One of the most crucial factors of fire safety is to predict the smoke density and emission including heat transfer at the stage of design. During fire, heat and smoke spread, density of toxic gases, efficiency of exhaust and ventilation system are analyzed with Computational Fluid Dynamics (CFD), which is a 3-dimensional simulation method.

With CFD, the area of interest is subdivided into a large number of cells or control volumes. In each cell, equations are written to relate the velocity, temperature, pressure, and other variables, to the values in the neighboring cells. These equations are then solved numerically, yielding a complete description of the flow throughout the domain. CFD analyses have a potential to save time in the design process, since all desired quantities can be measured at once. Especially in structures with high fire risk such as tunnels and stations, CFD analyses hold great importance.