Current Dust Control Practices on U.S. Longwalls 

by 

James P. Rider and Jay F. Colinet 

National Institute for Occupational Safety and Health 

ABSTRACT
 

The National Institute for Occupational Safety and Health (NIOSH) has conducted 

benchmarking surveys at longwall operations across the country to identify current operating 

practices and the types of controls being used. Gravimetric and instantaneous dust sampling 

was completed to quantify dust generation from major sources and determine the relative 

effectiveness of the different control technologies. Results from the underground dust surveys 

will be presented as an update on longwall dust control technology and operating practices. 

INTRODUCTION 

Longwall mining equipment and operational practices have improved dramatically from the 

early 1980s through the 1990s and this improvement continues today. By the late 1990s, 

longwall mine output accounted for 40% of all underground output in the U.S., and in 2004, 

longwall mines accounted for 51% of coal produced underground in the United States. 

Factors specific to longwall mines that supported productivity improvement include: higher 

capacity shearers, improved shield hydraulics and control, higher horsepower for equipment, 

wider face conveyors, and larger faces. Longwall panels averaged 940 ft wide and nearly 

10,000 ft long in 2002, compared to an average of 750 ft wide and 7,000 ft long in 1994. 

New longwall panels, currently in the planning stage, may be as wide as 1,500 ft wide and as 

long as 15,000 ft. Overall production from U.S. longwall mines in 2004 was over 189.5 

million tons. The average output from U.S. longwall mines has increased approximately 

115% over the last 15 years, from 1.9 to 4.12 million tons (Fiscor, 2003). 

Although significant gains in longwall dust control have been made, they have been 

challenged by substantial increases in coal extraction rates, which result in the potential to 

generate more dust (Webster et al., 1990). Average production during compliance sampling 

by mine operators has increased from an average of 2,800 tons per shift in 1990 to an average 

5,600 tons per shift in 2004. Consequently, longwall operations continue to have difficulty in 

maintaining consistent compliance with the federal dust standard of 2.0 mg/m3

. During a 

five-year span from 2000 through 2004, mine operators and Mine Safety and Health 

Administration (MSHA) inspectors collected 7,421, and 1,587 compliance dust samples, 

respectively. Analysis of these samples show that 14% of the mine operator samples and 15% 

of the MSHA samples were equal to or exceeded 2.1 mg/m3, the level at which a citation is 

issued (Niewiadomski, 2004). 

The control of respirable coal dust provides an ongoing challenge for coal mine operators. 

Ventilation and water sprays remain the primary methods utilized to control dust generated 

during longwall mining. To compensate for ever-increasing production, mine operators have 

increased face air velocities and water quantities in an attempt to protect mine workers from 

excessive dust exposures. This paper describes the on-going research effort to identify the 

current status of longwall mining and dust control technology being applied in the industry. 
LONGWALL SURVEYS 

Sampling Methodology 

Gravimetric dust samplers, identical to those used in compliance sampling, were operated at 

2L/min in conjunction with 10-mm Dorr-Oliver nylon cyclones. Samplers were utilized at 

stationary and mobile sampling locations to quantify the levels of respirable dust generated at 

prominent sources along the longwall face. Gravimetric sampling was conducted on-section 

for 4 to 6 hours, and mine personnel did not wear any of the samplers. Calculated 

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

levels and should not be compared to compliance sampling concentrations. 

Personal DataRAMS (PDRs) were used adjacent to the gravimetric samplers at select 

sampling locations to obtain a time-related profile of dust levels generated during each 

sampling period. The PDR is an MSHA-approved, instantaneous dust measuring device 

where dust-laden air passes through a sampling chamber and a light source. The amount of 

light deflection in the chamber is measured and provides a relative measure of the dust 

concentration. Instantaneous dust levels were stored at 10-second intervals in an internal data 

logger and then downloaded onto a computer for analysis. Dust levels measured with the PDR 

can be calculated for any time period of interest (e.g., head-to-tail or tail-to-head passes). 

Mobile dust sampling to determine the amount of dust generated by the shearer and by 

movement of advancing shields was conducted by a three-member NIOSH sampling team. 

