Information Circular 9465 

Handbook for Dust Control in Mining 

By Fred N. Kissell, Ph. D. 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

June 2003 
 

-------------------------------------------------------------

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DHHS (NIOSH) Publication No. 2003-147 
ii 

CONTENTS 

About this handbook....................................................................................................................................................

Page 

1 

Acknowledgments ....................................................................................................................................................... 1 

Chapter 1.—Dust control methods in tunnels and underground mines ....................................................................... 3 

Chapter 2.—Continuous miner and roof bolter dust control ..................................................................................... 23 

Chapter 3.—Longwall dust control ........................................................................................................................... 39 

Chapter 4.—Dust control in stone mines................................................................................................................... 57 

Chapter 5.—Surface mine dust control...................................................................................................................... 73 

Chapter 6.—Underground hard-rock dust control ..................................................................................................... 83 

Chapter 7.—Control of dust in hard-rock tunnels ..................................................................................................... 97 

Chapter 8.—How to find the major dust sources..................................................................................................... 109 

Chapter 9.—Dust respirators in mines and tunnels ................................................................................................. 119 

Index........................................................................................................................................................................ 129 

ILLUSTRATIONS 

1-1. Rollback of dust resulting from nonuniform airflow.......................................................................................... 5 

1-2. A half-curtain raises the air velocity to confine the dust cloud .......................................................................... 6 

1-3. Falling material drags air with it, so air must be extracted at the high-pressure side of the transfer point......... 7 

1-4. Spray-generated airflow carries dust back to the shearer operator ..................................................................... 9 

1-5. Water spray test that can lead to overrating spray effectiveness ...................................................................... 10 

1-6. Airborne capture performance of four types of spray nozzles.......................................................................... 11 

2-1. Machine-mounted scrubber design................................................................................................................... 24 

2-2. Dust scrubber used with blowing ventilation ................................................................................................... 26 

2-3. Excessive air blown toward the face will cause dust to bypass the scrubber inlets.......................................... 27 

2-4. Dust scrubber used with exhaust ventilation .................................................................................................... 28 

2-5. Half-curtain location......................................................................................................................................... 31 

2-6. Modified cutting cycle...................................................................................................................................... 32 

2-7. Antirollback water spray system ...................................................................................................................... 33 

3-1. Longwall dust sampling locations.................................................................................................................... 40 

3-2. Gob curtain forces air to stay on longwall face ................................................................................................ 44 

3-3. Typical respirable dust concentration profile around the shearer during the tail-to-head pass......................... 45
 

3-4. Air currents when using the shearer-clearer system......................................................................................... 46 

3-5. Support dust in the walkway dilutes as it moves downwind ............................................................................ 48 

3-6. Airflow at longwall headgate with a wing curtain............................................................................................ 48 

3-7. Transparent mesh partition retards the spread of shearer dust into the walkway ............................................. 51 

4-1. Conceptual approach to controlling crusher dust in a stone mine .................................................................... 60 

4-2. Jet fan ventilating a single straight heading...................................................................................................... 63 

4-3. Jet fan entrainment of mine air......................................................................................................................... 64 

4-4. Multiple headings a few crosscuts away from a fresh air pathway .................................................................. 66 

4-5. Airflows obtained with jet fan in operation...................................................................................................... 67 

4-6. Stopping built from damage-resistant brattice.................................................................................................. 69 

5-1. Corner flaps added to a deck shroud to reduce leakage.................................................................................... 75 

5-2. A circular shroud that can be raised and lowered improves dust collection efficiency.................................... 76 

6-1. Ore pass adjacent to steeply dipping ore body ................................................................................................. 84 

6-2. Wetting the top surface of the bottom belt ....................................................................................................... 87 

6-3. Wetting both surfaces of the bottom belt.......................................................................................................... 88 

6-4. Dust-laden air exhausted from transfer point enclosure ................................................................................... 89 

6-5. Effect of duct inlet position, air velocity, and air curtain use on dust levels .................................................... 92 

7-1. Results from a dust concentration survey......................................................................................................... 98 

7-2. Dust concentration measured near cutter head with TBM idle and operating.................................................. 99 

7-3. Auxiliary, or scavenger, system with adequate overlap ................................................................................. 100 

7-4. Auxiliary, or scavenger, system with no overlap ........................................................................................... 101 
 

iii 

CONTENTS—Continued 

7-5. Loss of ventilation efficiency from mismatched airflow directions ............................................................... 101 

7-6. Zone of low air movement is created because ducts have similar air quantities moving in opposite 

 directions ..................................................................................................................................................... 102 

7-7. TBM dust collection system........................................................................................................................... 102 

8-1. Mist eliminator for direct-reading instruments that use light scattering......................................................... 111 

8-2. Two gob-to-spillplate dust concentration gradients measured downwind of a longwall shearer ................... 113 

8-3. Air in return diluted by line curtain leakage................................................................................................... 114 

8-4. Cyclone shield for high-velocity air streams.................................................................................................. 115 

9-1. Half-mask replaceable-filter respirator........................................................................................................... 122 

9-2. Dust mask, also called a filtering facepiece ................................................................................................... 123 

9-3. Air helmet....................................................................................................................................................... 124 

TABLES 

3-1. Dust source contribution values from 13 longwalls ......................................................................................... 41 

4-1. Results of jet fan studies................................................................................................................................... 64 

4-2. Cost and leakage of five types of stone mine stoppings................................................................................... 70 

4-3. Pressure drop in stone mine airways ................................................................................................................ 70 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cfm cubic foot per minute 

ft foot 

ft2 square foot 

ft/min foot per minute 

gpm gallon per minute 

hr hour 

in inch 

in w.g. inch water gauge 

lb pound 

L/min liter per minute 

m meter 

m3 cubic meter 

mg milligram 

mg/m3 milligram per cubic meter 

mg/sec milligram per second 

min minute 

mm millimeter 

μm micrometer 

psi pound (force) per square inch 

sec second 
 

1 

HANDBOOK FOR DUST CONTROL IN MINING 

Fred N. Kissell, Ph.D.,1

1

Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

 Editor 

ABOUT THIS HANDBOOK 

This handbook describes effective methods for the control of mineral dusts in mines and tunnels. 

It assumes the reader is familiar with mining. The first chapter deals solely with dust control 

methods, regardless of the application. It is a brief tutorial on mining dust control and will be of 

help to the reader whose dust control problem does not conveniently fit any of the mining 

equipment niches described in later chapters. 

The subsequent chapters describe dust control methods for different kinds of mines and mining 

equipment. This includes underground coal and hard-rock mines, as well as surface mines, stone 

mines, and hard-rock tunnels. Because dust sampling has so many pitfalls, a chapter on methods 

used to sample dust is included. For those occasions when there is no practical engineering 

control, a chapter on respirators is also included. 

Except for those listed as “future possibilities” in the longwall chapter, the dust control methods 

described are practical and cost-effective for most mine operators. 

If controlling dust were a simple matter, dust problems in tunnels and mines would have been 

eradicated years ago. Unfortunately, most underground dust control methods yield only 25% to 

50% reductions in respirable-sized dust. Often, 25% to 50% reductions are not enough to 

achieve compliance with dust standards. Thus, mine operators must use several methods 

simultaneously, usually without knowing for sure how well any individual method is working. 

In fact, given a 25% error in dust sampling and day-to-day variations in dust generation of 50% 

or more, certainty about which control methods are most effective can be wanting. Nevertheless, 

over the years, some consensus has emerged on the best dust control practices. This handbook 

summarizes those practices. 
2 

ACKNOWLEDGMENTS 

Parts of this handbook were previously published in the Journal of the Mine Ventilation Society 

of South Africa and Tunnel Business Magazine. Much credit is also due to Joe Schall, the Giles 

Writer-in-Residence at The Pennsylvania State University, who helped to transform the awkward 

prose of the authors into something more readable. 
 

3 

CHAPTER 1.—DUST CONTROL METHODS IN TUNNELS 

AND UNDERGROUND MINES 

By Fred N. Kissell, Ph.D.2 

2

Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

In This Chapter 

9 Ventilation: dilution and displacement 

9 Water sprays: wetting and airborne capture 

9 Water additives: foam and wetting agents 

9 Dust collectors: filtration efficiency and inlet capture efficiency 

9 Reducing the generation of dust for cutting, drilling, blasting, crushing, and conveying 

This chapter will give you a general perspective on what 

works or doesn’t work. The chapter will also help if your 

dust control problem doesn’t fit any of the circumstances 

described in later chapters. 

This chapter describes the three major control methods used to reduce airborne dust in tunnels 

and underground mines: ventilation, water, and dust collectors. It also describes methods to 

reduce the generation of dust, so less has to be removed from the mine air. 

The ventilation methods provide the best use of air in the vicinity of workers and in the vicinity 

of dust sources. In this sense, the methods described are local ventilation methods. Most of the 

emphasis is on so-called displacement ventilation because it is the most effective dust control 

technique available. 

The section on water sprays outlines the dual role of sprays—wetting and airborne capture—and 

describes why wetting is more important. It also corrects some of the misconceptions about 

spray effectiveness and describes circumstances where sprays can actually increase the dust 

exposure of workers. 

The section on dust collectors outlines the circumstances under which dust collectors can be 

expected to function effectively. It also describes some common design and maintenance 

problems. 

The final section describes how to reduce the amount of dust that gets into the air in the first 

place, since once the dust is airborne it is always harder to control. 

 
4 

VENTILATION 

Ventilation air reduces dust by dilution and by displacement. Displacement ventilation is far more effective, but 

it is harder to implement. Several examples of displacement ventilation are provided. 

This section describes local ventilation methods for dust control. Ventilation air reduces dust 

through both dilution and displacement. The dilution mechanism operates when workers are 

surrounded by a dust cloud and additional air serves to reduce the dust concentration by diluting 

the cloud. The displacement mechanism operates when workers are upwind of dust sources and 

the air velocity is high enough to reliably keep the dust downwind. 

Dilution Ventilation. The basic principle behind dilution ventilation is to provide more air and 

dilute the dust. Most of the time the dust is reduced roughly in proportion to the increase in 

airflow, but not always. The cost of and technical barriers to increased airflow can be substantial, particularly where air already moves through ventilation ductwork or shafts at velocities of 

3,000 ft/min or more. 

Displacement Ventilation. The basic principle behind displacement ventilation is to use the 

airflow in a way that confines the dust source and keeps it away from workers by putting dust 

downwind of the workers. Every tunnel or mine passage with an airflow direction that puts dust 

downwind of workers uses displacement ventilation. In mines, continuous miner faces or tunnel 

boring machines on exhaust ventilation use displacement ventilation. Enclosure of a dust source, 

such as a conveyor belt transfer point, along with extraction of dusty air from the enclosure, 

is another example of displacement ventilation. 

Displacement ventilation can be hard to implement. However, if done well, it is the most effective dust control technique available, and it is worth considerable effort to get it right. The difficulty is that when workers are near a dust source, say, 10 to 20 ft from the source, keeping them 

upwind requires a substantial air velocity, typically between 60 and 150 ft/min. There is not 

always enough air available to achieve these velocities. 

To compensate for the lack of air, two techniques are used. The first is to reduce the crosssectional area of the air course between the worker and the dust source. This confines the dust 

source by raising the air velocity. Second, the turbulence of the dust source is reduced. 

A turbulent dust source creates dusty eddy currents of air that back up against the airflow and 

push upwind toward the worker. When the dust source is less turbulent, less air is required to 

confine the dust cloud. The best way to illustrate displacement ventilation is to consider four 

specific mining examples. 
5 

Example No. 1: Continuous miner faces 

on exhaust ventilation.—To confine the 

dust cloud at continuous miner faces, U.S. 

coal mine ventilation regulations require an 

average air velocity of 60 ft/min. This 

velocity is based on the entry cross-section 

without considering the area blocked by the 

equipment. However, 60 ft/min is a bare 

minimum, as it has been shown that 

120 ft/min is required for good dust control 

[USBM 1985]. This relatively high air 

velocity is required because a typical coal 

mine entry is about 18 ft wide, and over 

this width the air velocity is not uniform. 

The air velocity is much higher on the side 

next to the ventilation duct, as shown in 

figure 1-1. 

 Figure 1-1.—Rollback of dust resulting from nonuniform airflow. 

Air turbulence created by the 

machine water sprays causes the dust cloud 

at the cutting face to expand and back up 

against the weaker airflow on the side 

opposite the ventilation duct. In mining, 

this is called rollback. It is surprising how 

far dust can roll back to contaminate the 

incoming air breathed by mine workers. 

Rollback can be reduced by increasing the 

airflow. The air turbulence that causes rollback can be reduced by lowering the spray water 

pressure and aligning spray nozzles so that they are confined only to spray on the broken coal. 

Also, in high coal where the cross-sectional area is very large, a half-curtain in the entry is 

helpful. This curtain, shown in figure 1-2, is placed between the mining machine and the right or 

left rib, whichever is farthest from the mining machine [Jayaraman et al. 1986]. A half-curtain 

reduces the cross-sectional area of the entry and raises the air velocity to confine the dust cloud. 

In addition to the half-curtain, there are many possible mining applications where a temporary 

curtain or screen can be used to channel airflow or raise the air velocity to keep nearby workers 

upwind of a dust source. 

Example No. 2: Closed-face tunnel boring machine (TBM).—Cutter heads of hard-rock tunnel 

boring machines operate in what most would regard as an enclosed space. However, Myran 

[1985] has published recommended air quantities needed to confine dust to the cutter head space, 

and they are high. For example, a 20-ft-diam TBM requires 12,000 to 17,000 cfm. Why such 

high airflow for what is presumably an enclosed space? First, the stirring action of the large 

rotating cutter head creates a considerable amount of air turbulence. Second, there is far less 

enclosure of the cutter head than a casual inspection of a TBM would indicate. Depending on 

the TBM design, the entire belt conveyor access space can be open. Also, there is considerable 

open space when the grippers at the head expand to press out against the tunnel walls. Dust 

reduction efforts have focused on reducing the open space available for dust leakage by 
6

enclosing the conveyor tunnel and by installing 

single or even double sets of rubber dust seals 

between the grippers and TBM body. 

 Figure 1-2.—A half-curtain raises the air velocity to confine the dust cloud. 

Example No. 3: Conveyor belt transfer point 

enclosure.—In addition to maintaining high 

airflow, sometimes it is necessary to extract the 

air at the right location in order to adequately 

confine dust. Figure 1-3 shows a conveyor 

transfer point enclosure. The design of this and 

similar enclosures used in materials transport 

has been well worked out [Goldbeck and Marti 

1996; Swinderman et al. 1997]. In principle, 

a high degree of enclosure is possible, so even 

moderate airflow extracted from the enclosure 

should keep dust inside. However, the falling 

material drags air with it, creating an 

unbalanced pressure in the enclosure that 

pushes dust out of the high pressure end of the 

enclosure. The most effective designs address 

this issue by locating the exhaust port at the 

high-pressure end and exhausting sufficient air. 

Other designs incorporate steps to break the fall of the rock and thus diminish the amount of air 

moved. However, if the dust seals along the belt and the rubber flaps at the end of the enclosure 

are worn or missing, even the best designs available will leak dust. 

Example No. 4: Dust avoidance measures.—Dust avoidance refers to moving either the dust 

cloud or the workers so that the workers are upwind of the dust. The use of remote control on 

coal mining machinery is the best example of dust avoidance in mining. On longwall shearers, 

remote control has enabled the shearer operators to move upwind 15-20 ft and avoid direct contact with the dust cloud coming off the headgate-end shearer drum, which reduces their dust 

exposure by 68% [USBM 1984]. On continuous miners, remote control has enabled the operator 

to step back toward the intake by about 12 ft and reduce his or her dust exposure level by 50% or 

more [Divers et al. 1982]. 
7

Sometimes, it is possible to move the 

dust cloud or at least its outer edge. 

On longwall shearers, the so-called 

“shearer-clearer” system uses the airmoving capacity of water sprays to 

hold the dust cloud against the face 

and prevent it from moving out into 

the walkway. This can reduce worker 

dust exposure by 50% [Shirey et al. 

1985]. 

When workers are at the edge of a 

dust cloud, a small shift in the location 

of the workers or the location of the 

cloud can yield large benefits. However, if workers are in the middle of a 

dust cloud, dust avoidance has less 

chance of success because the distance 

moved must be greater. 

 Figure 1-3.—Falling material drags air with it, so air must be 

extracted at the high-pressure side of the transfer point. 

WATER SPRAYS 

When using water sprays, focus on uniform wetting more 

than airborne capture. 

The role of water sprays in mining is a dual one: (1) wetting of the broken material being 

transported and (2) airborne capture. Of the two, wetting of the broken material is far more 

effective. 

Wetting. Adequate wetting is extremely important for dust control. The vast majority of dust 

particles created during breakage are not released into the air, but stay attached to the surface of 

the broken material [Cheng and Zukovich 1973]. Wetting this broken material ensures that the 

dust particles stay attached. As a result, adding more water can usually (but not always) be 

counted on to reduce dust [Jankowski and Organiscak 1983; Ruggieri and Jankowski 1983; 

Zimmer et al. 1987]. For example, coal mine operators have been able to reduce the dust from 

higher longwall production levels by raising the shearer water flow rate to an average of 100 

gpm [Colinet et al. 1997]. Compared to the amount of coal mined, on a weight basis, this 100 

gpm is equivalent to 1.9% added moisture from the shearer alone. Unfortunately, excessive 

moisture levels can also result in a host of materials handling problems, operational headaches, 

and product quality issues, so an upper limit on water use is sometimes reached rather quickly. 

As a result, an alternative to simply adding more water is to ensure that the broken material is 

being wetted uniformly. 
8 

Uniformity of wetting was recognized as an important issue long ago by Hamilton and Knight 

[1957], who measured the amount of dust generated by dropping coal. By far the best dust 

reductions came from prespraying the coal with water and then mechanically mixing the coal and 

water together to achieve a uniformity of wetting. Subsequent mining experience has confirmed 

this. For example, releasing water at the cutting picks of rotating shearer drums has proven to be 

far more effective at suppressing longwall dust than using external sprays on the shearer body. 

This is because water released at the cutting picks gets mixed in with the broken coal, whereas 

water from external sprays usually provides just surface wetting. 

Increasing the number of sprays is another way to promote uniformity of wetting. Bazzanella 

et al. [1986] showed that dust suppression is improved by increasing the number of sprays on a 

shearer drum even when the total water flow and nozzle pressure were held constant with the use 

of smaller orifice nozzles. When 46 smaller orifice nozzles were substituted for the 17 original 

nozzles, dust was reduced by 60%. This is better than the dust reduction given by most dust 

control techniques. 

The benefits of improved mixing and uniformity of wetting have also been obtained with foam, 

with far greater effectiveness when the foam was mechanically mixed in with the coal 

[Mukherjee and Singh 1984] or mechanically mixed with silica sand [Volkwein et al. 1983]. 

The lessons from this knowledge about the use of water are twofold. First, it is best to wet the 

material fully during the breakage process. This is when most mechanical mixing is likely to 

take place. Wetting during breakage ensures that the benefits will carry over to any downstream 

secondary handling operation. Second, uniformity of wetting is best achieved by using more 

nozzles at lower flow rates and ensuring that the nozzles are aimed at the broken material rather 

than just spraying into the air and wetting an adjacent metal or rock surface. 

While it is always best to aim sprays at broken material, circumstances dictate the impracticality 

of locating spray nozzles where they might be easily damaged. For example, spray nozzles 

under the boom of a continuous miner are more effective than those on the top of the boom 

[Matta 1976]. However, top nozzles are more commonly used because sprays under the boom 

are damaged more often and are harder to maintain. 

Airborne capture. Under actual mining conditions, the typical water spray operating at 100 psi 

and 1-2 gpm gives no more than 30% airborne capture of respirable dust3

3

The author is aware of one notable exception to this 30% rule: water blast sprays in metal mines. These sprays, 

using a combination of water and compressed air, were first used many years ago to reduce dust in metal mine 

headings after blasting. Brown and Schrenk [1938] saw dust reductions of 90%-99% from water blast sprays within 

15 min after blasting. The reason for the difference (90%-99% instead of 30%) is that the water blast sprays had 

15 min to work on a single-event dust cloud confined to the end of the heading. Most of the dust in the cloud 

recirculated through the sprays again and again, whereas in most modern mining applications the dust cloud is 

generated continuously, and the dust only gets one pass of a few seconds through the sprays. This explains the 

30% spray effectiveness in modern mining applications. In more recent years, McCoy et al. [1985] measured the 

effectiveness of water spray nozzles using a closed chamber in which a single-event dust cloud was recirculated 

again and again through a spray. In a few minutes, the dust level was reduced by 90%, confirming the earlier 

observations of Brown and Schrenk, and others [van der Bank 1977]. 

[Courtney and Cheng

1977]. This is not as good as lab tests [Tomb et al. 1972] would lead one to believe. In lab tests, the 

 
9 

sprays were usually confined in a duct,

and all of the dust was forced to pass

through the spray. However, under 

actual mining conditions, dust clouds 

are unconfined. In all sprays, the

moving droplets exert drag on the 

adjacent air; thus, sprays act to move the 

air. Because of this air entrainment 

effect, if a spray is aimed at an 

unconfined dust cloud, it will carry in

air that spreads the cloud, thus making 

capture by the spray less efficient. 

Aside from making sprays less efficient, the air entrainment of sprays can create other problems. 

Figure 1-4 shows how some sprays on a longwall shearer actually raise the shearer operator s 

dust level. 

=

 Figure 1-4.—Spray-generated airflow carries dust back to 

the shearer operator. 

For many years, it was a common practice to discharge the motor-cooling water by 

aiming it at the coal face under the theory that it would capture some airborne dust. Although 

some dust was captured, a considerable airflow toward the coal face was also created. That 

airflow, upon reaching the coal face, simply turned around and carried the rest of the dust cloud, 

formerly confined to the face, back over the operator. Perhaps one-fourth of the cloud was captured, but the remaining three-fourths was blown back over the operator, raising the operator’s 

dust level threefold [USBM 1981]. 

Air entrainment of sprays can also lead to overrating their effectiveness. Figure 1-5 shows a 

conceptual example. A dust cloud is generated by a dust source, such as a belt transfer point, 

and the cloud surrounds much of the dust source (figure 1-5, left). A water spray is aimed at the 

cloud, and a dust sampler located on or near the source shows a substantial dust reduction when 

the spray is turned on. Most of this dust reduction is actually caused by the air currents induced 

by the water spray, which dilute and blow away much of the dust cloud (figure 1-5, right). 

Normally, this dust reduction would be misinterpreted as airborne capture by the spray droplets. 

A flawed spray application that appears in all types of 

mines is the so-called “water curtain.” It is based on the 

incorrect notion that dust particles passing across a 

barrier row of sprays will always be captured. 
 

Figure 1-5.—Water spray test that can lead to overrating spray effectiveness. 

10 

Attempts to improve the airborne capture efficiency of sprays have not met with practical 

success. One approach has been to reduce droplet size, based on the notion that capture by 

smaller droplets is more efficient. This effort has included atomizing or fog sprays, steam, 

sonically atomized sprays, compressed air-atomized sprays, and electrically charged atomized 

sprays [Bigu and Grenier 1989; McCoy et al. 1983]. These methods usually offer somewhat 

better dust capture and some economy in the use of water, but have many disadvantages that 

prevent their use in mining. Nozzles with very small orifices are more prone to clogging. Fine 

droplets are likely to evaporate quickly and release captured dust along with the minerals that 

had been dissolved in the water [McCoy et al. 1983]. 

Sprays that use less water fall short in the more important 

role of wetting the broken material. 

Despite the limitations of sprays, proper nozzle selection can enhance their use. Figure 1-6 

shows the airborne capture performance of some common spray nozzle types at different 

pressures. Atomizing sprays are the most efficient. Hollow-cone sprays are a close second and 

are the best choice for practical mining applications because they have larger orifice nozzles and 

are less likely to clog. Flat fan sprays are more appropriate for spraying into a narrow rectangular 

space because less water is wasted by spraying against an adjacent rock or metal surface. 
11 

High-pressure sprays. One way to 

improve sprays is to raise the water 

pressure. This raises the efficiency per 

unit use of water, as shown in 

figure 1-6.

 Figure 1-6.—Airborne capture performance of four 

types of spray nozzles. 

 Jayaraman and Jankowski 

[1988] tested the airborne capture of 

both conventional and high-pressure 

sprays at a full-scale model continuous 

miner face. A conventional spray 

system on the miner (100 psi, 19 gpm) 

gave 30% respirable dust reduc-tion. A 

high-pressure system (2,500 psi, 3 gpm) 

gave the same reduction, but with much 

less water. The two systems operating 

together (22 gpm) gave 59% dust reduction. The dual system would be the 

choice for underground use, providing 

both airborne capture and sufficient wetting of the broken material. 

A marked disadvantage of high-pressure 

sprays is that they entrain large volumes 

of air, often leading to more dispersal of 

dust than is captured. Because of this 

secondary dispersal, their application is 

limited to enclosed or semienclosed 

spaces, such as under the boom of a continuous mining machine. 

Aside from efforts to improve sprays, the most helpful 

action you can take is to provide an automatic feature that 

turns sprays on and off as needed. This allows sufficient 

wetting while helping to avoid the problems associated 

with overuse of water. 

Foam. For dust control, foam works better than water. It provides dust reductions of 20% to 

60% compared to water. Foam also can produce similar results at lower water use, that is, the 

amount of water needed to make the foam is less than the equivalent water spray. 

Seibel [1976] compared high-expansion foam to water sprays at a belt transfer point. Compared 

to water, the foam averaged an additional 30% dust reduction. Mukherjee and Singh [1984] 

found that foam released from a longwall shearer drum cut the dust an additional 50% compared 

to conventional water sprays on the drum. Also, the system used one-half the water of the 

conventional sprays. The drawback of the foam was high cost. Like water, foam works best 
12 

when it is mechanically mixed with the broken material. A comprehensive review of foam for 

dust control in mining and minerals processing has been given by Page and Volkwein [1986]. 

Wetting agents. Wetting agents receive a disproportionate amount of attention, perhaps because 

they seem to offer an easy fix to dust problems. Most interest has been in coal mining because of 

the hydrophobic nature of coal. The effectiveness of wetting agents has been the subject of considerable research over the years, without much of a definitive answer on how well they work. 

Various studies have shown a respirable dust control effectiveness compared to plain water, 

averaging about 25% and ranging from zero [MRDE 1981; Chander et al. 1991] to 25%-30% 

[Kost et al. 1980] to more than 40% [Meets and Neethling 1987]. It seems that wetting agent 

effectiveness depends on the type of wetting agent, type of coal, dust particle size, dust concentration, water pH, and water mineralogy [Hu et al. 1992; Kim and Tien 1994; Tien and Kim 

1997]. However, no general formula or methodology has emerged that would allow a mine 

operator to select a wetting agent appropriate for its specific coal (or rock) type. The only alternative is to try out a prospective wetting agent and discontinue its use if there is no clear benefit. 

However, given that the average effectiveness of a wetting agent is 25%, about the same as the 

accuracy of dust sampling methods, a wetting agent choice is never easy. 

DUST COLLECTORS 

Dust collectors can play a valuable role in dust reduction—if space is available to locate the collector and if the collector efficiency is high. Dust collectors range from low-volume filtration 

systems used in the cabs of mining equipment [Organiscak et al. 2000] to high-volume wet collectors used on continuous miners in coal mines [Volkwein et al. 1985]. 

The most difficult dust collector application occurs 

when the dust has a high percentage of silica and the 

air passing through the collector is reused. Then, any 

minor collector malfunction or design flaw will lead to 

excessive dust levels. 

It is important to recognize that the efficiency of a dust collector is the filtration efficiency of the 

unit times the capture efficiency of its inlet. For collectors properly designed to trap respirable 

dust, the filtration efficiency is usually quite high, in the 90%-95% range. The inlet capture efficiency is much more variable. The inlet capture efficiency is high, 80% or better, when the collector extracts air from an enclosed or semienclosed space, such as the cutter head space of a 

hard-rock TBM or the crusher on a longwall stageloader. If the coalbed is not too high, capture 

efficiency is also reasonable at continuous miner faces, which are dead-end spaces crammed with 

equipment. However, where there is less enclosure, such as in continuous miner faces in high 

coal, roadheader faces, or longwall shearer faces, inlet capture efficiency is poor, 50% or less, 

unless the collector air quantity is unreasonably high. 
13 

Collectors also exhibit many design and maintenance problems, as follows: 

Design problems. The designers of dust collection systems take many shortcuts to cut costs and 

reduce the amount of maintenance required, some of which also reduce the efficiency. For 

example, some of the fiber filters on cab filtration systems [Organiscak et al. 2000] and the 

flooded-bed panels on continuous miners [Colinet and Jankowski 2000] have been found to be 

too porous. A porous filter permits more airflow and allows for a smaller fan, but exhibits a poor 

collection efficiency for hard-to-trap respirable dust. Also, in recent years, continuous miner 

booms have been redesigned to move the collector inlets from the boom to the hinge point. This 

has had many benefits in cost and maintenance, but this location is farther from the dust source 

and thus has lowered the inlet capture efficiency [Jayaraman et al. 1992b]. 

Maintenance problems. Dust collectors in mines and tunnels can be high-maintenance equipment. Screens and filters clog often, sometimes more than once per shift. Gaskets disappear and 

access doors leak. Often, filters are not seated properly, and dusty air leaks around them. Filters 

also develop holes from mishandling and from abrasion by larger-sized particulate. Ductwork 

leading to the collector fills with coarse particulate, cutting off the airflow. Fans located on the 

inlet side of the collector suffer rapid erosion of their blades and are usually not designed for 

convenient blade replacement. High dust levels are the result. A major reason for excessive 

silica exposure during coal mine roof bolting is lack of maintenance on the bolting machine dust 

collector. 
14 

REDUCING THE AMOUNT OF DUST GENERATED 

When less dust is generated, less has to be removed from 

the mine air. 

Dust is generated by extraction, drilling, blasting, dropping, crushing, and conveying. Usually, 

there is some opportunity for improved control. 

Extraction. The machines that produce extraction dust are longwall shearers, continuous 

miners, tunnel boring machines, and roadheaders. For these, the deeper the cut and the larger the 

chips, the less the dust produced per pound of material removed [Ludlow and Wilson 1982]. 

