Controlling dust exposures in longwall 

mining utilizing a simple barrier

D.D. SWEENEY, J.M. SLAGLEY,

 D.A. SMITH AND J.P. RIDER

Daniel D. Sweeney, Jeremy M. Slagley and David A. 

Smith, are industrial hygiene master’s student, industrial hygiene 

director, graduate industrial hygiene program and environmental 

engineering and sciences director with the Department of Systems 

and Engineering Management with the Air Force Institute of 

Technology, Wright Patterson Air Force Base, OH; James P. Rider, 

member SME, is acting team leader, dust control, respiratory 

hazards control branch with the National Institute for Occupational 

Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA. 

Abstract

The United States coal mining industry has traditionally 

experienced difficulty in controlling dust levels below the 

occupational exposure limit. While improvements in face 

ventilation and water spray nozzles have decreased dust 

exposures, approximately eight percent of experienced coal 

miners are still developing Coal Worker’s Pneumoconiosis. 

This investigation tested the feasibility of enhancing existing 

engineering dust controls by mounting a simple barrier on 

a longwall shearer that separated the operators from the 

cutting drums. The barrier was constructed and tested above 

ground at the National Institute for Occupational Safety 

and Health Pittsburgh Research Laboratory longwall gallery test facility. A 96-percent reduction of respirable dust 

occurred at the headgate sampling position when tested at 

2.4 m/sec (480 ft/min). The average dust level decreased 

from 39 mg/m3

 to 1.5 mg/m3 by utilizing the barrier. 

Introduction

In spite of engineering controls, 

the United States coal mining industry exposes miners to dust levels exceeding the 2 mg/m3

 regulatory limit. 

In fact, because of the historical difficulties associated with controlling 

hazardous dust levels within the mining industry, the National Institute 

for Occupational Safety and Health 

(NIOSH) has identified its top strategic goal for the mining industry as reducing respiratory diseases (NIOSH, 

2008). Furthermore, dust samples 

collected over a four-year period 

from 1995 to 1999 (Niewiadomski, 1999) showed that 20 percent of 

longwall miners are overexposed to dust. An additional 

five-year study, from 2000 to 2004 (Niewiadomski, 2004), 

showed overexposure rates to be between 14 % and 15%. 

These high exposure rates have led approximately 8% of 

longwall miners with at least 25 years of mining experience to develop coal worker’s pneumoconiosis (Rider & 

Colinet, 2001). 

A possible engineering control for lowering dust 

exposures to longwall miners is the use of an air splitting barrier. A 1994 study using a full mesh partition 

barrier during underground longwall mining indicated 

a 52- percent dust reduction 31 m (100 ft) downstream 

of the shearer during the head-to-tail pass, but no reduction during the tail-to-head pass (U.S. Bureau of 

Mines, 1994). The conclusions of the study indicated a 

dust reduction was possible in underground longwall mining with the 

use of a barrier. However, the mesh 

barrier used limited visibilty to the 

point of being impracticle. Another 

disadvantage the study noted was 

the possbility of less air mixing due 

to the barrier, which could create 

higher concentrations of methane 

in gaseous mines. 

This current study investigates 

the feasibility of using either a partial or a full barrier mounted to a 

simulated coal mine longwall shearer between the cutting drum and the 

shearer operator. As with the 1994 

study, this investigation utilizes the 

barrier as an engineering control in conjunction with ventilating air to keep the dust generated by the cutting drum 

entrained in the airway separated from the operator. The 

primary differences with the current study are the barrier 

was constructed of clear acrylic for greater visibility and 

mounted to the shearer rather than the shield canopy.

Procedures 

Dust production and monitoring. To measure the 

effectiveness of the full and partial barrier, tests were 

performed in an above-ground, full-scale longwall test 

facility at the NIOSH Pittsburgh Research Laboratory 

(PRL). The simulated face is 38.13-m- (125-ft-) long and 

the height from floor to roof is 3.05 m (10 ft) as shown in 

Fig. 1 (Rider and Colinet, 2001). Twenty-four simulated 

shield supports 1.52-m- (5-ft-) wide cover the length of 

the test facility. A full scale wooden mock-up of a Joy 

4LS double ranging arm shearer was located approximately one half of the distance from the headgate to the 

tailgate. Ventilation for the longwall gallery was provided 

by three exhaust fans capable of supplying approximately 

59.9 m3

/sec (127,000 cu ft/min) of air along the face. A 

water spray system was available, but not used during 

this simulation.

