Crowds are a phenomenon of modern society. As the world population increases, so does the frequency of mass gatherings and mass events (Li et al, 2020). Instigated by a career in major events, I am fascinated by crowds, how they move, how they behave. When I began studying crowd safety, it became clear that most crowd disasters could have been avoided with simple strategies. However, in order to prevent, we must understand why they happen in the first place.
Over the last century in the UK, changes in legislation have supported the reduction of football related crowd disasters. Modernisation of communications and transport have allowed the sharing of training, skills and experience between countries across the world. However, disasters are still occuring, and since the pandemic, the event safety industry has faced significant issues such as loss of human resource, loss of experience and a shift in crowd behaviour, which all contribute to dangerous occurences. When disaster occurs, it is always due more than one reason, which I have previously discussed. However, this article focuses on the proximate cause, i.e. the trigger point of a crowd 'crush' or crowd turbulence (Helbing et al, 2007).
There are two main areas of academic study on crowds - physical (crowd dynamics) and psychological (crowd psychology). The reason a crowd come together can be fuelled by psychology (sport, politics, celebrations) but once this crowd form, dynamics swirls into the mix. Effective crowd management balances both crowd psychology and crowd dynamics.
Foule; How we perceive crowds
Over the last century, our perception of crowds and how they behave have evolved. The classical view, developed by notable names from France and Italy including Gustave Le Bon, Gabriel Tarde and Scopio Sighele perceived crowds as as collective mind, a single soul, void of reason and intellectually inferior to the individual (Le Bon, 1896). Tarde (1968) viewed crowds as 'hypnotic states' and a germ of society. By the end of the 19th century, crowds were viewed in a negative light. The French for crowd is foule, (one letter away from the English 'foul') which offers further insight to how crowds were perceived in the past. In fact, the study of crowds was in order to subvert and control them (Nye, 1975). However, modern researchers, spearheaded by Elias Canetti (Crowds and Power, 1962), have realised that crowds are far more rational, discriminate, not as violent as previously assumed and don't panic (Drury et al, 2009; Drury and Reicher, 2009; Templeton et al, 2015). Today, studies focus on shared social identity in crowds; where collective behaviour occurs when individuals shift from personal identity to identify as part of a group, resulting in reduction in stress, increase in well-being (Hopkins and Reicher, 2017), and mutual aid and cooperation in times of crisis (Drury et al, 2009; Yuan and Xiaoping 2018; Drury et al, 2019).
So why, if crowds are not as irrational as previously assumed, does a crowd 'crush' happen? There are many factors to consider; time, density, flow, surface area, time of day, weather, communication, management, type of event, type of environment, etc. but it all narrows down to density. The proximate cause of a 'crush' is insufficient information and space (Sime, 1999).
Density itself is not a risk without a trigger. When density increases in a crowd, flow decreases, which can shift the dynamic of the crowd from moving to 'jamming' (Zheng et al, 2010). An increase or decrease in crowd density can potentially be the difference between life or death. At densities of 2 people per metre squared (ppm²), people can move relatively freely and sway their arms as they walk together in a crowd. At a density of 3-4ppm², crowd flow decreases as people have less room to walk. This density is typical of a queue or standing audience.