Nevada Mining Association/ 

NIOSH Silica Dust Control Workshop 

for Metal/Nonmetal Mining 

 Elko, Nevada

Dust Control in 

Mineral Processing 

Operations 

Tuesday, Sept. 28, 2010 

Andrew B. Cecala 

Senior Research (Mining) Engineer 
1977 Federal Mine 

Safety and Health Act 

Sec 3. “Congress declares that (a) the first priority and 

concern of all in the coal or other mining industry must be the 

health and safety of it’s most precious resource - - the miner;” 
 

Engineering Control Technology 

Reducing workers exposure to silica/other 

respirable dust in underground and surface 

metal/nonmetal operations. 
Operations 

Metal/Nonmetal, Stone, 

and Sand & Gravel (2007) 

256,2%

12,014 

98%

Underground Surface
Miners 

Metal/Nonmetal, Stone, 

and Sand & Gravel Miners (2007) 

131,315, 

88%

17,862, 

12%

Underground Surface
Job Classifications Exceeding 

Permissible Exposure Limit 

2004–2008 MSHA Data 

• Stone polisher/cutter 34%

• Bagging operator 26%

• Cleanup man 18%

• Laborer, bullgang 17%

• Utility man 16%

• Dry screen plant operator 16%

• Crusher operator 13%
Maximizing Air Quality in Enclosed Cabs of 

Mobile Mining Equipment (Construction/Agriculture) 
Health Study (1996–1997) 

8 Different Surface Coal Operations in Pennsylvania 

1,236 miners: 6.7% classified 1/0 silicosis 

Clearfield County – 213 miners: 16% classified 1/0 silicosis 
What Level of Protection is Achieved? 
What is the Operator’s Level of Protection 

Inside the Enclosed Cab? 

 
 

Dust Control Efforts Discussed 

Presentation Outline: 

• Mineral processing dust control handbook 

• Dual-nozzle bag system 

• Clothes cleaning system 

• Overhead air supply island system (OASIS) 

• Push-pull ventilation system 

• Bag & belt cleaner device 

• Secondary dust sources 

• Worker’s impact on dust exposure 

• Total structure (mill) ventilation system 

• Reducing dust levels in iron ore processing operations 

• Improving ventilation in turkey barns 

• Wet suppression 

• Primary dump/conveyors/transfer points 

• Foreign work efforts 
NIOSH/IMA–NA Mineral Processing 

Dust Control Handbook 

To be patterned after the ACGIH Industrial Ventilation Handbook
Handbook Committee Members 

Members: 

Co–Chairmen: Andy O’Brien, Unimin Corporation 

 Andy Cecala, NIOSH 

 John Rounds, Unimin Corporation 

 Rick Fox, Unimin Corporation 

 Mark Shultz, Mine Safety and Health Administration 

 Robert Franta, Spraying Systems Company 

 Randy Reed, NIOSH 

 Joe Schall, Technical Writer/Editor, NIOSH 

 Jerry Joy, NIOSH 

 Pat Reeser, U.S. Silica Company 

 Jay Colinet, NIOSH 

IMA-NA Coordinator: Mark Ellis, President 
Handbook Progress 

0 20 40 60 80 100

Percentage Complete, %

Haul Roads, Stockpiles, and Open Areas

Enclosed Cabs

Secondary Source Control

Bulk Loading

Bagging

Conveying and Transport

Crushing and Screening

Drilling and Blasting

Water Application

Fundamentals of Dust Control

Introduction

Dust Control Handbook Section Progress
Dual-nozzle Bag System 
Product Blowback 
Product Rooster-tail 
Soiled Bags 
Dual-nozzle Design 

After filling completed, bag remains on fill nozzle for additional 3-5 seconds. 

Venturi effect exhausts each bag at 50 cfm. 
Dust Reductions 

Exhaust: 89% 

Transfer: 61% 

Intake: 79% 

Operator: 83% 

Background: 78% 
Product Blowback 

(Before and After) 
Product Rooster-tail (Before and After) 

 

89% reduction 
Soiled Bags (Before and After) 

 

78% reduction 
Bag Operator 

83% reduction 

Key: Depressurize the bag after filling is completed. 

