Evacuation Analysis - RIBA

Management Summary

To meet the UK building fire safety requirements either a prescriptive or performance-based fire analysis approach will need to be performed. In the case of performance-based analysis, also known as Fire Safety Engineering approach, crowd simulation tools can be used to determine the Required Safe Egress Time (RSET) which is compared to the Available Safe Egress Time (ASET). The ASET is often determined using a fire modelling tool. This use case will examine the stages involved in the UK RIBA guidelines to identify current UK fire safety practices and data exchanges performed during the building design phase.

Use Case Definition

When it comes to occupants' safety in buildings, prescriptive codes are in place. However, for special and more complex buildings such as stations, airports, high rises, the prescriptive rules are not always applicable. Therefore, a performance-based approach is used, which utilises either hand calculations or computer model simulations to determine evacuation times and possible bottlenecks in the building's design. For a given scenario, performance-based analysis has to determine the Available Safe Egress Time (ASET), which needs to be greater than the Required Safe Egress Time (RSET) plus a suitable safety margin.

  • ASET (commonly determined by the time required for certain fire parameters to reach identified critical life safety conditions) is driven by the fire development and determined by a fire simulation.
  • RSET (commonly defined as the time required to complete the evacuation) is driven by human behaviour and often determined by an evacuation simulation. 

Another approach is to use coupled fire and evacuation analysis, where the impact of fire hazards on the population is directly taken into consideration during the evacuation simulation and so RSET and ASET values are not explicitly determined. Although this approach is less common, it can provide more realistic results. 

In the ASET and RSET approach, the evacuation analysis is undertaken without exposing the population to the evolving fire atmosphere, and so the fire does not impact the evacuation dynamics in any way. In the coupled approach, the evacuating population are exposed to the developing fire hazards, which may have an impact on their performance or the decisions they make during the evacuation. Using such an analysis, it is possible to derive a more realistic estimation of evacuation times and to determine the impact of the evacuees' cumulative exposure to fire hazards i.e. number of expected fatalities and injury levels [1].

[1] Siddiqui AA, Ewer JA, Lawrence PJ, Galea ER, Frost IR. Building Information Modelling for performance-based Fire Safety Engineering analysis – A strategy for data sharing. J Build Eng. 2021;42(102794). http://dx.doi.org/10.1016/j.jobe.2021.102794


Aim and scope

The aim is to identify the performance based fire safety analysis workflow related to the evacuation design of a given structure in relation to the UK RIBA stages.

The focus will be on the building design stages, which are stage 2, 3 and 4 of RIBA.


  1. Identify the actors and stages involved in the evacuation design phase.
  2. Identify the workflow for evacuation modelling tools.
  3. Identify data exchange requirements to carry out evacuation analysis using modelling tools.
  4. Identify current IFC support for data exchange and limitations, together with areas for improvement.



  1. This use case is based on UK RIBA stages.
  2. Focused only on the design stages.


  • Approved Document B (AD B) [AD B is a prescriptive document that allows alternative solutions to be implemented for more complex scenarios. These alternative solutions are typically called fire engineering solutions or performance-based solutions.]
  • British Standard (BS) 7974:2001 – Application of Fire Safety Engineering principles to the Design of Buildings, code of practice [The BS 7974 is the main document that provides technical support for the development of fire engineering solutions, including human factors and computational modelling]



Fire Safety Engineering (FSE)

Occupant Movement Analysis (OMA)

Project Group



The documents reflect the current best practice and do not claim to be complete. They should not to be understood in the sense of a generally valid recommendation or guideline from a legal point of view. The documents are intended to support appointing and appointed parties in the application of the BIM method. The documents must be adapted to the specific project requirements in each case. The examples listed do not claim to be complete. Its information is based on findings from practical experience and is accordingly to be understood as best practice and not universally applicable. Since we are in a phase in which definitions are only emerging, the publisher cannot guarantee the correctness of individual contents.

  • Document Type : Use Case
  • GUID : CCEB0BA5-0E8F-4CA2-80E5-B6CF856BA003
  • Identifier : OMA-EVAC-RIBA
  • Life Cycle Stage : RIBA - plan of work
  • Revision : V1.1.1.0
  • Project Status : Approved
  • Maturity level : Example
  • Use Case: Draft
  • Processes: Draft
  • ER: Draft
  • Published on: Dec 6, 2021
  • Last change: Mar 1, 2022
  • Publisher: buildingSMART International
  • Author: Abualdenien, Jimmy | Kneidl, Angelika | Lawrence, Peter | Lehtoviita, Timo | Siddiqui, Asim | Thompson, Peter

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