A comminutor reduces the size of particles of frangible blast media from each particle's respective initial size to a size smaller than a desired maximum size. The frangible blast media may be entrained in a flow of transport gas. The comminutor includes an inlet and an outlet, both in fluid communication with an internal flow passageway. The internal flow passageway includes a first intermediate passageway which comprise the gap defined by two rotating rollers and a second intermediate passageway which includes an inlet disposed proximal the gap, extending in an upstream direction therefrom.