STATUS OF DUST CONTROL TECHNOLOGY 

ON U.S. LONGWALLS 

Jay F. Colinet, Ellsworth R. Spencer and Robert A. Jankowski 

NIOSH, Pittsburgh Research Center, P.O. Box 18070, Pittsburgh, PA 

ABSTRACT 

Longwall mining is the most productive method of underground coal mining in the United States (U.S.), and record levels 

of production have been reached in recent years. These ever-improving production levels have the potential to generate significantly higher quantities of respirable dust. Consequently, the 

longwall industry continues to struggle with controlling dust liberation and maintaining compliance with the federally-mandated respirable dust standard. In response, longwall operators have increased the application of primary dust controls, airflow and water flow, in an effort to improve respirable dust control and reduce 

worker exposure. 

Pittsburgh Research Center (PRC) personnel conducted 

dust surveys at 13 longwalls operating throughout the U.S. and 

collected information to: identify current operating practices on 

these longwalls, identify the types of dust controls in use, document the levels at which these controls are being applied, and 

measure the respirable dust levels present. This data was analyzed to quantify the dust levels generated by the major sources 

on the longwall section and to evaluate the relative effectiveness 

of the control technologies in use. 

INTRODUCTION 

Improvements in longwall equipment and mining practices 

have paved the way for the increases in production and productivity and longwall mining now accounts for over 40% of the coal 

produced underground in the U.S. The power made available to 

the shearer has increased by 90% in the past decade, while 

power to the face conveyor has more than doubled (Anon., 1995). 

These increases have allowed for faster mining and larger 

longwall panels. From 1984 to 1993, the average width and 

length of longwall panels have increased by 39% and 21%, respectively, so that the average size of the panel was over 230 m 

(750 ft) wide and nearly 2135 rn (7000 ft) long in 1994 (Anon., 1995). 

Longwall productivity has increased from an average of 1.4 metric 

tons per worker hour in 1983 to an average of 3.0 tons per worker 

hour in 1993. Average shift production has increased from 890 tons 

per shii in 1980 to approximately 3,250 tons per shift in 1994. 

Unfortunately, higher production levels generate greater 

quantities of respirable dust (Webster et al., 1990). Historically, 

longwall mining operations have had difficulty in maintaining compliance with federal dust standards and in the early 1980s, 31% 

of the longwall designated occupation (DO) samples collected by 

the Mine Safety and Health Administration (MSHA) exceeded the 

respirable dust standard (Niewiadomski and Jankowski, 1993). 

Longwalls continue to experience difficulty in maintaining compliance. For fiscal year 1994,20% of MSHA-collected DO samples 

exceeded the respirable dust standard and the percentage of 

longwall operations in noncompliance two or more times exceeded 21 % (Niewiadomski, 1996). Twenty-seven percent of 

longwall shearer operator samples collected by mine operators 

between 1988 and 1992 for compliance sampling exceed the 2.0 

mg/rn3 respirable dust standard (Anon., 1995a). In an effort to 

combat higher levels of dust generation, application levels for dust 

controls continue to be increased by longwall operators. 

PRC initiated a surveillance effort to quantify the levels of 

dust being generated by the various sources found on today's 

longwalls, identify the types of control technologies in use, and 

quantify the levels of application for these control technologies. 

Respirable dust surveys were completed at longwall mining operations located in Alabama, Colorado, Illinois, Pennsylvania, 

Utah and West Virginia to collect data representative of conditions 

found among different mining regions. 

SAMPLING METHODOLOGY 

Gravimetric dust samplers operating at 2 Umin with a 10-mm 

nylon cyclone preseparator were utilized with stationary and mobile sampling strategies to quantify the levels of respirable dust 

generated by the major sources on the longwalls. The reported 

gravimetric concentrations were calculated for actual sampling 

time, which was a maximum of six hours, and not converted to 

Mining Research Establishment (MRE) equivalent dust levels. 