Of the factors that impact cut depth, the one under the control of the mine operator is the sharpness and the lacing pattern of the cutting tools. Lab studies on conical cutting bits have shown 

that significantly worn bits without their carbide tips produce much more dust [Organiscak et al. 

1995]. 

Aside from using sharper cutting bits, water can be applied as described above. Another application of water that reduces cutting dust is water infusion of coal seams. Although it has been 

largely abandoned because of high cost, water infusion of coal seams will reduce dust by about 

50%. To infuse a coal seam, boreholes are drilled into the coal seam ahead of mining and large 

volumes of water are pumped in under high pressure to wet the coal [McClelland et al. 1987]. 

Somewhat analogous to cutting is the grinding action of longwall shields as they are pressed 

against the coal mine roof. This dust is released into the air as the shields are lowered and 

moved forward. The factors affecting dust generated by longwall shields and the methods used 

to control this dust have been discussed by Organiscak et al. [1985]. 

Drilling. In coal mines, the most common method of drill dust control is a dry collector with the 

intake at the tip of the drill bit. This arrangement provides excellent dust control if the collector 

is maintained properly [Divers and Jankowski 1987]. 

In hard-rock mines and tunnels, water injection through the drill steel has been effectively used 

to control dust for many years [ILO 1965; Page 1982]. Foam injection through the drill steel 

also can be used in those applications where excessive water can create a problem [Page 1982]. 

Problems with wet drills usually result from maintenance difficulties such as failure to clean out 

clogged lines or refill water tanks. Dry dust collectors with the inlet located at the collar of the 

drill hole have also worked [Page and Folk 1984], but not as well as water or foam. 

Blasting. Blasting is done at a time when workers are not expected to enter the affected area of 

the mine for the next hour or so [Knight 1980]. This allows some dust to settle out and the rest 
15 

to be carried away by the ventilation system. Water can help control dust by wetting down the 

blast area. 

 

Dropping. In removing and transporting mined material, the broken material is inevitably 

dropped. At longwall faces, the broken coal can fall 6 ft or more to the panline. At tunnelboring machines, rock removed at the crown can drop 25 ft or more. At conveyor belts, the 

dropping of material from one belt to another can be a major dust source. Where it is possible to 

do so, dust from falling material, whether at ore passes or at conveyor transfer points, is usually 

controlled by enclosure and exhaust ventilation [Marshall 1964]. 

Crushing. Crushers in mines range from small roll types used in coal mines to large gyratory 

types used in hard-rock mines and mills. Whatever the size and method of crushing, dust is 

controlled by water sprays and local exhaust ventilation. The amount of water and air needed to 

do the job is hard to specify. It depends on the type of material being crushed and the degree to 

which the crusher can be enclosed. Jayaraman et al. [1992a] obtained substantial reductions in 

crusher dust at a longwall by enclosing the entire stageloader-crusher unit, using 18 gpm of water 

inside the enclosure, and extracting 2,500 cfm of air from the enclosure. Rodgers et al. [1978] 

described how dust from a 5-ft gyratory crusher was reduced by using a 75,000-cfm exhaust 

ventilation system and a control booth for the operators. 

Conveying. Conveying by railcar usually generates little dust. Rubber-tired vehicles will 

kick up dust if the mine floor is dry. This dust from the floor can be reduced by wetting, 

by calcium chloride, or by any of the chemical preparations used to control dust at surface mines 

[ILO 1965; Kissell 1992]. 

A conveyor belt can generate large amounts of dust from several sources. Dust originates at 

transfer points. It is also shaken from the belt as the belt passes over the idlers. Spillage of 

material from the belt can also be a big contributor. Further, a high velocity of ventilation air 

will assist the release of dust by drying the material and releasing settled particulate. 

Methods to deal with belt dust are well known [Goldbeck and Marti 1996; Swinderman et al. 

1997]. If belt dust is high, the relevant questions to address are the following: 

1. Are transfer points enclosed? A simple enclosure with a spray or two inside of it may be 

adequate. If this is not enough, the air inside must be exhausted to a dust collector, with 

all of the leakage points on the enclosure sealed properly [Swinderman et al. 1997]. 

2. Is the material being conveyed adequately wet, but not so much that it leaves a sticky 

mud residue on the belt? When this residue dries, dust is released; thus, an end result of 

excessive wetting can be an increase in belt dust. 

3. Are the undersides of both the top and the bottom belts being wet [Ford 1973] so that 

dust sticking to the belt is not shaken loose by the idlers? Does the belt stay wet or is it 

drying out and releasing dust? 
16 

4. Are the belt scrapers working properly? Is a second set of scrapers being used? Has a 

belt-washing system been tried [Bennett and Roberts 1988; Stahura 1987]? 

5. Is the belt running true and not spilling its contents [Swinderman et al. 1997]? 

Chapter 6 on hard-rock mines contains more information 

on conveyor belt dust control. See page 86. 
17 

SUMMARY 

DUST CONTROL 

METHOD 

EFFECTIVENESS 

(Low is 10%-30%, 

moderate is 30%-50%, high 

is 50%-75%) 

COST AND 

DRAWBACKS 

Dilution ventilation Moderate High – more air may not be 

feasible 

Displacement ventilation, 

including enclosure with 

extraction of dusty air 

Moderate to high Moderate – can be difficult to 

implement well 

Wetting by sprays Moderate Low – too much water can be 

a problem 

Airborne capture by sprays Low Low – too much water can be 

a problem 

Airborne capture by high 

pressure sprays 

Moderate Moderate – can only be used 

in enclosed spaces 

Foam Moderate High 

Wetting agents Zero to low Moderate 

Dust collectors Moderate to high Moderate to high – possible 

noise problems 

Reducing generated dust Low to moderate Moderate 

Enclosure with sprays Low to moderate Moderate 

Dust avoidance Moderate Low to moderate 

Many methods have been tested to control dust in tunnels and underground mines. Poor results 

and difficult operating conditions have ruled out a high proportion. Those that have remained 

will reliably reduce dust if one makes a determined effort to deal with the problem. Inevitably, 

there is cost and inconvenience involved. However, the proper consideration and use of ventilation, water, and dust collectors can usually achieve a satisfactory result. 

REFERENCES4 

4

References that contain general information on dust control are: Hartman et al. [1997], Kissell [1992, 1996], 

Knight [1980], McPherson [1993], Swinderman et al. [1997], Tien [1999], and WHO [1999]. 

Bazzanella A, Becker H, Kemper F [1986]. Staubbekampfung in abbaubetrieben mit 

schneidender kohlengewinning. Gluckauf 122(11):728-735. Also available in translation as: 

Dust suppression in shearer faces, Gluckauf Translation 122(11):204-207. 

 
18 

Bennett DJ, Roberts AW [1988]. Carry-back measurements to evaluate the design, selection, 

and performance of belt cleaning systems. Mechanical Engineering Transactions, The Institution 

of Engineers, Australia. Vol. ME13, No. 4, December, pp. 215-221. 

Bigu J, Grenier MG [1989]. Reduction of airborne radioactive dust by means of a charged water 

spray. AIHA J 50:336-345. 

Brown CE, Schrenk HH [1938]. Control of dust from blasting by a spray of water mist. 

Pittsburgh, PA: U.S. Department of the Interior, RI 3388. 

Chander S, Alaboyun AR, Aplan FF [1991]. On the mechanism of capture of coal dust particles 

by sprays. In: Proceedings of the Third Symposium on Respirable Dust in the Mineral Industries 

(Pittsburgh, PA, October 17-19, 1990). Littleton, CO: Society for Mining, Metallurgy, and 

Exploration, Inc. 

Cheng L, Zukovich PP [1973]. Respirable dust adhering to run-of-face bituminous coals. 

Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 7765. NTIS No. PB 221­

883. 

Colinet JF, Jankowski RA [2000]. Silica collection concerns when using flooded-bed scrubbers. 

Min Eng Apr:49-54. 

Colinet JF, Spencer ER, Jankowski RA [1997]. Status of dust control technology on U.S. longwalls. In: Ramani RV, ed. Proceedings of the Sixth International Mine Ventilation Congress. 

Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 345-351. 

Courtney WG, Cheng L [1977]. Control of respirable dust by improved water sprays. In: 

Respirable Dust Control – Proceedings of Technology Transfer Seminars, Pittsburgh, PA, and 

St. Louis, MO, IC 8753, pp. 92-108. NTIS No. PB 272 910. 

Divers EF, Jankowski RA [1987]. Maintaining filters, bits can control respirable quartz dust 

during roof drilling. Coal Age Feb:57-59. 

Divers EF, Jayaraman NI, Custer J [1982]. Evaluation of a combined face ventilation system 

used with a remotely operated mining machine. Pittsburgh, PA: U.S. Department of the Interior, 

Bureau of Mines, IC 8899. NTIS No. PB83-156794. 

Ford VHW [1973]. Bottom belt sprays as a method of dust control on conveyors. Min Technol 

(U.K.) 55(635):387-391. 

Goldbeck LJ, Marti AD [1996]. Dust control at conveyor transfer points: containment, suppression, and collection. Bulk Solids Handling 16(3):367-372. 

Hamilton RJ, Knight G [1957]. Laboratory experiments on dust suppression with broken coal. 

London, U.K.: National Coal Board, Mining Research Establishment Report No. 2083. 
19 

Hartman HL, Mutmansky JM, Ramani RV, Wang YJ [1997]. Mine ventilation and air conditioning. Third Edition. New York: John Wiley & Sons, Inc. 

Hu Q, Polat H, Chander S [1992]. Effect of surfactants in dust control by water sprays. In: 

Proceedings of the Symposium on Emerging Process Technologies for a Cleaner Environment. 

Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 269-276. 

ILO [1965]. Guide to the prevention and suppression of dust in mining, tunnelling, and quarrying. Geneva, Switzerland: International Labour Organization. 

Jankowski RA, Organiscak JA [1983]. Dust sources and controls on the six U.S. longwall faces 

having the most difficulty complying with dust standards. Pittsburgh, PA: U.S. Department of 

the Interior, IC 8957. NTIS No. PB84-142058. 

Jayaraman NI, Jankowski RA [1988]. Atomization of water sprays for quartz dust control. Appl 

Ind Hyg 3:327-331. 

Jayaraman NI, Divers EF, Derick RL, Babbitt C [1986]. Evaluation of a new half-curtain technique for continuous miner faces. In: Proceedings of the Symposium on Respirable Dust. 

University Park, PA: The Pennsylvania State University. 

Jayaraman NI, Jankowski RA, Organiscak JA [1992a]. An update on stageloader dust control. 

In: Proceedings of Longwall USA (Pittsburgh, PA). 

Jayaraman NI, Jankowski RA, Whitehead KL [1992b]. Optimizing continuous miner scrubbers 

for dust control in high coal seams. In: Proceedings of New Technology in Mine Health and 

Safety Symposium. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., 

pp. 193-205. 

Kim J, Tien JC [1994]. Effect of added base on coal wetting ability of nonionic surfactant solutions used for dust control. Min Eng (London) 154(399):151-155. 

Kissell FN [1992]. Gas and dust control. In: SME Mining Engineering Handbook. Littleton, 

CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 1004-1020. 

Kissell FN [1996]. How to control air contaminants during tunnel construction. Pittsburgh, PA: 

U.S. Department of the Interior, Bureau of Mines, IC 9439. NTIS No. PB96-147558. 

Knight G [1980]. Generation and control of mine airborne dust. Canada Centre for Mineral and 

Energy Technology (CANMET) Report 80-27E. 

Kost JA, Shirey GA, Ford CT [1980]. In-mine tests for wetting agent effectiveness. Bituminous 

Coal Research, Inc. U.S. Bureau of Mines contract No. J0295041. NTIS No. PB82­

183344/XAB. ‌
20 

Ludlow J, Wilson RJ [1982]. Deep cutting = key to dust free longwalling. Coal Mining and 

Processing 19(8):40-43. 

Marshall L [1964]. Dust control at ore and waste pass dumps. Canad Min J Oct:84-86. 

Matta JE [1976]. Effect of location and type of water sprays for respirable dust suppression on a 

continuous mining machine. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

TPR 96. NTIS No. PB-254-677. 

McClelland JJ, Organiscak JA, Jankowski RA, Pothini BR [1987]. Water infusion for coal mine 

dust control: three case studies. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, RI 9096. NTIS No. PB88-120514. 

McCoy J, Melcher J, Valentine J, Monaghan D, Muldoon T, Kelly J [1983]. Evaluation of 

charged water sprays for dust control. Waltham, MA: Foster-Miller, Inc. U.S. Bureau of Mines 

contract No. H0212012. NTIS No. PB83-210476. 

McCoy JF, Schroeder WE, Rajan SR, Ruggieri SK, Kissell FN [1985]. New laboratory 

measurement method for water spray dust control effectiveness. AIHA J 46(12):735-740. 

McPherson MJ [1993]. Subsurface ventilation and environmental engineering. Kluwer Academic Publishers. 

Meets EJ, Neethling AF [1987]. Some experiences in the use of wetting agents to suppress dust 

at Sigma colliery. J Mine Vent Soc S Afr Oct:126-133. 

MRDE [1981]. Methods of reducing dust formation and improving dust suppression on longwall 

faces: final report on ECSC research project 7256-12/003/08. Mining Research and Development Establishment (U.K.). 

Mukherjee SK, Singh MM [1984]. New techniques for spraying dust. Coal Age June:54-56. 

Myran T [1985]. Tunnel boring machines in Norway: ventilation and dust problems. In: 

Proceedings of the Second U.S. Mine Ventilation Symposium (Reno, NV). 

Organiscak JA, Cecala AB, Heitbrink WA, Thimons ED, Schmitz M, Ahrenholtz E [2000]. 

Field assessment of retrofitting surface coal mine equipment cabs with air filtration systems. In: 

Bockosh GR, Karmis M, Langton J, McCarter MK, Rowe B, eds. Proceedings of the 31st 

Annual Institute of Mining Health, Safety and Research. Blacksburg, VA: Virginia Polytechnic 

Institute and State University, Department of Mining and Minerals Engineering, pp. 57-68. 

Organiscak JA, Khair AW, Ahmad M [1995]. Studies of bit wear and respirable dust generation. 

Transactions SME, Vol. 298. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 

Inc., pp. 1874-1879. 
21 

Organiscak JA, Listak JM, Jankowski RA [1985]. Factors affecting respirable dust generation 

from longwall roof supports. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

IC 9019. NTIS No. PB85 236453. 

Page SJ [1982]. An evaluation of three wet dust control techniques for face drills. Pittsburgh, 

PA: U.S. Department of the Interior, Bureau of Mines, RI 8596. NTIS No. PB82-177320. 

Page SJ, Folk M [1984]. Keystone achieves positive dust control during dry drilling. Eng Min J 

185(9):84-85. 

Page SJ, Volkwein JC [1986]. Foams for dust control. Eng Min J 187(10):50-52, 54. 

Rodgers SJ, Rankin RL, Marshall MD [1978]. Improved dust control at chutes, dumps, transfer 

points, and crushers in noncoal mining operations. MSA Research Corp. U.S. Bureau of Mines 

contract No. H0230027. NTIS No. PB297-422. 

Ruggieri SK, Jankowski RA [1983]. Fundamental approaches to longwall dust control. In: 

Proceedings of the Symposium on Control of Respirable Dust (Beckley, WV, Oct. 4-8, 1983). 

Seibel RJ [1976]. Dust control at a transfer point using foam and water sprays. Pittsburgh, PA: 

U.S. Department of the Interior, Bureau of Mines, TPR 97. NTIS No. PB-255-440. 

Shirey CA, Colinet JF, Kost JA [1985]. Dust control handbook for longwall mining operations. 

BCR National Laboratory. U.S. Bureau of Mines contract No. J0348000. NTIS No. PB86­

178159/AS. 

Stahura RP [1987]. Conveyor belt washing: is this the ultimate solution? TIZ-Fachberichte 

111(11):768-771. ISSN 0170-0146. 

Swinderman RT, Goldbeck LJ, Stahura RP, Marti A [1997]. Foundations 2: the pyramid 

approach to dust control and spillage from belt conveyors. Neponset, IL: Martin Engineering. 

Tien JC [1999]. Practical mine ventilation engineering. Chicago, IL: Intertec Publications. 

Tien JC, Kim J [1997]. Respirable dust control using surfactants. Appl Occ Env Hyg 12(12): 

957-963. 

Tomb TF, Emmerling JE, Kellner RH [1972]. Collection of airborne coal dust by water spray in 

a horizontal duct. AIHA J 33(11):715-721. 

U.S. Bureau of Mines [1981]. Technology news 118: Lower dust exposure of longwall shearer 

operator by relocating the machine cooling water sprays. Pittsburgh, PA: U.S. Department of the 

Interior, Bureau of Mines. 
22 

U.S. Bureau of Mines [1984]. Technology news 203: How to reduce shearer operators dust 

exposure by using remote control. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines. 

U.S. Bureau of Mines [1985]. Technology news 220: How twelve continuous miner sections 

keep dust levels at 0.5 mg/m3 or less. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines. 

van der Bank PJ [1977]. Fog nozzle water blast. J Mine Vent Soc S Afr Apr:81-82. 

Volkwein JC, Cecala AB, Thimons ED [1983]. Use of foam for dust control in minerals 

processing. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8808. NTIS 

No. PB84-131184. 

Volkwein JC, Thimons ED, Halfinger G [1985]. Extended advance of continuous miner 

successfully ventilated with a scrubber in a blowing section. In: Proceedings of the Second 

U.S. Mine Ventilation Symposium (Reno, NV). 

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Switzerland: World Health Organization. 

Zimmer RA, Lueck SR, Page SJ [1987]. Optimization of overburden drill dust control systems 

on surface coal mines. Int J Surf Min 1:155-157. 
 

23 

CHAPTER 2.—CONTINUOUS MINER AND ROOF BOLTER 

DUST CONTROL
 

By Fred N. Kissell, Ph.D.,5

5

Research physical scientist.

and Gerrit V. R. Goodman, Ph.D.6 

6

Mining engineer. 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA. 

In This Chapter 

9 Design and operation of machine-mounted scrubbers 

9 Dust control with scrubbers and blowing ventilation 

9 Dust control with scrubbers and exhaust ventilation 

9 Dust control with exhaust ventilation and no scrubber 

9 Dust control methods common to all continuous miner sections 

9 Dust control for roof bolters 

This chapter explains how to control dust at continuous miner sections in coal mines where the 

main dust sources are continuous miners and roof bolters. In relation to dust, there are three 

categories of continuous miner faces depending on the type of ventilation and whether or not a 

machine-mounted dust scrubber is used. These are— 

1. Mining machines with dust scrubbers used with blowing face ventilation 

2. Mining machines with dust scrubbers used with exhaust face ventilation 

3. Mining machines without scrubbers used with exhaust face ventilation 

The approach to dust control is somewhat different in all three of these. However, there are 

many dust control features (such as the need to provide adequate airflow) common to all continuous miner sections. 

For workers at roof bolter faces, there are two dust sources: 

1. Dust from the continuous miner when it is upwind. 

2. A malfunctioning dust collector on the bolter, which allows dust to escape 

DESIGN AND OPERATION OF MACHINE-MOUNTED SCRUBBERS 

Almost all new continuous miners are equipped with 

scrubbers. When the dust is excessive, it is possible that 

the scrubber needs some maintenance. 
24 

Machine-mounted scrubbers, 

which are installed on continuous miners, collect dust-laden 

air through one or more inlets 

near the front of the miner and 

discharge cleaned air at the back 

of the miner. Figure 2-1 shows 

a typical design. 

Figure 2-1.—Machine-mounted scrubber design. 

Inside the scrubber, the dustladen air passes through a knit 

wire-mesh filter panel that is 

wetted with water sprays, which 

causes the dust particles to be 

captured by the water. After 

passing through the filter panel, 

the airstream then enters a demister, which removes the dust-laden water droplets from the airstream. The cleaned air passes through the fan and is then discharged at the back of the scrubber 

unit. Some scrubber designs have ductwork on the rear of the miner, which permits the discharge of air on either side of the machine. 

Overall scrubber efficiency. The overall efficiency of the scrubber is determined by the fraction of face air that is drawn into the scrubber inlet (inlet capture efficiency) multiplied by the 

fraction of respirable dust removed from the captured air (filter efficiency). Overall efficiency 

ranges from 60% to 75% in most instances. However, several factors can cause the efficiency to 

decline. The most common is clogging of the filter panel. 

Inlet capture efficiency. In practice, the inlet capture efficiency can be reduced by both working factors and machine design factors. The main working factors causing loss in inlet capture 

efficiency are entries that are large, spray pressures that are too high, and the use of blowing 

ventilation systems. Ideally, a dust scrubber should function like an exhaust ventilation system, 

drawing clean air forward over the miner and confining the dust cloud to that part of the miner 

that is forward of the inlet. When the entry is large, however, the scrubber capacity may not be 

adequate to maintain sufficient forward airflow over the miner.7 

 

7

When the entry size increases, the open area increases by a greater proportion because some of the entry is blocked 

by the miner. 

The result is a rollback of dust, 

as depicted in figure 1-1. Excessive spray pressure or poorly aligned sprays also can cause rollback because of the turbulence and air movement they create. When air is delivered via blowing 

ventilation, and particularly with blowing duct, the amount of air delivered8 

8

The amount of air delivered to the face includes both the airflow (the air jet) from the duct and that portion of the 

surrounding air induced into the jet. 

to the face can 

exceed that removed by the scrubber. When this happens, dust-laden air is no longer confined to 

the front of the miner, but rolls back over the miner, contaminating the return air and the air 

breathed by workers. Specifics on how to deal with rollback are given later in this chapter. 

The machine design factors that impact inlet capture efficiency are the scrubber air quantity and 

the location of the inlets. The air quantity should always be as large as possible and the inlets as 
 

25 

far forward and close to the cutting drum as practical [Jayaraman et al. 1992]. On high-coal 

machines, the inlets are usually distributed under the cutting boom, which is a good location 

because it is where the dust cloud is thickest. On low-coal machines, the inlet is usually at the 

boom hinge point, which is not as good because it is farther from the cutting drum. However, 

since low-coal machines usually work in entries where the clearance over the machine is less, the 

rollback of dust that might result from using a hinge point inlet may be offset by higher forward 

air velocities through a narrower space over the miner. Mines in high coal that use a hinge point 

inlet never reach adequate capture efficiencies, even with very high scrubber airflows [Hole and 

Von Glen 1998].9 

 

9

Hole and Von Glen [1998] tested a scrubber for which the distance between the inlet and outlet was only about 

8.2 ft. Air entrainment into the outlet jet produced a low-pressure region on the side of the machine that caused air 

at the front of the machine to bypass the inlet, further reducing the inlet capture efficiency. 

One frequently asked question is what the airflow ratio should be, that is, the ratio of ventilation 

airflow to scrubber airflow. The most recent research [Fields et al. 1990] shows that this ratio is 

not particularly important for dust control, assuming there is enough ventilation airflow to dilute 

dust (and gas) and assuming that blowing systems are not used in a way10

10This is described in more detail in the next section.
 

that overpowers the 

scrubber and causes a loss in inlet capture efficiency. 

Filter efficiency. The thickness of the filter panel controls the filter efficiency. The original 

filter panel was made with 40 layers of stainless steel mesh knit from 85-micrometer stainless 

steel wire. Today, thinner filter panels containing 30, 20, and 10 layers of stainless steel mesh 

are available. The reduced filter thickness allows larger quantities of air to be moved by the 

scrubber, potentially improving inlet capture efficiency. However, thinner filters are less efficient at trapping dust. In a study by Colinet and Jankowski [2000], the 30-layer panel displayed 

a filter efficiency above 90% for respirable-sized dust, but the filter efficiency dropped too much 

when the thinner 20- and 10-layer panels were tested. 

Scrubber maintenance. When the dust is excessive, it is likely that the scrubber needs 

maintenance. More than likely, some cleaning of the filter panel or ductwork is required.11

11Schultz and Fields [1999] have noted that some scrubbers lose as much as one-third of their airflow after just one 

cut. Scrubber airflow can be monitored by measuring the filter differential pressure, the fan inlet pressure, or the 

fan motor current [Taylor et al. 1996]. 

The 

sprays should be checked to ensure they are completely wetting the entire filter panel, and not 

just the center. The density of the panel should also be checked to ensure that a panel of 

30 layers was purchased. 

Schultz and Fields [1999] reported a method used by one mine operator to 

block large pieces of coal from entering the scrubber inlets under the boom. 

The mine had installed a flap of conveyor belt about 8 inches inby each inlet 

and the flaps extended downward about 8 inches. The flaps forced the air to 

make an extra turn before entering the inlet, blocking the larger particles flying 

from the cutting drum. These flaps worked so well that the scrubber lost only 

10% of its airflow capacity after an entire shift of operation. 
26 

DUST CONTROL WITH SCRUBBERS AND BLOWING VENTILATION 

Dust scrubbers are most often used with blowing ventilation. When operator dust levels are too high, the most 

likely reason is that the operator is not spending enough 

time standing in front of the blowing line curtain. 

With blowing face ventilation, fresh air is directed behind the line curtain or through ventilation 

duct and then discharged from the end of the line curtain/duct toward the face. This fresh air 

dilutes and entrains dust at the mining face, and the dust-laden air then passes out of the immediate face area and into the dust scrubber. After the dust is removed from the air, the air is discharged backwards from the rear of the mining machine on the side of the machine opposite the 

line curtain. A typical scrubber-blowing ventilation arrangement is shown in figure 2-2. 

Figure 2-2.—Dust scrubber used with blowing ventilation. 

Remote placement of the mining machine operator. Although sections using blowing face 

ventilation use machine-mounted scrubbers, the operator can still be exposed to some of the 

respirable dust escaping the scrubber. This includes dust that escaped being drawn into the 

intake, as well as dust drawn into the intake but not collected by the filter panel. As a result, it 

can make a difference where the remote operator is located while operating the miner. A study 

by Jayaraman et al. [1987] in 

an Illinois mine measured 

the dust reduction benefits 

from positioning the operator in intake rather than 

return air, as shown in figure 2-2. The average intake 

level was 0.2 mg/m3

 and the 

average return level was 

3.1 mg/m.3 This shows that 

a 94% reduction in operator 

exposure could be obtained

by moving the operator to a 
 

27 

position in front of 

the line curtain.12 

12Gas emissions, MSHA guidelines regarding line curtain setback, and roof control plans may limit the selection of 

the best location from a dust exposure standpoint. 

More recently, 

Goodman and Listak 

[1999] measured 

0.79 mg/m3

 on a 

remote operator who 

spent most (but not 

all) of the time in 

front of the line 

curtain. The actual 

dust concentration 

of the intake air was 

0.13 mg/m3. Still, 

the dust reduction 

was 73% when 

compared to the 

return dust level of 

2.9 mg/m3

. 

Factors causing high dust levels. When remote operator dust levels are too high, the most 

likely reason is that the operator is not spending enough time standing in front of the blowing 

line curtain.13

13Some mines position the operator on the return side of the line curtain but very close to the line curtain. If the line 

curtain has a high leakage rate, this leakage air can reduce the operator’s dust level. Occasionally, a mine will slit 

the line curtain and position the operator in the clean air emerging from the slit. How well this works is not known. 

 When downwind dust levels are too high,14

14The miner helper, the shuttle car operator, or other positions downwind.

 it is likely that the scrubber needs 

maintenance. More than likely, some cleaning of the ductwork or filter panel is required. If the 

scrubber is operating properly, then the ventilation and the sprays should be checked. If the 

amount of air directed into the cutter boom region exceeds the amount of air withdrawn by the 

scrubber, then much of the dust cloud around the cutter boom will bypass the scrubber and move 

outby to contaminate the return (figure 2-3).

 

 Figure 2-3.—Excessive air blown toward the face will cause dust to bypass the 

scrubber inlets. 

 This is the rollback of dust described earlier in this 

chapter. This excess air may be reduced by winging out the line curtain at the end to lower the 

velocity of the air emerging from behind it [Schultz and Fields 1999] or to pull the line curtain 

back slightly. Jayaraman et al. [1988] described successful experiments in a mine where the 

operator erected a short line curtain during the slab cut to shield the miner from the air jet 

emerging from a blowing duct.15

15Dust problems caused by blowing too much air at the face are more prevalent when ventilation duct is used in 

place of blowing line curtain. This is because the jet of air from the duct is moving at a much higher velocity. Due 

to the higher velocity, the reach of the jet is extended and the amount of surrounding air entrained by the jet and 

pushed forward is much greater. The problem is common in Germany, where coal mine face ventilation systems use 

a blowing duct in combination with an exhaust system. The usual approach to reduce dust is to use a diffuser at the 

end of the blowing duct [Noack et al. 1989; Graumann and Gastberg 1984]. 

 However, the ability to use these techniques will depend on the 

amount of methane gas present, since limiting the fresh air may increase methane levels. 
 

28 

The dust cloud also can bypass the scrubber when the spray pressure is too high16

16Remedies include lowering the spray pressure to under 100 psi. The spray pressure is measured by removing a 

nozzle and attaching a hose that leads to a pressure gauge. See the section in this chapter on the antirollback spray 

system. 

or when directional sprays, such as in the “spray fan” system, are used. The resulting turbulence and air movement also will cause much of the dust cloud to bypass the scrubber inlet and move outby toward 

the operator. 

DUST CONTROL WITH SCRUBBERS AND EXHAUST VENTILATION 

As with blowing ventilation, the position of the operator is 

crucial for good dust control. 

When exhaust ventilation is used with a scrubber, fresh air is drawn through the mine entry 

toward the face. This air then passes into the scrubber where it is cleaned of dust and discharged 

back toward the line curtain. From the line curtain, the air passes to the return. Figure 2-4 shows 

a typical scrubber-exhaust ventilation arrangement with the miner operated by remote control. 

Figure 2-4.—Dust scrubber used with exhaust ventilation. 

changes his or her dust level. However, 

dust levels in exhaust ventilation 

sections can be lower than those in 

blowing ventilation sections because the 

mining machine operator has more 

options as to where to stand and stay out 

of the dust cloud. Also, the shuttle car 

operator is working in fresh air. 