Technology has been adopted by OEMs. 
Clothes Cleaning System 

A safe and effective method for 

removing dust from work clothes 
Clothes Cleaning 

Video link 

http://www.cdc.gov/niosh/mining/

products/product21.htm 
Cleaning 

Booth 
Vacuuming 
Single Air Hose 
Air Spray Manifold 
Inside Booth Inside Respirator 

Tubing connects dust monitor to cyclone inside of PPE 
Sampling Setup 
Half-mask Respirator 
Laboratory Testing (Pittsburgh Lab) 
Analysis of Three Air Spray Nozzles 

 Brass V Flat fan Circular 

Polyester Material 

3-inch Distance 
Cleaning Effectiveness at Increasing Distances 

Circular Air Nozzle – Polyester Material 

 3” 6” 9” 12” 
Cleaning Effectiveness: Air Pressure (30–5 psi) 

Cotton Material 

15 psi 10 psi 5 psi 

30 psi 25 psi 20 psi 
Cleaning Effectiveness: Nozzle Operating Time 

 5 sec 10 sec 15 sec 

Polyester 

Material 

 20 sec 25 sec 30 sec 
Soiling clothes with crushed limestone dust (rockdust) for testing 
Air Spray Manifold 

Final Design 
Vacuum 

Cleaning Time:

7 minutes 48 seconds 

 

Pre- Cleaning 

Post- Cleaning 
Air Hose 

Cleaning Time: 

 3 minutes 6 seconds 

Pre- Cleaning 

PostCleaning 
Air Spray 

Manifold 

Cleaning Time: 

17 seconds 

 

Pre- Cleaning 

Post- Cleaning 
Dosimeter Noise Measurements 

General Mill Levels: 91.5 dB 

Inside Booth – not operating 86.5 dB 

Inside Booth – operating 101.4 dB 

Outside Booth – operating 91.4 dB 

Outside Booth – not operating 90.6 dB 

Note: Hearing protection is required when using clothes cleaning system. 
Health and Safety Requirements 
Modification: Exhaust Air Outside 
Cleaning Effectiveness (18 seconds cleaning time) 
Clothes Cleaning Booth System (Wilson, NC) 

http://www.cleanclothbooth.com/ 
Overhead Air Supply Island 

System (OASIS) 
Air velocity of 375 ft/min flowing over worker 

Outside Air 

Intake 

Main Filter Unit 
Bag Loading and Stacking Area 

Bag Stacker 

Bag Operator 

OASIS 
Respirable Dust Reductions: 82–98% 

Key: Provide an envelope of clean filtered air down over the worker. 

Can be designed and installed in-house or by local engineering firms. 
Pallet Loading Dust Control System 

Two Problem Areas 

1. Dust Exposure 

2. Ergonomic 
Push-pull Ventilation System 

Blowing jets: 2–3” circular/1,200 ft/min 

Blowing volume: 470 cfm 

Exhaust volume: 2,500–2,800 cfm 
Loading height: knuckle level (28–30 inches) 

Air jets should be 10–12 inches above loading height (40 inches) 
Results 

• Lowers respirable dust exposure 

• Reduces back stress 

 

• Increases production, less downtime 

Bag Stacker’s Average Dust Reduction: 30–80%
Bag and Belt Cleaning Device (B&BCD) 

Cooperative research effort 

with silica sand company 




Soiled Bags 

 (Before and After) 

325 Mesh Product 

Dust Reduction: 78–93% 

reduction 

Key: Clean product from bags using mechanical/stationary 

brushes and air jets in contained unit under negative pressure. 