The sampling data generated from this survey can not be utilized 

for or compared to dust concentrations of compliance samples 

which are eight-hour, portal-to-portal samples. 

lnstantaneous dust measurements were used to augment 

the gravimetric sampling, particularly where short sampling durations precluded the collection of suitable mass with gravimetric 

samplers. Instantaneous measurements were obtained with the 

Real-time Aerosol Monitor (RAM), which displayed real-time dust 

measurements on an LCD readout and stored these measurements in a data logger for later analysis. 

Fixed Point Sampling 

Gravimetric dust samplers were located at the fixed sampling 

locations illustrated in Figure 1. The intake samplers (I) 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 stage 

loader to monitor dust levels liberated in the belt entry (B). The 

headgate samplers (H) were placed at approximately shield 10 

and were used to monitor the dust concentration of the air coming onto the face. The difference between dust levels measured 
at H and the outby locations (I, B) would be dust generation attributed to the stage loader-crusher dust source. The tailgate samplers (T) were placed approximately 10 shields from the tailgate 

end of the face and used to provide an indication of the total dust 

generation along the face. 

Fixed rampl~rx) Mobile rarnpllrq 

I intake U Upwind 

B Belt S Shearer 

H Headgate D Dovnwlnd 

Figure 1. Dust sampling locations for longwall surveys. 

At each of these sampling locations, at least 2 gravimetric 

samplers were located adjacent to one another and operated over 

the same sampling period. At these fixed sampling locations, 

samplers were typically started shortly after arrival upon the longwall 

face and operated continuously until sampling was completed. 

Mobile Sampling 

Mobile dust sampling was conducted by three sampling team 

members at locations shown in Figure 1 to determine the amount 

of dust generated by the shearer. Each of the team members 

maintained their relative position with the shearer as it moved 

across the face. The upwind samplers (U) were approximately 

7.6 m (25 ft) upwind of the headgate drum and measured the intake dust levels reaching the shearer. The downwind shearer 

samples (D) were collected approximately 15.2 m (50 ft) downwind of the tailgate shearer drum. The difference between the 

dust concentrations measured at D and U was attributed to dust 

generated by the shearer. The samples collected at the tailgate 

end of the shearer (S) provide an indication of the dust migration 

from the face into the walkway. 

At these mobile sampling locations, 4 gravimetric filters were 

worn by each team member. Two of the filters were used to measure dust levels during the head-to-tail pass, while the other two 

filters measured dust levels for the tail-to-head pass. The gravimetric pumps were tumed off during extended down times so that the 

measured dust concentrations represent dust levels during mining. 

Mobile sampling was also conducted to isolate the respirable 

dust liberated during shield movement on the head-to-tail passes. 

One team member was positioned approximately 7.6 m (25 ft) 

outby all shield movement while a second team member remained approximately 7.6 m inby all shield movement. Each 

team member carried a RAM and noted the beginning and ending time of the dust measurements. The average concentrations 

for these sampling periods were calculated and the difference 

between the outby and inby concentrations was attributed to dust 

liberated during shield movement. 

Control Parameter Monitoring 

Dust control parameters such as airflow, water flow and water pressure were measured. Vane anemometers were used to 

collect spot velocity readings at 10-shield intervals along the face 

during each sampling shift. Water flow meters were installed in 

the water line supplying the shearer sprays and periodic measurements of total water flow to the shearer were obtained. Hand-held 

pressure gages were used to measure the nozzle operating pressure on the shearer drum and external sprays. 