In a mine using a machine-mounted 

scrubber and exhaust ventilation, 

Goodman and Listak [1999] measured 

dust levels at the mining machine and at 

the remote operator location. The entry 

size was 10 ft by 20 ft. The scrubber 

flow was 9,500 cfm, and the air quantity 

exhausted by the line curtain was 

15,000 cfm. For the box cut (figure 2-4, 

left), the remote operator stood at 

locations A or B; for the slab cut 

(figure 2-4, right), at location A only. 

Both locations were parallel with the end 

of the line curtain. The dust level at the

As with blowing ventilation, the location where the mining machine operator stands greatly 
 

29 

right rear corner of the miner (the cab location on nonremote machines) was 4.3 mg/m3; the dust 

level for the remote operator location was 0.79 mg/m3

, about 80% lower than the cab location. 

Goodman and Listak also found that when the remote operator positioned himself at location A, 

he could move a few feet inby toward the face without his dust level increasing much. However, 

when he stood at location B and moved a few feet inby, his dust level rose significantly because 

he had moved out of the intake air zone. 

In another study of scrubbers and exhaust ventilation, Colinet and Jankowski [1996] used a fullscale lab model to assess the dust impact of moving the location of the remote operator while 

changing the distance from the end of the line curtain to the face, the line curtain airflow, and the 

water pressure. The entry size was 9 ft by 18 ft, and the scrubber flow was 7,800 cfm. Tests 

were done with the airflow ranging from 3,000 to 13,000 cfm, the line curtain-to-face distance 

from 30 to 40 ft, and the water spray pressure from 60 to 200 psi. Dust was measured at 

location A shown in figure 2-4, 5 ft inby location A, and 5 ft outby location A. Colinet and 

Jankowski found higher dust levels at the inby location and recommended that operators always 

position themselves either at location A, parallel to the end of the line curtain, or outby. At these 

recommended locations, changing the water pressure and line curtain-to-face distance had no 

effect on dust levels. Changing the airflow from 3,000 to 13,000 cfm produced a modest17 

17This amount is modest considering such a huge change in the airflow. 

0.5 mg/m3 decrease in dust. Colinet and Jankowski also point out that the scrubber exhaust must 

be on the same side of the entry as the line curtain and that this may require a crossover air duct 

at the rear of the miner. 

When the dust level is too high, the first thing to check is whether the operator is standing parallel to or outby the end of the line curtain. Other factors to check are whether the jet from the 

scrubber exhaust is on the same side of the entry of the line curtain, whether the line curtain end 

is outby the scrubber exhaust, and whether the air in the jet is all passing behind the line curtain 

rather than backing up against the intake air. To test if the air in the jet is all passing directly 

behind the line curtain, the contents of a dry powder fire extinguisher should be released into the 

scrubber exhaust stream. Then, observe whether all of the powder goes behind the line curtain. 

DUST CONTROL WITH EXHAUST VENTILATION AND NO SCRUBBER 

Exhaust ventilation alone can be a very effective way to 

control dust. The quantity of ventilation air is the most 

important factor in controlling dust exposure. 

With exhaust ventilation, fresh air is drawn up the mine entry to the face to dilute and entrain 

dust. Dust-laden air is then pulled from the face area and carried behind the line curtain or into 

ventilation duct and out of the face area. 
 

30 

Over 15 years ago, the U.S. Bureau of Mines (USBM) surveyed 12 continuous miner sections 

that were at or below 0.5 mg/m3

 during the previous 18 months [USBM 1985b]. Three features 

were common in all or most of the sections: good ventilation, good spray systems, and a modified cutting cycle. The last two of these are discussed later in this chapter. The first, good ventilation, is discussed here. 

Good ventilation. At all mines surveyed, the quantity of face ventilation air was the most 

important factor in controlling dust exposure.18

18A full-scale lab study by Colinet et al. [1991] reached the same conclusion. 

 The mean entry air velocity ranged from 63 to 

335 ft/min and averaged 122 ft/min. In all cases, the distance from the face to the end of the line 

curtain/duct was 15 ft or less. Eight of the mines used exhaust duct with an auxiliary fan. At the 

other mines, the exhaust line curtain was very well maintained, and leakage was minimized by 

sealing the floor/line curtain interface. The high entry air velocity, averaging 122 ft/min, 

reduced dust rollback significantly. Rollback takes place when turbulence from the water sprays 

causes the dust cloud to spread toward the miner operator. Because of the high air velocity, dust 

generated by coal extraction was usually confined to the face area, and any operator exposure 

was usually from intake sources such as shuttle car loading and haulage. 

Unfortunately, achieving a high ventilation air velocity is not always possible. Mine operators 

who cannot supply a high air velocity have three alternatives: a half-curtain, antirollback sprays, 

and remote control. The last two of these are discussed in the section on common dust control 

methods. The first, a half-curtain, is discussed here. 

Half-curtain. Mines in high coal may have difficulty achieving adequate air velocities because 

the cross-sectional area of the mine entry is larger than normal. Although the quantity of air 

delivered may be large, inadequate air velocities will permit the dust cloud at the face to roll 

back over the miner operator. The half-curtain [Jayaraman et al. 1986] is a piece of brattice cloth 

supported by two pogo sticks. It is placed perpendicular to the rib just inby the operator’s 

position and extends from roof to floor (figure 2-5).19

19The half-curtain shown in figure 2-5 is on the off-curtain (duct) side of the entry. It also can be placed on the curtain (duct) side of the entry. Some mines using exhaust duct have placed a narrow curtain at the end of the duct to 

enlarge the capture area of the duct. This might be described as a quarter-curtain rather than a half-curtain, since the 

area blocked is much less. Nevertheless, it can reduce dust for the same reason, particularly if the air velocity is in 

the critical 40-60 ft/min range, where minor differences in air velocity can make large differences in the dust level. 

 The half-curtain reduces the crosssectional area of the entry, thus increasing the air velocity in the region between the operator and 

the dust source. Results of a lab study show that the half-curtain performance depends largely on 

placement. The greatest improvement (86%) was achieved when the half-curtain was outby the 

end of the line curtain and just inby the operator. Underground tests show that with the halfcurtain, the respirable dust exposure of the operator was reduced by 50%. 

In gassy mines, caution must be used to ensure that hazardous accumulations of methane do not 

build up behind the half-curtain during the box cut. Jayaraman et al. [1986] also give procedures 

to follow when gas is present. 
 Figure 2-5.—Half-curtain location. 

 

31 

When dust levels are too high, the air velocity 

and the distance from the face to the end of the 

line curtain or duct should be checked. These 

are both critical.20

20See figure 6-5 on page 92. 

 Studies have shown that dust 

levels are much lower when the end of the line 

curtain or duct21

21When ventilation duct is used, a convenient way to keep the end close to the face is to incorporate a smaller 

diameter sliding section into the last fixed segment. 

is located close to the face. 

For this reason, the end of the exhaust line 

curtain or duct should be maintained within 10 

ft of the face. Also, when using exhaust 

ventilation, mean entry air velocities above 60 

ft/min have been shown to minimize dust. Both 

the 10-ft and 60-ft/min criteria are required by 

Mine Safety and Health Administration 

(MSHA) regulations. If these ventilation 

changes are not possible or if dust levels are 

still too high, the methods described in the next 

section should be considered. 

DUST CONTROL METHODS COMMON TO ALL CONTINUOUS MINER SECTIONS 

Many dust control methods are common to all continuous 

miner sections. These include good spray systems, 

a modified cutting cycle, remote control, good water filtration, and regular bit replacement. 

The first two dust control methods in this section, good spray systems and a modified cutting 

cycle, originated in the USBM survey [USBM 1985b] of continuous miner sections with dust 

levels of 0.5 mg/m3

 or less, as discussed in the last section. 

Good spray systems. All spray systems in the USBM survey were well maintained and 

completely functional. Water flow to the miners in the survey averaged 29 gpm. Also, sprays 
 

32 

were mounted on the flight conveyor with a total flow

averaging 5 gpm. These 

flight conveyor sprays 

served to add water to the 

cut material before discharge onto the shuttle car,

thereby reducing the operator’s exposure to this intake

dust source. 

Field studies by Matta

[1976] and by Courtney

et al. [1978] have shown

that sprays under the

boom are somewhat 

more effective than sprays 

on top. 

Modified cutting cycle. The USBM survey of low-dust continuous miner sections also found 

that two-thirds of the surveyed mines used a modified cutting cycle (figure 2-6). 

 Figure 2-6.—Modified cutting cycle. In this cutting cycle, the roof is 

trimmed last. 

The usual cutting cycle is to sump in at the roof and then shear down to the floor. With the modified cutting 

cycle, the machine sumps into the coal face a foot below the roof and then shears down to the 

floor. This is continued for at least two sump/shear sequences. The miner then backs up and 

trims the remaining rock and coal from the roof. 

This modified cutting cycle leaves the roof rock in place until it can be cut out to a free face, 

generating less dust (and particularly less quartz dust).22

22Jayaraman et al. [1988] describe experiments at a mine where the operator used a modified cutting procedure to 

deal with a high level of quartz dust that originated from cutting a sandstone floor. The miner sumped into the coal 

face about 6 inches above the floor and sheared upwards. The bench on the floor was then trimmed separately. This 

change, combined with a curtain to confine the dust cloud during removal of the slab, cut the dust concentration in 

half and also cut the quartz percentage in half. 

 Also, some operators have found that 

the modified cutting cycle provides better machine control. They reported that it prevents the 

machine from climbing into the roof when sumping high. 

Remote control. If machine operators can avoid dusty areas and remain in uncontaminated air, 

their dust exposure will be much lower.23 

23A downside of remote control is that it may remove the operator from a location that is protected from roof falls, 

such as the cab of a continuous miner. 

Remote control of the miner is the way to accomplish 

this. With exhaust ventilation, dust is avoided by moving away from the face and back into 

intake air. With blowing ventilation that uses a line curtain, dust is avoided by stepping in front 

of the line curtain. In either case, dust reductions of 90% are possible. Remote control allows 

the operator to step back and get away from the dust cloud that surrounds the machine. Several 

studies have shown how effective remote control can be [Divers et al. 1982; Jayaraman et al. 

1987; Goodman and Listak 1999]. 
 

33 

Remote control is one of the best, if not the best, dust 

control available for all kinds of mining machinery. 

Antirollback water spray system. A way to counter rollback resulting from low air velocity is 

to use an antirollback spray system (figure 2-7) [Jayaraman et al. 1984]. 

Figure 2-7.—Antirollback water spray system. 

 Most conventional 

spray systems consist of multiple nozzles (15 to 30) located across the top and along the side of 

the miner boom. Jayaraman et al. [1984] showed that many water spray systems produce enough 

air turbulence to overwhelm the primary airflow, causing dust rollback. Spray system 

characteristics that promote rollback are: 

(1) High spray pressure (over 100 psi), which increases air turbulence at the face more than it 

suppresses dust. Tests have shown that a moderate spray pressure of 100 psi, measured at the 

nozzle, is a practical maximum pressure. However, water flows should be as high as possible. 

The spray pressure is measured by removing a nozzle and attaching a hose that leads to a pressure gauge. 

(2) Top and side sprays with wide-angle cones that purposely overspray the cutter head or are 

set on the boom too far back from the cutter head. The longer the spray path, the more air is set 

in motion, and this air movement stirs up dust. A typical miner spray does most of its airborne 

dust collection in the first 12 inches; thus, top and side nozzles should be arranged for “low” 

reach and no overspray (figure 2-7, A and B). Flat fan sprays delivering about 1 gpm per nozzle 

are best suited for this application since 

the entire flow from the nozzle can be 

directed onto the cutter head. Underneath the boom, deluge-type nozzles 

delivering about 5 gpm per nozzle 

should be used to wet the broken coal. 

These nozzles should be mounted in a 

protected location close to the edge of 

the boom to ease servicing. 

In underground trials, the antirollback 

spray system reduced dust levels at the 

operator’s position by 40%24

24Without using the underboom sprays. 

 compared 

to conventional sprays. 

Good water filtration. Dirt and rust 

particles in the water line cause frequent 

clogging of spray nozzles. A simple, 

nonclogging water filtration system is 

available to replace conventional spray 

filters [Divers 1976]. The system 

consists of an in-line Y-strainer to 
34 

remove the plus 1/8-in material, a hydrocyclone to remove most of the remaining particles, and a 

polishing filter to remove the few particles that are not trapped by the hydrocyclone during 

startup and shutdown of the spray system. A new type of removable manifold that facilitates the 

quick changing of clogged sprays can also be used. To construct it, obtain a piece of 0.5-in wall 

pipe that is 0.5- to 2-ft long, depending on the intended location. Cut a lengthwise slot in the 

pipe. Weld the pipe to the miner with the slot facing forward. Fabricate a conventional spray 

bar from a second piece of pipe that slides into the slotted heavy wall pipe with the nozzles 

keyed into the slot and aimed out of the slot. Devise some means to hold the smaller pipe in 

place so that it can be removed to service the nozzles. 

Regular bit replacement. Routine inspection of the cutting drum and replacement of dull, 

broken, or missing bits improves cutting efficiency and helps to minimize dust. Also, 

Organiscak et al. [1996] showed that bits designed with large carbide inserts and smooth 

transitions between the carbide and steel shank typically produce less dust. 

 

Reduction of intake dust. Intake dust is often overlooked as a source of dust overexposure. 

Intake sources may include movement of outby equipment on dry roadways, feeder-breakers, 

and conveyor belts. Methods to reduce conveyor belt dust are described in chapter 6 on hardrock mines. Methods to reduce haul road dust are described in chapter 5 on surface mines. Potts 

and Jankowski [1992] measured the dust level impact of using belt air for face ventilation, both 

on continuous miner and longwall sections. 

Bolter dust collector maintenance. Occasionally, a malfunctioning bolter dust collector 

upwind of the miner will produce enough quartz dust to raise the exposure of the continuous 

miner operator. This is more likely to create a compliance problem on sections that are on 

reduced (more stringent) standards because of quartz in the coal. In such instances, additional 

quartz from the bolter, even in small amounts, will have significant impact. As much as 25% of 

the continuous miner operator’s quartz dust exposure can be attributed to dust from the bolting 

operation. The problem is usually a lack of maintenance on the bolter dust collector. 

DUST CONTROL FOR ROOF BOLTERS 

Dust at bolter faces originates from the continuous miner 

if it is upwind or from a malfunctioning dust collector at 

the bolter itself. In most instances, high dust exposures 

are easily remedied. 

Dust from upwind sources. If the bolter dust collection systems are operating properly, most of 

the bolter operator’s dust exposure is generated by the continuous miner when it is upwind. The 

best way to reduce this bolter exposure is to use double-split ventilation. If single-split 

ventilation is being used, then the cutting sequence must be designed to limit the amount of time 

that the continuous miner is upwind. 
35 

If the continuous miner has a scrubber and the bolter dust exposure is still high, the scrubber 

should be checked to ensure that it is operating properly. Other techniques for reducing the dust 

level of personnel downwind of a continuous miner have been described by Jayaraman et al. 

[1989]. 

Dust from the bolter. While most of the roof bolter operator’s dust exposure comes from 

upwind sources (e.g., the continuous miner), some bolting machines allow a significant amount 

of dust to escape the dust collector system, thus contaminating the region around the bolter. 

Such contamination is more likely when an insufficient amount of clean air is available to dilute 

the dust. 

When dry dust collection systems are leaking, dust emission from the blower exhaust is the most 

common problem. It is usually caused by damaged or improperly seated filters. Also, many roof 

bolter dust collectors show accumulations of dust between the filters and blower, which results 

from past or current filter leaks. With the filters removed and the access door open, this dust can 

be removed by back-flushing the system with compressed air or by running the blower for 

several minutes. 

Proper disposal of the dust that accumulates in the dust collector box can be important, since this 

dust is easily stirred up by mine traffic if just dumped onto the middle of the mine floor. 

Goodman and Organiscak [2002] compared two methods of cleaning the dust collector box. One 

was the common practice of using a metal rake to scrape the cuttings out of the collection box 

onto the mine floor. A second method was to collect the dust in a bag contained within the 

largest compartment of the dust box. When full of dust, the bag is carried to the rib and gently 

dumped. Comparisons of the bag versus the metal rake for cleaning the dust box showed that 

respirable coal dust and respirable silica dust exposures for the bolter operators dropped by a 

factor of two when the bag was used. Disposable bags are now available for some bolters. 

Dust from the drill hole can also pose a problem. A visible plume from the collar of the drill 

hole is a sign of inadequate airflow to the chuck or bit. The air leaks that cause inadequate 

airflow occur mainly at loose hose connections, through the pressure relief valve, and through 

poorly fitting dust collector access doors. It is common to find as much as 50% leakage. 

The bit type also makes a difference in the dust escaping from the drill hole. In one study, 

shank-type bits allowed from 3 to 10 times more dust to escape from the drill hole collar than 

“dust hog” bits [USBM 1985a]. Most of this dust escaped during the first few inches of bit 

penetration. Typically, the dust hog bits generate one-fifth of the dust generated by the shank 

bits in the initial 12 inches and one-third of the dust over the full length of the hole. 

Some years ago, MSHA did a survey to evaluate the effectiveness of improved maintenance on 

dry dust collection systems [Thaxton 1984]. During the survey, the mine operators replaced all 

duct hoses, filters, and the blower muffler, repaired the vacuum system and dust box seals, and 

cleaned the blower unit. Results showed major improvements in both the quartz percentages and 

the dust levels. 
36 

A small proportion of roof bolters use wet systems to control dust. In wet systems, hollow drill 

steels are used to deliver low-pressure water (2 gpm per chuck) to the bits. These systems offer 

improved bit life, faster drilling, and excellent dust control. However, wet drilling can create 

problems in coal mines that cannot tolerate additional water on the mine floor. Also, leaking 

water seals can splash water over the bolter operators, making for unpleasant working 

conditions. As a result, good maintenance of all seals is important. 

REFERENCES 

Colinet JF, Jankowski RA [1996]. Dust control considerations for deep-cut faces when using 

exhaust ventilation and a flooded-bed scrubber. Transactions SME, Vol. 302. Littleton, CO: 

Society for Mining, Metallurgy, and Exploration, Inc., pp. 104-111. 

Colinet JF, Jankowski RA [2000]. Silica collection concerns when using flooded-bed scrubbers. 

Min Eng 52(4):49-54. 

Colinet JF, McClelland JJ, Jankowski RA [1991]. Interactions and limitations of primary dust 

controls for continuous miners. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, RI 9373. NTIS No. PB91-241257. 

Courtney WG, Jayaraman NI, Behum P [1978]. Effect of water sprays for respirable dust suppression with a research continuous-mining machine. Pittsburgh, PA: U.S. Department of the 

Interior, Bureau of Mines, RI 8283. NTIS No. PB 279 881. 

Divers EF [1976]. Nonclogging water spray system for continuous mining machines: 

installation and operating guidelines. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, IC 8727. NTIS No. PB 265-934. 

Divers EF, Jayaraman NI, Custer J [1982]. Evaluation of a combined face ventilation system 

used with a remotely operated mining machine. Pittsburgh, PA: U.S. Department of the Interior, 

Bureau of Mines, IC 8899. NTIS No. PB83-156794. 

Fields KG, Atchison DJ, Haney RA [1990]. Evaluation of dust control for deep cut coal mining 

systems using a machine mounted collector. In: Proceedings of the 1990 International Symposium on Respirable Dust in the Mineral Industries, pp. 349-353. 

Goodman GVR, Listak JM [1999]. Variation in dust levels with continuous miner position. Min 

Eng 51(2):53-58. 

Goodman GVR, Organiscak JA [2002]. An evaluation of methods for controlling silica dust 

exposures on roof bolters. SME preprint 02-163. Littleton, CO: Society for Mining, Metallurgy, 

and Exploration, Inc. 
37 

Graumann K, Gastberg I [1984]. Ventilating the roadhead of drivages headed with boom-type 

machines (in German). Gluckauf 120(15):967-973. Also available in English: Gluckauf Translation 120(15):264-267. 

Hole BJ, von Glen FH [1998]. Dust capture effectiveness of scrubber systems on mechanical 

miners operating in larger roadways. Final report on project COL 310. Johannesburg, Republic 

of South Africa: Bluhm Burton Engineering. Available from Safety in Mines Research Advisory 

Committee (www.simrac.co.za). 

Jayaraman NI, Babbitt CA, O’Green J [1989]. Ventilation and dust control techniques for personnel downwind of continuous miner. Transactions SME, Vol. 284, Littleton, CO: Society for 

Mining, Metallurgy, and Exploration, Inc., pp. 1823-1826. 

Jayaraman NI, Colinet JF, Jankowski RA [1992]. Recent basic research on dust removal for coal 

mine applications. In: Proceedings of the Fifth International Mine Ventilation Congress 

(Johannesburg, Republic of South Africa), pp. 395-405. 

Jayaraman NI, Divers EF, Derick RL, Babbitt C [1986]. Evaluation of a new half-curtain technique for continuous miner faces. In: Proceedings of the Symposium on Respirable Dust. 

University Park, PA: The Pennsylvania State University. 

Jayaraman N I, Kissell FN, Schroeder W [1984]. Modify spray heads to reduce dust rollback on 

miners. Coal Age 89(6):56-57. 

Jayaraman NI, McClelland JJ, Jankowski RA [1988]. Reducing quartz dust with flooded-bed 

scrubber systems on continuous miners. In: Proceedings of the Seventh International Pneumoconiosis Conference (Pittsburgh, PA), pp. 86-93. 

Jayaraman NI, Stritzel DL, Jankowski RA [1987]. Improving health, safety, and productivity 

through the use of machine-mounted scrubbers. In: Proceedings of the 95th Annual Meeting of 

the Illinois Mining Institute (Mount Vernon, IL), pp. 62-75. 

Matta JE [1976]. Effects of location and type of water sprays for respirable dust suppression on 

a continuous mining machine. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

TPR 96. NTIS No. PB 254 677. 

Noack K, Hinderfeld G, Marx W-E, Marth W [1989]. Latest developments with ventilation 

techniques, water spray systems and gas emission judging methods in machine-driven headings. 

In: Proceedings of the 23rd International Conference of Safety in Mines Research Institutes 

(Washington, DC, Sept. 11-15, 1989). Pittsburgh, PA: U.S. Department of the Interior, Bureau 

of Mines, pp. 914-926. NTIS No. 89-225262/AS. 

Organiscak JA, Khair AW, Ahmad M [1996]. Studies of bit wear and respirable dust generation. 

Transactions SME, Vol. 298. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 

Inc., pp. 1874-1879. 
38 

Potts JD, Jankowski RA [1992]. Dust considerations when using belt entry air to ventilate work 

areas. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9426. 

Schultz MJ, Fields KG [1999]. Dust control considerations for deep cut mining sections. SME 

preprint 99-163. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc. 

Taylor CD, Kovscek PD, Thimons ED [1996]. Monitoring air flow through a machine-mounted 

dust scrubber. Appl Occ Env Hyg 11(7):813-816. 

Thaxton RA [1984]. Maintenance of a roof bolter dust collector as a means to control quartz. 

In: Proceedings of the Coal Mine Dust Conference (Morgantown, WV, Oct. 8-10, 1984), 

pp. 137-143. 

U.S. Bureau of Mines [1985a]. Technology news 219: Reducing dust exposure of roof bolter 

operators. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines. 

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keep their dust levels at 0.5 mg/m3 or less. Pittsburgh, PA: U.S. Department of the Interior, 

Bureau of Mines. 
 

39 

CHAPTER 3.—LONGWALL DUST CONTROL 

By Fred N. Kissell, Ph.D.,25

25Research physical scientist.

Jay F. Colinet,26

26Supervisory mining engineer. 

 and John A. Organiscak27 

27Mining engineer. 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA. 

In This Chapter 

9 Which dust source to address first 

9 How much air and water are needed 

9 Keeping dust out of the walkway 

9 Moving workers upwind 

9 Dealing with the stageloader-crusher 

9 Gob and wing curtains to aid airflow 

9 The shearer-clearer system
 

9 Modified support movement practices 

and 

9 Dust control for future longwalls 

Controlling longwall dust is not easy. Longwall production levels are high, and there are several 

different sources of dust to contend with. If dust levels are high, the initial effort should be 

devoted to finding which source is the cause. Then, efforts to reduce dust can be concentrated 

where they will have the most impact. 

To control dust at longwalls, a large amount of ventilation air and spray water must be used. The 

water must be sprayed correctly so as not to blow dust into the walkway. Techniques to change 

local airflow patterns can be helpful. The shearer-clearer, as well as gob and wing curtains, are 

examples of such techniques. 

DECIDING WHICH DUST SOURCE TO ADDRESS FIRST 

If a longwall is out of compliance with dust standards, 

knowing where the extra dust is coming from helps to get 

back in compliance quickly. 

The four major sources of dust at longwall faces are (1) the shearer, (2) the shields, (3) the 

stageloader-crusher, and (4) the intake. Finding the source of the extra dust involves two tasks. 
 

40 

First, the dust from each source must be measured. Second, these measurements must be 

compared to previous samples or to 

results from other longwalls in order 

to discover which dust source is causing the problem. 

Finding the amount of dust from 

each source. The first task is to take 

dust samples to measure the amount 

of dust from each source. Initially, 

fixed-site on-section28

28On-section means that sampling is done while the shearer is operating, not portal to portal.

dust samples 

should be taken at locations I and H 

shown in figure 3-1. 

Figure 3-1.—Longwall dust sampling locations. 

Location I gives 

the intake dust level. Location H is at 

shield 10 and includes the intake dust 

in addition to the stageloader-crusher 

dust. The stageloader-crusher dust is 

obtained by subtracting the dust level at I from the dust level at H. To ensure reasonable 

accuracy, a package of at least two samplers should be used for three shifts. 

If belt air is used to ventilate the longwall face, the belt air dust concentration at location B 

should be measured. If the airflow at both B and I is measured, a corrected average 

concentration from the two locations can be calculated.29

29If the concentration and airflow at I are CI and QI and at B are CB and QB, then the corrected average concentration 

is [(CI QI) + (CBQB)] / [QI+QB].

 The concentration at H then reflects30 

30The reason that concentration (mg/m3

) is used instead of dust make (mg/sec) is that the dust make value is subject
 

to error caused by air loss into the gob, which takes place between locations I and H. 

the addition of the stageloader-crusher dust31

31The concentration measured at H will contain a small amount of shearer dust from the cutout at the headgate. This 

error can be eliminated by turning off the sampling pump when the shearer is upwind of shield 10. 

 to the intake and belt dust. 

Separating out shearer dust is a harder task. It requires two people who follow the shearer as 

it cuts. Each person carries several dust samplers. One stays upwind of the shearer (location U 

in figure 3-1); the other stays downwind of the shearer (location D in figure 3-1). The shearer 

dust contribution is the difference between the upwind and the downwind dust concentration 

values,32

32This assumes that shield movement is far enough from the shearer to be subtracted out. 

locations U and D. 

Shield dust is measured in the same way, using upwind and downwind measurements, except 

that the sampling pumps are turned on only during the head-to-tail pass to minimize background 

dust levels. One person stays 25 ft upwind of shield movement; the other stays 25 ft downwind33 

33The 25-ft value is approximate and may vary slightly depending on circumstances. If the downwind person gets
 

too close to the shearer, the samplers will be biased upwards by shearer dust. If the downwind person gets too close 

to the moving shields, the samplers will be biased upwards because the shield dust, which falls mostly into the walk­
 

41 

of shield movement. This “mobile sampling” has been described more fully by Colinet et al. 

[1997] and Srikanth et al. [1995]. 

Source comparison with other longwalls. Once sampling is completed, the results should be 

compared to earlier results obtained at the same mine or to other longwalls. Colinet et al. [1997] 

give dust source contributions obtained from a survey of 13 longwalls (table 3-1). The average 

percent values reflect the average contribution of a given source. For example, on average, 

intake sources account for 9% of the dust at the longwalls that were surveyed. 

The concentration values in table 3-1 reflect dust levels measured only when the shearer was 

operating, using the sampling locations shown in figure 3-1 and explained in the accompanying 

text. Except for the intake, the values shown represent the difference between the upwind and 

downwind dust concentration values. They are not personal exposure values. 

Any dust source showing a contribution greater than the median value of table 3-1 is a likely 

source of the extra dust that has caused the longwall to go out of compliance. 

Table 3-1.—Dust source contribution values from 13 longwalls [Colinet et al. 1997] 

SOURCE AVERAGE 

PERCENT 

CONTRIBUTION 

MEDIAN 

CONTRIBUTION 

RANGE 

Intake 9 0.33 mg/m3 0.07-1.1 mg/m3 

Stageloader-crusher 15 0.78 mg/m3 0.29-1.3 mg/m3 

Shields 23 1.8 mg/m3 0.67-2.3 mg/m3 

Shearer 53 3.5 mg/m3 0.7-8.8 mg/m3 

way, has not fully mixed into that portion of the airflow moving through the shield legs and down the panline. See 

figure 3-5 and the accompanying explanation. 

BASIC LONGWALL DUST CONTROL TECHNIQUES 

Basic techniques are those widely used to control dust, applicable at 

every longwall. Mine operators can use high water and airflows and 

take measures to avoid blowing dust into the walkway. They can 

also move workers upwind, reduce dust from the stageloadercrusher, use a gob curtain, and use a shearer-clearer system. 

Raising airflow to control dust. Raising the airflow provides some benefit when the existing 

face air velocity is below 600 ft/min [Organiscak and Colinet 1999]. Over the years, longwall air 

quantities have risen to compensate for higher production levels [Haney et al. 1993; Ondrey et al. 

1994]. A survey by the Mine Safety and Health Administration in 1999 showed that longwalls 
42 

had an average intake air quantity of 71,000 cfm34

34For mines in coal under 8 ft, the average was 66,000 cfm; for mines 8 ft or more, 87,000 cfm. 

 and an average headgate-end face velocity of 

650 ft/min. Eighteen percent of longwalls exceeded 100,000 cfm in the intake airways. This 

high air quantity helps to control respirable dust by providing better dilution of dust sources.35 

35While increases in airflow are applicable at every longwall, it does not follow that such increases are always feasible. Depending on the age of the mine and the design of the ventilation system, major ventilation increases are not
 

always practical. Such mines will have to depend more on the other dust controls. 

For many years, there has been a concern that high air velocities would entrain settled dust. 

