We show a solution for a realistic tunnel fire simulation using a 2D-3D coupling strategy and a full multiphysics model for concrete (2D sections), known also as three fluids model (water, vapour, dry air). The computing times are too high for a real time solution. We investigate the applicability of the proper generalized decomposition (PGD) to obtain two goals: achieve a full 3D solution for the solid domain and reduce simultaneously the computing time. The first results are encouraging.