The dispersion of permeated hydrogen from a storage tank in a typical garage with adiabaticwalls and still air is studied analytically and numerically. Numerical simulations areperformed based on an original approach of a hydrogen mass source term introduction inthe hydrogen conservation equation in control volumes around the tank surface. Themaximum hydrogen concentration in an enclosure is always on the top surface of the tankand never reaches 100% by volume. Both the analytical analysis and numerical simulationshave demonstrated that diffusion and buoyancy contributions to the hydrogen transportfrom the tank surface are balanced within 1 min from the start of the process. The quasisteadystate conditions within the enclosure with approximately linear distribution ofhydrogen from the top to the bottom are established in about 1 h for both consideredpermeation rates: 1 NmL/hr/L of tank capacity and 45 NmL/hr/L the last being an equivalentto the SAE J2578 requirements. Finally, the numerical simulations demonstrated thatthe difference in hydrogen concentration between the garage ceiling and floor is negligiblecompared to the lower flammability limit of 4% by volume of hydrogen.