Dust control on longwalls – assessment of the state-of-the-art

J.P. Rider & J.F. Colinet

National Institute for Occupational Safety and Health, Pittsburgh, Pennsylvania, United States

ABSTRACT: Operating practices and resulting production from longwall faces are continually improving.

Consequently, longwall operators are continually seeking to improve the dust control capabilities on longwalls.

The National Institute for Occupational Safety and Health (NIOSH) has been conducting dust surveys at longwalls

throughout the country in an effort to document the types of controls that are being used and to quantify the

relative effectiveness of these controls. To date, surveys have been completed at longwalls in Alabama, Colorado,

Pennsylvania, Utah, andWestVirginia. In addition NIOSH has been reviewing longwall dust parameters provided

by mine operators to MSHA to assess the status of dust control technology being used throughout the industry.

Results from the underground dust surveys and information obtained from MSHA will be summarized in this

paper to provide an update on longwall dust control technology and practices.

1 INTRODUCTION

Improvements in longwall mining equipment and mining practices have led to substantial gains in longwall production levels, resulting in longwall mining

accounting for 51% of the coal produced underground

in the United States. 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. Longwall panels averaged 288 m (940 ft) wide and nearly 3062 m (10,000 ft)

long in 2002, compared to an average of 230 m (750 ft)

wide and 2135 m (7000 ft) long in 1994. New longwall

panels, currently in the planning stage, may be as wide

as 457.2 m (1500 ft) and as long as 4572 m (15,000 ft).

Cutting heights in 2002 averaged 215 cm (86 in) and

ranged between 121.9 and 396.2 cm (48 and 156 in)

(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 2800 tons per shift in 1990 to an average 5600 tons

per shift in 2004. Consequently, longwall operations

continue to have difficulty in maintaining consistent

compliance with the federal dust standard of 2 mg/m3.

During a five-year span from 2000 through 2004,

mine operators and Mine Safety and Health Administration (MSHA) inspectors collected 7421, and 1587

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).

Health surveillance data also indicate that overexposure to respirable dust in underground coal mines

continues to lead to the development of lung disease.

Results from the most recent full round (1992–1996)

of the CoalWorker’s X-ray Surveillance Program indicate that approximately 8% of the examined miners

with at least 25 years of mining experience were

diagnosed with Coal Worker Pneumoconiosis (CWP)

(category 1/0+). The continued development of CWP

in underground coal mine workers and the magnitude

of respirable dust over exposures in longwall mining occupations illustrate the need for improved dust

control technology on longwalls.

Ventilating air and water sprays are the primary

means used to control dust and methane in longwall

operations. 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.

2 LONGWALL DUST PARAMETERS

Longwall dust parameters provided to MSHA as part

of the mine’s ventilation plan were reviewed to assess

the status of control measures being used throughout the industry. Ventilation plans between the years

225
Figure 1. Range of velocity readings.

2000 to 2003, representing 44 longwall panels, were

analyzed to identify and quantify the different types

of longwall control features used to limit the miners’

exposure to respirable dust. A variety of dust control

measures were encountered when the dust parameters

were reviewed. Each longwall operator had a different

and unique approach to control respirable dust levels.

Figure 1 shows the range of minimum mean air

velocities required at the headgate and tailgate. The

average minimum headgate velocity was approximately 2.2 m/sec (430 ft/min) for all longwall operations. Eastern mines averaged 2.2 m/sec (440 ft/min),

while western operations averaged 2.0 m/sec (390 ft/

min). The average minimum volume of air reported

in the dust plans was approximately 24.5 m3/sec

(52,000 ft3/min). As expected, minimum air quantities were significantly higher for western operations,

32.1 m3/sec (68,000 ft3/min), compared to 21.1 m3/sec

(45,000 ft3/min) in the east. Approximately 28% of the

mine operators reported the use of beltway air as a

means to supplement the total volume of air reaching

the face. Nearly one-half of the longwall operators in

eastern U.S. mines utilize air deflectors on the first 3

or 4 shields as a means of helping move the air onto

the face and controlling dust levels when the shearer

was cutting out at the headgate.

