T e c h n i c a L P a P e r s

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Impact of air velocity 

and support advance 

on shield-generated dust
�

G.J. Chekan, J.p. rider, J.m. listak, 

J.f. Colinet and J.d. potts 

G.J. Chekan, J.P. Rider, member sme, J.M. Listak, J.F. 

Colinet, member sme, and J.D. Potts are lead research 

engineer, acting team leader, lead research engineer, acting 

branch chief and research engineer, with the national institute 

for occupational safety and health (niosh), pittsburgh, pa. 

Abstract 

Steady increases in longwall production have required 

operators to apply greater quantities of ventilating air in 

an effort to control and dilute respirable dust. Significant increases in shearer speeds necessitate that longwall 

supports also be advanced at a faster rate. Both of these 

factors may contribute to overall respirable dust levels on 

the longwall face because as supports are lowered and advanced, broken material falling from the top of the canopy 

is entrained directly into the air stream.To address this issue, 

the Pittsburgh Research Laboratory collected respirable 

dust samples from four longwall faces to characterize 

shield-generated dust. This paper investigates the influence 

of air velocity and shield advance rates on respirable dust 

levels. Also discussed are engineering controls currently 

used to reduce shield dust and alternative controls being 

investigated by the National Institute for Occupational 

Safety and Health (NIOSH). 

Introduction 

Reducing respirable dust levels

on longwalls through the development of engineering controls remains a primary health concern for

the National Institute for Occupational Safety and Heatlh (NIOSH),

industry, regulators and university

researchers. NIOSH researchers

from the Pittsburgh Research Laboratory conducted longwall dust surveys in an effort to better understand

the influence of both air velocity and

support advance on shield-generated respirable dust. 

Ultimately, this research will lead to lowering worker 

exposure to respirable coal and silica dust. 

Increased production has put a greater demand on 

longwall dust control systems as operators have had difficulty maintaining consistent compliance with federal dust 

standards. During the five-year period 2000-2004, analysis of mine operator and U.S. Mine Safety and Health 

Administration (MSHA) inspector samples shows that 

the percentage of these samples exceeding 2.1 mg/m3 

(the level at which a citation is issued) was 14% and 15%, 

respectively (Niewiadomski, 2004). 

Dust control technology employs both air and water as a means to limit, direct and 

eliminate respirable dust. Historically, longwall dust control research 

focused on reducing dust generated by the two largest sources: the 

shearer and stageloader. Increasing

air velocity on the face is a fundamental control used to dilute dust 

generated by these sources. A minimum longwall face air velocity of 2 

to 2.3 m/s (6.5 to 7.5 ft/sec) is recommended for proper dilution of dust 

along the face (Foster-Miller Assc., 

1982; Breuer, 1972). A research study conducted during the1980s found that face air velocities ranged from 

0.6 to 3.3 m/s (2 to 11 ft/sec), while average production 

was 735 t/shift (810 st/shift) (Jankowski and Organiscak, 

1983). The shearer and stageloader combined accounted 

for 82% of the total respirable dust generated. A second 

study during the 1990s showed that the range of air velocities increased to 1 to 7.6 m/s (3.3 to 25 ft/sec), while the 

average production increased nearly four-fold to 2,885 t/ 

shift (3,180 st/shift) (Niewiadomski, 2004). Despite increased production, the total dust contribution of the 

shearer and stageloader decreased to 68% as a result of 

improved dust control measures. Increased ventilation, 

improved water spray application at the shearer and enclosing the stageloader and adding water sprays were the 

primary modifications that led to this reduction (Colinet 

and Jankowski, 1997). 

Despite the above advances in dust control, due to 

faster shearer speeds or the presence of methane gas, 

higher air velocities are often required for dilution. Past 

studies (Hall, 1956; Hodkinson, 1960) have shown that, 

for low moisture coals, velocities in excess of about 2.3 

m/s (7.5 ft/sec) can increase dust levels. More recent studies (Tomb et al., 1991; Breuer, 1972) have shown that with 

adequate moisture on the coal, such as that provided by 

sprays, airflow may be increased beyond 5.1 m/s (16.7 ft/ 

sec), without significantly increasing the dust levels on 

the face. In these studies, the shearer and stageloader 

were being shielded from the face airflow by physical 

barriers, and/or water spray systems were being used to 

increase moisture and promote particle agglomeration. 

