Experiments have shown that exhalation from one person is able to penetrate the breathing zone of another person at a distance. Computational Fluid Dynamics (CFO) is used to investigate the dependency of the personal exposure on some physical parameters, namely: Pulmonary ventilation rate, convective heat output, exhalation temperature, and cross sectional exhalation area. Full-scale experimental results are used to calibrate/validate the CFD model. Respiration, although an inherently transient phenomenon, is simulated by steady-state CFD with reasonably good results.