The study of extinguishment using water mist has been motivated due to the phase-out of the use of halens and the search for alternative means that preserve all of the benefits of a clean total flooding agent without adverse environmental impact. With the numerical simulation, we analyzed a gas-liquid two-phase problem including water (liquid), air and methane (gas) using Eulerian equations for the liquid phase and the full Navier-Stokes equations for the gas phase. Gaseous mass, momentum and energy equations are integrated simultaneously by a Harten-Yee explicit non-MUSCL modified-flux type TVD scheme for the convective terms and a central difference scheme for the viscous terms. Liquid phase conservation equations are solved with an application of a flux-vector-splitting scheme. In the experiments in an open room (500x500x500 mm) we observed an interaction of the diffusion flame with the water mists. The results show remarkable flame quenching and a good agreement between the numerical and experimental results.