Dust sampling on these longwalls clearly indicates that if 

moisture content is adequate, increasing air velocity does 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

not promote dust generation from controlled sources, 

such as the shearer or stageloader. 

Studies conducted by the U.S. Bureau of Mines in 

the 1980s investigated support-generated dust as it related to geology, support design and cutting sequence 

(Organiscak et al., 1985). The studies found a correlation between support-generated dust and the geology 

of the immediate roof strata. Studies conducted during 

the early 1990s showed that shield dust was a significant 

contributor to the total dust generated from all sources 

(Colinet et al., 1997, Colinet and Jankowski, 1997). Dust 

attributed to shield movement almost doubled from 12% 

in the 1980s to 23% in the 1990s. NIOSH studies show 

that the primary factors responsible for this increase are 

most likely a combination of higher production and lack 

of effective control technology for shield dust (Rider 

and Colinet, 2006). Higher production rates have led to 

increased shearer speeds, which requires that shields be 

moved faster and in greater numbers. As shield supports 

are lowered and advanced, broken coal and/or rock falls 

from the top of the shield canopy and is being introduced 

directly into the air stream ventilating the longwall face. 

Also, the amount of air required to ventilate longwall 

faces continues to trend upward (Rider and Colinet, 

2006).This has the potential to entrain greater quantities 

of respirable dust during shield advance under certain 

conditions. Further complicating the issue, most longwall operations utilize a bi-directional cutting sequence. 

When mining from headgate to tailgate, shield movement 

upwind of the shearer also contributes to dust exposure 

of the shearer operators. In mines where roof rock is the 

main component on the shield canopy, the entrainment 

of respirable silica dust becomes more of an issue, since 

the quartz component of rock is the primary contributor 

to silica dust generation (Ramani et al., 1987). 

In laboratory studies, NIOSH conducted tests using a 

wind tunnel to study the basic behavior of dust dropped 

into an airstream under varying air velocities (Listak et 

al. 2001; Chekan et al., 2001; Chekan et al., 2004). The 

studies were designed to determine dust concentration 

as it relates to increasing both the air velocity and the 

shield rate of advance. Results from these laboratory tests 

showed two fundamental relationships for low moisture 

coals (<1%): 1) increasing the air velocity increases airborne dust concentrations and 2) increasing the rate at 

which respirable dust is introduced into the airstream 

(faster shield advance rate) also increases airborne dust 

concentrations. 

Tests in the wind tunnel were conducted at air velocities of 2 m/s, 4.1 m/s, 6.1 m/s and 8.1 m/s (0.6 ft/s, 1.2 

ft/s, 1.8 ft/s and 2.5 ft/s). Respirable dust concentrations 

increased as air velocity increased in a linear relationship, 

indicating that particle entrainment was greater than dilution effects. Respirable dust concentrations increased 

from 1.47 mg/m3 at 2.0 m/s (0.6 ft/s) to 19.84 mg/m3 at 

8.1 m/s (2.5 ft/s). Statistical analysis of the concentrations measured at each velocity resulted in significant 

differences at a 95% confidence interval. Analysis of the 

size distribution of the sampled dust showed an inverse 

relationship between velocity and mass median diameter 

of the dust. As velocity increased, the mass median diameter of the entrained dust particles decreased in a near 

linear manner. The mass median diameter was found to 

be 10.8 microns at 2.0 m/s (400 fpm) and decreased to 

7.7 microns at 8.1 m/s (1,600 fpm). Higher concentrations and finer particle size distributions suggest that at 

a moisture content of approximately 1, a portion of the 

dust particles were adhering to each other at the 2.0 m/s 

(400 fpm) velocity. As the velocity increases, the adhering 

forces are overcome by the increased energy supplied to 

the system, resulting in higher concentrations and smaller 

particle sizes in the airstream. Although the particle size 

decreased with increased velocity, dilution was not observed in any of the tests. In summary, the tests showed 

that adhesion of respirable dust to larger material and to 

other respirable particles plays an important role in determining the fraction of airborne dust that is measured 

as respirable. 