Ideally, the UPWIND sampling location was approximately 7.6-15.2 m (25-50 ft) upwind of 

the headgate cutting drum and measured intake dust levels reaching the shearer. The 

SHEARER sampling location was located between mid-shearer and the tailgate end of the 

shearer. The sampling crew member was usually positioned within a shield or two of the 

tailgate shearer operator. This data provided an indication of the amount of dust that has 

migrated from the face between the cutting drums. When possible, the DOWNWIND 

sampling location was approximately 7.6-15.2 m (25-50 ft) downwind of the tailgate drum. 

Due to shield movement patterns, this sampling location had to be adjusted at certain mines. 

Each team member maintained their relative position with the shearer as it moved across the 

face. The difference in dust levels between the UPWIND and DOWNWIND locations was 

dust generation attributed to the shearer. In addition, similar mobile sampling was conducted 

upwind and downwind of shield movement on selected head-to-tail passes to isolate dust 

liberated during shield advance. 

At each of these mobile sampling positions, each sampling crew member wore a sampling 

vest that contained two gravimetric pumps and four cyclones with appropriate filter cassettes 

(figure 1). Two of the four cyclones [attached to the sampling vest on the left and right sides 

of the chest area] were connected to the gravimetric pumps and used to sample dust levels 

during head-to-tail passes. The other two cyclones, also attached to the sampling vest on the 

left and right sides of the chest area, were used for sampling tail-to-head passes. If the shearer 

was stopped for an extended period (> 3 minutes), the gravimetric pumps were paused so that 

mobile sampling along the face was representative of dust levels during active mining. Along 

with the gravimetric sampling package, members of the sampling crew carried a PDR 

sampler. 

Mobile sampling was augmented with stationary sampling packages. At each stationary 

sampling location, two gravimetric samplers were located adjacent to one another and 

operated over the same sampling period. Stationary sampling locations included the intake, 
belt entry, shield 10, and approximately 10 shields from the tailgate. Intake samplers were 

typically located in the last open crosscut and used to isolate the dust contamination from 

sources outby the longwall face. If the mine was utilizing the belt entry as an additional 

intake, gravimetric samplers were located outby the last open crosscut and the stageloader to 

monitor dust levels liberated in the belt entry. The shield 10 samplers were used to monitor 

the dust concentrations of air coming onto the face. The difference between dust levels 

measured at shield 10 and the intake and belt sources represent an estimate of dust liberated 

by the stageloader/crusher dust source. The tailgate sampling package provided an indication 

of the total dust generated along the face. The samplers were typically started after arrival 

upon the longwall face and operated continuously until sampling was completed. PDR 

samplers were also placed at the shield 10 and tailgate sampling locations. 

In addition to dust measurements, sampling personnel monitored airflow and water quantities 

on the longwall section. During each shift of sampling, spot air velocity readings were taken 

with hand-held anemometers at 10-shield intervals down the face. These measurements were 

one-minute readings taken approximately one foot above the spill plate of the face conveyor. 

Also, a rough estimate of the area at each velocity sampling location was calculated to 

estimate the air quantity present. If possible, water flow meters were installed in the water 

line supplying the shearer and the line supplying the stageloader/crusher sprays. Periodic 

readings were taken from each of these meters to monitor the quantity of water being used to 

suppress dust. 

Survey Results 

Daily spot velocity readings were recorded approximately every 10 shields along the longwall 

face and were used to calculate the average face velocity. An increase in excess of 0.8 m/sec 

(157 ft/min) was seen when compared to average air velocities reported in the mid 1990s 

longwall study(Colinet et al., 1997). The average velocity of the surveyed longwalls was 3.4 

m/sec (665 ft/min). Seven of eight longwalls had average air velocities greater then 3.0 m/sec 

(600 ft/min), with two mines averaging over 4.1 m/sec (800 ft/min). Along with air velocity 

calculation, a rough estimate of the area under the shields at each velocity sampling location 

was used to calculate average air quantity for each face. Average air quantities increased 

approximately 65% when compared to the mid-1990 longwall study. The average volume of 

air moving down the face was approximately 31.6 m3

/sec (67,000 ft3/min), with a range 

between 24.3 to 39.1 m3

/sec (51,000 to 83,000 ft3/min). Air quantity observed for six of the 

eight longwalls was greater than 30.2 m3

/sec (64,000 ft3/min). 

