A mass gathering, as defined by World Health Organization is: “A planned or unplanned event at a specific location, attended by a huge number of people for a common purpose. This number is sufficient enough to strain the planning and response resources of the community, state or a nation hosting that event”.
The increasing influx of large numbers of people to mass gathering events may give rise to complex disastrous situations, thus require extreme planning and operational support for Public Safety & Security (PSS) preparedness by the organizers of mass gatherings or the governmental entities in general.
Hajj is one of the largest mass gatherings, where about 3 million Muslims gather in Makkah (Saudi Arabia), from over 140 countries, each year for a minimum of five days and up to 40 days. Following an exponential rise in the past decade, Makkah becomes the site of extreme crowd densities with huge inflow of crowd and quite vulnerable to serious disasters including stampede, accidents, construction failures, fires and communicable hazards. Factors that magnify these risks include: extended stays at Hajj sites, extreme heat, densities above 6 or 7 persons per square meter, individuals’ inability to move at concentrated regions and jostle to find breath, groups swept along in waves, struggling to avoid falling and being trampled, thus hundreds of deaths can occur as a result. Moreover, the advanced age of many pilgrims with premorbid health status adds to the mortality risks. In the past, these disasters took place many times during Hajj. In July 1990, 1426 people were killed in a crowd crush as a result of improper crowd control. In 1997, 343 pilgrims were killed and 1,500 injured in a fire incident. Similarly, in 2006, 346 deaths took place in stampede in Mina valley while throwing stones at pillars. In 2015, crane fell in the courtyard of Masjid-Al-Haram (grand mosque) causing a total of 512 casualties. Again, in September 2015 more than 2000 pilgrims were crushed due to stampede at Mina.
The disasters can be prevented through proper crowd management & control strategies and is usually expressed as a governmental responsibility under PSS departments. An effective PSS infrastructure for crowd management & control consists of the following key components:
- Preparedness & Incidence Response;
Monitoring involves a continuous process of observing real-world activities and supervising the crowd flow. Mitigation concerns preemptively preventing possible emergencies, planning exit points & escape routes etc. Preparedness deals with the timely preparations to handle dangerous situations such as firefighting, construction failures, or natural disasters. Incidence response involves timely rescue operations, emergency evacuations, crowd management, shelter and medical services during crisis. Recovery deal with the actions taken to return to a normal state. An efficient PSS infrastructure relies on smart planning and decision support systems that can provide quick and accurate identification and assessment of optimal strategies to be used for a real-world situation under a specific context.
With the advent of modern Modeling and Simulation (M&S) paradigms, there has been an increasing trend in the use of Modeling and Simulation in PSS planning and decision support. Crowd dynamics simulation models are now becoming useful in replicating scenarios of safety/mission critical systems in a risk-free, low cost, time independent and harmless experimental environment where modelers can exhaust trials of different nature to gain the insights of the system, compare different alternatives or to find best design parameters. Crowd modeling and simulation plays a vital role in solving evacuation problems. Modeling crowd behavior and the movement of each individual in a crowd can help reduce the number of deaths in a building or a public area. The population is growing exponentially which is making public places busier and causing crowd related disasters.
In recent years, crowd modeling and simulation technologies have gained tremendous momentum for investigating crowd dynamics. Crowd simulations can be distinguished into two broad areas. The first focuses on the realism of behavioral aspects like crowd evacuation simulation, sociological crowd models, or crowd dynamics models. The second area aims at a high-quality visualization of a crowd with a convincing visual result and an emphasis on rendering and animation methods. Another classification of crowd simulations is based on the size of the crowd and the approach used. Simulated crowd sizes may vary from tens or hundreds to a couple of hundred thousand or millions of individuals. Usually large crowds are treated as a whole (macro-scale) where the global trend of the crowd is the focus due to the high computational needs. For smaller crowds (microscale), individual behavior is modelled in detail to support the investigation of crowd dynamics at an individual level. In this paper, we place a balance between both extremes and use an intermediate approach (mesoscale). The crowd simulation size is reasonably large (10,000) but still possesses some unique individual attributes and behavior that can be incorporated when globally examining the crowd dynamics.