IN THE wake of the tragic Itaewon Halloween crowd surge, which killed at least 156 and injured 151 others, South Korean authorities are now searching for answers. The dead included 26 foreign nationals from Iran, China, Russia, the United States, Japan and elsewhere. What caused the deadly surge? Could the accident have been prevented? Who should be held responsible for the tragedy?

After the Itaewon disaster, police launched a 475-member task force to find its cause. During a Cabinet council meeting, President Yoon Suk Yeol acknowledged that South Korea lacks research on crowd management and said the government will soon meet with experts to review national safety rules.

While awaiting the results of the South Korean investigation, it would be apropos to listen to the opinion of Medhi Moussaïd, a research scientist at the Max Plank Institute in Berlin who studies crowd dynamics. Mr. Moussaïd was interviewed by Marianne Guenot of Business Insider about when crowding turns deadly. The interview is reproduced here practically verbatim for the guidance of our readers.

"Most people don't realize the danger... people should be better informed as cities become denser and big crowds more common.

“Crowd surging is driven by a simple principle. If a group of people becomes dense enough -- more than six or seven people per square yard -- a crowd starts acting like a fluid.

“At this point, the people inside largely lose the power to control their own movement.

“If someone is shoved, they will push their neighbor, who will fall on their neighbor, and so on and so forth.

"Then this movement is transmitted... It is a little like a ripple through water, as these movements spread, they grow bigger.

“The pressure from the wave can be too intense to bear for people in the crowd, especially if they are pushed into an obstacle. As seen in Seoul, it can be fatal.

"Those waves are pretty dangerous because people can be compressed against the walls and also against one another. And whenever two waves cross, people can feel the pressure from both sides."

What to do if you get caught in a crush?

In the overwhelming majority of cases, crowded events will be safe. But Moussaïd listed some things that could help if things ever turn dangerous.

“The main thing is awareness: if you feel too crowded, you're probably right. Move away quickly to a less dense spot. This can protect you and also relieve the pressure on others.

"If just a small part of people start doing that, it reduces the density and solves the problem," he said.

“Once the crowd reaches that critical threshold, however, the pushing wave can build very quickly. Then it is a case of survival.

"If you feel the pushing wave, don't try to resist. Go with it and keep your balance.

“Do your best to stay standing. If one person falls over, it will create a wave of people toppling. Those at the bottom of the pile are then likely to be crushed by the weight of the bodies above them.

“Hold your arms up against your ribcage like a boxer to make it easier to breathe. The pressure from the wave can cause people to faint and fall.

“Don't struggle against the flow of the crowd. If you push back, the pressure in the system will grow, which will make the situation worse for the next couple of seconds to minutes.

Reminiscent of the Itaewon tragedy is the crowd crush that occurred at the Ultra on February 4, 2006, which killed 73 people and injured around 400. Newspaper reports the next day more or less gave the following account of the tragedy.

About 30,000 people had gathered outside the stadium waiting to participate in the first-anniversary episode of the former television variety show Wowowee. Around 6 a.m., organizers of the show began handing out tickets to people in the crowd, many of whom had been camping outside the stadium for days to acquire them. After overhearing the news, people started trying to get ahead of the queue and became agitated. The crowds became more impatient and started pushing forward and shoving, Coincidentally, the gates happened to be on a sloped driveway. After the gates eventually gave way, people at the front collapsed from exhaustion while others behind them stumbled. The sloped driveway contributed to the worsening of the stampede.