Last Saturday, ~100,000 people went to Seoul's Itaewon bar district to celebrate Halloween and packed the neighborhood. People fell on a narrow, sloped alley and triggered a crowd collapse. Some 156 people, mostly young women, were crushed to death

First, it's important to note it wasn't a stampede. The victims weren't trampled to death by a panicked crowd. Many died slowly as their bodies were pressed so hard that their lungs couldn’t expand to take another breath. This could happen even when one is standing upright

There is no easy way to save people trapped in such a crush. Which is why a sergeant, Kim Baek-gyeom, has been hailed as a hero. He raced around the block to the top of the slope to get the crowd to back off. You can see him in this video youtube.com/watch?v=hteL_O… x/xx

He knew something that others around him didn't. Minutes ago, he had tried unsuccessfully to pull the bodies out of the crush, which had formed a dam that blocked the alley. But Kim's lone, desperate pleas were also an indictment of South Korean authorities’ colossal failure

They did almost nothing to prepare for the crowd, and they were slow to respond to clear warning signs. Survivors have unanimously pointed out the lack of police presence. But that's just the symptom of a bigger problem Read on or jump to article⤵

We spoke with an officer on duty that night, who described a total lack of awareness of crowd risks among police leaders before the disaster. And it was a night that everyone knew was going to be wild—the first Halloween after South Korea dropped an outdoor mask rule

Police in Itaewon knew, too, they were going to be outnumbered. Critically, just four days before the crush, the Itaewon police substation requested backup from the management, the officer said. They requested anonymity as they weren't allowed to disclose internal matters

The officer went to work last Saturday expecting help from so-called mobile police, a group of auxiliary police officers often tasked with crowd control at rallies and protests. But they weren't there

South Korea’s police chief has admitted that crowd control that night was inadequate. Police sent just 137 officers. Even Kim, the sergeant, was not supposed to be there—he was answering another call in the neighborhood when he saw the developing crisis

And a police notice, released two days before the crush about Halloween safety, makes no mention of the danger of crowds. It warns only of upskirting, sex crimes, theft, traffic congestion, and drug abuse

The officer who spoke with us said they had prepared for the event for a long time, even procuring blankets to keep drunk people warm, but there was not crowd training whatsoever

For those who lost loved ones in Itaewon, the police negligence is unforgivable. Steve Blesi, a father who lost his 20-year-old son, in the crush said they "completely failed." And I'll always remember the anguished words he said

“To die that way, that’s a horrible death. If I could, I’d die that way instead of my son. If I could get him back, I’d die 100 times that way to get my son back, because I know he suffered.” It's important to understand exactly what went wrong

In hindsight, the red flags prior to the crush were everywhere. At around this time last week, at 6:34pm local time, someone who saw the packed alley outside Itaewon subway called 112 (the country’s emergency number) to warn of a potential incident

“I’m so worried to see people going up and down the alley. I think people will get crushed because they keep getting pushed upward even though people can’t come down,” the caller said, according to transcripts released by the police

The next call, at 8:09pm, made clear just how quickly the situation was deteriorating. “We can’t move because so many people are being pushed and getting hurt,” the caller said. At this time, visitors who came by subway reported seeing crowds so big that some turned back

This is a critical time. To experts, getting carried by a crowd is a telltale sign that the density of people was reaching a dangerous level. Sadly, much of what we learned about crowd behavior came from past disasters, which are tragically common

Every few years since 1994, dozens if not hundreds have died from crowd incidents in the Hajj, the annual Islamic pilgrimage to Mecca. And there’s a chilling reason for the high death tolls that also explains the Itaewon crush

When a crowd becomes dense enough, it begins to behave like a fluid. Forces can ripple through a densely packed group of people from the outside, where people have no reason to panic and may unwittingly—and fatally—add to the pressure by approaching

In the case of the 2015 Hajj accident, which killed ~2,400 pilgrims, the relentless march of the crowd formed stacks of bodies 10 layers high until the upstream flow stopped. Most people died of compression asphyxiation, but some also had their lungs punctured by broken ribs

Back in Itaewon, these deadly signs were becoming apparent to those on the ground, and the urgency of the calls escalated as the evening progressed. The transcript of the last call before the crush is horrifying to read

“We are going to get crushed. Everyone is going crazy,” the caller said. Their last words were: “Ah! (screaming) Ah! (screaming) The Itaewon back alleyway. Itaewon back alleyway.” 11 such calls were made before the crush. Police said they sent officers in response to 4

I won't go into the detail of how the crush happened, and what followed was captured in images you've already seen: people desperately performing CPR on bodies on the street. But there are photos that most outlets didn't show, because they are graphic, that are important

I'm talking about the pileup of bodies at the front of the collapsed crowd. Just on the other side of the human wall, there was so much space. Many people who saw the photo on Reddit are perplexed. Why couldn't they just move to that space? Answer: They are completely stuck

Thus is the nature of crowd crushes: All it takes is one slip to cause a pileup, and once that happens, there are few things one can do to stop the slow and painful suffocation. The key here is PREVENTION. But how? It's not about how many officers you deploy

A lesson we learned came from Hong Kong 30 years ago. On New Year’s Eve 1992 at the city's Lan Kwai Fong nightlife district, some lost their footing on the slopes and caused a massive pile-on that killed 21. In many ways, Lan Kwai Fong and Itaewon are similar in many ways

Narrow streets. Slopes. Slippery streets from spilled beer. A possibly inebriated crowd. Bars and restaurants blasting loud music onto the street. For Hong Kong, the incident proved to be a pivotal moment

After an independent inquiry, a judge recommended a series of crowd control measures that would successfully help avert such disasters in the following decades. More than a heavy police presence, preventing crowds from building up in the wrong places has been key to safety

Every Halloween, Hong Kong authorities allow only one-way flow in Lan Kwai Fong and use a queueing system to prevent overcapacity. People are also banned from staying in areas considered as choke points, and adjacent roads are closed off to create buffer zones

None of that was done in Itaewon, where crowds moved in all directions and roads were not closed off to relieve the pressure of the crowd. In fact police were concerned with people spilling over to the road and blocking vehicular traffic

Crowd management is sadly a lesson that cities are learning the hard way over and over again. In fact, just the day after the Itaewon disaster, 11 people died in a crowd surge at a packed concert in the DRC. Two police officers were among those killed

Why does it keep happening? In South Korea's case, authorities were plain and simple unprepared. On the night when Steve Blesi was frantically calling his son to find out if he was safe, the head of the Korean police went to bed without knowing anything about the crowd crush

The police chief, Yoon Hee-keun, went to sleep at around 11pm, some 45 minutes after reports of the disaster flooded news channels and social media. He also missed a text message from an emergency situation officer at 11:32pm and a call 20 minutes later from the officer

Authorities have vowed to fully investigate the disaster and the police’s role in it. The release of the results could take weeks or even months, but what the public has learned so far has painted a picture of disorder inside the police force

For example, national police say they asked the Seoul subway operator to prevent trains from stopping at Itaewon station to limit the crowds. The company has denied this, saying it only received an official request one hour after the deadly crush

Blesi, the father who lost his son in the crush, said the authorities “completely failed." He tried calling his son for hours. Later that night, staff at the U.S. Embassy delivered the bad news after asking him, “Are you sitting down?”

Vera Sistenich, whose brother was in Lan Kwai Fong on New Year’s Eve 1992 and who studied the disaster later at Harvard, told us what triggers a crowd crush can be unclear and trivial, but the conditions allowing for it to become lethal are preventable