Dust extraction ventilation is used in the production of medium and low intensity of the dust. These include mechanical and finishing shops, some shops chemical plants, etc. Here, buildings are typically divide the floors, the height of the premises no more than 5 m strip inclined ducts is often impossible. With low content of small and relatively light dust ducts are laid horizontally. It also may include dust removal from the shelter, where there is a slight dusting: here the concentration of aching in the exhaust air is so insignificant that the air is thrown out without any treatment.
Ventilation is directed against the primary dust emission. which is a consequence of the process.
This source of dust pass and interested. However, the possibility of secondary dust imposes certain conditions on the forced ventilation of dusty rooms. It should be noted that the incoming air in the dusty room is always served dispersed with low velocities. On the filing of the concentrated flow is not speak.
Submission of fresh air in the upper zone is dictated primarily inadmissibility of resuspension of dust settling on the floor and building designs. From the above follows the rule: to have air-supply ducts needed so that the outgoing air does not impede the natural settling of the dust not only on the floor, but also in building construction, where the dust is removed with a wet method or a vacuum cleaner. In dusty areas are quite acceptable perforated ducts by the panel.
The ability of the dust a long time in the air, especially when air flow is extremely difficult to combat it. Any turbidity has settled dust - air jet or feet when walking on the dusty floor, is extremely undesirable. Practice shows that a poorly organized, dry cleaning dusty sometimes doubling its dust. This is an extreme case, but the increase in dust even at 20-30% due to the resuspension of settled dust does not lead to improved well-being of people. We note in passing that in still air particle mineral ached size of 1 micron is deposited at a rate of about 25 cm / h. In the air the same commercial premises, where unavoidable or that flows, dust particles of 2 microns by a relatively long time may soar, such as crushing shops dust sizes up to 3 microns almost do not settle.
If the floor is constantly wet, which is recommended for crushing and similar plants, there is no risk of resuspension of dust as the air stream, and legs. Under this condition, supply fresh air into the work area evenly with small speeds do not cause any negative effects. Tolerable daily intake air supply during summer in the work area (at 0.7 m above the floor) with constantly wet floors featured in the SI 155-61. Perhaps in some cases serve incoming air into the work zone and during the cold period of mechanical ventilation (with low rates), subject to constantly wet floor and the air in a considerable distance from the pockets of dust.