This report describes the fire dynamic conditions in natural ventilated tunnels. A summary of the today’s knowledge about the dynamic fire conditions in nonventilated road or railway tunnel is given. The concept of fire dynamic conditions includes the variation of different parameters in length and height at different ventilation conditions. This primarily applies to parameters such as fire development, heat and smoke gas dispersion, gas temperatures, heat radiation towards objects and surrounding wall construction, flame lengths and sight length and toxic conditions in the smoke gases.