RI 9693

REPORT OF INVESTIGATIONS/2013

Impact on Respirable Dust Levels When Operating 

a Flooded-bed Scrubber in 20-foot Cuts
Report of Investigations 9693 

Impact on Respirable Dust Levels When Operating a Flooded-bed

Scrubber in 20-foot Cuts 

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

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

December 2013
This document is in the public domain and may be freely 

copied or reprinted.

Disclaimer 

Mention of any company or product does not constitute endorsement by the National Institute for 

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

do not constitute NIOSH endorsement of the sponsoring organizations or their programs or 

products. Furthermore, NIOSH is not responsible for the content of these Web sites. All Web 

addresses referenced in this document were accessible as of the publication date. 

Ordering Information 

To receive documents or other information about occupational safety and health topics, contact 

NIOSH at 

Telephone: 1–800–CDC–INFO (1–800–232–4636) 

TTY: 1–888–232–6348 

CDC INFO: www.cdc.gov/info 

or visit the NIOSH Web site at www.cdc.gov/niosh. 

For a monthly update on news at NIOSH, subscribe to NIOSH eNews by visiting 

www.cdc.gov/niosh/eNews. 

Suggested Citation 

NIOSH [2013]. Impact on Respirable Dust Levels When Operating a Flooded-bed Scrubber in 

20-foot Cuts. By Colinet JF, Reed WR, Potts JD. Pittsburgh, PA: U.S. Department of Health and 

Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication 2014–105, RI 9693. 

DHHS (NIOSH) Publication No. 2014–105 

December 2013 

Cover photo by NIOSH. 
Contents 

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

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

Mine Sites Tested............................................................................................................ 4

Sampling Protocol ........................................................................................................... 5

Data Analysis .................................................................................................................. 9

Continuous Miner Results .................................................................................................. 9

Shuttle Car Results .......................................................................................................... 11

Roof Bolter Results .......................................................................................................... 11

Quartz Results.................................................................................................................. 12

Summary ....................................................................................................................... 13

Acknowledgements ....................................................................................................... 15

References .................................................................................................................... 16

Appendix A: Dust Survey at Mine A .............................................................................. 19

Introduction ...................................................................................................................... 19

Site Description ................................................................................................................ 19

Ventilation Plan Parameters ............................................................................................. 20

Results ............................................................................................................................. 20

Conclusions ...................................................................................................................... 24

Appendix B: Dust Survey at Mine B .............................................................................. 33

Introduction ...................................................................................................................... 33

Site Description ................................................................................................................ 33

Ventilation Plan Parameters ............................................................................................. 34

Results ............................................................................................................................. 35

Conclusions ...................................................................................................................... 39

Appendix C: Dust Survey at Mine C .............................................................................. 46

Introduction ...................................................................................................................... 46

Site Description ................................................................................................................ 46

Ventilation Plan Parameters ............................................................................................. 47

Results ............................................................................................................................. 48

Conclusions ...................................................................................................................... 51
Figures

Figure 1. Schematic of typical dust sampling locations at each mine. ............................. 6

Figure 2. Dust sampling packages located in the intake to the continuous miner (left) 

and on the right rear corner of the miner (right). .............................................................. 7

Figure 3. Dust sampling packages located on a shuttle car (left) and on a 

roof bolter (right). ............................................................................................................. 8

Figure A-1. Schematic of section sampled at Mine A. ................................................... 19

Figure B-1. Schematic of section sampled at Mine B. ................................................... 33

Figure C-1. Schematic of section sampled at Mine C. .................................................. 46

Figure C-2. Scrubber discharge at left rear corner of miner. ......................................... 52
Tables 

Table 1. Minimum plan parameters and levels measured by MSHA in 

baseline surveys ............................................................................................................. 4

Table 2. Summary of conditions observed during sampling at three mines .................... 5

Table 3. Average respirable dust concentrations around the continuous miner and 

in the section return ....................................................................................................... 10

Table 4. Average respirable dust concentrations at shuttle car cabs ............................ 11

Table 5. Average respirable dust concentrations at the roof bolter ............................... 12

Table 6. Quartz content in the immediate miner return with the scrubber off and on .... 13

Table A-1. Summary of adjusted respirable dust concentrations for the 

continuous miner ........................................................................................................... 21

Table A-2. Summary of adjusted respirable dust concentrations in the shuttle 

car cabs ......................................................................................................................... 22

Table A-3. Summary of roof bolter dust concentrations ................................................ 23

Table A-4. Respirable quartz levels in the continuous miner return .............................. 24

Table A-5. Continuous-miner-generated dust concentrations (mg/m3) for each cut ...... 27

Table A-6. Shuttle car loading times and dust concentrations with the scrubber off ..... 28

Table A-7. Shuttle car loading times and dust concentrations with the scrubber on ..... 30

Table B-1. Summary of adjusted respirable dust concentrations for the 

continuous miner ........................................................................................................... 35

Table B-2. Summary of adjusted respirable dust concentrations in the shuttle 

car cabs ......................................................................................................................... 36

Table B-3. Summary of roof bolter dust concentrations ................................................ 37

Table B-4. Respirable quartz levels in the continuous miner return .............................. 38

Table B-5. Continuous-miner-generated dust concentrations (mg/m3) for each cut ...... 41

Table B-6. Shuttle car loading times and dust concentrations with the scrubber off ..... 42

Table B-7. Shuttle car loading times and dust concentrations with the scrubber on ..... 44

Table C-1. Summary of adjusted respirable dust concentrations for the 

continuous miner ........................................................................................................... 48

Table C-2. Summary of adjusted respirable dust concentrations in the shuttle 

car cabs ......................................................................................................................... 49

Table C-3. Summary of roof bolter dust concentrations ................................................ 50

Table C-4. Respirable quartz levels in the continuous miner return .............................. 51

Table C-5. Continuous-miner-generated dust concentrations (mg/m3) for each cut ...... 54

Table C-6. Shuttle car loading times and dust concentrations with the scrubber off ..... 56

Table C-7. Shuttle car loading times and dust concentrations with the scrubber on ..... 58
ACRONYMS AND ABBREVIATIONS 

adj adjusted

avg average

CFR Code of Federal Regulations

CM continuous miner

conc concentration

CWP coal workers’ pneumoconiosis

FBS flooded-bed scrubber

int intake

MMU mechanized mining unit

MRE Mining Research Establishment

MSA Mine Safety Appliances

MSHA Mine Safety and Health Administration

na not available

NIOSH National Institute for Occupational Safety and Health

No. number

OMSHR Office of Mine Safety and Health Research

oper operator

PDM personal dust monitor

pDR personal DataRAM

PEL permissible exposure limit

PVC polyvinyl chloride

ret return

RB roof bolter

RRC right rear corner

SC shuttle car

SD standard deviation
UNIT OF MEASURE ABBREVIATIONS 

cfm cubic feet per minute

ft foot

in inches

in Hg inches of mercury

l/min liters per minute

mg milligrams

mg/m3 milligrams per cubic meter

min minute

mm millimeter

% percent

psi pounds per square inch

μg Microgram

μg/m3 micrograms per cubic meter

Impact on Respirable Dust Levels When Operating a 

Flooded-bed Scrubber in 20-foot Cuts

Jay F. Colinet,1

1

 Senior Scientist; Dust, Ventilation, and Toxic Substances Branch; Office of Mine Safety and Health 

Research (OMSHR); NIOSH, Pittsburgh, PA. 

W. 2 R. Reed, 

2

 Mining Engineer; Dust, Ventilation, and Toxic Substances Branch; OMSHR; NIOSH, Pittsburgh, PA. 

and J. Drew Potts3

3

 Branch Chief; Dust, Ventilation, and Toxic Substances Branch; OMSHR; NIOSH, Pittsburgh, PA 

Abstract 

Underground coal mining companies that operate continuous miner sections often apply to 

the Mine Safety and Health Administration (MSHA) for approval to take extended cuts to depths 

of up to 40 ft as a means of improving productivity. Historically, MSHA has granted approval of 

this practice if the mine has successfully demonstrated the ability to control the roof, methane, 

and respirable dust while extracting these extended cuts. A key component for controlling dust 

generated by continuous miners in 40-ft cuts has been the utilization of flooded-bed scrubbers. 

These fan-powered scrubbers pull dust-laden air from the mining face and remove respirable 

dust particles by passing the collected air through a wetted filter panel. The filtered air is then 

discharged back into the mine atmosphere. To effectively use scrubbers in faces that employ 

exhaust ventilation, the return ventilation curtain or tubing should be located outby the scrubber 

discharge on the continuous miner, which results in a setback distance from the face of

approximately 40 ft. Over the last several years, MSHA has emphasized that mines demonstrate 

effective dust control before granting approvals for taking extended cuts with extended curtain 

setbacks. Each mine operator must successfully demonstrate control of workers’ dust exposures 

in standard 20-ft cuts before MSHA considers approving extended cuts. 

The goal of the research conducted by the National Institute for Occupational Safety and 

Health (NIOSH) was to compare dust levels generated in 20-ft cuts when using traditional 

exhaust face ventilation without a scrubber to dust levels in 20-ft cuts when using extended 

curtain setbacks with a scrubber operating. Dust surveys were completed at three mines, with 

area and personal sampling conducted to quantify respirable dust concentrations on a cut-by-cut 

basis. Dust sampling results did not show a statistically significant difference (Wilcoxon twosample test, α = 0.05) in respirable dust concentrations between these two test conditions 

(scrubber-on and scrubber-off) at the continuous miner or shuttle car sampling locations at the 

face. However, with the scrubber operating, respirable dust concentrations in the return airstream 

downwind of the continuous miner showed reductions of 91%, 86%, and 40% at Mines A, B, 

and C, respectively. The reductions at Mines A and B were found to be statistically significant 

when using the Wilcoxon test. Likewise, reductions in respirable quartz dust levels in the 

continuous miner return were observed at all three mines, with statistically significant reductions 

of over 80% observed at Mines A and B. Although operation of the flooded-bed scrubber did not 

impact respirable dust levels in the face area, it did significantly reduce respirable and quartz 

dust levels downwind of the continuous miner. Consequently, operation of the flooded-bed 

scrubbers, in conjunction with the dust controls required in the MSHA-approved ventilation 

plans at these mines, was advantageous from a respirable dust control perspective.

 
2

Introduction 

During the mining and transport of coal, respirable dust is generated and can be liberated into

the air ventilating the mine. If mine workers inhale excess amounts of this respirable airborne 

dust, it can result in the development of coal workers’ pneumoconiosis (CWP). Likewise, if rock 

within or adjacent to the coal seam is extracted, respirable silica (quartz) dust can be liberated 

into the ventilating air. Inhalation of excess amounts of silica can lead to the development of 

silicosis. CWP and silicosis are disabling and potentially fatal lung diseases that cannot be cured 

[Cohen and Velho 2002], so it is critical to prevent mine workers from contracting these lung 

diseases.

The Federal Coal Mine Health and Safety Act of 1969 (Public Law 91-173) established a 

3 respirable coal mine dust standard of 2 mg/m over an eight-hour shift. This Act also required 

periodic occupational dust sampling with a personal gravimetric sampler on each mechanized 

mining unit (MMU) to demonstrate compliance with the dust standard. When the quartz content 

in an MSHA-collected respirable dust sample exceeds 5%, a reduced dust standard is calculated 

by dividing the percent quartz into 10. For example, if a sample contains 11% quartz, the 

3

reduced dust standard for that MMU would be 0.9 mg/m (10 ÷ 11% quartz = 0.9). 

In an effort to limit the respirable dust exposure of coal mine workers, MSHA requires each 

mine operator to establish an acceptable ventilation plan that details how the mine proposes to 

control worker respirable dust exposure by defining ventilation parameters and dust control 

*

technologies that will be used [30 CFR 75.371] . 

*Code of Federal Regulations. See CFR in references. 

This plan must be submitted to the appropriate 

MSHA district manager and approved by MSHA before mining can begin [30 CFR 75.370]. 

After the plan is approved, the following MSHA requirements apply: 

A person designated by the operator shall conduct an examination to assure compliance 

with the respirable dust control parameters specified in the mine ventilation plan. In those

instances when a shift change is accomplished without an interruption in production on a 

section, the examination shall be made anytime within 1 hour of the shift change. In those

instances when there is an interruption in production during the shift change, the 

examination shall be made before production begins on a section. Deficiencies in dust 

controls shall be corrected before production begins or resumes. The examination shall 

include air quantities and velocities, water pressures and flow rates, excessive leakage in 

the water delivery system, water spray numbers and orientations, section ventilation and 

control device placement, and any other dust suppression measures required by the 

ventilation plan [30 CFR 75.362 (a)(2)]. 

In addition to the above requirements, MSHA personnel assess the status of the dust controls 

during inspections to ensure that the plan parameters control respirable dust levels to or below 

the applicable dust standard. Typically, the mine will be permitted to exceed the minimum 

specified plan parameters by 120% and still be considered to be operating under the existing dust

control plan [MSHA 2012a]. 

 
3

In order to extract extended cuts (i.e., those that extend beyond 20 ft), mine operators must 

apply to MSHA for approval. MSHA does not grant approval until after completing an on-site 

evaluation of the proposed extended cut system. Initially, MSHA will only allow for extraction 

of extended cuts while MSHA personnel are present at the mine site conducting their evaluation. 

At all other times, the mine operator must follow the standard cut plan included in the MSHAapproved ventilation plan, which “should require that the ventilation curtain/tubing be 

maintained to not more than 20 ft from the deepest point of penetration the face has been 

advanced” [MSHA 2012b].

In underground coal mines in the United States, the majority of continuous mining machines 

in use today are equipped with a flooded-bed scrubber, which is a fan-powered dust collector. 

The scrubber pulls dust-laden air from the face and passes it through a wetted filter panel. Past 

research by Colinet et al. [USBM 1990] has shown that scrubbers can remove over 90% of the 

respirable dust that is pulled into the unit. Although MSHA does not consider the scrubber to be 

a ventilation device, it has been shown to assist in moving ventilating air to the face [Taylor et al. 

1996]. As a result of these dust collection and air-moving capabilities, flooded-bed scrubbers 

have become a key component for mines in receiving MSHA approval to take extended cuts of 

up to 40 ft as part of their approved ventilation plan. 

In order to realize the maximum effectiveness of scrubbers in mines using exhausting face 

ventilation, the mouth of the brattice curtain should be outby the discharge of the scrubber so that 

the scrubber exhaust can be directed into the return airway [Jayaraman et al. 1990]. This would 

require the curtain to be approximately 40 ft from the face. In extended cut approvals, MSHA 

grants a variance to the mining operation to allow for this extended curtain setback distance. 

Without this variance, flooded-bed scrubbers cannot be effectively used in faces with exhaust 

ventilation. Historically, mines have not requested and MSHA has not granted this curtain 

setback variance for use in 20-ft cuts. However, the use of a flooded-bed scrubber in 20-ft cuts 

along with an extended curtain setback could be advantageous for controlling dust. 

Researchers from the NIOSH Office of Mine Safety and Health Research (OMSHR), in 

partnership with MSHA and Alpha Natural Resources, completed a research project to evaluate 

the impact on respirable dust levels generated in 20-ft cuts with and without a flooded-bed 

scrubber operating. An extended curtain setback was used in cuts when the scrubber was 

operated. Respirable dust surveys were conducted at three Alpha underground coal mines 

(referred to here as Mines A, B, and C). Two of these mines did not have approval to operate a 

flooded-bed scrubber in their current ventilation plans. For these mines, mine management 

submitted a temporary plan to MSHA, which was approved by MSHA for use only during the 

NIOSH testing period. The third mine had the capability of operating a flooded-bed scrubber 

with an extended curtain setback to extract 40-ft cuts in its current plan, so no temporary plan 

was needed. However, the mine restricted the depth of the cuts taken during the NIOSH 

sampling to 20 ft to accommodate the test program parameters. 

Prior to NIOSH initiating each of its dust surveys at the individual mines, MSHA personnel 

visited the mines to ensure that the plan parameters specified in the approved ventilation plans 

for Mines A, B, and C were in use. MSHA also examined the scrubbers to document their proper 

operation and quantify the air quantities produced. Table 1 summarizes a portion of the plan 

parameter information gathered by MSHA during the baseline surveys. 
4

MSHA also conducted dust sampling during these visits to demonstrate that the approved 

plan parameters were successful in maintaining respirable dust at or below allowable levels. 

Under the operating conditions shown in Table 1, dust levels measured by MSHA over an 8-hour 

sampling period during the baseline surveys were within allowable levels. In addition to these 

baseline surveys, an MSHA representative participated in the subsequent NIOSH dust surveys at 

each mine and verified that minimum plan parameters were present during the NIOSH sampling. 

Table 1. Minimum plan parameters and levels measured by MSHA in baseline surveys 

Ventilation plan parameter Mine A Mine B Mine C

Minimum face airflow, cfm 7,000 7,000 5,000

MSHA-measured face airflow, cfm 8,792 9,068 10,612*

Minimum scrubber airflow, cfm 6,400 6,000 4,000

MSHA-measured scrubber airflow, cfm 7,067 7,604 4,160

Minimum number of sprays operating at 

start of each cut 51 42 33

Number of sprays found operating at start of 

each cut 51 42 33

Minimum spray operating pressure, psi 65 65 85

MSHA-measured spray operating pressure, 

psi 74 74 92

*Average = 7,218 cfm when airflow quantities from three flush cuts are omitted from calculation. 

Mine Sites Tested 

Each of the mines included in these surveys used line brattice to implement an exhausting 

face ventilation system. For the cuts with the scrubber off, the ventilation curtain was set back 

from the face a maximum of 20 ft. For the cuts with the scrubber operating, the ventilation 

curtain was set back a distance of up to 40 ft. 