Technology is being used by OEMs. 
Secondary Dust Sources 
Soiled 

Work 

Clothes 

Broken

Bags 


Bulk 

Loading 

Outside 

Increase in Dust Exposure from Secondary Sources 

CASE Increase Factor TLV Exposure Time 

Contaminated Work 

Clothes 10.1 1 hr 35 min 

Blowing Clothes with 

Compressed Air 2.4 3 hr 33 min 

Broken Bag (Fill Station) 3.2 4 hr 34 min 

Broken Bag (Conveyor) 6.9 3 hr 20 min 

Bulk Loading Outside 2.5 3 hr 48 min 

Bag Hopper Overflowing 12.2 2 hr 11 min 

Dry Sweeping Floor 5.7 9 hr 24 min 
Occurrence Totals for Overexposures 

Sources of Dust Estimated Occurrences to 

Exceed TLV 

Contaminated Work Clothes 1 

Bag Breakage During Filling 14-18

Bag Breakage During Conveying 6-10

Bulk Loading Outside 3-4 

Bag Hopper Overflowing 3-4 
Secondary Dust Sources 

• Be aware of the problem 

• Identify the problem 

• Control the problem 
Worker’s Impact on Dust Exposure 
Dust Exposures of Two Workers Using 

Different Work Practices 

0

1

2

3

4

5

6 Dust Exposure

1 2 3 4

Job Task

Worker #1 Worker #2
Total Mill Ventilation System 
Evaluation Site 

Clay Processing Structure 

 

• Three 8,500 cfm 

roof exhausters 

• 25,500 cfm 

system, 10 ACPH 

• Three wall louvers 

provide inlet for 

makeup air 
Smoke Bomb Release 
Immediately After Release 
2 Minutes After Release 
4 Minutes After Release 
6 Minutes After Release (one air change) 
Total Mill Vent System On and Off 
Dust Reduction at Sample Locations for 

Field Evaluation Site #1 

40% average reduction 

41.73 46.44

29.57

45.82

34.36

0

1 0

2 0

3 0

4 0

5 0

Dust Reduction, %

Sample Location

1 2 3 4 5
Site #2 

• 100,000 cfm system, 34 ACPH 

• Four 25,000 cfm propeller type 

wall exhausters 

• Open bay doors – inlet for 

makeup air 

• Material and installation (inhouse) minimal 
Dust Reduction at Sample Locations for 

Field Evaluation Site #2 

50,000 cfm (17 acph): 36% / 100,000 cfm (34 acph) : 63% 

0

2 0

4 0

6 0

8 0

Dust Reduction,%

1 2 3 4 6

Sample Location - Floor

2 Fans 4 Fans The technique has been adopted by the mineral processing 

operations and is a standard practice throughout the industry. 

Relatively New Primary Grinding Mill Facility

Average 

Respirable Dust 

Concentrations: 

0.0 mg/m3 

Wall Louvers 

Fans 
Total Mill Ventilation System 

Respirable Dust Reduction: 36%–63% reduction throughout 

entire structure 

Key: Common practice throughout the industry at mineral processing plants 
Reducing Dust Levels in Iron Ore Processing Plant 
Unique Facility:

940,000 ft2 structure with an internal air volume of 45,000,000 ft3

 
Iron Ore Facility 
High Respirable Dust Levels Result in Respirator Requirement Zone 
Major Objective: Optimize and balance airflow throughout structure 

Secondary Objective: Lower respirable dust levels in and around the twelve 

 primary grinding mills 
Ventilation Recommendation 

• Proposed two significant changes to concentrator structure 

ventilation: 1) balance intake and exhaust air volumes and 

2) create a directional airflow pattern 
Roof Fan Setup at Tilden 

Intake: 2 intake heaters/3 intake 

roof fans - 600,000 cfm 

Exhaust: 39 exhaust fans – 

1,930,500 cfm 

3.2 times more 

air exhausted 

Heater intake 

fan 
Roof Fan Setup at Tilden 

as of 9:30 a.m. 

Wednesday, March 10 

Intake: 2 intake heaters/12 intake 

roof fans – 1,045,000 cfm 

Exhaust: 19 exhaust fans – 

940,500 cfm 

Heater intake 

fan 

1.1 times 

more intake 

air 
Roof Fan Setup at Tilden 

as of 7:00 a.m. 

