Over the last five years, we have developed a range of stochastic techniques for simulating the evacuation of public building including hospitals, entertainment complexes, a sports stadium, office buildings and concourse areas in an underground train system. This paper describes how simulations are developed from an initial risk assessment, through the integration of 3D architectural models and simulations of crowd behavior to the validation of results against ‘live’ evacuation drills and information about previous evacuations. The motivation behind this work is to support a form of 'mitigation engineering'. Evacuation simulations help us to reduce the consequences associated with a broad range of adverse events including fires, structural collapses and terrorist actions.