Dust emission - a frequent and difficult localizable harmful. Industrial dust, as well as industrial gases, is diverse in composition and properties, the conditions of release and the action is exerted on the person.
Classification of industrial dusts can be made on different grounds. We mention some of them.
In action, exerted on the human body, the dust can be divided into three groups:
a) neutral - non-toxic dust that do not produce toxic effect on living organisms, the impact of the dust is mainly mechanical;
b) toxic - the dust of toxic substances, poisonous organism;
c) silikoznaya and asbestos dust - containing more than 10% of free silica or asbestos dust while this on its merits and is not poisonous, but causes severe lung disease - silicosis and asbestosis, respectively.
Descent dust somewhat arbitrarily divided into organic (animal and vegetable origin), mineral and mixed.
The size of dust particles distinguish very fine dust (0,1 - 1 micron) aerosol generator, small (2-10 microns), long in the air, middle (20-60 microns) and large (more than 60 microns), fast-settling .
Building codes (SNIP IT. 5-62) provides the following classification of dust on the grounds of its size:
Group I - very coarse;
Group II - coarse (fine sand for mortar);
Group III - Coarse (Portland);
Group IV - highly dispersed (ground quartz);
Group V-very fine.
Dust is attributed to a particular classification group based on its fractional composition, ie, the percentage by weight of certain factions of dispersion. Dispersity of dust measured by the size of dust particles in the micron or wandering particle velocity in cm / sec. Fractional composition of dust is usually made to divide the largest particles in the following six groups:
Percentage of different fractions of dust are usually determined by sieve analysis.
In addition to size play an important role and other properties of dust, namely:
a) The structure and shape of dust particles, and distinguish between fibrous dust and granular;
b) the ability of dust to stick together; distinguish dust and coagulable nekoaguliruyuschiesya;
c) the proportion of dust-raising material; distinguish heavy dust (lead, iron, heavy minerals) and light (flour, zinc oxide, wood dust, etc.).
Releasing properties of the dust material and the conditions of dust is very important when dealing with dust. These properties must be in the field of attention of the designer of industrial ventilation.
Terms of dust in a variety of industries. Dust occurs when crushing (crushing, grinding), when transporting crushed material in the packing and, when surface finish (polished, glyantsovka, vorsovka) for machining brittle materials, as well as a result of other processes. All those forks dust can be called basic or primary.
In industry, there are other, secondary dust. These primarily include particulate air pollution that occurred when cleaning. If cleaning is dry in the absence of vacuum cleaners, inevitably a significant flow of dust into the room. Sometimes with secondary dust is harder to fight than the main.
Dust control by general ventilation is almost no effect. Typically, dust should be captured at the site of its formation by local suction. Therefore, in most cases, designers of industrial ventilation are not interested in the amount of dust released, at least in terms of calculating the required air, the more that calculate how much dust enters the air, almost impossible.
Usually it is sufficient to know the degree of intensity of dust emission. It does not operate on numbers, and such conventional notions as intense dust emission (crushing and grinding, sandblasting, handling of bulk materials), a significant dust emission (roughing and polishing, working with the press - powders, packaging), a slight dust emission (in the textile, wood and paper-making industry).
Important to know the condition dust emission: the direction of the dust plume, the exact location of the source deposition, the intensity of the air jet near the dust cloud (eg, konvenktivnyh currents) and other similar circumstances. Construction of local shelters, placement of suction funnel, the location of the zonal pylepriemnikov - these issues can be addressed only by taking into account all factors.