Development of Fire Simulation Models for Radiative Heat Transfer and Probabilistic Risk Assessment

An essential part of fire risk assessment is the analysis of fire hazards and fire propagation. In this work, models and tools for two different aspects of numerical fire simulation have been developed. The primary objectives have been firstly to investigate the possibility of exploiting state-of-the-art fire models within probabilistic fire risk assessments and secondly to develop a computationally efficient solver of thermal radiation for the Fire Dynamics Simulator (FDS) code. In the first part of the work, an engineering tool for probabilistic fire risk assessment has been developed. The tool can be used to perform Monte Carlo simulations of fires and is called the Probabilistic Fire Simulator (PFS). In Monte Carlo simulation, the simulations are repeated multiple times, covering the whole range of variability of the input parameters and thus resulting in a distribution of results covering what can be expected in reality. In practical applications, advanced simulation techniques based on computational fluid dynamics (CFD) are needed because the simulations cover large and complicated geometries and must address the question of fire spreading. Due to the high computational cost associated with CFD-based fire simulation, specialized algorithms are needed to allow the use of CFD in Monte Carlo simulation. By the use of the Two-Model Monte Carlo (TMMC) technique, developed in this work, the computational cost can be reduced significantly by combining the results of two different models. In TMMC, the results of fast but approximate models are improved by using the results of more accurate, but computationally more demanding, models. The developed technique has been verified and validated by using different combinations of fire models, ranging from analytical formulas to CFD.