A street in the Itaewon district is packed with people on Saturday night in Seoul.
If you’re in a crowd and people are close enough to bump into you, it might get too crowded.
So says G. Keith Still, visiting professor of crowd science at the University of Suffolk and head of GKStill International, a consultancy that trains event organizers to recognize hazards.
Such events as the apparent crowd rush at jam-packed Halloween celebrations in the South Korean capital Seoul and the tragedy at the Astroworld festival in Houston in November 2021 have resulted in several deaths and injuries.
But the organizer, who has studied the dynamics of crowd behavior and safety for over 30 years, said organizers can help prevent crowding incidents by monitoring the density of a crowd in real time and the flow of people into one regulate the venue.
Mass density can be calculated in terms of the number of people per square meter, approximately one square yard. Younger, shorter people take up less space than older and taller people, but typically when you hit five people per square meter, Still said it gets uncomfortable — and anything fuller can become dangerous.
“When bodies touch, this high energy and density can lead to these surges and crowd collapses,” Still said.
A sign that a crowd has grown too dense is what Still calls the “wheatfield effect,” where people sway uncontrollably. He said an example can be seen in online videos of an Oasis concert in 2005 in Manchester, England, just before a big wave surged through the crowd towards the stage.
The key to preventing a disaster, Still said, is for organizers to monitor densities and, if they get high, slow or stop the flow of people entering the area. He said it was much more difficult to reduce crowds when the situation got too dense.
If a venue gets too crowded, Still said performers should stop and ask everyone to step back. Over the years, several artists including A$AP Rocky and Linkin Park have done just that.
When you’re in a crowd, Still said, you can help yourself stay safe by looking out for areas that are likely to get the most crowded and moving out of the crowd if you don’t have enough personal space.
You can learn more by viewing an interactive graphic here.