[en] The characteristics of the pressure waves transmitted by detonation of gaseous mixtures to the surrounding air were measured by tests made near the ground level in 1 to 54 m3 spherical balloons containing air-acetylene or air-ethylene mixtures. As concerns the peak overpressure Δp, a theoretical dimensional analysis in accordance with the experimental results shows that Δp can be expressed as a function of two independent variables, which are the radial distance R and the volume V of the balloon . A semi-empirical formula, including ground effects, is proposed and its present validity range is given. (author)