Crowd collapses and crushes
Crowd collapses and crushes are catastrophic incidents that can occur when a body of people become dangerously overcrowded. When a body of people reach or exceed a densities of four or five people per square metre, the pressure on each individual can cause the crowd to collapse in on itself, or become so densely packed that individuals are crushed and asphyxiated. At this density also a crowd can start to act like a fluid, sweeping individuals around without their volition. Such incidents can occur at large gatherings such as sporting, commercial, social or religious events, though the critical factor is crowd density rather than crowd size. It is estimated that some 66,000 people were injured in crowd collapse and crush incidents between 1992 and 2002, though crowd scientists believe this to be a gross underestimate. It is also believed that current legislation offers inadequate protection against such events being allowed to happen.
Background[edit]
One study has calculated there were 232 deaths and over 66,000 injuries in the ten years between 1992 and 2002,[1] and it is believed by crowd scientists that such incidents are both vastly under-reported and increasing in frequency. One estimate is that only one in ten crowd injuries occurring in doorbuster sales are reported, while many if not most injuries at rock concerts are unreported.[1]
Dynamics[edit]
The average individual occupies an oval floorspace approximately one ft deep by two foot wide (ie. 30cm by 60cm, or 0.14 square metre), and at densities of one to two per sq m individuals can move freely without contact. Even if people are moving quickly, at this density it is possible to avoid obstacles and the chance of a crowd-related incident is minimal. Even at three or four per sq m the risk is low;[2] however at densities of five per sq m the possibilities for individuals to move become limited, while at higher densities (six to seven per sq m) individuals become pressed against each other, and can be unable to move of their own volition. At this point a crowd can begin to act like a fluid, with individuals moved about by the pressure of those around them, and shockwaves can pass through the crowd as pressures within the crowd change.[3] The dangers inherent in these conditions is that the crowd will collapse in on itself, or become so densely packed that individuals are crushed and asphyxiated.
Crowd collapses[edit]
A crowd collapse occurs when a crowd is so dense that each individual is touching others all around, and is to an extent supported by those around. This can occur if the crowd is moving or stationary. If a person then falls, the support to those around is lost, while the pressure from those further out remains, causing people to fall into the void. This process is then repeated, causing a bigger void, and will progress until the pressure eases: meanwhile those who have fallen are at risk of being smothered by the weight of bodies on top, or be trampled as the crowd is swept over them.[4]
Crowd crushes[edit]
At even higher densities (up to nine per sq m) a crowd can become so packed that individuals/ people are crushed together to such an extent they can no longer breathe, and are asphyxiated. Such crowd crushes can occur when a moving crowd is funnelled into a smaller and smaller space, or when it meets an obstacle (such as a dead end, or a locked door), or when an already densely-packed crowd has an influx of people, causing a pressure wave towards those at the front of the crowd. In this situation those entering may be unaware of the effect on those in front, and continue to press in.[4]
Causes of death[edit]
In crowd collapse and crush incidents the most common cause of death is asphyxiation, caused either by vertical stacking, as people fall on top of one another, or by horizontal stacking, where people are crushed together or against an unyielding barrier. Victims can also exhibit fractures due to pressure,[5] or trampling injuries, when a crowd has swept over them where they have lain.[5]
See also[edit]
References[edit]
- ^ a b Pearl, p.4
- ^ Pearl p.6
- ^ Pearl p.7
- ^ a b Hajj crush: how crowd disasters happen, and how they can be avoided Leo Benedictus 3 October 2015 The Guardian
- ^ a b Mourners crushed at Stalin’s funeral Evgenii Evtushenko 1963
Sources[edit]
- Tracy Hresko Pearl, How US law leaves American crowds unprotected Univ. Kentucky Law Journal Vol 104:1 2015-16