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Source of Dust

When a mineral product is extracted, crushed, screened or handled small fragments generally below 75 microns particle size are released into the surrounding environment. The heavier particles generally above 20 microns settle out in the vicinity of the emission source. Wind and air disturbance can influence settlement. Particles below 20 microns move around with the air currents and can remain suspended for long periods of time. In still air conditions they will eventually settle out. Fine particles below 10 microns are normally not visible in their individual size and it is this fraction that is referred to as airborne dust (assuming still air conditions). Respirable dust is generally below 10 microns.


Airborne dust is a nuisance or hazardous to health depending on its chemical composition. In the Minerals Extraction Industry products containing silica or lead for example normally represent a health hazard. Particles below 5 microns are normally not collected in the nose or in the mucous of the mouth but pass directly to the lungs. This can build up in the lungs causing chronic diseases such as silicosis and pneumoconiosis.

Mineral Dust Examples

Legislation in most parts of the World set limits for:

(a) Control of dust to atmosphere from plant and exhaust stacks.

(b) Control of dust breathed in by the operators. For silica oxide (free silica) for example this can be as low as 0.1mg/Nm3 in the respirable range. Effects of respirable dust can be somewhat mitigated by wearing the correct PPE equipment appropriate to the health hazard.

The handling of materials containing harmful elements and dusts that give rise to high atmospheric emission levels therefore require special consideration in relation to plant design and the obvious need to remove the operators totally away from the working process - if possible. Experience shows that if allowed, a number of process designers ignore dust control in their plant philosophy so as to keep the capital cost below a perceived budget. In such cases when the plant starts operating, it is often the case that dust emission becomes unacceptable and expensive modifications such as sealing and/or retrofitting of dust control methods become necessary. This scenario can often be the most expensive solution and can result in confrontation with local government authorities and/or damaged relationships with neighbours. This initial impression may be difficult to eradicate.

There are three basic methods employed by Enviroflo Engineering to control dust within the bulk handling and minerals handling industries.

(A typical plant can sometimes have a combination of all three):

Click here to see examples of dust being produced

© Enviroflo Engineering, Nalco Limited, PO Box 11, Winnington Avenue, Northwich, Cheshire CW8 4DW