All of the continuous miners sampled were located on super sections—i.e., where two sets of 

mining equipment operate simultaneously within the same working section, and each set is 

ventilated by a separate split of intake air—with the sampled mining machine responsible for 

completing the development of entries on one side of the super section. Two shuttle cars were 

used to transport coal from the face to the section feeder. A twin-boom bolter was used to 

complete the installation of roof bolts. In the approved ventilation plans for each of the MMUs 

sampled, the bolting machine was permitted to travel downwind of the continuous miner once 

during each production shift. 

Appendices A, B, and C contain a diagram of the sections sampled at Mines A, B, and C, 

respectively. These appendices also contain additional information specific to each mine site. 

Table 2 provides a brief summary of the equipment and operating conditions at each mine during 

the NIOSH dust surveys. 
5

Table 2. Summary of conditions observed during sampling at three mines 

Mine parameter Mine A Mine B Mine C

Continuous miner model Joy 14 CM 15 Joy 12 CM 15 Joy 14 CM 15

Average mining height, in 62 94 65

Average face airflow, cfm 8,300 7,943 6,565

Average scrubber airflow, cfm 6,400 7,218 4,288

Scrubber filter panel density 30-layer 30-layer 30-layer

Number of water sprays operating 51 42 33

Spray type

BD3-5 hollow 

cone

BD3 hollow 

cone

BD3-5 hollow 

cone

Average water pressure, psi 99 68 100

Roof bolter model

Fletcher Roof 

Ranger II

Fletcher 

DDR-13

Fletcher Roof 

Ranger II

Average vacuum pressure, in Hg—left 16 14 15

Average vacuum pressure, in Hg—right 13 17 13

As noted in Table 2, all three mining machines used 30-layer filter panels in their respective 

flooded-bed scrubbers; however, the other parameters showed substantial variation across the 

three mines. For example, mining height varied by over 30 inches, while scrubber airflow varied 

by nearly 3,000 cfm. Consequently, the mines sampled during these surveys represent a range of 

operating conditions. 

Sampling Protocol 

Respirable dust measurements were made using the following instruments: (1) Thermo 

Scientific Model pDR-1000AN Personal Data Rams (pDRs); (2) Thermo Scientific Model 

PDM3600 Personal Dust Monitor (PDM); and (3) Mine Safety Appliances (MSA) Escort ELF 

sampling pumps (gravimetric samplers). The pDR samplers use light-scattering technology to 

provide real-time measurements of dust levels, which are stored in an internal data logger. Dust 

measurements were recorded by each pDR at five-second intervals throughout the sampling 

shift. The PDM sampler is a mass-based, real-time dust sampler that was operated at 2.2 l/min 

with a Higgins-Dewell cyclone. The PDM sampler recorded dust measurements at one-minute 

sampling intervals. Each MSA pump was operated at 2 l/min while connected to a Dorr-Oliver 

10-mm nylon cyclone fitted with a 37-mm-diameter PVC filter. All filters were pre- and postweighed at the OMSHR Pittsburgh lab, with the gain in dust mass and sampling time used to 

calculate the average respirable dust concentration for the sampling period. These time-weighted 

average dust concentrations were not converted to Mining Research Establishment (MRE) 

equivalent concentrations as described in 30 CFR 70.206 because they were not collected as 

compliance dust samples.

Because light-scattering instruments can be impacted by changes in dust composition and 

size distribution, the pDR manufacturer recommends that individual dust readings be corrected 

with a ratio calculated from adjacent gravimetric samplers [Thermo Scientific 2008]. 

Consequently, two gravimetric samplers were located side-by-side with a pDR sampler on area 

sampling racks. The average gravimetric concentration from the two samplers was divided by the 
6

pDR concentration for the entire sampling period to calculate a correction factor. The individual 

instantaneous dust readings from the pDR were then multiplied by this correction factor. The 

corrected pDR concentrations were used in all subsequent calculations. 

Area sampling packages as described above were placed at multiple sampling locations, as

illustrated in Figure 1. In addition, a gravimetric-only sampling package was operated in the 

miner return, with the filters from this sampling used for quartz analysis. A PDM sampler was 

worn by the continuous miner operator to assess his dust exposure. Each of these sampling 

locations will be discussed below in greater detail. 

Figure 1. Schematic of typical dust sampling locations at each mine. 

NIOSH researchers collected time study information related to the operation of the 

continuous miner. The start and stop times for each miner cut were used to calculate the average 

dust concentration during each cut. The times when each shuttle car entered and exited the active 

face were also recorded and used to calculate dust levels at each shuttle car while being loaded. 

When the continuous miner was not loading for periods of three min or longer, these downperiods were removed from the dust calculations so that the reported data would only represent 

dust generated during mining and loading. 

Isolation of miner-generated dust was accomplished by placing area sampling packages in 

both the immediate intake and return (locations C and E in Figure 1) for the continuous miner. 

Intake dust levels were subtracted from return dust levels to calculate the quantity of dust 

attributable to the miner. An area sampling package was also located on the right rear corner 

(RRC) of the continuous miner (location D). This sampling location assisted in monitoring dust 
7

rollback from the face. After the survey at Mine A was completed, an additional area sampling 

package was placed in the main return entry (location I) to expand the information obtained on 

differences in dust levels downwind of the miner. Figure 2 shows representative area sampling 

packages that were placed in the miner intake and on the rear corner of the continuous miner for 

each survey. 

Figure 2. Dust sampling packages located in the intake to the continuous miner (left) 

and on the right rear corner of the miner (right). 

An area sampling package was placed in each shuttle car cab (locations G and H) to monitor 

face area dust concentrations. The shuttle car dust concentrations are important for this study 

because their position with respect to the mining machine is consistent during mining and 

loading operations at the face. These data allow for a direct comparison of dust concentrations in 

the face area for the scrubber-on and scrubber-off test conditions. 

The roof bolting machine was operated downwind of the continuous miner on several 

occasions during the survey. Because miner-generated dust can significantly impact the exposure 

of downwind personnel [Jayaraman et al. 1988], NIOSH monitored dust concentrations with 

sampling packages placed in the bolter intake (location A) and on-board the bolter (location B). 

Because of differences in operating practices and bolter designs, the bolter-mounted sampling 

package could not be placed at identical locations for all three surveys. A detailed time study 

documented the bolter’s location and position with respect to the continuous miner (upwind or 

downwind) for each bolting cycle. Figure 3 illustrates representative locations for the sampling 

packages on the shuttle cars and roof bolters. 

Miner-generated dust was analyzed for quartz content for both the scrubber-on and scrubberoff conditions. This was accomplished by using two sets of cyclones/filters on the same area 

sampling rack, which was placed in the immediate miner return (location F). If the scrubber was 

being used (scrubber-on), the hoses for two filters were connected to the sampling pumps and the 

pumps were activated just before mining commenced. The pumps were placed on hold at the end 

of the cut and the hoses were removed from the pumps. A similar procedure was followed with 

the other two filters during scrubber-off cuts. Sampling times were recorded for both conditions 

to allow for the calculation of airborne concentration, as well as percentage of quartz in the 

sample. The quartz content of these filters was determined by the MSHA analytical lab in 

Pittsburgh through the use of the MSHA P7 analytical method [MSHA 1989]. 

Photo by NIOSH Photo by NIOSH
8

Figure 3. Dust sampling packages located on a shuttle car (left) and on a roof bolter (right). 

As found in research by Potts et al. [NIOSH 2011], during normal mining operations, a 

buildup of material can occur in flooded-bed scrubbers, diminishing their air-moving 

effectiveness. This possibility was monitored by using a pitot tube and differential pressure 

gauge to measure velocity head in order to calculate scrubber air quantity prior to the start of 

each 20-ft scrubber-on cut configuration. At the beginning of each mine survey, a full traverse of 

velocity measurements (15 to 21 points depending upon the cross-sectional area of the scrubber 

ductwork) was completed and used to calculate scrubber air quantity. During subsequent 

scrubber measurements, three center-line velocity head measurements were obtained and 

compared to the three center-line readings from the full traverse to ensure appropriate airflow 

through the scrubber prior to each cut. As specified in the ventilation plans, the 30-layer scrubber 

screen was removed and cleaned with water after each cut. Additional maintenance included 

cleaning the scrubber inlets and ductwork at the beginning of each shift. In a few instances, the 

demister also had to be removed and cleaned in order to obtain the required scrubber airflow. 

Air velocities in the entries and behind the exhaust line curtains were measured with a vane 

anemometer. An airflow measurement was taken at the face-side end of the ventilating curtain 

prior to the start of each cut. For cuts where the scrubber was going to be operated, this airflow 

measurement was taken before activation of the scrubber. Curtain configuration and length were 

also recorded. The exhaust brattice curtain was positioned just outby the scrubber exhaust for the 

scrubber-on tests and within 20 ft of the face during the scrubber-off tests. The scrubber 

discharged airflow either from the left or from the right rear corner of the miner, with that choice 

dictated at each mine by the location of the exhaust line brattice within the entry. 

Past research has shown that the mining machine’s external water spray system can have a 

dramatic impact on dust levels at the face [Organiscak and Beck 2010]. Therefore, the number of 

sprays operating and the operating pressure on the left and right side of the cutter head were 

monitored throughout the survey for adherence to the specifications in the ventilation plan for 

each MMU. Similarly, vacuum measurements were taken on the left and right drill heads of the 

roof bolting machine to ensure that the bolter dust collector was meeting the required operating 

levels.

Photo by NIOSH Photo by NIOSH
9

Data Analysis 

Detailed data on the cut locations, cutting times, face airflows, scrubber airflows, 

gravimetric, and real-time sampling dust concentrations for Mines A, B, and C are provided in 

the mine-specific survey reports in Appendices A, B, and C, respectively. In order to evaluate the 

impact of the flooded-bed scrubber in 20-ft cuts, the real-time sampling data and time study 

information were used to calculate dust concentrations on a cut-by-cut basis. As shown in the 

appendices, seven cuts were obtained for each of the scrubber-off and scrubber-on test conditions 

at Mines A and B, and four cuts were obtained for each of the test conditions at Mine C. Given 

the small sample sizes and the possibility that the dust data would not be normally distributed, it 

was necessary to use a nonparametric or distribution-free statistical test to analyze for differences 

between mean dust levels for each test condition. 

The Wilcoxon

1

1

 The Wilcoxon two-sample test is the nonparametric counterpart of the independent-samples t-test. 

Whereas the t-test analyzes original data values, the Wilcoxon test analyzes rank-transformed data 

values. Ranks represent relative position within an ordered set of data values. The Wilcoxon test involves 

a comparison of the mean or average ranks of the two groups, just as the t-test involves a comparison of 

the means of original data values. 

two-sample test (exact form) was used with a level of significance of α = 0.05 

to test the null hypothesis that the mean ranks of the two groups of dust data from the two test 

conditions were equal. Because the dust levels with the scrubber operating could be higher or 

lower than with the scrubber off, a two-tailed test was selected to identify any statistically 

significant differences between the two test conditions. If the computed probability (p-value) 

from the statistical test was less than 0.05, the observed difference between the mean ranks for 

the two test conditions was considered to be statistically significant. The average dust 

concentrations from the individual cuts, as shown in the tables in the appendices, were used to 

analyze the data for each sampling location at each mine. The mean dust concentrations for the 

scrubber-off and scrubber-on test conditions at each mine and the calculated p-values from the 

Wilcoxon test are provided in Tables 3, 4, and 6 to identify statistical significance. 

Continuous Miner Results 

The miner operator dust concentrations were calculated from the PDM data, and dust 

concentrations from all other sampling locations were calculated from pDR data. The dust 

concentrations for the miner operator, RRC, immediate miner return, and main return sampling 

locations had the intake dust levels subtracted out. Because increases in production can generate 

more dust [Webster et al. 1990] and increases in airflow can dilute dust levels [Hartmann 1973], 

the intake-adjusted dust levels were then normalized for differences in production and face 

airflow between cuts, assuming a linear relationship between these parameters and dust levels. 

For example, if average productivity for all cuts sampled during a mine survey was 0.28 shuttle 

cars per min and productivity for an individual cut averaged 0.36 shuttle cars per min, then the 

average dust level for this cut was multiplied by a factor of 0.78 (0.28 ÷ 0.36) to adjust for the 

higher-than-average productivity observed in the cut. The adjustment for differences in airflow 

were made in a similar manner, except that the factor was calculated by dividing the measured 

face airflow in an individual cut by the average face airflow of all cuts from the mine survey. 

 
10

The airflow normalization relationship is the inverse of the productivity relationship since the 

dust concentrations are expected to decrease with an increase in face air quantity. A summary of 

the average normalized respirable dust concentrations around the continuous miner and in the 

return from the three surveys is provided in Table 3. 

Table 3. Average respirable dust concentrations around the continuous miner 

and in the section return 

Mine Sampling location

Avg dust with 

scrubber off, 

mg/m3

Avg dust with 

scrubber on, 

mg/m3

Calculated

p-value

Dust

reduction with 

scrubber on

A CM*intake 0.08 0.07 - -

A CM operator 0.30 0.26 0.3310 13%

A CM RRC*1.27 1.02 0.6439 20%

A CM return 23.86 2.05 0.0005†

91%

A Section return na‡na‡na

‡

na‡

B CM intake 0.12 0.13 - -

B CM operator 0.55 0.46 0.6352 16%

B CM RRC 7.53 5.20 0.6200 31%

B CM return 12.13 1.66 0.0005†

86%

B Section return 4.81 0.74 0.0005†

85%

C CM intake 0.09 0.05 - -

C CM operator 0.25 0.32 0.8000 -28%

C CM RRC na

§

na

§

na

§

na

§

C CM return 14.37 8.64 1.000 40%

C Section return 6.73 4.80 0.400 29%

* Abbreviations: CM, continuous miner; RRC, right rear corner. 

†

Statistically significant difference. 

‡ No data available; section return sampling location added after completion of survey at Mine A. 

§ Water exposure of dust samplers invalidated data at this location for this mine. 

Intake dust concentrations to the continuous miner faces were well controlled at all three 

mines and averaged 0.09 mg/m3. Dust concentrations at the miner operator were 0.55 mg/m3

or 

lower and exhibited a maximum difference of 0.09 mg/m3

between scrubber-on and scrubber-off 

test conditions. These differences were not statistically significant. Dust concentrations at the 

RRC of the mining machine were somewhat variable from mine to mine, with no statistically 

significant difference despite the lower levels observed with the scrubber operating. However, 

major reductions in dust concentrations were observed in the immediate miner return when the 

scrubber was being operated. The reductions in average dust concentrations in the miner return at 

Mine A (21.81 mg/m3) and at Mine B (10.47 mg/m3) were statistically significant when 

evaluated using the Wilcoxon two-sample test with α = 0.05. At Mine C, difficult geologic 

mining conditions resulted in the fewest cuts sampled for any of the surveys. In addition, the 

variability in measured dust concentrations observed between the cuts was greater than that 

observed at Mines A and B. When combining these two factors, the 5.73 mg/m3

reduction in 

average miner return dust concentration with the scrubber operating at Mine C was not 

statistically significant. 
11

For the average dust concentrations measured in the section return at Mine B, the 4.07 mg/m3

reduction in dust concentration with the scrubber operating was statistically significant. A 

reduction of 1.93 mg/m3in the average section return dust concentrations was measured at Mine 

C, but this difference was not statistically significant due to the sampling issues previously 

identified for Mine C. 

Shuttle Car Results 

Time study data were collected to identify when each shuttle car entered the mining face to 

be loaded and when the car left the face. These time periods were used to calculate dust 

concentrations for each shuttle car while being loaded at the face. The individual dust 

concentrations were then used to calculate an average shuttle car dust concentration for each cut. 

The miner intake dust level was subtracted from the shuttle car dust level for each cut. The cut 

concentrations were used to calculate the average dust level with the scrubber off and the 

scrubber on at each mine. These average dust concentrations are summarized in Table 4. 

Table 4. Average respirable dust concentrations at shuttle car cabs 

Mine

Scrubber-off,

mg/m3

Scrubber-on,

mg/m3

Difference with 

scrubber on, 

mg/m3

Calculated

p-value*

A 0.27 0.28 -0.01 0.9272

B 0.03 0.07 -0.04 0.4272

C 0.35 0.43 -0.08 0.5429

* No statistically significant differences. 

As shown in Table 4, operation of the scrubber during these surveys did not have any

practical impact on dust concentrations at the shuttle car cab locations. The largest observed 

difference between scrubber-on and scrubber-off was an increase of only 0.08 mg/m3, which was 

not statistically significant. The observed dust levels were 0.43 mg/m3or lower, indicating that 

dust was not escaping the miner face and was not exposing the shuttle car operators to elevated 

levels under either test condition. 

Roof Bolter Results 

Time study information was collected on the roof bolter to identify when the bolter was 

operating and the relative position of the bolter with respect to the continuous miner. Average 

dust concentrations were calculated for each roof bolter place and are summarized in Table 5a 

for the bolter intake and Table 5b for the on-board sampling locations at each mine. 

When the bolter was positioned upwind of the miner, the intake air delivered to the bolter 

contained low levels of respirable dust and was 0.12 mg/m3

or lower at these mines. Because the 

bolter is only permitted downwind of the miner once per shift, only a limited amount of 

downwind data was obtained. At Mine A, the bolter was only operated downwind of the miner 

once during the entire survey, so no scrubber-on/scrubber-off comparison could be made. 

However, the data from Mines B and C illustrate substantial reductions in dust levels when the 
12

bolter was downwind and the scrubber was operating on the miner. Reductions of 34%–85% 

were measured at the bolter intake sampling location, with reductions of 51%–83% observed on 

the bolter. Because of the limited amount of data, statistical analysis was not completed. 

Table 5. Average respirable dust concentrations at the roof bolter 

a. Roof bolter intake sampling location 

Mine

RB*upwind of miner, 

mg/m3

RB downwind of miner 

with scrubber off, 

mg/m3

RB downwind of miner 

with scrubber on, 

mg/m3

Reduction with 

scrubber on

A 0.04 na†3.29 na†

B 0.12 5.97 0.92 85%

C 0.09 11.23 7.38 34%

* Abbreviation: RB, roof bolter. 