However, 10% of longwalls now have face air velocities exceeding 1,000 ft/min without experiencing any evident36

36Evident from underground measurements, at least. Recently, Listak et al. [2001] conducted lab studies to assess 

the impact of higher face velocities on shield dust. Dry (1% moisture) mixed-size particulate was dropped into an 

airstream flowing in a horizontal wind tunnel. Surprisingly, airflow increases resulted in much higher dust concentration levels. 

entrainment problems. This lack of dust entrainment is probably due to 

high water application rates in conjunction with shield washing. 

Using water to control dust. Dust generated by the shearer is reduced by increasing the quantity of water supplied to the shearer drums, so it is important to supply as much water as possible 

to the drums. In two separate studies, water flow to the shearer drums was increased about 50% 

and dust levels at the shearer were reduced about 40% [Shirey et al. 1985]. In a survey of 

13 longwalls, Colinet et al. [1997] report an average shearer water flow of 100 gpm, almost all of 

it to the drums. 

The number of sprays and the type of spray nozzle chosen are important for best dust control 

performance. For example, pick-point sprays at the outer edge of the vanes, now commonly 

used, are superior to the old cavity-filling sprays that were mounted on a pipe welded to the side 

of the vane [Jankowski et al. 1987]. Also, the greater the number of sprays, the more thoroughly 

water is mixed with the broken coal. In a test that varied the number of sprays, Bazzanella et al. 

[1986] showed that dust suppression is improved by increasing the number of sprays on a shearer 

drum, even when the total water flow and nozzle pressure were held constant with the use of 

smaller orifice nozzles. When 46 smaller orifice nozzles were substituted for the 17 original 

nozzles, dust was reduced by 60%. This finding shows that there should be at least one spray for 

each pick on the drum. 

Design of the water supply system is an important consideration if sprays are to be effective. 

Each water split should have its own flow meter and pressure gauge for convenient monitoring. 

All of the system components must be sized for the anticipated water flows, with particular attention devoted to the size of the pipe that goes through the ranging arm and connects to the feed 

lines in the drum spiral. Water filtration is often a source of headaches. The coarsest filter mesh 

size that can normally be used is 50 micron, and the stream of water should not bypass the filter 

mesh when it plugs up. 

Avoiding the migration of dust into the walkway. Since water sprays are known to entrain air 

and generate their own local air currents, they must be used in a way that allows dust from the 

drums to hug the face and not be blown out into the walkway. Figure 1-4 illustrates how sprays 

 
43 

on the body of a longwall shearer can actually raise the shearer operator=s dust level by blowing 

dusty air into the walkway. Because of this air-entrainment effect, it is generally better not to 

have sprays mounted on the shearer body, unless they are part of a “shearer-clearer” configuration as described below. 

Despite the need to keep sprays off of the shearer body, the motor cooling water must be discharged somewhere. The recommended location for these sprays is low on the end of the 

shearer, pointed straight down onto the panline so that they wet the coal on the panline and cause 

little air entrainment [Jankowski and Hake 1989].37 

37Some mines use the cooling water to wash the shearer haulage track. 

Excessive pressure on the drum sprays also blows dust into the walkway. In two separate studies 

[Pimentel et al. 1984; Kok and Adam 1986], the water pressure of the drum sprays was increased 

from 75 to 115 psi and 80 to 150 psi, respectively. In both instances, dust exposure of the 

shearer operators increased by 25% because the higher pressures on the trailing drum blew the 

dust into the walkway. Thus, the best drum spray pressure is in the range of 80 to 100 psi. 

Because of the tendency of high-pressure sprays to blow dust into the walkway, the water flow 

rate should always be raised by increasing the nozzle orifice size rather than the operating spray 

pressure.38

38The spray pressure is measured by removing one spray nozzle and attaching a hose that leads to a pressure gauge. 

 However, when the nozzle pressure is below 80 psi, the sprays may plug with coal 

particles pushed in from the outside. 

Moving workers upwind. Although measures can be taken to reduce the migration of dust into 

the walkway, the shearer-generated dust cloud at the face soon spreads from the panline to 

envelop the entire longwall face cross-section. Because of this dust cloud spreading, any mining 

practice or technology development that moves workers upwind of the shearer drums and moving supports is helpful. For example, use of remote control on shearers can significantly reduce 

dust exposure of the machine operators. A survey by the U.S. Bureau of Mines [1984] showed 

that exposure was reduced 68% by moving the operator just 20 ft upwind of the shearer body. 

Particular attention should be paid to the location of the tailgate-end shearer operator, who 

should always be positioned upwind of the tailgate-end drum to reduce dust exposure. 

Shearer operators can further reduce their dust exposure by moving as far upwind at the headgate 

as possible as the shearer cuts out at the headgate. 

Reducing dust from the stageloader-crusher. The stageloader-crusher can be a major dust 

source on longwall faces. To reduce this dust, the stageloader-crusher is enclosed with steel 

plates and strips of conveyor belting. All seals and skirts must be carefully maintained to ensure 

that dust stays inside the stageloader-crusher enclosure. Several sprays are mounted on internal 

spray bars, which usually span the width of the conveyor. Recommended spray bar locations are 

the mouth of the crusher, the discharge of the crusher, and at the stageloader-to-belt transfer 

point. Water pressure should be maintained below 60 psi, since high-pressure sprays may actually force dust out of gaps in the enclosure and into the intake air. During underground trials, 

covering the stageloader and adding spray manifolds to boost the water flow from 10 to 20 gpm 

yielded dust reductions of 79% at the headgate operator and 41% at support 20 [Organiscak et al. 

 
1986; Kelly and Ruggieri 1990b].39

44 

 

39These were old studies done at low (by today’s standards) production levels. Much higher water flows are necessary for today’s longwalls. 

The most important spray bar is the one located on the discharge side of the crusher [Jayaraman et al. 1992]. 

A few operators have attached dust collectors to the stageloader enclosure. This yielded no 

better results than just covering the stageloader and adding internal spray manifolds [Jayaraman 

et al. 1992]. Still, if enclosing the stageloader and adding internal sprays are not sufficient, a 

dust collector attached40

40A dust collector on the stageloader will see a very high particulate load, so horizontal ductwork should be avoided 

and access doors for cleanout should be provided. 

to the stageloader is the next step. 

Reducing dust from the intake. While the intake is usually the least significant source of longwall dust, it cannot be ignored. Reductions in intake dust from using homotropal ventilation, 

cleaning the panel belt, and adding water to the intake roadway have been discussed by 

Organiscak et al. [1986]. Other methods to reduce roadway dust are discussed in chapter 5 on 

surface mining. For mines that use belt air, the reduction of conveyor belt dust is discussed in 

chapter 6 on hard-rock mines. Work crews in the intake will often stir up dust, and rescheduling 

of work may be necessary. 

Using a gob curtain to aid airflow. A gob curtain is a brattice curtain installed from the roof to 

the floor between the first support and adjacent rib in the headgate entry. It prevents air from 

leaking into the gob, forcing more of the ventilation airflow to make a 90o turn and stay on the 

face side of the supports (figure 3-2).

Figure 3-2.—Gob curtain forces air to stay on longwall face. 

 This permits more dilution of dust in the region of the face 

near the headgate. Without a gob curtain, a substantial portion of intake air will pass into the 

gob, moving laterally behind the supports. During underground trials, the average face air velocity with the curtain installed was 35% 

greater than that without the curtain 

[Jankowski et al. 1993]. The most 

significant improvement was seen for 

the first 25 to 30 supports.41 

41Some operators use curtains or conveyor belt strips to seal the gaps between the first few shields. No data are 

available on how well this works to keep air on the face. 

Gob curtains also have a secondary 

benefit. When less air enters the gob, 

then less air returns to the face halfway down the shield line. Therefore, 

dust generated by gob falls is less 

likely to be entrained and carried back 

onto the face. 

Using the shearer-clearer system. 

A large portion of U.S. longwalls use 

a water spray system called a shearerclearer, specifically designed to hold shearer-generated dust against the face. The shearer-clearer 

 
takes advantage of the air-moving capabilities of water sprays to direct the dust cloud downwind 

along the panline, which prevents it from spreading out into the walkway (figure 3-3). 

 

 Figure 3-3.—Typical respirable dust concentration profile around the shearer during 

 the tail-to-head pass. 

 

45 

 The 

system consists of several shearer-mounted water sprays, oriented downwind, and one or more 

passive barriers, which split the airflow around the shearer into separate clean and contaminated 

air streams (figure 3-4). 

The air split in the shearer-clearer system is started by a splitter arm, with a strip of conveyor 

belting hanging from the splitter arm down to the panline. This belting extends from the top 

gobside corner of the shearer body to the cutting edge of the upwind drum. A spray manifold 

mounted on the splitter arm confines the dust cloud generated by the cutting drum, further 

enhancing the air split. The dust-laden air is drawn over the shearer body and held against the 

face by spray manifolds positioned between the drums on the face side of the machine. The air 

is then redirected around the downwind drum by a set of sprays located on the downwind end of 

the shearer. Operating pressure must be about 150 psi,42

42Proper pressure and spray placement are important if the expected reduction in dust is to be realized [Ruggieri 

et al. 1983]. 

measured at the nozzle, to ensure 

effective air movement. Total water flow rate with all sprays operating is about 12 gpm. 

In underground tests, the shearer-clearer reduced operator exposure from shearer-generated dust 

by at least 50% when cutting against the ventilation and 30% when cutting with the ventilation 

[Ruggieri et al. 1983; Jayaraman et al. 1985].43 

43Other experiments have been done to test a shearer-clearer in conjunction with passive barriers mounted on the 

shearer. The passive barriers gave no improvement in dust when added to the shearer-clearer. However, the passive 

barriers alone (without the shearer-clearer) gave a 25% reduction in shearer dust compared to the baseline (no barriers, no shearer-clearer) [Jankowski and Babbitt 1986; Kelly and Ruggieri 1990a]. 
 

Figure 3-4.—Air currents when using the shearer-clearer system. 

46 

A helpful installation manual for the shearer-clearer is 

available [Ruggieri and Babbitt 1983]. 

Cutter drum maintenance. Routine replacement of badly worn, broken, or missing bits 

improves cutting efficiency and helps reduce dust. Also, bits designed with large carbide inserts 

and smooth transitions between the carbide and steel shank typically produce less dust 

[Organiscak et al. 1996a]. The water sprays should be serviced along with the bits, since the 

number of operating drum sprays greatly impacts the amount of dust generated [Bazzanella et al. 

1986]. 

SITE-SPECIFIC LONGWALL DUST CONTROL TECHNIQUES 

Site-specific techniques can be effective when allowed by 

the local geology and suitable to the type of equipment 

used. Mines can use unidirectional cutting, modify their 

support movement practices, and use a wing curtain to aid 

airflow. 
 

47 

Using unidirectional cutting. Some mines in very high coal use a unidirectional cutting 

sequence because it offers operational advantages. Unidirectional cutting allows somewhat 

greater flexibility to place workers upstream of dust sources than bidirectional cutting. If the 

primary cut takes place as the shearer moves in the head-to-tail direction, the leading drum that 

cuts most of the coal is downwind of both shearer operators and roof support movers. Dust surveys [USBM 1984] have shown that cutting in the head-to-tail direction yields dust levels about 

40% less44

44The 40% figure refers only to shearer-generated dust measured at the shearer. Use of shearer remote control could 

increase or decrease this value. 

than cutting in the tail-to-head direction. 

On the other hand, if the primary unidirectional cut is in the tail-to-head direction, supports can 

be advanced just downwind of the shearer, keeping both shearer and support dust away from face 

workers. This cut direction works well when a shearer-clearer system is used to hold the dust 

against the face. 

Whether unidirectional cutting can be done depends on the type of equipment used and the local 

roof conditions. A head-to-tail cut requires most of the coal and rock to pass under the shearer, 

and sufficient clearance under the shearer is required to prevent clogging. Also, a head-to-tail 

cut may not be necessary if shearer dust has been avoided in some other way, such as remote 

control. When the supports are advanced during the cycle will depend on how much the supports 

are adding to the overall dust problem and how long the freshly cut roof can stand without 

falling. 

The downside of unidirectional cutting is that it may result in some loss in productivity by virtue 

of the reduction in cutting time. However, the cost of any expected productivity loss must be 

balanced against the cost of alternative dust controls. 

The most common unidirectional sequence is to cut coal on the tail-to-head pass, closely following the shearer with the support advance. With this sequence, no workers are exposed to 

support-generated dust, and the shearer dust is held in check with a shearer-clearer system operated in conjunction with remote control. 

Using modified support movement practices to reduce dust. During bidirectional cutting, 

support advance will occur in both cutting directions. Support movers can stay away from support dust by positioning themselves upwind of the moving supports. 

During the head-to-tail cut, shearer operators are exposed to any dust generated by support 

movement. Support dust tends to be generated directly over the walkway, so under the moving 

support the concentration in the walkway will be higher than in the adjacent support legs or 

panline. As this support dust moves downwind, the walkway concentration declines as the 

walkway dust cloud mixes with the air moving down the panline and the air moving through the 

support legs. As a result, some mine operators find that support-generated dust can be diluted 

more before it reaches the shearer operators by increasing the distance between support advance 

and the shearer from 20 to 50 ft (figure 3-5). 
48 

 Figure 3-5.—Support dust in the walkway dilutes as it moves 

downwind [Organiscak et al. 1985]. 

During the tail-to-head cut, with 

shield advance following downwind, shields should be pulled as 

closely behind the shearer as possible. This keeps the shield movers 

ahead of the shearer dust cloud, 

which progressively spreads into 

the walkway as it moves downwind from the shearer. In this 

case, a shearer-clearer system may 

be of considerable help to the 

shield movers, since it holds the 

dust cloud over the panline for a 

greater distance downwind of the 

shearer, as shown in figure 3-3.

Water application on the immediate roof also may help to suppress 

some of the support dust generated 

during lowering, advancing, and 

resetting of the roof supports. The 

immediate roof can be wetted by 

spraying the roof with one or more 

narrow-angle water sprays 

mounted on top of the shearer 

body, directing water downwind 

at an upward 45o angle. 

In addition, shield supports can be 

equipped with water sprays in the 

shield canopy that wet the broken 

roof debris on top of the shields. 

These achieve modest 25% 

reductions in shield-generated dust [Henke and Thiemann 1991], but are hard to maintain, 

especially since they soak the face workers. Mangolds et al. [1990] have reviewed the (mostly 

unsuccessful) attempts to control shield-generated dust. 

Using a wing curtain to aid airflow. The purpose of a wing curtain is to shield the shearer 

operators from the very high concentrations of dust generated as the headgate drum cuts into the 

headgate entry. The high-velocity primary airstream passing over and through the drum entrains 

and carries large quantities of dust out into the walkway and over both operators. When a wing 

curtain is installed between the panel-side rib and the stageloader (figure 3-6), it shields the headgate drum from the airstream as the drum cuts out into the headgate entry. 

Figure 3-6.—Airflow at longwall headgate with a wing curtain. 

The wing curtain is located 4 to 6 ft back from the corner of the face to provide maximum shielding without interfering with the drum. The curtain is only in place during the cutout operation 
49 

and is generally advanced every other pass. A wing curtain can reduce operator dust exposure 

by 50% to 60% during the headgate cutout [Jankowski et al. 1993; Cecala et al. 1987]. 

FUTURE POSSIBILITIES FOR LONGWALL DUST CONTROL 

Because of longwall production increases over the years, there is a 

continuing demand for better dust control. This section discusses 

dust control methods that might be used at future longwalls. Some 

are newer methods. Others are older methods that have been little 

used because of higher cost or operating difficulties. Examples of 

future possibilities are advances in production technology, water 

infusion, foam, a face partition, and high-pressure drum sprays. 

Advances in production technology. Any advance in longwall production technology that 

allows workers to move upwind of dust sources will reduce their dust exposure. This has already 

taken place through the use of remote control of shearers and batch control of shields. 

The implementation of more advanced technology has been delayed because of practical operating difficulties with these systems. For example, control packages are now available for complete automation of shield movement; however, they are not yet in wide use. 

Another advanced technology that offers lower longwall dust levels is the memory-cut system in 

which a computer logs the precise height of the drums as the shearer moves across the face. 

With such a system, the operators make the initial cut, and the computer controls several subsequent cuts while the operators wait in a less dusty location. Several memory-cut systems have 

been sold to mine operators. Again, they are not yet in regular use because of practical operating 

difficulties. 

Nothing works as well as measures that put workers 

upwind of dust sources. Because of this, any new 

technology that moves workers upwind can greatly 

reduce their dust exposure [Organiscak et al. 1996b]. 

High-Pressure Inward-Facing Drum Sprays. High-pressure water can have a significant 

impact on shearer-generated dust. The basic concept is to use high-pressure drum sprays to 

improve wetting of the coal and improve the airborne capture efficiency of the sprays. The 

nozzles are angled inward to avoid blowing the uncaptured dust cloud out into the walkway. 

An underground evaluation of high-pressure, inward-facing drum sprays gave good results 

[Jankowski et al. 1989]. Of those tested, the most effective spray system was the 30°, 800-psi 
50 

configuration. Not only was the dust reduction greater (39%), the concentration was lower at all 

sampling sites using this configuration. Also, wetting of the coal was improved since intake dust 

levels along the face were reduced by about 45%. 

A drawback of high-pressure sprays is that the small-orifice nozzles tend to clog unless the water 

is very clean. Also, space has to be found on the shearer for a booster pump or the pump located 

outby with a high-pressure line running to the shearer. Neither alternative may be feasible. 

Solid-stream (jet) sprays. Some preliminary longwall tests during the 1980s [Kost et al. 1985; 

Jankowski et al. 1987] showed that using solid-stream (jet) sprays on the shearer drum yielded 

30% less dust at the shearer operator position than the conventional conical sprays. Whether this 

dust reduction was due to better wetting of the coal or less boil-out from the drum is not clear. 

Followup tests to confirm these results under a variety of conditions were never done. 

Foam. Tests in two mines have shown that foam works well to lower dust when it is released 

from nozzles located on the shearer drums. In the first mine, the shearer operator dust exposure 

was cut by 56% compared to conventional water sprays on the drum. In the second mine, operator dust exposure was cut by 84%, and the dust level at the tailgate declined by 78% compared 

to water sprays [Laurito and Singh 1987; USBM 1989]. Also, during the test the foam system 

used less water than the conventional sprays. 

A test in a third mine measured the impact of foam applied with nozzles located on the ends of 

the shearer body. The effectiveness of this external foam application was less than 20%, indicating that for foam to be effective, it must be applied through the shearer drums so as to be thoroughly mixed with the coal. 

Long-term tests to assess feasibility and cost of foam at longwalls have not been done. 

Face partition. The concept of a face partition is to maintain two parallel splits of air along the 

longwall face by a transparent mesh partition (figure 3-7). This partition acts to retard the spread 

of shearer-generated dust into the walkway, reducing the dust exposure of the shearer operators 

and roof support movers [Organiscak and Leon 1993; Organiscak 1999]. During testing, a 1/8thinch mesh partition was hung from the roof supports to separate the walkway from the panline. 

When the partition stayed parallel to the face, walkway dust was cut in half. However, where 

supports were being advanced, there was always a short segment of mesh partition perpendicular 

to the airflow. This perpendicular segment caused a decline in partition effectiveness. Overall, 

the results were mixed. 

Water Infusion. To infuse a coal seam, boreholes are drilled into the coal seam ahead of mining 

and large volumes of water are pumped in under high pressure to wet the coal [McClelland et al. 

1987; Lama and Liu 1992; Stricklin 1987]. Water infusion has been used occasionally by mine 

operators for several decades. Although it is not widely used because of high cost, water 

infusion 
 

 

51 

of coal seams will reduce dust by about 50% in those seams that can be infused.45

45Many coal seams cannot be infused because of nonuniform seam permeability. 

 Many coal 

seams cannot be infused. Water infusion is much more economical if the holes have already 

been drilled to remove methane gas. 

 Figure 3-7.—Transparent mesh partition retards the spread of shearer dust into the walkway. 

Homotropal ventilation. With homotropal ventilation, intake air is routed up the tailgate entries 

and across the longwall face from tailgate to headgate, where it then passes into the gob. 

A separate split of air must be routed up the headgate entry to keep the headgate operator out of 

dusty return air [Stevenson 1985]. 

Because air routed up the tailgate entries is free from the headgate-side dust sources, the dust 

exposure of workers on the face is lower. The disadvantages of homotropal ventilation are that 

the tailgate-side entries must be kept in good condition and the gob at the headgate must remain 

open. Otherwise, the flow of air will be restricted. Keeping the tailgate entries and the headgate 

side of the gob open may require additional cribbing [Kelly and Jankowski 1984]. Homotropal 

ventilation may only be feasible in a small proportion of mines. 

Water proportioning. While it is well-known that more water added to the shearer drums will 

reduce dust, the maximum amount of water that can be added is usually limited by operational 

problems (such as softer clay floors and slipping conveyor belts) that are created by excessive 

water. Since the upwind drum is usually the one that contributes the most to worker dust exposure, some success in reducing dust might be obtained by proportioning more water to the 

upwind drum. However, solid evidence for an overall benefit is lacking [Kok and Adam 1986]. 
52 

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Bazzanella A, Becker H, Kemper F [1986]. Staubbekampfung in abbaubetrieben mit 

schneidender kohlengewinning. Gluckauf 122(11):728-735. Also available in translation as: 

Dust suppression in shearer faces, Gluckauf Translation 122(11):204-207. 

Cecala AB, Organiscak JA, Jankowski RA [1987]. Methane and dust controls for headgate cutouts. Min Sci & Technol 4:307-313. 

Colinet JF, Spencer ER, Jankowski RA [1997]. Status of dust control technology on U.S. longwalls. In: Ramani RV, ed. Proceedings of the Sixth International Mine Ventilation Congress. 

Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 345-351. 

Haney RA, Ondrey RS, Fields KG [1993]. Influence of airflow and production on longwall dust 

control. In: Proceedings of the Sixth U.S. Mine Ventilation Symposium (Salt Lake City, UT, 

June 21-23). Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc. 

Henke B, Thiemann M [1991]. Dust suppression during mining with self-advancing supports. 

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Technologie des Landes Nordrhein-Westfalen, Germany. 

Jankowski RA, Babbitt CA [1986]. Using barriers to reduce dust exposure of longwall face 

workers. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9037. NTIS 

No. 87 139572. 

Jankowski RA, Hake J [1989]. Dust sources and controls for high production longwall faces. 

In: Proceedings of Longwall USA (Pittsburgh, PA), pp. 117-132. 

Jankowski RA, Daniel JH, Kissell FN [1987]. Longwall dust control: an overview of progress in 

recent years. In: Proceedings of the 22nd International Conference of Safety in Mines Research 

Institutes (Beijing, China, Nov. 2-6, 1987), pp. 737-747. 

Jankowski RA, Jayaraman NI, Potts JD [1993]. Update on ventilation for longwall mine dust 

control. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 9366. NTIS 

No. PB94-112190. 

Jankowski RA, Whitehead KL, Thomas DJ, Williamson DL [1989]. High-pressure inwardfacing drum sprays reduce dust levels on longwall mining sections. In: Proceedings of Longwall 

USA (Pittsburgh, PA), pp. 231-242. 

Jayaraman NI, Jankowski RA, Kissell FN [1985]. Improved shearer-clearer system for double 

drum shearers on longwall faces. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, RI 8963. NTIS No. PB86-107844. 

Jayaraman NI, Jankowski RA, Organiscak JA [1992]. Update on stageloader dust control in 

longwall operations. In: Proceedings of Longwall USA (Pittsburgh, PA). 
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Kelly JS, Jankowski RA [1984]. Evaluation of homotropal ventilation for longwall dust control. 

In: Proceedings of the Coal Mine Dust Conference (Morgantown, WV, Oct. 8-10), pp. 92-100. 

Kelly J, Ruggieri S [1990a]. Evaluate fundamental approaches to longwall dust control: Subprogram A – Passive barriers/spray air movers for dust control. Waltham, MA: Foster-Miller, 

Inc. U.S. Bureau of Mines contract No. J0318097. NTIS No. DE 90-015511. 

Kelly J, Ruggieri S [1990b]. Evaluate fundamental approaches to longwall dust control: Subprogram C – Stageloader dust control. Waltham, MA: Foster-Miller, Inc. U.S. Bureau of Mines 

contract No. J0318097. NTIS No. DE 90-015510. 

Kok EG, Adam RFJ [1986]. Research on water proportioning for dust control on longwalls. 

Ketron, Inc. U.S. Bureau of Mines contract No. J0318096. 

Kost JA, Colinet JF, Shirey GA [1985]. Refinement and evaluation of basic longwall dust control techniques. BCR National Laboratory. U.S. Bureau of Mines contract No. J0318093. 

Lama RD, Liu Y [1992]. Control of respirable dust on longwall faces. In: Proceedings of the 

Fifth International Mine Ventilation Congress (Johannesburg, Republic of South Africa, Oct. 25­

30). 

Laurito AW, Singh MM [1987]. Evaluation of air sprays and unique foam application methods 

for longwall dust control. Engineers International, Inc. U.S. Bureau of Mines contract 

No. J0318095. NTIS No. PB89-189922. 

Listak JM, Chekan GJ, Colinet JF [2001]. Laboratory evaluation of shield dust entrainment in 

high-velocity airstreams. Transactions SME, Vol. 310. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 155-160. 

Mangolds A, Rajan S, Ruggieri S [1990]. Evaluate fundamental approaches to longwall dust 

control: Subprogram G – Reduction of shield-generated dust. Waltham, MA: Foster-Miller, Inc. 

U.S. Bureau of Mines contract No. J0318097. NTIS No. DE 90-015496. 

McClelland JJ, Organiscak JA, Jankowski RA, Pothini BR [1987]. Water infusion for coal mine 

dust control: three case studies. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, RI 9096. NTIS No. 88-120514. 

Ondrey RS, Haney RA, Tomb TF [1994]. Summary of minimum dust control parameters. In: 

Proceedings of the Fourth Symposium on Respirable Dust in the Mineral Industries (Pittsburgh, 

PA, Nov. 8-10, 1994). 

Organiscak JA [1999]. Investigation of longwall face ventilation air splitting methods for 

improved dust control. Transactions SME, Vol. 306. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 86-94. 
54 

Organiscak JA, Colinet JF [1999]. Influence of coal properties and dust control parameters on 

longwall respirable dust levels. Min Eng 51(9):41-48. 

Organiscak JA, Leon MH [1993]. Translucent face partition for longwall dust control. Proceedings of the Sixth U.S. Mine Ventilation Symposium (Salt Lake City, UT, June 21-23). Littleton, 

CO: Society for Mining, Metallurgy, and Exploration, Inc. 

Organiscak JA, Jankowski RA, Kelly JS [1986]. Dust controls to improve quality of longwall 

intake air. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 9114. NTIS 

No. PB 87-167573. 

Organiscak JA, Khair AW, Ahmad M [1996a]. Studies of bit wear and respirable dust generation. Transactions SME, Vol. 298. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 1874-1879. 

Organiscak JA, Listak JM, Jankowski RA [1985]. Factors affecting respirable dust generation 

from longwall roof supports. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, 

IC 9019. NTIS No. PB85-236453. 

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semiautonomous longwall operations. In: Proceedings of Longwall USA (Pittsburgh, PA), 

pp. 1-13. 

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In: Proceedings of the SME-AIME Annual Meeting (Los Angeles, CA, Feb. 26-Mar. 2), pp. 63­

82. 

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faces: design and installation manual. Waltham, MA: Foster-Miller, Inc. U.S. Bureau of Mines 

contract No. J0308019. NTIS No. PB 86-205416. 

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Mines contract No. J0308019. NTIS No. PB 86-205408. 

Shirey CA, Colinet JF, Kost JA [1985]. Dust control handbook for longwall mining operations. 

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Third Mine Ventilation Symposium (University Park, PA). 
55 

U.S. Bureau of Mines [1984]. Technology news 203: How to reduce shearer operators dust 

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dust. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines. 
 

57 

CHAPTER 4.—DUST CONTROL IN STONE MINES 

By Fred N. Kissell, Ph.D.,46

46Research physical scientist.

and Gregory J. Chekan47 

47Mining engineer. 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA. 

In This Chapter 

9 Drilling, blasting, and crushers 

9 Diesel particulate 

9 Enclosed cabs 

9 Ventilation with jet fans 

9 Stopping construction methods 

9 Propeller fans as main fans 

This chapter explains how to control dust in large-entry stone mines, including both silica dust 

and diesel particulate. Most stone mines are limestone mines, but a substantial minority are 

marble, sandstone, and granite mines. These mines differ from most others in that entry widths 

are 30 ft or more and entry heights are 25 ft or more. Such mines, developed with room-andpillar methods, have large open areas that can make ventilation and dust control more difficult. 

Because of the difficulty of ventilating stone mines, improved ventilation is a major focal point 

of this chapter. However, the chapter also covers the control of dust from drills, blasting, and 

crushers. Another part of the chapter covers enclosed cabs, an effective dust control technique 

for some workers. 

BACKGROUND 

The major dust compliance problem in stone mines is caused by silica (quartz) in the rock. 

Mines in high-silica rock, 8% or more, are far more likely to have a dust problem than those 

where there is less silica. Geographically, the limestone in the Northeastern and South Central 

United States has higher silica than the rest of the country. 

Chekan and Colinet [2002] have analyzed Mine Safety and Health Administration (MSHA) dust 

sampling results [MSHA 2001] from the stone industry. They have concluded that, on average 

across the United States, the workers exposed to the highest dust concentrations are rotary drill 

operators, front-end loader operators, truck drivers, and crusher operators. However, there are 

many regional differences. Also, occupations that work outside of cabs, such as blasters, roof 

bolters, and laborers, can be exposed to high dust levels. 
58 

CONTROL OF DUST FROM DRILLS, BLASTING, AND CRUSHERS 

Drills, blasting, and crushers produce the most dust in 

stone mines. Drill dust can usually be controlled by 

proper maintenance of the water supply system. Blasting 

dust is controlled by firing off-shift. Crusher dust, a more 

difficult problem, is usually managed (with varying success) by ventilation and water sprays. 

