Just how do you build the perfect Olympic stadium?
What have the Romans ever done for us....
Go with the flow
“The final element is to ensure that there are sufficient stairs and entrance points to the seating bowl and that each of these are appropriately sized for the flow of spectators.
“The UK has suffered from a series of stadium disasters resulting in tragic losses of life, and we have a duty to ensure that the venues we design are safe for those who visit them.”
Before a stadium can be licensed, it needs to demonstrate to the licensing authorities that people can get in and out safely and that there is enough space in and around the stadium. There are requirements for space per spectator on concourses, flow rate through turnstiles and “vertical circulation” within the stadium and seating bowl.
Populous employed specialist consultants to provide a detailed analysis – static and dynamic – of crowd flow. The static modelling is based on flow rates generated by the width of bridges, concourses and staircases, while dynamic modelling uses pixels to represent anticipated movement of spectators entering and leaving the stadium.
“In the case of the Olympic Stadium, this has involved detailed analysis of spectator movements over the five bridges that link the stadium island site with the rest of the park and then around the stadium,” Jones told us.
The work allowed the architects to identify any bottlenecks in the design before a shovel even entered the ground, and to make adjustments as needed.
“In exceptional circumstances, we can develop a plan for staged movement which requires the use of holding areas to moderate the flow of spectators,” Jones adds.
All this preparation – including communication systems for getting messages to the audience – has impressed Professor Chris Kemp, pro vice chancellor of Bucks New University, which specialises in the study of crowds and crowd management.
“Safety costs money. And they have built all the security infrastructure in to the Olympic Stadium and village right from the start. If they had to retrofit it, it would have cost hundreds of millions,” Kemp says.
Divide and rule
A decade ago, there was a tragic accident at the Roskilde music festival in Denmark. Something went wrong in the crowd and nine people were crushed to death. Professor Kemp began his research after this disaster and says that crowd safety is all about management.
Roskilde music festival in Denmark. Pic credit: Keith Still
Thanks to his and Still’s research, the organisers at Roskilde now separate the crowd into three sections: a front pen with 500 to 600 people; a second pen with between 800 and 900 people; and the rest of the 75,000 festival-goers behind a final barrier.
“We’ve been using special barriers with pressure sensors in them to measure the pressure on the barrier at events for many years,” says Kemp.
“The pressure at the front of a festival crowd can reach 6.4kN/s – the equivalent of eight people sitting on your chest for a second. But with a three-barrier system, the front pen still has quite high pressure – 4.6kN/s – the second pen registers barely anything – 0.5kN/s – and behind the third barrier, there is none at all.
“So the more barriers you use, the less the pressure on each, and the easier it is to manage the high-pressure areas.”
The density of the crowd is particularly important because beyond a critical point – between five and seven people per square metre – people stop behaving like people and start behaving like molecules in a fluid.
“At events like the Hajj pilgrimage, crowd density can reach eight to 15 people per square metre,” Kemp says. “When a crowd gets this dense, there is no room for people to do anything but move when the person next to them moves.
“A pressure wave can move through the crowd and a shockwave will reflect off barriers. Sometimes the reflected energy goes backwards, sometimes laterally. This lateral movement is very dangerous because it can cause people to fall, and that can trigger a crowd collapse.”
Still has a simple way of demonstrating how density affects crowd movement. “You can get quite a graphic image of this with a simple loop of string that encircles an area of one square metre,” he says.
“We have a series of videos that show how movements change as the number of people inside the string increases.”
Once you have more than three people in the loop, each individual is restricted. Marching in step relieves some of this difficulty, but as soon as one person in the crowd marches out of step, he or she becomes an obstacle. Click here for two people per square metre, here for three, four and six.
The key is to stop this from happening, and that is where crowd management comes in. “We do quite a lot of research into the psychology of crowds,” says Kemp.
“We did a study on policing and stewarding of crowds, for instance, and found that over half the people we asked found police and stewards threatening, mentioning their dark, intimidating uniforms.
"So we put the stewards in bright coloured uniforms – pink, orange and blue – and the perception radically shifted.”
Once they were dressed in day-glo brights, almost everyone questioned said that they saw the stewards as facilitating their fun day out.
This also suggests an easy way of managing the crowd. Stewards can wear colour-coded uniforms according to their role, which makes it easy to see what is going on.
In with the crowd
“We use a four-tier-plus-one structure. So we have volunteers in the crowd who if they spot something raise one hand and point with the other to the possible trouble spot. Then the second tier – the steward – comes to check it out. He or she reports to a supervisor who will make a decision about what to do, and all this is reported back to the crowd manager,” says Kemp.
Soft crowd profiling – knowing as much as possible about the crowd at a particular event – is also vital, according to Kemp
“If you know who you are going to be dealing with, you know what you need to have to make them safe and secure,” he says.
“For instance, we know that almost everyone at any event will have their ticket, some money and a mobile phone. Then they might bring warm clothes and water to drink. But they will usually forget sun cream.”
The more information you have about a crowd, from its likely mood through to how it will move at particular densities, the better you can manage it – which is not the same as controlling it.
“Crowd control is a totally different thing,” says Kemp. “Crowd management is strategic planning, orderly movement. Crowd control is about restriction and limitation of groups.”
Still is clear that no modern stadium, particularly one in the confines of a city, will ever meet the people-moving ideals of the ancient world. But the planners behind London 2012 have done all they can to give the ancient world a run for its money.
After all, if it is about management and queuing, we Brits are surely in with a chance of Olympic glory. ®
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