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 beg...
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 pm, 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 pm, 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. Sensing the motor had lost control of the steps, the escalator engaged the last line of defense. In the event of an emergency, an auxiliary break 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 pm, the third and final safety system failed, and the stairs began to plummet. Fans were flung forward and started streaming down the escalator.
Some lept 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 wanna have a guess?
It was an attraction in a theme park all the way back in 1896. It had no steps, a 25 degree incline, and it was essentially just a slow conveyor belt made of metal and wooden parts. It brought people up a full seven feet 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 two week 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. 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 Harrods in England installed a similar device, but the ride was so unsettling that Harrods had to put staff at the top to offer brandy to men and smelling salts to women just to calm their nerves.
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 braking 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. When there were people standing on the escalator in down direction, these escalators were feeding energy back into the grid.
The 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 two 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. At 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 break 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 escalators downhill acceleration continued. This is when the last line of defense kicked in. When the escalator 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 backstop 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 turn 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 ATAC severed its contract with Metro Roma in an attempt to wash its hands of the situation. But as the criminal inquest continued, it became clear that the problem went far deeper.
The 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.
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 ATAC Manager Renato Domico. 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 Domico 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 breaking load of our step is like greater 15 kilonewtons to 1.5 tons. So you can put an elephant on the step and it won't break. Well, I've never seen a step break in my work career. Never seen a step chain break either. I mean, it's does not happen. I mean, I'm not here to say that there are no accidents on an escalator, but the accidents I know, I mean, it's critical like that you, that you ensure the right maintenance.
That's the most important thing, because in the end, 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 a hundred 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 escalators 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.
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