To further investigate the relationships from these 

laboratory studies, a research effort was conducted in the 

field to characterize shield generated dust at four longwall mines. The longwall surveys would help ascertain 

if shield dust generation may be influenced by face air 

velocity and/or the rate of shield advance. 

Figure 1 

Percent weight distribution by size for coal samples collected from shield canopy at mines A and C. 

Figure 2 

Percent weight distribution by size for rock samples collected from shield canopy at mines A and C. 

Shield-dust size characterization 

from bulk samples 

Shield-generated dust differs from mining-gener-
	 	 		

	 	 	 	 	

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ated dust in that the fracture mechanism can be best 

described as a repeated crushing of the material on the 

canopy as the shields are continually lowered and reset. 

To better characterize the coarse and fine material on 

top of the canopy, bulk samples were collected at two 

of the four survey mines, mines A and C. Four coal 

samples and four rock samples, ranging in weight from 

13.6 to 18.2 kg (30 to 20 lb), were collected separately 

from the top of the shield supports at each mine. 

Sieve analysis was used to size the coarse material 

in eight different size fractions ranging from >25 mm to 

<38 μm. Figures 1 and 2 show the results as a percent 

weight of the total sample for both the coal and rock, 

respectively. The results show that for coal, more than 

half the sample by weight fractured primarily in the 

medium sizes, ranging from 12.5 mm to 150 μm. Mine 

A had 72.2% and Mine C had 58.2% of the coal sample 

in this range. Conversely, for rock, more than half the 

sample fractured in the two largest sizes, ranging from 

>25 mm to 12.5 mm at 65.7% and 67% for Mines A 

and C, respectively. As expected, coal, being the softer 

material, tended to fracture into a smaller size range 

from repeated shield crushing as compared to the rock. 

Light-scattering analysis was used to determine the 

respirable fraction (<10 μm) of the remaining product 

<38 μm in size. As shown in Figs. 1 and 2, this component averaged 2.2% for the coal samples and 1.5% for 

the rock samples. Analysis of this material shows that 

for both coal and rock, respirable dust was a small percentage of the total sample weight. Respirable dust 

averaged 41% of the remaining product <38 μm and as 

a result, made up less than 1% of the total material on 

the canopy by weight. 

Although shield dust is generated by a crushing 

mechanism, these results are similar to results from 

other studies that measured the amount of respirable 

dust in run-of-mine coal. Studies in continuous mining operations show that for typical run-of-mine product, approximately 0.5 to 1.0% of the sample by weight 

consists of respirable dust (Ramani et al., 1987; Cheng 

and Zukovich, 1973). These studies also showed that 

the amount of respirable dust that became airborne 

was related to moisture content. A significant portion (99.6%) of the respirable dust was agglomerating 

and adhering to the over-sized coal in the run-of-mine 

(ROM), primarily due to a high moisture content resulting from the large volumes of water used to suppress mining-generated dust. For shield dust, this may 

not be the case if canopy spray systems do not function 

properly. The lower moisture content may result in a 

higher percentage of the respirable dust becoming entrained into the airstream. 

Table 1 

Site specific information for each mine. 

Mine	 Location 		Shearer	 

Survey No. 		

of head to 		

tail passes	 

No. of shields	 

		on face	 

in minutes	 

Survey avg.	 

shearer pass	 

advanced/min.	 

Avg. No. of 		

shields time	 

Survey avg.	 

air velocity 

m/s 

a eastern	 Bi-directional	 6	 185	 27.5	 6.7	 1.7 

B	 Western	 Uni-directional	 5	 129	 14.0	 9.2	 2.3 

C	 eastern	 Bi-directional	 4	 156	 30.0	 5.2	 3.4 

D	 eastern	 Bi-directional	 8	 160	 31.5	 5.1	 4.2 

Figure 3 

Percent weight distribution of airborne dust on impactor 

stages versus cut points in microns. 

