it's not just the handrail.
12:06The speed of the steps themselves is also something that needs to be carefully controlled.
12:11Modern escalators use AC induction motors, which are extremely good at regulating their rotational speed.
12:17And this has an unexpected benefit on downward escalators.
12:22With enough people riding, their weight is enough that the motor no longer has to power the ride.
12:27Instead, the weight of the passengers themselves drives the chain and causes the motor to spin.
12:33As more people board, the force on the motor increases and it's pushed to turn faster.
12:38But modern AC induction motors work by creating a rotating magnetic field.
12:42When the motor tries to spin faster than the field, electric currents are induced inside it, which then create their own magnetic field.
12:49This new field pushes back in the opposite direction to the spin, creating a braking force, which resists the increase in speed.
12:56But something interesting happens when the motor resists like this.
13:01Rather than consuming energy, the physics of the motor flips, and it uses the excess mechanical energy to produce an electric current.
13:09This is called regenerative braking, and it's the same trick that electric vehicles use to recharge their batteries.
13:15In effect, the motor turns into a generator.
13:18The result is that on a busy day, many modern downward escalators aren't just moving people, they're actually generating electricity.
13:26Often, this is channeled back to the building's internal grid and used to power other devices, including the upward escalators.
13:33So, even the escalator that was invented by George Wheeler and was installed in 1920, the Paris Exhibition, et cetera.
13:45I mean, all these escalators were regenerated.
13:47What?
13:48Yeah, when there were people standing on the escalator in down direction, these escalators were feeding energy back into the grid.
13:55No! It's like the down escalator is a generator?
14:00This regenerative braking makes escalators extremely power efficient, but more importantly, it makes them inherently safe.
14:08But 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.
14:15And if left unchecked, it would start accelerating uncontrollably.
14:19The stairs would go plummeting down.
14:22Which is exactly what happened in Rome.
14:25After a nearly two year long investigation, the investigators published this 86 page report.
14:31Inside, it lists the exact sequence of events that led to the disaster.
14:35As fans crowded onto the escalator, their combined weight increased the load on the main motor.
14:41The motor tried to resist this change, but as more and more people funneled on, the force got too high.
14:46And eventually it hit a tipping point and the motor started accelerating uncontrollably.
14:51Safety sensors in the machine noticed this sudden change and triggered two things in short succession.
14:57First, the power to the motor was cut.
15:00And immediately after that, the main brake engaged.
15:03Two massive arms clamped down on the drum to lock it in place and avert a runaway.
15:10This brake should have had enough stopping power to bring the fully loaded escalator to a halt.
15:15Even under the massive strain.
15:17But it didn't.
15:18Tests after the incident showed that its braking force was far too low.
15:22Around 37% of the manufacturer's specification.
15:26The weakened brake struggled to slow the spinning motor and the escalator's downhill acceleration continued.
15:33This is when the last line of defense kicked in.
15:37When the escalator's speed rose by more than 20%, the auxiliary brake triggered, driving steel wedges into a disc on the driveshaft.
15:45But when investigators opened up this brake, they were shocked.
15:49The final mechanical backstop had been partially disabled.
15:52Someone had physically tied plastic straps around one of the two brake wedges and rendered it useless.
16:00With half the system unable to engage, its stopping power was cut by 50%.
16:07Just enough for the weight of all those passengers to overpower the brake and render the last line of defense useless.
16:15Investigators knew that these failures should have been automatically recorded in the error logs.
16:21But when they went to check, they found nothing.
16:24The error codes had been turned off.
16:27Meaning critical malfunctions could occur without leaving a trace.
16:30The only way this could happen was if they had been disabled on purpose.
16:34Meaning someone must have reprogrammed the system to stop recording fault codes.
16:40Next, investigators turned to the maintenance records.
16:43But they found these similarly incomplete.
16:46And evidence of major work on the escalator was nowhere to be found at all.
16:50With all the main safety systems compromised and critical alerts turned off, the escalator had been a ticking time bomb.
16:59All findings from the technical investigation pointed not to a manufacturing defect,
17:04but to a pattern of neglect and falsification by those in charge of keeping the machine safe.
17:09This left the prosecution with one clear question.
17:12Who was responsible?
17:14The trail of evidence led back to June 2017.
17:19When maintenance responsibilities for Rome's escalators shifted to a new contractor, Metro Roma.
17:26The transit authority, ATAC, severed its contract with Metro Roma in an attempt to wash its hands of the situation.
17:32But as the criminal inquest continued, it became clear the problem went far deeper.
17:37The investigators discovered that Metro Roma had been working hand in hand with the transit authority, ATAC, and together they presided over negligent maintenance and falsified records all across the network.
17:49By September 2019, 11 suspects were named and the courts had suspended three ATAC managers along with the chief of Metro Roma.
17:57The prosecution's findings were grave.
18:00In many cases, safety devices had been deliberately sabotaged to avoid escalator shutdowns.
18:06And those in charge had covered their tracks through a pattern of fraud and obstruction.
18:11In the midst of the public outrage, prosecutors recorded a chilling wiretap of ATAC manager Renato D'Amico.
18:18The translation?
18:19If you run the numbers, out of 700 escalators, there'd be like three or four more dropping.
18:24Come on.
18:25The prosecutors note in their report that D'Amico appeared uninterested in the possibility there might have been people on those three or four escalators.
18:33It was simply a matter of numbers and percentages to him.
18:36It was a callous remark and it painted a clear picture of the incident.
18:41This wasn't an engineering failure, it was a human one.
18:47But that brings us to a more fundamental question.
18:49I mean, how safe are escalators really?
18:52The truth is, when they're properly maintained, the safety margins on escalators are enormous.
18:57Each system is engineered to handle forces far beyond what they'll ever see in service.
19:02So the braking load of our step is like greater than 15 kilomutons, so 1.5 tons.
19:08So you can put an elephant on the step and a boat break.
19:12I've never seen a step break in my whole career.
19:16I've never seen a step chain break either.
19:18I mean, it's just not happening.
19:21I mean, I'm not here to say that there are no accidents on escalators.
19:25But the escalators, the accidents I know, I mean, it's critical that you ensure the right maintenance.
19:35That's the important thing.
19:37Because in the end, it's all about maintenance.
19:42When this is done right, the chances of a catastrophic failure are vanishingly small.
19:46And with around 1.5 million escalators worldwide, that really is how it should be.
19:52In the US and Canada alone, over 100 billion escalator trips are happening every year,
19:58making the escalator one of the most widely used forms of transport on the planet.
20:02On a scale that large, it's sometimes easy to point the finger at our technology when things go wrong.
20:07But the truth is, no matter how well designed our systems are, they all rely on people to maintain them.
20:14And perhaps, that's the lesson here.
20:17As humans, we have a duty of care, not just to ourselves, but to everyone around us.
20:23And sometimes that means taking responsibility for keeping each other safe.
20:32In a way, that's how the escalator's story began.
20:34With one person deciding to take responsibility for a problem that everyone else ignored.
20:39Back when Jesse Reno was at university, every day he had to climb more than 300 steps to get to his frat house.
20:46But while everyone else complained about this, Reno did something about it.
20:50He had the math, the science, and most importantly, the problem-solving skills to create the world's very first escalator,
20:56which he took to Coney Island.
20:58So how do you go from a frustrating everyday problem to an innovation that changes the world?
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