ABSTRACT The focus of this study is to outline the general requirements to accurately simulate the air quality in the breathing zone of a person using CFD when steep gradients of velocity@ temperature@ and contaminants are present near the person. In particular@ these steep gradients may result from the presence of personal ventilation devices@ or from body-emitted bio-effluents. Two configurations are discussed in the paper: a person sitting in an infinite domain with no nearby ventilation system (buoyancy-driven flow alone)@ and the case of a person sitting in a room with a combined displacement and personal ventilation system. The latter case compares the computational results with test data for validation purposes. Issues discussed in this paper include: (1) the importance of proper physical representation of the person near the breathing zone including the shoulders@ neck and chin@ (2) the effects of the thermal boundary conditions@ and (3) the effect of grid resolution. CFD results are obtained using the steady Reynolds- Averaged Navier-Stokes (RANS) method with the k-??and k-??families of turbulence models.