The concept of a downdraft table is simple, a plate is plasma cut while sitting on top of the table, and a blower pulls air out of the enclosed table below the plate. The reason this works so well is because almost all plasma smoke is ejected below the plate. The smoke is ejected out of the bottom of the kerf at a pretty high velocity, and tends to billow outward. As long as enough air is being pulled out of the table by the blower, none of the plasma smoke will escape.