Computational fluid dynamics based solvers have been developed for explosion modeling in hazards analysis. These include a numerical approach to simulate flame acceleration and deflagration to detonation transition in hydrogen-air mixture and two detonation solvers. The former solves fully compressible, multidimensional, transient, reactive Navier?Stokes equations with a chemical reaction mechanism for different stages of flame propagation and acceleration from a laminar flame to a highly turbulent flame and subsequent transition from deflagration to detonation. The model has been used to simulate flame acceleration (FA) and transition from deflagration to detonation (DDT) in a 2-D symmetric rectangular channel with 0.04 m height and 1 m length which is filled with obstacles. Comparison has been made between the predictions using a 21-step detailed chemistry as well as a single step reaction mechanism. The effect of initial temperature on the run-up distances to DDT has also been investigated. Comparative study has also been carried out for two detonation solvers. One is based the reactive Euler equations while the other is based on the simpler programmed C-burn method. Comparison has shown that the relatively simple CJ burn approach is unable to capture some very important features of detonation when there are obstacles present in the cloud.