Substantial variations in operating conditions were encountered during the surveys. 

Comparing panel widths observed in these latest surveys with panel widths reported in a mid 

1990s longwall study (Colinet et al., 1997) showed an increase of approximately 25%. Face 

panel widths ranged between 237.7 and 304.8 m (780 and 1,000 ft), and the average face 

width was 272.2 m (893 ft). Also, the average cutting height was 2.7 m (9 ft) with a range 

between 2.1 and 3.4 m (7 and 11 ft). Six of the eight mines surveyed to date utilized a 

bidirectional cutting sequence, with two mines employing unidirectional cutting. 

Along with an escalation of air down the face, the use of water to the shearer has increased in 

an effort to control dust liberating from the face. An average of 492.0 L/min (130 gpm) was 

observed at the shearer for these longwall operations. The number of shearer drum sprays 

ranged between 35 and 62, and the average drum spray pressure was approximately 1034.2 

kPa (150 psi). In the 1995 study, the average water usage at the shearer was 378.5 L/min (100 
 

gpm) with an average drum spray pressure of 965.3 kPa (140 psi). Half of the mines surveyed 

utilized crescent sprays on the ranging arms. 

Air-moving directional sprays systems were observed on the headgate side of the shearer at 

seven of the eight longwalls. Splitter arms used to keep fugitive dust away from the shearer 

operators were unique to each mining operation. The length and number of directional sprays 

varied greatly. The minimum length of the splitter arm was 2.7 m (9 ft), and the maximum 

length was 4.6 m (15 ft). The number of sprays ranged between 6 to 19. The type of spray, 

spacing between the sprays, and the directional angle of the sprays were mine specific. 

Sprays were directed downwind, toward the face, and in the direction of the roof and panline. 

Extension arms attached to the end of splitter arms were observed at three longwalls. The 

length of the extension arms ranged between 45.7 to 61.0 cm (18 to 24 inches) and were 

angled between 30 and 45 degrees toward the face. Two mines used venturi sprays which 

were mounted on top of the splitter arm. Average spray pressures were approximately 689.5 

kPa (100 psi) when hollow cone sprays were utilized and in excess of 1551.3 kPa (225 psi) 

when venturi sprays were operated. 

Deflector or sloughing plates were observed at three western longwalls. At one operation, a 

single plate spanned the length of the shearer and 6 venturi sprays were evenly spaced across 

the top of the plate. At the other two operations, deflector plates were split into three 

independent sections. Each section had five hollow cone sprays evenly spaced across the top 

of the plate. Various types of spray manifolds were observed at the eastern longwalls. Three 

or four manifolds consisting of four or five sprays were evenly spaced across the length of the 

shearer. The manifolds were either located on the face side of the shearer or on the top of the 

shearer close to the face. One operation, located spray manifolds toward the middle of the 

shearer and elevated the manifolds 15.2 to 30.5 cm (6 to 12 inches) off the shearer body. 

Manifolds located above the lump breaker or on the shearer body to control dust in the 

tailgate drum area were observed on all but one longwall. A minimum of 4 and maximum of 

16 sprays were directed toward the cutting drum or down onto the conveyor. One operation 

utilized a series of higher pressure sprays and directed them downwind just inside the spill 

plate. The sprays formed a water curtain that was effective at keeping fugitive dust out of the 

walkway. A tailgate splitter arm was observed on one longwall. 

The minimum, average, and maximum dust levels for stationary and mobile gravimetric 

sampling locations are shown in figures 2 and 3. Intake dust levels were consistently low 

indicating very little dust contamination was occurring from outby sources. The maximum 

dust level measured was 0.34 mg/m3

 with the majority of the operations below 0.20 mg/m3. 

