SILICA DUST CONTROLS FOR 

SURFACE MINES 

John A. Organiscak 

Senior Research Engineer 

National Institute for Occupational Safety and Health 
NORMAL SILICOSIS 
2004–2008 MSHA Dust Samples

Mining Commodity % of Dust Sample Exceeding 

the Standard Due to Quartz

Coal 11%

Metal 21%

Nonmetal 18%

Stone 13%

Sand & Gravel 12%

***Equipment operators most frequently exceed the standard.
Surface Mining Equipment 

Drills Bulldozers 

Trucks & Loaders 
BEST PRACTICES FOR SURFACE 

MINE DUST CONTROL 

• Drill dust collection systems 

• Enclosed cab filtration systems 

• Controlling haulage road dust 

• Controlling dust at the primary hopper dump 
DRILL DUST COLLECTION SYSTEMS

1. Dry Dust Collector System 

2. Wet Suppression 
1. Dry Dust Collector Systems 
Drill Shroud Leakage 

Drill Stem 

Leakage Collector Dump 

Dust Emissions From 

Dry Collection Systems 
Drill Shroud Leakage 

• Maintain tight shroud enclosure with the ground 

• Maintain at least 3:1 collector-to-bailing airflow ratio 
Shroud Height Effects 
Shroud Height and Airflow Effects 
Adjustable Height Shroud 

Angle Drill Shroud 

• Dust emissions below 0.5 mg/m3 
Horizontal Shelf Laboratory Testing 

• 70%–80% dust reduction @ 2:1 collector-to-bailing airflow ratio 
Horizontal Shelf Field Testing 

• 55%–66% dust reduction at two mines 

• Examine more robust designs 
Drill Stem Leakage 

• Maintain good seal between drill stem and table 

• Use air ring seal 
Maintain Good Drill Stem and Table Seal 
Air Ring Seal 

• 41%–70 % dust reduction 

• Large chip elimination 
Collector Dump

0.53 – 1.34 mg/m3 0.16 – 0.24 mg/m3

• Shroud dump discharge close to the ground 
Maintain Dust Collector as Specified by 

Manufacturer 

• 51% dust reduction after 

replacing broken collector 

fan belt 

• 83% dust reduction from 

replacing torn deck 

shroud 
2. Wet Suppression 

• Add small amounts of water to reduce visible dust cloud 

• Operational problems can occur from excessive water 
 Water Separator 

Increases Roller Bit 

Life 

• 98% with separator 

• 96% without separator 

• Bit life increased 4.5 

times 

Limited to large drill stems 
Smaller Drill Stem Water Separator
Smaller Drill Stem Water Separator Study

Wet vs Dry Drilling

0.0

100.0

200.0

300.0

400.0

500.0

600.0

dry wet

Concentration, mg/m3

Wet 

Dry 
ENCLOSED CAB FILTRATION SYSTEMS 

• Integrated into HVAC 

systems 

• Protection factors vary: 

– Drills 2.5 to 84 

– Bulldozers 0 to 45 

• Field studies of 

refurbishing old cabs 

• Laboratory study of cab 

filtration systems 
Refurbish Cabs

• Ceiling-mounted heating and AC units 

• External filter and fan units 

• Improve cab enclosure seals 
Enclosed Cab Field Studies 

Ascending 
Ensure Good Cab Integrity and 

Positive Pressurization

Hard to Seal Gaps
Use High Efficiency Respirable Dust Filters

• Intake filter > 95% on respirable-sized dusts 

• Use an efficient recirculation filter 
Additional Benefits of Good Filtration 

Clean HVAC 

Dirty HVAC 
Minimize Dust Sources in Cab 

Test Results: 

• Seasonal dust level increased 

from 0.04 to 0.68 mg/m3

• Floor heater use increased dust 

levels from 0.03 to 0.26 mg/m3 

Solutions: 