The quantity, type, and pressure of the shearer cutting drum sprays reported by longwall operators varied

with each longwall operation. The number of sprays

ranged between a low of 30 and a high of 62. According to the ventilation plans, between 75 and 90% of the

drum sprays are required to be operational when mining. The type of spray preferred by the majority of the

operators was the Conflow 2801 with either full-cone,

flat-fan, or hollow-cone spray patterns. The range

and frequency of drum spray pressures are shown in

figure 2. Sixty-one percent of the longwalls reported

drum spray pressures between 620.5 and 758.4 kPa (90

and 110 psi). The average drum spray pressure was

Figure 2. Pressure ranges for shearer drums sprays and

splitter arm sprays.

620.5 kPa (90 psi). Thirteen operations reported using

crescent sprays on the ranging arms as a means of controlling fugitive dust. The number of crescent sprays

ranged between 4 and 11, with an average spray pressure of 586.1 kPa (85 psi), and varied between 448.2

and 689.47 kPa (65 and 100 psi).

The ventilation plans showed that 39 out of 44 operations utilized a headgate splitter arm as a means of

either suppressing or moving fugitive dust away from

the personnel operating the shearer. The length of the

splitter arm, type of sprays, distance between sprays,

angle of the sprays, and spray pressure varied greatly

between mines. The number of sprays mounted on the

splitter arm ranged between 2 and 20. The majority

of the ventilation plans stated that at least 90% of the

splitter arm sprays are required to be operational when

mining.Approximately 15% of the operations reported

utilizing an extension of the splitter arm that angled

between 30 and 45 degrees toward the face. A variety

of spray patterns were used, including full cone, hollow

cone, vee-jet and flat fan. Approximately 30% of the

operators reported using venturi sprays. Splitter arm

sprays were angled 20 to 30 degrees up or down and

directed toward the shield tips or pan line. The angle

of the sprays directed with the airflow ranged between

10 and 45 degrees. The majority of the splitter arm

sprays were aimed at the headgate drum, especially

the sprays positioned on the splitter arm upwind of the

cutting drum. Headgate splitter arm spray pressure varied greatly, as shown in figure 2. Sixty-eight percent

of the sprays operated with spray pressure at or above

689.5 kPa (100 psi).

Manifolds located on the tailgate side of the shearer

or tailgate splitter arms were reported on nearly all

the longwall operations. The majority of the western

operations used the splitter arm technology to direct

fugitive dust downwind, while most eastern operations utilized spray manifolds to suppress or move

dust generated by the tailgate drum. The number of

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sprays on the tailgate splitter arm ranged between 3

and 10, while the spray pressure varied between 551.6

and 689.5 kPa (80 and 100 psi). The sprays were either

directed at the tailgate drum or angled from 10 to 45

degrees in the direction of the airflow. Nearly 60% of

the operations utilized a manifold located on the tailgate side of the shearer or in the lump breaker area.

Manifolds positioned on the tailgate side of the shearer

directed the spray plume downwind. Spray pressures

ranged between 344.8 and 861.8 kPa (50 and 125 psi).

All but 4 operations operated with spray pressure

below 689.5 kPa (100 psi), with the average pressure

of approximately 551 kPa (80 psi). Lump breaker manifolds consisted of 4 to 6 sprays with pressures ranging

between 620.5 and 827.4 kPa (90 and 120 psi) and

directed toward the pan line.

Thirty-five operations reported using sprays on the

top deck or on the face side of the shearer to confine

and move dust away from the mine operators. Nineteen

of the thirty-five operations utilized between 2 and 6

spray manifolds spaced evenly across the shearer. Each

manifold was equipped with a range of 2 to 16 sprays.

Shearer body spray configurations consisting of 3

spray manifolds with 3 or 4 sprays per manifold were

the most commonly reported spray system and were

utilized by nearly 25% of operators. One out of five

operations used between 4 and 6 venturi sprays spaced

evenly and positioned either at the shearer centerline

or the gob side of the shearer. Shearer spray pressure

ranged between 482.6 and 1034.2 kPa (70 and 150 psi).

