five people per square meter by g keith still

A stampede is uncontrolled concerted running as an act of mass impulse among herd animals or a crowd of people. Cattle are particularly prone to stampedes. Any sudden, unusual event can set one off, such as a horse shaking itself, a lightning strike, or even just a tumbleweed. Other species that stampede include elephants, walruses, wild horses, rhinoceros, and humans. Human crushes often occur during religious pilgrimages and professional sporting and music events. They also occur in times of panic (e.g. as a result of a fire or explosion) as people try to get away.

Crushes are very often referred to as stampedes but, unlike true stampedes, they can cause many deaths. They typically occur when members at the back of a large crowd continue pushing forward not knowing that those at the front are being crushed, or because of something that forces them to move. It has been suggested that crowd density rather than size is important, with a density of about four people per square meter beginning to be dangerous, even if the crowd is not very large.

A large animal stampede typically eliminates everything in its path. With livestock, cowboys attempt to turn the moving herd into itself, so that it runs in circles rather than running off a cliff or into a river and avoids damaging human life or property. Tactics used to make the herd turn into itself include firing a pistol, which creates noise to make the leaders of the stampede turn. Animals that stampede, especially cattle, are less likely to do so after having eaten and spread out in smaller groups to digest. To further reduce the risk of stampedes, cowboys sometimes sing or whistle to calm the herds disquieted by nightfall. Those on watch at night avoid doing things which could startle the herd and even distance themselves before dismounting a horse or lighting a match. Sometimes people purposefully induce cattle to stampede as a component of warfare or hunting, such as some Native Americans, who were known to cause American bison to kill themselves at a ‘buffalo jump’ (hunters herded the bison and drove them over a cliff).

Academic experts who study crowd movements and crushing disasters oppose the use of the term ‘stampede.’ ‘The rhetoric of ‘stampede’ is often used to imply that the crowd is animalistic or mindless,’ University of Sussex crowd behavioral expert Anne Templeton told ‘Newsweek,’ commenting on the 2015 Mina disaster, which occurred during the Hajj outside Mecca, Saudi Arabia. ‘The density of the Hajj has been shown to reach up to 6–8 people per square meter, so I would be very surprised if a stampede (implying people running mindlessly) could occur in the first place.’

Most reported ‘stampedes’ are better understood as ‘progressive crowd collapses’: ‘beginning at densities of about six or seven persons per square meter, individuals are pressed so closely against each other they are unable to move as individuals, and shockwaves can travel through a crowd which, at such densities, behaves somewhat like a fluid. If a single person falls, or other people reach down to help, waves of bodies can be involuntarily precipitated forward into the open space. One such shockwave can create other openings in the crowd nearby, precipitating further crushing. Unable to draw breath, individuals in a crowd can also be crushed while standing. Journalistic misuse of the term ‘stampede,’ says Edwin Galea of the University of Greenwich, is the result of ‘pure ignorance and laziness … it gives the impression that it was a mindless crowd only caring about themselves, and they were prepared to crush people.’ In reality, individuals are directly crushed by others nearby who have no choice, and those who can choose are too distant from the epicenter to be aware of what is happening.

It is believed that most major crowd disasters can be prevented by simple crowd management strategies. Human stampedes can be prevented by organization and traffic control, such as barriers. On the other hand, barriers in some cases may funnel the crowd towards an already-packed area. One problem is lack of feedback from people being crushed to the crowd pressing behind – feedback can instead be provided by police, organizers, or other observers, particularly raised observers, such as on platforms or horseback, who can survey the crowd and use loudspeakers to communicate and direct a crowd. After the 1883 crush known as the ‘Victoria Hall’ disaster which killed 183 children, a law was passed in England which required all public entertainment venues to be equipped with doors that open outwards, for example using crash bar latches that open when pushed. Crash bars are still required by many building codes.

There is risk of a crush when crowd density exceeds about four people per square meter. For a person in a crowd a signal of danger, and a warning to get out of the crowd if possible, is the sensation of being touched on all four sides. A later, more serious, warning is when one feels shock waves travelling through the crowd, due to people at the back pushing forward against people at the front with nowhere to go. Keith Still of the Fire Safety Engineering Group, University of Greenwich, said ‘Be aware of your surroundings. Look ahead. Listen to the crowd noise. If you start finding yourself in a crowd surge, wait for the surge to come, go with it, and move sideways. Keep moving with it and sideways, with it and sideways.’

Deaths from human crushes and stampedes are found to be caused primarily by ‘compressive asphyxiation’ (they lack the physical space for their ribcages to expand enough to breathe); trampling is a lesser killer. In a crowd crush people are subjected to compressive forces by being pushed from all sides (or against a barrier such as a wall) with nowhere to move into. In a progressive crowd collapse one person falls, creating a space in the crowd into which others fall, creating an even larger hole. Those who have fallen are squashed by the weight of many people on top of them (vertical stacking). Compression in either case is often fatal. A crush is typical of a crowd pushed into a confined area; a progressive crowd collapse may occur in a large crowd moving steadily forwards along a confined route.

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