• Use good housekeeping practices 

• Remove floor heaters 

• Rubber mats better than carpeting 

• Gritless sweeping compounds 

(non-petroleum based) 
Keep Doors Closed During Equipment 

Operation 

• 0.81 mg/m when briefly opened to add drill steels 3

• 0.09 mg/m3

 with door closed 
Link to enclosed cab video 

http://www.cdc.gov/niosh/mining/products/product81.htm 
Difficult to Field Quantify Cab 

Performance Factors 

•Airflow 

•Filter loading 

•Leakage 
Cab Filtration System Experiments 

Cab Performance Measure: 

• Particle count penetration or 

protection factor 

Laboratory Test Variables: 

• Intake filter efficiency 

• Intake filter resistance (Simulate 

filter loading) 

• Intake air leakage 

• Recirculation filter efficiency 

• Wind infiltration 

• Addition of an intake pressurizer 
Key Results of Laboratory Cab Testing

90% efficient recirculation filter improved both cab protection factor 

and the time to reach it after the door is closed 
Intake Pressurizer Effects 

Cab pressure reflective of enclosure integrity and 

intake air quantity, not intake air quality! 
Intake Air Leakage Effects 

Intake filter loading proportionally increases 

airflow through leakage areas! 
Cab Mathematical Model*

* Organiscak JA and Cecala AB. Doing the Math: The effectiveness of enclosedcab air-cleaning methods can be spelled out in mathematical equations. Rock 

Products, October 2009, pp. 20-22.

( ) wIII

RRI

inside

outside

QlQ

QQ

C

C PF

++−

+

==

ηη

η

1 (Ideal Conditions)

Where: 

QI = Intake air quantity into the cab (QI > 0), volume per unit time,

ηI = Intake filter efficiency (ηI < 1), fractional,

l = Intake air leakage, fractional portion of intake air quantity,

QR = Recirculation filter airflow, volume per unit time,

ηR = Recirculation filter efficiency, fractional,

QW = Wind quantity infiltration into the cab, volume per unit time.
Cab Model Calculations 

1) Baseline Design: QI = 40 ft3/min, QR = 200 

ft3/min, ηI = 0.95, l = 0, and ηR = 0; PF = 20 

2) With a 5% air leak around the intake filter 

gasket: l = 0.05; PF =10 

3) Adding a 75% efficient recirculation filter: 

ηR = 0.75; PF = 49 

4) A 75% efficient recirculation filter without a 

5% leak: l = 0; PF = 95 
CONTROLLING HAULAGE 

ROAD DUST 
Average Airborne Particle Size 

Distribution 
Typical Gravimetric Dust Concentrations 
Dust Dissipation Effect 

Total:Resp. ≈ 8 to 10:1 Thoracic:Resp. ≈ 3 to 4:1 
Treatment of Unpaved Road Services

• Water effective with reapplications 

• Salts, surfactants, soil cements, bitumens, 

films (polymers) extend time of effectiveness 
Increase Distance Between Vehicles 
PRIMARY CRUSHER HOPPER DUMP 
Enclose the Primary Hopper Dump 

• Staging curtains reduce dust billowing out 
Use Water Sprays to Suppress the Dust 

• Start by adding 1% moisture by weight 

• Use photocell or mechanically controlled sprays 
Prevent Dust Roll Back Under Vehicle 

• Tire stop reduces rollback underneath equipment 

• Water sprays knock down and redirect dust 
CONCLUSIONS 

• Dry and wet drill dust collection systems are very effective 

– Tightly sealed shroud around drill hole critical for dry systems 

– Wet systems can increase bit wear, problematic in cold climates 

– Assumes quality control and maintenance programs 

• Cabs can provide a 10- to 50-fold dust reduction 

– Good filtration system 

– Tightly sealed cab for achieving positive pressurization 

– Assumes quality control and maintenance programs 

• Road dust can effectively be mitigated by routine wetting 

• Enclosed hopper dumps contain dust → spray capture 
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.

Disclaimer
Questions or Comments? 

 

John A. Organiscak, 412-386-6675, jorganiscak@cdc.gov