Sunday, 25 October 2015

Crowd crush: What happens in a human stampede


Crowd crush: What happens in a human stampede
The flames spread rapidly, and most of the audience rushed to the main door to escape. As they crushed into the narrow hallway, people fell into a huge pile with heads and arms sticking out of the door, too tightly packed to be pulled free. As the inferno engulfed the venue in just over five minutes, 100 died, crushed to death under a two-metre stack of bodies.


Another 230 people at the Station Nightclub on that night in 2003 suffered burns and injuries, and even more developed post-traumatic stress disorder or depression after the horrific episode.
Mike, who was near the front, spent almost 30 minutes trapped in the foetal position, with his arms around his chest to allow him room to breathe. People lying on top of him screamed with fear as they burned and suffocated. Then they went quiet.
“When I watch the video, I can’t believe I was actually in there, that I survived, and there’s nothing left to the place,” he told NBC News in a chilling interview afterwards. “You can still see the red tile floor of where I was laying, trapped under a bunch of bodies, alive, barely alive, dead bodies.”
After watching a video of the Station Nightclub fire, Tasmanian Julian Lambert, who lives in Colorado, realised that he would probably have perished in the crush. He decided to educate himself by studying articles and videos on the phenomenon, and this week wrote an hugely popular Reddit post on the subject after the death count in the Saudi Arabia hajj stampede topped 2000.
“I started to notice the pattern of crowd crushes being the main causes of deaths in fires due to people only attempting to exit the way they entered, poorly designed buildings, panic, etc,” he told news.com.au. “When I started specifically researching crowd disasters, I couldn’t believe how deep the rabbit hole went, and more importantly how real the problem is becoming in our society, and how I might face it in my lifetime.”
PACKED IN
It’s when crowd density reaches very high levels that it becomes dangerous. At four people per square metre, you’re in a tightly packed crowd but able to rotate 360 degrees, just brushing people on all sides. At five or six people per square metre, you start to lose that freedom of movement, by seven there’s some danger and by eight or nine, you risk being crushed.
“When people start to move in very high density crowds, each individual physically doesn’t have enough space around them to behave like a normal person who acts based on decisions anymore, but rather the entire crowd starts moving like a fluid, forced forward by the pressure of the people walking forwards behind them,” explains Julian. “The crowd starts to literally behave by the laws of fluid dynamics, and can experience shock waves that ripple up and back through the mass of people when a push comes from any given direction ... anyone who’s been in a moshpit knows what I’m talking about.”
Long before you begin to be physically crushed, at a density of just five people per square metre, mass movement can trigger a tragedy.
CROWD CRUSH
When a very large, high density crowd like the one seen at the hajj moves in one direction in a confined space, they may reach a “choke point” or bottleneck. “If the choke point is too narrow for the entire crowd to fit through, people literally just plug it up and are unable to squeeze through the gap anymore,” says Julian.
It could be a hallway, like the one at Station Nightclub. It could also be a doorway that’s insufficient for the number of people, as seen at a Who concert disaster in Cincinnati in 1979, when 11 died. It could be a stairway, like the one at Ibrox Park football ground in Glasgow 1971, where 66 died and more than 200 were injured.
It could be another crowd coming in a different direction, which is what is thought to have happened at the hajj, with a road closure leading two groups to collide at an intersection.
Worst of all, there could be a total blockage. In the deadliest hajj pilgrimage disaster before this year (they are a regular occurrence), an estimated 1426 died at Mecca because pedestrian tunnel exits were blocked.
The hajj had been largely accident-free since the Jamarat Bridge choke point was overhauled almost a year ago, remodelled with multiple tiers, 12 entry points and five levels by Manchester crowd science professor Keith Still.
But Dr Still told news.com.au that simply changing the bridge wasn’t enough. “Over 60 years, this site has developed — built by men, not God — and it’s not a balanced system, the new bridge is part of a complex system, If you change any part of a complex system, then the whole system dynamic changes. You need to understand the holistic impact.”
The people at the back of the crowd often have no idea what’s happening at the front, so they continue moving forward, crushing those in front. They may have no choice in the matter, if they are being carried forward in a sea of bodies, or they may be fleeing a fire or other danger. Even if people at the front are screaming for the crowd to move back, as Julian says, “the ones who can hear them are already too stuck in the flow to do anything, and the ones who can do something can’t hear.”
In the deadliest association football disaster in history, at Peru’s Estadio Nacional de Lima in 1964, police fired tear gas at the crowd as home fans invaded the pitch. The crowd panicked and fled, slamming up against corrugated iron shutters at the end of the tunnels, with 328 dying from suffocation and internal haemorrhaging and 500 injured.
CROWD COLLAPSE
One of the world’s worst football disasters, the Hillsborough disaster in Sheffield, occurred when a barrier broke and fans began falling on top of each other. As many as 96 were killed and 766 injured, with fans tearing holes in the fences in an effort to save other fans.
This is known as “crowd collapse” and occurs when someone falls, and a river of people being pushed along behind topples over in a domino effect. Those under the pile of bodies start to asphyxiate, and the heap of people becomes the choke point.
The Ibrox disaster occurred when thousands of spectators were leaving the ground and someone, possibly a child being carried on his father’s shoulders, fell on the stairs, causing a devastating chain-reaction.
There is a particular risk if people are moving down a steep or slippery slope, and there doesn’t even have to be movement for people to fall, if a grandstand or barrier collapses, for example.
Despite the rhetoric, people do not die from being trampled underfoot. They die of suffocation or “compressive asphyxiation”, either under a pile of bodies on the ground, or even while standing up if the pressure of people is too strong for them to breathe out.
SAVING YOURSELF
Often in these cases, there’s something wrong with the design of the venue — the number and size of exits, position of barriers and strength of stands, for example. But crowd management is vital, too.
At Hillsborough, police were blamed for allowing too many people into the packed stadium, and bad planning at the hajj has caused a crush or collapse every few years for decades, killing hundreds each time.
Good crowd control may involve having someone in a raised position directing people with a megaphone, as well as properly thought-out overflow and a lack of obstructions or choke points. In mosh pits, security is often positioned over a barrier at the front to lift people out if they are being crushed.
But even the best-laid plans at best-designed venue can fail in a major emergency, when people may start panicking, pushing and running into one place.
It’s important to stay calm and move slowly if you can, but if you’re being crushed and carried along in the flow of the crowd, there’s some further advice. “When you feel a shock wave, absolutely do not fight it,” says Julian. “That’s one of the quickest ways to fall over. What you should instead do is let it carry you wherever it needs to, and then immediately start moving sideways, and diagonally backwards if that’s possible, avoid falling over at all costs though.”
Aim to hold your arms rigidly around your chest to give yourself space to breathe. If you are knocked over, try to fall in a rigid foetal position with your arms over your face and chest, as Vargas did when he managed to survive the deadly crowd at Station Nightclub.
“Although there’s been some excellent headway made in the field of crowd management, these disasters are still happening all the time due to people ‘in charge’ of these crowds not being experts in the field or often even consulting them, and almost never preparing for worst-case scenarios,” says Julian. “Almost out of self-preservation I gobbled the, sometimes brutal, information up ... even awareness of this phenomenon can keep people safe.”

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