The primary interest of this study concerns the atomization of liquid metal in a high speed nozzle flow, in order to control the drop-size distribution. The relationship between the droplet diameter and the disruption data has been obtained by replacing the original flow by a simpler one. This change results from a force balance and by using dynamical similarity. This procedure allows one to work at ambient temperature and employ less restricting data values such as the gas velocity. Observation of the disruption by high speed photography allows some explanation of the mechanism of break-up in action; the particular impingement of gas on liquid is found to be mainly responsible for the rapid disintegration of the liquid layer. Measurements of the main geometric parameters of the spray by video image analysis under different flow conditions have led to a simple non-dimensional relation for the mass median droplet diameter. The control of the liquid film thickness together with the respective inertia forces of each fluid, rather than fluid properties, take a major part in the formation of droplets.