Commercially available respirable coal dust was fed 

into the longwall gallery at the headgate and tailgate 

drums and at three points near the headgate drum by a 

screw type feeder into mini educators. Compressed air 

carried the coal dust from the educators into the gallery to produce dust at or near the headgate and tailgate 

drums.

Real-time aerosol monitors (RAM), for instantaneous dust measurements were employed to collect the 

dust samples during testing. The RAM is a portable dust 

measurement device where dust-laden air was pulled at 
2 L/min through a 10-mm (0.4-in.) cyclone that separated 

the respirable dust and passed it through a light source. 

The amount of light deflection in the chamber was considered to be representative of the dust concentration 

(GCA, 1979). 

FIGURE 1 

Simulated full-scale longwall facility at NIOSH-PRL. Arrows indicate RAM locations.

Four RAMs were used to measure dust levels. The 

cyclones (Fig. 2) were suspended from the shield supports 

at breathing zone level near shields 10, 12, 15 and 18 to 

approximate the shearer operator and the jacksetter positions. 

FIGURE 2 

Suspended cyclone.

 Measurements were averaged and recorded every 

two seconds. The instantaneous dust concentrations were 

downloaded to a multichannel data acquisition system 

for monitoring throughout the test and for subsequent 

analysis. Although not considered a primary standard for 

dust levels, the RAMs were used to measure dust in relative concentrations throughout the experiment. A 2007 

study on RAMs concluded that the analyzers provided 

accurate relative dust levels for ventilation face velocities greater than 1 m/s (200 ft/min). The study concluded 

real time sampling is beneficial in research studies for 

measuring relative rather than absolute concentrations; 

therefore, values reported in this article should be considered relative rather than absolute concentrations (Listak 

et al, 2007)

Dust tests were conducted at three different ventilation face velocities for each barrier configuration: no barrier, the partial barrier and the full barrier. Each test was 

run for 10 minutes. The face velocity remained relatively 

consistent between configurations for each respective 

ventilation speed, which was measured upstream of the 

mock shearer near shield number six with a direct read 

anemometer. The results are shown in Table 1 for each 

test configuration (± one standard deviation). 

Table 1 

Face velocities for each configuration.

Fan speed No barrier Partial barrier Full barrier

(m/sec) (m/sec) (m/sec)

Low	 2.4	±	1.0	 2.5	±	0.8	 2.5	±	0.8

Medium	 3.4	±	1.1	 3.4	±	1.0	 3.4	±	1.0

High	 4.2	±	1.4	 4.3	±	1.4	 4.3	±	1.4

Barrier construction

Two barrier configurations were tested on the mock 

shearer (Fig. 3A), a partial barrier leaving approximately 

a 0.6 m (2 ft) gap between the top of the barrier and the 

shield (Fig. 3B) and a full barrier extending to the top of 

the shields (Fig. 4).

The full barrier was constructed of 1.22-x-0.61 m (4-

x-2 ft) clear acrylic sheets with a thickness of 0.95 cm 

(0.37 in.). Each sheet was mounted in series to a wooden 

frame that extended the full length of the shearer just 

beyond each cutting drum. Rubber sheets attached to 

the top of the barrier created a flexible seal that could adjust with the shield height as shown in Fig. 4. The partial 

barrier was constructed by removing the flexible rubber 

from the top of the acrylic sheets, leaving approximately 

a 0.6-m (2-ft) gap between the top of the barrier and the 

upper shield. The blue portion shown in the figure was 

a protective coating on the acrylic sheets that was later 

removed. 

 Results

The results of each 10 minute test session were compiled to obtain an average (n=300) respirable dust exposure level in mg/m3

. Results were compared for statistical 

significance using JMP software (SAS Institute Inc., Cary, 

North Carolina). Each configuration was compared using 

analysis of variance (ANOVA) with a significance level 

of alpha less than 0.05. When a significant difference was 

observed between groups, Tukey-Kramer comparisons 

were used to determine which configuration within the 

group showed a statistically significant difference. 

The greatest reduction in measured dust levels was 

at the headgate sampling position with the average face 

velocity at 2.4 m/sec (480 ft/min). The reduction varied 

between 39 mg/m3 without the barrier to 1.5 mg/m3 with 

the partial barrier, equating to a 96-percent reduction. 

Similar reductions were noticed at the mid and high ventilation velocities for the headgate sampling position, 

bringing the dust levels close to zero with either barrier 

in place. At the remaining two shearer operator positions, 

dust levels also decreased significantly with both the 

partial and full barriers compared with no barrier for 

all ventilation rates (Prob > F 0.0001 for all cases). 