Sampling strategy 

To sample shield-generated dust, surveys were conducted at longwall mines using mobile sampling. Mobile sampling involved the wearing of dust sampling 

instruments by several NIOSH personnel moving along 

the longwall face to isolate dust generation from shield 

advance or shearer cutting. To isolate shield-generated 

dust, NIOSH personnel would position themselves upwind and downwind of all shield movement during the 

head-to-tail pass only, so that dust generated by the 

shearer was downwind of both mobile sampling locations. However, on some longwall faces using shearer-activated shield advance, the shields typically were 

advanced within two shields of the headgate drum. 

When these conditions were present, shield dust samples could not be collected because shield dust could 

not be separated from shearer-generated dust. 

Shield dust samples were obtained at four mines 

where sufficient distance was available to isolate shield 

advance. One person was located directly upwind of 

shield advance. The second person was located directly downwind of shield advance to collect shield dust 

samples before air dilution influenced the concentration. Shield dust is calculated as the difference in dust 

concentrations between position one (upwind of shield 

movement) and position two (downwind of shield 

movement). 

Two types of instruments were used to collect dust 

samples. Marple cascade impactors were used to collect 

dust samples to determine the size distribution of dust 

particles (less than 50 μm) that become airborne during shield advance. These samples were collected from 

two of the four mines. The cascade impactor is a seven-
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

stage instrument that measures the size distribution of 

airborne particles and separates dust into aerodynamic 

sizes or cut points ranging from 21 to 0.025 μm. As dustladen air is drawn into the instrument using a pump operated at 2 L/min (0.53 gpm), the aerosol stream moves 

with relatively low velocity over the upper stages and 

increases in velocity at each subsequent stage. The dust 

collection process is made possible through the use of 

mylar substrates on each of the instrument’s stages. 

Those particles with higher inertia (larger particles) 

will “impact” the mylar substrate and be collected on 

the upper stages, whereas smaller particles will pass 

through the stage openings and be collected on the subsequent lower stages. The mylar substrates were coated 

with silicone grease to minimize particle bounce from 

one stage to the next. 

The substrates are pre- and post-weighed to determine the mass distribution on each stage of the impactor. The amount of dust collected on each stage is based 

on the mass median diameter (MMD) of the particle. 

MMD gives an overall measure of the size distribution 

of the particles. Specifically, MMD is the particle size 

at which 50% of the particles are greater than the cut 

point and 50% of the particles are smaller than the cut 

point. 

The main sampling instrument used in all four 

longwall surveys was the Thermo-Fisher personal DataRAM (pDR). The pDR measures and records the 

concentration of respirable airborne particulate from 

0.1 to 10 microns using a light-scattering technique. 

Light-scattering instruments offer only a relative measure of dust concentrations. However, the logged data 

was adjusted to a the gravimetric sampler concentration to correct each logged concentration value (Listak 

et al., 2007; Chekan et al., 2006). The pDR provides 

continuous record of particulate levels so that dust concentrations can be evaluated over any time interval during the sampling period. Using spreadsheet software, 

concentration data logged by the unit can be analyzed 

during the exact time of each head-to-tail pass. For all 

surveys, the pDRs were set to log concentrations at 

10-second intervals. 

During each sampling shift, 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. Face 

velocity for each sampling day was calculated by averaging the 10-shield interval velocity readings. Table 

1 summarizes site-specific information for each mine. 

Results from cascade impactors 

Impactor samples were collected at mines B and C. 

Figure 3 graphs the percent weight on the seven stages 

versus the cut points in microns. The graph shows that 

the size distribution of airborne particles is similar in 

trend for both mines. Averaging data from both mines, 

87.4% of the dust by weight was 10 μm or greater. The 

respirable dust (<10 μm) constituted 12.6% of the sample. This size distribution is similar to results from other 

studies that have characterized airborne dust using cascade impactors from various sources in both longwall 

and continuous mining sections (Potts et al., 1990, Seixas 

et al., 1995). The MMD for Mine B and Mine C were 

27.5 μm and 32.7 μm, respectively, which is in agreement with the findings by Potts et al. that the MMD of 

support-generated dust was usually greater than 21 μm. 