MINING CONDITIONS AND CONTROLS 

A variety of operating conditions were encountered in sampling the different mines throughout the country. Table 1 summarizes the parameters that were observed or measured during the 

individual mine visits. Five of the mines were utilizing a bidirectional cutting sequence, seven mines were taking unidirectional 

cuts and one mine was using a half-face cutting sequence. Average face width was found to be 220 m (720 ft) with an average 

mining height of 2.3 m (7.7 ft). Since many variations in face 

widths, mining heights, cutting sequences, web depths and tram 

speeds were observed, a tons per minute (tpm) calculation was 

made for the cutting passes to facilitate relative productivity comparisons between mines. As shown in Table 1, nearly a three-fold 

difference in tpm was observed. The lowest level was found to be 

11.9 tpm for Mine A, while the highest level was found to be 35.4 

tpm at Mine C. Therefore, Mine C has the potential to produce 

three times more dust than Mine A, if uniform dust-generation is 

assumed. Obviously, the physical characteristics of the coal 

seam, the depth of cut, the type and maintenance of the cutting 

bits, and dust controls being applied will have major impacts on 

actual dust generation. 

Airflow and water application remain the primary dust controls and Figure 2 summarizes the data collected for these parameters. The average air velocity calculated from the spot velocity 

readings taken on the longwall faces was 2.5 m/s (497 fpm), with 

measured values ranging from 1.0 to 7.6 m/s (193 to 1500 fpm). 

The average velocity on the face of the surveyed longwalls represents an increase of over 0.5 m/s (1 00 fpm) when compared to 

the average air velocity data reported in a 1983 Bureau of Mines 

study (Jankowski and Organiscak, 1983). Past research 

(Jankowski et al., 1993) has indicated that air velocities greater 

than 2.0 m/s (400 fpm) should be utilized for improved dust control. Utilizing a rough estimate of the area under the shields for 

each face, an average air quantity of 19.2 m3ls (40,700 cfm) was 

calculated. The maximum air quantity observed was 50.0 m3/s 

(106,000 cfm). This data shows that on average, longwall operators are applying more air on longwall faces than ever before. 

Likewise, the use of water has greatly increased in an effort to 

control higher levels of dust liberation. Average water usage at 

the shearer was found to be 379 Lpm (100 gpm) at an average 

drum spray pressure of 965 kPa (140 psi). In the 1983 Bureau 

study, average water flow to the shearer was found to be 238 Lpm 

(63 gpm) at a drum spray pressure of approximately 414 kPa (60 

psi). Previous research (0' Green et al., 1994) has indicated that 

drum spray pressures above 690 kPa (100 psi) can aggravate 

shearer operator dust exposure by forcing dust into the walkway. 

Recommended operating pressure for nozzles in shearer drums 

is between 480 and 690 kPa (70 and 100 psi). Only 3 of the 13 

longwalls surveyed had drum spray pressure in the recommended 

range, with nine operations having pressures that are above the 

recommended range. This control parameter is one of the most 

important when considering shearer operator dust 

exposure and is relatively easy to control. The preferred method 

of reducing nozzle pressure would be to select a larger orifice di- 
Table 1. Summary of longwall parameters 

I M 1 (575) 

Headgate to Shie 

Cutting Metric tons1 

Cutting height minute 

sequence m cutting 

(fi) - 

Unidi- 2.0 ll.9T-H 

T-H cut (6.5) 

1.8 13.9 T-H 

Bidi- (6.0) 11 .O H-T 

Unidi- 3.4 35.4 T-H 

T-H cut (1 1 .O) p~ 

2.7 

Half-face* (9.0) 21.7* 

Unidi- 3.1 23.1 T-H 

T-H cut (1 0.0) 

Unidi- 2.1 11.3 T-H 

T-H cut (7.0) 

Half-web 2.7 32.9 T-H 

Bidi- (9.0) 28.2 H-T 

1.8 19.1 T-H 

Bidi- (6.0) 23.0 H-T 

1.7 27.6 T-H 

Bidi- (5.5) 20.7 H-T 

UnidiH-T cut (8.0) 31.5 H-T 

UnidiH-T cut (6.8) 18.9 H-T 

Unidi26.6 H-T 

12.7 T-H 

Bidi- (5.5) 15.9 H-T 

1 60 cleanup, Shield 60 to Tailgate cut; Tail 

Face air flow Shearer Drum 

V Q water pressure 

mlsec m3/sec Umin kPa 

(fpm) (*) (gpm) (psi) 

. . I . . , , 

ate to Shield 60 cleanup, Shield 60 to Headgate cut. 

