Dust

 

Good Practice Page 2.

Loading/Unloading Activities

Dust is most easily entrained in the wind when the material is falling through the air at points of transfer. It is therefore important to reduce the drop heights wherever practicable. Photograph 19 shows coal being stockpiled from a conveyor which has a sleeve attached to it to prevent the wind picking up dust as the material falls. In addition it may be necessary to protect the activities from wind by erecting a screen or using a natural barrier such as the high-wall of a site.

Photograph 19. Sleeve on end of conveyor to reduce apparent drop height

 

Fine spray or fog suppression (Photographs 20 & 21) C0002 can also be used in loading bays which are exposed to the wind and therefore a likely source of fugitive dust.

Photograph 20. Automatic fog dust suppression and lorry wetting system	Photograph 21. Automatic fog dust suppression and lorry wetting system

 

Processing

The increased usage of mobile crushing and screening units in aggregate operations has had the effect of reducing dust problems in many situations. Where they are deployed in hard rock quarries, they are usually situated "in-pit", either close to the blasted face or on a bench in the quarry where there is sufficient space. This keeps the operation below original ground level and therefore less likely tocause problems with dust.

Mobile units have the option of covers over the conveyors and screen decks, which will have the dual benefit of keeping the material drier when it is raining, and limiting the dust pick-up when it is dry.

Where fixed plant is already in existence, or where it is the preferred option, the solutions to any dust problem will vary depending on the type of equipment used. Generally complete enclosure is best with use of air extraction and filter equipment as appropriate. Water sprays can also be used and the use of surfactants can be helpful.

Material storage

A number of measures can be taken here. Material waiting to be loaded out is often close to the site entrance and therefore near the boundary. For a number of reasons (of which minimising dust is one) these stock piles can be arranged in bays, with concrete walls containing and sheltering the material (Photograph 22). Covering the bays or the material might also help to reduce fugitive dust. In some situations it might be necessary to dampen the material, perhaps with a fine spray (Photograph 23).

Photograph 22. Stockpiles held in bays	Photograph 23. Fine spray keeping dust down in stockpile

 

Transport by conveyor within site

Where conveyors are used, either as the major transfer system or simply as part of the processing, the transfer points should be sheltered from the wind, possibly using an enclosure. Indeed, it may be necessary to protect the whole conveyor by partially (Photograph 24) or completely enclosing it (Photograph 25). Drop heights should be minimised and water sprays (Photograph 26) C0002 can be beneficial. It is good operational practice to make sure the belts are automatically cleaned with scrapers or brushes, and the scrapings should be collected.

Photograph 24. Covered conveyors in the processing plant	Photograph 25. Completely enclosed field conveyor

 

Photograph 26. Fine conveyor spray at transfer point

Transport of material by vehicle within site

Occasionally, it may be possible to pave some of the internal roads, but the use of large dump trucks usually makes this impracticable. Exhausts and cooling fans on these machines should be directed above the horizontal to avoid disturbance of the ground.

Factors such as vehicle speed are important, and speeds should be restricted as there is a direct relationship between the speed and the amount of material that is thrown up in the air. Routing the dump trucks away from exposed areas near the site boundary will reduce a number of environmental impacts, including dust.

A key factor will be the nature and dryness of the surface ground material. Unsurfaced and paved roads should be dampened when there is the danger of dust being generated. This can be done using water sprays from fixed pipes (Photograph 27), water guns C0002 or by using a water bowser (Photograph 28). Where surfaced or paved roads are used, they should be swept and washed regularly (Photograph 29).

Photograph 27. Dampening haul road with fixed water sprays	Photograph 28. Tractor and trailer bowser unit for haul roads

 

Photograph 29. Tractor mounted road sweeper

However, current management practices are often based upon reactive control measures, triggered by the experience or interpretation of the mine operatives to the on-site emissions, and to the availability of dust suppression equipment and staff. Furthermore, it is common place for the application of wet dust suppression methods to be applied to the whole of the unpaved travelled quarry road network, rather than targeting specific problem areas. This can have significant economic and environmental costs on quarrying operations by unnecessary water usage.

