Numerical simulations of the propagation of plasma blobs in the scrape-off layer (SOL) of the Frascati Tokamak Upgrade (FTU) are presented. The maximum distances that a plasma blob may travel in the radial direction are calculated under FTU physical conditions and geometry, taking into account the dissipation due to the presence of dust. It is found that a relatively small amount of nanometre iron dust particles can dissipate blobs before they reach the wall. The amount of dust required is of the same order as, or smaller than, that needed to produce hyper-velocity dust particles, so that a consistent interpretation is reached for experiments in FTU where evidence of the dust impact ionization was reported.