Headgate to Shield 60 cleanup, Shield 60 lo Tailgate cut; Tailgate to Shield 60 cleanup, Shield 60 to Headgate cut 

ameter in the spray nozzles to increase flow and reduce pressure. 

A pressure regulator could be installed in the water supply line to 

the drums if greater reductions in pressure are needed. 

Nearly all of the shearers were equipped with an air-moving, 

shearer-clearer type of external spray system on the body of the 

machine. This spray system is designed to confine dust generated at the shearer drums near the face so that the ventilating air 

can carry the dust away from the shearer operators before the 

dust migrates into the walkway. All of the shearers were also 

equipped with radio remote control units, which should allow the 

shearer operators to position themselves in areas protected by 

the shearer clearer sprays. However, the tailgate shearer operator or! most of the longwalls would routinely travel downwind of the 

tailgate drum to observe the roof horizon during head-to-tail cutting passes or the floor horizon during tail-to-head passes. By 

positioning himself two to three shields downwind of the tailgate 

drum, the tailgate operator would typically increase his exposure 

to higher concentration dust clouds. At several operations, the 

tailgate operator would further complicate his dust exposure by 

lagging a greater distance behind the shearer to help the jack 

setter(s) advance shields. 

DUST CONTROL EFFECTIVENESS 

Table 2 summarizes the dust sampling results for both the 

stationary and mobile gravimetric sampling locations. 

Dust generation attributed to shield movement is also included 

in Table 2. The minimum, average and maximum dust levels from 

the stationary sampling locations and from shield movement are 

illustrated in Figure 3. 

The dust concentrations shown in Figure 3 indicate that 

mixed levels of success are being achieved for the mines sur- 
Kev 

Mlnlrnurn 

Average 

Marlmum 

SHEARER 

WATER. 

DRUM 

PRESSURE. 

kPa = 100 

Figure 2. Range of primary dust control parameters measured during surveys. 

SAMPLING LOCATION 

Figure 3. Range of dust concentrators measured at stationary sampling locations 

and for shield advance. 

veyed. Comparison between the minimum and maximum dust 

levels at the intake sampling location shows over a ten-fold increase in respirable dust levels measured at different mines. Two 

of the longwalls had very low intake entry dust of approximately 

0.1 mg/m3, while one operation had a very contaminated intake 

level of 1.1 mg/m3. The remaining operations had intake levels 

between 0.3 and 0.6 mg/m3. At both of the mines with the low 

intake levels, the intake entries were very wet with standing water at various locations along the entries so that minimal dust was 

generated by equipment travel. 

Six of the longwalls were utilizing the belt entry to bring intake air to the longwall face. In these operations, the dust liberated in the belt entry would be carried to the face and could add 

to face dust levels. For the six longwalls utilizing belt air, the average dust level in the belt entry just outby the stage loader was 

found to be 0.6 mg/m3, while the average intake concentration in 

these mines was 0.5 mg/m3. On average, the belt entry has the 

potential to add to face dust levels. However, this increase in intake dust levels appears to be negated by the potential for increased dilution that can be obtained with additional air brought 

up the belt entry (Potts and Jankowski, 1992). The average air 

quantity found on the face for the mines utilizing belt air was 26.0 

m3/s (55,000 cfm). For the other seven mines, the average air 

quantity on the face was 13.2 m3ls (28,000 cfm). At the mines 

utilizing the belt entry as an intake, the additional quantity of air 

available on the face would negate the average 0.1 mg/m3 increase in dust generated in the belt entries. 