The ALSF Review L0089 proposes the development of a system that could detect the onset of a dust problem, its specific location and be able to mobilise the required mitigation measures. This proactive system would provide quarry operators with a vital tool to mitigate the onset of dust problems prior to the actual emission. Such a system has been developed for on-site dust control 457, where significant dust plumes from large dump trucks can constitute a significant hazard to vehicle movement. It is based on being able to predict various levels of "problem" (related to values of PM10 associated with health and visibility issues) from the evaporation rate, road material and vehicle speed. While this was developed for in-pit use, it may be possible to extend it to nuisance dust deposited outside the site boundary. The Dust Action Plan proposed in the Good Practice Guide L0091 could encourage the development of this type of system.

Haulage of material off site

All lorries leaving site should be properly sheeted (Photograph 30) to prevent dust escaping onto the public highways. It may also be advantageous to sheet vehicles being used for internal transfer of dusty materials.

Material should be loaded and unloaded in areas protected from the wind and drop heights should be minimised. There should also be an effective wheel wash system (Photograph 31) close to but inside the side entrance, to prevent mud getting onto the public road which will dry to produce a dust hazard.

Photograph 30. Sheeting bay for HGVs	Photograph 31. An effective wheel wash

 

 

Summary of Good Practice

There is a significant amount of information in the Good Practice section, which has been summarised in Tables 11 (for MPAs) and 12 (for operators).

Table 11. Summary of good practice for Mineral Planning Authorities.

Consider the need to agree or specify planning conditions relating to the: layout of the site, design of stockpiles; hard surfacing of vehicle areas; containment of conveyors and processing plant and dust collection equipment; use of bowsers, sprays and vapour masts on haul-roads, stockpiles, transfer points; design of material-handling systems, drop heights, wind guards, loading points; limiting levels of dust measured in a specific way; provision of monitoring facilities.

Agree the method of monitoring dust (how and where), together with the limits.

 

Table 12. Summary of good practice for operators.

The impact of dust on the environment can be reduced by planning and design through the development and implementation of a Dust Management Plan. The plan should: identify dust sources; set out dust management and control methods; describe the dust monitoring strategy; explain how any failures will be addressed; and, describe the ongoing review process of continuous improvement. be a "living" document, which supports continuous review and improvement of dust management. be continuously updated and amended to reflect changes and/or improvements due to the on-going process of continuous improvement. Specific control methods are outlined below.
Activity	Possible dust control methods
Soil handling and storage	Restrict the duration of the activity. Seal and seed storage mound surfaces as soon as is practicable. Where possible, protect surfaces from winds until disturbed areas are sealed and stable.
Overburden handling and storage	Protect exposed material from wind (by keeping material within voids or protecting them by topographical features). Spray exposed surfaces of mounds to maintain surface moisture unless mound surface has formed a crust after rainfall or is grassed. Minimise handling.
Drilling and blasting	Use dust extraction equipment, such as filters, on exhaust air emissions from drill rigs. Remove the dusty material collected from the area of blast prior to detonation. Delay blasting if conditions are unfavourable.
Loading/Unloading Activities	Reduce drop heights wherever practicable. Protect activities from wind by erecting a screen or using a natural barrier.
Processing	Locate processing plant "in-pit" where possible. Complete enclosure is usually best with use of air extraction and filter equipment as appropriate. Use water sprays, adding surfactants if required.
Material storage	Dampen material. Protect from wind and store in bays or under cover. Screen material to remove dusty fractions prior to external storage.
Transport by conveyor within site	Protect by use of wind and roof boards. Shelter transfer points from wind with an enclosure. Use scrapers to clean belts, with collection of scrapings for disposal. Minimise drop heights and protect from wind. Use water sprays.
Transport by vehicle within site	Pave roads where possible. Restrict vehicle speed. Water un-surfaced and paved roads. Route trucks away from exposed, sensitive areas where possible.
Haulage of material off-site	Wheel or body wash inside the site and at an appropriate distance from site entrance. Load and unload in areas protected from wind. Minimise drop heights. Sheet or cover loaded vehicles. Use water sprays/spray curtains to moisten material. Sweep/wash paved roads. Use paved roads where practicable.

 

 

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