Approximately 40% of the shearer sprays operated

with pressures at or above 689.5 kPa (100 psi).

3 LONGWALL SURVEYS

3.1 Sampling methodology

Gravimetric dust samplers, identical to those used in

compliance sampling, were operated at 2L/min in conjunction with a 10-mm Dorr-Oliver nylon cyclone.

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 MSHAapproved, 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. The PDR samples were utilized in an active sampling mode where dust laden air

was pulled through a 10-mm Dorr-Oliver cyclone at

a flow rate of 2 L/min. 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 5.2–7.6 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 5.2–7.6 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. 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 headto-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

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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 stage

loader 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 stage-loader/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.

3.2 Survey results

A variety of operating conditions were encountered

when surveys were conducted at the different mines

throughout the country. Six of the eight mines surveyed to date utilized a bidirectional cutting sequence,

with two mines employing unidirectional cutting. Face

panel widths ranged between 237.7 and 304.8 m (780

and 1000 ft), and the average face width was 272.2 m

(893 ft). Comparing panel widths observed in this latest series of surveys with panel widths reported in

a 1995 longwall study (Colinet et al., 1995) showed

close to a 25% increase. The average cutting height

was 2.7 m (9 ft) with a range between 2.1 and 3.4 m

(7 and 11 ft).

During the surveys, daily spot velocity readings

were recorded approximately every 10 shields along

the longwall face and were used to calculate the

average face velocity. The average velocity of the surveyed longwalls was 3.4 m/sec (665 ft/min), which

represents an increase of over 0.8 m/sec (50 ft/min)

when compared to average air velocities reported in

the 1995 longwall study. 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. 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). Average air

quantities calculated in this current series of longwall

surveys increased approximately 65% when compared

to the mid-1990 longwall study.

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. The average

water usage at the shearer observed during the eight

most recently completed surveys was 492.0 L/min

(130 gpm). 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). One-half of the surveyed mines utilized six to eight crescent sprays on

the ranging arms.

Studies (O’Green et al., 1994) have shown that

shearer drum water sprays are very effective at minimizing dust generated at the point of coal fracture but

can increase airborne respirable dust levels if operated

at overly high water pressure. Instead of suppressing

dust, the drum sprays may force the dust out away from

the cutting drum causing excessive turbulence around

the cutting drums. The increased turbulence leads to

higher dust levels at the shearer and downwind. Larger

orifice sprays could be utilized to increase water volume and reduce operating pressure. Increased flow

to the drum-mounted sprays should result in a more

uniform wetting of the coal product, which may also

reduce conveyor-generated dust.

External spray systems with air-moving directional

sprays were observed at the headgate side of the

shearer on seven of the eight surveyed longwalls. The

splitter arm technology used to keep fugitive dust away

from the shearer operators was unique to each mining operation. The lengths varied between 2.7 and

4.6 m (9 and 15 ft) with the number of sprays ranging

between 6 to 19. Spray spacing on the splitter arm and

the directional angle of the sprays varied greatly at each

operation. Extension arms attached to the end of splitter arms and angled between 30 and 45 degrees toward

the face were utilized at three mines. Venturi sprays

located on top of the splitter arm were observed at two

operations. Splitter arm spray pressures were approximately 689.5 kPa (100 psi) when hollow cones sprays

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Figure 3. Range of dust concentrations measured at the

stationary sampling locations.

were utilized and in excess of 1551.3 kPa (225 psi)

when venturi sprays were operated.

A variety of spray configurations were employed

on the body of the shearers during the mine surveys.

Deflector or sloughing plates were observed at three

western mine sites. One of the three operations used

a single plate spanning the length of the shearer with

6 venturi sprays evenly spaced across the top of the

deflector plate. Deflector plates were split into three

independent sections on two of the longwall operations. Each section had five hollow cone sprays evenly

spaced across the top of the plate. At eastern mine sites

a series of spray manifolds were used the majority of

the time. Three or four manifold consisting of four or

five sprays were evenly spaced across the length of the

shearer. The manifold were either located on the face

side of the shearer or on the top of the shearer close

to the face. One mining operational moved the spray

manifolds toward the middle of the shearer and elevated the manifolds 15.24 to 30.48 cm (6 to 12 in) off

the shearer body.