The dust levels measured at shield 10 represent the concentration of the intake air coming onto the face and would include 

contamination from the outby sources in the intake, the belt and 

stage loader-crusher generated dust. The average concentration 

observed at shield 10 was 1 .I mg/m3 which is a relatively high 

quantity because it represents 55% of the 2.0 mg/m3 dust standard. The difference between the intakeibelt concentration and 

the concentration measured at shield 10 would primarily be dust 

generated by the stage loader-crusher unit. On average, this difference was found to be 0.7 mg/m3 and indicates that improvements in stage loader-crusher dust control should be pursued. At 

a minimum, the stage loader-crusher unit should be properly enclosed with belting or steel plate to prohibit dust escape and water sprays should be installed to reduce dust liberation. Belting or 

brattice can also be installed at the crusher inlet and stage loader 

to belt transfer to reduce dust liberation. Additional dust control 

can be achieved with water-powered scrubbers, fan-powered 

scrubbers or foaming agent added to the spray water. 

Tailgate dust levels exhibited a wide range of values with 

over a ten-fold difference between the minimum and maximum 

dust levels observed. The lowest observed dust level at the tailgate was from the face that had the highest air quantity, while the 

longwall with the highest tailgate dust level had the lowest quantity of ventilating air on the face. Tailgate dust levels for 9 of the 

13 longwalls were grouped in a relatively narrow band between 2 

and 4 mg/m3. 

As shown in Table 2, the dust levels at the tailgate location 

can be substantially lower than the dust levels measured at the 

downwind shearer mobile sampling location. The mobile sampling primarily represents dust generated during active mining, 

while the tailgate concentrations include all down time. In addition, high concentration dust clouds generated at a source (i.e. 

shearer) can become diluted as the cloud mixes with the ventilating air as the cloud disperses along the face. 

Mobile sampling was conducted on the head-to-tail pass so 

that shield generated dust could be isolated from dust liberated by 

the shearer. In two mines, shields were advanced downwind of 

the shearer during the tail-to-head pass so that no shield dust 

measurements were made at these mines. Average dust generation attributed to shield movement was found to be l .5 mg/m3. A 

relatively clear-cut division in shield generated dust was observed. Five of the mines had shield dust levels below 1.2 mg/m3, 

with an average concentration of 1.0 mg/m3. The shield dust concentrations from the other six mines were all above 1.8 mg/m3, 

with an average concentration of 2.0 mg/m3. Four of the five 

mines with low shield dust were located in the eastern U.S., while 

five of the six with high shield dust were located in the west. Previous research (Organiscak et al., 1985) had indicated that those 

mining operations that leave coal at the roof typically generate 

higher quantities of shield dust than those operations leaving only 

rock at the roof. Dust results from these longwall surveys support 

Upind Shearer Downw~nd Upwind Shearer Downwind 

SAMPLING LOCATION 

Figure 4. Summary of mobile sampling results for cutting passes. 
Table 2. Summary of average gravimetric dust concentrations from longwall surveys 

this trend in that the mines in the west were operating in high coal 

seams and typically left some coal at the roof. In the eastern 

mines no coal was left at the roof. 

Figure 4 summarizes mobile dust sampling results for the 

cutting passes. All of the dust levels displayed (minimum, average, maximum) for each of the sampling locations were higher for 

the head-to-tail passes. When cutting in the head-to-tail direction, 

the headgate drum is cutting along the floor in an exposed position where the ventilating air can readily pass over the drum. 

When cutting from tail-to-head, the headgate drum is shielded 

from the ventilating air by the coal face, which makes it more difficult for the dust to be entrained in the airstream. Dust levels at 

the upwind location for the head-to-tail passes are higher than for 

the tail-to-head direction and include dust generated by shield 

movement upwind of the shearer. 

Figure 5 summarizes mobile sampling results for the cleaning passes. In general, the head-to-tail passes had lower dust 

concentrations than the tail-to-head passes. These dust levels 

Mine 

A 

B 

C 

D 

E 

F 

G 

H 

I 

J 

K 

L 

M 

Upwind Shearer Dmnwtnd Upwind Shearer Domwind 

SAMPLING LOCATION 

flgure 5. Summary of mobile sampling results for cleaning passes. 

