Safety first: evacuating large crowds

Safety first: evacuating large crowds

The new open-air arena in Ta’ Qali

One of the projects that we have been very excited about in the past few weeks is the crowd evacuation planning for the new recreational space in the site situated between the National Football Stadium and the formal gardens of the Ta’ Qali National Park. Using a performance-based approach, we were able to determine the maximum number of occupants that the arena could hold when used for the purpose of hosting a typical large-scale event.

Performance-based design

In safety engineering, it is increasingly becoming standard practice to perform emergency planning of large crowds using performance-based design in favour of assessing compliance to prescriptive guidelines.

The benefit of performance-based design, a simulation technique which consists of an analysis of scenarios to determine which design alternatives will meet the desired goals, is especially apparent in projects that do not match the prescriptive requirements specified in guidelines such as fire safety guidelines. This is because a performance-based approach can be used to illustrate the flow of people traffic in different scenarios and use the outputs from these models to compare, for example, the time needed for evacuation to be complete before safety conditions become untenable. This method also offers architects more flexibility in the architectural design, providing them with the possibility to discuss different options with their clients, something that would not be possible when using prescriptive guidelines.

It also offers mass event organisers insights on practices that can be adopted to evacuate their clients safely from a particular spot and also allow them to assess whether one site has more favourable evacuation features than another.

Based on realistic situations

Performance-based assessments are carried out using an evacuation simulation software that has been validated against the relevant codes, fire drills and literature that captures the evidence from previous experiments. The fact that this type of design is based on realistic situations and characteristics means that fire and safety engineers can have a higher level of confidence in the results that they obtain through such methods, particularly in complex situations. Given that the simulation process also generates visual results, it is particularly useful to have these studies to visualise certain criteria, such as, for example, where crowd congestions are being formed and how these insights can be integrated by the management team to facilitate evacuation planning.

A number of advantages

A useful feature of performance-based design is that this type of assessment can be applied to emergency planning in both indoor and confined outdoor areas. For open air venues, for instance, prescriptive guidelines assume that occupants are standing next to the exit, and that they can leave the site immediately once evacuation begins. In reality, exits are often at some distance from the main occupied area. Performance-based assessment consider this important element in that they take into account not only the flow through the exits but also the movement of people from their initial location to the final exit leading them out of the event venue.

Not only. With performance-based design, you can also take into account other important factors that will have a bearing on the evacuation, such as the occupants’ age, their physical disabilities and levels of toxicity, all of which influence the time taken to travel to the exit. This means that when adopting a performance-based approach, the fire and safety engineer is able to provide more realistic insights and forecasts of the dynamics of the evacuation process, such as, for example, how long it is likely to take to be completed.