My job belongs to HVAC, so I can answer this question better than others.
We classify intire process in 2 cycles
1, Return cycle and
2, supply cycle
1, Return cycle- in this cycle Air returns from working area through return trenches due to vaccume generated by axial fans, air passes through a filter where micro dust particles and other cantamination removes and collected in vaccume suction bags , after filter system decides that how to use this air means have to take inside or need to exast, this depend on requirement of machines and outside weather.
2 , supply cycle, this starts from air washers where water sprey system install, rest quantity of micro dust particles totally removed by water sprey, and mousures add on , after this crosses through eliminators where heavy water particles being removed and supply fan sent it in diffusers which delivers it in department