The Crush Point : How Fluid Dynamics Can Help You Manage Crowds


#1

There is a term which is adroitly coined as ‘crush point’. A crush point exists at the point where two objects meet. The objects can be moving toward each other, or one object can be moving toward a stationary object. More ominously, the crush point could occur in a crowd when the movement of crowd improperly managed.

Crowds are a reality of urban life. On roads and sidewalks, in elevators and malls, we are a part of ‘them’ in the course of a day, without thinking by what mechanism our brain manoeuvres ever so easily, hardly touching a stranger’s shoulder. Crowds are often considered as a city-life inconvenience, but many a times when we are happy to be a part of the crowd be it a Metallica concert or a cricketing bonanza at the magnificent Eden Gardens, or at Forever 21’s big sale.

However, a word of caution. Things get really dangerous if the crowd continues to get denser, or people make unexpected movements. The flow can become turbulent and chaotic, with people being pushed randomly in different directions. Such activities often lead to disasters, wherein, one person stumbles, therefore causing others to fall at their places. This can only end in trampling or stumbling in a further domino movement. It is known as the “black hole effect,” with people getting ■■■■■■ in.

So the question then is ‘Are there ways to keep large crowds safe?’

John Fruin, is one of the founders of crowd studies in the U.S. In a 1993 paper, “The Causes and Prevention of Crowd Disasters,” he said, “At occupancy of about 7 persons per square meter the crowd becomes almost a fluid mass. Shock waves can be propagated through the mass sufficient to lift people off of their feet and propel them to distances of 3 m (10 ft) or more. People may be literally lifted out of their shoes, and have clothing torn off. Intense crowd pressures, exacerbated by anxiety, make it difficult to breathe.”

As the nature and behaviour of human crowds is so unpredictable, researchers hesitate to give general advice on how to manage them. (The strategy they advise is to stay out of the crowd in the first place.) For better, much of the responsibility for crowd safety falls on the organisers of the event rather than the individuals participating in it.

So much trouble right? Well the part is that crowd disasters, in general, are man-made disasters which can be completely prevented with proactive planning and flawless execution by dedicated groups of well-trained personnel.

So when you plan for an event, remember to note when can the crowd you are expecting to turn up starts behaving like a fluid. A very important point to remember here is to identify the bottlenecks in the flow. Bottlenecks usually relate to the Bernoulli’s theorem. In fluid dynamics, Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. The decrease in speed due to congested exits causes density to increase, which again speeds up the way people are leaving the exits, thereby causing a stampede at the gates.

In our pH tests as well as all other events, the first thing that comes to our planning team’s mind is to find out exit points and the ways leading to these points. We always have a rescue plan ready for crowd evacuation in order to ensure safety. Point of advice: Diverting the crowd to the nearest exit point is as important as not creating bottlenecks in the flow to avoid high density. Always try to keep the crowd well informed about the entry and exits points, and make sure that the crowd comes in batches if the entry points cannot accommodate all the numbers at the same time.

The irony is that a crowd is risky only when it starts behaving like a fluid but fluid dynamics is also the saviour in such circumstances. It can help you avoid stampede like situations by planning and executing the safe movement of crowd.

Also, if you are a part of such a crowd, remember to always navigate, observe and go with the flow and try to get out of the crowd as soon as you get space. If you are falling, get support of the next person to avoid getting crushed in the crowd. These simple science principles can save your life, if applied, when organisers fail to meet crowd safety standards.