For example, at the taildrum position at the high 

ventilation rate, a 59-percent decrease in dust level 

was measured. This result demonstrates that even 

at lower concentrations, which may be closer to true 

underground exposure levels, the barrier is still very 

effective at reducing dust levels. Although in most 

cases, a significant difference was also found between 
the dust levels for the partial versus the full barrier, these 

differences were not of practical significance. Figure 5 

summarizes the dust level results.

FIGURE 3 

Mock longwall shearer with: A: no barrier and b: the partial Barrier.

FIGURE 4

Full barrier mounted on mock-shearer.

FIGURE 5 

Respirable dust levels for low, medium and high relative 

face velocities.

At the jacksetter sampling position, the dust levels 

increased significantly with the placement of the barrier, 

with the exception of the full barrier at 2.4 m/sec (480 ft/

min), which had a slight decrease in the dust levels (Prob 

> F 0.0001 for all cases).

At all positions, increasing ventilation rate decreased 

dust levels with and without the barrier in place with the 

highest decrease in dust levels measured at the headgate 

drum by 84 percent from the low to high ventilation.

Discussion

The results of this study suggest 

a barrier mounted on a longwall 

shearer in combination with forced 

ventilation may reduce dust exposure to shearer operators. Additionally, increasing the ventilation rate 

further reduces the dust exposure. 

The current study, however, indicates a significant decrease in dust 

concentration can be achieved by 

either a full or partial barrier. One 

drawback to the barrier is there may 

be an increase in dust exposure to the 

jacksetter. A possible cause of the increased downwind exposure may be 

that eddy currents were created at the end of the barrier, 

which resulted in a turbulent area downwind of the barrier. Utilizing a series of sprays in the tailgate drum area 

in conjunction with the barrier could result in the dust 

plume being directed toward the face and may increase 

the size of the clean air envelope created by the barrier. 

Further testing of the barrier in combination with water 

spray nozzles needs to be conducted to determine if the 

downwind dust exposure could be decreased. 

The barrier may also reduce operator visibility of the 

cutting drum. Figure 6 demonstrates the visibility of the 

cutting drum while the dust was being generated. Although the coal dust adhered to the acrylic sheeting, a 

water spray system could be utilized to keep the shield 

clean. Additionally, the operator would be able to see the 

top of the drum by simply looking over the barrier.

 Furthermore, the barrier constructed in this study 

would not have been sturdy enough to withstand the 

harsh conditions faced in underground coal mining. In 

order to be of practical use, the barrier would need to be 

constructed of hardened materials, such as a bullet-proof 

clear acrylic, be mounted on a flexible hinge and be capable of continuous or rapid cleaning so as not to block 

the operator’s view of the longwall face. The final product 

would need to withstand bombardment from coal shrapnel as well as not interfere with the top of the shields.

Finally, as noted in the 1996 mesh partition study, a 

barrier may increase methane concentrations near the 

coal face. This might not occur as the barrier is mounted 

to the shearer and, therefore, constantly moving. Methane concentrations would need to be closely monitored 

during underground testing of this barrier design.

Conclusions

The test results indicate that a significant reduction 

of respirable dust can be achieved from either a partial 

or full barrier mounted between the cutting drums of 

the longwall shearer and the shearer operators. As high 

as a 96 percent reduction in respirable dust levels was 

measured at the shearer operators’ positions with low 

ventilation rate. Additionally, at the high ventilation rate, 

dust levels were reduced by 59 percent. Dust exposure 

was also reduced by increasing the ventilation face velocity with or without the barrier in place by as much as 

80 percent. While the barrier used in this study was not 

built to withstand the rigorous conditions found in underground longwall operations, the model demonstrates the 

preliminary feasibility of such a control.
The barrier may decrease the operators’ visibility of 

the coal face and would likely need a self cleaning mechanism such as a spray cleaner. Additionally, the barrier 

may increase methane concentrations. Therefore, any 

underground testing would require close monitoring of 

methane levels at the coal face. 

FIGURE 6 

View of headgate cutting drum through partial barrier.

Disclaimer

The views expressed in this paper are those of the 

authors and do not reflect the official policy or position 

of the United States Air Force, the Department of Defense, the National Institute for Occupational Safety and 

Health or the United States government.

Acknowledgments

The authors would like to thank the National Institute 

of Occupational Safety and Health and the Health Pilot 

Research Project Training Program of the University of 

Cincinnati Education and Research Center Grant #T42/

OH008432-03 for supporting this work. They would also 

like to thank Steve Guffey and Dan Conaway who helped 

conceive the project.

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