† No data available. 

b. On-board sampling location‡

Mine

RB upwind of miner, 

mg/m3

RB downwind of miner 

with scrubber off, 

mg/m3

RB downwind of miner 

with scrubber on, 

mg/m3

Reduction with 

scrubber on

A 0.12 na†3.62 na†

B 0.30 5.65 0.94 83%

C 0.16 12.26 6.06 51%

† No data available. 

‡ Sampling package located near return-side-operator at Mine A, in the center of the walk-through bolter 

at Mine B, and in the operator’s cab at Mine C.

In addition to dust generated by the continuous miner, bolter operators can be exposed to dust 

generated from installing bolts. However, when comparing the concentrations measured at the 

bolter intake location when upwind of the miner to those measured on the bolter, increases in 

dust concentrations of only 0.07 to 0.18 mg/m3 were observed, indicating that the vacuum 

collection systems on these bolters were effective in capturing bolter-generated dust. NIOSH 

personnel measured the vacuum pressure at each drill head multiple times during each shift. All 

of the measured vacuum readings provided in Table 2 exceeded the minimum vacuum pressure 

required by MSHA. 

Quartz Results 

A gravimetric sampling package was placed in the immediate miner return and collected dust 

samples that were analyzed for quartz content. The quartz analysis provided the mass of quartz 

on each filter, which allowed for calculation of the quartz percent and concentration. In order to 

address the differences in production rates for the various cuts, the quartz concentrations from 

each cut were normalized based upon the average number of shuttle cars per min of sampling 

time. These values were used to calculate an average quartz concentration for the scrubber-off 

and scrubber-on test conditions. Table 6 summarizes the average quartz data from samples 

collected at each of the three mines. 
13

The percent quartz found in the samples with the scrubber on showed mixed trends in that the 

percent was higher in Mines A (0.3%) and C (2.3%) and lower in Mine B (-0.9%). However, 

operation of the scrubber lowered the quartz mass and adjusted concentrations in all three mines. 

Results from Mines A and B were very similar with reductions in mass and concentration greater 

than 80%, which were statistically significant with the Wilcoxon test. At Mine C, the highest 

quartz percentages of all mines were observed. However, the reductions in mass (55%) and 

concentration (14%) with the scrubber on were not as great at Mine C and these differences were 

not statistically significant. 

Table 6. Quartz content in the immediate miner return with the scrubber off and on 

Quartz content in gravimetric samples Mine A Mine B Mine C

Quartz percent with scrubber off 6.8 3.7 14.3

Quartz percent with scrubber on 7.1 2.8 16.6

Quartz mass with scrubber off, μg 202 38 387

Quartz mass with scrubber on, μg 31 7 175

Reduction in mass with scrubber on 86% 82% 55%

Adjusted quartz concentration with scrubber off, μg/m31,282 255 1,602

Adjusted quartz concentration with scrubber on, μg/m3177 45 1,385

Calculated p-value 0.0022*0.0022*0.3939

Reduction in quartz concentration with scrubber on 86% 82% 14%

* Statistically significant difference. 

Summary 

Respirable dust samples were collected from continuous miner sections at three underground 

coal mines to evaluate the impact of operating a flooded-bed scrubber in 20-ft cuts with exhaust 

face ventilation and an extended curtain setback. The dust levels observed with the scrubber 

operating were compared to dust levels measured in 20-ft cuts without a scrubber operating and 

the exhaust ventilation curtain advanced to within 20 ft of the face. Area dust sampling with 

gravimetric and light-scattering instrumentation was conducted in the intake and return airways 

of the continuous miner, on the continuous miner, in the shuttle car cabs, and at the roof bolting 

machine. A personal dust monitor (PDM) was worn by the continuous miner operator to measure 

the dust exposure at the operator’s position. Time study information was collected by NIOSH 

researchers so that the dust data could be analyzed on a cut-by-cut basis, with extended 

downtimes removed from the calculations. MSHA personnel participated in the dust surveys and 

monitored operating parameters specified in the individual mine ventilation plans to ensure that 

minimum plan parameters were present during each survey. Three days of sampling were 

conducted at each of the mine sites. When sufficient data were available, the Wilcoxon twosample test (α = 0.05) was used to determine the statistical significance of differences in mean 

dust levels between the two test conditions. 
14

Analysis of the data from the three surveys supports the following findings: 

 Intake dust concentrations to the continuous miner faces were well controlled at all 

three mines and averaged just under 0.1 mg/m3.

 There were no statistically significant differences in dust concentrations between test 

conditions for the continuous miner operator at each mine, with a maximum 

difference in average dust concentration of only 0.09 mg/m3.

 With the scrubber operating, dust concentrations at the right rear corner of the miner 

were 22% lower at Mine A and 31% lower at Mine B. However, these reductions 

were not statistically significant. 

 Dust concentrations in the return immediately downwind of the miner were at least 

40% lower when the scrubber was operating. At Mines A and B, statistically 

significant reductions of 91% and 86% were observed, respectively. 

 A sampling package was added in the section return for the surveys conducted at 

Mines B and C. A statistically significant reduction of 85% was observed in section 

return dust concentrations at Mine B with the scrubber operating, and a reduction of 

29% was observed at Mine C.

 There were no statistically significant differences in dust concentrations measured at 

the shuttle cars between test conditions. The maximum difference measured at the 

shuttle cars between test conditions at any of the mines was 0.08 mg/m3.

 When the roof bolter was operating downwind of the continuous miner, intake dust 

concentrations to the bolter were reduced by 85% at Mine B and 34% at Mine C 

when the scrubber was operated. Limited data for these conditions prevented 

statistical analysis. At Mine A, the bolter was only downwind of the miner one time 

during the survey, so no comparison could be made. 

 Quartz mass and concentrations in the continuous miner return were reduced at all 

three mines when the scrubber was operating. At Mines A and B, statistically 

significant reductions of over 80% were measured. 

Results from the surveys at these three mines show that there were no statistically significant 

differences in dust concentrations at the continuous miner operator, the right rear corner of the 

miner, or in the shuttle car cabs when the flooded-bed scrubber was operated. However, 

statistically significant reductions in respirable and quartz dust levels in the miner and section 

return were measured during the surveys. As a result, dust exposures for personnel located 

downwind of the miner would be reduced through operation of the flooded-bed scrubber, with no 

adverse impact to workers located in the face area. Therefore, from a dust control perspective, 

operation of the flooded-bed scrubber would be beneficial. 

It should be noted that these results were achieved with the 30-layer scrubber filter panels 

being cleaned after each 20-ft cut, which was found to be necessary in order to maintain scrubber 

airflows at the required levels. To illustrate, airflow measurements were taken in the scrubber 

after completion of one 20-ft cut during which the scrubber was operated but before the filter 

panel had been cleaned. On three different occasions during the survey at Mine B, measurements 

were taken after completion of one cut with the scrubber operating. An average drop in scrubber 

airflow of 2,000 cfm was observed, which represented an average reduction of 29% when 
15

compared to the quantities available at the beginning of each of these cuts. At Mine C, a scrubber 

airflow reading was taken after one cut and before the filter panel was cleaned. A drop in airflow 

of 1,500 cfm was measured, which represented a reduction of 35%. These numbers emphasize 

the critical need to clean the 30-layer filter panel after each cut. A previous research study by 

Potts et al. [NIOSH 2011] recommended the cleaning of scrubber filter panels after every 40 ft of 

advance when using a 20-layer filter. In addition, the minimum operating parameters specified in 

the ventilation plans were present prior to the start of each cut and contributed to the results 

observed during these surveys. 

Acknowledgements 

The authors would like to acknowledge the invaluable access provided by Alpha Natural 

Resources to its mine sites and the assistance provided by the mining personnel at each of the 

mines. Also, the authors appreciate the effort and assistance provided by numerous MSHA 

personnel through input into the test protocol, completion of baseline surveys at each MMU, 

quartz analysis of filters at MSHA’s Pittsburgh laboratory, and for their efforts in verifying plan 

parameters and providing additional assistance to NIOSH personnel during sampling at each of 

the mines. The authors express appreciation to Linda McWilliams of NIOSH for her guidance 

and assistance in completing the statistical analysis of the dust data. Finally, the authors would 

like to acknowledge the significant contributions of NIOSH technicians Jason Driscoll and Milan 

Yekich for their assistance during the mine surveys and in preparing the dust sampling 

equipment for each of these surveys. 
16

References 

CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office 

of the Federal Register. 

Cohen R, Velho V [2002]. Update on respiratory disease from coal mine and silica dust. Clinics 

in Chest Medicine 23(4):811–826.

Hartmann HL [1973]. Mine atmospheres and gases. In: Cummins AB, Given IA eds. SME 

Mining Engineering Handbook. Vol. 1. Baltimore: Port City Press, pp. 16-2–16-4. 

Jayaraman NI, Babbitt C, and O’Green J [1988]. Ventilation and dust control techniques for 

personnel downwind of continuous miner. SME Transactions, Vol. 284, Littleton, CO: Society 

for Mining, Metallurgy, and Exploration, Inc., pp. 1823–1826.

Jayaraman NI, Volkwein JC, Kissell FN [1990]. Update on continuous miner dust scrubber 

applications. Mining Engineering 42(3):281–284. 

MSHA [1989]. Determining the quartz content of respirable dust by FTIR. Arlington, VA: U.S. 

Department of Labor, Mine Safety and Health Administration, Information Report 1169. 

MSHA [2012a]. Coal mine health inspection procedures. Arlington, VA: U.S. Department of 

Labor, Mine Safety and Health Administration, MSHA Handbook Series, Handbook Number: 

PH89-V-1(23). 

MSHA [2012b]. Procedures for evaluation of requests to make extended cuts with remote 

controlled continuous mining machines. Arlington, VA: U.S. Department of Labor, Mine Safety 

and Health Administration, Procedure Instruction Letter NO. I12-V-11. 

NIOSH [2011]. Evaluation of face dust concentrations at mines using deep-cutting practices. By: 

Potts JD, Reed WR, Colinet JF. Pittsburgh, PA: U.S. Department of Health and Human Services, 

National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2011-

131, RI 9680. 

Organiscak JA, Beck TW [2010]. Continuous miner spray considerations for optimizing 

scrubber performance in exhaust ventilation systems. Mining Engineering 62(10): 41–46.

Taylor CD, Rider JP, Thimons ED [1996]. Changes in face methane concentrations using high 

capacity scrubbers with exhausting and blowing ventilation. Littleton, CO: Society for Mining, 

Metallurgy, and Exploration, Pre-print 96-167. 

Thermo Scientific [2008]. Model pDR-1000AN/1200 instruction manual. Franklin, MA: Thermo 

Scientific, pp. 35–36.
17

USBM [1990]. Laboratory evaluation of quartz dust capture of irrigated-filter collection systems 

for continuous miners. By: Colinet JF, McClelland JJ, Erhard LA, Jankowski RA. Pittsburgh, 

PA: U.S. Department of the Interior, Bureau of Mines, RI 9313. 

Webster JB, Chiaretta CW, Behling J [1990]. Dust control in high productivity mines. Littleton, 

CO: Society for Mining, Metallurgy, and Exploration, Pre-print 90-82. 

19

Appendix A: Dust Survey at Mine A 

Introduction 

The purpose of this study was to compare face dust levels for two cutting conditions: (1) a 

standard 20-ft cut arrangement with no scrubber and a maximum 20-ft exhaust curtain setback, 

and (2) a 20-ft cut with exhaust curtain setbacks of up to 40 ft and operation of a flooded-bed 

scrubber. A three-day survey was conducted, alternating between both conditions on a cut-by-cut 

basis. This strategy results in minimizing the effects of changes in operating conditions from day 

to day. For operating conditions known to affect face dust concentrations—including face 

airflow and the number, orientation, type, location, and pressure of external water sprays—

attempts were made to maintain these conditions in a consistent state throughout the study. 

Site Description 

This dust survey was conducted on the left side of a nine-entry super section, as shown in 

Figure A-1. Coal was mined using a Joy 14CM15 continuous mining machine and two Joy 

standard cab (off-curtain) shuttle cars. During the survey, entries 1 through 4 were developed 

with No. 3 and No. 4 entries used for intake air and No. 1 and No. 2 entries used as returns. The 

section beltline and feeder/breaker were located in No. 5 entry on a neutral air split. Mining 

height averaged 62 in, including the extraction of approximately 14 in of top rock. The pillars 

were on 60-ft centers with 20-ft entry widths, resulting in a 40-ft X 40-ft pillar dimension. The 

continuous miner faces were ventilated using exhausting curtain. Blowing or exhausting curtain 

can be used to ventilate the bolter faces and the mine uses a dual-head, Fletcher Roof Ranger II 

to install the bolts. 

Figure A-1. Schematic of section sampled at Mine A. 
20

Ventilation Plan Parameters 

To assure normal operating conditions, the mine’s adherence to the dust control parameters 

stipulated in the ventilation plan was monitored and corrective actions were taken when 

parameters fell outside required limits (less than the minimum specified or exceeding 120% of 

the minimum specified). The ventilation plan parameters used on this section for this study 

included the following minimum ventilation quantities: 15,000 cfm in the last open crosscut, 

7,000 cfm at the face-side end of the brattice curtain on the continuous miner faces, 6,400 cfm 

scrubber airflow, and 4,000 cfm at the face-side end of the curtain on the bolter faces. A 30-layer 

filter panel was used in the scrubber. Maximum curtain setbacks were 20 ft for the nonscrubber 

cuts and 40 ft for the scrubber cuts. The continuous miner was equipped with 51 water sprays 

(3-5 Spraying System hollow cone), all of which had to be operational at the start of the cut and 

at least 40 had to be operational at all times. The minimum spray pressure was 65 psi. 

Of the plan parameters monitored for the survey, curtain airflow on the continuous miner 

faces was the most difficult to maintain within 120% of the specified minimum level of 

7,000 cfm. Based on this minimum, airflows between 7,000 and 8,400 cfm were targeted. The 

average curtain airflow during the survey was 8,300 cfm (SD = 670). At times it was difficult to 

keep airflows below 8,400 cfm, with 6 of 14 cuts being greater than this quantity; however, the 

airflows exhibited a fairly tight range of 2,200 cfm. The targeted scrubber airflow was between 

6,400 and 7,680 cfm. Measured scrubber airflows averaged 6,400 (SD = 270), with only one 

reading falling outside the targeted range. The targeted curtain airflow on the bolting faces was 

between 4,000 and 4,800 cfm. Disregarding bolting activities in Room No. 9, which occurred in 

the last open crosscut, the average curtain airflow on the bolting faces was 4,400 cfm (SD = 370) 

and airflows on only 2 of 13 bolting faces fell outside of the targeted range. Airflow 

measurements in the last open crosscut, as well as water spray pressures, conformed well to the 

ventilation plan used during the survey. In general, mine personnel were able to adhere to the 

temporary ventilation plan approved for this dust survey. 

Results

Table A-1 provides a summary of respirable dust concentrations around the mining machine, 

including miner intake, return, right rear corner, and operator locations, for each of the 14 cuts 

analyzed during the survey. Detailed data for each miner cut are provided in Table A-5 near the 

end of this appendix. The dual numbering system for cuts represents the shift number followed 

by the number of the cut extracted during that shift. Dust attributable to mining activity was 

calculated by subtracting the intake dust concentration from the measured dust concentration at 

each of the other sampling locations. The dust concentrations have been adjusted based on the 

measured productivity and airflow for each cut. The number of cars loaded per min was used as 

the measure of productivity and all dust levels were normalized to the average productivity 

observed throughout the study of 0.37 cars per min. For example, productivity during Cut No. 

1-1 was 0.34 cars per min. Therefore, dust concentrations measured for this cut were normalized 

by multiplying by a correction factor of 1.09 (0.37/0.34) to adjust for the lower-than-average 

productivity. Likewise, average airflow during the survey was divided into the actual airflow 

measured for each cut to calculate the correction factor for normalizing the dust concentrations 

for differences in face airflow. 
21

Table A-1. Summary of adjusted respirable dust concentrations for the continuous miner 

a. Scrubber-off

Cut

No.

Cut

location

Scrubber

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs*/

min

CM

*

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC*

dust,

mg/m3

CM

return

dust,

mg/m3

1-1 4-heading 0 8,200 8:20 8:54 0.33 0.00 0.17 0.90 25.31

1-3 3-left 0 9,600 10:11 10:31 0.50 0.03 1.19 2.02 12.94

1-5 1-heading 0 8,600 12:18 12:42 0.34 0.01 0.21 0.10 28.15

2-2 4-heading 0 7,400 9:04 9:29 0.36 0.02 0.21 0.44 20.36

2-5 2-left 0 9,000 12:58 13:14 0.43 0.19 0.09 0.05 20.11

3-1 2-heading 0 8,000 8:21 8:38 0.30 0.11 0.00 1.67 34.97

3-3 1-left 0 7,700 11:47 12:09 0.41 0.23 0.20 3.69 25.21

* Abbreviations: SC, shuttle car; CM, continuous miner; RRC, right rear corner. 

b. Scrubber-on

Cut

No.

