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After Astroworld, a crowd scientist explains the deadly dynamics of crowd surges


Who is to blame for the deaths of eight people at the Astroworld Festival last Friday? Houston police have opened a criminal investigation. Meanwhile, concertgoers have already filed more than 20 lawsuits against the event organizers and against the rapper, Travis Scott, who continued to perform for more than half an hour after officials declared a mass casualty event. Earlier today, we caught up with a crowd safety expert, Keith Still, to talk about the science behind how a concert crowd can transform into an uncontrollable mass that threatens human life. A warning here that this conversation contains some graphic details that might be upsetting for some listeners.

KEITH STILL: Imagine you've got people on all sides. Even a slight movement gets amplified throughout the crowd because as the mass of one body pushes against another, it gathers momentum. So a very, very small movements in a high-density environment can create what's called shockwaves. So initially, you'll see crowds sway, and at that point, you should be trying to unwind the crowd density. But once you get the crowd surge, you can then result in what's called a progressive crowd collapse. So the crowd actually falls on top of each other. And at that point, as people struggle to get up. Arms and legs get twisted together. Blood supply starts to be reduced to the brain. It takes 30 seconds before you lose consciousness, and around about six minutes, you're into compressive or restrictive asphyxia. That's a generally the attributed cause of death - not crushing, but suffocation.

CORNISH: I understand that you've done some consulting when it comes to events. But is there anything that really can be done to prevent something like this from happening?

STILL: Yes - an appropriate crowd management plan, trained crowd managers, a design which is fit for its intended purpose. So for a clinky, plunky, la, la, la-type (ph) band, this design may well work perfectly. But you put a high-energy performer and a high-energy crowd and high density in that same space, then you have high risk. So understanding the difference - what works, what doesn't work - that's the science of crowd dynamics.

CORNISH: I notice you talked about the energy coming from the stage. And by way of background, people have been reporting about the previous occasions that this performer, Travis Scott, had been arrested for reckless conduct at shows or inciting a riot. Is that something that really does make a difference, kind of how the performer engages what's going on?

STILL: Yes. And that's why you design your system around that type of performance. In Denmark, for instance, Roskilde - they could have a performer of this nature in there because they have penned areas and restrict the number of people in each section, making sure there is plenty of space for that crowd to move and enjoy themselves without the risk of crushing.

CORNISH: Once a problem begins to develop and a crowd becomes too dense or rowdy, what can be done to reassert control, to calm things down?

STILL: Well, the performer can stop. I mean, we've seen a number of instances - in fact, you go to YouTube, and you see lots of examples where the performer stops, the show stops, and they communicate with the crowd. Make sure that everybody's on your feet, and that can then restart. So there are processes and procedures in place. However, again, that's part of the management responsibility - to make sure that those processes and procedures are understood, implemented and carried out in the event of an emergency.

CORNISH: For those of us now who are hearing this news, maybe thinking about what it's like to be in a situation like this, is there anything - any advice you have for the average person who's in a crowd and feels that things are starting to go awry?

STILL: I think situational awareness - just be aware of the density of people ahead of you and around you. And you know, if you're aware of the potential of a risk, then back out of it. But once you're in a high-density surge environment, there's very little you can do as an individual. It is up to things like the building design or the operations manager or the safety design of any system to make sure they've got a safe environment. So you should never be in that position.

CORNISH: Keith Still is a professor of crowd science at the University of Suffolk. Thank you for your time.

STILL: Thank you.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

Over two decades of journalism, Audie Cornish has become a recognized and trusted voice on the airwaves as co-host of NPR's flagship news program, All Things Considered.
Mano Sundaresan is a producer at NPR.
Christopher Intagliata is an editor at All Things Considered, where he writes news and edits interviews with politicians, musicians, restaurant owners, scientists and many of the other voices heard on the air.