Control of drill dust. Drill dust is suppressed by water injected through the drill steel, a common practice for many years [ILO 1965]. Usually, respirable dust is reduced by 95% or better 

[MSA Research Corp. 1974]. However, this does not prevent dust from entering the air during 

the initial collaring period as the drill hole is started. Various means have been tried to prevent 

the escape of dust during collaring. These range from simple handheld sprays to elaborate types 

of suction traps around the end of the drill steel. None of these are very efficient. 

Drills powered by compressed air are much less common than in the past, eliminating the dust 

problems associated with their use. For example, if some of the compressed air operating the 

drill leaks into the front head of the drill and escapes down the drill steel, it will cause dry drilling and carry dust out of the hole. Compressed air escaping through the front head release ports 

will atomize some of the water in the front head. This atomized water evaporates rapidly and, 

if the water is dirty, many dust particles will remain in the air [Sandys and Quilliam 1982]. 

MSA Research Corp. [1974] has listed the factors that can lead to high dust levels on drills. 

Many result from lack of proper maintenance. These are failure to use water, inadequate quantities of water, plugged water holes in the drill bit, dull drill bits, and dry collaring. 

Control of blasting dust. Control of blasting dust is described in more detail in chapter 6, the 

chapter on hard-rock mines. Water is used to spray the blast area beforehand. Ventilation is 

used to exhaust fumes and dust via an untraveled return and between shifts. In most cases, the 

faces are shot during an off-shift, so no workers are in the mine at the time of the blasts. Studies 

have shown [Chekan and Colinet 2002] that in stone mines the retention time of the dust is usually less than 2 hr. If ambient levels of silica dust are high after this period or if workers are 

exposed to an excessive amount of dust from blasting when they reenter the mine, it usually indicates that the ventilation needs to be improved. 

Control of dust from crushers. Dust from crushers is controlled by water sprays and local 

exhaust ventilation from the crusher enclosure. The amount of water needed to do the job is hard 

to specify. It depends on the type of material crushed and the degree to which water will cause 

downstream handling problems. If the rock is dry, a starting point is to add a water quantity 

equivalent to 1% of the weight of the material being crushed [Quilliam 1974]. The nozzle 
 

59 

pressure of sprays at the grizzly and crusher jaw should be below 60 psi to avoid stirring the dust 

cloud and reducing the capture efficiency of the ventilation system.48 

48Chapter 1, the dust control methods chapter, has a more comprehensive discussion on why high spray pressures 

should be avoided most of the time. 

The amount of air required for dust control depends on how much the crusher can be enclosed. 

Enough air should be exhausted from a plenum under the crusher to produce a strong indraft at 

the jaw, grizzly, and any other openings around the crusher. The required airflow is usually 

large. For example, Rodgers et al. [1978] have described how dust from a 5-ft cone crusher was 

reduced by using a 75,000-cfm49

49Large air quantities may be required because falling rock induces its own airflow. Pring [1940] investigated the 

amount of air required to produce an indraft in surge bins at crusher installations. About 35,000 cfm was required at 

a large crusher installation.

exhaust ventilation system and a control booth for the 

operators.50

50If large (80% or more) dust reductions are sought for workers near a crusher, the most practical way to achieve 

this is to provide an enclosed and pressurized control booth supplied with filtered air. 

 Yourt [1969] has given a comprehensive set of design principles for dust control at 

crushing and screening operations. 

Crushers need lots of air and lots of water because they 

break lots of rock. 

In stone mines, dust that escapes the crusher is hard to contain because of the large crosssectional area of the entries. Figure 4-1 shows a conceptual approach to controlling crusher dust 

in a limestone mine. The crusher is located in a crosscut that has been benched to facilitate 

dumping from trucks. The crusher operator is located in an enclosed booth that is pressurized 

with filtered air. The crosscut is divided by a stopping (or leak-tight curtain) that essentially puts 

the crusher and dump point in a stub heading. Air is exhausted from a plenum under the crusher 

to create an indraft at the crusher jaws. It is then directed through the stopping. Dust in this air 

can be removed with a baghouse or directed into the return. 

Directing air through the stopping creates an inward air movement in the travelway. Because of 

this inward air movement, dust that escapes the crusher is more likely to stay confined within the 

stub heading and not escape into the rest of the mine. If the air velocity in the travelway is not 

high enough to confine the dust, a “half-curtain” approach might be helpful. Installing a halfcurtain in the travelway reduces the cross-sectional area and raises the air velocity. The higher 

air velocity provides better dust confinement.51 

51The half-curtain is described more fully in chapter 2 on continuous miner dust control and chapter 1 on dust control methods. 

The arrangement shown in figure 4-1 has the air doing double duty. It first confines dust in the 

crusher, then in the travelway. Whether all of this is necessary will depend on the circumstances 

in each individual mine. An enclosed operator booth alone may be adequate. However, it is 
 

60 

hard to reliably get better than a 90% dust reduction in such booths under real mining conditions, 

so additional measures to reduce dust may be required. 

 

Figure 4-1.—Conceptual approach to controlling crusher dust in a stone mine. 

CONTROL OF DIESEL PARTICULATE 

Diesel particulate control is included in this chapter because new MSHA diesel rules may require 

upgrades to stone mine ventilation systems and diesel equipment. A detailed but readable review 

of diesel particulate controls has been written by Schakenberg and Bugarski [2002]. Essentially, 

the technology selected depends on how much the particulate must be reduced. Moderate particulate reductions may be obtained by better engine maintenance, engine derating, biodiesel fuel, 

fuel-water emulsions, and oxidation catalysts in conjunction with low-sulfur fuels. Large particulate reductions (80% or better) can be obtained with ceramic particulate filters on the engine 

tailpipe. Also, new low-emissions engines are available. These new engines can lower the particulate level as much as 75% if the existing engine has an old design. 
 

61 

Some reduction in diesel particulate levels can be achieved by running haulage trucks in return 

airways. However, since other equipment in the mine is also powered with diesel engines, the 

benefits of return haulage may be minimal. In many mines, the haulage truck horsepower is only 

a fraction of the installed diesel horsepower in the mine. 

Reduction in diesel particulate can be obtained with improvements in the ventilation, as 

described in later sections on jet fans and stoppings. Head [2001a,b,c] recently wrote three 

helpful articles on better ventilation and reducing diesel emissions in stone mines. 

USING ENCLOSED CABS TO CONTROL SILICA DUST AND DIESEL PARTICULATE 

Cabs can reduce dust if their dust control systems are 

properly designed and maintained. Don’t expect a dust 

reduction over 75%, though. There is more information on 

enclosed cabs in chapter 5, the surface mining chapter. 

A high proportion of stone mine workers exposed to high dust levels can be protected with 

enclosed cabs or control booths. Haulage trucks in stone mines are often equipped with cabs. 

These cabs, if properly designed and maintained, can greatly lower the dust exposure of the truck 

drivers. 

Impact of retrofitting. Chekan and Colinet [2002] recently measured the efficiency of an 

enclosed cab on a 27-year-old haulage truck in a limestone mine. In this study, the cab was 

originally equipped with a heating and air-conditioning unit that did not filter the intake air or 

pressurize the cab. Dust level measurements showed that its overall efficiency in reducing 

respirable silica dust was only 33%. The cab was then sealed and retrofitted with a new heating 

and air-conditioning unit that filtered the air and slightly52

52To a pressure of 0.01 in w.g. 

 pressurized the cab. A new set of dust 

measurements gave an overall efficiency of 75% for respirable silica dust. This 75% overall 

efficiency figure was in line with dust efficiency results obtained with newer trucks.53 

53These figures represent the overall cab efficiency, which is calculated from the inside and outside dust concentration values. Usually the filters have much higher efficiency values. However, leakage of dust into the cab and dust 

sources in the cab (such as dirty boots) cause the overall efficiency to be lower. 

Cab filtration systems. Cab filtration systems can also trap diesel particulate if they are 

designed with this goal in mind. In underground stone mines, the level of diesel particulate is 

usually much higher than that found at surface mines, so the filtration of diesel particulate 

becomes an important consideration. Diesel particulate is much smaller in size than respirable 

mineral dusts, such as silica dust. So, if this diesel particulate is to be trapped by the cab filtration system, the filter must be much finer than that normally used to trap respirable dust. These 
62 

finer filters, usually designated as HEPA filters, have a higher pressure drop and require a more 

powerful fan.54

54MSHA recommends that HEPA filters always be used. 

 They also require more frequent cleaning or replacement. 

Efficiency to expect. When considering the use of cabs, it is important to recognize that the 

75% efficiency figure cited above is a typical efficiency value for a relatively new cab with an 

average level of maintenance. Higher efficiency values can be obtained, but they are the exception rather than the rule. A sustained efficiency over 75% is hard to achieve under realistic 

underground mining conditions. The main reasons for this include poor or aging seals on the 

cab, the operator opening the cab door for work-related tasks, and the operator bringing dirt into 

the cab without performing a regular cleaning of the interior. 

FACE AREA VENTILATION WITH JET FANS 

Jet fans can aid stone mine ventilation if these guidelines 

for their use are closely followed. 

A jet fan is a freestanding fan designed to induce additional air movement through a mine airway. Typically, no ductwork is attached to the fan, and the high-velocity55

554,000 to 9,000 ft/min or more. 

 exhaust jet from the 

fan entrains additional air from around the fan and pushes it forward. Usually jet fans do not 

outperform those fans with attached ductwork. However, for ductwork to be effective it must be 

extended close to the working face where it is subject to blast damage. Jet fans are located farther away and can always be temporarily moved around a corner to avoid the direct path of a 

blast. 

Jet fans have two applications. They are used to ventilate a straight single heading provided it is 

not too long, and they are used to ventilate a portion of the mine a few crosscuts away from the 

main pathway of fresh air. Jet fans cannot be used to ventilate an entire mine or even to move air 

more than a few crosscuts. 

Jet fan ventilation of single headings. Figure 4-2 shows a jet fan placed to ventilate a straight 

single heading. It is placed at the entrance of the heading on the intake air side. It must be close 

to the rib, pointed straight ahead, and with the inlet extended slightly into the crosscut. Performance inevitably suffers when other locations are used. Keeping the fan within a foot or two of 

the rib ensures that the jet expands only on one side, increasing its penetration. Extending the 

inlet into the crosscut reduces recirculation. 

Several studies have measured the performance of vane-axial fans at single headings like that 

shown in figure 4-2. Matta et al. [1978] used a 20,000-cfm fan to ventilate a heading 28 ft wide 

by 165 ft long. The height ranged from 17 ft at the crosscut to 9 ft at the face. Tracer gas tests 

 
63 

showed that 5,000 cfm of 

fresh air was reaching the face 

at 150 ft. A smaller 12,000­

cfm fan with a 3-ft outlet 

nozzle pushed 6,000 cfm of 

fresh air to the face, and a 

10,000-cfm compressed airpowered venturi air mover 

gave 3,500 cfm of fresh air to 

the face. The airflow in the 

crosscut was 57,000 cfm. 

Figure 4-2.—Jet fan ventilating a single straight heading. 

Matta et al. got better results 

when the fan had a nozzle 

attached. Lewtas [1980] 

obtained similar findings. 

Lewtas achieved the best air 

jet penetration when the 

nozzle was a truncated cone 

attached to a 1-ft-long straight 

section at the outlet. The 

sides of the cone were sloped at 18o from the axis; the ratio of the outlet diameter to the fan 

diameter was 0.68. 

Brechtel et al. [1985] tested a jet fan in a larger heading, 55 ft wide by 30 ft high by 320 ft long. 

An 88,000-cfm jet fan was surprisingly effective, with 66,000 cfm of fresh air reaching the face, 

according to the tracer gas dilution tests. Airflow in the crosscut was 124,000 cfm. 

Dunn et al. [1983a] tested jet fans in two different sizes of headings. Both were wide relative to 

their depth, probably the main factor leading to the high ventilation efficiencies. For example, 

in a heading of medium cross-section, 45 ft wide by 21 ft high by 115 ft long, a 7,000-cfm fan 

inclined up at 10o forced 6,700 cfm of fresh air to the face. There was 14,000 cfm in the crosscut. In another heading with a large cross-section, 52 ft wide by 38 ft high by 150 ft long, 

a 14,000-cfm jet fan inclined upwards at 12o forced all of the 14,000 of fresh air to the face. The 

baseline ventilation with no fan was 4,500 cfm. A larger fan performed no better because only 

15,000 cfm of fresh air was available in the crosscut. 

Table 4-1 shows the results of all of the large-entry tests. The face ventilation effectiveness is 

the fresh air delivered to the face divided by the fan quantity, expressed as a percentage. 
 

64 

Table 4-1.—Results of jet fan studies 

Researcher Cross-sectional 

area, ft2 

Length, 

ft 

Area-tolength 

ratio 

Fan size, cfm 

Face 

ventilation 

effectiveness, % 

Matta et al. [1978] 476-252 165 ~2:1 20,000 30 

Matta et al. [1978] 476-252 165 ~2:1 12,000 with nozzle 50 

Matta et al. [1978] 476-252 165 ~2:1 10,000, venturi 35 

Brechtel et al. [1985] 1,650 320 5:1 88,000 75 

Dunn et al. [1983a] 945 115 8:1 7,000, up 10o 96 

Dunn et al. [1983a] 1,976 150 13:1 14,000, up 12o 100 

Overall, these results show that jet fans can work reasonably well in a dead heading if the heading is large enough, the fan is properly located, and enough fresh air is provided to the fan inlet. 

The best results were obtained when the heading area to length ratio was high. A nozzle should 

be used to improve the jet penetration. Also, it may help to angle the fan upwards by 10o, per the 

findings by Dunn et al. [1983a]. 

Jet fans in headings should always be tested for recirculation by releasing smoke at location S in 

figure 4-2 and observing whether any travels back to the fan inlet. If recirculation to the fan inlet 

is present, it may help to attach a short length of ventilation duct to the inlet and then extend the 

other end of the duct upwind in the crosscut. 

Jet fan ventilation of multiple headings a few crosscuts away from fresh air pathway. Jet 

fans have great potential for moving air short distances. However, ensuring an adequate quantity 

of fresh air can be difficult. Figure 4-3 shows a jet fan placed in the center of an airway and indicates how the air jet spreads as it moves away from the fan. 

 Figure 4-3.—Jet fan entrainment of mine air. 

This jet spreading results from the 

entrainment of the air next to the jet, and the amount of air entrained can be surprisingly high— 
65 

9 to 15 times the air quantity passing through the fan [Dunn et al. 1983b]. Air can also be 

entrained from crosscuts ahead of the fan, as shown in figure 4-3. Unfortunately, much of the 

entrained air is contaminated air that is recirculated back from the face, not fresh air. 

Fresh air and recirculation. The challenge when using jet fan ventilation is how to place the 

fan to maximize the amount of fresh air. Having some recirculated air is not necessarily a problem. Studies have shown that recirculated air becomes a problem only when it is substituted for 

fresh air rather than added to a fixed quantity of fresh air [Kissell and Bielicki 1975]. 

As an example of how recirculated air can substitute for fresh air, figure 4-4 shows a portion of a 

mine a few crosscuts away from a fresh air pathway. Without a jet fan in operation, the mine air 

circulation in this part of the mine was directly from location 1 to location 2. A 14,000-cfm jet 

fan was placed close to a pillar at location A and directed toward the face area [Dunn et al. 

1983a]. In this location, the fan worked well since the air movement it generated brought an 

average of 10,000 cfm of fresh air to faces FA through FD. Location B, close to the opposite 

side of the pillar, was almost as effective in relation to fan placement. 

Experimenting with other locations, when the fan was placed at either of the two locations close 

to the adjacent pillar, marked X and Y, fresh air delivery was cut by 40% and 80%, respectively. 

Even though the distance from A and B is less than 100 ft, X and Y are too far from the intake 

air source, permitting recirculated air to return on both sides of the fan and diminish the fresh air. 

However, for fan locations A and B, the recirculated air returns only on one side, the left side, 

since the rib on the right side serves as a natural barrier. Figure 4-5 shows the airflows obtained 

with the jet fan in operation at location A. The airflow directions show that all of the fresh air 

was being directed toward the working faces, even though there was also a large amount of recirculated air. 

Important conclusions from this work done by Dunn et al. were that fans must be placed in the 

incoming fresh airflow. In the larger airways, it helped to angle the fan upwards by 10o. Also, 

under this work it was concluded that larger-capacity fans ventilate more effectively if enough 

intake fresh air is available. 

If you want to move air for distances greater than those 

shown in figure 4-5, forget about jet fans. Use ventilation 

ductwork or build stoppings. 
Figure 4-4.—Multiple headings a few crosscuts away from a fresh air pathway. 

66 
 

Figure 4-5.—Airflows obtained with jet fan in operation. 

67 
68 

METHODS OF STOPPING CONSTRUCTION 

In mines with large entries, stopping construction is a 

major task. Fortunately, some innovative stopping 

designs are available. 

Well-built low-leakage stoppings are essential for good mine ventilation. Adam et al. [1986] 

have experimented with alternative stopping designs for large mine openings. The work was 

undertaken to develop construction techniques and cost data and to measure leakage rates on 

full-scale structures in an oil shale mine where the entries were 30 ft high by 55 ft wide. Six fullsize stoppings and one overcast were built. Leakage was measured before and after a full-scale 

face blast. The lessons learned are applicable to today’s stone mines. 

Muckpile stoppings. Muckpile stoppings elicited the most interest from mine operators. These 

were simply piles of waste material stacked in crosscuts. However, the air leakage from this type 

of stopping was far too high, possibly because there were not many fines in the waste. Adam 

et al.’s recommendation for achieving less leakage was to use a “pipe and sheeting” stopping in 

main entries and a “brattice and wire-mesh” stopping in individual panels. 

Pipe and sheeting stoppings. The pipe and sheeting stopping is formed on 5- and 6-inch telescoping, 1/4-inch wall, square-section steel tubes. These tubes were set into shallow holes that 

had been drilled into the floor on 7.5-ft centers. At the roof, directly above each floor hole, an 

8-in-long, 3-in by 3-in by 3/8-in piece of angle iron was attached using a 2-ft resin roof bolt. The 

top of each telescoping member was welded to a roof angle. The connection between the two 

tubes was also welded. Corrugated metal sheets were then fastened to the vertical support members on the high-pressure side using self-drilling screws. All sheeting seams and the stopping 

perimeter were then sealed with a polyurethane foam. 

Brattice and wire mesh stopping. To build a brattice and wire-mesh stopping, short pieces of 

threaded rod, 1/2-inch in diameter by 4 inches long, were first welded every 2 ft to a section of 

angle iron 4 inches by 4 inches by 1/4 inch by 10 ft long. This angle iron was then bolted to the 

roof and floor using 2-ft resin bolts on 3-ft centers. Next, a wire fencing layer was placed across 

the opening, and each panel of fence was attached to the angle base on the roof and floor. Then, 

brattice with velcro strips sewn down the vertical edges were attached to the angle bars on the 

high-pressure side. The velcro seams were then fastened to create a sealed wall of brattice. Following the brattice installation, a second layer of wire fence was attached across the drift in a 

fashion similar to the first. The two layers of fence sandwiching the brattice were then securely 

fastened to the threaded rod with roof bolt plates, washers, and nuts. Finally, all velcro seams 

and the stopping perimeter were sealed with polyethylene foam. 

Blast relief with damage-resistant brattice. Close to the face, some blast relief is needed. 

A stopping of “damage-resistant brattice” (figure 4-6) can be used [Thimons et al. 1978]. 

Damage-resistant brattice consists of vertical brattice panels joined by velcro seals. To form a 
 

69 

stopping of damage-resistant brattice, a strip of velcro is sewn to each edge of a roll of brattice 

cloth on the same side of the fabric. The end of the roll is wrapped around a wooden 2 by 4 that 

is slightly shorter than the width of the roll. The 2 by 4 is then bolted to the roof, with the brattice hung down to the floor. The operation is repeated to extend a curtain all the way across the 

entry. Adjacent cloth panels are sealed to each other with the velcro. The velcro strips are sewn 

to the same side of adjacent panels so that they separate by peeling rather than shearing. Next, 

other wood 2 by 4s are bolted to the ribs. Velcro is then stapled on and the adjacent brattice curtain attached. Blast forces can split the seams between the panels and at the ribs, but they can 

easily be reattached. When blast forces are no longer a concern at that location, adjacent panels 

can be stapled together. Also, wire mesh can be placed on either side to make a more pressureresistant brattice and wire-mesh stopping. 

 

Figure 4-6.—Stopping built from damage-resistant brattice. 

Table 4-2 shows the leakage and cost of the three types of stoppings, along with two types of 

muckpile stoppings. With the exception of the muckpile stoppings, the leakage values were 

reasonable. However, the costs were high because there were such large entries to be sealed. 
Table 4-2.—Cost and leakage of five types of stone mine stoppings 

Type of stopping Cost 

(2001 prices) 

Leakage in cfm/1,000 ft2 

at 0.10 in w.g. 

Pipe and sheeting $15,000 80 

Brattice and wire-mesh $7,000 160 

Damage-resistant brattice $2,400 200 (before blast) 

Muckpile stopping $5,800 5,100 

Muckpile and brattice stopping $2,400 2,200 

70 

Because of the high stopping costs, Adam et al. [1986] also considered a wide variety of alternatives in the room-and-pillar layout to reduce the number and size of stoppings required. Typical 

alternatives were longer pillars along a stopping line, development of bleeder entries, ventilation 

from adjacent panels, and reduced-width “hourglass” crosscuts that were widened on the retreat 

benching operation. These alternatives were then weighed in a cost-efficiency model that considered the volume mined per unit stopping area, haulage distance, and equipment tram distance. 

Adam et al. concluded that stopping size and cost could be reduced by any of several costeffective alternatives. 

PROPELLER FANS AS MAIN FANS 

Save money by using propeller fans. 

Improved dust control in many stone mines will require installing new main fans. Many stone 

mines have access exclusively through parallel drift entries, that is, they have no shafts or slopes. 

Because the pressure drop associated with moving air through large entries is low, these mines 

may be able use low-pressure, high-volume propeller fans as main fans. Grau et al. [2002] have 

measured air quantities and pressure drops in two stone mines having only parallel drift entries 

and no shafts or slopes. Results are shown in table 4-3. 

Table 4-3.—Pressure drop in stone mine airways 

Mine Airway 

length, ft 

Air quantity, 

cfm 

Fan pressure, 

in w.g. 

A 2,400 350,000 0.12 

B 7,000 280,000 0.06 

These air quantities and fan pressures are well within the reach of large-diameter (10- to 12-ft) 

propeller fans. Such fans will be much less expensive to purchase and operate as main fans than 

vane-axial fans delivering the same airflow and pressure. 
71 

REFERENCES 

Adam ME, Brechtel CE, Agapito JFT [1986]. Improved stopping, door, and overcast construction for oil shale mines. J. F. T. Agapito & Associates, Inc. U.S. Bureau of Mines contract 

No. J0145020. NTIS No. PB87-174918. 

Brechtel CE, Adam ME, Agapito JFT [1985]. Development of effective face ventilation systems 

for oil shale mining. J. F. T. Agapito & Associates, Inc. U.S. Bureau of Mines contract 

No. H0134033. NTIS No. PB86-159829. 

Chekan GJ, Colinet JF [2002]. Silica dust sources in underground limestone mines. In: Proceedings of the 33rd Annual Institute on Mining Health, Safety and Research (Roanoke, VA, Aug. 

11-13, 2002). 

Dunn MF, Kendorski FS, Rahim MO, Mukherjee A [1983a]. Testing jet fans in metal/nonmetal 

mines with large cross-sectional airways. Engineers International, Inc. U.S. Bureau of Mines 

contract No. J0318015. NTIS No. PB84-196393 

Dunn M, Kendorski F, Rahim MO, Volkwein J [1983b]. Auxiliary jet fans and how to get the 

most out of them for ventilating large room-and-pillar mines. Eng Min J Dec:31-34. 

Grau RH III, Robertson SB, Mucho TP, Garcia F, Smith AC [2002]. NIOSH ventilation 

research addressing diesel emissions and other air quality issues in nonmetal mines. SME preprint 02-187. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc. 

Head HJ [2001a]. Proper ventilation for underground stone mines. Aggregates Manager Jan: 

20-22. 

Head HJ [2001b]. Calculating UG mine ventilation fan requirements. Aggregates Manager 

Apr:17-19. 

Head HJ [2001c]. Managing diesel emissions in underground mines. Aggregates Manager 

Jun:17-18. 

ILO [1965]. Guide to the prevention and suppression of dust in mining, tunnelling, and quarrying. Geneva, Switzerland: World Health Organization, International Labour Office. 

Kissell FN, Bielicki RJ [1975]. Methane buildup hazards caused by dust scrubber recirculation 

at coal mine working faces: a preliminary estimate. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8015. NTIS No. PB-240 684/1/XAB. 

‌

‌
72 

Lewtas TA [1980]. Assessment of induction fan effectiveness. Foster-Miller Associates, Inc. 

U.S. Bureau of Mines contract No. J0387223. NTIS No. PB82-2359870. 

Matta JE, Thimons ED, Kissell FN [1978]. Jet fan effectiveness as measured with SF6 tracer 

gas. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8310. NTIS No. PB288 173/8/XAB. 

MSA Research Corp. [1974]. Control of respirable dust in noncoal mines and ore processing 

mills – handbook. U.S. Bureau of Mines contract H0220030. NTIS No. PB 240 646. 

MSHA [2001]. Sampling results from 1996 to 2000 from the metal/nonmetal mine inspection 

data (MNMID). Pittsburgh, PA: U.S. Department of Labor, Mine Safety and Health Administration, Pittsburgh Safety and Health Technology Center, Dust Division. 

Pring RF [1940]. Dust control in large-scale ore concentrating operations. American Institute of 

Mining and Metallurgical Engineers, Technical Publication No. 1225. 

Quilliam JH [1974]. Sources and methods of control of dust. In: The ventilation of south African gold mines. Yeoville, Republic of South Africa: The Mine Ventilation Society of South 

Africa. 

Rodgers SJ, Rankin RL, Marshall, MD [1978]. Improved dust control at chutes, dumps, transfer 

points, and crushers in noncoal mining operations. MSA Research Corp. U.S. Bureau of Mines 

contract No. H0230027. NTIS No. PB 297-422. 

Sandys MPJ, Quilliam JH [1982]. Sources and methods of dust control. In: Environmental Engineering in South African Mines. Yeoville, Republic of South Africa: The Mine Ventilation 

Society of South Africa. 

Schnakenberg GH Jr., Bugarski AD [2002]. Review of technology available to the underground 

mining industry for control of diesel emissions. Pittsburgh, PA: U.S. Department of Health and 

Human Services, Public Health Service, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002-154, 

IC 9462. 

Thimons ED, Matta JE, Kissell FN [1978]. Bureau of Mines damage-resistant brattice. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8270. NTIS No. PB-278-607. 

Yourt GR [1969]. Design principles for dust control at mine crushing and screening operations. 

Can Min J 90(10):65-70. 
 

73 

CHAPTER 5.—SURFACE MINE DUST CONTROL 

By John A. Organiscak,56

56Mining engineer. 

 Steven J. Page,57

57Research physical scientist. 

Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA. 

Andrew B. Cecala,1

 and Fred N. Kissell, Ph.D.2 

In This Chapter 

9 Drill dust control: wet and dry 

9 Enclosed cabs on drills and mobile equipment 

9 Haul road dust control 

Overburden drilling generates most of the respirable dust that affects workers at surface mines. 

Both wet and dry methods are available to reduce this drill dust. Overburden removal by mobile 

excavation equipment such as bulldozers, front-end loaders, and haulage trucks can be dusty, 

particularly under dry and windy conditions. Tightly enclosed cabs with dust filtration systems 

can substantially lower the dust exposure of both drill and mobile equipment operators. Haul 

road dust control can be achieved by water application or chemical application. 

DRILL DUST CONTROL 

Drill dust is controlled with wet or dry systems. Wet 

systems can be more efficient, but may freeze in the 

winter. Dry systems require careful maintenance of the 

drill deck shroud. An improved deck shroud is shown. 

Wet Suppression. Wet drilling systems pump water into the bailing air from a water tank 

mounted on the drill. The water droplets in the bailing air trap dust particles as they travel up the 

annular space of the drilled hole, thus controlling dust as the air bails the cuttings from the hole 

[Page 1991]. 

In wet drilling systems, typical water flow rates are 0.1 to 2.0 gpm depending on the size and 

type of drill and the moisture level of the overburden. The drill operator controls the flow using 

a control valve located in the cab. Some drills are equipped with a flow meter to give the operator a visual sign of the flow rate. Raising the water flow will improve dust capture, but too much 

water causes operational problems. Because of this, the drill operator must exercise care in finding the best water flow rate. 
 

74 

To operate the drill at the best water flow rate, the operator slowly increases the amount of water 

just to the point where visible dust emissions abate. The visible dust abatement point is easy to 

identify. Increasing water flow beyond the dust abatement point does not yield much improvement in dust control, but will most likely cause increased tricone bit degradation and possible 

seizing of the drill stem. If the cuttings look moist, it usually indicates that too much water is 

being used. This approach to adjusting the water flow can be effective; however, the time delay 

between adjusting the valve and expulsion of the cuttings from the hole can be several seconds. 

Finding the proper water flow is not as crucial with drills using drag bits, but the cuttings still 

should not look moist. Particular care in finding the proper flow setting must be exercised when 

drilling through alternating dry and wet strata. 

Tests show that wet suppression systems can effectively control respirable dust. In testing, control efficiencies for 8-in holes varied widely, from a low of 9.1% at a flow of 0.2 gpm to a high 

of 96.3% at a flow of 1.2 gpm. The most significant increase in efficiency is usually between 0.2 

and 0.6 gpm. Above this, the efficiency levels off. For those drills tested, a flow rate approaching 1.0 gpm began to cause operational problems [Zimmer et al. 1987]. 

The most obvious drawback to wet system drilling occurs when the outside temperatures drop 

below freezing. The entire system must then be heated while the drill is in operation; during 

downtime the system must be drained. 

Dry Collection. Dry collection systems require an enclosure around the area where the drill 

stem enters the ground. This enclosure is constructed by hanging a rubber or cloth shroud from 

the underside of the drill deck. The enclosure is then ducted to a dust collector, the clean side of 

which has a fan. The fan creates a negative pressure inside the enclosure, capturing dust as it 

exits the hole during drilling. The dust is removed in the collector, and clean air is exhausted 

through the fan. 