Figure 4 graphs the respirable dust concentrations 

calculated for the final four stages. Concentrations are 

calculated using the sampling time, pump rate and the 

mass weight on that specific stage. The graph shows a 

trend in that the highest concentrations occur at the 3.5 

and 2.0 micron range and concentration increases relative to velocity. 

Figure 4 

Impactor respirable dust concentrations calculated from 

final four stages. 

Results from personal DataRAM 

Table 2 shows the pDR concentration, air velocity 

and number of shields moved per minute for each headto-tail pass at each mine. Also shown are the mean, 

standard deviation and the 95% confidence interval using t-distribution for the pDR concentration. Average 

pDR concentrations ranged between 0.71 mg/m3 to 2.57 

mg/m3 indicating that advancing shields are generating 

and entraining a significant amount of respirable dust 

in the walkway. 

Figure 5 graphs the mean concentration from Table 

2, versus the average air velocity for each mine from 

Table 1. 

Figure 5 

Average pDR concentration versus average air velocity 

at each mine. 

Figure 5 shows that, except for mine C, higher 

air velocity tends to increase dust concentration. How-
	 	 	 	 	 	

					

	 	 				 					 	 	

	 	 	 	

ever, Fig. 6 plots the average pDR concentration per 

shift versus the air velocity and illustrates that there is 

not a consistent trend in concentration as air velocity 

increases. 

Figure 6 

Average pDR dust concentrations versus increasing air 

velocity on a per shift basis. 

Large variations in pDR concentrations were 

evident for the head-to-tail passes on each shift. A possible explanation for this variation could be that caving 

behind the shields in the gob may be causing spikes in 

the respirable dust concentrations. 

Figure 7 graphs the mean concentration from Table 2, 

versus the average number of shields advanced for each 

mine, from Table 1.

Table 2 

pDR concentration, air velocity and shield advance for each head-to-tail pass at each mine. 

Mine	 

a 

Head to	 

tail pass	 

1	 

2	 

3	 

4	 

5	 

6	 

Shift	 

1 

2 

3 

pDR	 

concentration	 

mg/m3 

0.50	 

0.39	 

1.44	 

0.88	 

1.02	 

1.94	 

Velocity	 

per shift	 

m/s	 

1.61 

1.94 

1.60 

No. of	 

shields	 

advanced/min.	 

6.9	 

6.6	 

7.7	 

7.4	 

6.2 

6.0 

pDR concentration 

mean 

1.03	 

standard 

deviation 

0.59	 

95% confidence 

interval (+, -) 

0.62	 

B	 

1	 

2	 

3	 

4	 

5	 

1 

2 

1.83	 

1.35	 

0.45	 

1.81	 

0.48	 

2.15 

2.46 

12.9	 

9.9 

9.9	 

9.9 

6.1 

1.18	 0.68	 0.85 

C 

1	 

2	 

3	 

4	 

1 

2 

0.58	 

0.51	 

0.87	 

0.88	 

3.58 

3.18 

5.6 

6.0	 

5.1 

4.9 

0.71	 0.19	 0.31 

D	 

1	 

2	 

3	 

4	 

5	 

6	 

7	 

8	 

1 

2 

3 

1.35	 

1.11	 

2.90	 

3.57	 

3.96	 

2.75	 

2.48	 

2.42	 

4.29 

3.91 

4.52 

5.0 

5.0	 

5.0 

5.5 

5.7	 

5.5 

5.0 

4.2 

2.57	 0.98	 0.82 

 Based on the average shield movement for the particular mine, Fig. 7 shows that three of 

the four mines show a trend, as the number of shields 

advanced per minute increases, so does the concentration. The exception is mine D, which has the lowest rate 

of shield advance and the highest pDR concentration. 