Thursday, March 11 

Intake: 2 intake heaters/12 intake 

roof fans – 1,045,000 cfm 

Exhaust: 24 exhaust fans – 

1,128,000 cfm 

1.1 times more 

air exhausted 

Heater intake 

fan 
Respirable Dust Averages 

0

0.2

0.4

0.6

0.8

1

1.2

Respirable Dust (mg/m3)

9th Day 9th Night 10th Day 10th Night 11th Day

Testing Period

Primary Pebble Flotation
Results from Ventilation Change 

to Balance and Optimize Airflow 

• Respirable dust levels lowered by 31% in the primary 

grinding area, third ventilation design 

• Respirable dust levels slightly lowered in pebble mill 

and flotation areas 
Poor Dumpster Placement (Used Collector Bags) 
Dust Collector Evaluation vs. Water Spray Application 
Water Spray 

Application 

5 - 29 pct reduction 
Improving Ventilation in Turkey Farms 
Problem: Poor air quality causes 

high dust levels, ammonia, and humidity. 
Turkey Growth 

Birth to 18 Weeks 

Finisher

38.9%

Grower

33.3%

Brooder

27.8%
Poults: Brooder Barn 
Grower 

Barn 
Finisher Barn 
Airflow and Ammonia Measurements 
Testing During Winter Months 
Heaters for Warming Barns 
Curtain Running the Length of the Barn 
Installation of Curtains to Force Heat Downward 

Comparison

 Birds: heated barn 2.3–2.8 lbs 

heavier 

 Normal Barn: 2,000 gallons propane 

Curtain Barn: 1,100 gallons propane 

Estimated savings: $1.5 million in heating cost, 

while also yielding additional profit because of 

heavier and healthier birds. 
Wet Suppression 
Water Application 

Two Methods: 

• Airborne dust prevention: achieved by 

 direct spraying of the ore to prevent dust 

 from becoming airborne 

• Airborne dust suppression: involves 

 knocking down dust already airborne by 

 spraying the dust cloud and causing the 

 particles to collide, agglomerate, and to fall 

 out from the air 
Water Considerations: 

• Has a limited residual effect due to 

evaporation; will need to be reapplied at 

various points throughout the process 

• Obviously, under-application is ineffective 

• Over-application in amount/volume can cause 

various problems, impacting equipment and 

the overall process 

Rule of Thumb: A good starting point is in the 0.5–1.0% moisture 

range. Early stages of process (course product) is not as critical as later 

stages. Ideally, vary the amount/volume at each application to determine 

the optimal design. 
Other Considerations: 

• Important to ensure that dust particles 

stay attached to the ore material 

• Uniformity of wetting is important 

• Best application is spraying ore with 

water and then mechanically mixing 

together 

• Ideal system should be automated so 

that sprays are only activated when ore 

is actually being processed 

 
Nozzle Location 

• Nozzle should be located upstream of transfer 

points

• Locate nozzles at locations for best mixing 

• Nozzles should be an optimum target distance 

from the ore, far enough to provide coverage, but 

close enough so that air currents do not carry 

droplets away from intended target 

• Droplet size should be considered 
Effective Spray Pattern and Distance From Ore 
Ineffective/Effective Water Application 
Droplet Size: 

• To keep dust from becoming airborne: 

Water droplet sizes above 100 microns 

 should be used. 

 

• To knock down existing dust in air: 

Water droplets should be in a similar 

 size range to the dust particles. 

 
Water droplet size should be matched to the size of the dust particles. 
Spray 

Pattern 

and Nozzle

Type 

Medium to large droplet sizes, wide range pressures and flows. Normally 

used when sprays are further from dust sources. 

Produce small to medium droplet sizes. 

Small to medium droplet sizes over wide range flow and spray angles, 

used in narrow enclosed spaces. 

Two designs: hydraulic (fine droplets) and air-assisted (finest droplets). 