Cut

location

Scrubber

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs/

min

CM

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC

dust,

mg/m3

CM

return

dust,

mg/m3

1-2 3-heading 5,900 7,400 9:20 9:47 0.34 0.08 0.22 0.83 2.55

1-4 4-heading 6,600 7,700 11:14 11:45 0.41 0.01 0.39 0.44 2.03

2-1 1-heading 6,400 8,100 7:38 8:13 0.25 0.12 0.35 1.49 2.69

2-3 3-left 6,300 8,800 9:59 10:18 0.37 0.15 0.19 0.39 1.70

2-4 3-heading 6,700 8,800 11:32 12:25 0.34 1.05†0.21 0.04 1.58

3-2 2-heading 6,500 7,900 9:44 11:14 0.44 0.02 0.00 0.64 1.75

3-4 3-heading 6,600 9,000 13:01 13:32 0.29 0.05 0.48 3.29 2.02

† Not included in calculation of average intake concentration. 

c. Impact of scrubber performance 

Test conditions and statistics

CM 

intake

CM 

operator

CM

RRC

CM 

return

Average concentration with scrubber off, mg/m30.08 0.30 1.27 23.86

Average concentration with scrubber on, mg/m30.07 0.26 1.02 2.05

Calculated p-value for cut data - 0.3310 0.6439 0.0005‡

Percent reduction in concentration with scrubber on - 13% 20% 91%

‡

Statistically significant difference 

The intake dust level in Cut No. 2-4 was atypically high and was attributed to the intake 

pumps not properly positioned in the primary intake during this cut. Due to low dust levels 

(0.04 mg/m3) at the RRC of the mining machine during Cut No. 2-4, intake dust levels were 

assumed to be 0.00 mg/m

3

for this cut. Average respirable dust concentrations were 91% lower 

in the return when using the scrubber, decreasing from 23.86 mg/m3 (scrubber-off) to 2.05 mg/m3

(scrubber-on). This difference was statistically significant when using the Wilcoxon two-sample 

test, with α = 0.05. Average dust concentrations on the RRC of the mining machine averaged 

1.01 mg/m3 when using the scrubber versus 1.29 mg/m3 when not using the scrubber; however, 

this difference was not statistically significant. 
22

If continuously exposed to the average return dust concentration measured with the scrubber 

off (23.86 mg/m3) for only 30 min, a mine worker’s respirable dust exposure would exceed the 

permissible exposure limit (PEL) of 2.0 mg/m3(assumes conversion of the resulting 

concentration to an MRE equivalent). Consequently, use of the flooded-bed scrubber is 

recommended because a statistically significant reduction in return dust levels of over 90% was 

observed when the scrubber was operated. 

Table A-1 also shows personal dust monitor (PDM) data collected at the continuous miner 

operator occupation. These data are corrected for intake dust concentrations as well as 

productivity. There is no statiscally significant difference in miner operator exposures when 

comparing the scrubber-on condition to the scrubber-off condition, averaging 0.26 mg/m3

and 

0.30 mg/m3, respectively. The data collected around the continuous miner and in the shuttle car 

cabs indicate that the dust levels at the face were controlled when adhering to the requirements 

stipulated in the ventilation plan used during testing, regardless of scrubber use. 

Table A-2 shows the average of the shuttle car dust data collected during the study for each 

cut while the cars were being loaded at the face. The individual dust concentrations measured for 

each shuttle car loading period with the scrubber off and on are provided at the end of the 

appendix in Tables A-6 and A-7, respectively. These data isolated the shuttle car dust exposures 

when located at the face during miner cutting and loading activities and do not include exposures 

when in transit or at the feeder/breaker. Intake dust concentrations were subtracted from shuttle 

car concentrations to arrive at adjusted shuttle car concentrations resulting from face activities. 

Shuttle car dust concentrations when loading at the face averaged 0.27 mg/m3 with the scrubber 

off, versus 0.28 mg/m3 with the scrubber on; however, this difference was not statistically 

significant (p-value = 0.9272). 

Table A-2. Summary of adjusted respirable dust concentrations in the shuttle car cabs 

Cut number 

with 

scrubber off

Cut location 

with scrubber 

off

SC*dust with 

scrubber off, 

mg/m3

Cut number 

with 

scrubber on

Cut location 

with scrubber 

on

SC dust with 

scrubber on, 

mg/m3

1-1 4-heading 0.52 1-2 3-Heading 0.15

1-3 3-left 0.37 1-4 4-Heading 0.64

1-5 1-heading 0.21 2-1 1-Heading 0.29

2-2 4-heading 0.34 2-3 3-Left 0.23

2-5 2-left 0.14 2-4 3-Heading 0.53

3-1 2-heading 0.03 3-2 2-Heading 0.09

3-3 1-left 0.29 3-4 3-Heading 0.01

Average - 0.27 - - 0.28

* Abbreviation: SC, shuttle car. 

Table A-3 shows respirable dust concentrations in the vicinity of the return-side bolter 

operator and in the intake air split for the bolting machine. The intake levels were subtracted 

from the return-side levels to estimate bolter-generated dust. The bolting machine generated very 

little dust (approximately 0.10 mg/m3

) when proper face ventilation was maintained (in this case 

4,000 cfm) and the dust collector equipment was in good working order. The dust collector 

suction pressures averaged 15.7 in Hg (SD = 0.8) on the return-side of the bolter and 12.5 in Hg 

(SD = 0.5) on the intake-side. However, significant exposures to respirable dust can occur when 
23

the bolter machine operates downwind of the continuous mining machine. Bolter place No. 1-4 

was bolted downwind of mining operations when the scrubber was in use. It was noted in the 

time study data that place No. 1-4 lost ventilating air from 11:27 to 11:32, causing dust levels to 

dramatically spike. Consequently, this time segment was removed from the calculation of dust 

levels. For place No. 1-4, respirable dust concentrations ranged from 3.29 mg/m3

(intake) to 

3.62 mg/m3(return-side operator) in the vicinity of the bolter when operating downwind of the 

miner under the scrubber-on condition. As shown in the miner return, these dust levels could be 

nearly a magnitude of order higher during scrubber-off conditions. 

Table A-3. Summary of roof bolter dust concentrations 

Place

No.

Face

location

Face 

airflow,

cfm

Position of 

RB* with 

respect to 

CM*

Start

time

End 

time

RB

intake 

dust,

mg/m3

RB

operator 

dust,

mg/m3

RB

generated 

dust,

mg/m3

1-1 2-heading 4,400 upwind 7:53 8:08 0.08 0.01 0.00

1-2 4-heading 5,000 upwind 9:17 9:36 0.03 0.01 0.00

1-3 3-left 4,100 upwind 10:45 11:03 1.98†0.22 void†

1-4 3-heading 4,400 downwind‡11:29 11:44 3.29 3.62 0.33

1-5 4-heading 4,800 upwind 12:05 12:19 0.01 0.06 0.05

2-1 2-heading 4,300 upwind 7:12 7:30 0.05 0.31 0.26

2-2 1-heading 4,500 upwind 8:32 8:45 0.06 0.10 0.04

2-3 4-heading 4,100 upwind 9:50 10:04 0.05 0.12 0.07

2-4 3-left 10,000 upwind 10:25 10:45 0.05 0.10 0.05

2-5 3-heading 4,100 upwind 12:44 13:03 0.01 0.16 0.15

3-1 1-heading 4,100 upwind 7:21 7:28 0.05 0.09 0.04

3-2 2-heading 4,100 upwind 8:55 9:12 0.02 0.11 0.09

3-3 2-heading 4,000 upwind 11:36 11:54 0.05 0.15 0.10

3-4 1-left 5,100 upwind 12:30 12:47 0.00 0.08 0.07

Avg - - - - - - - 0.10

* Abbreviations: RB, roof bolter; CM, continuous miner. 

†

 Problem with intake sampler position voided dust reading and calculation of bolter-generated dust. 

‡

Scrubber operating on miner while bolter was downwind. 

Table A-4 displays the mass, percentage, and concentration of miner-generated respirable 

quartz for samples collected in the miner return for both the scrubber-off and scrubber-on 

conditions. The percentage of quartz in miner-generated dust was not affected by operation of 

the scrubber and averaged approximately 7%. However, use of the scrubber did reduce the 

measured mass of miner-generated quartz dust by 85% from 202 μg to 31 μg. Due to the 

difference in production between the test conditions, the quartz concentrations were normalized 

based upon the average number of shuttle cars per min of sampling time (0.24 cars/min). The 

adjusted quartz concentration showed a statistically significant difference with the Wilcoxon test 

and a reduction of 86% when the scrubber was operating. Based upon the quartz levels measured 

downwind of the miner with the scrubber off, an exposure to 1,282 μg/m3 of quartz for only 

30 min would result in a miner’s exposure that exceeds 100 μg/m3

(assumes conversion to an 

MRE equivalent). Consequently, operation of the scrubber is recommended in order to 

significantly reduce the quartz exposure for workers located downwind of the miner. 
24

Table A-4. Respirable quartz levels in the continuous miner return 

a. Scrubber-off

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc,

μg/m3

1 567952 101 3.736 17.60 266 7.1 1,316.8 0.29 1,089.8

1 566872 101 3.374 231 6.8 1,143.6 0.29 946.4

2 566870 58 2.796 23.16 199 7.1 1,715.5 0.28 1,470.5

2 567944 58 2.578 175 6.8 1,508.6 0.28 1,293.1

3 567949 61 2.960 21.36 183 6.2 1,500.0 0.23 1,565.2

3 566875 61 2.252 155 6.9 1,270.5 0.23 1,325.7

b. Scrubber-on

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc,

μg/m3

1 566890 80 0.633 3.93 37 5.9 231.3 0.24 231.3

1 566880 80 0.624 38 6.1 237.5 0.24 237.5

2 566883 126 0.384 1.49 31 8.1 123.0 0.21 140.6

2 566881 126 0.369 32 8.7 127.0 0.21 145.1

3 566863 86 0.358 1.93 25 7.0 145.4 0.20 174.4

3 566871 86 0.307 20 6.5 116.3 0.20 139.5

c. Impact of scrubber performance 

Test conditions and statistics

Quartz mass,

μg

Quartz conc,

μg/m3

Adjusted 

quartz conc,

μg/m3

Average quartz content with scrubber off 202 1,409.2 1,281.8

Average quartz content with scrubber on 31 163.4 178.1

Calculated p-value - - 0.0022*

Percent reduction in quartz content with scrubber on 85% 88% 86%

* Statistically significant difference. 

Conclusions 

The purpose of this study was to compare face dust levels for two cutting conditions: (1) a 

standard 20-ft cut advance without the scrubber operating and a maximum 20-ft curtain setback 

and (2) a 20-ft cut advance with the scrubber operating and a curtain setback of up to 40 ft. The 

mine’s adherence to the dust control parameters stipulated in the temporary ventilation plan were 

monitored by MSHA personnel, and corrective actions were taken when parameters fell outside 

required limits (less than the minimum specified or exceeding 120% of the minimum specified). 
25

In general, mine personnel were able to adhere to the levels specified in the temporary 

ventilation plan. A summary of the results follows: 

 Average respirable dust concentrations were 91% lower in the return when using the 

scrubber, decreasing from 23.86 mg/m3 to 2.05 mg/m3. This difference is statistically 

significant. 

 Dust concentrations on the RRC of the mining machine averaged 1.02 mg/m3 when

using the scrubber versus 1.27 mg/m3 when not using the scrubber. However, this 

difference is not statistically significant. 

 There is no statistically significant difference in miner operator exposures when 

comparing the scrubber-on condition to the scrubber-off condition, averaging 

0.26 mg/m3

and 0.30 mg/m3, respectively. 

 Shuttle car dust concentrations when loading at the face averaged 0.28 mg/m3 with 

the scrubber versus 0.27 mg/m3 without the scrubber. However, this difference is not 

statistically significant. 

 The bolting machine generated very little dust (approximately 0.10 mg/m3) when 

proper face ventilation was maintained (in this case 4,000 cfm), and the dust collector 

was in good working order. 

 For one bolting cycle, respirable dust concentrations ranged from 3.29 mg/m3

to 

3.62 mg/m3in the vicinity of the bolter when operating downwind of the miner under 

the scrubber-on condition. 

 The percentage of quartz in miner-generated dust was not affected by operation of the 

scrubber and averaged approximately 7%. However, use of the scrubber reduced the 

amount of miner-generated quartz dust by 86% from 1,282 μg/m3to 177 μg/m3, and 

this difference is statistically significant. 

The data collected for this study indicate that the mine was able to control dust levels in the 

vicinity of the mining machine, regardless of scrubber use, when adhering to the requirements 

stipulated in the temporary ventilation plan used during this survey. However, operation of the 

scrubber resulted in statistically significant reductions of respirable coal and quartz dust 

downwind of the miner. Without the scrubber operating, a short exposure downwind of the 

mining machine of 30 min (assumes average dust concentrations measured during the study and 

converted to an MRE equivalent) would result in an overexposure to respirable coal mine dust 

(>2.0 mg/m3) and respirable quartz dust (>100 μg/m3

).

27

Table A-5. Continuous-miner-generated dust concentrations (mg/m3

) for each cut 

Cut

No.

Cut

location

Face

airflow,

cfm

FBS*

airflow,

cfm

CM*

start 

time

CM

end 

time

Total

cut 

time,

min

No.

SC*

SCs/

min

CM

int

dust 

conc

CM

oper

dust 

conc

CM

RRC*

dust 

conc

CM

ret 

dust 

conc

Adj†

CM

oper

dust 

conc

Adj†

CM

RRC

dust 

conc

Adj†

CM

ret

dust 

conc

1-1 4-heading 8,200 0 8:20 8:54 34 11 0.33 0.00 0.16 0.81 22.85 0.17 0.91 25.62

1-2 3-heading 7,400 5,900 9:20 9:47 27 9 0.34 0.08 0.29 0.94 2.71 0.22 0.94 2.86

1-3 3-left 9,600 0 10:11 10:31 20 10 0.50 0.03 1.64 2.39 15.15 1.19 1.74 11.19

1-4 4-heading 7,700 6,600 11:14

11:33

11:26

11:45

24 10 0.41 0.01 0.44 0.53 2.44 0.39 0.47 2.19

1-5 1-heading 8,600 0 12:18 12:42 24 8 0.34 0.01 0.20 0.10 24.98 0.21 0.10 27.17

2-1 1-heading 8,100 6,400 7:38 8:13 35 9 0.25 0.12 0.36 1.15 1.98 0.35 1.53 2.76

2-2 4-heading 7,400 0 9:04 9:29 25 9 0.36 0.02 0.23 0.50 22.24 0.21 0.50 22.84

2-3 3-left 8,800 6,300 9:59 10:18 19 7 0.37 0.15 0.34 0.52 1.75 0.19 0.37 1.60

2-4 3-heading 8,800 6,700 11:32

12:06

11:41

12:25

28 10 0.34 1.05 0.19 0.04 1.37 0.21 0.04 1.49

2-5 2-left 9,000 0 12:58 13:14 16 7 0.43 0.19 0.29 0.25 21.75 0.09 0.05 18.55

3-1 2-heading 8,000 0 8:21 8:38 17 5 0.30 0.11 0.00 1.51 29.53 0.00 1.73 36.29

3-2 2-heading 7,900 6,500 9:44

11:10

10:00

11:14

20 9 0.44 0.02 0.00 0.82 2.21 0.00 0.67 1.84

3-3 1-left 7,700 0 11:47 12:09 22 9 0.41 0.23 0.46 4.64 30.34 0.20 3.98 27.17

3-4 3-heading 9,000 6,600 13:01 13:32 31 8 0.26 0.05 0.43 2.43 1.51 0.48 3.03 1.86

Avg - 8,350 6,430 - - - - 0.37 - - - - - - -

* Abbreviations: FBS, flooded-bed scrubber; CM, continuous miner; SC, shuttle car; RRC, right rear corner. 

† Adjusted dust concentrations have intake levels subtracted and are normalized for differences in face airflow and production (SCs/min). 
28

Table A-6. Shuttle car loading times and dust concentrations with the scrubber off 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-1 1 8:20:19 8:21:29 0.00 0.15

1-1 2 8:22:24 8:23:19 0.00 0.11

1-1 1 8:25:48 8:26:51 0.02 0.33

1-1 1 8:29:03 8:30:13 0.00 0.45

1-1 2 8:35:28 8:36:45 0.00 0.18

1-1 1 8:37:16 8:38:55 0.00 1.16

1-1 1 8:43:00 8:44:21 0.00 0.24

1-1 1 8:46:24 8:47:23 0.00 0.32

1-1 2 8:47:48 8:49:13 0.01 0.89

1-1 1 8:50:20 8:51:49 0.00 1.16

1-1 2 8:52:27 8:53:53 0.00 0.75

Cut avg - - - - 0.52

1-3 1 10:11:05 10:12:16 0.00 0.26

1-3 2 10:13:00 10:14:06 0.00 0.53

1-3 1 10:14:51 10:15:41 0.01 0.25

1-3 2 10:17:16 10:18:10 0.00 0.81

1-3 1 10:19:50 10:21:06 0.24 0.20

1-3 2 10:21:54 10:22:46 0.01 0.52

1-3 1 10:23:27 10:24:41 0.00 0.22

1-3 2 10:26:05 10:27:16 0.00 0.36

1-3 1 10:27:58 10:29:21 0.00 0.27

1-3 2 10:30:35 10:31:11 0.00 0.30

Cut avg - - - - 0.37

1-5 2 12:18:05 12:19:38 0.00 0.13

1-5 1 12:20:33 12:21:33 0.01 0.28

1-5 2 12:22:40 12:23:30 0.01 0.24

1-5 1 12:25:00 12:25:57 0.01 0.37

1-5 2 12:27:14 12:28:48 0.00 0.29

1-5 1 12:32:44 12:33:58 0.01 0.18

1-5 2 12:36:18 12:37:58 0.00 0.10

1-5 1 12:38:59 12:41:40 0.02 0.12

Cut avg - - - - 0.21

2-2 1 9:03:46 9:05:27 0.12 0.00

2-2 2 9:05:57 9:07:29 0.07 0.02

2-2 1 9:07:54 9:09:11 0.01 0.44

2-2 2 9:10:44 9:11:54 0.00 0.73

2-2 1 9:13:06 9:14:41 0.00 0.31

2-2 2 9:15:54 9:17:13 0.02 0.11

2-2 1 9:21:24 9:22:44 0.00 0.98

2-2 2 9:23:01 9:25:39 0.01 0.24

2-2 1 9:26:57 9:28:38 0.00 0.24

Cut avg - - - - 0.34

* Shuttle car (SC) dust levels shown have the intake dust subtracted; if less than zero, zero is shown. 
29