The dust that escapes dry collection systems has several possible sources: the shroud around the 

drill deck, the drill stem access hole in the drill deck, the dust collector dump, and the dust 

collector exhaust. Determining which is the problem is not difficult. The presence of a visible 

dust cloud is a good sign that respirable dust is present, even though such clouds are mostly 

larger-sized particles. 

The integrity of the drill deck shroud, including how well it seals to the ground, is probably the 

single most important factor contributing to the effectiveness of a dry collection system. The 

shrouded volume under the drill deck should be at least 1.8 times the volume of the hole and 

should be at a negative pressure of at least 0.2 in w.g. The minimum ratio of dust collector air to 

bailing air flow recommended for most drills with a rectangular shroud is 3:1, with higher ratios 

desirable. Openings in the shroud lower its capture efficiency. The most common open area is 

the gap between the bottom of the shroud and the ground. With a ground gap of 6 to 9 inches or 

less, dust capture will usually be satisfactory for a 3:1 airflow ratio. However, as the ground gap 

increases, dust capture efficiency decreases, and a considerable amount of dust may escape 

[Page 1991]. 
 

75 

During drilling, it is sometimes necessary to raise the drill for two reasons: (1) the driller/helper 

needs to shovel the cuttings to prevent them from falling back into the hole, and (2) the operator 

must be able to observe when the coal seam has been reached and stop drilling. As a result, there 

are times when a ground gap cannot be avoided. However, it is important for good dust control 

to keep the gap to a minimum. 

The effectiveness of the dust collection system also decreases if significant leaks are present 

from holes in the shroud. Most deck shrouds are rectangular and constructed from four separate 

pieces of rubber belting attached to the deck. Thus, leakage occurs at the corner seams as the 

individual pieces of belting separate from one another. Adding corner flaps to the shroud (figure 

5-1) [Page and Organiscak 1995] can help to reduce this corner leakage. 

 

Figure 5-1.—Corner flaps added to a deck shroud to reduce leakage. 

Improved shroud design for dry collection systems. A new type of circular rubber shroud is 

much superior to the traditional rectangular design because it has no corner seams and it can be 

easily raised and lowered to make a better seal at the ground [NIOSH 1998] (figure 5-2). The 

circular shroud is attached to the drill deck with steel banding. A second much thicker steel band 

is attached to the bottom of the shroud to maintain shape and provide weight. The shroud is 

raised and lowered through activation of a hydraulic cylinder and lift wires attached to the 

bottom steel band. The bottom can be raised almost to the drill deck and lowered to make contact with the ground after raising and leveling the drill. Raising and lowering of the shroud is 

helped by using thin sheet rubber and cutting the rubber so the shroud has a slight conical shape. 

The shroud also has a small trap door that can be manually opened to shovel the cuttings out of 
76

an access hole without having to 

raise the shroud above the ground 

and lose dust capture efficiency. 

During testing, the circular shroud 

had a dust reduction efficiency of 

99% or better. Comparable tests on 

the common square shrouds typically achieve 95%, so the amount of 

dust escaping from the circular 

shroud is lower by a factor of five. 

 Figure 5-2.—A circular shroud that can be raised and lowered improves dust collection efficiency. 

Maintenance of dry collection 

systems. A recent field survey of 

six highwall drills [Organiscak and 

Page 1999] has shown that proper 

maintenance is crucial to the performance of dry collection systems. 

During the survey, the dry dust collection systems on four of the six 

drills were malfunctioning, and dust 

levels were very high. The collector 

fan on one drill was not operating 

because the drive belts were broken. Another drill had one-quarter of the shroud material missing. 

The two remaining drills had dust escaping from underneath the shroud due to sloped and uneven 

ground conditions. When these problems were corrected, dust was reduced by 51% to 88%. 

Other maintenance-related dust sources were also identified during this survey. Dust was escaping 

from torn drill stem seals at the top of the drilling tables. Dust was discharged from a collector’s 

exhaust because the collector filter was torn, and dust was entrained by the wind when the gathered 

fines in the collector were dumped 4 ft onto the ground. The problems with the drill stem seal and 

collector discharge were easily fixed by replacing the worn items. Wind entrainment of dust from 

dumping of the collector was reduced by attaching a cloth shroud to the dust discharge port [Page 

and Organiscak 1995] and extending it down to within a few inches of ground level. 

ENCLOSED CABS ON DRILLS AND MOBILE EQUIPMENT 

Enclosed cabs can work well to reduce dust, but high 

efficiencies require a lot of maintenance. Cab sealing is 

important. 

Dust surveys on drills and bulldozers have shown that enclosed cabs can effectively control the 

operator’s dust exposure. In practice, many enclosed cabs do not provide adequate dust pro­
77 

tection [Organiscak and Page 1999]. The cab protection factors (outside versus inside dust level) 

measured on rotary drills ranged from 2.5 to 84; those measured on bulldozers ranged from 1 to 

45. Newer cabs were usually better sealed and cleaner; older cabs tended to be more poorly 

sealed and dirtier. 

Older cabs can be improved by being retrofitted with systems that heat, cool, and filter the air 

and by being tightly sealed. Both steps are necessary to ensure good dust control. First, the cab 

needs to have a high quality of recirculated and incoming filtered airflow. Second, the cab structure must be adequately sealed so that clean make-up air pressurizes the cab, keeping out dust 

that would otherwise be blown in by the wind. 

A recent cab retrofit study by Cecala et al. [2002a,b] showed the importance of cab sealing and 

pressurization. A poorly sealed cab with no pressurization showed no improvement in dust levels even when retrofitted with a new filtration/air-conditioning system. However, a cab retrofitted with a new filtration/air-conditioning system and pressurized to 0.2-0.4 in w.g. gave a 

protection factor of 52. Another cab pressurized to 0.01-0.15 in w.g. gave a protection factor of 

10. An earlier study by Organiscak et al. [2000] also concluded that cabs must be pressurized to 

offer adequate protection. Very small one-person cabs need at least 25 cfm of make-up air for 

adequate pressurization, and larger cabs proportionally more. Also, it was found that pressurization must be continuous and the operator must always keep the doors and windows closed. During the study, the operator of one drill opened the cab door to collar the next hole, letting notable 

amounts of dust enter the cab. Although the operator then shut the cab door during the drilling 

operation, the air filtration system took about 7 min to remove the dust cloud. 

Since positive pressurization cannot be achieved unless cabs are leak-tight, cabs should be 

checked regularly for leaks. Doors should be on a single hinge, with intact tight gaskets. Bifold 

and slider doors leak too much. Flexible boots must be on all control linkages entering the cab 

and the boot seams sealed with silicone caulking. All other seams and gaps should also be sealed 

with silicone. A flashlight can be used to check for gaps, and a smoke bomb released inside the 

cab will reveal even the smallest leaks. Older cabs are often hard to seal properly. 

Cecala et al. [2002a,b] also make recommendations on the design and installation of filtration/ 

air-conditioning systems. For effective filtration, the system should have two fans, one to 

recirculate inside air through a filter and a second to pressurize the cab with outside make-up air 

passed through a second filter. The filters must be designed to trap small-sized respirable dust. 

About 75% of the air passing through the cab should be recirculated, thus keeping the airconditioning unit to a reasonable size. The inlet for the make-up air should be located high on 

the cab and away from outside dust sources [NIOSH 2001a] to extend filter life and reduce airconditioner maintenance. 

Inside the cab, several actions can be taken to reduce dust. Air outlets should be at the top and 

inlets at the bottom. This top-to-bottom airflow keeps down the dust originating from dirty work 

clothes, boots, and a dirty floor. Potential dust sources on the cab floor also need to be relocated 

or removed. The fans on floor heaters will stir up dust, so these heaters should be moved higher 

up in the cab [NIOSH 2001b; Cecala et al. 2001]. Cab interiors should also be vacuumed and 

cleaned regularly to remove the dust that drifts in through open windows or is carried in on the 
78 

operator’s shoes and clothing. In many instances, a thick layer of sweeping compound on the 

cab floor will reduce dust [NIOSH 2001c]. 

HAUL ROAD DUST CONTROL 

The best dust control method depends on the type of road 

aggregate. Spillage is a consideration in selecting the 

dust control. 

Many methods are available for haul road dust control. Water application to the road surface is 

the most obvious, but there are many others. These include: 

• Salts—hygroscopic compounds such as calcium chloride, magnesium chloride, hydrated 

lime, sodium silicates, etc. Salts increase roadway surface moisture by extracting moisture 

from the atmosphere. 

• Surfactants—such as soaps and detergents. Surfactants decrease the surface tension of water, 

which allows the available moisture to wet more particles per unit volume. 

• Soil cements—compounds that are mixed with the native soils to form a new surface. Examples are calcium or ammonium lignon sulphonate, portland cement, etc. 

• Bitumens—compounds derived from coal or petroleum such as coherex peneprime, asphalt, 

oils, etc. 

• Films—polymers that form discrete tissues, layers, or membranes such as latexes, acrylics, 

vinyls, fabrics, etc. 

• Soil cements, bitumens, and films—These form coherent surface layers that seal the road surface, thereby reducing the quantity of dust generated. 
79 

Chlorides. Chlorides are the most commonly used products for haul road dust control. A study 

by Rosbury and Zimmer [1983a,b] showed that the highest control efficiency measured for a 

chemical dust suppressant, 82%, was for calcium chloride 2 weeks after application. Average 

efficiencies hovered in the 40% to 60% range over the first 2 weeks after application, then 

decreased with time. After the fifth week beyond application, the limited data show a control 

efficiency of less than 20%. The effectiveness of chlorides is enhanced by good roadway 

preparation, that is, a good crown and good drainage at the shoulder. Also, it is helpful to loosen 

at least 1-2 inches of the existing roadway surface. This allows the chloride to penetrate evenly 

into the gravel. To enhance dust control efficiency, the roadway surface should not be compacted before applying chlorides. 

It is important that the gravel be kept close to the optimum moisture just before applying chlorides. The product will thus be absorbed much more quickly and evenly into the gravel. Chloride 

should never be applied to dry gravel in that it will not be evenly absorbed and may show failure 

in spots. Also, rain on a freshly treated surface will leach out and dilute the chloride, causing it 

to run off the road. Therefore, application should be postponed if rain is forecast for that day. 

Water and chemical suppressants. Untreated plain water is commonly used for roadway dust 

control. The study by Rosbury and Zimmer [1983a,b] showed that watering once per hour 

resulted in a control efficiency of about 40%. Doubling the application rate increased the control 

effectiveness by about 15% to 55%. Chemical dust suppressants (primarily salts and lignons) 

can be more cost-effective than watering under some conditions. However, all chemical dust 

suppressants (with infrequent watering) share one common failing compared to frequent watering. Material spillage on roadways is very common, and the material spilled is subject to 

reentrainment. With frequent watering, newly spilled material is moistened at close intervals. 

When chemicals are applied with infrequent watering, newly spilled material could go for long 

periods before being moistened. Therefore, in mines where spillage cannot be controlled, watering alone is better for dust control. 

In many instances, chemical suppressants have an advantage over plain water. In locations 

where trackout from an unpaved road to a paved road creates a dust problem, chemical 

suppressants are a good choice. Watering actually aggravates the trackout problem with moisture and mud; chemical suppressants, particularly bitumens and adhesives, leave the road dry. 

Finally, some mines have a dust problem in winter when temperatures are subfreezing but little 

moisture is present. The case for chemical suppressants over water in such instances is clear. 

Road aggregate and dust control. Different types of road aggregate dictate different 

approaches to dust control. Recommendations based on specific road aggregate are: 

1. Gravel with few fines. In gravel road surfaces with not enough fines, only watering will be 

effective. Chemical dust suppressants can neither compact the surface (because of the poor 

size gradation) nor form a new surface, and water-soluble suppressants will thus leach. 

2. Sand. In compact sandy soils, bitumens, which are not water-soluble, are the most effective 

dust suppressant. Water-soluble suppressants such as salts, lignons, and acrylics will leach 
80 

from the upper road surface. However, in loose, medium, and fine sands, bearing capacity 

will not be adequate for the bitumen to maintain a new surface. 

3. Good gradation. In road surfaces with a good surface gradation, all chemical suppressant 

types offer potential for equally effective control. 

4. Silt. In road surfaces with too much silt (greater than about 20% to 25% as determined from 

a scoop sample, not a vacuum or swept sample), no dust suppression program is effective, 

and the road should be rebuilt. In high-silt locations, the chemical suppressants can make the 

road slippery and are not able to compact the surface or maintain a new road surface because 

of poor bearing capacity. Further, rutting under wet conditions requires that the road be 

graded, which destroys chemical dust suppressant effectiveness. If the road cannot be 

rebuilt, watering is the best program. 

If there is uncertainty about the gradation of the gravel or if there is doubt about the equipment 

and products to be applied, the process can be tried on a 500- to 1,000-ft test section of the road. 

If the process fails at the test section level, then only a small investment and time are lost. 

REFERENCES 

Cecala AB, Organiscak JA, Heitbrink WA [2001]. Dust underfoot: enclosed cab floor heaters 

can significantly increase operator’s respirable dust exposure. Rock Prod 104(4):39-44. 

Cecala AB, Organiscak JA, Heitbrink WA, Zimmer JA, Fisher T, Gresh RE, et al. [2002a]. 

Reducing enclosed cab drill operators’ respirable dust exposure at surface coal operations with a 

retrofitted filtration and pressurization system. SME preprint 02-105. Littleton, CO: Society for 

Mining, Metallurgy, and Exploration, Inc. 

Cecala AB, Organiscak JA, Page SJ, Thimons ED [2002b]. Reducing silica exposure in aggregate operations. AggMan Jan:24-28. 

NIOSH [1998]. Hazard controls: New shroud design controls silica dust from surface mine and 

construction blast hole drills. Cincinnati, OH: U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, HC27, DHHS (NIOSH) Publication No. 98-150. 

NIOSH [2001a]. Technology news 485: Improved cab air inlet location reduces dust levels and 

air filter loading rates. Pittsburgh, PA: U.S. Department of Health and Human Services, Public 

Health Service, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health. 

NIOSH [2001b]. Technology news 486: Floor heaters can increase operator’s dust exposure in 

enclosed cabs. Pittsburgh, PA: U.S. Department of Health and Human Services, Public Health 

Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety 

and Health. 
81 

NIOSH [2001c]. Technology news 487: Sweeping compound application reduces dust from 

soiled floors within enclosed operator cabs. Pittsburgh, PA: U.S. Department of Health and 

Human Services, Public Health Service, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health. 

Organiscak JA, Page SJ [1999]. Field assessment of control techniques and long-term dust variability for surface coal mine rock drills and bulldozers. Int J Surf Min Reclam Env 13:165-172. 

Organiscak JA, Cecala AB, Heitbrink WA, Thimons ED, Schmitz M, Ahrenholtz E [2000]. 

Field assessment of retrofitting surface coal mine equipment cabs with air filtration systems. In: 

Bockosh GR, Karmis M, Langton J, McCarter MK, Rowe B, eds. Proceedings of the 31st 

Annual Institute of Mining Health, Safety and Research. Blacksburg, VA: Virginia Polytechnic 

Institute and State University, Department of Mining and Minerals Engineering, pp. 57-68. 

Page SJ [1991]. Respirable dust control on overburden drills at surface mines. In: Proceedings 

of the American Mining Congress Coal Convention (Pittsburgh, PA). 

Page SJ, Organiscak JA [1995]. An evaluation of improved dust controls for surface drills using 

Rotoclone collectors. Eng Min J Nov:30-31. 

Rosbury, KD, Zimmer RA [1983a]. Cost-effectiveness of dust controls used on unpaved haul 

roads. Volume 1: Results, analysis, and conclusions. PEDCo Environmental, Inc. U.S. Bureau 

of Mines contract No. J0218021. NTIS No. PB 86-115201. 

Rosbury, KD, Zimmer RA [1983b]. Cost-effectiveness of dust controls used on unpaved haul 

roads. Volume 2: Data. PEDCo Environmental, Inc. U.S. Bureau of Mines contract 

No. J0218021. NTIS No. PB 86-115219. 

Zimmer RA, Lueck SR, Page SJ [1987]. Optimization of overburden drill dust control systems 

on surface coal mines. Int J Surf Min 1:155-157. 

‌
 

83 

CHAPTER 6.—UNDERGROUND HARD-ROCK DUST CONTROL 

By Fred N. Kissell, Ph.D.,58

58Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

and Jozef S. Stachulak, Ph.D., P.Eng.59 

59Chief mines ventilation engineer, Inco Ltd., Copper Cliff, Ontario, Canada. 

In This Chapter 

9 Ore pass dust control 

9 Drill dust control 

9 Blasting dust control 

9 Conveyor belt dust control 

9 Transfer point and crusher dust control 

9 Roadheader dust control 

and 

9 How much ventilation air to use 

This chapter discusses respirable dust control in underground hard-rock mines. These mines use 

a wide variety of extraction methods, but they have many common dust sources and dust control 

needs. Ore passes, drills, blasting, conveyor belts, transfer points, crushers, and load-haul-dump 

operations can be major sources of dust. Roadheaders, which are sometimes used in hard-rock 

mines, produce dust in large quantities. For the most part, dust in hard-rock mines is controlled 

with ventilation air, water sprays, and dust collectors. It is also important to prevent dust from 

getting into the air in the first place. Good dust control practices will reduce overall mine ventilation requirements. 

Lack of maintenance is the main source of dust problems in hardrock mines according to Rodgers [1974], who conducted a dust 

survey of hard-rock mines several decades ago. Rodgers found that 

spray systems had clogged sprays, dust enclosures had improperly 

fitted skirts, and ductwork was plugged and had leaks. Today’s 

mines have better maintenance programs (we think), but when dust 

levels are high, maintenance is still the first topic to address. 

The Mining Association of Canada [MAC 1980] and Knight [1980] provide good general information about hard-rock dust control. For conveyor belt dust control, Goldbeck and Marti [1996] 

and Swinderman et al. [1997] are valuable sources of information. 
 

84 

ORE PASS DUST CONTROL 

Falling rock moves air. That’s the ore pass dust problem 

in a nutshell. 

Ore and waste passes (figure 6-1) produce large quantities of airborne respirable dust. 

 Figure 6-1.—Ore pass adjacent to steeply 

dipping ore body. (Courtesy of the Society for 

Mining, Metallurgy, and Exploration (SME) 

(www.smenet.org).) 

 The broken rock delivered to the passes contains a considerable amount of attached dust from preceding 

operations such as blasting and loading. The grinding action on the rock as it falls down the pass 

produces even more dust. However, the main problem is that the falling rock entrains air, producing a powerful “piston effect” that generates pressure surges of dusty air. 

Good ore and waste pass design can help to relieve these pressure surges. For example, if the ore 

and waste passes are located near each other, connecting them on several levels will relieve the 

pressure. Also, dusty air in the passes can be discharged into a return airway [Marshall 1964; Pullen 

1974]. The Mining Association of Canada [MAC 

1980] recommends exhausting sufficient air from 

the ore and waste pass system to indraft 200 ft/min 

air velocity at all leakages, assuming that one 

tipping location is open continuously. Discharging 

this air into a return airway eliminates the need to 

install a dust collector.60

60Dust collectors located underground must be able to handle high-humidity air and possibly some condensation. 

No matter what the ore and waste pass design, a critical step in dust control is to prevent its escape and 

dispersal into working areas by confining dust 

within the passes. This confinement can be accomplished by a system of stoppings and airtight doors 

over the ore and rock pass tipping locations. However, since some leakage from these doors is inevitable, another approach to dust control at tipping 

locations is to isolate them from travelways. This 

isolation is accomplished by locating the tipping 

locations in short, dead-end (stub) headings that 

have local exhaust dust collection systems. 

Dust from ore and waste passes will be reduced if 

the rock is thoroughly wetted before delivery to the 

tipping site. More water can be added at the tipping 

site by spraying the rock as it falls into the pass. 

However, too much water at ore passes can be 
85 

objectionable for many reasons. These include (1) an adverse impact on crushing and milling; 

(2) accumulation of a large quantity of water on top of the material in the chute, which creates a 

hazard for workers on the lower levels; and (3) plugging of chutes caused by water-softened clay 

minerals. 

Ore pass dust control is addressed by ILO [1965], Geldenhuys [1959], Kneen [1959], Gray et al. 

[1961], and Foster [1965]. Ore pass design has been discussed by Hambley [1987]. An extreme 

case of ore pass pressurization caused by falling material has been discussed by McPherson and 

Pearson [1997]. 

DRILL DUST CONTROL 

Good drill dust control requires good maintenance. 

Drill dust is suppressed by water injected through the drill steel, which has been a common 

practice for many years [ILO 1965]. Usually, respirable dust is reduced by 95% or better [MSA 

Research Corp. 1974]. This does not, however, prevent dust from entering the air during the 

initial collaring period as the drill hole is started. Various means have been tried to prevent the 

escape of dust during collaring. These range from simple handheld sprays to elaborate types of 

suction traps around the end of the drill steel. None of these are very efficient. 

Drills powered by compressed air are much less common than in the past, eliminating the dust 

problems associated with their use. For example, if some of the compressed air operating the 

drill leaks into the front head of the drill and escapes down the drill steel, it will cause dry drilling and carry dust out of the hole. Compressed air escaping through the front-head release ports 

will atomize some of the water in the front head. This atomized water evaporates quickly and, 

if the water is dirty, many dust particles will remain in the air [Sandys and Quilliam 1982]. 

MSA Research Corp. [1974] has listed the factors that can lead to high dust levels on drills. 

Many result from lack of proper maintenance. These are failure to use water, inadequate quantities of water, plugged water holes in the drill bit, dull drill bits, and dry collaring. 

BLASTING DUST CONTROL 

Water and ventilation are necessary, but the key to reducing dust exposure is blasting off-shift. 
 

86 

Water is important in controlling dust generated by blasting. The area surrounding the blast 

(walls, floor, and back) should be thoroughly sprayed beforehand. This precaution will prevent 

dust settled out during previous operations from becoming airborne. A uniform rock moisture 

content61

61Weight of water in the rock divided by the weight of rock. 

 of only 1% greatly reduces dust compared to dry rock [Quilliam 1974]. However, 

since it is difficult to wet rock uniformly under realistic mining conditions, the optimum 

moisture content can be much higher.62

62Quilliam [1974] recommends 5%, but this seems high to us. 

 The water used for dust suppression, particularly in 

drilling and in blasting, should be as clean as possible, because the evaporation of dirty water can 

also release dust. 

Sufficient ventilation is critical for the control of blasting dust since water alone is usually 

inadequate. Blasting dust and fumes should be diluted quickly and exhausted to the surface63 

63Much of the dust will be deposited in the return airways. For example, Ford [1976] found that 45% of a 4-μm
 

particle size dust cloud was deposited within a distance of 600 ft. Bhaskar et al. [1988] measured 38% deposition of 

respirable dust at air velocities over 300 ft/min and 67% deposition at an air velocity of 165 ft/min. Stachulak et al. 

[1991] measured a 66% decrease in respirable dust in a 500-ft vertical return air raise. 

via an untraveled return route. If this is not possible, the common practice is to arrange the 

blasting schedule so that the contaminated air will pass through working places when the miners 

are absent. 

CONVEYOR BELT DUST CONTROL 

A conveyor belt can generate large amounts of respirable dust from 

several sources. If the belt is not clean, dust is knocked from the 

belt as it passes over the idlers. Belt scraping and washing will 

reduce this dust source, and if the belt is dry, just wetting it can help. 

Also, much respirable dust originates at belt transfer points. 

Belt cleaning by scraping and washing. Conveyor belts are usually equipped with belt scrapers; some have belt washers as well. Several manufacturers sell scrapers and washers; these play 

an important role in reducing the amount of dust generated by conveyor belt carryback. Carryback is that portion of the carried material that sticks to the belt instead of falling off at the head 

pulley. It becomes airborne dust as the belt dries and passes over the return idlers. When dust 

levels are high, the usual approach is to add a second or even third scraper rather than trying to 

get a single scraper to work better. 

While multiple scrapers will reduce dust, they may be more efficient at spillage control than respirable dust control. Roberts et al. [1987] have shown that with each successive scraping, both 

the percentage of fines and the moisture level of the carryback substantially increase. This 
87 

shows that the larger material is preferentially removed by scraping and the smallest fines (which 

generate respirable dust) tend to stay stuck to the belt. 

If multiple scrapers do not remove enough carryback to cut the respirable dust sufficiently, 

a water wash system may be necessary. These systems spray the belt with water in addition to 

scraping it. Stahura [1987] has written a comprehensive discussion of conveyor belt washing. 

Planner [1990] has reported on the average belt-cleaning efficiency of water sprays when used 

with primary and secondary scrapers. In the Planner study, water sprays placed between the 

primary and secondary scrapers reduced carryback from 11.1% to 3.4%. In another test, water 

sprays added to a secondary scraper reduced carryback from 13.9% to 1.1%. 

Belt sprays also reduce airborne dust. Rodgers et al. [1978] added a 150-gpm water spray 

system to dry scrapers on a 54-in belt at a taconite processing plant. The sprays reduced 

respirable dust by 48% and total dust by 78% compared to dry scrapers alone. More recently, 

Baig et al. [1994] reported that airborne (respirable and float) coal dust levels were reduced 80%­

90% when their belt scrapers were augmented with spray wash boxes. 

Wetting of dry belts. Several studies have shown that wetting the bottom (return) belt can 

reduce dust from a dry belt. For example, Courtney [1983] measured the respirable dust reduction from a single 0.33-gpm spray onto the top surface (the noncarrying surface) of the bottom 

belt. The goal was to prevent dust from being knocked loose by the tail pulley and upper idlers. 

The spray was followed by a piece of ordinary floor carpet that wiped the belt to prevent 

channeling of the water. The spray and carpet were mounted close to the tail pulley so that the 

belt was wet as it passed 

around the tail pulley and 

moved outby over the upper 

idlers (figure 6-2). 

Figure 6-2.—Wetting the top surface of the bottom belt. 

Respirable dust reduction from 

installation of the spray and 

carpet averaged 75%. 

A 2-gpm spray without the 

carpet worked about as well. 

Slippage from excessive wetting was not a problem, as 

water usage was low (only 

2 gpm) and the belt then 

traveled for 5,000 ft before 

passing over the drive at the 

head end. 
 

 

88 

A decade earlier than Courtney, Ford [1973] tested a system that wetted both surfaces of the bottom belt (figure 6-3).

 

Figure 6-3.—Wetting both surfaces of the bottom belt. 

 A spray in the loop take-up near the belt head wetted the carrying surface 

so that dust was not knocked loose by the ingoing trip over the lower idlers. Then, near the tail 

pulley, the noncarrying surface of the bottom belt was wetted by a second spray for the trip 

around the tail pulley and across the upper idlers, similar to the system described by Courtney. 

Sprays were mounted so as to wet the entire width of the belt, and they were controlled automatically to operate only when the belt ran. A belt plow was used in place of the carpet. Respirable dust was reduced by 67% with a total (all sprays) water flow of 0.53 gpm.64 

64Low-flow spray nozzles are prone to clogging because of their small orifice size. To avoid nozzle clogging while 

reducing water use, control timers have been developed to cycle belt sprays on and off (BWI Eagle, Inc.). Timers 

also allow better control over the degree of belt wetting. 

TRANSFER POINT AND CRUSHER DUST CONTROL 

Transfer points. The traditional approach to transfer point dust control is to tightly enclose the 

transfer point, exhaust the dust-laden air from the enclosure through a duct, and either remove 

the dust from the air with a dust collector or discharge the dust to a return airway (figure 6-4). 

Transfer point dust control can be difficult because the falling rock has a “piston effect” due to 

air entrainment. This air entrainment draws mine air in at the top of the transfer point enclosure, 

and it can push dusty air out of the bottom of the enclosure. The piston effect of the falling rock 

can be reduced by lowering the drop distance, by using “rock ladders” to break the fall of the 

rock, and by increasing the enclosure size so that entrained air can circulate back to the top of the 

enclosure. Tight enclosure of the transfer point requires adjustable skirtboard sealing systems, 

a means to prevent belt sag in the loading zone, and careful sealing of belt entry and exit locations, among others. The usual airflow guideline is to plan for 200 (or more65

65MAC [1980] recommends adding 25% to the 200 ft/min as a safety factor. Yourt [1969] recommends that if a 

loaded belt is leaving the enclosure the air velocity be set at 200 ft/min plus the belt speed to counteract the drag 

effect. For instance, if the belt speed is 300 ft/min, then the air velocity into all unavoidable openings should be 

500 ft/min. Rodgers [1974] gives a rule of thumb of 700-800 cfm of exhaust ventilation per foot of belt width. 

) ft/min air velocity 

through all unavoidable openings. 
 Figure 6-4.—Dust-laden air exhausted from transfer 

point enclosure. 

89 

Duct takeoffs from transfer point (and 

crusher) enclosures must be designed to 

avoid picking up large particulate. The 

Mining Association of Canada [MAC 1980] 

recommends that the takeoff air duct be at 

least 6 ft from the falling rock to avoid 

picking up particles. Yourt [1969] suggests 

that the base of the takeoff cone be large 

enough so that the velocity of air exhausted 

is 500 ft/min or less. 

In addition to proper design of takeoffs, the 

ductwork leading to the dust collector or 

return airway must be designed to prevent 

dust settling. Yourt [1969] suggests that 

risers be installed at a steep angle, not less 

than 58o, and that horizontal runs be sized 

for a velocity of at least 3,000-3,500 ft/min. ACGIH [2001] suggests a velocity of 3,500-4,000 

ft/min. Cleanout ports should always be provided in horizontal ductwork. 

Another way to reduce dust at transfer points is to provide an enclosed sliding chute to transfer 

the material. Sliding chutes and spouts are widely used in materials handling; much information 

on them is available [Page 1991; Mody and Jakhete 1987]. 

There is a wealth of information on how to reduce transfer point dust [MAC 1980; Goldbeck and 

Marti 1996; Swinderman et al. 1997; Mody and Jakhete 1987; Yourt 1969; ACGIH 2001; 

Organiscak et al. 1986]. 

Crushers. Crushers in mines range from small roll types used in coal mines to large cone types 

used in hard-rock mines and mills. Whatever the size and method of crushing, dust is controlled 

by water sprays and local exhaust ventilation from the crusher enclosure. The amount of water 

needed is hard to specify. It depends on the type of material crushed and the degree to which 

water will cause downstream handling problems. If the rock is dry, a starting point is to add a 

water quantity equivalent to 1% of the weight of the material being crushed [Quilliam 1974]. 