Intake 

0.24 

0.25 

0.35 

0.25 

0.30 

0.33 

0.37 

0.35 

0.07 

1.10 

0.62 

0.59 

0.08 

may once again reflect the shielding of the shearer drums from 

the face airflow. For the head-to-tail passes, the cowls on the 

shearer would shield the drums from the face airflow, but on the 

tail-to-head passes, the drums would be exposed directly to the 

airflow. 

The difference between dust levels immediately upwind and 

downwind of a dust source was dust generation attributed to that 

source. For example, the difference between the downwind and 

upwind shearer sampling locations was used to calculate the dust 

generated by the shearer. Calculation of the dust contributions 

from the intake, stage loaderlcrusher, shield advance and the 

shearer for each mine was completed and results are listed in 

Table 3. The dust contribution from each of these sources was 

weighted based upon pass times calculated from time study data 

collected at each mine. For example, if the head-to-tail passes 

at a mine accounted for 60% of the total cycle time for a complete 

pass across the face, the dust levels generated by the shearer 

during the head-to-tail pass would receive a 60% weighting. The 

dust levels generated on the tail-to-head pass would receive a 

40% weighting. If shields were advanced during the head-to-tail 

pass, shield dust would also receive a 60% weighting. 

Figure 6 illustrates the average contribution from each of the 

sources for the mines surveyed. The shearer remains the largest 

source of dust on the longwall and accounts for over half of all 

dust generation during mining. At mines J and M, the shearer 

produced over 82% of the dust on the longwall face. At both of 

these mines, the downwind dust levels were much higher than for 

the other 11 mines and at each mine, the shearer cut a substantial amount of rock along the face. In addition, these mines had 

the lowest quantity of ventilating air on the face. 

Shield movement and the stage loaderlcrusher units can 

also generate substantial quantities of dust. With the higher production levels found on today's longwalls, the need to advance a 

larger number of shields during a given shift has increased and 

Belt 

0.25 

nla 

0.46 

nla 

nla 

0.52 

nla 

0.63 

Ma 

0.88 

nla 

0.80 

nla 

Shield 

10 

0.54 

0.93 

1.39 

1.07 

1.35 

1.21 

0.79 

1.76 

0.42 

1.81 

0.96 

1.18 

0.98 

Shield 

dust 

0.90 

1.20 

2.05 

1.80 

n/a 

nla 

1.0 

1.02 

0.67 

2.26 

1.80 

2.19 

1.87 

U~wind shearer 

H - T 

1.43 

2.55 

3.43 

2.25 

2.20 

0.98 

1.84 

2.70 

1.73 

2.87 

5.54 

2.19 

3.45 

T - H 

0.77 

2.30 

3.95 

1.76 

1.60 

1.48 

0.86 

3.05 

1.03 

2.29 

4.31 

1.78 

1.73 

Shearer 

H - T T- H 

0.70 

2.77 

3.42 

2.36 

2.80 

2.83 

2.50 

2.93 

2.29 

7.27 

5.35 

3.64 

11.07 

Tailgate 

0.96 

1.72 

3.27 

2.05 

2.70 

3.7 

3.16 

3.51 

2.16 

5.64 

2.91 

3.91 

10.04 

0.69 

5.31 

3.52 

3.17 

4.35 

2.98 

1.34 

3.30 

2.54 

5.47 

4.60 

7.20 

6.46 

Downwind shearer 

H - T T - H 

2.23 

3.94 

8.93 

3.72 

2.95 

3.55 

2.94 

5.35 

4.17 

26.55 

7.97 

3.36 

18.57 

1.05 

4.45 

6.96 

2.69 

4.85 

4.71 

1.79 

2.90 

2.61 

6.07 

4.67 

10.38 

17.84 
Table 3. Contributions during mining from major longwall dust sources 

thus increased the potential dust exposure from this source. Similarly, with more coal and rock being processed through the stage 

loader and crusher during a given shift, the quantity of dust liberated at this source can also be significant. On average, shield 

advance accounted for 23% of the dust-make, while the stage 

loader/crusher contributed nearly 15%. 