However, Fig. 8 plots shield advance rates on a shift basis for each mine versus the pDR concentrations. Similar 

to velocity, the data reveals that there is not a consistent 

trend in concentration as shield advance rates increase. 

Once again, the variances in pDR concentrations could 

not be explained, but may be attributed to the geology 

of the roof strata. 

Discussion of shield dust control 

The majority of the dust liberated by shield movement was observed dropping off the canopy between 

the shields as they were lowered and advanced. Springactuated side plates were used to close the gap between 

shields and prevent material from the canopy from 

falling into the walkway. These are generally effective 

when the support is set; however a gap is created as the 

shield is lowered for advance. Most of the shield dust 

becomes entrained whenever the gap is created, as the 

material falls between the supports and directly into the 

airstream. 

Shield spray systems have been used to wet the unconsolidated coal/rock on the tops of shields before it 

becomes exposed to ventilating air during shield advance. The primary dust control method, available on 

most shield supports, is a spray system that consists of 
six to 10 sprays mounted on top of the canopy to add 

moisture to the material. The sprays are typically activated when the shield is lowered and advanced, with 

an operating pressure range from 350 to 2800 kPa and 

a flow rate of 9 to 28 L/min. Adding moisture can be an 

effective means of controlling dust, however, the effectiveness of these spray systems has not been documented. Factors that determine the effectiveness of these 

systems are the spray location, number, and spacing; 

how uniformly the sprays wet the material across the 

canopy; and how long these sprays operate as designed. 

As with all water spray systems, regular maintenance is 

imperative for proper performance, and some operators have expressed difficulty in maintaining the shield 

sprays through the life of a longwall panel because of 

their location. NIOSH is currently investigating a directional spray system in the laboratory that, if successful, 

will direct shield dust toward the face, away from the 

walkway airstream, and be located on the underside of 

the shield for easier maintenance. 

A control technology investigated by the Bureau 

of Mines in the early 1990s involved a foam spray that 

would adhere to the roof in front of the support as it was 

lowered, advanced and reset.The foam would penetrate 

the broken material on top of the canopy, increasing its 

moisture content, thereby lowering support-generated 

dust. Initial studies were inconclusive due to slow shield 

advance in the mines where trials were conducted.With 

faster shield movement on longwalls today, this control may show more promise. A primary administrative 

control is dust avoidance. Operational changes such as 

unidirectional cutting may allow for greater flexibility 

to place workers upstream of the dust sources than bidirectional cutting. Depending on roof conditions, this 

may allow the operators to modify the cut sequence so 

that shields are only advanced downwind of the shearer. 

Activating the shields as close to the tailgate drum as 

possible and keeping the jacksetter upwind of the advancing shields may keep the worker in a clean air envelope created by the shearer’s directional spray system 

and thus protect the worker from elevated dust levels. 

Figure 7 

Average pDR concentration versus average number of 

shields moved per minute at each mine. 

Figure 8 

Average pDR concentration versus increasing shield 

advance rate on a per shift basis. 

Summary 

Substantial gains in production have led to increasing levels of air and water usage to control dust generation from all longwall sources. Research and application 

of control technologies have focused on the shearer 

and stageloader/crusher, which were the two highest 

sources of respirable dust as characterized by a U.S. Bureau of Mines study in the 1980s. A similar study by 

the Bureau in the 1990s indicated that dust liberation 

during shield movement was beginning to emerge as a 

significant contributor to dust generation on longwalls. 

As shields are advanced, material drops off of the shield 

canopy directly into the airstream. Increases in shearer 

speed, have resulted in a greater numbers of shields 

being advanced at a faster rate and in closer proximity 

to the headgate shearer operator. The faster advance 

rate minimizes the time available to dilute dust prior 

to reaching the shearer operator on head-to-tail passes. 

This may elevate dust exposure associated with supportgenerated dust. 

