The dense phase transport mode requires a low air speed, less than 10 m/s, while the vacuum or depression have very high values, over 800mbar. In this mode, the air speed is not able to develop the force necessary for the floating of the dust particles, therefore the transported mass of dust remains compact and is transported entirely in “blocks”, as for the transport of viscous or liquid materials. The energy required for this type of transport is comparable to that of semi-dense phase transport, which is very low.