Mine 

A 

B 

C 

D 

F 

G 

H 

I 

J 

K 

L 

M 

Avg 

SUMMARY 

PRC conducted dust surveys on numerous longwall operations in the early 1980s to document what types of control technologies were being used and quantify the dust generated by the 

major sources on the longwall. Significant changes to the 

longwall equipment and operating practices have been implemented since this survey and average shift production is now over 

3.5 times higher than in 1980. Consequently, longwall operators 

are attempting to control higher levels of respirable dust generation and continue to have difficulty in maintaining compliance with 

the respirable dust standard. In response, mine operators have 

substantially increased the levels of the dust control parameters 

that are applied on longwalls. PRC personnel recently completed 

dust surveys on 13 longwall operations to evaluate the dust levels being generated on these longwalls and the types and effec- 

> 

tiveness-$ the control technology in use. 

The use of ventilating air and spray water are the primary 

means used by longwall operators to control dust generation and 

worker exposure. Average air flow on the face was found to be 

2.5 m/s (500 fpm) with an estimated air quantity of 19.2 m3/s 

(40,000 cfm). This average air velocity represents an increase of 

0.5 m/s (1 00 fpm) over the average level observed in a Bureau of 

Mines survey of longwalls in the early 1980s. However, 7 of the 

13 mines surveyed had air velocities below 2.0 m/s (400 fpm) 

Figure 6. Average dust contribution 01 major dust sources on longwall faces. 

% 

Shearer 

34.7 

44.8 

59.5 

37.4 

59.7 

36.3 

30.0 

65.5 

82.9 

44.3 

59.8 

84.6 

53.3 

which has been suggested as a minimum recommended velocity 

in previous publications. Six of the mines surveyed were utilizing 

the belt entry as an additional entry to carry intake air to the face. 

The average quantity of air found on the face in those mines utilizing belt air was nearly twice as high as those mines that didn't. 

Four of these mines had average face air velocities that were over 

2.7 m/s (525 fpm). Dust levels measured in the belt entry were 

found to be nearly equal to the average dust level in the main intake entry, which indicates that a positive influence on face dust 

levels would be realized in those mines using the belt as an additional intake entry. 

All but one longwall had water spray systems on the shearer 

that were based upon the principles of the shearer clearer spray 

system. This spray system is designed to prevent shearer generated dust from reaching the walkway in the area around the 

shearer. Longwall operators are also applying larger quantities 

of water at the shearer in an effort to control respirable dust. Average water flow to the shearer was found to be 379 Lpm (100 

gpm), which represents and increase of nearly 150 Lpm (40 gpm) 

over levels applied in the early 1980s. Operating pressure at the 

shearer drum sprays was found to vary greatly between the mines 

that were surveyed with a minimum pressure of 172 kPa (25 psi) 

and a maximum of 2070 kPa (300 psi). Only 3 of the 13 mines 

were operating in the range of 265 to 690 kPa (70 to 100 psi) 

which was shown by previous research to minimize dust liberation. The majority of the measured drum pressures were well 

above 690 kPa (100 psi) which increases the potential for the 

drum sprays to force dust from the face into the walkway. 

The average level of dust generated during mining by the 

intake, stage loader/crusher, shield advance and shearer were 

contribution, 

Shields 

27.1 

31.1 

19.4 

30.1 

16.9 

35.6 

25.7 

21.2 

7.0 

30.0 

21.8 

10.1 

23.0 

' 