Crushers need lots of air and lots of water because they 

break lots of rock. 

The amount of air required depends on how much the crusher can be enclosed. Enough air 

should be exhausted from a plenum under the crusher to produce a strong indraft at the jaw, 

grizzly, and any other openings around the crusher. The design guidelines for determining the 

required airflow are the same as those for transfer points. The unavoidable open area is 
 

90 

calculated and multiplied by a 200 ft/min indraft velocity.66

66Plus a 25% safety factor [MAC 1980]. See also footnote 8. 

 The required airflow is usually 

large. For example, Rodgers et al. [1978] have described how dust from a 5-ft cone crusher was 

reduced by using a 75,000-cfm67

67Large air quantities may be required because falling rock induces its own airflow. Pring [1940] investigated the 

amount of air required to produce an indraft in surge bins at crusher installations. About 35,000 cfm was required at
 

a large crusher installation.

exhaust ventilation system and a control booth for the operators.68

68If large (80% or more) dust reductions are sought for workers near a crusher, the most practical way to achieve 

this is to provide an enclosed and pressurized control booth supplied with filtered air. 

 Yourt [1969] has given a comprehensive set of design principles for dust control at crushing and screening operations. If there is an ore pass above the crusher, precautions should be 

taken to ensure that it is not pulled empty. 

If the crusher can be located in a short, dead-end (stub) heading, then air can be drawn into the 

crusher in the usual way and then discharged from the heading through ductwork. This design 

approach creates an air movement into the stub heading that confines any dust that escapes the 

crusher.69 

69The benefits of locating a crusher in a stub heading are explained in more detail in chapter 4 on stone mines. 

MAC [1980], Walker [1961], Phimister [1963], and Ahuja [1979] have described dust control 

methods used for large crushers at underground locations. Foam is also used to control dust at 

crushers, particularly where water use must be limited. Use of foam is described in chapter 1 on 

dust control methods. 

VENTILATION OF PRODUCTION AREAS 

Production areas are ventilated by directing an air split from the main ventilating stream through 

the workings. Sandys and Quilliam [1982] have recommended that a minimum air velocity of 

100 ft/min is needed to remove mineral dust in headings where track- and tire-mounted loaders 

are used for mucking ore. Dust generated by moving equipment can be reduced by applying 

water or chemicals (most commonly hygroscopic salts) to the roadways.70 

70Reduction of roadway dust is discussed at greater length in chapter 5 on surface mines. 

New MSHA regulations on diesel particulate, enacted in 

2001, will require even more air in U.S. mines unless the 

particulate level can be reduced by other means. 

However, if enough air is supplied to meet the requirements of the diesel equipment in the 

heading, then the mineral dust is well controlled. The usual diesel airflow criterion has been to 

supply 100-125 cfm per horsepower of diesel equipment, all equipment being cumulative in any 

one split. 
 

91 

Stachulak [1989] has pointed out that, not long ago, 10,000 cfm71

71The usual guideline was 50 cfm per square foot of face area, equal to a velocity of 50 ft/min. 

 was adequate for most 

development headings. However, some mines are now driving single drifts requiring 80,000 cfm 

to meet legal requirements for the diesel equipment. 

In development headings, a blowing system kept to within 100 ft of the face will usually provide 

a satisfactory dust level. Exhaust systems can do a good job of removing dust when the end of 

the duct is held within 10 ft of the dust source. However, keeping a 10-ft distance can be difficult in development headings because of potential blast damage to the duct. 

ROADHEADER DUST CONTROL 

Dust control methods for machines like roadheaders 

usually depend on some degree of dust cloud confinement. In mines where methane is released along with 

the dust, confining the dust cloud will raise the methane 

concentration. 

Roadheaders are occasionally used in hard-rock mines, but they are also used in many other 

underground excavations, from tunnels to wine storage caves. They have a reputation for generating dust for several reasons. Headings excavated by roadheaders are often larger in crosssection, and it can be hard to supply enough ventilation air to confine the dust cloud at the face. 

Some aspects of roadheader design also contribute to dust buildup. The cutting boom is narrow, 

so there is little of the dust cloud confinement provided by a wide boom. Also, the operator 

compartment is sometimes located far forward where the dust is inevitably higher. Finally, 

remote control of the machine, the best way to deal with dust, may not be available. 

Below are the various methods used to control roadheader dust, assuming that the material being 

excavated generates no methane gas.72 

72Lowering spray pressures will reduce the air turbulence. When air turbulence is reduced, methane concentration
 

levels may rise. When a half-curtain is used at a gassy face, methane can build up behind the curtain. A good discussion of roadheader dust control, both with and without methane, is in Hole and Belle [1999]. 

Ventilation-based controls. For a ventilation-based dust control, provide an adequate air volume using an exhaust duct with the duct inlet located close to the face. The volume should be 

sufficient to provide a forward air velocity in the heading of at least 60 ft/min based on the crosssectional area of the empty heading. The duct inlet should be at least 10 ft forward of the operator and within 5 ft of the face.73

73These recommended air velocities and duct distances are target values based on average conditions, assuming that 

remote control is not used. If a mine is under more stringent standards because of silica in the dust, more air may be 

needed. 

 Decreases in the air volume and increases in the duct inlet 
 

92 

distance can have a big effect on dust levels (figure 6-5) [Ford and Hole 1984]. 

 

 Figure 6-5.—Effect of duct inlet position, air velocity, and air curtain use on dust levels (from Ford 

and Hole [1984]). 

The second step in ventilation-based dust control is to locate and use water sprays so as to minimize air turbulence at the face. High-pressure sprays or nozzles located to spray out into the 

open air will produce air turbulence. This turbulence will cause the dust cloud to expand and 

back up (rollback) against the ventilation air, covering the machine operator [Hole and Belle 

1999]. To minimize turbulence, the water sprays on the boom should be located close to the cutting head to wet only the cutting head and the broken rock falling down from it. The water pressure (as measured at the spray nozzles) should be limited to 100 psi or less. If more water must 

be applied, larger orifice nozzles should be used. If the rock on the gathering pan must be 

wetted, only high-volume, low-pressure nozzles should be used. Finally, in headings where the 

cross-sectional area (not counting the machinery) is over 100 ft2

, a half-curtain should be considered in order to raise the air velocity for better dust confinement. Dust rollback and use of a halfcurtain are explained more fully in chapter 1 on dust control methods. 

Machine-based controls. Three machine-based controls are available to lower roadheader dust. 

First and most important is remote control. In conjunction with exhaust ventilation, remote control of the roadheader allows the machine operator to step back away from the dust cloud at the 

cutting face. In most cases, it is the most effective way to lower the operator’s dust level. 

The second control is to use a wet-head machine with low-pressure sprays. Several research 

studies have shown that wet heads will yield moderate dust reductions. The downside of wet 

heads is that the sprays can produce turbulence that causes the dust cloud to expand and roll back 

against the ventilation air, covering the machine operator with dusty air. For this reason, the 

nozzle pressure should be held below 50 psi. Hole and Belle [1999] report that a roadheader wet 

head operating at 20 psi and 6 gpm gave a 40% dust reduction compared to external sprays. 
 

93 

The third machine-based dust control is to use a Coanda air curtain to hold the dust cloud against 

the cutting face and away from the operator. Air curtains for dust control were devised in Germany and the United Kingdom. They are available as an option on some new machines. The 

greatest benefit is obtained when the ventilation quantity is low and the exhaust duct inlet cannot 

be held close enough to the cutting face. In underground testing, dust rolling back from the face 

was reduced by 80% when air curtains were used74

74The testing was done in a 16.5-ft by 12-ft arched section heading. Air curtains may not work as well in largersized headings. 

(figure 6-5) [MRDE 1983; Hole and Belle 

1999]. 

The best way to approach roadheader dust control will depend on individual circumstances. 

Providing sufficient airflow, keeping the exhaust duct inlet close to the cutting face, and using 

remote control will normally be sufficient to control dust. However, sufficient airflow and 

remote control are not always available. Keeping the duct inlet close to the face subjects it to 

damage by the cutter head. Therefore, if these conventional ventilation and remote-control 

remedies cannot be used, a half-curtain should be tried. Also, it might be possible to cut the face 

in two steps, first on the duct side, after which the duct is moved forward, and then the other 

side. Diligent replacement of worn picks can always help as well. 

If all else fails, the operator of the roadheader should have a respirator or a fully enclosed cab 

that is equipped with an air filtration system. Cabs with filtration systems are discussed in 

chapter 5 on surface mines. Dust respirators are discussed in chapter 9. 

REFERENCES 

ACGIH [2001]. Industrial ventilation: a manual of recommended practice. 24th ed. Cincinnati, 

OH: American Conference of Governmental Industrial Hygienists. 

Ahuja RC [1979]. Underground air filters solve dome dust problems. Can Min J Jul:54-57. 

Baig NA, Dean AT, Skiver DW [1994]. Successful use of belt washers. In: Proceedings of the 

American Power Conference. Chicago, IL: Illinois Institute of Technology, pp. 976-978. 

Bhaskar R, Ramani RV, Jankowski RA [1988]. Experimental studies on dust dispersion in mine 

airways. Min Eng Mar:191-195. 

Courtney WG [1983]. Single spray reduces dust 90%. Coal Min & Process Jun:75-77. 

Ford VHW [1973]. Bottom belt sprays as a method of dust control on conveyors. Min Technol 

(U.K.) 55(635):387-391. 

Ford VHW [1976]. Investigations into the deposition of airborne respirable dust along underground airways. Mining Research and Development Establishment (MRDE) Report No. 65. 

National Coal Board, U.K. 
94 

Ford VHW, Hole BJ [1984]. Air curtains for reducing exposure of heading machine operators to 

dust in coal mines. Ann Occup Hyg 28(1):93-106. 

Foster KJ [1965]. The ore pass: a return airway. Can Min J Oct:79-81. 

Geldenhuys WH [1959]. Ore pass dust control. J Mine Vent Soc S Afr 12(Jan):pp. 22-23. 

Goldbeck LJ, Marti AD [1996]. Dust control at conveyor transfer points: containment, suppression, and collection. Bulk Solids Handling 16(3):367-372. 

Gray BJ, MacAulay CA, Yourt GR [1961]. Dust control at underground dumps, chutes, and 

crusher. Can Min J Oct:64-69. 

Hambley D [1987]. Design of ore pass systems for underground mines. CIM Bull 

80(897):25-30. 

Hole BJ, Belle BK [1999]. Road header environment control (phase I, II, and III). Final report 

on project COL 603. CSIR Miningtek, Republic of South Africa. Available from Safety in 

Mines Research Advisory Committee (www.simrac.co.za). 

ILO [1965]. Guide to the prevention and suppression of dust in mining, tunnelling, and quarrying. Geneva, Switzerland: World Health Organization, International Labour Office. 

Kneen T [1959]. Dust control at dumps and passes. Can Min J Aug:93-98. 

Knight G [1980]. Generation and control of mine airborne dust. CANMET report 80-27E. 

Ottawa, Ontario, Canada: Canada Centre for Mineral and Energy Technology. 

MAC [1980]. Design guidelines for dust control at mine shafts and surface operations. 3rd ed. 

Ottawa, Ontario, Canada: Mining Association of Canada. 

Marshall L [1964]. Dust control at ore and waste pass dumps. Can Min J Oct:84-86. 

McPherson MJ, Pearson N [1997]. The airblast problem in the orepasses of the Grasberg mine, 

PT Freeport, Indonesia. In: Ramani RV, ed. Proceedings of the Sixth International Mine Ventilation Congress (Pittsburgh, PA, May 17-22, 1997), pp. 113-117. 

Mody V, Jakhete R [1987]. Dust control handbook for minerals processing. Martin Marietta 

Corp. U.S. Bureau of Mines contract No. J0235005. NTIS No. PB88-159108. 

MRDE [1983]. Application of air curtains and other methods for controlling ventilation and 

providing clean air at the workplace. Final report on ECSC research project 7256-12/030/08. 

National Coal Board, Mining Research and Development Establishment, U.K. 

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95 

MSA Research Corp. [1974]. Control of respirable dust in noncoal mines and ore processing 

mills – handbook. U.S. Bureau of Mines contract H0220030. NTIS No. PB 240 646. 

Organiscak JA, Jankowski RA, Kelly JS [1986]. Dust controls to improve quality of longwall 

intake air. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 9114. NTIS 

No. PB87-167573. 

Page J [1991]. Examples of good and bad chute design. In: Proceedings of the Chute Design 

Conference. Bionic Research Institute, Republic of South Africa. 

Phimister G [1963]. Ventilation and dust control in an underground crushing-conveying system. 

J Mine Vent Soc S Afr 16(1):1-10. 

Planner JH [1990]. Water as a means of spillage control in coal handling facilities. In: Proceedings of the Coal Handling and Utilization Conference (Sydney, Australia). Barton, Australia: 

Institution of Engineers Australia, pp. 264-270. 

Pring RF [1940]. Dust control in large-scale ore concentrating operations. American Institute of 

Mining and Metallurgical Engineers, technical publication No. 1225. 

Pullen PF [1974]. Dust control at vertical ore and waste passes. Can Min J 95(9):30-31. 

Quilliam JH [1974]. Sources and methods of control of dust. In: The ventilation of south African gold mines. Yeoville, Republic of South Africa: The Mine Ventilation Society of South 

Africa. 

Roberts AW, Ooms M, Bennett D [1987]. Bulk solid conveyor belt interaction in relation to belt 

cleaning. Bulk Solids Handling 7(3):355-362. 

Rodgers SJ [1974]. Survey of past and present methods used to control respirable dust in noncoal mines and ore processing mills – final report. MSA Research Corp. U.S. Bureau of Mines 

contract No. H0220030. NTIS No. PB 240 662. 

Rodgers SJ, Rankin RL, Marshall MD [1978]. Improved dust control at chutes, dumps, transfer 

points, and crushers in noncoal mining operations. MSA Research Corp. U.S. Bureau of Mines 

contract No. H0230027. NTIS No. PB 297-422. 

Sandys MPJ, Quilliam JH [1982]. Sources and methods of dust control. In: Environmental engineering in south African mines. Yeoville, Republic of South Africa: The Mine Ventilation Society of South Africa. 

Proceedings of the Fourth U.S. Mine Ventilation Symposium (Berkeley, CA, June 5-7, 1989). 

Stachulak JS, Dainty ED, McPherson MJ [1991]. The phenomenon of dust deposition in exhaust 

ventilation shafts at INCO mines. J Mine Stachulak JS [1989]. Ventilation strategy and unique 

air conditioning at INCO Limited. In: Vent Soc S Afr Nov:183-195. 
96 

Stahura RP [1987]. Conveyor belt washing: is this the ultimate solution? TIZ-Fachberichte 

111(11):768-771. ISSN 0170-0146. 

Swinderman RT, Goldbeck LJ, Stahura RP, Marti A [1997]. Foundations 2: the pyramid 

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Hill Consolidated Ltd. mine, Australia. J Mine Vent Soc S Afr 14(11):223-233. 

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Can Min J 90(10):65-70. 

‌
 

97 

CHAPTER 7.—CONTROL OF DUST IN HARD-ROCK TUNNELS 

By Fred N. Kissell, Ph.D.75 

75Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

In This Chapter 

9 Finding the dust source 

9 Ventilation and dust collector malfunctions 

9 Upgrading the dust controls 

9 Design stage ventilation planning 

This chapter explains how to reduce respirable dust76

76An information source for controlling methane and diesel fumes in tunnels is Kissell [1996]. 

in hard-rock tunnels during excavation by 

using tunnel boring machines (TBMs). The first steps in combating a dust problem are to take 

dust samples to pinpoint the source, check the ventilation system, and check the dust collector. 

If the ventilation system and dust collector are operating properly, then other dust controls such 

as water sprays and conveyor belt scrapers must be upgraded. For tunnels in the design stage, 

recommended air quantities are provided. 

FINDING THE DUST SOURCE AND LOOKING FOR VENTILATION MALFUNCTIONS 

The first steps in fighting a dust problem are to take dust 

samples to pinpoint the source, check the ventilation 

system, and check the dust collector. Without knowing the 

exact source, efforts to reduce dust are hit-and-miss 

(mostly miss). 

Taking samples to pinpoint the dust source. In tunnels with high levels of airborne dust, the 

first task is to pinpoint where the dust enters the airstream. Most dust originates from rock 

breakage at the tunnel face, but the location where this dust enters the airstream can vary. Dust 

can leak from behind the TBM face shield, from gaps in the ventilation duct, or from a malfunctioning dust collector. It can be entrained into the air from the muck on a moving conveyor 

belt. It can even be shaken loose from the underside of the belt as it passes over the idlers. As a 

start, to locate the dust source, dust samples and air quantity measurements should be taken at the 

following locations: 
(1) At the portal or at the base of the entrance shaft 

(2) At a location one-third of the way from the portal to the TBM 

(3) At a location two-thirds of the way from the portal to the TBM 

(4) At the rear of the TBM trailing gear, about 50 ft toward the portal 

(5) At the middle of the TBM trailing gear 

(6) At the front of the TBM trailing gear 

(7) At the front of the TBM where ground support is installed 

(8) At the outlet of any ventilation duct if the outlet is inside the tunnel 

The dust samples can be 8-hr gravimetric filter samples, or they can be measurements taken 

with a light-scattering dust monitor. If the latter is used, repetitive readings must be made 

to ensure that observed changes in the dust level are not the result of changes in the TBM 

cutting rate. 

Figure 7-1 gives the results from a dust concentration survey in a tunnel with an exhaust ventilation system. 

 

98 

 

Figure 7-1.—Results from a dust concentration survey. 

Both gravimetric filter and light-scattering measurements were made at regular 

intervals between the portal and the front of the TBM. The figure shows that, for this tunnel, 

most of the dust breathed by workers entered the airstream between the TBM and the portal, 

either from the conveyor belt or a leaking ventilation duct. 

After the initial sampling, additional sampling in and around the TBM and trailing gear with a 

light-scattering dust monitor can provide useful information. Possible dust sources at the TBM 

include leakage from the head or from ventilation duct, emissions from rock drilling and 
 

99 

conveyor transfer points, or the stirring of settled dust by work activities and cooling fans. To 

assess which of these are relevant, a light-scattering dust monitor can be used to measure the dust 

level close to each suspected source. 

Figure 7-2 demonstrates the value of additional sampling around the TBM.

 

Figure 7-2.—Dust concentration measured near cutter head with TBM idle and operating. 

 In this tunnel, the 

only dust level of any consequence was measured at the front of the TBM near the cutter head as 

the cutter head operated. As the figure shows, the dust concentration rose (with little delay) after 

the cutter head began to rotate, then immediately dropped when the cutter head stopped. Rising 

and falling concentration profiles of this sort were only measured close to the cutter head, which 

indicates that the dust was leaking out somewhere close to the cutter head. 

Checking the ventilation system. Air quantity measurements, taken at the same locations as the 

dust samples, are to ensure that the ventilation system is operating properly. Hidden leaks in 

ventilation ductwork are common and may cause abnormally low air velocities in a portion of 

the tunnel. Thus, high dust levels may result from the simple failure to deliver enough air. Ventilation systems with multiple fans will inevitably leak and recirculate some air. The recirculated 

air will usually contain dust, and the amount of recirculation may be enough to create a dust 

problem. 

If recirculation is a concern, small holes should be drilled in the ventilation duct and the air pressure checked with the static pressure port of a Pitot tube. Exhaust systems should be under negative pressure, and blowing systems under positive pressure. Short regions of ductwork next to 

the fans may have the pressure reversed because of system imbalances, but reversed pressure 

regions should make up a very minor part of the ductwork. 
 

100 

If the dust concentration at the front of the TBM is much higher than that measured elsewhere, 

check to ensure that the ventilation duct is extended far enough forward. Exhaust duct must 

extend as far as the forwardmost worker, and ideally an additional 10 ft or more. Blowing duct 

must extend to within 20 ft of the forwardmost worker, assuming the jet of air emerging from the 

duct is unobstructed. 

Unusually warm air from the TBM electrical equipment may 

indicate a malfunctioning ventilation system. 

Occasionally, the ventilation system design includes some faults. Faulty designs inevitably 

result in higher dust levels. A common ventilation fault is the failure to provide overlap in 

auxiliary, or scavenger, systems. Figure 7-3 shows a properly operating scavenger system. The 

main fan acts to bring in clean air; the scavenger fan inlet is located in the clean air stream. 

 

Figure 7-3.—Auxiliary, or scavenger, system with adequate overlap. 

Figure 7-4 shows what happens when the proper overlap between the main duct inlet and the 

scavenger inlet is not maintained. The scavenger fan picks up some contaminated air returning 

from the face, so the amount of clean air delivered to the face is reduced. 

Clean air delivery also suffers in mismatched scavenger systems. Figure 7-5 shows a blowing 

main ventilation duct mismatched to a blowing scavenger system. The scavenger fan intake is a 

mixture of clean air from the main duct and contaminated air returning from the face. 

Another common problem found in tunnel ventilation systems is the low velocity zone created 

by moving similar quantities of air through ductwork in opposite directions. For example, figure 7-6 shows a tunnel with 5,000 cfm in a scavenger fan fresh air duct and 5,000 cfm in a dust 
 

 

101 

collector duct. Because these two ducts have similar air quantities moving in opposite directions, 

there is a zone of low air movement between them. Therefore, dust sources in this zone can produce high dust concentrations. 

 

Figure 7-4.—Auxiliary, or scavenger, system with no overlap. 

 

Figure 7-5.—Loss of ventilation efficiency from mismatched airflow directions. 

It should be noted that if the scavenger fan duct shown in figure 7-6 moved air in the opposite 

direction, the air quantity delivered to the immediate face area would be increased from 5,000 

to 10,000 cfm, and the amount of air moving through the zone between the ducts would be 

10,000 cfm. 
 

 Figure 7-6.—Zone of low air movement is created because ducts have similar air quantities moving in 

opposite directions. 

 

102

Checking the dust collector. Most dust is removed via the dust collector system (figure 7-7), 

so it is important that the system works properly. 

 

Figure 7-7.—TBM dust collection system. 

 Dust collectors in mines and tunnels can be 

high-maintenance equipment. Screens and filters often clog. Gaskets disappear, and access 

doors leak. Ductwork leading to the collector fills with coarse particulate that cuts off the airflow. Fans located on the inlet side of the collector suffer rapid erosion of their blades. Filters 

can be improperly seated, with air leaking around them. Filters also develop holes from abrasion 

by larger sized particulate. A dust sample and an air quantity measurement taken in the collector 

outlet will reveal if the filters are working properly and whether the air quantity is adequate. 
103 

UPGRADING THE DUST CONTROLS 

Upgrade the other dust controls when checks of the ventilation 

and dust collector show no correctable problems. The water 

spray system should adequately wet the broken rock. 

The dust controls on the drills and conveyor should also be 

upgraded if they are sources of dust. Consider using foam 

to control dust. 

Water sprays. Water sprays have two roles: (1) airborne capture and (2) surface wetting of the 

broken rock. Of the two, airborne capture is less effective. The typical water spray gives no 

more than 30% capture of respirable dust [Courtney and Cheng 1977]. Because of this, adequate 

surface wetting of the broken rock is most important. The vast majority of dust particles created 

during breakage are not released into the air, but stay attached to the surface of the rock [Cheng 

and Zukovich 1973]. Wetting the broken rock ensures that the dust particles stay attached. 

A key factor is the uniformity with which the rock is wetted [Hamilton and Knight 1957]. For 

example, in coal mining, releasing water near the cutting picks of rotating shearer drums is far 

more effective at suppressing longwall dust than external sprays on the shearer body, because the 

rotating drums act to mix the coal and the water. Increasing the number of sprays can also promote uniformity of wetting. For example, Bazzanella et al. [1986] showed that dust suppression 

is improved by increasing the number of sprays on a shearer drum, even when the total water 

flow and nozzle pressure were held constant by using smaller orifice nozzles. Increasing the 

number of nozzles on the drum from 17 to 46 lowered respirable dust by 60%. This is better 

than the dust reduction afforded by most other techniques. 

The lessons from this knowledge are twofold. First, it is best to fully wet the material during the 

breakage process. This is when most mechanical mixing is likely to take place, and it ensures 

that the benefits will carry over to any downstream secondary handling operation. Because of 

this improved mixing, it is better to have an additional 30 gpm at the cutter head than to have 

10 gpm at each of three conveyor transfer points downstream. Also, it gives more time for the 

water to soak in and the excess to drain away. Second, best uniformity of wetting is achieved by 

using more nozzles at lower flow rates and ensuring that the nozzles are aimed at the broken 

material rather than just wetting an adjacent metal or rock surface. 

As little as 1% of moisture on dry rock significantly reduces dust. However, since it is hard to 

achieve a uniform application of such a low moisture level underground, the best moisture content might be as high as 5%. Whether this much water is always practical is another matter, 

so one should ensure that the water is being uniformly applied before automatically raising the 

flow rate. For instance, on a TBM, sprays located on the rotating head will be more effective 

than fixed sprays at the crown, and sprays aimed to intercept the falling muck will be more effective than those aimed at the uncut face. One way to improve the airborne capture of water sprays 

is to raise the pressure to 500 psi or more. However, a marked disadvantage of high-pressure 

sprays is that they entrain large volumes of air. This can lead to more dispersal of dust than is 
104 

captured. Because of this, their application is limited to enclosed or semienclosed spaces, such 

as the cutting head area of a TBM. 

 

Aside from efforts to improve spray effectiveness, one of the most helpful actions a contractor 

can take is to provide some automatic feature that turns sprays on and off as needed. This allows 

sufficient wetting while helping to avoid the problems associated with overuse of water. If the 

dust standard is below 1 mg/m3

 because of silica, then spray water should be clean because the 

evaporation of dirty water can release dust from dissolved minerals. Frequent clogging of spray 

nozzles from particulates in the water line can also be a problem. In such cases, water line filtration can reduce clogging. 

Control of drill dust. It is better to control drill dust at the source than to depend on ventilation 

to carry the dust cloud away. Drill dust controls can be particularly effective. The best method 

is to introduce water through a hollow drill stem [ILO 1965; Page 1982]. Less effective are 

water sprays at the collar of the hole and dry dust collectors that capture the dust cloud near the 

collar and filter it out [Page and Folk 1984]. Most failures of drill dust controls are readily found 

and corrected. Rather than mechanical breakdown of the controls, malfunctions generally result 

from oversights such as a failure to turn on water or to service clogged filters. 

Control of conveyor dust. Conveyor belts can generate large amounts of dust. Methods to deal 

with belt dust are well known [Goldbeck and Marti 1996; Swinderman et al. 1997]. The following questions must be addressed if belt dust is high. 

1. Are transfer points enclosed? A simple enclosure with a spray or two inside of it may be 

adequate. If this is not enough, the air inside must be exhausted to a dust collector or 

ventilation duct, with all of the leakage points on the enclosure sealed properly 

[Swinderman et al. 1997]. 

2. Is the material being conveyed adequately wet, but not so much that it leaves a sticky 

mud residue on the belt? When this residue dries, dust is released. Thus, an end result of 

excessive wetting can be an increase in belt dust. 

3. Are the undersides of both the top and the bottom belts being wetted [Ford 1973] so that 

dust sticking to the belt is not shaken loose by the idlers? Does the belt stay wet or is it 

drying out and releasing dust? 

4. Are the belt scrapers working properly? Is a second set of scrapers being used? Has a 

belt washing system been installed [Bennett and Roberts 1988; Stahura 1987]? 

5. Is the belt running true and not spilling its contents [Swinderman et al. 1997]? 

More information on conveyor belt dust control can be 

found in chapter 6 on hard-rock mines. See page 86. 
105 

Foam. The use of foams for dust control has been studied extensively in coal mines. Here, 

foam works better than water, providing dust reductions in the 20%-60% range compared to 

water. Foam also can produce similar results at lower water use. Seibel [1976] compared 

15-20 gpm of high-expansion foam to 19 gpm of water at a belt transfer point. Compared to 

water, the foam averaged 30% more dust reduction. Mukherjee and Singh [1984] found that 

foam released from a longwall shearer drum cut the dust 50% compared to conventional sprays 

on the drum. Also, the system used only half the water. The drawback of foam is high cost. 

The benefits of improved mixing and uniformity of wetting have also been obtained with foam. 

Foam effectiveness was far greater when it was mechanically mixed in with the coal [Mukherjee 

and Singh 1984] or silica sand [Volkwein et al. 1983]. Page and Volkwein [1986] have published a comprehensive review of foam for dust control in mining and minerals processing. 

DESIGN STAGE VENTILATION PLANNING 

● The quantity of air needed for dust control 

● Whether to use exhaust or blowing ventilation 

When tunnel excavation is underway, major ventilation upgrades are usually not practical. 

However, for tunnels in the design stage, sufficient airflow must be planned into the design. 

Ideally, ventilation systems should be designed to achieve 100 ft/min air velocity throughout the 

tunnel, including the TBM and its trailing gear. This 100 ft/min must be regarded as a minimum 

if the rock has over 10% of crystalline silica. For large-diameter tunnels, 60 ft/min is the minimum. Other considerations, such as dilution of methane gas or diesel fumes, may require higher 

velocities. 

Whether to use exhaust or blowing ventilation is always a key issue. Within the region of the 

TBM and trailing gear, exhaust ventilation is best for dust control. When exhaust ventilation is 

used, the zone of low air movement between the ventilation and dust collector ducts (see figure 7-6) is avoided, and both systems work together to maximize fresh air delivery. Between the 

rear of the trailing gear and the portal, the main ventilation system could be either exhaust or 

blowing. If the main ventilation system is exhaust, then the ventilation and dust collector ducts 

from the trailing gear must feed directly into it. If the main system is blowing, then some overlap with the TBM trailing gear systems must be maintained, as shown in figure 7-3. 

