The application describes an automated system for carrying out tests using a cascade impactor 10 of the type having multiple impactor stages each comprising a respective stage body 30, the stage bodies being shaped to enable them to be assembled in a stack in which they locate one upon another. The system includes an expander device 90 having respective arms for supporting each of the stage bodies, and a mechanism for separating the arms along the axial direction to disassemble the impactor 10.