Intake 

17.4 

6.5 

6.2 

7.6 

8.2 

13.2 

12.3 

2.2 

5.5 

16.6 

10.9 

0.4 

8.9 

calculated: The shearer continues to be the most significant 

source of respirable dust generation on longwall faces and accounts for over 50% of the dust generation on the faces. Comparison of dust levels measured during cutting passes shows that 

dust levels for head-to-tail cuts were higher than those measured 

for tail-to-head cuts. During clean-up, dust levels were higher on 

the tail-to-head passes. Higher dust levels on the head-to-tail 

cuts and tail-to-head clean-ups may be resulting from the shearer 

Dust source 

Stage 

loader 

20.8 

17.6 

14.9 

24.9 

15.2 

14.9 

32.0 

11.1 

4.6 

9.1 

7.5 

4.9 

14.8 

drums being more directly exposed to the ventilating air. Consequently, in those mining operations utilizing unidirectional cutting 

sequences, dust liberation may be minimized if cutting was completed in the tail-to-head direction. 

Dust generated during shield movement was found to contribute an average of 23% to the total respirable dust on the face. 
The shield-dust results support earlier research which indicated 

that greater levels of respirable dust are generated during shield 

advance if coal is left at the roof. Four of the five mines with shield 

dust levels below 1.2 mg/m3 were operating in mining heights less 

than 2.0 m (6.5 ft), and none of these mines were leaving coal at 

the roof. Five of the six mines with shield dust levels above 1.8 

mg/m3 were operating with mining heights greater than 2.1 m (6.8 

R) and typically left several inches of roof coal. 

The stage loaderlcrusher is another potentially significant 

source of respirable dust and accounted for approximately 15% of 

the average dust generation on the longwall. Most of the mines 

surveyed had enclosed crushers and stage loaders with water 

sprays operated inside the enclosed units. However, a few operations had stage loaderlcrusher units that were not adequately 

enclosed and dust contributions from the stage loaderlcrusher 

accounted for over 25% of the dust measured on the longwall at 

these mines. 

The primary means of controlling dust levels on longwall 

faces is achieved by using water sprays in an effort to reduce the 

amount of respirable dust that is liberated and supplying ventilating air to dilute and remove airborne respirable dust. Results from 

these surveys suggest that ventilating air and spray water both 

must be properly applied to minimize worker dust exposure on 

high production longwall faces. 

REFERENCES 

Anonymous, 1995, Lonawall Mining, Energy Information Administration, DOEIEIA-TR-0588, 60 pp. 

Anonymous, 1995a, Criteria for a Recommended Standard: Occu~ational Ex~osure to Res~irable Coal Mine Dust, National 

Institute of Occupational Safety and Health, DHHS (NIOSH) 

NO. 95-1 06, 336 pp. 

Jankowski, R.A., and Organiscak, J.A., 1983, Dust Sources and 

Controls on the Six U.S. Longwalls Having the Most Difficulty 

Complying with Dust Standards, U.S.Bureau of Mines IC 8957, 

19 PP. 

Jankowski, R.A., Jayaraman, N.I., and Potts, J.D., 1993, Update 

on Ventilation for Longwall Mine Dust Control, U.S. Bureau of 

Mines IC 9366,ll pp. 

Niewiadomski, G.E., and Jankowski, R. A., 1993,"Longwall Dust 

Trends and Developments in Longwall Dust Controls", Proceedinaa of the Sixth U.S. Mine Ventilation Symposium, Salt 

Lake City, Utah, pp 551-556. 

Niewiadornski, G.E., 1996, Mine Safety and Health Administration, private communication. 

O'Green, J.E., McNider, T.E., Gallick, J.M., Jarrett, R.J., and 

Jankowski, R.A., 1994, An Overview of General Operating 

Experience as It Relates to Longwall Dust Control. Proceed- 

& of Longwall USA, Pittsburgh,Pennsylvania, pp.221-233. 

Organiscak, J.A., Listak, J.M., and Jankowski, R.A.,1985, Factors Affecting Respirable Dust GenerationFrom Longwall Roof 

Supports. U.S. Bureau of Mines IC9019, 19 pp. 

Potts, J.D., and Jankowski, R. A,, 1992, Dust Considerations 

When Using Belt Entry Air to Ventilatework Areas, U.S. Bureau of Mines RI 9426, 12 pp. 

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 pp.