Table A-6. Shuttle car loading times and dust concentrations with the scrubber off 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

2-5 1 12:57:36 12:58:38 0.16 0.01

2-5 2 12:59:13 12:59:59 0.24 0.59

2-5 1 13:01:17 13:02:00 0.21 0.01

2-5 2 13:03:33 13:04:35 0.18 0.05

2-5 1 13:06:10 13:07:39 0.54 0.00

2-5 2 13:10:18 13:11:24 0.07 0.07

2-5 1 13:11:56 13:13:56 0.06 0.22

Cut avg - - - - 0.14

3-1 1 8:21:00 8:22:26 0.12 0.00

3-1 2 8:24:09 8:25:01 0.12 0.03

3-1 1 8:26:15 8:27:16 0.11 0.04

3-1 2 8:28:44 8:31:06 0.11 0.05

3-1 1 8:34:42 8:37:37 0.10 0.00

Cut avg - - - - 0.02

3-3 2 11:46:55 11:47:58 0.11 0.32

3-3 1 11:48:58 11:49:49 0.16 0.00

3-3 2 11:51:53 11:52:48 0.46 0.28

3-3 1 11:53:45 11:54:39 0.59 0.14

3-3 2 11:56:10 11:57:49 0.54 0.00

3-3 1 11:59:17 12:00:30 0.16 0.94

3-3 2 12:01:30 12:02:45 0.08 0.26

3-3 1 12:03:48 12:05:16 0.05 0.36

3-3 2 12:07:07 12:08:59 0.12 0.29

Cut avg - - - - 0.29

Survey

avg

- - - - 0.27

*

Shuttle car (SC) dust levels shown have the intake dust subtracted; if less than zero, zero is shown. 
30

Table A-7. Shuttle car loading times and dust concentrations with the scrubber on 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-2 1 9:20:01 9:21:42 0.05 0.09

1-2 2 9:22:38 9:23:50 0.12 0.09

1-2 1 9:25:08 9:26:40 0.06 0.48

1-2 2 9:28:37 9:29:52 0.15 0.10

1-2 1 9:31:43 9:33:53 0.21 0.00

1-2 2 9:36:40 9:38:20 0.09 0.01

1-2 1 9:40:08 9:41:17 0.00 0.41

1-2 2 9:42:14 9:44:01 0.00 0.10

1-2 1 9:45:05 9:46:32 0.00 0.11

Cut avg - - - - 0.15

1-4 1 11:14:13 11:15:28 0.00 0.07

1-4 2 11:16:06 11:16:44 0.00 2.94

1-4 1 11:18:17 11:19:23 0.00 0.29

1-4 2 11:20:05 11:21:10 0.00 2.22

1-4 1 11:24:55 11:25:55 0.00 0.13

1-4 2 11:32:48 11:33:35 0.00 0.19

1-4 1 11:34:18 11:35:22 0.00 0.28

1-4 2 11:36:38 11:38:15 0.00 0.17

1-4 1 11:40:25 11:42:15 0.00 0.10

1-4 2 11:43:11 11:45:21 0.00 0.05

Cut avg - - - - 0.64

2-1 2 7:37:50 7:39:19 0.16 0.03

2-1 2 7:47:38 7:48:28 0.21 0.66

2-1 1 7:50:18 7:51:28 0.25 0.32

2-1 2 7:53:06 7:54:16 0.11 0.00

2-1 1 7:56:24 7:57:30 0.10 0.07

2-1 2 7:58:52 7:59:52 0.09 0.06

2-1 1 8:03:30 8:04:27 0.04 0.52

2-1 2 8:08:27 8:09:49 0.06 0.39

2-1 1 8:11:40 8:13:22 0.03 0.53

Cut avg - - - - 0.29

2-3 1 9:59:14 10:00:10 0.30 0.51

2-3 2 10:01:16 10:02:00 0.39 0.16

2-3 1 10:03:04 10:03:54 0.05 0.23

2-3 2 10:06:30 10:07:20 0.01 0.20

2-3 1 10:08:40 10:09:25 0.02 0.42

2-3 2 10:12:44 10:13:50 0.09 0.00

2-3 1 10:16:55 10:18:07 0.07 0.11

Cut avg - - - - 0.23

*

Shuttle car (SC) dust levels shown have the intake dust subtracted; if less than zero, zero is shown. 
31

Table A-7. Shuttle car loading times and dust concentrations with the scrubber on 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

2-4 2 11:31:30 11:32:55 0.00 0.19

2-4 1 11:33:57 11:35:32 0.00 0.51

2-4 2 11:37:39 11:39:02 0.00 0.65

2-4 1 11:39:41 11:40:59 0.00 0.64

2-4 2 12:05:34 12:09:02 0.00 0.33

2-4 1 12:09:50 12:11:18 0.00 0.64

2-4 2 12:13:03 12:15:01 0.00 1.33

2-4 1 12:18:20 12:19:52 0.00 0.20

2-4 2 12:20:45 12:22:36 0.00 0.48

2-4 1 12:23:25 12:25:13 0.00 0.28

Cut avg - - - - 0.53

3-2 2 9:43:46 9:44:32 0.03 0.02

3-2 1 9:45:51 9:46:34 0.02 0.05

3-2 2 9:48:29 9:49:27 0.02 0.03

3-2 1 9:50:37 9:51:39 0.02 0.04

3-2 2 9:54:15 9:55:07 0.02 0.02

3-2 1 9:56:22 9:57:13 0.02 0.04

3-2 2 9:59:32 10:00:24 0.02 0.10

3-2 1 11:10:17 11:11:40 0.03 0.05

3-2 2 11:12:56 11:14:14 0.02 0.44

Cut avg - - - - 0.09

3-4 1 13:00:45 13:01:41 0.11 0.00

3-4 2 13:02:55 13:04:08 0.08 0.02

3-4 1 13:04:51 13:06:13 0.05 0.00

3-4 2 13:08:02 13:09:31 0.05 0.00

3-4 1 13:10:08 13:12:45 0.05 0.02

3-4 2 13:16:20 13:19:05 0.04 0.00

3-4 1 13:19:45 13:21:34 0.04 0.02

3-4 2 13:24:02 13:27:08 0.04 0.01

Cut avg - - - - 0.01

Survey

avg

- - - - 0.28

*

Shuttle car (SC) dust levels shown have the intake dust subtracted; if less than zero, zero is shown.

33

Appendix B: Dust Survey at Mine B 

Introduction 

The purpose of this study was to compare respirable dust concentrations for two cutting 

conditions: (1) a standard 20-ft cut with a maximum 20-ft exhaust curtain setback and no 

flooded-bed scrubber operating, and (2) a 20-ft cut with an exhaust curtain setback up to 40 ft 

while operating a flooded-bed scrubber. A three-day dust survey was conducted alternating 

between both conditions on a cut-by-cut basis. This strategy was used to minimize the effects of 

changes in day-to-day operating conditions. For operating conditions known to affect face dust 

concentrations—including face airflow and the number, orientation, type, location, and pressure 

of external water sprays—attempts were made to maintain these conditions in a consistent state 

throughout the study. 

Site Description 

This dust survey was conducted on the right side of an eight-entry super section, as shown in 

Figure B-1. Coal was extracted using a Joy 12CM15 continuous mining machine and two Joy 

standard cab (off-curtain) shuttle cars. A dual-head, Fletcher DDR-13 roof bolter was used to 

install bolts. During the survey, entries 5 through 8 were developed, with intake air traveling up 

entry No. 5 and splitting to each side of the super section. Entries No. 8 and No. 9 (outby the 

faces being cut during the survey) were for return air. Mining height averaged 94 in, including 

the extraction of up to 30 in of top rock. The pillars were 60 ft x 80 ft with approximately 16-ftwide entries. The continuous miner and roof bolter faces were ventilated with exhausting curtain 

hung on the right side of the entry. 

Figure B-1. Schematic of section sampled at Mine B. 
34

Ventilation Plan Parameters 

Prior to the NIOSH study, the mine had received approval from MSHA for a temporary 

ventilation plan that would be used throughout the study and allow for use of the scrubber. To 

assure consistent operating conditions, the mine’s adherence to the parameters stipulated in the 

temporary ventilation plan was monitored on a periodic basis. Corrective actions were taken 

prior to initiating mining activity, when parameters fell outside required limits (less than the 

minimum specified or exceeding 120% of the minimum specified). The ventilation plan 

parameters required for this study included the following minimum ventilation quantities: 

7,000 cfm at the face-side end of the brattice curtain on the continuous miner faces, 6,000 cfm 

scrubber airflow, and 5,000 cfm at the face-side end of the curtain on the bolter faces. A 30-layer 

pleated filter panel was used in the scrubber. Maximum curtain setbacks were 20 ft for the 

non-scrubber cuts and 40 ft for the scrubber cuts. The continuous miner was equipped with 42 

water sprays (No. 3 hollow cone), with at least 36 sprays operational at all times. The minimum 

acceptable spray pressure was 65 psi. 

Of the plan parameters monitored for this survey, obtaining airflow on the continuous miner 

faces and through the scrubber at the minimum or within 120% of the specified minimum level 

required the most effort. To meet plan parameters, face airflows between 7,000 and 8,400 cfm 

were required and were achieved in 12 of the 14 cuts sampled. The average curtain airflow 

during the survey was 7,943 cfm (SD = 390). Two cuts were out of the desired range, with 

airflow slightly exceeding the 8,400 cfm limit. Typically, an airflow reading was taken at the 

face in preparing for the upcoming cut and then adjustments to the ventilation curtains on the 

section had to be made in order to increase/decrease airflow to achieve the desired range. 

The targeted scrubber airflow was between the 6,000 and 7,400 cfm. Measured scrubber 

airflows averaged 7,218 cfm (SD = 123), with only one reading falling above the targeted range 

by 24 cfm. However, it should be noted that in order to achieve suitable scrubber airflows it was 

necessary to clean the filter panel after each 20-ft cut. Once during each of the three days of 

sampling, the airflow capacity of the “dirty scrubber” was checked after the scrubber had been 

used to complete one 20-ft cut and prior to any cleaning. The airflow through the dirty scrubber 

had dropped an average of 2,090 cfm, which represented a 29% reduction from the initial 

airflow. The significant amount of rock cut in each face was thought to contribute to this drop in 

scrubber airflow. 

The targeted curtain airflow on the bolting faces was between 5,000 and 6,000 cfm. For 11 of 

the 14 bolter faces, the measured airflow was within the desired range. For the other three places, 

airflow exceeded 6,000 cfm. 

Water spray pressures were checked on the left and right side of the miner head twice during 

each shift. Operating pressure averaged 68 psi on both sides of the head. In general, mine 

personnel were able to adhere to the temporary ventilation plan approved for this dust survey. 
35

Results 

Use of real-time dust samplers enabled analysis of the data to be completed on a cut-by-cut 

basis. A total of 14 cuts were sampled, with the scrubber operated during seven of the cuts. 

Tables at the end of this appendix contain the raw data that were calculated for the various 

sampling instruments and sampling locations. Average dust concentrations were then calculated 

for scrubber-off and scrubber-on conditions in order to evaluate the impact on dust levels. Table 

B-1 summarizes cut locations and time, face and scrubber airflow, and dust concentrations 

generated around the continuous miner. The dual-numbering system for cuts represents the shift 

number followed by the number of the cut extracted during that shift. The miner operator dust 

concentrations were calculated from the PDM data, while data from all other sampling locations 

were calculated from pDR data. The dust concentrations for the miner operator, RRC, immediate 

return, and main return sampling locations had the intake dust levels subtracted out and were 

normalized for differences in productivity and face airflow, as discussed in the Data Analysis 

section of this report. 

As shown in Table B-1c, all dust concentrations with the scrubber off were higher to varying 

degrees at the miner operator, rear corner, immediate return, and main return. However, only the 

86% and 85% reductions in the return entries were statistically significant when using the 

Wilcoxon two-sample test, with α = 0.05.

Table B-1. Summary of adjusted respirable dust concentrations for the continuous miner 

a. Scrubber-off

Cut

No.

Cut

location

FBS*

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs*/

min

CM

*

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC*

dust,

mg/m3

CM

return

dust,

mg/m3

Main 

return 

dust,

mg/m3

1-1 8-heading 8,064 0 7:59 8:27 0.32 0.19 1.71 5.13 7.92 3.09

1-3 6-right 8,448 0 10:34 10:54 0.53 0.04 0.71 1.47 10.32 4.19

2-1 8-heading 8,640 0 7:57 8:29 0.37 0.18 0.21 23.22 10.37 5.82

2-3 7-heading 7,728 0 10:05 10:38 0.40 0.09 0.10 5.16 19.02 6.31

2-5 7-heading 8,400 0 12:38 13:02 0.42 0.08 0.18 14.62 16.36 6.50

3-1 6-right 7,105 0 7:44 8:15 0.39 0.17 0.09 1.21 12.91 2.67

3-3 7-right 7,680 0 11:08 11:46 0.34 0.12 0.88 1.88 8.04 5.08

*Abbreviations: FBS, flooded-bed scrubber; SC, shuttle car; CM, continuous miner; RRC, right rear 

corner. 

b. Scrubber-on

Cut

No.

Cut

location

FBS

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs/

min

CM

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC

dust,

mg/m3

CM

return

dust,

mg/m3

Main 

return 

dust, 

mg/m3

1-2 7-heading 7,872 7424 9:28 9:55 0.33 0.17 0.98 6.82 2.21 0.78

1-4 6-right 7,920 7089 12:09 12:31 0.41 0.13 0.00 5.46 1.23 0.43

1-5 5-heading 8,204 7077 13:20 13:39 0.42 0.11 0.98 6.65 2.11 0.79

2-2 6-heading 7,808 7151 8:59 9:37 0.40 0.05 1.06 5.63 1.79 0.90

2-4 8-heading 7,840 7283 11:45 12:14 0.34 0.08 0.18 2.23 0.95 0.92

3-2 6-heading 7,813 7234 9:50 10:15 0.40 0.30 0.00 4.99 1.27 0.56

3-4 6-heading 7,673 7271 12:16 12:57 0.38 0.06 0.00 4.65 2.10 0.78
36

c. Impact of scrubber performance 

Test condition and statistics

CM

intake,

mg/m3

CM

oper,

mg/m3

CM

RRC,

mg/m3

CM

return,

mg/m3

Main 

return,

mg/m3

Average dust concentration with scrubber off 0.12 0.55 7.53 12.13 4.81

Average dust concentration with scrubber on 0.13 0.46 5.20 1.67 0.74

Calculated p-value for cut data - 0.635 0.620 0.001†0.001†

Percent reduction in concentration with scrubber 

on - 16% 31% 86% 85%

† Statistically significant difference. 

Table B-2 summarizes the shuttle car dust concentrations collected during the study. These 

data isolate dust levels at the shuttle cars when located at the face during miner cutting and 

loading activities, and do not include exposures to dust while the cars are in transit or at the 

feeder/breaker. Intake dust concentrations were subtracted from shuttle car concentrations to 

arrive at adjusted shuttle car concentrations resulting from face activities. Dust concentrations in 

the shuttle car cabs were very low and averaged less than 0.1 mg/m3

, with one exception. Dust 

levels for cut 2-1 were substantially higher than for the other 13 cuts (shown in Table B-6) and 

were excluded from calculating the average dust level with the scrubber off. Cut 2-1 was the first 

lift in entry 8, with intake air coming through the last open crosscut. From the shuttle car data, it 

appears that a portion of the ventilating air was traveling down entry 8 and not flowing behind 

the return curtain. The dust levels at the RRC of the miner for this cut were also the highest 

levels observed during the survey, which supports the argument that dust-laden air from the face 

was traveling down the entry. The continuous miner operator was standing in the crosscut and 

therefore was not exposed to elevated dust rollback down the entry. Shuttle car dust 

concentrations when loading at the face averaged 0.07 mg/m3 with the scrubber on versus 

0.03 mg/m3 with the scrubber off. This difference was not statistically significant using the 

Wilcoxon test (p-value = 0.4272). 

Table B-2. Summary of adjusted respirable dust concentrations in the shuttle car cabs 

Cut number 

with 

scrubber off

Cut location 

with scrubber 

off

SC*dust with 

scrubber off, 

mg/m3

Cut number 

with 

scrubber on

Cut location 

with scrubber 

on

SC dust with 

scrubber on, 

mg/m3

1-1 8-heading 0.05 1-2 7-heading 0.04

1-3 6-right 0.04 1-4 6-right 0.01

2-1 8-heading na 1-5 5-heading 0.17

2-3 7-heading 0.02 2-2 6-heading 0.06

2-5 7-heading 0.06 2-4 8-heading 0.18

3-1 6-right 0.02 3-2 6-heading 0.02

3-3 7-right 0.01 3-4 6-heading 0.04

Average - 0.03 - - 0.07

*Abbreviation: SC, shuttle car. 

Table B-3 shows respirable dust concentration in the intake air supplying the roof bolter 

places and at the mid-bolter in the vicinity of the roof bolter operators. The intake concentrations 

were subtracted from the mid-bolter concentrations to estimate bolter-generated dust. The bolting 
37

machine generated very little dust (0.20 mg/m3) with proper face ventilation maintained and the 

dust collector equipment in good working order. The dust collector vacuum pressures averaged 

14 in Hg (SD = 0.7) on the intake-side of the bolter and 17 in Hg (SD = 0.5) on the return-side. 

The minimum required pressure was 12 in Hg. 

Table B-3. Summary of roof bolter dust concentrations 

a. Bolter operating location and dust levels

Place

No.

