The dispersion and loss of helium inside a single-car residential garage attached to a single-family house was experimentally characterized by recording time-resolved helium concentrations at multiple locations in the garage and at a single location in the house during and following helium releases near the floor of the garage. Helium served as a surrogate for hydrogen for safety reasons, and helium release rates were adjusted to provide the same constant volume flow rate as that required to release 5 kg of hydrogen over a four hour period. Supporting measurements included compartment leakage, temperature, and atmospheric wind conditions. Helium was released upwards either as momentum- or buoyancydominated flows. Experiments were performed with the garage empty or with one of two conventional mid-sized automobiles parked over the release location. Six tests with the garage naturally ventilated and six tests employing forced ventilation with a fan are described. A variety of parameters were used to characterize the mixing behavior. Conclusions emphasized include: a) the role of Froude number on helium mixing behavior, b) the development of upper and lower helium concentration layers in the garage during a release, c) the measurable, but limited, effects of atmospheric wind on the results, d) the relatively efficient transfer of helium from the garage into the house during the releases, e) the ability of a vehicle to trap a high helium concentration in the engine compartment and, particularly, the undercarriage during a helium release and the relatively rapid drop in these levels to those of the surrounding garage at the end of the release, f) the relatively slow buildup of helium in the passenger compartment and trunk of a vehicle during a helium release and subsequent slow decay following cessation of the flow, g) the effectiveness of active ventilation in reducing helium concentrations in the garage to levels below those corresponding to flammable concentrations of hydrogen, and h) the trapping of helium/air mixtures corresponding to highly flammable hydrogen mixtures inside the vehicles even when active garage ventilation was employed.