In this article, the steady-state concentration boundary layer adjacent to a ceiling wall of a stagnation-point flow region resulting from hydrogen impinging leakage is investigated. Flow in neighborhood of the stagnation point is treated as Hiemenz flow, while the concentration equation governs the concentration distribution in the boundary layer. The assumptions of the boundary layer theory are invoked to simplify both the momentum and the concentration equations. Comparison between the CFD simulation and the current boundary layer approximation shows a good agreement. Both momentum and concentration boundary layer thicknesses are estimated as well as local friction factor and local mass transfer. Also, the study is extended to include some cases of unsteady leakage. The effects of the unsteadiness parameter on the local friction factor and mass transfer rate as well as momentum and concentration boundary layer thicknesses are analyzed. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.