ABSTRACT
The subject matter covered in this chapter is fundamental to the field of industrial ventilation. It deals with the motion of gaseous and particulate contaminants in relation to the air with which they are mixed; in other words, with their segregation tendencies. The chapter talks about a classification based on physical rather than hygienic properties of the various airborne substances. Dusts are finely divided solids that may become airborne from the original state without any chemical or physical change, other than fracture. Fumes are solid, air-borne particles that have resulted from some chemical or physical process that involved a change of state—usually a thermal process of oxidation, sublimation, or evaporation and condensation. If the liquid is a water solution of a solid, evaporation of the water takes place after mist formation and a system of dry particles in atmospheric suspension, having the same composition as the material dissolved in the mother liquor, results.