Average dust levels at the intake sampling location were reduced by 53% when compared to 

the average intake samples measured during the previous (1995) longwall surveys. Half of 

the longwalls surveyed used belt air as a supplementary air source. For these longwalls, the 

average dust level in the belt entry was 0.41 mg/m3

, while the average intake concentration 

was 0.18 mg/m3, approximately 2.3 times less than the belt entry dust concentrations. 

The dust level monitored at shield 10 is a good indication of the dust entering the face from 

the stageloader/crusher along with intake and belt outby sources. Average dust concentration 

found at shield 10 was 0.67 mg/m3

. Dust levels associated with the stageloader/crusher 

operation can be determined by looking at the difference between intake/belt and shield 10 

dust concentrations. On average, the amount of dust that can be attributed to the 

stageloader/crusher was 0.48 mg/m3

. A good indication of the amount of total dust generated 

along the face was monitored at the tailgate sampling location. Dust levels ranged between 
1.04 mg/m3

 to 3.88 mg/m3 and averaged 2.56 mg/m3. Reductions in dust levels monitored at 

the stationary sampling locations in the belt entry, at shield 10, and at the tailgate ranged 

between 27% and 39% when compared to the 1995 study. 

Average dust concentrations at the upwind and shearer mobile sampling locations were higher 

for the head-to-tail passes (figure 3). Dust levels at these two sampling locations reflect dust 

liberated from shields being advanced when mining head-to-tail. At the shearer sampling 

location dust generated by the shearer, primarily the headgate drum is also included. Isolating 

dust generated by the shearer is accomplished by subtracting the upwind sampling 

concentrations from the downwind concentrations. Average shearer-generated dust was found 

to be 2.06 mg/m3 when mining head-to-tail and 2.82 mg/m3 while cutting tail-to-head. Higher 

dust levels produced by the shearer were evident while mining tail-to-head when the headgate 

drum is the primary cutting drum. Shearer operators downwind of the headgate drum may be 

exposed to fugitive dust caused by the cutting action of the drum. This is not the case when 

mining head-to-tail when the dust generated by the primary cutting drum (tailgate drum) is 

downwind of the headgate shearer operator and possibly the tailgate shearer operator. 

A comparison of levels at shield 10 with upwind samples for tail-to-head passes showed an 

increase of 0.49 mg/m3

. Dust liberated by face spalls, from the face conveyor, and dust 

migrating from the gob may be causing the increase in dust levels. 

When comparing average dust levels from the UPWIND and SHEARER sampling locations, 

dust levels increased 0.51 mg/m3 for tail-to-head cuts and 0.31 mg/m3 for head-to-tail cuts. In 

the 1995 study, the increase in dust levels was 1.85 mg/m3 and 1.29 mg/m3 for tail-to-head 

and head-to-tail cuts when comparing the two sampling locations. This suggests that the 

increased air velocity down the face in conjunction with the directional spray systems have 

had a positive effect of confining fugitive dust close to the face and away from the walkway. 

Instantaneous dust samples measured with the PDR were used to calculate relative dust 

concentrations at each sampling location along the face. These relative dust measurements 

calculated from PDR data were based upon time study data obtained on a per-pass basis. 

Extended downtimes and wedge cut dust concentrations were excluded from the average PDR 

dust concentration. The PDR dust levels were adjusted based upon the ratio between the 

average dust concentrations obtained from the two gravimetric samplers divided by the dust 

concentration obtained from the PDR. 

Figures 4 and 5 illustrate adjusted PDR mobile sampling results from a typical head-to-tail 

and tail-to-head pass. Figure 4 shows that OUTBY dust levels are relatively low [averaging 

approximately 0.50 mg/m3

]. Significant increases in dust levels are found at the UPWIND 

sampling location. This supports the hypothesis that much of the dust liberated during headto-tail passes is generated by advancing shields. Examining data at the SHEARER sampling 

location shows that the directional spray system in conjunction with the high velocity/volume 

of air moving down the face has a positive effect on diluting high dust levels generated by 

shield movement. Dust levels at the DOWNWIND sampling location [approximately 1 shield 

inby the tailgate shearer operator] are approximately equivalent to the dust levels recorded by 

the SHEARER samplers. 

