1. Decomposition 
Decomposition is one of the cornerstones of computational thinking as the studied system is broken down into smaller parts that are more manageable and easier to analyze. In this case, the aim of the study is to obtain a high-quality image that is visually impressive as well as provides basic information of the flow behavior. 
To understand the main disturbances affecting the flow behavior,  the effect of the ventilation system and the presence of the  train on it are analyzed separately. The first one determines the overall flow behavior and the second will disturb the flow inside the tunnel causing turbulences. Since the image must communicate clearly the case studied, the most important variables affecting the flow are visualized independently too. These are the pressure difference, as this will define the flow movement inside the tunnel, the temperature and the smoke. The last two are the variables that influence most the possible survival of the trapped passengers. Therefore, their understanding is essential to provide a solid ventilation security system.