Face

location

Face 

airflow,

cfm

Position of 

RB* with 

respect to 

CM*

Start

time

End 

time

Scrubber

status

RB intake

dust,

mg/m3

RB center

dust,

mg/m3

1-1 7-heading 5,515 upwind 7:30 8:05 na 0.12 0.42

1-2 8-heading 5,550 miner off 8:56 9:28 na 0.06 0.29

1-3 7-heading 6,000 downwind 10:26 10:52 off 4.75 3.18

1-4 6-right 7,480 miner off 11:26 11:54 na 0.06 0.31

1-5 6-right 5,880 miner off 12:50 13:23 na 0.14 0.54

2-1 7-heading 5,376 upwind 7:31 8:06 na 0.04 0.02

2-2 8-heading 5,670 combined†9:30 10:05 on 0.76 0.90

2-3 6-heading 5,760 upwind 10:28 11:00 na 0.19 0.39

2-4 7-heading 6,000 upwind 11:16 11:51 na 0.18 0.16

2-5 8-heading 5,880 downwind 12:36 13:07 off 7.18 8.12

3-1 6-right‡5,670 miner off 8:35 8:49 na 0.16 0.25

3-2 6-right 21,560 downwind 9:43 10:19 on 1.01 0.85

3-3 6-heading 5,712 upwind 10:55 11:29 na 0.09 0.28

3-4 7-right 19,296 downwind 12:05 12:54 on 1.00 1.06

* Abbreviations: RB, roof bolter; CM, continuous miner. 

† Continuous miner operating upwind of bolter during first 7 min of bolter operation. 

‡

Partial cut—only 3 rows of bolts installed. 

b. Impact of continuous miner on dust levels at the roof bolter 

RB position and status of CM

RB intake,

mg/m3

RB center,

mg/m3

Average dust concentration when RB upwind or with CM not operating 0.12 0.30

Average dust concentration when RB downwind of CM with scrubber off 5.97 5.65

Average dust concentration when RB downwind of CM with scrubber on 0.92 0.94

Percent dust reduction when downwind of CM with scrubber on 85% 83%

Past research has shown that significant exposures to respirable dust can occur when the 

bolting machine operates downwind of the continuous mining machine [Jayaraman et al. 1988]. 

During this survey, the bolter was downwind of the miner during five different cuts. For two of 

these cuts, the scrubber was not operating and dust levels measured by the intake bolter package 

averaged 5.97 mg/m3. The scrubber was operating during three cuts with the bolter downwind 

and average intake dust levels were 0.92 mg/m3. Although an 85% difference in dust levels was 

observed, the small number of samples did not warrant testing for a statistically significant 

difference. A similar difference was observed at the sampling location on the bolter. 
38

Table B-4 displays the mass, percent, and concentration of quartz for miner-generated 

respirable dust from the immediate return for samples collected for both the scrubber-off and 

scrubber-on conditions. Despite a substantial amount of rock being cut, the quartz levels were 

less than 4%. However, use of the scrubber did reduce the average miner-generated quartz dust 

mass by 83% from 38 μg to 7 μg. In order to account for differences in productivity, the quartz 

concentrations were normalized relative to the shuttle cars/min for each cut. As shown in Table 

B-4c, the adjusted quartz concentrations illustrated a difference of 82%, which was statistically 

significant (Wilcoxon test). 

Table B-4. Respirable quartz levels in the continuous miner return 

a. Scrubber-off

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc*,

μg/m3

1 629561 71 0.786 5.54 30 3.8 211.27 0.40 200.70

1 629628 71 0.859 6.05 30 3.5 211.27 0.40 200.70

2 629566 67 1.260 9.40 39 3.1 291.04 0.39 283.58

2 629573 67 1.270 9.48 49 3.9 365.67 0.39 356.30

3 566996 87 1.091 6.27 41 3.8 235.63 0.36 248.72

3 629565 46 0.555 6.03 21 3.8 228.26 0.36 240.94

* Concentrations adjusted based upon an average of 0.38 shuttle cars per min. 

b. Scrubber-on

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc*,

μg/m3

1 629570 81 0.277 1.71 8 2.9 49.38 0.38 49.38

1 629617 81 0.288 1.78 11 3.8 67.90 0.38 67.90

2 629557 78 0.240 1.54 8 3.3 51.28 0.37 52.67

2 629599 78 0.229 1.47 7 3.1 44.87 0.37 46.08

3 566992 76 0.209 1.38 3 1.4 19.74 0.39 19.23

3 566987 76 0.217 1.43 5 2.3 32.89 0.39 32.05

* Concentrations adjusted based upon an average of 0.38 shuttle cars per min. 

c. Impact of scrubber performance 

Test condition and statistics

Quartz mass,

μg

Quartz conc,

μg/m3

Adjusted 

quartz conc,

μg/m3

Average quartz content with scrubber off 38 257.19 255.16

Average quartz content with scrubber on 7 44.34 44.55

Calculated p-value - - 0.0022†

Percent reduction in quartz content with scrubber on 82% 83% 82%

† Statistically significant difference. 
39

Conclusions 

The purpose of the study was to compare face dust levels for two cutting conditions: (1) a 

standard 20-ft cut with a maximum 20-ft curtain setback and no scrubber operating, and (2) a 

20-ft advance with curtain setbacks of up to 40 ft while operating a flooded-bed scrubber. 

Because the approved ventilation and dust control plan for this mechanized mining unit (MMU) 

did not contain provisions to use a flooded-bed scrubber, the mine obtained a temporary plan for 

use during NIOSH testing. To assure consistent operating conditions throughout the survey, 

MSHA personnel assisted in the study by monitoring the mine’s adherence to the dust control

parameters stipulated in the temporary ventilation plan. Airflow adjustments were made by mine 

personnel throughout the survey in an effort to maintain levels within required limits (minimum 

specified in the plan or up to 120% of the minimum specified). In general, mine personnel were 

successful in meeting the conditions specified in the temporary ventilation plan. Key findings 

from the survey include: 

 Average respirable dust concentrations were 86% lower behind the miner return 

curtain with the scrubber operating, decreasing from 12.13 mg/m3 to 1.66 mg/m3

. 

This difference is statistically significant (Wilcoxon test, α = 0.05).

 Average respirable dust concentrations were 85% lower in the main return with the 

scrubber operating, decreasing from 4.81 mg/m3to 0.74 mg/m3. This difference is 

statistically significant (Wilcoxon test). 

 Average quartz concentration in the immediate miner return was reduced by 82% 

with the scrubber operating, decreasing from 255 μg/m3 to 45 μg/m3. This difference 

is statistically significant (Wilcoxon test). 

 Average dust concentrations at the continous miner operator (0.55 vs. 0.46 mg/m3) 

and at the right rear corner of the mining machine (7.53 vs. 5.20 mg/m3) were lower 

with the scrubber operating, but the differences are not statiscally significant 

(Wilcoxon test). 

 Average dust concentrations in the shuttle car cabs when loading at the face averaged 

0.07 mg/m3 with the scrubber on versus 0.03 mg/m3 with the scrubber off, but this 

difference is not statistically significant (Wilcoxon test). 

 Dust concentrations generated by the bolting machine averaged 0.20 mg/m3.

 The bolter operated downwind of the miner for five cuts during the dust survey. For 

two of these cuts, the scrubber was not operated and dust concentrations at the bolter 

intake averaged 5.97 mg/m3. For the other three cuts, the scrubber was operated and 

dust concentrations at the bolter intake averaged 0.92 mg/m3. This 85% reduction was 

not tested for statistical significance but was consistent with the statistically 

significant differences measured in the returns when comparing the scrubber-off and 

scrubber-on conditions. 

The data collected for this study indicate that operation of the flooded-bed scrubber with an 

extended curtain setback did not result in a statistically significant difference in dust 

concentrations at the continuous miner operator and shuttle car operator positions when 

compared to dust concentrations generated with standard cutting conditions. However, operation 

of the scrubber did result in at least an 85% reduction in respirable dust in the return airstreams 
40

and an 82% reduction in respirable quartz. These differences were statically significant. It should 

be noted that these results were obtained with the MMU operating under conditions specified in 

a temporary ventilation plan that was approved for use during this survey. 

The statistically significant differences measured in respirable dust concentrations downwind 

from the miner when the scrubber was operating support a recommendation that mine 

management seek to use the flooded-bed scrubber on a regular basis. Reduced respirable and 

quartz dust exposures could be expected for mine personnel positioned downwind of the 

continuous miner. Although not statistically significant, dust concentrations around the miner 

were also lower with the scrubber operating. 
41

Table B-5. Continuous-miner-generated dust concentrations (mg/m3) for each cut 

Cut

No.

Cut

location

Face

airflow,

cfm

FBS*

airflow,

cfm

CM*

start 

time

CM

stop 

time

Total 

cut

time,

min

No.

SC*

SCs/

min

CM

int

dust 

conc

CM

oper

dust 

conc

CM

RRC*

dust 

conc

CM

ret 

dust 

conc

Main

ret

dust 

conc

Adj†

CM

oper 

dust 

conc

Adj†

CM

RRC

dust 

conc

Adj†

CM

ret

dust 

conc

Adj†

main

ret

dust 

conc

1-1 8-heading 8,064 0 7:59 8:27 28 9 0.32 0.19 1.58 4.36 6.62 2.70 1.71 5.13 7.92 3.09

1-2 7-heading 7,872 7,424 9:28 9:55 27 9 0.33 0.17 1.02 6.06 2.08 0.85 0.98 6.82 2.21 0.78

1-3 6-right 8,448 0 10:34

10:46

10:43

10:54

17 9 0.53 0.04 0.95 1.91 13.23 5.39 0.71 1.47 10.32 4.19

1-4 6-right 7,920 7,089 12:09 12:31 22 9 0.41 0.13 0.13 5.88 1.42 0.58 0.00 5.46 1.23 0.43

1-5 5-heading 8,204 7,077 13:20 13:39 19 8 0.42 0.11 1.14 7.07 2.32 0.94 0.98 6.65 2.11 0.79

2-1 8-heading 8,640 0 7:57 

8:15

8:10 

8:29

27 10 0.37 0.18 0.37 20.47 9.24 5.27 0.21 23.22 10.37 5.82

2-2 6-heading 7,808 7,151 8:59 

9:06 

9:12 

9:20

9:03 

9:08 

9:14 

9:37

25 10 0.40 0.05 1.17 5.94 1.93 1.00 1.06 5.63 1.79 0.90

2-3 7-heading 7,728 0 10:05 

10:18

10:10 

10:38

25 10 0.40 0.09 0.20 5.54 20.16 6.75 0.10 5.16 19.02 6.31

2-4 8-heading 7,840 7,283 11:45 12:14 29 10 0.34 0.08 0.24 2.08 0.93 0.91 0.18 2.23 0.95 0.92

2-5 7-heading 8,400 0 12:38 13:02 24 10 0.42 0.08 0.26 14.86 16.61 6.65 0.18 14.62 16.36 6.50

3-1 6-right 7,105 0 7:44 

7:53 

8:03

7:49 

7:59 

8:15

23 9 0.39 0.17 0.26 1.52 14.66 3.17 0.09 1.21 12.91 2.67

3-2 6-heading 7,813 7,234 9:50 10:15 25 10 0.40 0.30 0.00 5.50 1.62 0.88 0.00 4.99 1.27 0.56

3-3 7-right 7,680 0 11:08 

11:18

11:15 

11:46

35 12 0.34 0.12 0.92 1.83 7.44 4.74 0.88 1.88 8.04 5.08

3-4 6-heading 7,673 7,271 12:16 

12:36

12:19 

12:57

24 9 0.38 0.06 0.00 4.69 2.15 0.84 0.00 4.65 2.10 0.78

Avg - 7,943 7,218 - - - - 0.39 - - - - - - - - -

*

 Abbreviations: FBS, flooded-bed scrubber; CM, continuous miner; SC, shuttle car; RRC, right rear corner. 

†

 Adjusted dust concentrations have intake levels subtracted and are normalized for differences in face airflow and production (SCs/min). 
42

Table B-6. Shuttle car loading times and dust concentrations with the scrubber off 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-1 1 7:59:03 7:59:58 0.19 0.00

1-1 2 8:01:52 8:02:45 0.17 0.00

1-1 1 8:05:36 8:06:12 0.20 0.00

1-1 2 8:08:53 8:09:48 0.14 0.00

1-1 1 8:11:52 8:12:58 0.08 0.00

1-1 2 8:14:50 8:15:57 0.48 0.00

1-1 1 8:17:55 8:18:45 0.34 0.25

1-1 2 8:20:42 8:21:40 0.20 0.03

1-1 1 8:23:43 8:24:46 0.11 0.18

1-1 1 8:26:07 8:26:40 0.09 0.00

Cut avg - - - - 0.05

1-3 2 10:34:00 10:35:10 0.00 0.02

1-3 1 10:36:17 10:37:10 0.06 0.12

1-3 2 10:38:08 10:39:00 0.03 0.05

1-3 1 10:39:50 10:40:45 0.06 0.04

1-3 2 10:41:32 10:42:16 0.02 0.07

1-3 1 10:46:23 10:47:37 0.01 0.01

1-3 2 10:48:30 10:49:42 0.02 0.04

1-3 1 10:50:38 10:51:37 0.05 0.04

1-3 2 10:52:32 10:53:21 0.02 0.03

Cut avg - - - - 0.05

2-1 1 7:57:11 7:58:21 0.15 0.60

2-1 2 7:59:52 8:00:35 0.13 6.91

2-1 1 8:01:52 8:02:36 0.19 2.76

2-1 2 8:03:58 8:05:03 0.16 1.08

2-1 1 8:06:23 8:07:31 0.23 1.17

2-1 2 8:08:54 8:09:43 0.18 0.85

2-1 1 8:15:00 8:16:43 0.42 5.10

2-1 2 8:18:16 8:19:37 0.23 17.84

2-1 1 8:21:07 8:22:15 0.14 2.79

2-1 2 8:23:38 8:24:25 0.12 2.57

2-1 2 8:26:11 8:26:44 0.11 0.36

2-1 2 8:28:00 8:28:37 0.11 0.20

Cut avg - - - - 3.52†

2-3 1 10:05:50 10:07:04 0.00 0.03

2-3 2 10:08:06 10:09:01 0.02 0.02

2-3 1 10:18:25 10:19:34 0.06 0.06

2-3 2 10:20:35 10:21:35 0.11 0.00

2-3 1 10:22:45 10:23:40 0.05 0.01

2-3 2 10:24:29 10:25:17 0.04 0.05

2-3 1 10:26:26 10:27:12 0.07 0.00

2-3 2 10:28:57 10:30:40 0.07 0.00

2-3 1 10:32:05 10:33:35 0.18 0.00

*

Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 

† Data excluded from calculation of average dust concentration for cuts with the scrubber off. 
43

Table B-6. Shuttle car loading times and dust concentrations with the scrubber off 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

2-3 2 10:34:58 10:35:45 0.26 0.00

2-3 2 10:36:49 10:37:37 0.30 0.00

Cut avg - - - - 0.02

2-5 1 12:38:17 12:39:27 0.07 0.00

2-5 2 12:40:18 12:40:47 0.01 0.05

2-5 1 12:41:59 12:43:02 0.03 0.46

2-5 2 12:45:28 12:46:51 0.19 0.00

2-5 1 12:49:14 12:49:57 0.03 0.00

2-5 2 12:51:00 12:51:49 0.02 0.02

2-5 1 12:53:10 12:53:43 0.02 0.07

2-5 2 12:55:05 12:56:25 0.08 0.00

2-5 1 12:57:22 12:58:24 0.15 0.00

2-5 2 12:59:33 13:00:00 0.03 0.02

2-5 2 13:01:29 13:01:50 0.28 0.00

Cut avg - - - - 0.06

3-1 2 7:44:14 7:45:13 0.14 0.00

3-1 1 7:48:01 7:48:44 0.14 0.02

3-1 2 7:53:04 7:54:04 0.10 0.00

3-1 1 7:55:32 7:56:22 0.13 0.11

3-1 2 7:58:10 7:59:00 0.13 0.00

3-1 1 8:03:11 8:04:20 0.12 0.02

3-1 2 8:05:48 8:06:58 0.14 0.00

3-1 1 8:09:27 8:10:33 0.27 0.02

3-1 2 8:12:03 8:13:15 0.23 0.00

3-1 2 8:14:17 8:15:01 0.17 0.00

Cut avg - - - - 0.02

3-3 2 11:08:14 11:09:23 0.12 0.00

3-3 1 11:11:37 11:12:38 0.16 0.00

3-3 2 11:14:25 11:15:00 0.16 0.00

3-3 1 11:18:02 11:18:45 0.21 0.00

3-3 2 11:20:28 11:21:21 0.17 0.00

3-3 1 11:23:37 11:24:25 0.14 0.00

3-3 2 11:27:12 11:28:03 0.16 0.00

3-3 1 11:30:34 11:32:03 0.11 0.02

3-3 2 11:33:36 11:34:25 0.09 0.00

3-3 1 11:36:55 11:37:42 0.07 0.05

3-3 2 11:39:31 11:40:27 0.06 0.00

3-3 1 11:43:30 11:44:12 0.07 0.00

3-3 1 11:45:07 11:45:35 0.06 0.00

Cut avg - - - - 0.01

Survey

avg - - - - 0.04

*

Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 

† Data excluded from calculation of average dust concentration for cuts with the scrubber off. 
44

Table B-7. Shuttle car loading times and dust concentrations with the scrubber on 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-2 1 9:28:50 9:29:35 0.06 0.05

