I investigate three applications related to toxic exposure in buildings and demonstrate the use of Computational Fluid Dynamics (CFD) to address important issues: 1. Improving containment of airborne hazardous materials in an existing room containing a downdraft table. CFD is used to find a ventilation configuration that ensures better containment of the hazardous material and hence improved worker safety. 2. Modeling gas transport in a large indoor space. The goal of this study is to understand how the level of detail of the CFD model affects its accuracy. Comparison of predictions with experimental data will be presented. 3. Understanding the delivery efficiency of hydrogen peroxide vapor (HPV) through the existing air ducts to decontaminate buildings. The aim of this exercise is to develop a predictive capability to determine the transport of HPV through ducts and the spatial concentration of HPV in the building.