The evaluation of different evacuation models for assessing road tunnel safety analysis

The current state-of-the-art presents a multiplicity of evacuation models for simulating emergency scenarios. Each model involves different methodological solutions to represent the same process and each one has its strengths and limitations. In addition, they have their own specific features and often practitioners do not have a thorough understanding of the variables that could be input into the models and how they will affect the results. Thus, there is a need to analyse the differences between the models, why they occur and how they affect the calculations. This study compares three evacuation models (FDS+Evac, STEPS, Pathfinder) and the analytical calculations provided in the Society of Fire Protection Engineers (SFPE) Handbook, each of them using different simulation methods. The case-study is the Lantueno tunnel in Spain (a two-bore road tunnel with an emergency link tunnel between the two bores). The results initially show that, when considering evacuation scenarios with a single available exit and favourable response times, the obtained evacuation times do not differ significantly between the models. In a second step, the analysis of more complex scenarios has allowed the determination of the main factors of occupant–fire interactions that cause the differences between the models: the use of unfavourable pre-evacuation times and the exit selection process under low visibility conditions. These differences occur in relation to: (1) modelling method, (2) degree of depth of the analysis of the fire conditions during the calibration of the inputs, and (3) user’s experience in applying appropriate safety factors when using only one model.