Evacuation Analysis - RIBA

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To meet the UK building fire safety requirements, either a prescriptive or performance-based fire analysis approach is required. For the performance-based analysis, also known as Fire Safety Engineering approach, pedestrian modelling tools can be used to determine the Required Safe Egress Time (RSET). The RSET value is then compared to the Available Safe Egress Time (ASET) value which is often determined using a fire modelling tool. This use case uses the stages specified in the UK Royal Institute of British Architects (RIBA) guidelines to develop a process map that includes proposed openBIM based data sharing.

The normal practice in relation to fire safety in buildings is to apply a prescriptive approach. However, for more complex buildings, 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].

This use case uses the stages specified in the UK Royal Institute of British Architects (RIBA) guidelines [2] to develop a process map that includes proposed openBIM based data sharing. 

[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

[2] RIBA. Plan of Work for Fire Safety Consultation. 2018. Available from: https://www.architecture.com/knowledge-and-resources/resources-landing-page/plan-of-work-for-fire-safety-consultation)

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)

Presenting the overall process in practice, including the involved actors and the data exchange among them during the relevant RIBA stages: