RI 9680 

REPORT OF INVESTIGATIONS/2011 

Department of Health and Human Services 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Report of Investigations 9680 

Evaluation of Face Dust Concentrations at Mines Using Deep-Cutting 

Practices 

J. Drew Potts, W.R. Reed, and Jay F. Colinet 

DEPARTMENT OF HEALTH AND HUMAN SERVICES
 

Centers for Disease Control and Prevention
 

National Institute for Occupational Safety and Health
 

Office of Mine Safety and Health Research
 

Pittsburgh, PA • Spokane, WA
	

January 2011
 
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DHHS (NIOSH) Publication No. 2011–131 

January 2011 

SAFER • HEALTHIER • PEOPLETM 
Table of Contents
 

Abstract........................................................................................................................ 1
 

Introduction .................................................................................................................. 2
 

Sampling Protocol and Data Analysis .......................................................................... 3
 

Underground Dust Surveys.......................................................................................... 6
 

Exhausting Ventilation ................................................................................................. 7
 

Blowing Ventilation....................................................................................................... 9
 

No-curtain Ventilation................................................................................................. 11
 

Bolting Operations ..................................................................................................... 12
 

Recent Developments Using Blocking Sprays ........................................................... 13
 

Conclusions ............................................................................................................... 14
 

References................................................................................................................. 15
 

Appendix A: MINE A CASE STUDY .......................................................................... 25
 

Mine-specific Information........................................................................................ 25
 

Shuttle Car Data Analysis....................................................................................... 26
 

Miner-generated Dust ............................................................................................. 29
 

Miner Operator Data Analysis................................................................................. 29
 

Bolter Operations Data Analysis ............................................................................. 30
 

Dust-control Monitoring........................................................................................... 30
 

Summary ................................................................................................................ 31
 

Appendix B: MINE B CASE STUDY .......................................................................... 37
 

Mine-specific Information........................................................................................ 37
 

Shuttle Car Data Analysis....................................................................................... 38
 

Miner-generated Dust ............................................................................................. 40
 

Miner Operator Data Analysis................................................................................. 41
 

Bolter Operations Data Analysis ............................................................................. 41
 

Summary ................................................................................................................ 42
 

Appendix C: MINE C CASE STUDY .......................................................................... 46
 

Mine-specific Information........................................................................................ 46
 

Shuttle Car Data Analysis....................................................................................... 47
 

Miner-generated Dust ............................................................................................. 48
 
Miner Operator Data Analysis................................................................................. 49
 

Bolter Operations Data Analysis ............................................................................. 49
 

Dust-control Monitoring........................................................................................... 50
 

Summary ................................................................................................................ 50
 

Appendix D: MINE D CASE STUDY .......................................................................... 57
 

Mine-specific Information........................................................................................ 57
 

Shuttle Car Data Analysis....................................................................................... 58
 

Miner-generated Dust ............................................................................................. 61
 

Miner Operator Data Analysis................................................................................. 62
 

Bolter Operations Data Analysis ............................................................................. 62
 

Dust-control Monitoring........................................................................................... 63
 

Summary ................................................................................................................ 63
 

References Cited in Appendix D............................................................................. 64
 

Appendix E: MINE E CASE STUDY .......................................................................... 69
 

Mine-specific Information........................................................................................ 69
 

Shuttle Car Data Analysis....................................................................................... 71
 

Miner-generated Dust ............................................................................................. 75
 

Bolter Operations Data Analysis ............................................................................. 76
 

Dust-control Monitoring........................................................................................... 76
 

Summary ................................................................................................................ 77
 

References Cited in Appendix E............................................................................. 78
 

Appendix F: MINE F CASE STUDY........................................................................... 83
 

Mine-specific Information........................................................................................ 83
 

Shuttle Car Data Analysis....................................................................................... 85
 

Miner-generated Dust ............................................................................................. 86
 

Miner Operator Data Analysis................................................................................. 86
 

Bolter Operations Data Analysis ............................................................................. 87
 

Dust-control Monitoring........................................................................................... 88
 

Summary ................................................................................................................ 88
 

Reference Cited in Appendix F ............................................................................... 89
 
Figures
 

Figure 1. Area sampling locations for a typical section layout. Note: PDMs Are not 

shown. ................................................................................................................ 17
 

Figure 2. Pie chart depicting the magnitude of scrubber airflow reduction during the cut 

as a percentage of total cuts measured.............................................................. 21
 

Figure 3. Mine operator and shuttle car cab position at the start of the no-curtain cut for 

the initial heading development beyond the last open crosscut.......................... 22
 

Figure 4. Mine operator and shuttle car cab position at the end of the no-curtain cut for 

the initial heading development beyond the last open crosscut.......................... 23
 

Figure A-1. Mine A continuous miner spray configuration. ............................................ 25
 

Figure A-2. Plan view of the mine A operating section. ................................................. 26
 

Figure A-3. Shuttle car dust exposures with exhausting face ventilation when the miner 

was driving a heading......................................................................................... 27
 

Figure A-4. Shuttle car dust exposures with blowing face ventilation when the miner was 

driving a heading. ............................................................................................... 28
 

Figure A-5. Shuttle car dust exposures with blowing face ventilation when the miner was 

turning a right crosscut. ...................................................................................... 29
 

Figure B-1. Mine B continuous miner spray configuration. ............................................ 37
 

Figure B-2. Plan view of Mine B section........................................................................ 38
 

Figure B-3. Shuttle car dust levels when miner was driving a straight heading............. 39
 

Figure B-4. Miner return dust levels during Cut No. 4. .................................................. 41
 

Figure C-1. Mine C continuous miner spray configuration............................................. 46
 

Figure C-2. Plan view of the mine C continuous miner development section................ 47
 

Figure D-1. Mine D continuous miner spray configuration............................................. 57
 

Figure D-2. Plan view of mine D continuous miner section. .......................................... 58
 

Figure D-3. Shuttle car dust levels at the face when the miner was driving headings 

without the use of line curtain. ............................................................................ 60
 

Figure D-4. Shuttle car dust levels at the face when the miner was driving right 

crosscuts without the use of curtain.................................................................... 60
 

Figure D-5. Shuttle car dust levels at the face when the miner was driving a heading
 

with the use of blowing curtain............................................................................ 61
 

Figure D-6. Miner return dust levels at 5-sec intervals for each cut............................... 62
 

Figure E-1. Mine E continuous miner spray configuration. ............................................ 69
 

Figure E-2. Plan view of the mine E continuous miner Section No. 4. .......................... 70
 

Figure E-3. Plan view of the satellite entries driven off the mains on Section No. 4...... 70
 

Figure E-4. Shuttle car cab dust levels at the face when driving a heading with the use
 

of blowing curtain................................................................................................ 73
 

Figure E-5. Shuttle car cab dust levels at the face when driving an entry without the use
 

of blowing curtain................................................................................................ 73
 

Figure E-6. Shuttle car cab dust levels at the face when turning a right crosscut with the
 

use of blowing curtain. ........................................................................................ 74
 

Figure E-7. Shuttle car cab dust levels at the face when turning a left crosscut with the
 

use of blowing curtain. ........................................................................................ 74
 

Figure E-8. Miner return dust levels at 5-sec intervals for each cut that did not use
 

ventilation curtain................................................................................................ 76
 
Figure F-1. Mine F continuous miner spray configuration. ............................................ 84
 

Figure F-2. Plan view of the operating section at Mine F. ............................................. 85
 

Figure F-3. Shuttle car cab dust levels when loading at the active face. ....................... 86
 

Tables 

Table 1. Shuttle car cab dust levels when loading at the face....................................... 18
 

Table 2. Time weighted average levels for the shuttle car, miner, and bolter operators 19
 

Table 3. Miner operator exposure levels and miner-generated ..................................... 20
 

dust levels during regular- and deep-cuts depths.......................................................... 20
 

Table 4. Bolter operator exposure levels and machine-generated ................................ 24
 

dust levels at regular- and deep-cut depths .................................................................. 24
 

Table A-1. Shuttle car dust levels when loading at the face for Cuts No. 1, 2, and 3 .... 33
 

Table A-2. Shuttle car dust levels when loading at the face for Cuts No. 4, 5, and 6 .... 34
 

Table A-3. Shuttle car dust levels when loading at the face for Cut No. 7..................... 35
 

Table A-4. Continuous miner-generated dust during production as measured with pDRs 

calibrated with gravimetric samplers................................................................... 35
 

Table A-5. Miner operator exposures during production as measured with a PDM
 

instrument........................................................................................................... 36
 

Table A-6. Bolter-generated dust and bolter operator exposures during the bolting cycle
 

........................................................................................................................... 36
 

Table B-1. Shuttle car dust levels when loading at the face during Cuts No. 1 through 3
 

........................................................................................................................... 43
 

Table B-2. Shuttle car dust levels when loading at the face during Cuts No. 4 through 6
 

........................................................................................................................... 44
 

Table B-3. Miner-generated dust levels during the regular- and deep-cut depths for each
 

cut....................................................................................................................... 45
 

Table B-4. Miner operator dust levels during the regular- and deep-cut depths for each
 

cut....................................................................................................................... 45
 

Table B-5. Bolter operator exposure levels during the regular- and deep-cut depths for 

each bolted room................................................................................................ 45
 

Table C- 1. Shuttle car dust levels when loading at the face during Day 1 of the study 52
 

Table C- 2. Shuttle car dust levels when loading at the face during Day 2 of the study 53
 

Table C- 3. Shuttle car dust levels when loading at the face during Day 3 of the study 54
 

Table C- 4. Miner-generated dust levels during the regular- and deep-cut depths........ 55
 

Table C- 5. Miner operator dust exposure levels net of intake dust level during the
 

regular- and deep-cut depths.............................................................................. 55
 

Table C- 6. Bolter machine-generated dust levels and bolter operator exposures for the
 

regular- and deep-cut depths.............................................................................. 56
 

Table D-1. Shuttle car cab dust levels when loading at the face during Day 1 of the
 

study................................................................................................................... 65
 

Table D-2. Shuttle car cab dust levels when loading at the face during Day 2 of the
 

study................................................................................................................... 66
 
Table D-3. Shuttle car cab dust levels when loading at the face during Day 3 of the
 

study................................................................................................................... 67
 

Table D-4. Miner-generated dust levels during the regular- and deep-cut depths......... 68
 

Table D-5. Bolter-generated dust levels and operator exposures for each bolting
 

sequence............................................................................................................ 68
 

Table E-1. Shuttle car cab dust levels when loading at the face during Cuts No. 1
 

through 4 ............................................................................................................ 79
 

Table E-2. Shuttle car cab dust levels when loading at the face during Cuts No. 5
 

through 7 ............................................................................................................ 80
 

Table E-3. Shuttle car cab dust levels when loading at the face during Cuts No. 8
 

through 10 .......................................................................................................... 81
 

Table E-4. Miner-generated dust levels during the deep- and regular-cut depths......... 82
 

Table E-5. Bolter-generated dust levels and operator exposures for each bolting
 

sequence............................................................................................................ 82
 

Table F-1. Shuttle car cab dust levels when loading at the face on Day 1 .................... 90
 

Table F-2. Shuttle car cab dust levels when loading at the face on Day 2 .................... 91
 

Table F-3. Shuttle car cab dust levels when loading at the face on Day 3 .................... 92
 

Table F-4. Miner-generated dust levels during the deep- and regular-cut depth ........... 93
 

Table F-5. Miner operator dust levels during the deep- and regular-cut depths ............ 93
 

Table F-6. Bolter-generated dust levels and operator exposures for each bolting
 

sequence............................................................................................................ 94
 
ACRONYMS AND ABBREVIATIONS 

CFR Code of Federal Regulations 

CI confidence interval 

EIA Energy Information Administration 

MSHA Mine Safety and Health Administration 

NIOSH National Institute for Occupational Safety and Health 

No. number 

PDM personal dust monitor 

pDR personal DataRAM 

PVC polyvinyl chloride 

RAM real-time aerosol monitor 

TWA time weighted average 

USBM United States Bureau of Mines 
UNIT OF MEASURE ABBREVIATIONS 

USED IN THIS REPORT
 

cfm cubic foot per minute 

o degree 

ft foot 

fpm foot per minute 

gpm gallon per minute 

in inch 

in Hg inch of mercury 

μg/m3 microgram per cubic meter 

mg/m3 milligram per cubic meter 

mm millimeter 

% percent 

psi pound-force per square inch 

Evaluation of Face Dust Concentrations at Mines Using 

Deep-Cutting Practices
 

J. Drew Potts, W.R. Reed, and Jay F. Colinet 

National Institute for Occupational Safety and Health 

Abstract
 

Dust surveys were conducted at six underground mines to determine if deep-cut mining practices 

expose face workers to higher levels of respirable dust by comparing levels during the first 20 ft 

of advance (regular-cut depth) during the deep cut to levels during the final 10 to 20 ft of 

advance (deep-cut depth). The studies were conducted at mines where the Mine Safety and 

Health Administration (MSHA) had approved an extended curtain setback distance with 

operation of a flooded-bed scrubber to permit taking deep cuts of up to 40 ft. In general, all of 

the selected mines exercised good dust control practices by maintaining water sprays, scrubber 

airflows, proper curtain setback distances and providing sufficient airflow to the active faces. 

These practices minimized variability in dust levels related to factors other than the depth of cut. 

To ensure proper scrubber functioning, the scrubber screen was back-flushed before 

commencing each cut. Both exhausting and blowing face ventilation configurations were 

studied. All of the operations surveyed for this study were able to successfully implement deepcutting methods without significantly increasing the dust exposures of face workers during the 

cutting and bolting cycles. 

For exhausting face ventilation, field data indicate that scrubber airflow is the most important 

factor for controlling dust. Clogging of the scrubber screen can result in lower airflows; 

therefore, the screen must be periodically tapped and back-flushed. Data collected for this study 

indicate that 20-mesh screens should be cleaned for every 40 ft of advance because 22% of the 

deep-cut sequences surveyed for this study experienced a 20% to 35% decrease in scrubber 

airflow over the course of the cut. For blowing face ventilation, field and laboratory data indicate 

that maintaining a proper curtain-to-scrubber airflow ratio of 1.0 and a curtain setback distance 

that allows the miner operator to stand at the mouth of the curtain helps control dust. Curtain 

airflows should be measured before activation of the scrubber regardless of ventilation type 

(exhausting or blowing) to avoid erroneously overinflating the ratio. The curtain setback 

variance should be greater than the maximum cutting depth to allow miner operators to maintain 

their position at the mouth of the curtain when the miner is fully extended into the cut. Greater 

curtain setback distances associated with deep-cutting methods may result in cuts that do not 

require ventilation curtain, such as the initial heading developments beyond the last open 

crosscut. For these cuts, dust levels were generally lower during development of deep cuts when 

compared to regular cuts. However, adequate ventilation of cuts without ventilation curtain is 

dependent on a properly functioning scrubber. Dust levels on the bolting faces did not appear to 
be affected by the longer cycles associated with deep-cut mining practices when curtain airflow 

was measureable and the curtain was periodically advanced in sync with the bolting machine. 

Introduction 

In 2008, underground coal mines in the United States produced over 357 million tons of coal 

[EIA 2008], with over half of this production coming from continuous mining operations. 

MSHA determined that over 800 continuous mining units were in operation in 2010 

[Niewiadomski 2010]. During the mining of coal, respirable coal dust is liberated into the air, 

potentially exposing mine workers. Likewise, during the extraction of the coal, rock within or 

surrounding the coal seam may be cut, liberating respirable silica into the air. Overexposure to 

respirable coal dust can lead to the development of coal workers’ pneumoconiosis, while 

overexposure to silica dust can lead to silicosis. Both of these lung diseases can be disabling or 

fatal, depending upon the severity of the disease that develops. Consequently, to prevent the 

development of occupational lung disease, mining operations are responsible for controlling 

concentrations of respirable dust in the mine atmosphere where miners work or travel. 

The Federal Coal Mine Health and Safety Act of 1969 (Public Law 91-173), generally referred to 

3 as the Coal Act, established the current respirable coal mine dust standard of 2.0 mg/m . 

Compliance with this standard is monitored through periodic collection of occupational and area 

dust samples with an approved gravimetric sampling pump. However, if the silica content of the 

collected sample is greater than 5%, then a reduced dust standard is calculated by dividing 10 by 

the percent silica in the sample. For example, if the compliance sample contains 10% silica, a 

3 reduced dust standard of 1.0 mg/m is enforced on that mining unit. Enforcement of a reduced 

3 dust standard is designed to limit exposure to respirable silica dust to a maximum of 100 μg/m . 

The Mine Safety and Health Administration (MSHA) is responsible for enforcing the respirable 

dust regulations. Prior to starting a new mining section, mine operators are required to develop a 

mine ventilation plan designed to control methane and respirable dust, and they must submit the 

plan to MSHA for approval. The dust control portion of the mine ventilation plan specifies the 

types of dust controls, work practices, and maintenance procedures to be used on each shift to 

limit dust concentrations to acceptable levels. 

Implementation of these dust regulations has had a significant impact on the respirable dust 

exposure of mine workers and on the prevalence of lung disease. In April of 1968, the U.S. 

Bureau of Mines (USBM) conducted sampling at over 20 mines to quantify respirable dust levels 

for select occupations [USBM 1970]. Results of this sampling showed that the average dust 

3 3 exposure levels were 5.63 mg/m for the continuous miner operator and 3.39 mg/m for the roof 

bolter operators [Colinet et al. 2010]. For MSHA inspector samples collected in 2009, the 

3 3 average dust exposure levels were 0.81 mg/m for the continuous miner operator and 0.60 mg/m

for roof bolter operators. These average dust exposure levels represent all valid samples collected 

for these occupations and show substantial reductions compared to the 1968 results. 

Unfortunately, samples show that individual shift concentrations above the applicable standards 

continue to occur. For example, continuous miner operator samples from 2006 through 2009 

3 show that 6.7% of the samples exceeded 2.0 mg/m , while 13.0% of samples exceeded their 

reduced dust standard [MSHA 2010]. 

2
 
Traditionally, ventilation and water sprays have been the primary methods used to control dust 

generation from the continuous miner. The miner was operated by a worker positioned in an 

operator’s cab located at the back right corner of the machine. This worker was not permitted to 

travel under unsupported roof, thereby limiting the depth of mining cuts to 20 ft. 

As continuous mining equipment was modified, new mining techniques also evolved. Today, 

most continuous mining machines are equipped with remote control units and flooded-bed 

scrubbers. The remote control unit has allowed the miner operator to move off of the miner and 

stand in the entry while operating the machine. Therefore, the miner operator can remain under 

supported roof while the mining machine advances under unsupported roof to extract cuts that 

extend beyond 20 ft. However, for MSHA to approve curtain setback distances greater than 20 ft 

to permit deep cuts, the mine must demonstrate that the roof integrity will allow for advances 

beyond 20 ft and adequate ventilation can be provided to the face to control methane and dust 

levels. The flooded-bed scrubber is a fan-powered dust collector, which induces airflow to the 

face and collects over 90% of the respirable dust drawn into the unit when properly maintained 

[McClelland et al. 1992]. Consequently, the combination of remote control and a flooded-bed 

scrubber has allowed continuous miner units to extract deep cuts. Approximately 70% of miner 

units are extracting deep cuts [Niewiadomski 2010]. 

On June 3, 2008, MSHA issued a procedure instruction letter entitled Procedures for Evaluation 

of Requests to Make Extended Cuts With Remote Controlled Continuous Mining Machines (PIL 

No. I08-V-3). This procedure provides guidance for evaluating requests for approval of deep cuts 

and raises emphasis on effectively controlling respirable dust throughout the entire cut. 

Stakeholders inquired about available data regarding dust levels for different portions of deep 

cuts, but NIOSH was not aware of any existing data. In response, NIOSH initiated an 

underground study to evaluate dust levels generated throughout the extended cut, while also 

monitoring the performance of the dust collectors used on the miners and roof bolters. NIOSH 

used sampling instrumentation and techniques to allow for a comparison of dust levels generated 

during advancement of the first 20 ft (regular cut) of a deep cut to levels during advancement of 

the final 10 to 20 ft (deep cut) of a deep-cut. Dust surveys were conducted at six mines under a 

variety of operating conditions, with the results summarized in this report. 

Sampling Protocol and Data Analysis 

The dust sampling protocol used both area and personal sampling techniques to evaluate face 

dust concentrations on continuous mining sections using deep-cutting methods. Neither the area 

nor personal sampling techniques used to conduct the underground surveys followed compliance 

sampling requirements prescribed by Title 30 of the Code of Federal Regulations (CFR). More 

specifically, the sampling devices were not operated portal to portal (30 CFR 70.201), nor were 

they converted to an equivalent concentration as measured with an MRE instrument (30 CFR 

70.206). Rather, all of the concentrations reported are based on time weighted averages (TWAs). 

Area samplers were turned on and off at the working faces, and sampling times average between 

five and seven hours. The personal sampling devices were programmed to start operating when 

the workers reached the face, and to run for a period of eight hours. Respirable dust 

measurements were made using the following real-time and gravimetric sampling equipment: 

3
 
(1)	 Thermo Scientific Model 1000AN personal DataRams (pDRs) 

(2)	 Thermo Scientific Model 3600 personal Dust Monitors (PDMs) 

(3)	 MSA Escort Elf sampling pumps with MSA filters and Dorr-Oliver 10-mm cyclones 

(gravimetric samplers) 

Figure 1 shows a plan view of the area sampling packages for a section layout when a exhausting 

curtain was used to ventilate the active face. Area sampling was conducted with a package 

consisting of two gravimetric samplers and one pDR. The pDR utilizes light scattering 

technology to measure relative dust levels in real-time, which are stored in an internal data 

logger. The data collected with the pDR, combined with a detailed time study, allowed 

researchers to determine dust concentrations during specific periods of time. The gravimetric 

samples were used to calibrate the pDRs and consisted of MSA pumps that drew dust-laden air at 

2.0 liters/minute through 10-mm nylon cyclones to deposit the respirable dust fraction onto preweighed 37-mm PVC filters. All filters were pre- and post-weighed at the NIOSH controlled 

environment weighing lab in Pittsburgh, providing the data from which respirable dust 

concentrations were calculated. Correction factors to calibrate the pDR data, as recommended by 

the manufacturer (Thermo Scientific), were calculated by dividing the daily average gravimetric 

concentration by the daily average pDR concentration for each sampling location. The 

instantaneous readings from the pDRs were then multiplied by the correction factors. Isolation of 

bolter- and miner-generated dust was accomplished by placing the area sampling packages in the 

immediate intake and return for each piece of equipment. Intake dust levels were subtracted from 

return dust levels to determine the portion of dust attributable to a particular piece of equipment. 

Area sampling packages were also hung in the shuttle car cabs to monitor potential operator 

exposure levels. 

Due to the mobility of the bolter and miner operators, belt-wearable PDMs were used, instead of 

area sampling packages, to monitor the dust exposures of these workers. PDMs are mass-based 

samplers, which provide real-time dust measurements that do not require a gravimetric 

calibration. 

Real-time dust data allowed researchers to analyze dust level fluctuations from start to finish for 

each deep cut. A detailed time study was conducted to record when each shuttle car entered and 

exited the active face. The shuttle car cab dust levels were of particular importance for this study 

because each car’s position with respect to the mining machine remained consistent throughout 

advancement of the face. This data allowed direct determination of dust levels around the mining 

machine at various depths. Of particular importance was a comparison of dust levels during the 

first 20 ft of advancement, which represents a regular-cut depth, to dust levels during the last 10 

to 20 ft of advancement, the deep-cut depth. Miner operator exposure levels and miner-generated 

dust levels were also determined for the regular- and deep-cut depths. Mines using deep-cutting 

methods also have longer bolting cycles. Therefore, a similar time study was conducted on the 

bolter faces, allowing a comparison of dust level fluctuations as the bolting machine advanced. 

Since the objective of the study was to compare dust levels during the regular cut to levels during 

the deep cut, it was important to examine variables that changed during an individual cut 

sequence. During our field studies we were able to measure two operating parameters, 

productivity and scrubber airflow, that changed frequently when comparing the regular cut to the 

deep cut. It is a generally accepted principle and common practice to assume that dust levels and 

productivity exhibit a linear relationship with one another. For example, if cut A was mined at a 

4
 
production rate of 1 car per minute and cut B was mined at a production rate of 2 cars per 

minute, one would expect cut B concentrations to be double that of cut A. Therefore, all of the 

miner operator exposure levels and mining machine-generated dust levels presented in this report 

were normalized based on the measured productivity for each cut sequence. The number of cars 

loaded per minute was used as the measure of productivity, and dust levels for each particular 

mine were normalized to the average productivity observed throughout the survey. For example, 

if the average productivity for the section was 0.37 cars per minute and productivity during the 

regular-cut depth for Cut No. 1 was 0.41 cars per minute, then the dust levels measured for this 

cut were normalized by multiplying by a correction factor of 0.90 (0.37/0.41). 

Data analysis focused on determining whether or not dust levels during the deep-cut depth were 

significantly different than dust levels during the regular-cut depth. When determining statistical 

significance, the most commonly used confidence level for scientific experimentation is 95%. A 

less stringent but still robust standard that involved calculating 85% confidence intervals (CIs) 

for the sample means and comparing the values for overlap was used for this project due to the 

nature of the collected data. It is often difficult to obtain enough underground data to document 

changes in dust levels using a 95% confidence level criterion because fluctuations in operating 

parameters that are known to affect these levels can occur within and between individual cuts, 

adding variability to the data. These operating parameters include, but are not limited to, curtain 

airflows and setback distances, water spray pressures and quantities, and positioning of mine 

personnel. Using the 85% CI calculations allowed researchers to draw conclusions from the data 

with a reasonable degree of certainty. Comparisons that met more stringent statistical 

significance criterion are noted in the text. 

Measurements other than dust were necessary to fully understand the effects of deep-cutting 

methods on face dust levels. As the miner advances into the deep cut, a buildup of material may 

occur in the flooded-bed scrubber filter, diminishing its effectiveness. This situation was 

monitored by measuring scrubber airflow at the beginning and end of each cut using a pitot tube 

and manometer. At the beginning of the study, velocity head traverse readings of the scrubber 

duct were measured using a pitot tube and manometer. The traverse readings included top, 

center, and bottom measurement points at each sampling port provided by the manufacturer, 

resulting in 15 to 18 readings. Scrubber airflow was determined based on the average of the 

readings. Succeeding scrubber airflow measurements were made using a single-point pitot tube 

reading, which was calibrated to the traverse readings. 

Likewise, with the bolting machine, a buildup of material in the dust collection box may 

diminish the performance of the dry dust collection system. Therefore, the suction pressure of the 

bolter’s dust collection circuit was periodically measured and recorded throughout the bolting 

sequence, using a vacuum gauge at the drill heads. 

Airflow delivered to the active cutting and bolting faces was measured using an electronic vane 

anemometer. Measurements were taken at the face-side mouth of the curtain. Following mine 

protocol, curtain airflow at the exhausting face ventilation mines was measured before activation 

of the scrubber and after activation at the blowing face mines. Curtain configuration and length 

were also recorded. 

5
 
Underground Dust Surveys
 

A total of six underground dust surveys were conducted to complete this project. Two surveys 

were conducted at mines using exhausting face ventilation, two at mines using blowing 

ventilation, and two at mines using either blowing or exhausting curtain, depending on their 

location on the section. In-depth mine case studies on the findings at each of these mines, labeled 

A through F, are included in the Appendices. All of the mines were able to use deep-cutting 

practices without hindering their ability to limit the dust exposures of face workers. However, 

researchers were able to identify some practical operating parameters to ensure the successful 

use of deep-cutting methods from the perspective of dust control. 

Table 1 shows a summary of the 47 cuts examined for this study. The table includes face 

ventilation type, orientation of the cut, a mine identifier (A through F), curtain airflow, the 

starting and ending scrubber readings, curtain-to-scrubber airflow ratios, and shuttle car cab dust 

levels when loading at the face during the regular and deep portions of the cut. The number of 

data points used to calculate each reported shuttle car cab dust level in Table 1 ranged between 6 

and 13, with the average equal to 9. These numbers are derived from the data tables in the 

appendices. Table 1 also shows a determination as to whether or not the differences in dust levels 

between the deep and regular cuts were significant by comparing the 85% CIs for the averages. 

Following mine-specific protocol, the curtain airflows presented in Table 1 were measured 

before activation of the scrubber for the exhausting faces and after activation of the scrubber for 

the blowing faces. Combining all data presented in Table 1, the average shuttle car cab dust 

3 3 levels when loading at the face were 0.96 mg/m during regular-cut depth and 1.04 mg/m during 

the deep-cut depth, which was not a statistically significant (85% CIs) difference. As mentioned 

earlier, shuttle car cab dust levels when loading at the face were used as the primary indicator of 

face area dust levels because their positions with respect to the mining machine remained 

consistent throughout advancement of the face. 

Some of the shuttle car cab dust levels that are presented in Table 1 for the blowing face 

ventilation cuts appear to be relatively high. However, the levels represent short-term exposures 

during cutting and loading activities and are not reflective of full-shift exposures. Most of the 

shuttle cars’ time was spent in transit to and from the feeder/breaker. For example, the highest 

shuttle car dust levels when loading at the face were measured at Mine A when using blowing 

face ventilation. The average value of these levels (from Appendix A, Tables A-1, A-2, and A-3) 

3 equaled 4.84 mg/m . When loading, transit, and the dumping sequence were included in the 

calculation at Mine A, the average shuttle car cab dust level during blowing face ventilation cuts 

3 was 1.98 mg/m . Furthermore, when miner down and move times were included in the 

calculation of the shuttle car cab dust level, the TWA exposure for the entire sampling period 

3 was 1.20 mg/m on day 2 of the study at Mine A when all of the cuts were made using blowing 

face ventilation. 

Table 2 shows all of TWA exposure levels for the entire sampling periods at the miner, bolter, 

and shuttle car operators for each of the surveyed mines. Two miner operator exposures are listed 

for Mine C because two mine workers alternated between operator and helper duties on an 

every-other-cut basis. The missing data in Table 2 are explained in the Appendices. The highest 

6
 
3 TWA exposure level measured during the study was 1.76 mg/m , and most levels were below 1.0 

3 mg/m . 

Table 3 shows miner operator exposure levels and miner-generated dust levels during the 

regular- and deep-cut sequences for each of the 47 cuts listed in Table 1. All of the presented 

values were normalized for productivity. Combining all data, the average miner operator 

3 3 exposures were 0.95 mg/m during the regular-cut depth and 0.93 mg/m during the deep-cut 

3 depth. The average miner-generated levels were 2.02 mg/m during the regular-cut depth and 

3 1.23 mg/m during the deep-cut depth. Only the difference in miner-generated dust levels was 

significant (85% CIs). This significant difference occurred due to the no-curtain cuts, which is 

explained in the ―No-curtain Ventilation‖ section of this report. 

An analysis follows for the different types of face ventilations encountered during the study, 

including exhausting, blowing, and no-curtain. These sections of the publication draw 

information from the Appendices and present an inter-mine perspective in order to draw 

conclusions regarding the use of the deep-cutting method and its effects on respirable dust levels 

in the bolting and mining face areas. 

Exhausting Ventilation 

In general, face area dust levels, as measured in the shuttle car cabs when loading at the face, 

were quite low during the exhausting face ventilation cuts conducted at Mines A, B, and C, 

3 3 averaging 0.20 mg/m during regular-cut depth and 0.35 mg/m during deep-cut depth. This 

difference is not statistically significant (85% CIs). 

A significant difference was measured for several cuts at Mine C. This mine used two shuttle 

cars to transport coal to the feeder/breaker. One car had a standard cab configuration, while the 

other was equipped with an off-standard cab configuration. The analysis completed for Mine C, 

which is detailed in Appendix C, found that dust levels in the off-standard cab were 0.2 to 0.4 

3 mg/m higher (95% CIs) during the deep-cut sequence when compared to the regular-cut 

sequence. This difference may have resulted because the off-standard cab was on the same side 

of the entry as the exhaust tubing and, as the cut was advanced, the cab’s position approached the 

mouth of the tubing, where it was exposed to dust rollback. This difference was not observed in 

the standard cab, which was on the off-curtain side of the entry. A laboratory study conducted by 

NIOSH made similar observations concerning the off-standard side cab. The study found that 

increasing the curtain setback distance from 30 to 40 ft, significantly increased dust levels at the 

off-standard shuttle car position by placing it near the mouth of the curtain [Goodman et al. 

2006]. Therefore, when using deep-cutting methods with exhausting face ventilation, it is 

beneficial to use shuttle cars with cabs located on the off-curtain side of the entry to help ensure 

that dust levels do not increase with increasing depth of cut. 

A stepwise linear regression analysis was conducted on the exhausting face ventilation data 

contained in Table 1 to determine if independent variables affected shuttle car cab dust levels 

(dependent variable), including curtain airflow, scrubber airflow, and the curtain-to-scrubber 

airflow ratio. The mine identifier was also included as an independent variable to account for any 

inter-mine differences. Calculations of the values for kurtosis (2.1) and skewness (1.5) associated 

7
 
with the dependent variable did not indicate a substantial deviation from an assumption of 

normality. Other model assumptions included the following: 

(1) Curtain airflow remained constant throughout the cut. 

(2) The starting scrubber airflow prevailed during the regular-cut depth. 

(3) The ending scrubber airflow prevailed during the deep-cut depth. 

The scrubber airflows presented in Table 1 for Mine C were the only levels measured and 

reported by mine personnel and based on single center-point pitot tube readings. Since centerpoint readings are typically higher than full-traverse calculations, actual scrubber levels for Mine 

C were probably somewhat lower than those reported in the table. All other scrubber airflow 

measurements were conducted by NIOSH personnel and were adjusted based on a full-traverse 

pitot tube study of the scrubber duct as explained in the ―Sampling Protocol and Data Analysis‖ 

section of this report. 

Scrubber airflow was the only independent variable found to be significant (95% CIs) for the 

stepwise linear regression analysis. Due to the presence of collinearity between the scrubber and 

curtain airflows, a cause-and-effect relationship between curtain airflow and dust levels cannot 

be ruled out, however, scrubber airflow explained more of the variability in the dust levels. Dust 

levels increased as the scrubber airflow decreased for cuts using exhausting face ventilation. The 

importance of scrubber airflow when using exhausting face ventilation was also identified in a 

recent laboratory study, which concluded that a 20% decrease in scrubber airflow produced a 

significant increase in dust levels on the curtain side of the machine as well as in the return 

[Organiscak and Beck, forthcoming]. As shown in Figure 2, a pie chart depicting the reductions 

in scrubber airflows measured from start to finish for all of the 47 deep cuts surveyed for this 

study, 22% of the cuts experienced a drop in the range of 20% to 35%. This figure conveys the 

importance of keeping the scrubber screens clean. All of the mines in the study used 20-mesh 

screens and experienced some average reduction in scrubber airflow during the course of the 

deep cut. Typical mine practices, as prescribed by the mine ventilation plans and manufacturer 

recommendations, involve cleaning the scrubber screens at least twice during a shift. The above 

data suggest that cleaning the screens by tapping out the contaminants and back-flushing with 

water should be conducted before each deep cut to ensure maximum scrubber airflow. 

For the exhausting ventilation cuts shown in Table 3, the average miner operator exposure levels 

3 during the regular- and deep-cut depths were both low at 0.55 mg/m during the regular-cut 

3 depth and 0.83 mg/m during the deep-cut depth. This difference is not statistically significant 

(85% CIs). In general, all of the exhausting face ventilation mines surveyed for this study 

positioned the miner operator on the off-curtain side of the entry in an area that was parallel to, 

or outby, the inlet mouth of the curtain. From a dust control perspective, research has shown this 

to be the best location for the operator [Colinet and Jankowski 1996]. Curtain setback distances 

were maintained between 30 and 50 ft at the surveyed mines to help ensure that the scrubber 

exhaust was not directed against the curtain line. 

Use of deep-cutting techniques necessitates the use of greater curtain setback distances. Several 

research projects have been conducted to examine the effects of greater curtain setbacks on face 

area dust levels when using exhausting face ventilation. Mixed results have been reported. One 

laboratory study reported no change in dust levels in areas parallel to, and outby, the mouth of 

8
 
the exhausting curtain on the off-curtain side of the machine when the setback distance was 

increased from 30 to 40 ft [Colinet and Jankowski 1996]. The other laboratory study found 

significantly higher dust levels at the parallel position when increasing the setback from 30 to 40 

ft [Goodman et al. 2006]. The machine-mounted water spray systems used for the two laboratory 

studies were substantially different and may have led to the discrepancies in findings. Another 

study, conducted underground, compared curtain setback distances of greater than 30 ft to 

distances less than 30 ft [Goodman 2000]. It found lower dust levels at the rear corners of the 

machine when using greater curtain setbacks. Based on these mixed results, it appears that the 

ideal curtain setback distance at mines using deep-cutting methods and exhausting face 

ventilation may be dependent on mine-specific water spray and ventilation parameters. In any 

case, to prevent the discharged scrubber airflow from striking the curtain line and blowing it 

against the rib, the curtain setback distance should be at least 30 ft. When the exhausting curtain 

is blown against the rib by the scrubber discharge, the airflow reaching the face is diminished. 

Blowing Ventilation 

From Table 1, dust levels in the shuttle car cabs when loading at the face during the blowing face 

3 ventilation cuts conducted at Mines A, D, E, and F averaged 1.96 mg/m during the regular-cut 

3 depth and 2.32 mg/m during the deep-cut depth. This difference was not statistically significant 

(85% CIs). In fact, 13 of the 18 blowing face cuts experienced no significant change when 

comparing deep-cut dust levels to regular-cut levels. 

The curtain airflows presented in Table 1 for the blowing face ventilation cuts were measured 

after activation of the scrubber. This is an important distinction to make because both this field 

study and another laboratory study found that curtain airflow, as measured at the face-side mouth 

of the blowing curtain, can increase significantly upon activation of the scrubber [Taylor et al. 

1997]. When the scrubber airflow and pre-activation blowing curtain airflow were similar, 

curtain airflows increased from 40% to 56% upon activation of the scrubber. At the blowing face 

ventilation mines surveyed for this study, the average ratio of airflow in the last open crosscut to 

the highest measured scrubber airflow ranged between 1.9 and 5.8. Since there was an 

abundance of airflow available in the last open crosscut, the additional air measured behind the 

curtain upon activation of the scrubber was likely a combination of re-circulated and fresh air. 

From a dust perspective, the curtain airflow reading after activation of the scrubber at these 

mines is important because it represents the actual airflow forced to the face during operating 

conditions. 

As shown in Table 1, dust levels in the face area at Mine D increased as the depth of cut 

increased during the heading cut when using blowing face ventilation. This may be explained by 

a suspected less than ideal curtain-to-scrubber airflow ratio and may be due to the fact that the 

magnitude of scrubber airflow measured after this particular cut was the lowest observed value 

for blowing curtain cuts at 5,100 cubic ft per min (cfm). A laboratory study conducted by the 

USBM found that the ideal curtain-to-scrubber airflow ratio for controlling dust when using 

blowing face ventilation is 1.0, when curtain airflow is measured before activation of the 

scrubber [Jayaraman et al. 1992]. As mentioned previously, curtain airflows on the blowing faces 

surveyed for this study were measured after scrubber activation. The ratio measured at Mine D 

9
 
after completion of the cut, and with the scrubber running, was 1.82, the second highest value 

observed during the study. Assuming that the scrubber boosted airflow at Mine D was similar to 

what occurred during the Taylor study [1997], which had similar post activation scrubber (6,000 

cfm) and curtain airflows (8,600 cfm), the estimated ending curtain-to-scrubber airflow ratio for 

the Mine D with the scrubber off is 1.30, which is a significant deviation from the ideal ratio of 

1.0. The Jayaraman study also found that decreasing the scrubber airflow from 7,500 to 4,000 

cfm was the most significant factor for increasing dust at all positions. It is interesting to note 

that scrubber airflows during this particular cut at Mine D dropped from 7,300 to 5,100 cfm, 

which was very close to laboratory conditions. Cut No. 18 at Mine E also experienced a 

substantial drop in scrubber airflow over the course of the cut but did not experience higher dust 

levels; however, it appears that the ending curtain-to-scrubber airflow ratio at Mine E was more 

favorable than at Mine D. 

At Mine E, one of the four heading cuts using blowing face ventilation experienced significantly 

higher dust levels during the deep-cut depth. This was most likely caused by a change in shuttle 

car routes during the cut, which placed the cabs directly in the mining machine’s return airflow 

for the last half of the cut. At Mine F, two of the eight heading cuts using blowing ventilation 

experienced significantly higher dust levels during the deep-cut depth; however, no 

determination could be made concerning the cause for this difference, as similar operating 

conditions were observed during all cuts. As shown in Appendix F, when all of the data collected 

at Mine F was combined for analysis, no significant (85% CIs) difference was found when 

comparing deep-cut dust levels to regular-cut levels. For the blowing ventilation cuts at Mine A, 

neither of the individual heading cuts demonstrated significant changes in dust during the deepcut depth; however, when the data were combined, the dust levels were significantly (85% CIs) 

higher during the deep-cut depth. Higher deep-cut dust levels when driving headings were offset 

by lower deep-cut dust levels during the right crosscut development at Mine A, resulting in an 

overall change in dust levels that was not statistically significant (85% CIs) when comparing the 

regular-cut depth to the deep-cut depth. 

A stepwise linear regression analysis, similar to the one conducted for the exhausting face data, 

was conducted on the blowing face ventilation data contained in Table 1. Again, calculations of 

the values for kurtosis (2.1) and skewness (1.3) associated with the dependent variable did not 

indicate a substantial deviation from an assumption of normality. The stepwise regression 

analysis found that only the identifier for Mine A was a significant independent variable (95% 

CIs), indicating that Mine A dust levels were significantly higher than those for the other three 

blowing face ventilation mines. As with the exhausting ventilation data set; collinearity existed 

in the airflow related independent variables. Additional regression analyses that involved 

separately comparing each independent variable to the dependent variable cannot rule out curtain 

and scrubber airflows as cause-and-effect variables, however, the mine identifier variable 

explained most of the variability in the dust levels. 

For the blowing ventilation cuts shown in Table 3, the average miner operator exposure levels 

3 3 were 2.44 mg/m during the regular-cut depth and 2.10 mg/m during the deep-cut depth. This 

difference is not statistically significant (85% CIs). Mines A, D, and E properly positioned the 

miner operator at the mouth of the blowing curtain [Goodman and Listak 1999]. Mine F’s 

approved ventilation plan precluded this positioning. The plan, which allows for 30-ft cuts, 

requires that the blowing curtain be within 10 ft of the face at the start of the cut and, after 

10
 
advancing the face 10 ft, requires its attachment to the last row of bolts. With these requirements, 

it was impossible for the miner operator to stand at the mouth of the curtain, resulting in higher 

dust exposure levels for the miner operator. During the last day of the survey at Mine F, the 

curtain setback distances exceeded plan, and the miner operator was able to position himself at 

the mouth of the blowing curtain. As a result, miner operator exposure levels dropped 3.94 

3 3 mg/m to an average level of 0.23 mg/m during production. From a dust control perspective, the 

allowable curtain setback should be greater than the maximum cutting depth to ensure that miner 

operators can maintain their position at the mouth of the blowing curtain. 

Several research projects have been conducted to examine the effects of greater curtain setbacks 

on face area dust levels when using blowing face ventilation. Two laboratory studies [Goodman 

2000 and Jayaraman et al. 1992] found that increasing the curtain setback distance (20 to 40 ft in 

the Goodman study and 25 to 35 ft in the Jayaraman study) reduced dust rollback at the rear 

corners of the mining machine when using blowing ventilation. An underground blowing face 

study reported that dust levels at the right rear (operator’s cab) of the mining machine initially 

increased when increasing the curtain setback distance from 25 to 35 ft but then decreased when 

increasing the setback from 35 to 50 ft [Volkwein et al. 1985]. Dust levels during the dustier slab 

cut were actually slightly lower when comparing the 50-ft setback to the 25-ft setback. The 

Volkwein study also found no degradation in methane dilution when increasing curtain setbacks 

from 25 to 50 ft. The results of these studies indicate that the greater curtain setbacks associated 

with deep-cutting methods at mines using blowing curtain were not detrimental to effective face 

ventilation. 

No-curtain Ventilation 

At mines using deep-cutting methods, greater curtain setback distances may result in cuts that do 

not require the installation of line curtain, such as the initial entry developments beyond the last 

open crosscut. Mines with smaller pillar dimensions will experience more of these cuts because 

the distance between the crosscuts is less. From Table 1, dust levels in the shuttle car cabs when 

loading at the face during the no-curtain ventilation cuts conducted at Mines B, D, and E 

3 3 averaged 0.46 mg/m during the regular-cut depth and 0.15 mg/m during the deep-cut depth. 

This difference is statistically significant (95% CIs). In fact, 9 of the 15 no-curtain cuts 

experienced significantly lower dust levels during the deep-cut depth when compared to the 

regular-cut depth. Lower shuttle car cab dust levels during the deep-cut portion of the no-curtain 

cuts can be explained by better scrubber inlet capture efficiencies and improved shuttle car 

positioning relative to the scrubber exhaust and intake airway. 

As described earlier, area sampling was conducted upwind and downwind of the mining machine 

to determine dust generation during the regular- and deep-cut sequences. As seen in Appendix D, 

the mining machine at Mine D generated significantly (85% CIs) less dust during the deep-cut 

depth when compared to the regular-cut depth for cuts that did not use ventilation curtain. 

Assuming constant return ventilation airflow throughout each particular cut, lower dust 

generation indicates improved scrubber capture during the deep-cut depth. Improved capture 

occurs because the airflow reaching the face is essentially limited to what the scrubber is 

drawing after the miner extends beyond the influence of primary ventilation. In essence, a perfect 

11
 
1.0 curtain-to-scrubber airflow ratio is created. In addition, primary ventilation airflow is usually 

perpendicular to the direction of cut during no-curtain cuts. The dustiest portions of the cuts 

occur when the miner is beginning the first sump and slab cuts and primary airflow sweeps 

across the cutting drum and under the boom of the miner. If the primary ventilation air velocities 

are high enough, scrubber inlet capture efficiencies decrease. Lower dust generation during the 

deep-cut depth partially explains lower shuttle car cab dust levels; however, shuttle car cab 

position is also a contributing factor. 

As shown in Figure 3, when beginning the sump and slab lifts in no-curtain heading cuts, the 

scrubber exhaust is often located in or directed outby the last open crosscut, resulting in dust 

rollback into the shuttle car haulageway. This rollback can result in significant shuttle car 

operator exposures because the airflow in the haulageway is often low due to the placement of 

check and fly curtains in the entries. As shown in Figure 4, advancement of the cut results in the 

scrubber exhaust being directed into the last open crosscut, where the dusty air is quickly swept 

away from the workings, thereby reducing shuttle car operator exposure levels. Further face 

advancement places the shuttle car cab directly into the intake airway during the deep cut. 

For the no-curtain cuts shown in Table 3, the average miner operator exposure levels were very 

3 3 low, 0.24 mg/m during the regular-cut depth and 0.11 mg/m during the deep-cut depth. This 

difference is not statistically significant (85% CIs). Due to the close proximity of no-curtain cuts 

to the last open crosscuts, the miner operators are able to position themselves in the intake 

airway, resulting in very low dust exposure levels. 

Bolting Operations 

When using deep-cut mining techniques, bolting operations are also subjected to longer cycle 

times. A buildup of material in the dust collection box may lower the suction pressure of the dry 

dust collection system, increasing operator exposure levels and bolting machine dust generation. 

One objective of this study was to determine if the bolting machine’s dust collection efficiency 

decreased during a typical deep-cut bolting cycle. This was done by measuring the suction 

pressure of the bolter’s dust collection system before and after each bolting cycle. Table 4 shows 

curtain airflows, face ventilation type, dust collector suction pressures, operator exposure levels, 

and bolter machine-generated dust levels during the regular- and deep-cut depths for 29 bolting 

cycles monitored for the study. Only bolting cycles conducted upwind of the miner were 

analyzed in Table 4 because miner generated dust, when compared to bolter generated dust, 

accounted for the majority of bolter operator exposures during downwind cycles. Mine C lists 

the bolter suction as nonapplicable (N/A) because the bolting machine used wet drilling 

techniques as opposed to a dry collection system. No attempt was made to analyze bolter 

machine dust generation during no-curtain cycles due to uncertainty related to determining a 

representative location for the return sampling package. Missing data for each mine are described 

in the Appendices. 

Comparing only bolting cycles that had both left- and right-side data available, no statistically 

significant (85% CIs) difference was observed in the average dust exposure levels between the 

3 3 left-side operator at 0.45 mg/m and the right-side operator at 0.48 mg/m . Therefore, all 

subsequent analyses group these data (left and right) together. As shown in Table 4, no 

12
 
degradation in bolter suction pressure was observed during individual bolting cycles. As a result, 

no statistically significant (85% CIs) difference was observed when comparing the average 

3 3 operator exposure level of 0.40 mg/m during regular-cut depth to 0.58 mg/m during deep-cut 

depth. Similar to the left- and right-side analysis, only operator exposure levels that had both 

regular- and deep-cut data available were compared. The only significant (95% CIs) difference 

occurred when comparing exposures for ventilated rooms to non-ventilated rooms. The average 

3 operator exposure level for ventilated room cycles was 0.40 mg/m , while the exposure for non3 ventilated rooms was 0.96 mg/m . Ventilating the rooms with an average air quantity of 5,800 

3 cfm reduced the average operator exposure level by approximately 0.56 mg/m , which 

underscores the importance of maintaining line curtain airflows during the bolting cycles. 

Similarly, no statistically significant (85% CIs) difference was observed in bolter dust generation 

3 when comparing regular- to deep-cut depth. Both were low at 0.12 mg/m for regular-cut depth 

3 and 0.14 mg/m for deep-cut depth. 

The intra-mine analyses presented in the Appendices led to similar conclusions in that no 

significant (85% CIs) changes in bolting operation dust levels were found when comparing the 

regular- to the deep-cut portion of the cycle. A few general observations were made that may 

lead to improved practices at deep-cut mines. First, at Mine A, although only one bolting cycle 

was involved, dust levels appeared to have increased as the bolting cycle progressed when 

curtain ventilation was not measureable. This dust accumulation effect was not observed for 

ventilated cuts at Mine A. A similar upward trend in dust levels was observed at Mine F, where 

the blowing curtain was initially set and then not advanced with the progress of the bolting 

machine. As the distance between the bolter and the mouth of the curtain increased, less air may 

have reached the operators for dilution of drill-generated dust. These observations, while not 

statistically significant (85% CIs), reinforce prudent practices of maintaining measureable 

airflow to the bolting rooms, as well as periodically advancing the line curtain to assure that 

fresh air reaches the work areas. 

Recent Developments Using Blocking Sprays 

As shown in the Appendices, none of the mines surveyed for this study made use of blocking 

sprays to lower respirable dust exposures. When using exhausting face ventilation and a floodedbed scrubber, a laboratory study demonstrated that blocking sprays can significantly lower dust 

levels on the off-curtain side of the mining machine during the slab cut [Organiscak and Beck, 

forthcoming]. For this lab study, two hollow cone sprays were located on each side of the mining 

machine body approximately 2 ft outby the scrubber inlet and 2 ft above ground level. The two 

sprays were 3-in apart on a vertical axis and were angled 15 degrees away from the mining 

machine body and toward the face. For this particular study, hollow cone sprays were found to 

be better than flat fan sprays for controlling airborne dust. When using blowing face ventilation 

and a flooded-bed scrubber, a study demonstrated that blocking sprays improved suppression of 

the dust cloud underneath the boom of the miner in the laboratory and lowered dust levels at the 

rear corners of the machine and at the operator’s position during field testing [Goodman 2000]. 

The laboratory and field blocking spray systems designed for the Goodman study used vertically 

oriented flat fan sprays instead of hollow cone sprays, which were not tested. Results of these 

studies indicate that further dust reductions may be achieved on continuous mining sections 

13
 
through the implementation of blocking spray technology on mining machines equipped with 

flooded-bed scrubbers. 

Conclusions 

All of the six mines surveyed for this study were able to successfully implement deep-cut mining 

practices without significantly increasing the dust exposures of face workers during cutting and 

bolting cycles. Researchers observed the implementation of mining practices that have 

previously been shown to benefit dust control during deep-cut depth, and, in some cases, they 

were able to demonstrate the importance of these measures. While most known flooded-bed 

scrubber and deep-cut dust control practices appear to be widely implemented by the mining 

industry, none of the operations surveyed for this study used blocking sprays on the mining 

machines to improve dust control. Studies have demonstrated the benefits of using blocking 

sprays to control dust on both exhausting [Organiscak and Beck, forthcoming] and blowing 

[Goodman 2000] faces, indicating that implementation of this technology could further improve 

industry-wide respirable dust exposure levels. 

Field data indicated that the most important factor for controlling dust on the exhausting faces 

was scrubber airflow volume. This fact, combined with the observation that 22% of the deep cuts 

surveyed for this study experienced a drop in scrubber airflow in the range of 20% to 35%, 

suggests that the scrubber screens should be cleaned more frequently than the common 

manufacturer recommendation of twice a shift. Screens should be tapped and back-flushed 

before each deep cut. All of the mines surveyed for this study used 20-mesh scrubber screens. 

This study also verified that, when using exhausting face ventilation, the shuttle car cabs should 

be located on the off-curtain side of the entry to help ensure that the shuttle car operator exposure 

levels do not increase during the deep cut. In general, all the exhausting face ventilation mines 

employed proper miner operator positioning at a location parallel to or outby the face-side mouth 

of the curtain [Colinet and Jankowski 1996]. Research is inconclusive on the proper curtain 

setback distance for deep cuts with exhausting face ventilation [Colinet and Jankowski 1996; 

Goodman et al. 2006; Goodman 2000], and the ideal setback distance is likely dependent on 

mine-specific water spray and ventilation conditions. However, the setback distance should be 

great enough to prevent the scrubber exhaust from blowing the line curtain against the rib. This 

distance is generally greater than 30 ft. 

When using blowing face ventilation, the importance of maintaining the proper curtain-to

scrubber airflow ratio of 1.0 was apparent during one cut when this ratio deteriorated (increased) 

and dust levels sharply increased. The ideal airflow ratio of 1.0 was determined in the laboratory, 

where curtain airflow was measured before activation of the scrubber [Jayaraman et al. 1992]. 

Laboratory [Taylor et al. 1997] and field testing observed 40% to 54% increases in curtain 

airflow upon activation of the scrubber when the scrubber capacity and pre-activation curtain 

airflows were similar. Therefore, mine ventilation plans should stipulate that curtain airflow be 

tested before activation of the scrubber to avoid erroneously inflating the curtain-to-scrubber 

airflow ratio. Mine practices should also ensure sufficient curtain setback distance to allow miner 

operators to maintain their position at the face-side mouth of the curtain for the entire cut. In 

order to achieve this objective, a curtain setback distance that is greater than the allowed deep

­

­

14
 
cut depth would have to be permitted. Several studies have demonstrated no degradation in face 

ventilation effectiveness when using curtain setbacks of up to 50 ft [Goodman 2000; Jayaraman 

et al. 1992; Volkwein et al. 1985]. The curtain setback requirement contained in the ventilation 

plan at one mine surveyed for this study prevented the miner operator from standing behind the 

blowing curtain, where dust levels were over 90% lower than in the entry. Miner operator 

exposure levels at the lesser curtain setback mine were higher than at the other mines, where the 

operators spent the majority of their time at the mouth of the curtain. 

At mines using deep-cutting methods, the use of greater curtain setback distances results in some 

cuts that do not require the installation of curtain. For these cuts, dust levels were lower during 

deep-cut depth when compared to regular-cut depth due to improved worker positioning and 

better scrubber inlet capture efficiencies as the cuts progressed. However, effective ventilation 

of no-curtain cuts is entirely dependent upon proper scrubber functioning. 

When adequately ventilated, dust exposures on the bolting faces and bolting machine dust 

generation did not appear to be affected by the longer bolting cycles associated with deep-cut 

mining practices at the mines surveyed for this study. However, although not statistically 

significant (85% CIs), some data did indicate the potential for higher exposures during longer 

bolting cycles if either curtain airflow was not measureable or the curtain was not advanced as 

the bolting cycle progressed. In addition, bolter operator exposure levels during bolting cycles 

3 that were ventilated with an average curtain airflow level of 5,800 cfm were 0.56 mg/m lower 

than exposures when no face airflow was detected. 

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scrubber performance in exhaust ventilation systems. Paper presented at the SME Annual 

Meeting, Phoenix, AZ, February 28–March 3, 2010, Preprint 10–204. 

Taylor DT, Rider JP, Thimons ED [1997]. Impact of unbalanced intake and scrubber flows on 

th face methane concentrations. In: Ramani RV, ed. Proceedings of the 6 International Mine 

Ventilation Congress. Chapter 27. Littleton, CO: Society for Mining, Metallurgy, and 

Exploration, pp. 169–172. 

USBM [1970]. Proceedings of the Symposium on Respirable Coal Mine Dust. Washington, DC: 

Department of the Interior, U.S. Bureau of Mines, USBM Information Circular 8558, p. 253. 

Volkwein JC, Thimons ED, Halfinger G [1985]. Extended advance of continuous miner 

nd successfully ventilated with a scrubber in a blowing section. In: Proceedings of the 2 U.S. Mine 

Ventilation Symposium. New York: Taylor and Francis, pp. 741–745. 

16
 
 

 

 

 

 

Miner 

Bolter 

C 

B 

A 

D 

Shuttle Car 

Shuttle Car 

Check Curtain 

E 

F 

C 

D 

A 

B 

E 

F 

Bolter Intake 

Bolter Return 

Shuttle Car 2 

Shuttle Car 1 

Miner Return 

Miner Intake 

Figure 1. Area sampling locations for a typical section layout. Note: PDMs Are not shown. 

17
 
Table 1. Shuttle car cab dust levels when loading at the face 

Note: Significance column compares deep-cut levels to regular-cut 

levels by comparing the 85% CIs of the averages. 

18
 
Table 2. Time weighted average levels for the shuttle car, miner, and bolter operators 

19
 
Table 3. Miner operator exposure levels and miner-generated 

dust levels during regular- and deep-cuts depths 

20
 
Figure 2. Pie chart depicting the magnitude of scrubber airflow reduction during the cut as 

a percentage of total cuts measured. 

21
 
Figure 3. Mine operator and shuttle car cab position at the start of the no-curtain cut for 

the initial heading development beyond the last open crosscut. 

22
 
Figure 4. Mine operator and shuttle car cab position at the end of the no-curtain cut for the 

initial heading development beyond the last open crosscut. 

23
 
Table 4. Bolter operator exposure levels and machine-generated 

dust levels at regular- and deep-cut depths 

24
 
Appendix A: MINE A CASE STUDY 

Mine-specific Information 

Mine A used a Joy 12CM12 continuous miner. The miner spray configuration is shown in Figure 

A-1.

Figure A-1. Mine A continuous miner spray configuration. 

 A total of 38 dust suppression sprays were operated at a pressure of not less than 70 pounds 

per square inch (psi) as required by the mine ventilation plan. The sprays used in spray blocks 1, 

3, 4, 6, and 7 were Model 6508 and those in spray blocks 2, 5, 8, 9, and 10 were Model 6512. 

The ventilation plan required the scrubber capacity to be a minimum of 9,000 cfm using a 20

o layer (12-in x 26-in) scrubber filter. The duct work spray was a full-cone spray with a 106 angle 

and an orifice size of 0.234-in. It operated at 6.4 gal per min (gpm) at 45 psi. 

­

25
 

The cut sequence for Mine A was as follows: 

(1) 20-ft sump cut, right side 

(2) 20-ft slab cut, left side 

(3) 20-ft sump cut, right side 

(4) 20-ft slab cut, left side 
Figure A-2 shows a plan view of the mining section of Mine A at the time of this study.

Figure A-2. Plan view of the mine A operating section. 

When 

cutting on the right side of the section (Entries No. 5, 6, and 7), the mine used blowing curtain 

ventilation. The mine used exhausting curtain when cutting on the left side (Entries No. 1, 2, 3). 

Entry No. 4 could be ventilated with either technique. The bolting operations also used blowing 

and exhausting curtain ventilation depending on their location, similar to the continuous miner. 

Mine A was operating sweep air ventilation, with Entry No. 7 serving as the intake and Entry 

No. 1 serving as the return. Entries No. 2 through No. 6 were neutral. The belt was in Entry No. 

4. The main intake airflow averaged 38,700 cfm. Mining height was approximately 10 ft with 

entry width averaging 20 ft. There were two partings in the coal seam consisting of a 6-in band 

of bottom slate and an 18-in band of slate approximately 16-in below the roof. 

The dust survey for Mine A was conducted over 3 consecutive days from February 3, 2009, to 

February 5, 2009. The third day of the study did not yield any data because the continuous miner 

was down due to low water-spray pressure. 

Shuttle Car Data Analysis 

Tables A-1, A-2, and A-3 show the shuttle car data collected during the study. On Day 1 of the 

study, the mine used three shuttle cars; however, only two were sampled. Therefore, the loading 

periods for the third shuttle car do not contain dust concentration data as indicated in the tables. 

On Day 2 of the study, the mine only used two shuttle cars; therefore, dust concentrations for all 

of the loading periods are presented. Dust exposures were analyzed for the following unique 

deep-cut conditions: 

1. Continuous miner driving a heading with exhausting face ventilation 

2. Continuous miner driving a heading with blowing ventilation 

3. Continuous miner turning a right crosscut with blowing ventilation 

Figure A-3 is a plot of shuttle car dust exposures for three cuts under condition 1—continuous 

miner driving a heading with exhausting face ventilation. The x-axis corresponds to the 

sequential load number during the cut. There were 18 to 19 loads per 40-ft cut; therefore, load 9 

26
 
represents the transition from regular- to deep-cut depth. When driving a heading using 

exhausting face ventilation, shuttle car dust levels were very low during both the regular- and the 

3 3 deep-cut sequence, averaging 0.19 mg/m during the regular-cut sequence and 0.56 mg/m

during the deep-cut sequence. In fact, the difference between these averages was not statistically 

significant (85% CIs), indicating that using deep cutting methods did not impact shuttle car dust 

th levels under condition 1. A spike in the shuttle car cab’s dust level was observed during the 15

load in Entry No. 2. The reason for this spike is unknown. 

Figure A-3. Shuttle car dust exposures with exhausting face ventilation when the miner was 

driving a heading. 

Figure A-4 is a plot of shuttle car dust exposures for two cuts under condition 2—continuous 

miner driving a heading with blowing ventilation. Data collected during development of Entry 

No. 5, as shown in Table A-2, are not included in the plot because it was only 25 ft deep, 

resulting in an insufficient number of deep-cut data points. When driving a heading using 

blowing ventilation, dust exposures at the shuttle cars increased during loading in the deep-cut 

3 sequence. Dust levels averaged 4.08 mg/m when loading during the regular-cut depth and 6.38 

3 mg/m during the deep-cut depth. The 85% CIs for these averages did not overlap, indicating a 

statistically significant difference. 

27
 
Figure A-4. Shuttle car dust exposures with blowing face ventilation when the miner was 

driving a heading. 

Figure A-5 is a plot of shuttle car dust exposures for one cut under condition 3—continuous 

miner turning a right crosscut with blowing ventilation. When operating under these conditions, 

dust exposures in the shuttle cars decreased during loading in the deep-cut sequence. Dust levels 

3 3 averaged 5.26 mg/m when loading during the regular-cut depth and 3.55 mg/m during the 

deep-cut depth. The 85% CIs for these averages did not overlap, indicating a statistically 

significant difference. 

During the study conducted at Mine A, the use of deep-cutting techniques had little bearing on 

the dust exposure levels of the shuttle car operators. When loading, transit, and the dumping 

sequences were included in exposure calculations, the shuttle cars averaged dust levels were 0.98 

3 3 mg/m during the regular-cut depth and 1.22 mg/m during the deep-cut depth, which is not a 

statistically significant (85% CIs) difference. While the depth of cut did not affect dust levels, 

ventilation type had a very pronounced impact on the shuttle car operators’ exposure levels. 

3 During production, the average shuttle car exposure was 0.22 mg/m when using exhausting 

3 ventilation and 1.98 mg/m when using blowing ventilation, a highly statistically significant 

(95% CIs) difference. 

28
 
Figure A-5. Shuttle car dust exposures with blowing face ventilation when the miner was 

turning a right crosscut. 

Miner-generated Dust 

Table A-4 shows miner-generated dust levels during the regular- and deep-cut sequences for 

each room development. The last column of Table A-4 adjusts dust levels based on the measured 

productivity for each cut sequence using the normalization process described earlier in the 

―Sampling Protocol and Data Analysis‖ section. This process normalizes dust levels to 

productivity using the average number of cars loaded per minute for the section, which was 

observed to be 0.37 cars per minute for Mine A. 

When using exhausting ventilation, miner-generated 3 dust levels averaged 1.78 mg/m during 

3 regular-cut depth and 2.07 mg/m during deep-cut depth. When using blowing ventilation, 

3 3 miner-generated dust levels averaged 2.47 mg/m during regular-cut depth and 2.46 mg/m

during deep-cut depth. The differences in these averages were not statistically significant (85% 

CIs), indicating that exposures downwind of the miner were unaffected by deep-cutting 

practices. 

Miner Operator Data Analysis 

Table A-5 shows miner operator exposure levels as measured with a PDM device during each 

cut of the study. The levels presented in the table isolate production time only and are not 

indicative of shift average levels, which were much lower. Dust exposures were adjusted for 

productivity. Depth of cut did not significantly (85% CIs) impact the miner operator’s exposure 

3 3 levels for either ventilation type, averaging 0.80 mg/m during regular-cut depth and 1.36 mg/m

29
 
3 during deep-cut depth with exhausting face ventilation, and 2.92 mg/m during regular-cut depth 

3 and 2.05 mg/m during deep-cut depth with blowing face ventilation. However, the miner 

operator’s exposure level was significantly higher when turning a right crosscut. For this cut, the 

miner operator was positioned away from the mouth of the blowing curtain, and his average 

3 exposure to respirable dust increased to 5.17 mg/m . This may be remedied by dropping the 

curtain back a couple of roof bolts after the heading is cut to allow the operator to remain at the 

mouth of the curtain during the right turn. Resetting the curtain may also improve shuttle car 

exposures. The effects of this action on worker exposure levels should be verified using a realtime device such as a pDR or PDM. 

Bolter Operations Data Analysis 

Table A-6 shows bolter data collected at Mine A, including bolter-generated dust and left- and 

right-side operator exposure levels. Dust levels are further segmented into the regular- (0–20 ft) 

and deep-cut (20–40 ft) positions in the entry. Bolting operations in Entry No. 2 were conducted 

downwind of mining operations. All other bolting sequences were conducted upwind of the 

miner. During Day 1 of the study, both bolted entries were set up with exhausting curtain; 

however, no measureable airflow was detected behind the curtain. During Day 2, the entries 

were set up with blowing ventilation, and the airflow readings behind the curtain were 5,200 cfm 

for Entry No. 6 and 3,400 cfm for Entry No. 7. It is interesting to note that, when no airflow was 

measured, dust levels did appear to increase as the bolting sequence progressed from regular- to 

deep-cut depth, indicating a possible accumulation of dust due to low circulation of air. 

However, increases in dust levels were not observed on Day 2, when airflow behind the curtain 

was measureable. In addition, the dust exposure levels of the bolter operators, when operating 

downwind of the miner, were almost twice the levels experienced when operating upwind of the 

3 miner. Exposures when operating downwind of the miner were 3.00 mg/m at the left-side 

3 position and 2.19 mg/m at the right-side position. This mine minimized downwind bolting 

operations, and the shift average dust exposure levels of the bolter operators were low 

3 throughout the study. The left-side operator’s shift average dust exposure level was 0.99 mg/m

on Day 1 of the study. Day 2 left-side data were lost due to a PDM battery failure. The right-side 

3 3 operator’s shift average dust exposure levels were 1.06 mg/m on Day 1 and 0.91 mg/m on Day 

2. The bolting machine’s contribution to dust in the return air (bolter-generated dust) was not 

3 significant throughout the study compared to other sources, averaging less than 0.1 mg/m . 

Dust-control Monitoring 

Throughout the study, the line curtain and airflow to the face were well maintained. When using 

exhausting curtain, the average starting scrubber airflow was 11,500 cfm, while airflow delivered 

to the face averaged 11,500 cfm before activation of the scrubber and 16,700 cfm after 

activation. Similarly, when using blowing curtain, the average starting scrubber airflow was 

10,800 cfm, while airflow behind the curtain was 9,600 cfm before activation of the scrubber and 

14,800 after activation. 

As mentioned earlier, one of the concerns was that the scrubber would become clogged with 

particles as the mining cycle progressed through the deep cut, diminishing its effectiveness. This 

30
 
condition was not observed at Mine A, as the average scrubber airflow dropped only 4% from 

start to finish during the cuts. The scrubber screen was tapped and back-flushed before each cut, 

a practice that should be continued to assure proper scrubber function. Likewise, no degradation 

in bolter suction pressures was observed during the study, as every reading registered 12 inches 

of mercury (-in Hg). 

Summary 

1.	 When driving a heading using exhausting face ventilation, shuttle car dust levels during 

loading did not appear to be affected by deep-cut practices. 

2.	 When driving a heading using blowing face ventilation, shuttle car dust levels appeared 

to be higher during loading in the deep-cut sequence when compared to the regular-cut 

sequence. 

3.	 When turning a right crosscut using blowing ventilation, shuttle car dust levels appeared 

to be lower during loading in the deep-cut sequence when compared to the regular-cut 

sequence. 

4.	 Average shuttle car dust levels during the regular- and deep-cut sequences were similar 

when loading, transit, and dumping operations were included in the calculation. 

5.	 When loading, transit, and dumping operations were included, dust levels in the shuttle 

3 cars were 1.76 mg/m higher when using blowing ventilation versus exhausting 

ventilation. To minimize the dust exposure levels of the shuttle car operators, preference 

should be given to exhausting over blowing face ventilation when possible, particularly 

in Entry No. 4, which can be ventilated either way without interfering with shuttle car 

traffic. 

6.	 Deep-cut practices did not influence miner-generated dust levels during the study. 

7.	 Deep-cut practices did not influence miner operator exposure levels during the study. 

8.	 3 During production, the miner operator’s dust exposure levels increased by 4.10 mg/m

when turning a right crosscut as compared to driving a heading. During this cut, the 

miner operator was positioned away from the mouth of the blowing curtain. If the 

ventilation plan allows, this may be remedied by dropping the curtain back a couple of 

roof bolts after the heading is cut to allow the operator to remain at the mouth of the 

curtain during the right turn. Resetting the curtain may also improve the shuttle car 

operator exposure levels. The effects of this action on worker exposure levels should be 

verified using a real-time device such as a pDR or PDM. 

9.	 The bolter operators’ dust exposure levels increased as the bolting cycle progressed when 

airflow behind the curtain was not measureable. Airflow levels of 3,400 to 5,200 cfm 

were sufficient to clear the bolting face of accumulated dust. 

10.	 Scrubber performance did not significantly degrade during the deep-cut sequence as 

scrubber airflow dropped by an average of 4% from start to completion of the cuts. 

31
 
11. Bolter dust collector suction pressure did not significantly degrade due to deep-cutting 

practices and remained consistent at 12 in Hg for each measurement. 

32
 
Table A-1. Shuttle car dust levels when loading at the face for Cuts No. 1, 2, and 3
 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth.
 

Airflows are before scrubber activation.
 

33
 
 Table A-2. Shuttle car dust levels when loading at the face for Cuts No. 4, 5, and 6 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth.
 

Airflows are after scrubber activation.
 

34
Table A-3. Shuttle car dust levels when loading at the face for Cut No. 7 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth.
 

Airflows are after scrubber activation.
 

Table A-4. Continuous miner-generated dust during production as measured with pDRs 

calibrated with gravimetric samplers 

Note: Airflows are before scrubber activation. 

35
 
Table A-5. Miner operator exposures during production as measured with a PDM 

instrument 

Note: Airflows are before scrubber activation. 

Table A-6. Bolter-generated dust and bolter operator exposures during the bolting cycle 

36
 
Appendix B: MINE B CASE STUDY 

Mine-specific Information 

Mine B used two Joy 14CM15 miners on this section. The miner spray configuration is shown in 

Figure B-1.

Figure B-1. Mine B continuous miner spray configuration. 

A total of 30 dust suppression sprays were operated at a pressure of not less than 75 

psi as required by the mine ventilation plan—19 sprays were located at the top of the ripper, 8 

sprays were located at the top of the pan, and 3 sprays were located at the throat of the chain 

conveyor. The ventilation plan required the scrubber capacity to be a minimum of 4,000 cfm. 

The plan also required the line curtain to be maintained within 50 ft of the deepest point of 

penetration with the minimum required airflow from the curtain to be 4000 cfm with the 

scrubber on and 3600 cfm with the scrubber off. 

The cut sequence for Mine B was as follows: 

(1) 20-ft sump cut, left side 

(2) 20-ft slab cut, right side 

37
 
(3) 20-ft sump cut, right side 

(4) 20-ft slab cut, left side 

Figure B-2 shows a plan view of the Mine B at the time of this study. 

Figure B-2. Plan view of Mine B section. 

The mine used a split 

ventilation configuration with Entry No. 5 serving as the primary intake and Entries No. 1 and 

No. 8 serving as the returns. All other entries were neutral, including the beltway, which was 

located in Entry No. 4. Mining height varied between 54-in and 78-in with entry width averaging 

20 ft. In Entry No. 3, the floor rock narrowed enough (17-in) to allow extraction of a lower and 

thinner (13-in) coal seam, resulting in a 78-in mining height in that entry. Pillar dimensions were 

80 ft by 60 ft. The deep-cut depths were 40 ft. 

The Mine B dust survey was conducted on April 14 and 16, 2009. April 15 was a minescheduled down-production day. 

Shuttle Car Data Analysis 

Tables B-1 and B-2 show the shuttle car data collected during the study. Sampling was only 

conducted on the miner located on the left side of the section, which was responsible for mining 

Entries No. 1, 2, 3, and 4. The miner on the right side was not sampled. Three unique types of 

deep cuts were evaluated for this study: 

(1) Continuous miner driving a heading with exhausting curtain 

(2) Continuous miner driving a heading without curtain 

(3) Continuous miner turning a left crosscut without curtain 

Headings and left crosscuts represented the only types of cuts used on the left side of the section 

as all crosscuts were turned toward return airflow. 

Figure B-3 is a plot of shuttle car dust exposures for three cuts when the miner was driving a 

heading with exhausting curtain. The x-axis corresponds to the sequential load number during 

the cut. As seen in the plot, the number of cars for each deep cut varied between entries due to 

the fact that mining height also varied between entries. 

38
 
Figure B-3. Shuttle car dust levels when miner was driving a straight heading. 

The lack of any apparent trend in Figure B-3 indicates that cutting depth did not affect the dust 

exposure levels of the shuttle car operators when the miner was driving a heading with 

exhausting face ventilation. During Cuts No. 2, 3, and 5, the average dust exposures in the cabs 

3 3 attributable to face operations were 0.54 mg/m for the regular-cut sequence and 0.48 mg/m for 

the deep-cut sequence. This difference was not statistically significant when comparing the 85% 

CIs for the averages. 

Similar results were observed for the cuts completed without the use of ventilation curtain. 

Ventilation curtain was not needed for several of the cuts because of the variance allowing the 

curtain to be maintained within 50 ft of the deepest point of penetration. When driving a heading 

3 without curtain, dust levels in the cabs were 0.23 mg/m during the regular-cut depth and 0.36 

3 mg/m during the deep-cut depth. When turning a left crosscut without curtain, dust levels were 

3 3 0.25 mg/m for the regular-cut depth and 0.12 mg/m for the deep-cut depth. Each of these 

comparisons was not statistically significant (85% CIs). 

An analysis of individual cuts found no significant change in dust levels when comparing the 

regular- to the deep-cut depth. No differences were found despite the fact that the mine 

experienced a wide range of scrubber airflows and face ventilation conditions between cuts. 

Table B-3 summarizes these conditions: 

(1) Cuts without exhausting curtain 

(2) Cuts using exhausting curtain; airflows measured behind the curtain before activation of 

the scrubber ranged from 5,130 to 9,000 cfm. 

(3) Starting scrubber airflows ranging from 7,020 to 7,940 cfm 

(4) Ending scrubber airflows ranging from 4,820 to 7,500 cfm 

39
 
Miner-generated Dust 

Table B-3 shows miner-generated dust levels during the regular- and deep-cut sequences for 

each room development. The last column of Table B-3 uses the previously described 

normalization process to adjust dust levels based on the measured productivity for each cut 

sequence. The average number of cars loaded per minute for the section at Mine B was 0.31. 

Miner-generated dust levels were lower during the deep-cut sequence when compared to the 

regular-cut sequence for four of six cuts, indicating that dust capture may have been improving 

as mining depth increased. Averaging all cuts, the miner-generated dust level was 66% lower 

3 during the deep-cut sequence (1.52 mg/m ) when compared to the regular-cut sequence (4.51 

3 mg/m ). This improved dust capture was most apparent during Cut No. 4. Figure B-4 shows 

miner return dust levels for Cut No. 4 as mining depth increased. This cut was unique because 

the miner had just begun to drive the Entry No. 4 heading after all crosscut entries had been 

opened. The miner was operating just inby the crosscut and over 19,000 cfm of air was sweeping 

across the miner during the initial sump, preventing effective capture of dust by the scrubber. It 

is interesting to note, however, that miner-generated dust levels continued to decrease as mining 

depth increased. This may be due to the fact that airflow reaching the face is essentially limited 

to what the scrubber is drawing after the miner extends beyond the influence of curtain or entry 

ventilation, minimizing dust blowby at the mouth of the scrubber. For all other heading cuts 

observed during the study, the miner was sumped into the coal by at least 10 ft before the cut 

began, preventing the ventilation air from sweeping over the head of the miner at the beginning 

of the cut. Eliminating the unique Cut No. 4 from the calculation indicates that miner-generated 

dust is reduced by an average of 28% during the deep-cut depth. Cut No. 3 was the only heading 

cut that experienced increased miner-generated dust levels as the cutting depth increased. This 

may be explained by the fact that scrubber airflow performance degraded by the largest 

percentage (35%) during Cut No. 3 when compared to all other cuts. Miner-generated dust also 

appeared to be somewhat higher during the deep-cut sequence for Cut No. 6, when the miner was 

driving a left crosscut. 

40
 
Figure B-4. Miner return dust levels during Cut No. 4. 

Miner Operator Data Analysis 

Table B-4 shows the miner operator exposure levels as measured with a PDM device during each 

cut of the study. The last column of Table B-4 shows levels normalized for productivity. Depth 

of cut appeared to have no bearing on the miner operator’s dust exposure level. The operator’s 

exposure level was very low for both the regular-cut and deep-cut sequences, averaging 0.66 

3 3 mg/m for the regular-cut sequence and 0.45 mg/m for the deep-cut sequence. In general, the 

operator maintained his position on the off-curtain side of the miner, parallel to or slightly outby 

the mouth of the exhaust curtain. 

Bolter Operations Data Analysis 

Table B-5 shows bolter operator dust exposure levels during the regular- and deep-cut sequences 

for each room that was bolted. Exposures were determined from PDM devices worn by the 

operators. Only Rooms No. 2 and 3 were conducted upwind of mining operations. For these 

rooms, there were no discernable differences in dust levels when comparing the regular- to deepcut depth. This may be explained by the fact that throughout the study there was very little dropoff in the suction pressure of the bolting machine’s dust collection system when comparing the 

start of the bolting cycle to the end of the cycle. Suction pressures did vary somewhat from day 

to day and when comparing the left side of the machine to the right side; however, measurements 

were always between 12 and 17 in Hg, which appeared to be sufficient for controlling dust. 

Likewise, the line curtain was well maintained and provided adequate airflow (2,920 to 4,680 

cfm) to each bolting face. Dust exposures on the bolting faces increased by approximately 0.4 

3 mg/m when bolting was conducted downwind of mining operations during the study. In general, 

41
 
daily-average bolter operator dust exposure levels were quite low throughout the 2-day study, 

3 falling between 0.30 and 0.82 mg/m . 

Summary 

1.	 When driving a heading and using exhausting face ventilation, no statistically significant 

(85% CIs) difference was observed in the shuttle car operators’ dust exposure levels when 

comparing the regular-cut sequence to the deep-cut sequence. 

2.	 When driving a heading without the use of ventilation curtain, no statistically significant 

(85% CIs) difference was observed in the shuttle car operators’ dust exposure levels when 

comparing the regular-cut sequence to the deep-cut sequence. 

3.	 When turning a left crosscut without the use of ventilation curtain, no statistically significant 

(85% CIs) difference was observed in the shuttle car operators’ dust exposure levels when 

comparing the regular-cut sequence to the deep-cut sequence. 

4.	 Averaging all cuts, the miner-generated dust level was 66% lower during the deep-cut 

sequence when compared to the regular-cut sequence. This may be due to the fact that 

airflow reaching the face is essentially limited to what the scrubber is drawing after the miner 

extends beyond the influence of curtain or entry ventilation, maximizing dust capture at the 

mouth of the scrubber. Eliminating the unique Cut No. 4 from the calculation indicates that 

miner-generated dust is reduced by an average of 28% during the deep-cut depth. 

5.	 Cut No. 3 was the only heading cut that experienced increased miner-generated dust levels as 

the cutting depth increased. This may be explained by the fact that scrubber airflow 

performance degraded by the largest percentage (35%) during Cut No. 3 when compared to 

all other cuts. 

6.	 Miner-generated dust was somewhat higher during the deep-cut sequence for Cut No. 6, 

when the miner was driving a left crosscut. 

7.	 Depth of cut had no bearing on the miner operator’s dust exposure levels. 

8.	 The bolter operators’ dust exposure levels did not increase as the bolting cycle progressed 

into the deep-cut depth. 

42
 
Table B-1. Shuttle car dust levels when loading at the face during Cuts No. 1 through 3 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. Airflows are 

before scrubber activation. 

43
 
Table B-2. Shuttle car dust levels when loading at the face during Cuts No. 4 through 6
 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth.
 

Airflows are before scrubber activation.
 

44
 
Table B-3. Miner-generated dust levels during the regular- and deep-cut depths for each 

cut 

Note: Dust levels are adjusted for productivity. 

Table B-4. Miner operator dust levels during the regular- and deep-cut depths for each cut 

Note: Dust levels are adjusted for productivity. 

Table B-5. Bolter operator exposure levels during the regular- and deep-cut depths for 

each bolted room 

45
 
Appendix C: MINE C CASE STUDY 

Mine-specific Information 

Mine C used a Joy 12CM continuous miner on this section. A total of 50 sprays were operated— 

33 dust suppression sprays were operated at a pressure of not less than 100 psi. Additionally, 14 

cooler sprays, along with 2 scrubber sprays and 1 fogger spray, were operated at 50 psi. The 

minimum numbers of sprays required by the mine ventilation plan to be operational were 29 dust 

suppression, 12 cooler, 2 scrubber, and 1 fogger sprays. The miner spray configuration is shown 

in Figure C-1. 

Figure C-1. Mine C continuous miner spray configuration. 

Figure C-2 shows a plan view of the continuous miner section surveyed for this study. The 

section used a sweeping ventilation configuration, with Entry No. 5 serving as the intake and 

Entry No. 1 serving as the return. All other entries were neutral, including the beltway, which 

was located in Entry No. 3. Mining height varied between 106 and 120-in, with entry width 

averaging 20 ft. The mine used a combination of exhaust tubing and curtain to ventilate the 

active faces, which was required to be no more than 40 ft from the unbolted face. The mine 

46
 
ventilation plan required airflows at the face when cutting coal to be a minimum of 8000 cfm 

with the scrubber off and 12000 cfm with the scrubber on. When cutting rock, the minimum 

airflows at the face are set at 11000 cfm with the scrubber off and 13000 cfm with the scrubber 

on. Tubing was used on Days 1 and 2 of the study, and curtain was used on Day 3. Pillar 

dimensions were approximately 110 x 70 ft. The deep-cut depths were 40 ft. The cut sequence 

for Mine C was as follows: 

(1) 20-ft sump cut, left side 

(2) 20-ft slab cut, right side 

(3) 20-ft sump cut, right side 

(4) 20-ft slab cut, left side 

The Mine C dust survey was conducted on the June 9, 10, and 11, 2009. 

Figure C-2. Plan view of the mine C continuous miner development section. 

Shuttle Car Data Analysis 

Tables C-1, C-2, and C-3 show the shuttle car data collected during the study. Mine C used a Joy 

12CM miner on the section with two 12-ton Joy shuttle cars. Shuttle Car Cab No. 2 had a leftside (off standard) operator’s cab, while Car No. 1 had a right-side (standard) cab. Two unique 

types of deep cuts were evaluated for this study: 

(1) Continuous miner driving a heading with exhausting face ventilation 

(2) Continuous miner turning a right crosscut with exhausting face ventilation 

These two types of deep-cuts represented the only types of cuts used on this section as all 

crosscuts were turned toward intake air. 

Throughout the study, dust levels attributable to face operations, as measured in the shuttle car 

3 cabs, were very low, averaging from 0.05 to 0.48 mg/m . When driving a heading using 

exhausting face ventilation, dust levels in the standard cab attributable to face operations were 

not significantly (85% CIs) different when comparing the regular-cut depth average of 0.06 

47
 
3 3 mg/m to the deep-cut depth average of 0.12 mg/m . For the off-standard cab, dust levels were 

3 significantly (95% CIs) higher for deep-cut sequence, averaging 0.07 mg/m during regular-cut 

3 depths and 0.31 mg/m during deep-cut depths. A similar phenomenon was observed during 

development of the right cross-cuts. When driving the cross-cuts, dust levels from face 

3 operations in the standard cab were not influenced by depth of cut, averaging 0.05 mg/m during 

3 the regular-cut depths and 0.07 mg/m during the deep-cut depths. However, dust levels in the 

off-standard cab when developing the cross-cuts were, again, significantly (90% CIs) higher 

3 during the deep-cut sequence, averaging 0.11 mg/m during the regular-cut depth and 0.48 

3 mg/m during the deep-cut depth. In general, dust levels in the off-standard cab attributable to 

3 face operations during loading were 0.2 to 0.4 mg/m higher during the deep-cut sequence. This 

may have resulted because the off-standard cab was on the same side of the entry as the exhaust 

tubing/curtain. As the cut advanced, the cab got closer to the mouth of the tubing/curtain and 

may have experienced some dust rollback. 

The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.13 to 0.39 mg/m , indicating that use of deep-cutting techniques did not hinder 

the mine’s ability to limit the exposure levels of the shuttle car operators. 

Miner-generated Dust 

Table C-4 shows miner-generated dust levels during the regular- and deep-cut sequences for 

each room development. Miner-generated dust levels could not be determined during Day 1 

(Cuts No. 1 and 2) of the study because an automatic rock dusting device was attached to the 

return end of the exhaust tubing, which resulted in contamination of the downwind samples. 

When tubing was used to ventilate the active faces, which occurred on Day 1 (Cuts No. 1 and 2) 

and Day 2 (Cuts No. 3 through 5) of the study, the continuous miner and bolting machine shared 

a common return; however, the miner return samples were still deemed to be valid on Day 2 of 

the study due to the negligible amount of dust generated by the bolting machine. The bolting 

3 machine was found to generate less than 0.10 mg/m during operation on Day 3 of the study. The 

last column of Table C-4 normalizes the data to allow a comparison of miner-generated dust 

during the regular- and deep-cut depths by adjusting dust levels based on productivity. The 

average number of cars loaded per minute for the section was 0.40. 

Due to the invalidity of miner return data collected on Day 1, only one right crosscut 

development was analyzed for miner dust generation—Cut No. 6 on Day 3. For this particular 

3 cut, dust levels were higher during the deep-cut depth, averaging 1.32 mg/m during the regular3 cut depth and 4.62 mg/m during the deep-cut depth. This particular cut was ventilated with 

exhaust curtain so it is possible that airflow levels fluctuated during the cut. However, for safety 

reasons related to shuttle car traffic, researchers were unable to periodically monitor airflow 

levels behind the curtain during production. When all data were grouped together, minergenerated dust levels were not significantly (85% CIs) different when comparing the average of 

3 3 1.77 mg/m during the regular-cut depth to the average of 2.19 mg/m during the deep-cut depth. 

48
 
Miner Operator Data Analysis 

Table C-5 shows the miner operator exposure levels as measured with a PDM device during each 

cut of the study for both the regular- and deep-cut depths. These exposures are net of intake dust 

levels and represent exposures resulting from face operations. The last column of Table C-5 

shows the values normalized for productivity. The operator’s exposure level was very low for 

both the regular-cut and deep-cut sequences. When driving a heading, the operator’s exposure 

3 3 level averaged 0.33 mg/m during the regular-cut depth and 0.55 mg/m during the deep-cut 

depth. When developing the right crosscut, the miner operator’s dust exposure level averaged 

3 3 0.57 mg/m during the regular-cut depth and 0.92 mg/m during the deep-cut depth. Neither 

unique cut produced a statistically significant (85% CIs) variation in dust levels when comparing 

regular- to deep-cut depth. When all data were grouped together, miner operator dust exposure 

levels during production were not significantly (85% CIs) different when comparing the average 

3 3 dust level of 0.42 mg/m during the regular-cut depth to 0.69 mg/m during the deep-cut depth. 

The daily average dust exposure levels for the miner operators were very low throughout the 

3 study, ranging from 0.34 to 0.57 mg/m , indicating that use of deep-cutting techniques did not 

hinder the mine’s ability to limit the exposure levels of the miner operators. 

Bolter Operations Data Analysis 

Table C-6 shows bolter operator dust exposure levels during the regular- and deep-cut sequences 

for each room that was bolted. Exposures were determined from PDM devices worn by the 

operators. The right-side operator’s PDM malfunctioned on Day 1 (Rooms No. 1 and 2) of the 

study and experienced battery failure during bolting operations in the last room surveyed for this 

study, resulting in lost data as indicated in the table. Bolter intake and return data are also 

displayed in Table C-6. Bolter return data for Days 1 and 2 (Rooms No. 1 through 5) were 

invalid due to contamination from rock dust and miner-generated dust on those days. On Day 3, 

exhausting curtain was used instead of tubing so the bolter had an independent return, allowing 

isolation of machine-generated dust for Rooms No. 6 and 7. 

After adjusting for intake dust levels, the bolter operators’ exposure levels to dust from machine 

3 operations averaged less than 0.10 mg/m during the 3-day study. Likewise, bolter-generated 

3 dust as measured in the return and net of intake dust levels averaged less than 0.10 mg/m . Mine 

C used a Fletcher DDR-13-A bolter equipped with wet drilling technology, which appears to be a 

very effective method for limiting operator exposure to dust. One concern associated with a dry 

dust collection system is that its filtration system may become over-loaded with dust during 

bolting in deep-cut rooms, resulting in less dust capture and higher operator exposure levels as 

the bolter is advanced. Use of wet drilling eliminates this concern. 

The daily average dust exposure levels for the bolter operators were very low throughout the 

3 study, ranging from 0.11 to 0.55 mg/m , indicating that use of deep-cutting techniques did not 

hinder the mine’s ability to limit the exposure levels of the bolter operators. 

49
 
Dust-control Monitoring 

Face ventilation at Mine C, using tubing and curtain, was well maintained throughout the study. 

On the miner faces, the tubing was initially set about four roof bolts back from the face and was 

advanced at least once during the cut to the last row of bolts. The miner operator properly 

maintained his position parallel to or slightly outby the mouth of the tubing. The exhaust curtain 

was maintained in a similar fashion. Mine C has a variance permitting the scrubber to be 

exhausted on the right side of the machine and toward the face, which allows the mine to 

maintain its curtain closer to the face without interference from the scrubber discharge. This 

technique appeared to be highly effective for dust control at this particular mine. Face ventilation 

airflows are shown in Tables C-4, C-5, and C-6. Average airflow on the miner faces was 17,400 

cfm, ranging from 14,300 to 21,500 cfm. Average airflow on the bolting faces was 3,900 when 

using tubing and 10,300 when using curtain. Primary intake airflow was approximately 27,000 

cfm during our study. 

As mentioned earlier, one of the concerns was that the scrubber would become clogged with 

particles as the mining cycle progressed through the deep cut, diminishing its effectiveness. 

Scrubber airflows, measured at the start and end of each cut, are shown in Tables C-4 and C-5. 

The scrubber was not used during the first half of Cut No. 1 because the mine has a variance to 

de-activate the scrubber until it clears the right-side rib during crosscut development. 

Diminishing performance was minimal at Mine C, as the average scrubber airflow dropped only 

6% from start to finish during the cuts. The scrubber screen was tapped and back-flushed before 

each cut, which is a practice that should be continued to assure proper scrubber function. 

Summary 

50
 

1.	 When driving a heading using exhausting face ventilation, dust levels in the standard-cab 

shuttle car attributable to face operations were not significantly (85% CIs) different when 

3 comparing the regular-cut depth to the deep-cut depth, averaging 0.06 mg/m during the 

3 regular-cut depth and 0.12 mg/m during the deep-cut depth. 

2.	 When driving a heading using exhausting face ventilation, dust from face operations in 

the off-standard cab were significantly (95% CIs) higher for the deep-cut sequence, 

3 3 averaging 0.07 mg/m during the regular-cut depth and 0.31 mg/m during the deep-cut 

depth. 

3.	 When driving the right crosscuts with exhausting face ventilation, dust levels from face 

3 operations in the standard cab were not influenced by depth of cut, averaging 0.05 mg/m

3 during the regular-cut depth and 0.07 mg/m during the deep-cut depth. 

4.	 When driving the right crosscuts with exhausting face ventilation, dust from face 

operations in the off-standard cab were significantly (90% CIs) higher during the deep3 3 cut sequence, averaging 0.11 mg/m during the regular-cut depth and 0.48 mg/m during 

the deep-cut depth. 

5.	 In general, dust levels in the off-standard cab attributable to face operations during 

3 loading were 0.20 to 0.40 mg/m higher during the deep-cut sequence. This may have 
resulted because the off-standard cab was on the same side of the entry as the exhaust 

tubing/curtain. As the cut advanced, the cab got closer to the mouth of the tubing/curtain 

and may have experienced some dust rollback. 

6. 	 The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.13 to 0.39 mg/m , indicating that use of deep-cutting techniques did not 

hinder the mine’s ability to limit the exposure levels of the shuttle car operators. 

7.	 Miner-generated dust levels were not significantly (85% CIs) different when comparing 

the regular- to deep-cut depth, averaging 1.77 during the regular-cut depth and 2.19 

3 mg/m during the deep-cut depth. 

8.	 Miner operator dust exposure levels were not significantly (85% CIs) different when 

comparing the regular- to deep-cut depth, averaging 0.42 during the regular-cut depth and 

3 0.69 mg/m during the deep-cut depth. 

9.	 The daily average dust exposure levels for the miner operators were very low throughout 

3 the study, ranging from 0.34 to 0.57 mg/m , indicating that use of deep-cutting 

techniques did not hinder the mine’s ability to limit the exposure levels of the miner 

operators. 

10. After adjusting for intake dust levels, the bolter operators’ exposure levels to dust from 

3 bolting operations averaged less than 0.10 mg/m during the 3-day study. Likewise, 

bolter-generated dust as measured in the return and net of intake dust levels averaged less 

3 than 0.10 mg/m . 

11. The daily average dust exposure levels for the bolter operators were very low throughout 

3 the study, ranging from 0.11 to 0.55 mg/m , indicating that use of deep-cutting 

techniques did not hinder the mine’s ability to limit the exposure levels of the bolter 

operators. 

51
 
Table C- 1. Shuttle car dust levels when loading at the face during Day 1 of the study 

Note: The bolded data rows are excluded from the reported average dust levels because they 

occurred after the miner cut through to the adjacent entry. Shaded areas show deep-cut depth, 

and clear areas show regular-cut depth. Airflows are before scrubber activation. 

52
 
Table C- 2. Shuttle car dust levels when loading at the face during Day 2 of the study 

Note: Shaded areas are deep cuts, clear areas are regular cuts. Airflows are before scrubber 

activation. 

53
 
Table C- 3. Shuttle car dust levels when loading at the face during Day 3 of the study 

Note: Shaded areas are deep cuts, clear areas are regular cuts. Airflows are before scrubber 

activation. Bolded text indicates when continuous miner broke through crosscut. 

54
 
Table C- 4. Miner-generated dust levels during the regular- and deep-cut depths 

Note: Dust levels are adjusted for productivity. 

Table C- 5. Miner operator dust exposure levels net of intake dust level during the regularand deep-cut depths 

Note: Dust levels are adjusted for productivity. 

55
 
Table C- 6. Bolter machine-generated dust levels and bolter operator exposures for the 

regular- and deep-cut depths 

56
 
Appendix D: MINE D CASE STUDY 

Mine-specific Information 

Mine D used two Eimco 2810 continuous miners. The miner spray configuration is shown in 

Figure D-1. 

Figure D-1. Mine D continuous miner spray configuration. 

A total of 20 dust suppression sprays were operated at a pressure of not less than 75 

psi as required by the mine ventilation plan—14 sprays at the top of the cutter drum, 4 pan 

sprays underneath the cutter drum (2 on each side of the miner), and 2 throat sprays. The 

ventilation plan required the scrubber capacity to be a minimum of 6,000 cfm using a 20-mesh 

scrubber filter. The plan also required the line curtain to be maintained within 50 ft of the deepest 

point of penetration with minimum required curtain airflows of 6000 cfm with the scrubber on 

and 5400 cfm with the scrubber off. Roof bolter faces required minimum curtain airflow of 3000 

cfm. 

The cut sequence for Mine D was as follows: 

(1) 15-ft sump cut, right side 

(2) 15-ft slab cut, left side 

57
 
(3) 15-ft sump cut, left side 

(4) 15-ft slab cut, right side 

Figure D-2 shows a plan view of the continuous mining section on Day 1 of the study. 

Figure D-2. Plan view of mine D continuous miner section. 

The 

section was expanded to 10 entries on Day 2 and 11 entries on Day 3. The section used a 

sweeping ventilation configuration with Entries No. 8 and 9 serving as the intakes and Entries 

No. 1, 2, and 3 serving as the returns. All other entries were neutral, including the beltway, 

which was located in Entry No. 5. Mining height averaged 80-in, and entry width was 20 ft. 

Pillar dimensions were 30 x 40 ft. The depth of deep cuts were approximately 30 ft. Mine D is 

required to use line curtain when the distance from the point-of-origin to the coal face exceeds 50 

ft. Note: The point-of-origin is defined as the point at which the curtain will originate in order to 

direct the air to the face, usually the inby corner of the first outby pillar. Due to the small pillar 

size used at Mine D, this distance was only exceeded once during the study. The Mine D dust 

survey was conducted on August 11, 12, and 13, 2009. 

Shuttle Car Data Analysis 

Tables D-1, D-2, and D-3 show the shuttle car data collected during the study. Along with the 

two continuous miners, Mine D used three Narco shuttle cars on the section. The mine’s 

ventilation plan requires that the continuous miners not be operated simultaneously. The survey 

was conducted on the right side of the section, where the miner was responsible for developing 

all entries to the right of the beltway. Two shuttle cars were operated behind this miner, and both 

had a standard cab configuration. Three unique types of deep-cuts were evaluated for this study: 

(1) Continuous miner driving a heading without ventilation curtain 

(2) Continuous miner turning a right crosscut without curtain 

(3) Continuous miner driving a heading with blowing curtain 

Figure D-3 is a plot of shuttle car dust exposures for six cuts (No. 2, 3, 4, 6, 7, and 8) where the 

miner was driving a heading without ventilation curtain. The x-axis corresponds to the sequential 

load number during the cut. A downward trend in shuttle car dust levels is evident during the 

development of each entry. This trend most likely resulted from shuttle car positioning with 

58
 
respect to ventilation airflow. For all of the no-curtain heading cuts, the left and right crosscuts 

were open to ventilation airflow, which was from right to left. During the initial sump, the 

miner’s scrubber exhaust was outby the crosscuts, resulting in rollback into the shuttle car travel 

way. Ventilation airflow in the shuttle car travel way was not measureable for Cuts No. 2 and 6; 

away from the face for Cuts No. 3, 4, and 8; and toward the face for Cut No. 7. As the cut 

advanced, the scrubber exhaust was directed into the left crosscut, where it was quickly swept 

away from the workings. As the miner further advanced the heading, the shuttle car cabs traveled 

past the outby pillars, placing them directly into intake air. When driving a heading without the 

use of blowing curtain, shuttle car cab dust levels were 85% lower during the deep-cut sequence, 

3 3 averaging 0.62 mg/m during the regular-cut depth and 0.09 mg/m during the deep-cut depth. 

This result is significant when comparing the 95% CIs for the averages. 

Figure D-4 is a plot of shuttle car dust exposures for two cuts (No. 1 and 5) where the miner was 

driving a right crosscut without curtain. These cuts are representative of blowing face ventilation 

because the scrubber exhaust coursed through the shuttle car travel way during the development 

of these entries. Again, a downward trend in shuttle car dust levels is evident. Lower shuttle car 

cab dust levels when mining the deep-cut portion of the right crosscuts are most likely explained 

by two factors. First, similar to the heading cuts without curtain, the shuttle car cab position 

improved with respect to the intake airflow as the crosscuts were advanced. In addition, miner 

dust generation levels averaged 66% lower (see ―Miner-generated Dust‖) during the deep-cut 

depth when compared to the regular-cut depth during this survey, resulting in less dust in the 

shuttle car travel ways when mining the deep-cut portion of the right crosscuts. When developing 

a right crosscut without the use of blowing curtain, shuttle car cab dust levels were 59% lower 

3 (95% CIs) during the deep-cut sequence, averaging 0.74 mg/m during the regular-cut depth and 

3 0.30 mg/m during deep-cut depth. 

Figure D-5 is a plot of shuttle car dust exposures for Cut No. 9, where the miner was driving a 

heading with the use of blowing curtain. An upward trend in shuttle car cab dust levels is evident 

as the entry is advanced. An examination of face and scrubber airflow quantities may explain this 

increase. Airflow delivered to the face by the blowing curtain during this cut was approximately 

9,300 cfm. The scrubber airflow was 7,300 cfm at the start of the cut, degrading to 5,100 cfm at 

the completion of the cut. Previous laboratory research demonstrated that a curtain-to-scrubber 

airflow ratio, before scrubber activation, of 1.0 is optimal for dust control on blowing curtain 

faces [Jayaraman et al. 1992]. The research also demonstrated that dust levels can increase 

significantly when either too much or too little air is delivered to the face. In this case, the 

airflow ratio, after scrubber activation, increased from 1.3 at the start of the cut to 1.8 by the end 

of the cut. Assuming the scrubber boosted airflow by 40%, a situation observed in a laboratory 

study at similar airflows [Taylor et al. 1997], the airflow ratio at Mine D, before scrubber 

activation, is estimated to have worsened from 0.9 to 1.3, which could have adversely impacted 

face area dust levels. Low ending scrubber airflow volumes may also have increased dust levels 

[Jayaraman et al. 1992]. When the miner was driving a heading with the use of blowing curtain, 

shuttle car cab dust levels were 72% higher (95% CIs) during the deep-cut sequence, averaging 

3 3 0.75 mg/m during the regular-cut depth and 2.73 mg/m during the deep-cut depth. 

The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.11 to 0.53 mg/m , indicating that use of deep-cutting techniques did not hinder 

the mine’s ability to limit the exposure levels of the shuttle car operators. 

59
 
Figure D-3. Shuttle car dust levels at the face when the miner was driving headings without 

the use of line curtain. 

Figure D-4. Shuttle car dust levels at the face when the miner was driving right crosscuts 

without the use of curtain. 

60
 
Figure D-5. Shuttle car dust levels at the face when the miner was driving a heading with 

the use of blowing curtain. 

Miner-generated Dust 

Table D-4 shows miner-generated dust levels during the regular- and deep-cut sequences for 

each room development. The last column of Table D-4 adjusts dust levels based on the measured 

productivity for each cut sequence, with the average number of cars loaded per minute being 

0.44. 

Miner-generated dust was lower during the deep-cut sequence when comparing it to the regularcut sequence for each of the nine cuts surveyed during the study. In fact, miner-generated dust 

3 levels dropped significantly (95% CIs) from an average level of 2.69 mg/m during the regular3 cut depth to 0.91 mg/m during the deep-cut depth (a 66% drop). Figure D-6 shows miner return 

dust levels at 5-sec intervals for each cut. Return dust levels are clearly higher during the initial 

sump and slab cuts, which are visually discernable on the graph. During the second sump and 

slab cuts, the dust levels are much lower and cannot be differentiated on the graph. This decrease 

may be due to the fact that airflow reaching the face is essentially limited to what the scrubber is 

drawing after the miner extends beyond the influence of the ventilation curtain or primary intake 

airflow. The resulting lower air velocities at the face lead to improved scrubber capture 

efficiencies. 

The mine also provided an ample amount of air for dilution of miner-generated dust during the 

study, averaging 30,700 cfm. In general, miner-generated dust was very low for both the regularand deep-cut sequences. 

61
 
Figure D-6. Miner return dust levels at 5-sec intervals for each cut. 

Miner Operator Data Analysis 

The miner operator properly maintained his position in intake air throughout the study, resulting 

in extremely low dust exposure levels. Because levels were so low, no differentiation could be 

made between exposures during the deep- and regular-cut sequences. Day 3 miner operator 

exposure data were lost due to an improperly loaded filter cartridge in the PDM device. The 

3 daily average dust exposure levels for the miner operator were 0.08 mg/m on Day 1 and 0.02 

3 mg/m on Day 2. Use of deep-cutting techniques did not hinder the mine’s ability to limit the 

exposure levels of the miner operators. 

Bolter Operations Data Analysis 

Table D-5 summarizes the bolting sequences conducted during the study at Mine D. The mine 

used a dual-head Fletcher Roof Ranger II machine to perform roof bolting operations. The bolter 

operators maintained adequate blowing ventilation at the faces, averaging 5,800 cfm during the 

study. They also performed routine maintenance to the bolting machine’s dust collection system, 

which assured proper suction pressure for dust capture. All bolting operations were conducted 

upwind of mining operations. As a result of these conditions, the bolter operators’ daily average 

dust exposure levels were extremely low during the study, ranging between 0.05 and 0.22 

3 mg/m . Because levels were so low, no differentiation could be made between exposures during 

the deep- and regular-cut sequences. Use of deep-cutting techniques did not hinder the mine’s 

ability to limit the exposure levels of the bolter operators. 

62
 
Dust-control Monitoring 

As mentioned earlier, one of the concerns was that the scrubber would become clogged with 

particles as the mining cycle progressed through the deep cut, diminishing its effectiveness. 

Table D-4 shows scrubber airflows at the start and end of each cut. A 26% average drop-off in 

scrubber airflow was observed from the start to the end of the cuts. However, this decrease in 

scrubber airflow did not produce a negative effect on downwind dust levels at Mine D, nor did it 

appear to affect the dust exposure levels of the face workers. Two factors may have contributed 

to this observation. First, as discussed in the ―Miner-generated Dust‖ section of this report, dust 

capture appears to improve as the cutting depth increases beyond the influence of face ventilation 

airflow. In addition, higher pressure drops across the loaded scrubber filters may be improving 

scrubber efficiencies associated with respirable-sized particles enough to somewhat compensate 

for the processing of lower volumes of air. 

As with the continuous miner, no degradation in the bolting machine’s dust control circuit was 

observed during completion of the bolting sequence in the deep-cut rooms. Suction 

measurements were taken at the start, middle, and end of each bolting sequence, and all 

measurements were between 16 and 18-in Hg, which provided excellent dust control. 

Summary 

1.	 When driving a heading without the use of blowing curtain, shuttle car cab dust levels 

3 were 85% lower during the deep-cut sequence, averaging 0.62 mg/m during the regular3 cut depth and 0.09 mg/m during the deep-cut depth. 

2.	 When developing a right crosscut without the use of blowing curtain, shuttle car cab dust 

3 levels were 59% lower during the deep-cut sequence, averaging 0.74 mg/m during the 

3 regular-cut depth and 0.30 mg/m during the deep-cut depth. 

3.	 When the miner was driving a heading with the use of blowing curtain, shuttle car cab 

3 dust levels were 72% higher during the deep-cut sequence, averaging 0.75 mg/m during 

3 the regular-cut depth and 2.73 mg/m during the deep-cut depth. This may have resulted 

from a less than ideal ending curtain-to-scrubber airflow ratio or due to low ending 

scrubber airflow. 

4.	 The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.11 to 0.53 mg/m , indicating that use of deep-cutting techniques did not 

hinder the mine’s ability to limit the exposure levels of the shuttle car operators. 

5.	 Miner-generated dust levels averaged 66% lower during the deep-cut sequence when 

comparing it to the regular-cut sequence. 

6.	 Use of deep-cutting techniques did not hinder the mine’s ability to limit the exposure 

3 levels of the miner operator, which were very low (< 0.10 mg/m ) throughout the study. 

63
 
7.	 Use of deep-cutting techniques did not hinder the mine’s ability to limit the exposure 

3 levels of the bolter operators, which were very low (0.05 to 0.22 mg/m ) throughout the 

study. 

8.	 A 26% average drop-off in scrubber airflow was observed from the start to the end of the 

cuts. However, this decrease in scrubber airflow did not produce a negative effect on 

downwind dust levels at Mine D nor did it appear to affect the dust exposure levels of the 

face workers. 

References Cited in Appendix D 

Jayaraman NI, Jankowski RA, Whitehead KL [1992]. Optimizing continuous miner scrubbers 

for dust control in high coal seams. In: Proceedings of New Technology in Mine Health and 

Safety, SME Annual Meeting. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 

pp. 193–205. 

Taylor DT, Rider JP, Thimons ED [1997]. Impact of unbalanced intake and scrubber flows on 

th face methane concentrations. In: Ramani RV, ed. Proceedings of the 6 International Mine 

Ventilation Congress. Chapter 27. Littleton, CO: Society for Mining, Metallurgy, and 

Exploration, pp. 169–172. 

64
 
Table D-1. Shuttle car cab dust levels when loading at the face during Day 1 of the study 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

65
 
Table D-2. Shuttle car cab dust levels when loading at the face during Day 2 of the study 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

66
 
Table D-3. Shuttle car cab dust levels when loading at the face during Day 3 of the study
 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth.
 

Curtain airflow was measured after activation of the scrubber.
 

67
 
Table D-4. Miner-generated dust levels during the regular- and deep-cut depths 

Note: Dust levels are adjusted for productivity. 

Table D-5. Bolter-generated dust levels and operator exposures for each bolting sequence 

68
 
Appendix E: MINE E CASE STUDY 

Mine-specific Information 

Mine E used two Joy 12C continuous miners. The miner spray configuration is shown in Figure 

E-1. 

Figure E-1. Mine E continuous miner spray configuration. 

A total of 46 dust suppression sprays (48 if using spray fan) were operated at a pressure of 

not less than 100 psi—15 sprays at the top of the cutter drum, 10 pan sprays underneath the 

cutter drum (5 on each side of the miner), 3 throat sprays, 12 side sprays (6 on each side of the 

miner), and 6 gathering head sprays behind the cutter motor (3 on each side of the miner). The 

mine ventilation plan only required 39 sprays to be operational. The ventilation plan required the 

scrubber capacity to be a minimum of 5,000 cfm. The plan also required the line curtain to be 

maintained within 40 ft of the deepest point of penetration and the minimum face curtain airflow 

was 6000 cfm. 

Figure E-2 shows a plan view of the main entries for the study at Mine E. The mine used a split 

ventilation configuration to develop the mains, with Entries No. 6 and 7 serving as the intakes 

and Entries No. 1, 2, 8, and 9 serving as the returns. All other entries were neutral, including the 

69
 
beltway, which was located in Entry No. 5. Only Cuts No. 9 and 10 were conducted in the mains. 

The first eight cuts of the study were driven in three satellite entries driven off the right side of 

the section perpendicular to Entry No. 9, as shown in Figure E-3. These satellite entries were 

ventilated using a sweeping configuration, with Entry No. S1 serving as the intake, Entry No. S2 

serving as the neutral, and Entry No. S3 serving as the return. The mining height throughout the 

study averaged 7 ft, with entry widths maintained at 20 ft. Pillar dimensions were 40 x 40 ft. The 

deep-cut depth ranged from 32 to 40 ft. Several cuts mined on Day 2 of the study were not 

analyzed because they were less than 30 ft in depth. The mine had a maximum curtain setback 

distance of 40 ft; however, due to small pillar dimensions, several cuts were mined without the 

use of curtain. The Mine E dust survey was conducted over 3 consecutive days from October 20 

through 22, 2009. 

70
 

Figure E-2. Plan view of the mine E continuous miner Section No. 4. 

Figure E-3. Plan view of the satellite entries driven off the mains on Section No. 4. 
Shuttle Car Data Analysis 

Tables E-1, E-2, and E-3 show the shuttle car data collected during the study. Testing was 

completed on one continuous miner with three to four battery-powered, 10.5-ton Stamler shuttle 

cars for each cut. All shuttle cars had a standard cab configuration, placing the operators on the 

off-curtain side of the entry. Four unique types of deep cuts were evaluated for this study: 

(1) Continuous miner driving a heading with blowing curtain 

(2) Continuous miner driving an entry without curtain 

(3) Continuous miner turning a right crosscut with blowing curtain 

(4) Continuous miner turning a left crosscut with blowing curtain 

Figure E-4 is a plot of shuttle car cab dust levels for four cuts (No. 1, 3, 9, and 10) when the 

miner was driving a heading and blowing curtain was used to ventilate the face. The x-axis 

corresponds to the sequential load number during the cut. For Cuts No. 1 and 3, the curtain 

length exceeded 100 ft, and the airflow quantities presented in Table E-1 for these cuts were 

measured at the face-end mouth of the curtain. For Cuts No. 9 and 10, the blowing curtain was 

less than 10 ft in length and served only to deflect a portion of the entry air toward the face. 

Curtain airflows could not be determined for Cuts No. 9 and 10, so the airflow quantities 

presented in Table E-3 for these cuts are the entry airflow levels. When driving a heading with 

the use of blowing curtain, no consistent trend was apparent in dust levels as mining depth 

increased. Dust exposure levels in the shuttle car cabs when loading at the face averaged 0.74 

3 3 mg/m during the regular-cut depth and 0.84 mg/m for the deep-cut depth. This difference was 

not statistically significant, indicating that depth of cut had no bearing on dust levels when the 

miner was driving a heading and blowing curtain was used. 

Figure E-5 is a plot of shuttle car cab dust levels for four cuts (No. 5, 6, 7, and 8) when the miner 

was driving an entry without ventilation curtain. All of the cuts without curtain occurred during 

the perimeter mining phase of the section development. As shown in Figure E-3, perimeter 

entries were driven to the left and perpendicular to satellite Entry No. S1. Intake airflow traveled 

down Entry No. S1, sweeping from left to right and perpendicular to the perimeter entries. 

During the initial sump, the scrubber exhaust was located in the crosscut between Entries No. S1 

and S2, resulting in rollback into the shuttle car travel way. As the cut was advanced, the 

scrubber exhaust was directed into Entry No. S1 and was quickly swept away from the workings. 

As the miner further advanced the perimeter entry, the shuttle car cabs traveled past the pillar 

line separating Entries No. S1 and S2, placing them directly into intake air. A downward trend in 

shuttle car dust levels was evident during the development of each entry. When driving an entry 

without the use of blowing curtain, shuttle car cab dust levels were 77% lower (95% CIs) during 

3 3 the deep-cut sequence, averaging 0.30 mg/m during the regular-cut depth and 0.07 mg/m

during the deep-cut depth. Lower dust levels during the deep-cut sequence most likely resulted 

from operator positioning, as described in previous sections, and may be due to improved dust 

capture by the scrubber. The improved scrubber capture associated with deep-cut techniques that 

did not use blowing curtain is discussed in the next section, ―Miner-generated Dust.‖ 

Figure E-6 is a plot of shuttle car cab dust levels for Cut No. 2 when the miner was turning a 

right crosscut with blowing curtain. No clear trend is apparent in dust levels as mining depth 

3 increases. Dust exposures in the shuttle car cabs when loading at the face averaged 1.24 mg/m

71
 
3 during the regular-cut depth and 1.13 mg/m for the deep-cut depth. This difference was not 

statistically significant (85% CIs), indicating that depth of cut had no bearing on dust levels 

during development of the right crosscut. 

Figure E-7 is a plot of shuttle car cab dust levels for Cut No. 4 when the miner was turning a left 

crosscut with blowing curtain. Again, no clear trend in dust levels is apparent. Dust exposures in 

3 3 the shuttle car cabs averaged 1.49 mg/m during the regular-cut depth and 1.10 mg/m during the 

deep-cut depth. This difference was not statistically significant (85% CIs), indicating that depth 

of cut had no bearing on dust levels during development of the left crosscut. 

The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.10 to 0.42 mg/m , indicating that use of deep-cutting techniques did not hinder 

the mine’s ability to limit the exposure levels of the shuttle car operators. 

72
 
Figure E-4. Shuttle car cab dust levels at the face when driving a heading with the use of 

blowing curtain. 

Figure E-5. Shuttle car cab dust levels at the face when driving an entry without the use of 

blowing curtain. 

73
 
Figure E-6. Shuttle car cab dust levels at the face when turning a right crosscut with the 

use of blowing curtain. 

Figure E-7. Shuttle car cab dust levels at the face when turning a left crosscut with the use 

of blowing curtain. 

74
 
Miner-generated Dust 

Table E-4 shows miner-generated dust levels during the regular- and deep-cut sequences for each 

room development. The last column of Table E-4 adjusts dust levels based on the measured 

productivity for each cut sequence using an average productivity of 0.54 cars per minute. 

The average miner-generated dust was lower during the deep-cut sequence when comparing it to 

the regular-cut sequence for each of the four cuts that did not use a ventilation curtain. In fact, 

3 miner-generated dust levels dropped 63% from an average level of 1.50 mg/m during the 

3 regular-cut depth to 0.55 mg/m during the deep-cut depth. Figure E-8 shows miner return dust 

levels at 5-sec intervals for each of the four cuts that did not use curtain. Return dust levels are 

clearly higher during the initial sump and slab cuts, which are visually discernable on the graph. 

During the second sump and slab cuts, the dust levels are much lower and cannot be 

differentiated on the graph. The decrease may be due to the fact that airflow reaching the face 

was essentially limited to what the scrubber was drawing after the miner extended beyond the 

influence of the ventilation curtain or primary intake airflow. The resulting lower air velocities at 

the face lead to improved scrubber capture efficiencies. 

No statistically significant (85% CIs) difference in dust levels between the regular- and deep-cut 

depths was observed when blowing curtain was used to ventilate the faces. Under this scenario, 

when comparing the regular- to the deep-cut depth, miner-generated dust levels were quite low 

3 3 for both cutting depths and averaged 0.69 mg/m during regular-cut depth and 0.62 mg/m during 

deep-cut depth. 

At Mine E, the 35- to 40-ft curtain setback distance was well maintained throughout each room 

development. This setback distance appeared to ensure fresh intake airflow for dilution, while 

not creating excessive air velocities at the face. Laboratory research has indicated that when the 

curtain-to-scrubber airflow ratio, before scrubber activation, exceeds 1.0, dust levels in the face 

area may increase due to decreased scrubber capture[Jayaraman et al. 1992]. It is interesting to 

note that Cut No. 2 at Mine E had the highest measured curtain-to-scrubber airflow ratio of 2.1 

(17,800/8,500) after scrubber activation, and it also had the highest miner-generated dust levels 

3 (1.04 to 1.35 mg/m ) for curtained cuts. Although the airflow ratio at Mine E was measured after 

scrubber activation, it is likely that the scrubber-off airflow ratio was still well above 1.0 because 

a previous laboratory study found that activation of scrubbers with airflows in the range of 6,000 

to 10,000 cfm had minimal impact on blowing curtain airflows in the range of 10,000 to 14,000 

cfm [Taylor et al. 1997]. 

75
 
Figure E-8. Miner return dust levels at 5-sec intervals for each cut that did not use 

ventilation curtain. 

Bolter Operations Data Analysis 

Table E-5 summarizes the bolting sequences conducted during the study at Mine E. The mine 

used a dual-head Bucyrus RB2-88 machine to perform roof bolting operations. Routine 

maintenance on the bolting machine’s dust collection system was performed regularly, which 

assured proper suction pressure for dust capture. Most bolting operations were conducted upwind 

of mining operations. As a result of these conditions, the bolter operators’ daily average dust 

3 exposure levels were low during the study, ranging between 0.52 and 0.83 mg/m . Bolter3 generated dust levels were also low, averaging less than 0.2 mg/m on the two cuts (No. 4 and 7) 

where these levels could be isolated. Very few deep-cut rooms were available for analysis of 

bolting operations because perimeter entries were not bolted and most of the cuts on Day 2 of the 

study were less than 30 ft deep. Of the two that qualified as deep-cut depth with similar starting 

and ending conditions (Rooms No. 2 and 13), no statistically significant (85% CIs) difference in 

bolter operator exposures was measured when comparing bolting during the first 20 ft of depth to 

the remaining room depth. Room No. 4 was disqualified because bolting operations were 

downwind of the miner during the deep-cut depth. Use of deep-cutting techniques did not appear 

to adversely impact bolter operator dust exposure levels during the two cuts that were analyzed 

for this survey. 

Dust-control Monitoring 

As mentioned earlier, one of the concerns was that the scrubber would become clogged with 

particles as the mining cycle progressed through the deep cut, diminishing its effectiveness. 

76
 
Table E-4 shows scrubber airflows at the start and end of each cut. An 8% average drop-off in 

scrubber airflow was observed from the start to the end of the cuts. However, this decrease in 

scrubber airflow did not produce a negative effect on downwind dust levels at Mine E, nor did it 

appear to affect the dust exposure levels of the face workers. Two factors may have contributed 

to this observation. First, as discussed in the ―Miner-generated Dust‖ section of this report, dust 

capture appears to improve as the cutting depth increases beyond the influence of face ventilation 

airflow. In addition, higher pressure drops across the loaded scrubber filters may be improving 

scrubber efficiencies associated with respirable-sized particles to compensate somewhat for the 

processing of lower volumes of air. 

As with the continuous miner, no degradation in the bolting machine’s dust control circuit was 

observed during completion of the bolting sequence in the deep-cut rooms. Suction 

measurements were taken at the start and end of each bolting sequence and 80% of these were 

between 9 and 14-in Hg, which provided excellent dust control. 

Summary 

1.	 When the miner was driving a heading and blowing curtain was used to ventilate the face, 

3 dust exposures in the shuttle car cabs averaged 0.74 mg/m during the regular-cut depth 

3 and 0.84 mg/m during the deep-cut depth. This difference is not statistically significant 

(85% CIs), indicating that depth of cut had no bearing on dust levels. 

2.	 When the miner was driving an entry without the use of blowing curtain, shuttle car cab 

dust levels were 77% higher during the regular-cut sequence, when compared to the 

3 3 deep-cut, averaging 0.30 mg/m during the regular-cut depth and 0.07 mg/m during the 

deep-cut depth. This result is significant at a 95% CIs. 

3.	 When the miner was turning a right crosscut with blowing curtain, dust exposures in the 

3 shuttle car cabs when loading at the face averaged 1.24 mg/m during the regular-cut 

3 depth and 1.13 mg/m during the deep-cut depth. This difference is not statistically 

significant (85% CIs), indicating that depth of cut had no bearing on dust levels. 

4.	 When the miner was turning a left crosscut with blowing curtain, dust exposures in the 

3 3 shuttle car cabs averaged 1.49 mg/m during the regular-cut depth and 1.10 mg/m during 

the deep-cut depth. This difference is not statistically significant (85% CIs), indicating 

that depth of cut had no bearing on dust levels. 

5.	 The daily average dust levels for the shuttle car cabs were very low throughout the study, 

3 ranging from 0.10 to 0.42 mg/m , indicating that use of deep-cutting techniques did not 

hinder the mine’s ability to limit the exposure levels of the shuttle car operators. 

6.	 Miner-generated dust was 63% lower during the deep-cut sequence when comparing it to 

the regular-cut sequence for the four cuts that did not use ventilation curtain. 

7.	 No statistically significant (85% CIs) difference in miner-generated dust levels was 

observed between the regular- and deep-cut depths when blowing curtain was used to 

ventilate the faces. 

77
 
8.	 Use of deep-cutting techniques did not adversely impact bolter operator dust exposure 

levels during this survey. 

9.	 An 8% average drop-off in scrubber airflow was observed from the start to the end of the 

cuts. However, this decrease in scrubber airflow did not produce a negative effect on 

downwind dust levels at Mine E nor did it affect dust exposure levels in the face area. 

References Cited in Appendix E 

Jayaraman NI, Jankowski RA, Whitehead KL [1992]. Optimizing continuous miner scrubbers 

for dust control in high coal seams. In: Proceedings of New Technology in Mine Health and 

Safety, SME Annual Meeting. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 

pp. 193–205. 

Taylor DT, Rider JP, Thimons ED [1997]. Impact of unbalanced intake and scrubber flows on 

th face methane concentrations. In: Ramani RV, ed. Proceedings of the 6 International Mine 

Ventilation Congress. Chapter 27. Littleton, CO: Society for Mining, Metallurgy, and 

Exploration, pp. 169–172. 

78
 
Table E-1. Shuttle car cab dust levels when loading at the face during Cuts No. 1 through 4 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. Airflow 

measured after activation of the scrubber. 

79
 
Table E-2. Shuttle car cab dust levels when loading at the face during Cuts No. 5 through 7 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

80
 
Table E-3. Shuttle car cab dust levels when loading at the face during Cuts No. 8 through 

10
 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

81
 
Table E-4. Miner-generated dust levels during the deep- and regular-cut depths 

Note: Dust levels are adjusted for productivity. 

Table E-5. Bolter-generated dust levels and operator exposures for each bolting sequence 

82
 
Appendix F: MINE F CASE STUDY
 

Mine-specific Information 

Mine F used two Joy 14CM15 continuous miners. The miner spray configuration is shown in 

Figure F-1. A total of 52 dust suppression sprays were available to be operated at a pressure of 

not less than 60 psi. Forty-six were operated, but the mine ventilation plan required that only 34 

of the sprays be operational. The mine ventilation plan required the line curtain to be maintained 

within 10 ft outby the continuous miner boom when exhausting ventilation was used. If blowing 

ventilation was used, the curtain was required to be maintained within 10 ft of the deepest point 

of penetration at the beginning of the mining cycle; as mining progresses the curtain was to be 

extended to the last row of permanent supports. The plan also specified minimum curtain 

airflows to be as follows: when the scrubber is being used, the minimum face curtain airflow for 

exhausting face ventilation system will be 6000 cfm or the volume of air necessary for a mean 

entry air velocity of 60 fpm, whichever is greater. For a blowing face ventilation system, the 

quantity of air discharged from the inby end of the curtain will be balanced with the rated 

volume of air discharged by the scrubber. Otherwise, without the scrubber, a minimum curtain 

airflow of 5000 cfm will be maintained. 

83
 
Figure F-1. Mine F continuous miner spray configuration. 

Figure F-2 shows a plan view of the continuous mining section studied at Mine F. When cutting 

on the right side of the section (Entries No. 5, 6, and 7), the mine used blowing curtain 

ventilation. Exhausting curtain was used when cutting on the left side (Entries No. 1, 2, and 3). 

Entry No. 4, which could be ventilated with either curtain arrangement, used blowing curtain 

during the study. Bolting operations were ventilated similar to mining operations. The active 

section was ventilated using a sweeping configuration from right to left. Entry No. 7 served as 

the intake, and Entry No. 1 served as the return. Entries No. 2 through 6 were neutral. The belt 

was in Entry No. 4. The main intake airflow measured in the last open crosscut ranged from 

29,800 to 65,800 cfm. Mining height varied from 6 to 6.5 ft, with the miner extracting 

approximately 1.5 ft of top-rock to reach a competent roof strata. Entry widths were 20 ft. Deepcut depths at Mine F were 30 ft, and the mine used a cutting sequence consisting of the 

following: 

(1) 20-ft sump cut, right side 

(2) 20-ft slab cut, left side 

(3) 10-ft sump cut, left side 

(4) 10-ft slab cut, right side 

84
 
Figure F-2. Plan view of the operating section at Mine F. 

The Mine F dust survey was conducted over 3 consecutive days from January 12 through 14, 

2010. An equipment preparation error resulted in the loss of PDM data collected during Day 1 of 

the study. 

Shuttle Car Data Analysis 

Tables F-1, F-2, and F-3 show the shuttle car data collected during the study. One shuttle car 

load was determined to be invalid on Day 2 (Table F-2) of the study because the miner was down 

for several minutes while the car was located in the face area. When driving Entry No. 4 on Day 

3 (Table F-3), the mine used the third shuttle car, which was dedicated for use on the left side of 

the section. The third car was not equipped with an area sampling package, so data were not 

collected for half of the loads during this cut. The right-side Joy 14CM15 continuous miner and 

two Highlander 1021 9-ton shuttle cars were evaluated for each cut during the study. All shuttle 

cars had a standard cab configuration, placing the operators on the curtain side of the entry. A 

total of six shuttle car loads were needed to advance the face 10 ft; therefore, the last six loads in 

the cutting sequence occurred during deep-cut depth, including a 10-ft sump cut on the left side 

of the entry and a 10-ft slab cut on the right side. Due to the narrowness of pillars (45 x 60 ft) at 

Mine F, deep-cuts were not used to drive crosscut entries. Therefore; all collected deep-cut data 

are for heading developments. 

Figure F-3 is a plot of shuttle car dust exposures for each of the eights cuts. The x-axis 

corresponds to the sequential load number during the cut. The number of loads required to 

complete each cut varied from 15 to 19 due to factors including shuttle car loading, ceiling 

height, and origin of the cut with respect to the last row of roof bolts. The average number of 

loads to complete a 30-ft cut was 17.5; therefore, the transition between regular-cut depth and 

deep-cut depth occurred between Loads No. 11 and 12, depicted by a vertical line in Figure F-3. 

No clear pattern is visible when comparing dust levels on the right side (deep-cut depth) of the 

transition to levels on the left side (regular-cut depth). When cutting a heading and using blowing 

3 face ventilation, shuttle car dust levels at the face averaged 1.77 mg/m during the regular-cut 

3 sequence and 2.13 mg/m during the deep-cut sequence. This difference was not statistically 

significant (85% CIs), indicating that the use of deep-cutting techniques did not affect shuttle car 

dust levels at Mine F. 

85
 
The daily average dust levels for the shuttle car cabs were low throughout the study, ranging 

3 from 0.21 to 0.61 mg/m . Shuttle car operator exposures benefited from large amounts (> 60,000 

cfm) of primary airflow for dilution of miner-generated dust in the travel ways and from the 

mine’s practice of wetting the travel ways to reduce dust entrainment from vehicle tires. 

Figure F-3. Shuttle car cab dust levels when loading at the active face. 

Miner-generated Dust 

Table F-4 shows miner-generated dust levels during the regular- and deep-cut sequences for each 

room development. The last column of Table F-4 adjusts dust levels based on the measured 

productivity using the previously described normalization process and Mine F’s average cars 

loaded per minute of 0.43. 

Miner-generated dust levels were very low during both the regular- and the deep-cut sequences, 

3 3 averaging 0.78 mg/m for the regular-cut depth and 0.69 mg/m for the deep-cut depth. The 

differences between these dust levels was not statistically significant (85% CIs), indicating that 

using deep-cutting techniques did not impact miner dust generation. Low miner-generated dust 

levels were achieved through good scrubber maintenance and high section airflow (> 60,000 

cfm), which effectively diluted dust not captured by the scrubber. 

Miner Operator Data Analysis 

Table F-5 shows miner operator dust exposure levels as measured with a PDM device for each 

cut. As mentioned previously, the PDM data collected on Day 1 of the study were lost due to an 

equipment preparation error. The levels presented in the table isolate production time only and 

86
 
are not indicative of shift average levels, which were much lower. Dust exposures are adjusted 

for productivity. Depth of cut did not significantly (85% CIs) impact the miner operator’s 

3 3 exposures, which averaged 2.63 mg/m during the regular-cut sequence and 2.55 mg/m during 

the deep-cut sequence. 

During the first 2 days of our study at Mine F, blowing brattice curtain was hung from the third 

row of bolts outby the face at the start of each cut. The curtain was advanced to the last row of 

bolts after the face was advanced 10 ft. This practice did not allow the miner operator to stand at 

the mouth of the curtain, where dust levels were much lower. On Day 3, greater curtain setback 

distances of up to 40 ft were observed and the operator was able to maintain a position at the 

mouth of the curtain throughout the cuts. As a result of this improved positioning, the miner 

3 operator’s dust exposure levels during production decreased from an average of 4.17 mg/m on 

3 Day 2 to 0.22 mg/m on Day 3. 

3 The miner operator’s average dust exposures over the entire sampling period were 1.71 mg/m

3 on Day 2 and 0.81 mg/m on Day 3. These levels include downtime, cuts mined on the left side 

(exhausting curtain side) of the section, and cuts mined on the right side (blowing curtain side) of 

the section. Each side of the section had its own continuous mining machine and roof bolter. The 

miner operator alternated between taking cuts on the left and right side of the section throughout 

the study. This practice allowed maintenance to be conducted on the idled mining machine 

without interrupting production. Routine miner maintenance included cleaning the scrubber 

screen, as well as replacing worn bits and clogged water sprays before each cut. 

Bolter Operations Data Analysis 

Bolting operations at Mine F were completed using a Fletcher RRII-13BC-F bolter. Table F-6 

shows bolter-generated dust levels as well as exposure levels for the intake- and return-side 

bolter operators at regular- and deep-cut depths. Bolter dust generation data for Room No. 2 

were invalid because the downwind area sampling package could not be placed in the immediate 

airflow return for the machine due to its position in the heading. Like the miner faces, the bolting 

faces were ventilated with blowing curtain. 

No significant (85% CIs) difference was observed when comparing the average dust exposure of 

3 3 the intake-side bolter operator (1.14 mg/m ) to the return-side operator (1.35 mg/m ) during 

bolting operations. Likewise, bolter operator exposure levels were not statistically significant 

(85% CIs) when comparing bolting operations at regular-cut depth to deep-cut depth, averaging 

3 3 0.87 mg/m during regular-cut depth and 1.62 mg/m during deep-cut depth. While not 

statistically significant, dust levels during the deep-cut portion of the room were double those 

during the regular-cut, which may have resulted from the fact that the ventilation curtain was not 

advanced as the bolter moved toward the face. Unlike the continuous miner, the bolting machine 

does not have a secondary air-moving device, such as a scrubber or water fan spray system, to 

maintain the flow of air toward the face as the machine advances away from the mouth of the 

curtain. Therefore, ventilation air tends to short circuit behind the bolter following the path of 

least resistance as the machine progresses beyond the influence of the blowing curtain. This 

occurrence progressively diminishes dust dilution at the operator positions. Data suggest that 

periodically advancing the curtain during the bolting cycle at Mine F may reduce bolter operator 

dust exposure levels. The mine did an excellent job at keeping the bolting machine upwind of 

87
 
continuous miner operations. As measured over the entire sampling period, the bolter operators’ 

3 average dust exposure levels were low during the study, ranging from 0.61 mg/m to 1.02 

3 mg/m . 

No statistically significant (85% CIs) difference was observed in dust levels generated by the 

bolting machine when comparing regular-cut depth to deep-cut depth. Bolter-generated dust 

3 levels averaged 0.35 mg/m during the study at an average curtain airflow rate of 5,500 cfm. 

Dust-control Monitoring 

Throughout the study, the curtain lines that provided ventilation to the active faces were well 

maintained. Blowing curtain was supported by pogo sticks to maintain a consistent quantity of 

airflow during each cut. Before commencing mining at the active face, an attempt was made to 

match the curtain airflow to the rated scrubber airflow by adjusting the curtain overlap into the 

open crosscut. Table F-4 shows curtain and scrubber airflow measurements for each cut. Curtain 

airflow measurements were made after activation of the miner scrubber. The average scrubber 

airflow dropped 5% from 8,860 cfm at the start of the cut to 8,440 cfm at completion due to 

material loading on the 20-mesh scrubber screen. The average blowing curtain airflow quantity 

was 6,650 cfm, resulting in a curtain-to-scrubber airflow ratio of approximately 0.8 with the 

scrubber running. This ratio is well below ideal according to past research that found the best 

ratio to be 1.0 before activation of the scrubber [Jayaraman et al. 1992]. The identified ideal 

ratio involved a configuration with the scrubber inlet located under the boom of the miner. The 

scrubber inlet on the miner used at Mine F was located on the top left side of the machine just 

behind the boom hinge point. It is unclear whether the recommended operating ratio of 1.0 

would apply to this type of configuration. The mine could benefit from determining the ideal 

curtain-to-scrubber airflow ratio to minimize dust levels in working areas around the continuous 

miner using its pDR dust sampling device. 

The largest degradation in scrubber airflow occurred during Cut No. 8, when scrubber airflow 

dropped 10% from 9,100 cfm at the start of the cut to 8,200 cfm at the end. Despite this drop, no 

degradation in scrubber dust capture was measured during the cut. When comparing regular- to 

3 deep-cut depth during Cut No. 8, miner-generated dust levels were 0.58 mg/m during regular3 cut depth and 0.29 mg/m during deep-cut depth. Likewise, the miner and shuttle car operators’ 

dust exposures did not worsen during the deep-cut sequence. For this study, the scrubber screen 

was tapped and back-flushed before each cut. This is a good practice to assure proper scrubber 

function. 

As with the continuous miner, no degradation in the bolting machine’s dust control circuit was 

observed during completion of the bolting sequence in the deep-cut rooms. Suction 

measurements were taken periodically throughout the bolting sequences and all measurements 

were between 12 and 15-in Hg, which appeared to provide good dust control. 

Summary 

	 3 1. When using blowing curtain, shuttle car dust levels at the face averaged 1.77 mg/m

3 during the regular-cut sequence and 2.13 mg/m during the deep-cut sequence. This 

88
 
difference was not statistically significant (85% CIs), indicating that the use of deep-cuts 

did not affect shuttle car dust levels at Mine F. 

2. 	 The daily average dust levels for the shuttle car cabs were low throughout the study, 

3 ranging from 0.21 to 0.61 mg/m . Shuttle car operator exposures benefitted from large 

amounts (> 60,000 cfm) of primary airflow for dilution of miner-generated dust in the 

travel ways and from the mine’s practice of wetting the travel ways to reduce dust 

entrainment from vehicle tires. 

3.	 Miner-generated dust levels were very low during both cutting sequences, averaging 0.78 

3 3 mg/m during the regular-cut sequence and 0.69 mg/m during the deep-cut sequence. 

The differences between these dust levels were not statistically significant (85% CIs), 

indicating that using deep-cutting techniques did not impact miner dust generation. 

4.	 Isolating for production time only, depth of cut did not significantly (85% CIs) impact the 

3 miner operator’s exposures, which averaged 2.63 mg/m during the regular-cut sequence 

3 and 2.55 mg/m the deep-cut sequence. 

5.	 When curtain setback distances allowed miner operators to stand at the mouth of the 

blowing curtain during the entire cut, their dust exposure levels during production were 

3 dramatically reduced from 4.17 to 0.22 mg/m . 

6.	 The miner operator’s average dust exposure levels over the entire sampling period were 

3 3 1.71 mg/m on Day 2 and 0.81 mg/m on Day 3. 

7.	 Bolter operator exposure levels were not statistically significant (85% CIs) when 

comparing bolting operations at regular-cut depth to deep-cut depth, averaging 0.87 

3 3 mg/m during regular-cut depth and 1.62 mg/m during deep-cut depth. 

8.	 As measured over the entire sampling period, the bolter operators’ average dust exposure 

3 levels were low during the study, ranging from 0.61 to 1.02 mg/m . 

9.	 No statistically significant (85% CIs) difference was observed in dust levels generated by 

the bolting machine when comparing regular-cut depth to deep-cut depth. Bolter3 generated levels averaged 0.35 mg/m during the study at an average curtain airflow rate 

of 5,500 cfm. 

10.	 The mine could benefit from using its pDR dust sampling device to determine the ideal 

curtain-to-scrubber airflow ratio to minimize dust levels in working areas around the 

mining machine. 

Reference Cited in Appendix F 

Jayaraman NI, Jankowski RA, Whitehead KL [1992]. Optimizing continuous miner scrubbers 

for dust control in high coal seams. In: Proceedings of New Technology in Mine Health and 

Safety, SME Annual Meeting. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 

pp. 193–205. 

89
 
Table F-1. Shuttle car cab dust levels when loading at the face on Day 1 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

90
 
Table F-2. Shuttle car cab dust levels when loading at the face on Day 2 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

91
 
Table F-3. Shuttle car cab dust levels when loading at the face on Day 3 

Note: Shaded areas show deep-cut depth, and clear areas show regular-cut depth. 

92
 
Table F-4. Miner-generated dust levels during the deep- and regular-cut depth 

Note: Dust levels are adjusted for productivity. 

Table F-5. Miner operator dust levels during the deep- and regular-cut depths 

Note: Dust levels are adjusted for productivity. 

93
 
Table F-6. Bolter-generated dust levels and operator exposures for each bolting sequence 

94
 
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