1-2 2 9:31:20 9:32:00 0.33 0.00

1-2 1 9:35:10 9:35:52 0.29 0.00

1-2 2 9:37:40 9:38:25 0.18 0.01

1-2 1 9:40:05 9:40:58 0.12 0.17

1-2 2 9:43:18 9:44:40 0.04 0.03

1-2 1 9:46:27 9:47:15 0.09 0.05

1-2 2 9:50:00 9:51:00 0.24 0.00

1-2 1 9:53:24 9:54:07 0.03 0.08

Cut avg - - - - 0.04

1-4 2 12:09:08 12:10:10 0.05 0.00

1-4 1 12:11:08 12:11:49 0.49 0.00

1-4 2 12:12:45 12:13:40 0.23 0.00

1-4 1 12:15:08 12:15:57 0.18 0.01

1-4 2 12:18:23 12:19:30 0.21 0.00

1-4 1 12:20:32 12:21:49 0.07 0.00

1-4 2 12:22:52 12:24:25 0.10 0.00

1-4 1 12:25:44 12:26:38 0.02 0.03

1-4 2 12:28:13 12:29:00 0.02 0.03

1-4 2 12:30:10 12:30:47 0.03 0.00

Cut avg - - - - 0.01

1-5 1 13:20:50 13:21:57 0.02 0.02

1-5 2 13:24:09 13:24:59 0.10 0.05

1-5 1 13:25:38 13:26:26 0.26 0.18

1-5 2 13:27:13 13:28:21 0.03 0.36

1-5 1 13:29:30 13:30:25 0.07 0.04

1-5 2 13:31:14 13:32:10 0.02 0.38

1-5 1 13:32:52 13:33:45 0.21 0.41

1-5 2 13:36:00 13:36:51 0.09 0.04

1-5 2 13:37:57 13:38:43 0.04 0.03

Cut avg - - - - 0.17

2-2 2 8:59:48 9:00:47 0.07 0.13

2-2 1 9:02:10 9:02:47 0.07 0.26

2-2 2 9:06:39 9:07:33 0.07 0.03

2-2 1 9:12:11 9:13:05 0.07 0.00

2-2 2 9:20:23 9:21:17 0.07 0.04

2-2 1 9:23:13 9:24:21 0.07 0.00

2-2 2 9:25:44 9:26:49 0.07 0.00

2-2 1 9:28:05 9:29:20 0.07 0.00

2-2 2 9:31:05 9:32:23 0.07 0.26

2-2 1 9:34:03 9:34:55 0.07 0.00

2-2 1 9:36:03 9:36:50 0.07 0.00

Cut avg - - - - 0.07

*

Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 
45

Table B-7. Shuttle car loading times and dust concentrations with the scrubber on 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

2-4 1 11:45:00 11:45:50 0.07 0.08

2-4 1 11:47:29 11:48:21 0.07 0.00

2-4 2 11:49:57 11:50:36 0.07 0.00

2-4 1 11:53:29 11:54:15 0.07 0.00

2-4 1 11:55:55 11:56:36 0.07 0.31

2-4 2 11:58:45 11:59:56 0.07 0.32

2-4 1 12:01:54 12:03:10 0.07 0.26

2-4 2 12:05:19 12:06:22 0.07 0.59

2-4 1 12:08:19 12:09:17 0.07 0.13

2-4 2 12:11:06 12:11:45 0.07 0.05

2-4 2 12:13:07 12:13:47 0.07 0.00

Cut avg - - - - 0.16

3-2 1 9:50:30 9:51:32 0.73 0.00

3-2 2 9:52:28 9:53:14 0.25 0.00

3-2 1 9:55:00 9:55:50 0.27 0.00

3-2 2 9:56:33 9:57:42 0.25 0.00

3-2 1 9:59:09 10:00:10 0.96 0.00

3-2 2 10:00:59 10:01:59 0.26 0.00

3-2 1 10:03:35 10:04:30 0.16 0.00

3-2 2 10:05:23 10:06:17 0.09 0.01

3-2 1 10:07:53 10:08:53 0.06 0.16

3-2 2 10:10:56 10:11:53 0.04 0.00

3-2 2 10:13:38 10:14:23 0.06 0.00

Cut avg - - - - 0.02

3-4 1 12:16:23 12:17:06 0.04 0.03

3-4 2 12:18:01 12:19:01 0.06 0.00

3-4 1 12:36:23 12:37:08 0.02 0.07

3-4 2 12:38:20 12:39:20 0.05 0.05

3-4 1 12:40:35 12:41:50 0.04 0.00

3-4 2 12:43:02 12:43:52 0.05 0.02

3-4 1 12:47:17 12:48:14 0.03 0.07

3-4 2 12:50:20 12:51:04 0.08 0.00

3-4 1 12:53:58 12:54:43 0.02 0.18

3-4 1 12:55:44 12:56:30 0.22 0.00

Cut avg - - - - 0.04

Survey

avg

- - - - 0.07

*

Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 
46

Appendix C: Dust Survey at Mine C 

Introduction

The purpose of this study was to compare respirable dust levels from a standard 20-ft cut 

with a maximum 20-ft exhaust curtain setback and no flooded-bed scrubber operating to a 20-ft 

cut with an exhaust curtain setback of 40 ft while operating a flooded-bed scrubber. A three-day 

dust survey was conducted, alternating between both test conditions on a cut-by-cut basis. This 

strategy was designed to minimize the effects of changes in day-to-day operating conditions. 

Unfortunately, a number of the cuts had atypical ventilation patterns in the face, which 

complicated comparison of the data. For operating conditions known to affect face dust 

concentrations—including face airflow and the number, orientation, type, location, and pressure 

of external water sprays—attempts were made to maintain these conditions in a consistent state 

throughout the study. 

Site Description 

This dust survey was conducted on the left side of a nine-entry super section as shown in 

Figure C-1. Coal was extracted using a Joy 14 CM 15 continuous mining machine and two Joy 

standard cab (off-curtain) shuttle cars. A dual-head, Fletcher Roof Ranger II roof bolter was used 

to install bolts. During the survey, the miner developed entries 1 through 5, with intake air 

traveling up entries 3 and 4 and entries 1 and 2 used for return air. Entry 5 contained the 

feeder/breaker and section belt and was isolated in the ventilation plan. Mining height averaged 

65 inches, including the extraction of up to three ft of rock. The miner was cutting 20-ft-wide 

entries. The faces were ventilated with exhausting curtain hung on the left side of the entry. 

Figure C-1. Schematic of section sampled at Mine C. 
47

Challenging mining conditions were encountered during the survey with a steep rise in the 

coal seam, which made shuttle car travel and cutting with the continuous miner more difficult. 

As a result, the mining unit did not achieve normal levels of production during the NIOSH 

sampling period. 

Ventilation Plan Parameters 

In an effort to assure consistent operating conditions, the mine’s adherence to the parameters 

stipulated in the ventilation plan was monitored by MSHA personnel. Corrective actions were 

taken prior to initiating mining activity when parameters fell outside required limits (less than the 

minimum specified in the plan or greater than 120% of plan parameters). The ventilation plan 

parameters required on this MMU included the following minimum ventilation quantities: 

5,000 cfm at the face-side end of the brattice curtain on the continuous miner faces, 4,000 cfm 

scrubber airflow, and 4,000 cfm at the face-side end of the curtain on the bolter faces. A 30-layer 

pleated filter panel was used in the scrubber. Maximum curtain setbacks were 20 ft for the 

scrubber-off cuts and 40 ft for the scrubber-on cuts. The continuous miner was equipped with 33 

water sprays (BD 3-5 hollow cone), with at least 30 sprays operational at all times. The 

minimum allowable spray pressure was 85 psi. 

For the plan parameters monitored during the survey, obtaining the required airflow on the 

continuous miner faces was the most challenging. Typically, an airflow reading was taken at the 

face in preparing for the upcoming cut and then adjustments to the ventilation curtains on the 

section had to be made in order to increase/decrease airflow to achieve the desired range. To 

meet plan parameters, face airflows between 5,000 and 6,000 cfm were desired and were 

achieved in 4 of the 8 cuts sampled. The average curtain airflow during the survey was 6,565 

cfm (SD = 1396). Four cuts were out of the desired range, with measured airflow exceeding the 

6,000 cfm upper limit. 

The targeted scrubber airflow was between 4,000 and 4,800 cfm. Measured scrubber airflows 

averaged 4,288 (SD = 131), with all readings falling within the targeted range. However, it 

should be noted that in order to achieve suitable scrubber airflows it was necessary to clean the 

30-layer filter panel after each 20-ft cut. Once during the survey, the airflow capacity of the 

“dirty scrubber” was checked after the scrubber had been used to complete one 20-ft cut and 

prior to any cleaning. The airflow through the dirty scrubber had dropped 1,549 cfm, which 

represented a 35% reduction from the initial airflow. The significant amount of rock being cut in 

each face was thought to contribute to this substantial drop in scrubber airflow. 

The minimum required curtain airflow on the bolting faces was 4,000 cfm. For all seven of 

the bolter faces, the measured airflow exceeded this quantity. 

Water spray pressures on the miner were checked during each shift to ensure the 85 psi 

minimum pressure was achieved. Operating pressure averaged 101 psi and 99 psi on the left and 

right sides of the miner, respectively. In addition, the required number of sprays was operating 

during each cut. 
48

Results 

Utilization of real-time samplers allowed for data analysis on a cut-by-cut basis. A total of 

eight cuts were sampled, with the scrubber operated during four of the cuts. The raw data that 

were calculated for the various sampling instruments and sampling locations are included at the 

end of this appendix. These raw data were used to calculate average dust concentrations for 

scrubber-off and scrubber-on test conditions in order to evaluate the scrubber impact on dust 

levels. Table C-1 summarizes cut locations and time, face and scrubber airflow, and dust 

concentrations generated around the continuous miner. The miner operator dust concentrations 

were calculated from the PDM data, while data from all other sampling locations were calculated 

from pDR data. Since the continuous miner was mining uphill, water from the boom sprays was 

draining down the top deck of the miner and onto the sampling package located at the right rear 

corner of the machine. This water was running onto the pDR sampler, which caused the pDR to 

stop operating during each of the first two sampling shifts. Therefore, it was decided to abandon 

this sampling location for shift 3, so no valid data were obtained at the RRC of the miner. The 

dust concentrations for the miner operator, immediate miner return, and main return sampling 

locations had the intake dust concentrations subtracted out and then were normalized for 

differences in productivity and for differences in face airflow, assuming a linear relationship 

between these parameters and dust levels. For example, average productivity for all cuts sampled 

during the survey was 0.28 shuttle cars per min (Table C-5), while productivity for Cut 1-1 

averaged 0.36 shuttle cars per min. Dust levels for Cut 1-1 were then multiplied by a factor of 

0.78 (0.28 ÷ 0.36) to adjust for the higher-than-average productivity observed in Cut 1-1. The 

airflow was adjusted similarly, with the factor calculated by dividing the measured face airflow 

by the average face airflow of all cuts (Table C-5).

Table C-1. Summary of adjusted respirable dust concentrations for the continuous miner 

a. Scrubber-off

Cut

No.

Cut

location

FBS*

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs*/

min

CM

*

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC*

dust†,

mg/m3

CM

return

dust,

mg/m3

Main 

return 

dust, 

mg/m3

1-2 5-heading 0 5,070 8:54 10:41 0.24 0.06 0.23 na 21.16 6.67

2-1 2-heading 0 6,348 7:47 8:56 0.32 0.02 0.02 na 5.63 4.58

2-2 1-heading 0 5,280 9:15 10:42 0.29 0.26 0.61 na 5.47 8.26

3-2 3-left 0 9,200 11:20 12:56 0.35 0.03 0.12 na 25.21 7.40

*Abbreviations: FBS, flooded-bed scrubber; SC, shuttle car; CM, continuous miner; RRC, right rear 

corner. 

† Water inundation of samplers at this location caused data to be lost. 

b. Scrubber-on

Cut

No.

Cut

location

FBS

airflow,

cfm

Entry

airflow,

cfm

Start

cut

End

cut

SCs/

min

CM

intake

dust,

mg/m3

CM

oper

dust,

mg/m3

CM

RRC

dust†,

mg/m3

CM

return

dust,

mg/m3

Main 

return 

dust,

mg/m3

1-1 3-heading 4,300 5,757 7:58 8:22 0.36 0.02 0.49 na 9.55 na

1-3 4-heading 4,400 5,910 11:34 12:19 0.33 0.05 na na 7.17 3.29

2-3 3-heading 4,360 7,560 11:52 12:58 0.23 0.10 na na 9.04 8.19

3-1 5-heading 4,100 7,398 9:18 10:16 0.15 0.03 0.14 na 8.81 2.91

† Water inundation of samplers at this location caused data to be lost. 
49

c. Impact of scrubber performance 

Test condition and statistics

CM

intake,

mg/m3

CM

oper,

mg/m3

CM

RRC†,

mg/m3

CM

return,

mg/m3

Main 

return, 

mg/m3

Average dust concentration with scrubber off 0.09 0.25 na 14.37 6.73

Average dust concentration with scrubber on 0.05 0.32 na 8.64 4.80

Calculated p-value for cut data - 0.8000 na 1.0000 0.4000

Percent reduction in concentration with scrubber 

on - -28% na 40% 29%

† Water inundation of samplers at this location caused data to be lost. 

As shown in Table C-1, the dust concentrations around the continuous miner and in the main 

return exhibited substantial variability within each test condition. Given this variability and the 

limited amount of data, no statistically significant differences (Wilcoxon test with α = 0.05) were 

observed between the scrubber-off and scrubber-on test conditions at the miner operator, the 

miner return, or the main return. Results show a 0.07-mg/m3

increase in average dust levels at 

the miner operator when comparing scrubber-on to scrubber-off, while average dust levels in the 

immediate and main returns show reductions of over 3 mg/m3and nearly 2 mg/m3, respectively. 

Table C-2 summarizes the shuttle car dust concentrations collected during the study. These 

data isolate the dust levels at the shuttle cars when the cars are located at the face during miner 

cutting and loading activities, but do not include exposures while in transit or at the 

feeder/breaker. Intake dust concentrations were subtracted from shuttle car concentrations to 

arrive at adjusted shuttle car concentrations resulting from face activities. Dust concentrations in 

the shuttle car cabs also exhibited a substantial amount of variability within each test condition. 

Once again, no statistically significant differences were found between the test conditions with 

the Wilcoxon test (p-value =0.5429), with only a 0.08-mg/m3

difference in average dust 

concentrations measured in the shuttle car cabs. 

Table C-2. Summary of adjusted respirable dust concentrations in the shuttle car cabs 

Cut number 

with 

scrubber off

Cut location 

with scrubber 

off

SC*dust with 

scrubber off, 

mg/m3

Cut number 

with 

scrubber on

Cut location 

with scrubber 

on

SC dust with 

scrubber on, 

mg/m3

1-2 5-heading 1.29 1-1 3-heading 0.23

2-1 2-heading 0.02 1-3 4-heading 1.33

2-2 1-heading 0.01 2-3 3-heading 0.01

3-2 3-left 0.07 3-1 5-heading 0.15

Average - 0.35 - - 0.43

* Abbreviation: SC, shuttle car. 

Table C-3 shows respirable dust concentrations in the intake air supplying the roof bolter 

places and in the bolter cab. These dust concentrations were normalized for differences in face 

airflow similarly to the miner dust levels discussed previously. The dust collector vacuum 

pressures averaged 15 in Hg (SD = 0.7) on the left side of the bolter and 13 in Hg (SD = 0.5) on 

the right side. The minimum required pressure was 12 in Hg. 
50

Past research has shown that significant exposures to respirable dust can occur when the 

bolting machine operates downwind of the continuous mining machine [Jayaraman et al. 1988]. 

During this survey, the bolter was downwind of the miner during three different cuts. For two of 

these cuts, the scrubber was not operating and dust concentrations measured by the intake bolter 

package averaged 11.23 mg/m3

. The scrubber was operating during one cut with the bolter 

downwind, and the intake dust concentration was 7.38 mg/m3, resulting in a 34% reduction in 

dust concentration with the scrubber operating. Similarly, a 51% reduction in dust concentrations 

was observed for the samples located in the bolter cab. Given the small number of samples, no 

statistically significant difference could be calculated between the bolter-downwind dust 

concentrations with the scrubber off and the scrubber on. 

Table C-3. Summary of roof bolter dust concentrations 

a. Bolter operating location and dust levels 

Place

No.

Face

location

Face 

airflow,

cfm

Position of 

RB* with 

respect to 

CM*

Start

time

End 

time

Scrubber

status

RB intake

dust,

mg/m3

RB cab

dust,

mg/m3

1-1 3-heading 4,000 downwind 8:59:25 9:30:20 off 9.21 8.47

1-2 5-heading 10,140 upwind 11:02:00 11:28:10 na 0.13 0.25

2-1 1-heading 12,800 downwind 7:11:54 8:07:21 off†13.25 16.04

2-2 2-heading 4,420 upwind 9:48:14 10:06:10 na 0.06 0.11

2-3 3-heading 4,360 upwind 11:11:53 11:40:24 na 0.07 0.13

3-1 4-left 10,800 downwind 8:47:30 10:00:13 on

‡

7.38 6.06

3-2 5-heading na upwind 10:47:30 10:57:49 na na na

* Abbreviations: RB, roof bolter; CM, continuous miner. 

† Miner upwind but only operating from 7:46:42 to 8:01:48. 

