This paper presents a 3D finite element analysis of the effect caused by a blast inside a reinforced concrete tunnel. The simulated explosion was caused by the crash of a heavy vehicle transporting inflammable material (LPG). The finite element technique was used to analyze the structural problems on the tunnel reinforced concrete structure considering the fire action and the subsequent explosion (blast) effect, incorporating appropriate material models. Through FEM software the tunnel behavior was described with regard to structural safety. Indeed, tunnels must be designed to withstand damage factors, so it is desirable that if such an explosion did occur, the tunnel should be able to return to service in safety as soon as possible with minor repairs. Therefore, following the presented analysis, the most important factors influencing the dynamic response and the damage of the structure could be identified. The simulation involved aspects of thermal analysis and structural problems and the tensions in the structure generated by the effect of temperature caused by the fire and by the blast overpressure were analyzed. Following this approach, the most important factors influencing the dynamic response and damage of structure can be identified and appropriate preventive measures can be designated.