Figure 5 shows dust levels to be relatively low at the three shearer sampling locations when 

mining tail-to head. These dust levels are very similar to the outby dust levels measured at 

Shield 10 and the OUTBY sampling location. The spike in dust levels at the SHEARER and 

DOWNWIND sampling locations as the shearer approached the headgate is explained by 
shield advances. Because of unstable roof conditions, shields were pulled in advance of the 

shearer. The SHEARER and DOWNWIND samplers were inby the advancing shields and 

significant increases in dust levels were evident. These dust levels closely correspond to dust 

levels at the UPWIND sampling location when mining head-to-tail. 

CONCLUSIONS 

In the past decade, longwall operations have seen a significant increase in production and 

productivity and consequently, the potential to liberate more respirable dust is much greater. 

In an effort to control the exposure of respirable dust to longwall workers, mine operators 

have made substantial increases in the application of dust control technology. 

Sampling data obtained from surveys conducted by NIOSH researchers show that a wide 

variety of control technology applications exists across the industry. These differences may 

be explained by differing operating conditions and equipment. Although the type of control 

technology used to regulate the amount of dust exposure seems to be mine specific, a number 

of similarities also exist and are viewed as keys for successful dust control: 

•	 All operations are using a version of directional water sprays (shearer clearer) in an 

effort to confine dust near the face and away from workers. 

•	 Increased air velocity down the face in conjunction with the directional spray systems 

had a positive effect of confining fugitive dust close to the face. 

•	 The vast majority of operations are using some form of splitter arms on the headgate 

side of the shearer to contain dust liberation from the headgate drum. 

•	 Spray manifolds located on the shearer seem to be effective at keeping the dust close 

to the face. 

•	 Splitter arms and/or directional sprays are being used successfully at the tailgate end 

of the shearer to provide protection for the tailgate shearer operator. 

•	 Increased air quantity (approximately 65%) provides greater dilution. 

•	 Water quantity has increase by approximately 30%. 

Also, sampling data has shown that dust liberation and worker exposure from shield advances 

is significant. Given that the majority of sampled longwalls are utilizing bidirectional cutting 

sequences, the shearer operators are being exposed to this dust during the head-to-tail cutting 

pass. Additional research is needed to identify effective control technologies for limiting dust 

exposure to shield dust. 
 

REFERENCES 

Colinet, J.F., Spencer, E.R., and Jankowski, R.A., 1997, Status of Dust Control Technology 

on U.S. Longwalls, Proceeding, 6th International Mine Ventilation Congress, May 17-22, 

Pittsburgh, Pa., Chapter 55, pp 345-351. 

Fiscor, Steve, 2003, Total Number of Longwalls Drop to 52 – US Longwall Census 2003, 

Coal Age, February, 2003, pp 20-24. 

Niewiadomski, G.E., 2004, Mine Safety and Health Administration, private communication. 

Webster, J.B., Chiaretta, C.W. and Behling, J., 1990, Dust Control in High Productivity 

Mines, SME Annual Meeting, Preprint 90-82, Salt Lake City, Utah, 9 pages. 
 

 

Figure 1 – Sampling crew member wearing sampling vest containing gravimetric pumps, 

cyclones with appropriate filter cassettes, and carrying a PDR sampler. 
0.00 

0.50 

1.00 

1.50 

2.00 

2.50 

3.00 

3.50 

4.00 

Dust Concentration (mg/m3 ) 

Min Average Max 

Intake Belt Shield 10 Tailgate 

Sampling Locations 

Figure 2 – Dust levels measured at the stationary sampling locations. 
0.00 

1.00 

2.00 

3.00 

4.00 

5.00 

6.00 

7.00 

8.00 

Dust Concentration (mg/m3 ) 

Min Average Max 

Head to Tail Tail to Head 

Upwind Shearer Downwind Upwind Shearer Downwind
 

Sampling Locations
 

Figure 3 – Dust levels measured at the mobile sampling locations for head-to-tail and tail-tohead passes. 
Figure 4 – Adjusted PDR dust levels for a head-to-tail pass. 
Figure 5 - Adjusted PDR dust levels for a tail-to-head pass.