(NEW YORK) — As investigators in Seoul, South Korea continue to determine how 154 partygoers were killed in a crowd crush during a Halloween party over the weekend, crowd control experts say the incident should serve as a reminder about the importance of proper management.

“The first trigger of this incident wasn’t when the first person fell, it happened when [organizers] approved this failed crowd management plan,” Paul Wertheimer, the founder of Crowd Management Strategies, a crowd safety consulting service, told ABC News.

According to Wertheimer, future event organizers and municipalities can avoid a similar fate by focusing on the crowd control plans first and foremost. At the same time, attendees can also be prepared to avoid getting hurt in case of an emergency.

On Monday, South Korea’s national police apologized for failing to properly oversee the party in the Itaewon neighborhood. They said only 137 officers were on hand during the outdoor party, which had over 100,000 people.

“It was foreseen that a large number of people would gather there,” said Hong Ki-hyun, chief of the National Police Agency’s Public Order Management Bureau.

One middle school student and five high school students were killed in the incident as streets and alleyways were clogged with people trying to flee the scene. At least two Americans were among the 19 foreigners killed during the incident, officials said.

Wertheimer, who has analyzed deadly crowd incidents over the years including last year’s crowd crush at the Astroworld music festival, said it was unwise for South Korean officials and event organizers to hold a party that large without any sort of plan.

He noted that crowd safety experts have warned organizers across the world that younger populations are gathering in greater numbers for events due to the amount of time they spent sheltered in place during the pandemic.

“We’ve seen many events this year where young people want to do something big in larger crowds and attention should have been paid to this crowd,” Wertheimer said.

One of the fundamental rules in crowd control is knowing how much density can be put in a given space, according to G. Keith Still, a visiting professor of crowd science at the University of Suffolk in the U.K.

Still, who has consulted event organizers for decades, said the alleyways in the Itaewon neighborhood appeared to have been too narrow for the crowds and that should have raised alarms before the Halloween party started.

“An analogy I like to use is a car tachometer,” Still told ABC News. “You never drive a car before it reaches that red line on the meter. It’s the same with crowded places. If you don’t know where that red line is, you shouldn’t be holding that big of a crowd.”

Even with the limited number of officers, organizers could have put together an emergency plan to keep that many people moving, Still noted.

“Hold people back earlier and then release at that bottleneck and then hold and then release,” he said. “You put three or four officers at those sections and make sure they can see the crowd ahead [and] you can prevent these critical densities.”

The biggest problem is not having a national or international regulatory policy when it comes to crowd events, Wertheimer said. While some cities, localities and event venues may have their own regulations, it’s still a patchwork of rules that differ from place to place, he said.

Wertheimer said there will likely be new rules and regulations that come about because of the Seoul incident. But it’s going to take a fundamental change across the board.

“We know concerts with standing room only are some of the most dangerous events,” he said.

In the meantime, Wertheimer said event attendees can be prepared for potential crowd crushes by knowing where the closest exit is.

If an attendee becomes claustrophobic or short of breath because of the large crowds, Wertheimer recommends to leave immediately and get some air.

“Your biological system will tell you if you’re in danger. Listen to it,” Wertheimer said.

If a person is stuck in a crowd crush, Wertheimer said not to scream or call for help as it would use up oxygen. Use hand gestures, if possible, to get attention, he said.

Ultimately, Wertheimer said the responsibility for crowd safety lies with organizers and local officials.

“Kids should never be the ones who do crowd control,” he said. “The buck stops with the promoter.”

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