When volcanoes erupt explosively, particles are ejected and deposit on the ground. Numerical models for particle transports are important for both the hazard assessment and the eruptive dynamics. Total grainsize distributions are necessary for numerical simulations of particle transport. Comparing field data and numerical simulations, we show the representative sampling distance required to have reasonable grainsize distributions. Numerical models of tephra dispersal require better parameterizations. We have firstly developed 2D model with Cellular Automata (CA) method and expanded it to 3D. In our 3D model, diffusion is described with a random velocity corresponding fluctuations of turbulence. The implementation of plume significantly improves the description of particle distributions. Ballistic trajectories are modeled in 3D with a Discrete Event Simulation (DES) method. Multiparticle simulations are implemented including particle-particle collisions. We show the effect of collisions on travel distance. This model is applied to the hazard assessment of Vulcano Island (Italy).