Both types need to be located close to the dust source. 

Common dust control application areas and the type of 

spray nozzle typically used for that application 

Air 

Atomizing

Hydraulic 

Fine Spray

Hollow 

Cone

Flat 

Spray

Full 

Cone

Airborne Dust Suppression

Jaw crushers ● ● ●

Loading terminals ● ●

Primary dump hopper ● ●

Transfer points ● ●

Dust Prevention

Stackers, reclaimers ● ●

Stockpiles ● ●

Transfer points ● ● ●

Transport areas/roads ●

.
Water Cleanliness 

• If spray nozzles become plugged with 

sediment or debris, rendered ineffective 

• Because the water used at most operations 

is from a settling pond, water purity is a 

great concern 

• Water filtering system is critical. A hydrocyclone system with a built-in accumulator 

flush should be considered as the first 

stage of a filtering system 
Nozzle Maintenance 

• Erosion and wear 

• Corrosion 

• Accidental damage 

• Checking nozzle 

performance 
Primary Dump/Conveyors/Transfer Points 
Primary Dump 

Two Dust Sources: Billowing and Rollback 
Control Methods

Billowing: 

• Suppress 

• Enclose 

• Filter (LEV) 

Rollback: 

• Tire stop water spray system 


Installing Clear 

Plastic Stripping 
Plastic Stripping and Tire Stop Water Spray System 



Other Application of Plastic Stripping to 

Enclosed Areas 
Conveyor Belt Dust: 

Four Main Sources of Dust Generation and Liberation: 

• Ore is dumped onto belt 

• Ore travels on belt 

• Ore dropping from underside return idlers 

(carryback dust) 

• Ore transferred from belt 

 

 

Airborne Dust 
Conveyor Belt Considerations 

One challenge with conveyors is the number of belts 

used and the total distance traveled throughout the 

operation. When belts are outside, dust liberation is 

not as critical as within a facility. 

Another challenge is their ability to liberate dust while 

operating whether they are loaded or empty. 

Controlling dust from conveyors requires 

constant vigilance by maintenance staff to repair 

and replace worn and broken parts, and to 

perform constant housekeeping. 

Spillage: Poor Conveyor Housekeeping Practices 

Carryback Dust 
Conveyor Belt Control Techniques 

• Suppression 

• Enclosures 

• Belt scrapers 

• Belt wash 

• Effective belt loading 

Conveyor Water Sprays: 

• High-volume, high-pressure sprays should be avoided. 

• Amount of moisture applied should be varied and tested. The 0.5 to 

1.0% moisture to product ratio is a good starting point. Excess 

moisture can cause slippage problems (belt performance). 

• Some studies show wetting return side of conveyors can also 

minimize dust liberation. Can locate sprays on top (wetting product) 

and bottom (belt bottom and idlers) at same location. 

• Fan sprays are most common; they minimize volume for the amount 

of coverage. Advantageous to place at beginning of process. 

• Using more spray nozzles at lower flow rates and positioning them 

closer to the ore/product is more advantageous. 
Enclosures 
Ineffective Belt Loading 
Impact-absorbing Belt Cradles 
Conclusion 

80-90%

80-90%

30-80% 

90-99%

65-99%

80-98%

35-65%
 Disclaimer 

The findings and conclusions in this presentation are those of the 

authors and do not necessarily represent the views of NIOSH. 

Mention of any company or product does not constitute 

endorsement by the National Institute for Occupational Safety and 

Health (NIOSH). In addition, citations to Web sites external to 

NIOSH do not constitute NIOSH endorsement of the sponsoring 

organizations or their programs or products. Furthermore, NIOSH 

is not responsible for the content of these Web sites. All Web 

addresses referenced in this presentation were accessible as of 

the date the presentation was originally delivered.
Andy Cecala 

Dust Control, Ventilation, and 

Toxic Substances Branch 

Pittsburgh, Pittsburgh 

Phone: 412-386-6677

E-mail: acecala@cdc.gov or 

aic1@cdc.gov