The intent of these field surveys was to record realtime dust levels using pDRs, directly downwind of shield 

movement, before shield dust concentrations were influenced by shearer-generated dust and/or the impact of 

dilution. Analysis of resulting data shows that both air 

velocity and frequency of shield movement have an effect on dust concentrations. However, data analysis suggests that the combined influence of both variables can 

raise or lower dust concentrations and neither variable 

appears to have a stronger effect than the other on dust 

levels. Laboratory research by NIOSH in a wind tunnel 

to study the fundamental relationship between air velocity and dust levels clearly indicates that increased air velocities have the potential to raise the level of airborne 

respirable dust (Listak et al. 2001, Chekan et al., 2001; 

Chekan et. al., 2004). The tests showed that regardless 

of the percentage of respirable dust in the test samples, 

increases in air velocity still resulted in higher levels of 

respirable dust. It is important to note that these results 

were obtained with dry dust (<1% moisture) dropped 

directly into the airstream without any method of dust 

control in use. Dilution or decreasing levels of airborne 

respirable dust with increasing air volume were not observed. This was attributed to greater air velocity, creating particle separation in the respirable range and 

entraining more dust, thus overcoming the effects of 

dilution. 
 

Field studies through the 1980s and 1990s, and more 

recently completed longwall surveys show that shield 

dust is a growing source of respirable dust on longwall 

faces. Studies show a strong relationship between the 

rock and quartz in the sample (Ramani et al., 1987). 

In mines where roof rock is the main component on 

the canopy, the entrainment of respirable quartz dust 

becomes more of an issue, as elevated quartz in the dust 

samples results in a reduced permissible exposure limit. To lower dust exposure to workers, mine operators, 

shield manufacturers and government researchers will 

need to work closely together in the future to mitigate 

this emerging dust source. 

References 

Breuer, H., 1972. “Progress in Dust and Silicosis Control,” Gluckauf, 

108(18), pp. 806-814. 

Chekan G.J., Listak JM and Colinet JF, 2001. “Laboratory Testing 

to Quantify Dust Entrainment During Shield Advance.” Proceedings 7th International Mine Ventilation Congress. Krakow, 

Poland. June 17-22, 2001. pp. 291-298. 

Chekan G.J., Listak J.M. and Colinet J.F., 2004. “Factors Impacting 

Respirable Dust Entrainment and Dilution in High Velocity Airstreams. SME Transactions 2002. Vol. 312, pp. 186-192. 

Chekan G.J., Colinet J.F.,Kissel F.N.,Rider, J.P.,Vinson,R.P.,Volkwein, 

J.C. 2006. “Performance of a Light Scattering Dust Monitor in 

Underground Mines.” SME Transactions 2006. Vol. 320, pp. 21-24. 

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Colinet, J.F.; Spencer, E.R., Jankowski R.A. 1997. Status Proceedings 

of The 6th International Mine Ventilation Congress, Pittsburgh, 

Pennsylvania, May 18-22, 1997, Chapter 55, pp. 345-351. 

Colinet, J.F. and Jankowski, R.A., 1997. “Ventilation Practices on Longwall Faces in the United States,” Proceedings of Ventilation `97, 

Ottawa, Ontario, Canada, September 14-17, 1997, Session 12-3. 

Foster-Miller Associates Inc., 1982. “Evaluating Longwall Dust Sources and Control Technology,” Interim Technical Progress Report, 

BuMines Contract Report HO202016, 85 pp. 

Hall, D.A., 1956.	�“Factors Affecting Airborne Dust Concentrations 

with Special Reference to the Effects of Ventilation,” Transactions of the Institution of Mining Engineers, Vol. 115, pp. 245-275. 

Hodkinson, J.R., 1960. “The Relation Between Ventilation Airspeed 

and Respirable Airborne-Dust Concentration in Coal Mines,” 

Colliery Engineering, Vol. 37, No.6, pp. 236-239. 

Jankowski, R.A.and Organiscak, J.A. 1983. “Dust Sources and Controls on the Six U.S. Longwall Faces Having the Most Difficulty 

Complying With Dust Standards,”US Bureau Of Mines IC 8957, 

19 pp. 

Listak J.M., Chekan G.J., Colinet J.F., 2001. Laboratory Evaluation 

of Shield Dust Entrainment in High Velocity Airstreams. SME 

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