The Use of Advanced Evacuation Modelling for Building Design using MassMotion

Introduction

Evacuation modelling simulates human behaviour during emergency situations and is based on crowd dynamics and pedestrian movement within a defined geometry. Evacuation modelling can be applied to a wide array of building and infrastructure work.

In the past, the development of buildings has been based on prescriptive recommendations provided in various building regulations and codes. Current and future buildings are becoming more and more bespoke and the application of prescriptive recommendations is proving very restrictive to building designers. As a result of this, performance based design is now seen as a more appropriate method to allow building designers realise unconventional buildings.

The use of advanced evacuation modelling has become an integral part of the performance based design process to ensure buildings remain ‘safe’ for their occupants. While traditional hand calculations can be used for simple evacuation scenarios they are often not sufficient for complex designs. For such complex designs, advanced evacuation modelling can and has been used to:

  • demonstrate and calculate overall building evacuation time,
  • calculate queuing times and flow rates through exits and stairs,
  • identify bottle necks along evacuation routes and,
  • provide the overall design team and stake holders with an understanding of how the building operates in evacuation mode.

This case study explores advanced modelling using the MassMotion software package and provides an example of where evacuation modelling has proven beneficial in a shopping centre containing existing heritage protected structures.

Shopping Centre, Ireland

Project Description

The Shopping Centre (which cannot be named for commercial reasons) is located in Ireland. The centre contains 36,000m² of car parking, 28,000m² of retail development, 3,000m² of commercial space, 135 residential units and a 122 bedroom hotel. At peak times the shopping centre can accommodate up to 8,000 people at any one time.

A number of heritage protected structures including an old railway terminus building dating back to the 19th century have been integrated into the modern shopping centre development. This required a sensitive approach and assessment to retain the existing features, structure and facade while refurbishing the building to achieve life safety requirements and the new uses.

The Analysis

Arup Fire provides ongoing fire engineering services to the shopping centre management team for this large shopping centre. As a majority of the buildings in the shopping centre are protected structures and therefore cannot be altered, advanced evacuation modelling has become an integral part of their service. MassMotion was used to demonstrate that while code compliant means of escape is not always provided from the existing protected structures, sufficient means of escape to ensure the safe egress of occupants is available.

While a large amount of fire engineering and egress analysis has been carried out on the existing shopping centre, evacuation modelling has become particularly useful in the recent fit out of an existing protected structure. Compliant escape capacity was achieved; however it was not possible to provide code compliant travel distances from the upper floors of the unit as this would mean altering the protected structure, which was not possible.

MassMotion was used to demonstrate to the local approving authorities that when one exit was discounted due to fire the escape time from the unit was dictated by the compliant escape width rather than the non-compliant travel distance: occupants will be queuing longer than the time taken to travel to the exit. To further demonstrate the robustness of the theory the speed of the occupant at the furthest travel point was set to an average of 0.675m/s to simulate a mobility impaired person (MIP).

Results

The use of MassMotion and evacuation modelling showed that the overall queuing time in the retail unit would be approximately 130 seconds and the time required for an MIP to travel an extended distance to the exit was 64 seconds. This demonstrated that the escape time for the MIP is dictated by the compliant escape width rather than the non-compliant travel distance. Therefore the extended travel distance in the unit does not pose an issue for an evacuating MIP.

The images below show the position of the MIP at the furthest point of travel at the beginning of the simulation and at 50 seconds. It can be clearly seen that the MIP has reached the back of the queue of evacuating occupants and the extended travel distance does not affect the overall means of escape of the MIP.