This work examines particle separation mechanisms as factors that influence dust generation due to the flow of granular materials. A model was developed to predict particle separation forces that requires knowledge of some process variables and of some material properties. In granular flow conditions, the biggest separation forces occur during material impact. Therefore, a test method and apparatus were developed to determine the impact of falling material on a pile as an indicator of the separation forces created. Five factors that influence impaction forces of falling granular material were investigated: drop height, material flow, material moisture content, material size distribution, and material type. Drop height was varied between 0.25 and 1.25 m, whereas material flow was varied between 0.1 kg/s and 0.6 kg/s. The moisture content of the parent material was varied between 0 and 1.2% for all materials except lactose for which moisture content was varied between 1 and 6%. The size distribution of the granular material was adjusted by classifying the materials into three fractions with aerodynamic diameters of d<5mum, 525mum for each of four test materials: titanium dioxide, limestone, glass beads, and lactose. Impact forces are high when particles fall with high velocities and land on hard surfaces. Coarse, high density materials with a high moisture content dropped at high drop heights showed high impaction forces.