‡ Miner begins operating upwind at 9:17:46. 

b. Impact of continuous miner on dust levels at the roof bolter 

RB position and status of CM 

RB intake,

mg/m3

RB cab,

mg/m3

Average dust concentration when RB upwind or with CM not operating 0.09 0.16

Average dust concentration when RB downwind of CM with scrubber off 11.23 12.26

Average dust concentration when RB downwind of CM with scrubber on 7.38 6.06

Percent dust reduction when RB downwind of CM with scrubber on 34% 51%

Table C-4 displays the mass and the percentage of quartz for miner-generated respirable dust 

from the immediate return for samples collected for both the scrubber-off and scrubber-on test 

conditions. As previously indicated, a substantial amount of rock was being cut in all of the 

entries. Quartz levels ranged from 12.9% to 23%, except for the last cut taken with the scrubber 

off. For this cut, the average quartz percentage was 7.9%. This cut was taken in the crosscut 

between entries 3 and 2 and was the only cut not taken up a heading. The quartz concentrations 

were normalized to account for differences in productivity from cut to cut. With the scrubber 

operating, the average quartz concentration was reduced by 14% from 1,602 μg/m3

to 

1,385 μg/m3

. There was no statistically significant difference (Wilcoxon test) between the 

quartz concentrations for the two test conditions. 
51

Table C-4. Respirable quartz levels in the continuous miner return 

a. Scrubber-off

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc*,

μg/m3

1 130 130 3.887 14.95 893 23.0 3,434.62 0.24 4,007.05

1 46 130 3.894 14.98 756 19.4 2,907.69 0.24 3,392.31

2 64 174 1.727 4.96 239 13.8 686.78 0.31 620.32

2 1 174 0.916 2.63 124 13.5 356.32 0.31 321.84

3 61 98 1.936 9.88 160 8.3 816.33 0.35 653.06

3 66 98 2.016 10.29 151 7.5 770.41 0.35 616.33

* Concentrations adjusted based upon an average of 0.28 shuttle cars per min. 

b. Scrubber-on

Shift

Gravimetric 

filter 

number

Sampling 

time,

min

Dust 

mass,

mg

Avg

dust 

conc,

mg/m3

Quartz 

mass, 

μg

Quartz, 

%

Quartz 

conc,

μg/m3

Shuttle 

cars/

min

Adjusted 

quartz 

conc*,

μg/m3

1 560 79 1.807 11.44 324 17.9 2,050.63 0.34 1,688.76

1 65 89 1.679 9.43 270 16.1 1,516.85 0.34 1,249.17

2 53 74 0.839 5.67 108 12.9 729.73 0.23 888.37

2 69 74 0.736 4.97 100 13.6 675.68 0.23 822.56

3 322 63 0.654 5.19 121 18.5 960.32 0.15 1,792.59

3 56 63 0.619 4.91 126 20.4 1,000.00 0.15 1,866.67

* Concentrations adjusted based upon an average of 0.28 shuttle cars per min. 

c. Impact of scrubber performance 

Test condition and statistics

Quartz mass,

μg

Quartz conc,

μg/m3

Adjusted 

quartz conc,

μg/m3

Average quartz content with scrubber off 387 1,495.36 1,601.82

Average quartz content with scrubber on 175 1,155.54 1,384.69

Calculated p-value - - 0.3939

Percent reduction in quartz content with scrubber on 55% 23% 14%

Conclusions 

The purpose of the study was to compare face dust levels for two cutting conditions: (1) a 

standard 20-ft cut with a maximum 20-ft exhaust curtain setback and no scrubber operating, and 

(2) a 20-ft advance with exhaust curtain setbacks of up to 40 ft while operating a flooded-bed 

scrubber. To assure consistent operating conditions throughout the survey, MSHA personnel 

assisted in the study by monitoring the mine’s adherence to key dust control parameters 

stipulated in the ventilation plan: face airflow, scrubber airflow, water spray pressure, and 

number of sprays operating. Adjustments were made by mine personnel throughout the survey in 

an effort to maintain levels within required limits. 
52

Difficult geologic conditions were present during the survey (steep rise in the coal seam), 

which complicated mining and reduced production levels. In addition, substantial cut-to-cut 

variability was observed in the respirable dust concentrations obtained for each test condition. 

Key findings and observations from the survey include: 

 No statiscally significant differences (Wilcoxon test, α = 0.05) in respirable dust 

levels were observed between the two operating conditions tested during this survey. 

 Although not statistically significant, several sampling locations exhibited a drop in 

average respirable dust concentrations with the scrubber operating, as follows: 

o in the miner return, average dust concentrations decreased from 12.12 mg/m3 

to 8.75 mg/m3

o in the main return, average dust concentrations decreased from 6.73 mg/m3to 

4.80 mg/m3

o with the bolter working downwind of the miner, dust concentrations in the 

intake air to the bolter decreased from 11.23 mg/m3 to 7.38 mg/m3

 As shown in Figure C-2, the scrubber discharge was not equipped with vanes to direct 

the scrubber exhaust toward the return curtain. This likely allowed a portion of the 

scrubber discharge air to cause turbulence and disruption in the entry airflow. 

Figure C-2. Scrubber discharge at left rear corner of miner. 

Photo by NIOSH
53

 After one cut with the scrubber operating was completed, the scrubber airflow was 

measured before the filter panel was cleaned. Results showed a 35% reduction in air 

quantity, illustrating the necessity of cleaning the filter panel after each cut. 

 The differences in the types of cuts sampled for the two test conditions complicated 

the comparison of dust levels generated during this survey. For example, for all of the 

cuts with the scrubber operating, the headings were advanced between 35 and 50 ft 

beyond the last open crosscut. During these cuts, the miner operator was most often 

positioned in the heading alongside of the shuttle car being loaded. For three of the 

cuts with the scrubber off, the miner was taking a flush cut or the face had only been 

advanced 10 ft beyond the last open crosscut. In these cases, the miner operator was 

positioned in the last open crosscut and was not as close to the miner and shuttle car. 

For these cuts, the ventilating air was flowing perpendicular to the miner, rather than 

parallel to the miner as is the case when the heading is further developed. Also, only 

one crosscut was sampled during the survey and it was the initial cut for that crosscut. 

Consequently, only a partial line curtain was hung in the heading to provide 

ventilation for this initial cut. 

 Substantial quantities of quartz-bearing rock were being cut in all entries. 

Maintenance of all dust controls is critical to minimize exposure to quartz, which was 

found to be over 12% for all but one cut. 

The data collected for this study indicated that operation of the flooded-bed scrubber with an 

extended curtain setback did not result in a statistically significant difference in respirable dust 

concentrations when compared to standard cutting conditions. However, the available data did 

show that operation of the scrubber resulted in measured reductions in dust concentrations in the 

miner return, the main return, and in the bolter intake when located downwind of the miner. 

Consequently, the data suggest that continued operation of the scrubber would be beneficial. 
Table C-5. Continuous-miner-generated dust concentrations (mg/m3

) for each cut 

Cut

No.

Cut

location

Face

airflow,

cfm

FBS*

airflow,

cfm

CM*

start 

time

CM

stop 

time

Total 

cut

time,

min

No.

SC*

SCs/

min

CM

int

dust 

conc

CM

oper

dust 

conc

CM

RRC*

dust 

conc

CM

ret 

dust 

conc

Main

ret

dust 

conc

Adj†

CM

oper 

dust 

conc

Adj†

CM

RRC

dust 

conc

Adj†

CM

ret

dust 

conc

Adj†

main

ret

dust 

conc

1-1 3-heading 5,757 4,300 7:58

8:20

8:15

8:23

20 7 0.36 0.02 0.72 na 13.79 na 0.49 na 9.55 na

1-2 5-heading 5,070 0 8:54

9:00

9:15

9:39

10:17

10:39

8:57

9:11

9:24

10:06

10:36

10:41

71 17 0.24 0.06 0.31 na 23.34 7.40 0.23 na 21.16 6.67

1-3 4-heading 5,910 4,400 11:34

11:45

12:02

11:42

11:56

12:19

36 12 0.33 0.05 void‡na 9.38 4.33 void‡na 7.17 3.29

2-1 2-heading 6,348 0 7:47

8:20

8:53

8:02

8:50

8:55

47 15 0.32 0.02 0.04 na 6.58 5.36 0.02 na 5.63 4.58

2-2 1-heading 5,280 0 9:15

9:31

9:50

9:59

10:25

9:27

9:46

9:55

10:01

10:42

51 15 0.29 0.26 1.05 na 7.26 10.83 0.61 na 5.47 8.26

2-3 3-heading 7,560 4,350 11:52

11:58

12:08

12:23

12:42

12:46

11:53

12:03

12:17

12:34

12:43

12:58

39 9 0.23 0.10 void‡na 6.43 5.84 void‡na 9.04 8.19

*

 Abbreviations: FBS, flooded-bed scrubber; CM, continuous miner; SC, shuttle car; RRC, right rear corner. 

† Adjusted dust concentrations have intake levels subtracted and are normalized for differences in face airflow and production (SCs/min). 

‡

 PDM sampler revealed an error code for flow rate out of range, likely indicating that the sampling hose was pinched during this cut. 
Table C-5. Continuous miner-generated dust concentrations (mg/m3

) for each cut (Continued) 

Cut

No.

Cut

location

Face

airflow,

cfm

FBS*

airflow,

cfm

CM*

start 

time

CM

stop

time

Total 

cut

time,

min

No.

SC*

SCs/

min

CM

int

dust 

conc

CM

oper

dust 

conc

CM

RRC*

dust 

conc

CM

ret 

dust 

conc

Main

ret

dust 

conc

Adj†

CM

oper 

dust 

conc

Adj†

CM

RRC

dust 

conc

Adj†

CM

ret

dust 

conc

Adj†

main

ret

dust 

conc

3-1 5-heading 7,398 4,100 9:18 

9:27

9:23

10:16

54 8 0.15 0.03 0.09 na 4.07 1.36 0.14 na 8.81 2.9

3-2 3-left 9,200 0 11:20

11:30

11:39

11:48

11:58

12:10

12:15

12:19

12:27

12:40

12:44

12:55

11:23

11:32

11:40

11:53

12:01

12:12

12:16

12:23

12:37

12:41

12:51

12:56

40 14 0.35 0.03 0.13 na 22.27 6.56 0.12 na 25.21 7.40

Avg - 6,565 4,288 - - - - 0.28 - - - - - - - - -

*

 Abbreviations: FBS, flooded-bed scrubber; CM, continuous miner; SC, shuttle car; RRC, right rear corner. 

† Adjusted dust concentrations have intake levels subtracted and are normalized for differences in face airflow and production (SCs/min). 
56

Table C-6. Shuttle car loading times and dust concentrations with the scrubber off 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-2 2 8:54:20 8:54:42 0.04 0.51

1-2 1 8:55:36 8:56:49 0.04 3.47

1-2 2 9:00:00 9:03:10 0.09 3.42

1-2 1 9:04:24 9:11:05 0.15 5.00

1-2 2 9:15:20 9:20:03 0.08 0.32

1-2 1 9:21:07 9:24:26 0.06 3.83

1-2 2 9:39:03 9:44:40 0.06 0.26

1-2 1 9:46:00 9:51:24 0.05 0.83

1-2 2 9:53:05 9:55:56 0.04 0.11

1-2 1 9:57:36 9:59:29 0.04 0.25

1-2 2 10:00:02 10:05:54 0.04 0.08

1-2 2 10:16:34 10:18:22 0.04 2.08

1-2 1 10:19:00 10:21:45 0.04 1.37

1-2 2 10:22:26 10:25:37 0.05 0.07

1-2 1 10:28:36 10:30:33 0.05 0.14

1-2 2 10:31:09 10:35:53 0.05 0.02

1-2 1 10:38:59 10:40:40 0.05 0.21

Cut avg - - - - 1.29

2-1 1 7:46:42 7:47:07 0.02 0.02

2-1 2 7:48:28 7:50:00 0.04 0.00

2-1 1 7:51:20 7:53:13 0.05 0.06

2-1 2 7:54:26 7:56:18 0.01 0.01

2-1 1 7:57:28 8:00:01 0.06 0.04

2-1 2 8:01:25 8:01:48 0.06 0.00

2-1 1 8:20:28 8:22:18 0.02 0.08

2-1 2 8:24:53 8:27:10 0.01 0.00

2-1 1 8:28:53 8:32:15 0.01 0.02

2-1 2 8:33:36 8:36:21 0.01 0.00

2-1 1 8:38:07 8:42:07 0.01 0.01

2-1 2 8:43:36 8:46:08 0.00 0.00

2-1 1 8:47:26 8:50:05 0.01 0.02

2-1 2 8:53:23 8:53:33 0.03 0.00

2-1 2 8:55:12 8:55:34 0.03 0.00

Cut avg - - - - 0.02

2-2 1 9:15:18 9:16:46 0.08 0.49

2-2 2 9:18:31 9:20:02 0.37 0.00

2-2 1 9:21:58 9:23:20 0.05 0.01

2-2 2 9:24:49 9:27:11 0.04 0.00

2-2 1 9:30:40 9:32:30 0.14 0.00

2-2 2 9:34:00 9:35:58 0.01 0.00

2-2 1 9:37:36 9:39:59 0.09 0.00

2-2 2 9:41:35 9:43:37 2.30 0.00

* Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 
57

Table C-6. Shuttle car loading times and dust concentrations with the scrubber off 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

2-2 1 9:45:50 9:50:16 0.29 0.00

2 9:51:48 9:55:29 0.46 0.00

2-2 1 9:59:12 10:01:20 0.27 0.00

2-2 2 10:24:52 10:26:08 0.02 0.00

2-2 1 10:27:20 10:27:35 0.01 0.00

2-2 2 10:28:45 10:32:46 0.14 0.00

2-2 1 10:35:30 10:41:49 0.02 0.00

Cut avg - - - - 0.01

3-2 2 11:20:23 11:22:34 0.01 0.01

3-2 2 11:30:03 11:31:48 0.02 0.00

3-2 2 11:38:38 11:40:28 0.02 0.02

3-2 2 11:47:50 11:49:47 0.03 0.00

3-2 1 11:52:03 11:53:26 0.03 0.25

3-2 2 11:58:10 12:01:16 0.03 0.07

3-2 2 12:09:44 12:11:49 0.03 0.05

3-2 2 12:15:09 12:15:48 0.03 0.00

3-2 2 12:19:20 12:20:43 0.03 0.00

3-2 1 12:22:28 12:23:20 0.03 0.58

3-2 2 12:27:13 12:29:26 0.03 0.00

3-2 1 12:31:36 12:33:24 0.03 0.06

3-2 2 12:35:47 12:36:31 0.03 0.11

3-2 2 12:40:06 12:40:44 0.12 0.00

3-2 2 12:43:56 12:48:20 0.03 0.00

3-2 2 12:50:14 12:51:30 0.03 0.00

3-2 2 (cont) 12:54:40 12:55:53 0.03 0.00

Cut avg - - - - 0.07

Survey

avg

- - - - 0.35

* Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 
58

Table C-7. Shuttle car loading times and dust concentrations with the scrubber on 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

1-1 1 7:58:04 7:58:35 0.04 0.23

1-1 1 7:59:00 8:03:28 0.04 0.12

1-1 1 8:06:24 8:07:50 0.04 0.16

1-1 2 8:09:33 8:11:30 0.04 0.67

1-1 1 8:12:28 8:14:54 0.04 0.12

1-1 1 8:19:59 8:20:46 0.04 0.08

1-1 1 8:21:57 8:22:39 0.11 0.24

Cut avg - - - - 0.23

1-3 1 11:33:40 11:34:30 0.04 0.20

1-3 1 11:36:14 11:38:26 0.05 0.60

1-3 1 11:40:00 11:41:45 0.03 2.10

1-3 1 11:44:50 11:47:40 0.03 7.73

1-3 1 11:50:27 11:52:27 0.05 3.64

1-3 1 11:53:40 11:56:20 0.05 7.85

1-3 1 12:02:36 12:03:34 0.04 1.03

1-3 1 12:06:15 12:07:03 0.07 1.08

1-3 1 12:08:47 12:09:51 0.05 0.31

1-3 1 12:11:44 12:14:14 0.06 0.12

1-3 1 12:15:29 12:16:26 0.07 0.52

1-3 1 12:18:32 12:19:07 0.07 4.61

Cut avg - - - - 1.33†

2-3 1 11:51:46 11:52:30 0.04 0.00

2-3 1 11:57:55 12:03:10 0.02 0.07

2-3 2 12:08:12 12:13:04 0.06 0.00

2-3 2 12:15:25 12:17:02 0.17 0.00

2-3 1 12:23:05 12:23:57 0.12 0.00

2-3 1 12:26:09 12:29:46 0.42 0.05

2-3 2 12:31:53 12:34:06 0.09 0.00

2-3 2 12:41:39 12:42:30 0.07 0.00

2-3 2 12:45:34 12:48:14 0.04 0.00

2-3 1 12:49:50 12:52:28 0.04 0.02

2-3 1 12:54:27 12:55:49 0.03 0.00

2-3 1 12:57:29 12:58:09 0.03 0.02

Cut avg - - - - 0.01

3-1 2 9:17:46 9:19:20 0.04 0.30

3-1 1 9:20:17 9:21:42 0.05 0.25

3-1

1 (cont) 9:23:29 9:29:41 0.04 0.06

3-1 1 (cont) 9:29:58 9:32:27 0.03 0.09

3-1 2 9:33:41 9:41:18 0.03 0.13

3-1 1 9:42:40 9:45:20 0.03 0.02

3-1 2 9:47:11 9:52:52 0.02 0.11

* Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 

† Line curtain too close to face with scrubber operating until 12:05. Cut average calculated after this time. 
59

Table C-7. Shuttle car loading times and dust concentrations with the scrubber on 

(Continued) 

Cut

No.

SC 

No.

SC

begin 

loading

SC

end 

loading

Intake 

dust, 

mg/m3

SC*

dust, 

mg/m3

3-1 2 9:54:16 10:03:47 0.03 0.22

3-1 1 10:06:06 10:09:21 0.03 0.13

3-1 2 10:10:59 10:16:04 0.02 0.17

Cut avg - - - - 0.15

Survey

avg

- - - - 0.43

* Shuttle car (SC) dust levels have intake levels subtracted; if less than zero, zero is shown. 

† Line curtain too close to face with scrubber operating until 12:05. Cut average calculated after this time. 
Delivering on the Nation’s promise: 

safety and health at work for all people 

through research and prevention 

To receive NIOSH documents or more information about 

occupational safety and health topics, please contact NIOSH: 

Telephone: 1–800–CDC–INFO 

TTY: 1–888–232–6348 

CDC INFO: www.cdc.gov/info 

or visit the NIOSH Web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews.

DHHS (NIOSH) Publication No. 2014-105

SAFER • HEALTHIER • PEO PLETM