The majority of the surveyed mines made use of

manifolds located above the lump breaker or on the

shearer body to control dust in the tailgate drum area.

A minimum of 4 and maximum of 16 sprays were

directed toward the cutting drum or down onto the

conveyor. One mining 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

at one mine.

The minimum, average and maximum dust levels

for stationary gravimetric sampling locations are

shown in figure 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

Figure 4. Range of mobile sampling measurements.

the operations below 0.20 mg/m3. 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

2.5 times less than the belt entry dust concentrations.

Although the average dust levels in the belt entry levels are relatively low on average, the belt entry has the

potential to add to face dust levels. However, according

to past research studies (Potts and Jankowski, 1992)

potential increases in face dust levels seemed to be

negated by the potential for increased dilution with

the additional air reaching the face.

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. The difference between intake/belt

dust levels and shield 10 concentrations is primarily

the dust contributed by the stageloader/crusher. On

average, the amount of dust that was attributed to

the stageloader/crusher was 0.48 mg/m3. Dust levels

measured at the tailgate sampling location provided

a good indication of the amount of total dust generated along the face that reaches the tailgate area. Dust

levels ranged between 1.04 mg/m3 to 3.88 mg/m3 and

averaged 2.56 mg/m3.

The volume of air introduced on longwall faces in

recent years has had a major impact on dust levels at

the stationary sampling locations. 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.

Reductions in dust levels at the other stationary sampling locations 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 4). Dust levels at these

two sampling locations reflect dust liberated from

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Figure 5. Adjusted PDR concentrations for a typical head-to-tail pass.

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/m3when 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.

Comparing dust 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 perpass 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 5 and 6 illustrate adjusted PDR mobile

sampling results from a typical head-to-tail and tailto-head pass. Figure 5 shows that OUTBY shield

movement 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 head-to-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 at diluting

high dust levels generated by shield movement. Dust

levels at the DOWNWIND sampling location [approximately 1 shield inby the tailgate shearer operator and

1 to 2 shields outby shield movement] are approximately equivalent to the dust levels recorded by the

SHEARER samplers.

Figure 6 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

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Figure 6. Adjusted PDR concentrations for a typical tail-to-head pass.

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.

4 CONCLUSION

Although the number of longwall sections has

decreased over the past decade, the production and

productivity from today’s operating longwalls is much

greater. Consequently, the potential to liberate significantly more respirable dust exists. Mine operators have

made substantial increases in the application of dust

control technology in an effort to control dust exposure

on longwalls.

Longwall dust parameters obtained from MSHA

ventilation plans and sampling data from eight surveys conducted by NIOSH indicate that a wide variety

of control technology applications exists across the

industry. These differences may in part be a reflection of differing operating conditions and equipment.

Regardless, a number of similarities also exist and

indicate that these controls are viewed as keys for

successful dust control:

• Intake dust levels are generally well controlled.

• The velocity and quantity of air being utilized has

been increased.

• The volume of water supplied to shearer dust control

sprays has also been increased.

• 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.

• 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.

• 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.

In addition, sampling results indicate that significant dust liberation and worker exposure is resulting

during shield advance. 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. & 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.CoalAge. February, 2003,

pp. 20–24.

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

O’Green, J.E., McNider, T.E., Gallick, J.M., Jarrett, R.J. &

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

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Experience as It Relates to Longwall Dust Control, Proceedings of Longwall USA, Pittsburgh, Pa., pp. 221–233.

Potts, J.D. & Jamkowski, R.A. 1992. Dust Considerations

When Using Belt Entry Air to Ventilate Work Areas. U.S.

Bureau of Mines RI 9426, 12 pp.

Webster, J.B., Chiaretta, C.W. & Behling, J. 1990. Dust Control in High Productivity Mines, SME Annual Meeting,

Preprint 90–82, Salt Lake City, Utah, 9 pp.

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