Ventilation estimates must consider a realistic estimate of air leakage in the ductwork. In planning a tunnel ventilation system, a duct leakage of 20%-50% can be expected. The most common mistake in ventilation system design is the failure to consider enough leakage. Contractors 

should avoid using flexible, spiral-wound ventilation duct for any purpose other than as a short 

connection between sections of rigid metal duct. The pressure drop in spiral-wound duct is very 

high compared to smooth metal duct. 
106 

Finally, designers of ventilation systems must also plan to extract a sufficient quantity of air from 

the cutter head area behind the dust shield in order to prevent dusty air from leaking out. Myran 

[1985] has given the following recommendations on the amount of air that should be extracted: 

Tunnel Airflow 

diameter, ft range, cfm 

10 4,000-6,000 

15 7,000-10,000 

20 12,000-17,000 

25 19,000-26,000 

These airflows can be hard to achieve because they require large fans and ductwork, not to mention large dust collectors. Why such high airflow from what is presumably an enclosed space? 

First, the stirring action of the large rotating cutter head creates considerable source turbulence, 

which disrupts the normal inflow of air that acts to contain the dust. Second, there is far less 

enclosure of the cutter head than a casual inspection of a TBM would indicate. Depending on 

the TBM design, the entire belt conveyor access space can be wide open. Also, there is open 

space when the grippers at the head expand to press out against the tunnel walls. In addition to 

raising the airflow, dust reduction efforts have focused on reducing the open space available for 

the dust to leak out by enclosing the conveyor tunnel and by installing single or even double sets 

of rubber dust seals between the grippers and TBM body. 

REFERENCES 

Bazzanella A, Becker H, Kemper F [1986]. Staubbekampfung in abbaubetrieben mit 

schneidender kohlengewinning. Gluckauf 122(11):728-735. Also available in translation as: 

Dust suppression in shearer faces, Gluckauf Translation 122(11):204-207. 

Bennett DJ, Roberts AW [1988]. Carry-back measurements to evaluate the design, selection, 

and performance of belt cleaning systems. Mechanical Engineering Transactions, The Institution 

of Engineers, Australia. Vol. ME13, No. 4, December, pp. 215-221. 

Cheng L, Zukovich PP [1973]. Respirable dust adhering to run-of-face bituminous coals. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 7765. NTIS No. PB 221-883. 

Courtney WG, Cheng L [1977]. Control of respirable dust by improved water sprays. In: 

Respirable Dust Control – Proceedings of Technology Transfer Seminars, Pittsburgh, PA, and 

St. Louis, MO, IC 8753, pp. 92-108. NTIS No. PB 272 910. 

Ford VHW [1973]. Bottom belt sprays as a method of dust control on conveyors. Min Technol 

(U.K.) 55(635):387-391. 
107 

Goldbeck LJ, Marti AD [1996]. Dust control at conveyor transfer points: containment, suppression, and collection. Bulk Solids Handling 16(3):367-372. 

Hamilton RJ, Knight G [1957]. Laboratory experiments on dust suppression with broken coal. 

London, U.K.: National Coal Board, Mining Research Establishment Report No. 2083. 

ILO [1965]. Guide to the prevention and suppression of dust in mining, tunnelling, and quarrying. Geneva, Switzerland: International Labour Organization. 

Kissell FN [1996]. How to control air contaminants during tunnel construction. Pittsburgh, PA: 

U.S. Department of the Interior, Bureau of Mines, IC 9439. NTIS No. PB96-147558. 

Mukherjee SK, Singh MM [1984]. New techniques for spraying dust. Coal Age June:54-56. 

Myran T [1985]. Tunnel boring machines in Norway: ventilation and dust problems. In: 

Proceedings of the Second U.S. Mine Ventilation Symposium (Reno, NV). 

Page SJ [1982]. An evaluation of three wet dust control techniques for face drills. Pittsburgh, 

PA: U.S. Department of the Interior, Bureau of Mines, RI 8596. NTIS No. PB82-177320. 

Page SJ, Folk M [1984]. Keystone achieves positive dust control during dry drilling. Eng Min J 

185(9):84-85. 

Page SJ, Volkwein JC [1986]. Foams for dust control. Eng Min J 187(10):50-52, 54. 

Seibel RJ [1976]. Dust control at a transfer point using foam and water sprays. Pittsburgh, PA: 

U.S. Department of the Interior, Bureau of Mines, TPR 97. NTIS No. PB-255-440. 

Stahura RP [1987]. Conveyor belt washing: is this the ultimate solution? TIZ-Fachberichte 

111(11):768-771. ISSN 0170-0146. 

Swinderman RT, Goldbeck LJ, Stahura RP, Marti A [1997]. Foundations 2: the pyramid 

approach to dust control and spillage from belt conveyors. Neponset, IL: Martin Engineering. 

Volkwein JC, Cecala AB, Thimons ED [1983]. Use of foam for dust control in minerals 

processing. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8808. NTIS 

No. PB84-131184. 
 

109 

CHAPTER 8.—HOW TO FIND THE MAJOR DUST SOURCES 

By Fred N. Kissell, Ph.D.,77

77Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

and Jon C. Volkwein1 

In This Chapter 

9 Instruments for measuring dust 

9 How to calculate the amount of dust from a source 

9 How to get a valid concentration measurement 

9 Sampling to assess control technology effectiveness 

When there is more than one source of dust, sampling may be required to find which dust 

sources are most significant. Then, efforts to reduce dust can be concentrated where they will 

have the most impact. 

This chapter explains how to perform dust source sampling. It describes two kinds of 

instruments that are available and discusses their limitations. It explains how environmental 

variables such as concentration gradients, dust dilution, and production changes can impact dust 

measurements. It also suggests practical ways to improve the validity of dust source measurements under adverse conditions, such as high-velocity airflow or the presence of water mist in 

the air. 

Dust source sampling at coal mine longwalls and at 

tunnels is more complicated. Chapters 3 and 7 have more 

information on sampling in those circumstances. 

TWO KINDS OF INSTRUMENTS FOR MEASURING DUST 

Gravimetric samplers. The conventional gravimetric sampler is a good device for measuring 

dust because it is the instrument used for compliance measurements. This dust sampler consists 

of an air pump, a small cyclone that separates out the respirable size fraction of the dust cloud, 

and a filter to collect the respirable dust. 

In coal mines, the Mine Safety and Health Administration (MSHA)-approved gravimetric 

sampler uses a 10-mm Dorr-Oliver cyclone operating at an airflow of 2.0 L/min [30 CFR78

78Code of Federal Regulations. See CFR in references. 

 74 

(2002)]. A correction factor of 1.38 is applied to make the results consistent with the U.K. MRE 

sampler, the instrument on which the 2.0 mg/m3

 coal dust standard is based. 
 

110 

In noncoal mines, the gravimetric sampler uses a 10-mm Dorr Oliver cyclone operating at 

1.7 L/min. No correction factor is applied, consistent with MSHA’s metal/nonmetal regulations 

[30 CFR 57.5001 (2002)]. 

In tunnels under construction, Occupational Safety and Health Administration (OSHA) regulations [29 CFR 1910.1000 (2002)] apply, so any gravimetric sampler with an OSHA-approved 

cyclone operating at the recommended flow rate is satisfactory. 

To get the best possible accuracy with gravimetric samplers, sampling pumps must be calibrated 

[MSHA 1999], the cyclones must be clean and the filters must be weighed accurately. For accurate filter weighing, the filters must be desiccated to remove moisture, and the weighing must be 

done in a temperature- and humidity-controlled room. Extra attention is required if the amount 

of silica is being measured. Page et al. [2001] found that when the dust mass on the filter is 

below 0.5 mg, the silica error climbs rapidly. In such cases, it may be necessary to sample with 

one filter for several shifts to accumulate sufficient mass on the filter. 

Even when these precautionary steps are followed, gravimetric dust samplers do not give very 

precise results when used under field conditions. Recent testing [Kissell and Sacks 2002] has 

shown that the measured dust concentration has a relative standard deviation (RSD) averaging 

12% when samplers are placed within a few inches of each other at a fixed site underground. 

Under poor sampling conditions, such as outside in the wind and rain, RSD values as high as 

50% have been found for a filter mass as high as 3.5 mg [Page et al. 2001]. 

Direct-reading dust instruments. The most common direct-reading instruments measure dust 

using a light-scattering technique. These instruments are valuable for short-term relative comparisons, such as comparing dust levels with a fan turned on and then turned off or comparing 

dust levels at two adjacent locations. Direct-reading instruments can also discern if a 

background dust source will cloud data interpretation. However, since dust levels are constantly 

rising and falling as mining proceeds, multiple readings must always be taken to ensure that a 

representative dust level is being measured. 

Dust concentration values from direct-reading instruments cannot be interpreted as absolute 

gravimetric values. Direct-reading instruments that use light scattering are too sensitive to shifts 

in the size distribution of the dust, as well as a host of other factors that cause errors [Williams 

and Timko 1984; Smith et al. 1987; Tsai et al. 1996]. In field use, when compared to gravimetric 

samplers, measurement errors of 100% in direct-reading dust instruments are not unusual [Page 

and Jankowski 1984]. These errors are especially high at concentrations under 0.5 mg/m3

. 

Lastly, direct-reading dust instruments based on light scattering can be adversely affected by 

water mist in the air. Water mist causes them to show a dust level much higher than the actual 

level. Adding a mist eliminator designed by Cecala et al. [1985]79

79A commercial version of the mist eliminator (Model 3062 Diffusion Dryer) is available from TSI, Inc., Shoreview, MN. 

can correct this problem. The 
111 

mist eliminator consists of a 24-in-long wire-mesh tube surrounded by calcium sulfate desiccant 

(figure 8-1). It is placed between the detector and the 10-mm cyclone used to preclassify the 

respirable size range and removes water mist without trapping dust. 

 

Figure 8-1.—Mist eliminator for direct-reading instruments that use light scattering [Cecala et al. 1985]. 

The most useful direct-reading dust instruments collect a 

gravimetric filter sample along with an electronic record of 

the average light-scattering value. The users of such 

instruments can then make the comparisons needed to 

assess the validity of the light-scattering value.80 

80Currently, only one direct-reading sampler is approved for use in underground coal mines—the 

personal DataRAM made by Thermo Anderson, Smyrna, GA. 

HOW TO CALCULATE THE AMOUNT OF DUST FROM A PARTICULAR SOURCE 

Calculating the amount of dust from a particular source is not complicated. The dust concentrations upwind and downwind of the source are measured. Also, the volume of air passing the 

source is obtained by measuring the air velocity and cross-sectional area of the airway. The difference in the dust concentration values multiplied by the air volume gives the mass of dust generated by the source. This mass of dust can be calculated in terms of unit of time (mg/min) or 

unit of production (mg/ton), if production data are available [Volkwein 1979]. 

Another approach to calculating the amount of dust from a source is to turn the dust source on 

and off, if it is practical to do so. The dust concentration can be measured by a direct-reading 

instrument or by two packages of gravimetric samplers alternately turned on and off along with 

the dust source. The amount of dust produced by the source is then calculated from the difference in the readings. The problem is obtaining a valid concentration measurement. 

 
 

112 

OBTAINING A VALID CONCENTRATION MEASUREMENT 

Many environmental factors can invalidate dust source 

measurements. 

To avoid sampling errors caused by environmental factors, review the following dust sampling 

checklist. 

DUST SAMPLING CHECKLIST 

1. Is there little to no airway concentration gradient? 

2. Is the sampling location within 100 ft of the dust source? 

3. Is there no air dilution between the dust source and the sampling 

location? 

4. Is the air velocity past the source and past the sampling location 

at least 50 ft/min but not over 800 ft/min? 

5. Is the type and amount of material mined during sampling 

representative of normal mining conditions? 

If the answer to all of the above questions is “yes,” then dust sampling may be done without further precautions other than keeping the instruments at least 3 ft above the mine floor.81

81People and passing equipment will kick up dust, making floor samples invalid. 

 If the 

answer to any question is “no” or “I don’t know,” then the following sampling precautions must 

be considered. 

Checklist item No. 1: Sampling in airways with a concentration gradient. Many sampling 

locations have large concentration gradients. At such locations, the measured concentration 

changes as the sampler is moved. In fact, moving the sampler a foot one way or the other may 

change the dust concentration reading more than any other factor. For example, Kost and 

Saltsman [1977] showed that a gravimetric sampler located 3 ft in front of a continuous miner 

operator may indicate a respirable dust concentration twice that of the operator’s, whereas only a 

few feet behind the operator the indicated concentration may be half. This reflects a concentration gradient observed by moving closer to or farther away from the dust source. 
 

113 

Other concentration gradients can be observed by 

moving from side to side in an airway. Such sideto-side concentration gradients exist because the 

dust cloud from the source has not fully mixed 

into the airstream.82

82In some places, such as behind a coal mine line curtain, there may be a top-to-bottom gradient. Vertical gradients 

are likely when the air passage height is greater than the width, especially when the dust source releases heat. 

The concentration gradient at 

longwall faces demonstrates this incomplete mixing. The disparity in concentrations depends on 

the distance between the source (the shearer) and 

sampling point. Figure 8-2 shows two crosssectional concentration gradients measured at least 

200 ft downwind of the shearer.

 Figure 8-2.—Two gob-to-spillplate dust concentration gradients measured downwind of a 

longwall shearer [Kissell et al. 1986]. 

 Even at this distance, shearer dust, mainly in the panline and 

spillplate, has not dispersed equally into the walkway and area around the support legs. 

Because concentration gradients are so common in 

underground operations, any sampling program to 

measure the amount of dust produced by a source 

should test for gradients first. This testing is 

accomplished by using a direct-reading instrument, moving it back and forth across the airway, 

or by using three or more gravimetric samplers 

spaced evenly across the airway. When concentration gradients are found, multiple samplers 

must be used to obtain valid results. 

Checklist item No. 2: Sampling within 100 ft of the source to avoid dust deposition 

problems. A way to reduce the impact of dust gradients across mine entries might be to move 

farther downwind from the source so that the dust has more time to mix evenly into the airstream. However, this does not work in practice because turbulent deposition of dust particles 

causes a decrease in the concentration over relatively short distances. For example, in experiments on a 7-ft-high U.K. longwall face, Ford [1976] found that 45% of a 4-μm particle size dust 

cloud was deposited within a distance of 600 ft. At other longwalls where face heights were 

lower, deposition increased. In a U.S. study over a similar 600-ft distance in an uncluttered mine 

airway, Bhaskar et al. [1988] measured 38% deposition of respirable dust at air velocities over 

300 ft/min and 67% deposition at an air velocity of 165 ft/min. Because of this high deposition 

rate, dust sampling aimed at calculating a source emission should be done within 100 ft of 

the source. 

Checklist item No. 3: Sampling where air dilution has lowered the dust concentration. The 

validity of sampling results is also affected if the airstream being sampled is not representative of 

the dust source. For example, when sampling is done downwind of mining machines, the measured concentration is not always a reliable indicator of the amount of dust produced by that 
 

114 

machine. The intake air is likely to contain some 

dust even before it reaches the machine, so the 

amount of intake dust must also be measured and 

subtracted from the downwind measurement. 

Also, if air is gained or lost between the source 

and sampling point, corrections must be made. 

Line curtain leakage (figure 8-3), a common 

occurrence on continuous miner faces, is an 

example of how air is gained, thereby diluting the 

dust level measured in the return. 

 Figure 8-3.—Air in return diluted by line curtain leakage [Kissell et al. 1986]. 

 As the heading 

advances, the amount of air gained will increase; 

in fact, a leakage of 50% is common. To calculate 

a machine dust emission rate in this case, it is 

necessary to multiply the measured concentration 

by the airflow at the sampling point. Comparisons 

can then be made on the basis of dust weight per 

unit time or per ton of material mined. 

If air is lost between the source and the sampling 

point, no change in dust concentration will occur. 

However, the machine emission rate cannot be calculated unless it is known exactly how much air 

was lost. 

Checklist item No. 4: Sampling in a lowvelocity airflow under 50 ft/min. In workplaces 

where the airflow is less than 50 ft/min, the magnitude of the source can be roughly assessed by 

moving a direct-reading instrument alternately 

toward and away from it. This movement must be 

repeated many times, preferably from different directions, to ensure that any observed increases 

in dust level result from getting closer to the source rather than from an extraneous factor, such 

as a change in production. 

Checklist item No. 4: Sampling in high-velocity airflow over 800 ft/min. In air streams with 

velocities up to 300 ft/min, neither the air velocity nor the cyclone inlet orientation has any 

impact on the dust concentration measured by the sampler [Caplan et al. 1973]. However, at air 

velocities over 300 ft/min, both the air velocity and the cyclone inlet orientation have an impact. 

Cecala et al. [1983] found that when the Dorr-Oliver cyclone inlet83

83Strictly speaking, it is the vortex finder clamp that is pointed directly into the wind. The inlet enters the cyclone at 

a slight angle. 

is pointed directly into the 

wind, it oversamples when the air velocity exceeds 800 ft/min. At 2,000 ft/min, it oversamples 

by 35%. When the cyclone inlet is at a right angle to the wind or pointed downwind, it undersamples when the air velocity exceeds 300 ft/min. 
115 

Cecala et al. [1983] also tested a shielded cyclone to see if a shield would reduce the over- and 

undersampling. The shield was a 1-in-wide strip of aluminum sheet bent into a cylinder. This 

cylinder was then wrapped around the top of the cyclone and bolted to the hole in the back of 

the vortex finder clamp (figure 8-4).

Figure 8-4.—Cyclone shield for high-velocity air streams. 

 Testing showed that the shield successfully reduced both 

the over- and undersampling to within 14% of the true value up to the highest velocity tested 

(2,000 ft/min). 

Another way to sample high-velocity airstreams is to use 

an isokinetic probe, in which the velocity of the air 

entering the probe is matched to that of the airstream 

[Quilliam 1994]. However, because the equipment is more 

specialized and less portable, isokinetic sampling is more 

suited to labs and industrial sites than underground 

mines. 

Checklist item No. 5: Sampling during changes in the type of material cut and changes in 

production. In coal mines, cutting rock bands in the coal will cause a wide variation in dust levels. A rock band is a band of rock, typically shale, layered within the coal seam. The amount of 

dust generated by cutting the rock band is much greater than that from cutting the coal, so even a 

minor rock band will cause dust levels to increase substantially. 

Variations in production also cause 

substantial dust level changes. 

Shift-to-shift changes in production 

by a factor of two are common in 

all types of mines. Dust 

concentration values may be 

corrected for shift production when 

production changes are due to 

incidents such as equipment 

breakdowns. In this case, a lower 

shift dust concentration is due to 

less mining time. However, if shift 

production is low because of hard 

cutting through rock, dust levels 

may be higher due to the rock itself. 

If the concentration level data are 

then corrected for production, the 

errors will be magnified greatly. 

The only course of action is to 

sample when the type and amount 

of material mined are representative 

of normal mining conditions. 
116 

In-depth information on dust instrumentation and 

measurements can be obtained from Baron and Willeke 

[2001]. Raymond [1998] describes the equipment and 

procedures used by MSHA to maintain a modern dust 

sample weighing facility. Parobeck and Tomb [2000] 

describe MSHA procedures to measure the silica 

content of mine dust samples. 

SAMPLING TO ASSESS CONTROL TECHNOLOGY EFFECTIVENESS 

Most mine operators depend on compliance sampling to assess whether any control technology 

that they installed works as promised. Although the methods described above require more 

effort, they are a better way to measure control technology effectiveness simply because it is 

easier to measure a change in a dust source when that source is isolated from other dust sources. 

However, it pays to keep in mind that the relative standard deviation of gravimetric samplers 

under typical field conditions is 12%. Additional error is contributed by environmental variables 

such as production changes and concentration gradients. In addition to these errors, the evaluation of a dust control method is constrained by the combined error of measurements with and 

without controls. For these reasons, assessment of dust control effectiveness is limited to those 

technologies that give at least a 25% change in dust levels. 

REFERENCES 

Baron P, Willeke K [2001]. Aerosol measurement. New York: Wiley Interscience Publishers. 

Bhaskar R, Ramani RV, Jankowski RA [1988]. Experimental studies on dust dispersion in mine 

airways. Min Eng 40(3):191-195. 

Caplan KJ, Doemeny LJ, Sorenson S [1973]. Evaluation of coal mine dust personal sampler 

performance. U.S. Department of Health, Education, and Welfare contract PHCPE-R-70-0036 

Cecala AB, Volkwein JC, Thimons ED [1985]. Adding steam to control dust in minerals 

processing. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8935. NTIS 

No. PB 85-198885. 

Cecala AB, Volkwein JC, Timko RJ, Williams KL [1983]. Velocity and orientation effects on 

the 10-mm Dorr-Oliver cyclone. Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, RI 8764. NTIS No. PB 83-214387. 

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, Office 

of the Federal Register. 
117 

Ford VHW [1976]. Investigations into the deposition of airborne respirable dust along underground airways. Mining Research and Development Establishment (MRDE) Report No. 65. 

National Coal Board, U.K. 

Kissell FN, Sacks HK [2002]. Inaccuracy of area sampling for measuring the dust exposure of 

mining machine operators in coal mines. Min Eng 54(2):33-39. 

Kissell FN, Ruggieri SK, Jankowski RA [1986]. How to improve the accuracy of coal mine dust 

sampling. AIHA J 47(10):602-606. 

Kost JA, Saltsman RD [1977]. Evaluation of the respirable dust area-sampling concept as 

related to the continuous miner operator. Bituminous Coal Research, Inc., Report L-792. 

MSHA [1999]. Calibration and maintenance procedures for coal mine respirable dust samplers. 

Arlington, VA: U.S. Department of Labor, Mine Safety and Health Administration, IR 1240. 

Page SJ, Jankowski RA [1984]. Correlations between measurements with RAM-1 and gravimetric samplers on longwall shearer faces. AIHA J 45(9):610-616. 

Page SJ, Organiscak JA, Mal T [2001]. The effects of low quartz mass loading and spatial variability on the quartz analysis of surface coal mine dust samples. Appl Occup Environ Hyg 

16(9):910-923. 

Parobeck PS, Tomb TF [2000]. MSHA’s programs to quantify the crystalline silica content of 

respirable mine dust samples. SME preprint 00-159. Littleton, CO: Society for Mining, 

Metallurgy, and Exploration, Inc. 

Quilliam JH [1994]. Isokinetic sampling. J Mine Vent Soc S Afr 10(7):153. 

Raymond LD [1998]. Coal mine dust sample processing. Arlington, VA: U.S. Department of 

Labor, Mine Safety and Health Administration, IR 1249. 

Smith JP, Baron PA, Murdock DJ [1987]. Response characteristics of scattered light aerosol 

sensors used for control monitoring. AIHA J 48(3):219-229. 

Tsai CJ, Shih TS, Lin JD [1996]. Laboratory testing of three direct-reading dust monitors. 

AIHA J 57:557-563. 

Volkwein JC [1979]. Dust control in bagging operations. In: Industrial Hygiene for Mining and 

Tunneling – Proceedings of a Topical Symposium. Cincinnati, OH: American Conference of 

Governmental Industrial Hygienists. 

Williams KL, Timko RJ [1984]. Performance evaluation of a real-time aerosol monitor. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 8968. NTIS PB 84-199710. 

‌
 

119 

CHAPTER 9.—DUST RESPIRATORS IN MINES AND TUNNELS 

By Fred N. Kissell, Ph.D.,84

84Research physical scientist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

and William A. Hoffman85 

85Physical scientist, National Personal Protective Technology Laboratory, National Institute for Occupational Safety 

and Health, Pittsburgh, PA. 

In This Chapter 

9 MSHA regulations for coal mines 

9 MSHA regulations for metal/nonmetal mines 

9 OSHA regulations for tunnel construction 

9 Types of respirators used in mines and tunnels 

9 Filter materials and filter efficiencies 

9 Donning, seal checking, and maintenance 

9 Filter service life 

and 

9 Respirator information resources 

In many cases, engineering controls are not adequate to achieve satisfactory dust levels, so respirators must be used. This chapter explains the Federal regulations governing the use of dust 

respirators in mines and tunnels and describes the most common dust respirators used. Filter 

materials and filter efficiencies for respirators are discussed. This chapter also gives some guidelines for respirator use and recommends sources for more dust respirator information. Respirator 

effectiveness in reducing dust exposure usually exceeds the effectiveness of most engineering 

control methods. 

RESPIRATOR REGULATIONS 

Different regulations govern respirator use in coal mines, 

metal/nonmetal mines, and tunnels under construction. 

Coal mines under Mine Safety and Health Administration (MSHA) jurisdiction. Coal mine 

operators are required to meet dust standards using only engineering control methods. Typical 

engineering control methods include ventilation and water sprays. Respirators are not regarded 

as an engineering control method, so respirators cannot be used in lieu of engineering controls. 
 

120 

However, if dust levels exceed the 2.0 mg/m3 coal dust standard,86

86If the coal contains silica, the standard is lowered according to a formula prescribed by MSHA. 

approved respirators must be 

made available87

87Operators must also maintain a supply of respirators consistent with this need. 

to workers [30 CFR88

88Code of Federal Regulations. See CFR in references. 

 70.300] while new engineering controls are being instituted. Respirators must also be provided to workers exposed to high-inhalation hazards for short 

periods.89 

89In the MSHA program policy manual, the term “short periods” is interpreted as the time required to drill three or 

four holes for trolley hangers, to drill shot holes in a roof fall, etc. 

Coal mine operators may also choose to establish a respiratory protection program, as set forth 

by the American National Standards Institute (ANSI Z-88.2-1969)90

90The current version is ANZI-88.2-1992, but the MSHA regulations are based on the 1969 version. 

 [ANSI 1969; 30 CFR 

72.710]. Such programs must include written procedures containing provisions for training, fittesting, maintenance, recordkeeping, and a requirement that users be clean-shaven [MSHA 

1995]. According to MSHA, if there is a respiratory protection program, the existence of such a 

program may form the basis for further extensions of abatement times or help to create an argument that a violation is less serious. However, a program will not prevent the issuance of citations for exceeding the dust standard. 

Metal/nonmetal mines under MSHA jurisdiction. MSHA metal/nonmetal regulations are 

somewhat less restrictive than the coal regulations. Removal of dust by engineering controls 

remains the required method. However, when accepted engineering control measures have not 

been developed or when the dust standard is exceeded on an occasional basis, respiratory equipment may be used without a citation being issued, provided that all of the following requirements 

are met: 

1. The respirators used must be approved by NIOSH under 42 CFR 84. 

2. A respiratory protection program, as set forth by ANSI Z-88.2-1969 [ANSI 1969], 

is or has been instituted [30 CFR 56.5005; 30 CFR 57.5005]. 

3. When respiratory protection is used in atmospheres immediately dangerous to life, 

a second worker with backup equipment and rescue capability is required. 

Tunnels under Occupational Safety and Health Administration (OSHA) jurisdiction. 

Under OSHA, engineering controls are also the required method of dealing with dust. However, 

OSHA regulations permit respirators to be used in place of engineering controls if engineering 

controls are not feasible or while engineering controls are being instituted [29 CFR 

1910.134(a)(1)]. 

If respirators are used, a respiratory program is required to ensure that respirators are used properly and employees are protected [29 CFR 1910.134(c)]. This program has several required elements. The major ones are [OSHA 1998a]: 
 

121 

1. A worksite-specific document explaining the respiratory protection program. 

2. Selection of a designated administrator who is qualified to oversee the program. 

3. A medical evaluation to determine the employee’s ability to use a respirator. 

4. Fit-testing of respirators to ensure minimal leakage. 

5. Training in respirator use and care, particularly “user seal checks” by the wearer. 

The OSHA “Voluntary Use” Program. For workplaces that are in compliance with dust 

standards, employers can permit their workers to wear air-purifying respirators under a 

“voluntary use” arrangement if they choose to do so [29 CFR 1910.134(c)(2)]. In this case, 

a program document, a medical evaluation, and respirator maintenance are all still required. 

No training is required [OSHA 1998b], but employees must be provided with advisory information [29 CFR 1910.134 appendix D]. Fit-testing is not necessary [OSHA 1998c], and less 

experience is required of the program administrator. 

Some of the voluntary use program requirements (program document, medical evaluation, and 

respirator maintenance) do not apply to workers who voluntarily use dust masks [OSHA 1998b]. 

However, users of dust masks must be provided with the advisory information in 29 CFR 

1910.134 appendix D. 

TYPES OF RESPIRATORS USED IN MINES AND TUNNELS 

Mine operators usually choose half-mask respirators, 

dust masks, or air helmets equipped with particulate 

filters.91

91All must be NIOSH-approved under the requirements of 42 CFR 84. The half-mask replaceable filter respirators 

and the dust masks are classified as “air-purifying respirators” (APRs); the air helmet is classified as a “powered airpurifying respirator” (PAPR) because it is powered by a small fan. 

 Half-mask respirators and dust masks are convenient for confined surroundings. Air helmets are suitable when more space is available, such as at longwall 

faces in high coal. 

Half-mask replaceable-filter respirators. Half-mask replaceable-filter respirators (figure 9-1), 

also known as reusable half-masks, consist of a filter-holding unit, fabricated from molded plastic or rubber, that contains intake and exhaust valves. Soft rubber is used to form a facepiece 

around the filter-holding unit, which forms a seal against the wearer’s face. This seal prevents 

dust-laden air from bypassing the filter as the user inhales. If the facepiece seal is leak-tight, 

the respirator should remove 90% or more of the respirable dust. 
 

 

Figure 9-1.—Half-mask replaceable-filter respirator. 

122 

Although the half-mask replaceable-filter respirators do a reasonable job of dust removal when 

the facepiece seal is leak-tight, the seal can occasionally cause skin irritation. These respirators 

also interfere with conversation and may interfere with eyeglasses or goggles. 

Many different types of filter materials are 

available for half-mask respirators. Some filter materials are degraded by oil mist. The 

replaceable filter cartridges are designated 

according to their level of oil resistance, 

as follows: 

Type N filters are Not resistant to oil; 

Type R filters are oil-Resistant up to 

one shift; and 

Type P filters are oil-Proof. 

For coal dust or for mineral dusts such as 

silica, any of these types of filters is satisfactory. Some mines have oil mist sources; 

the most common are percussion drills. 

These mines should use type R or type P 

filters. 

The dust (or mist) collection efficiency of 

filter materials also varies; the efficiency 

is specified along with the oil resistance. 

Filter cartridges are available in three 

efficiency levels: 95%, 99%, and 99.97%, 

designated as 95, 99, and 100. For example, an N95 filter is 95% efficient; an N100 filter is 

99.97% efficient. 

Actually, filter efficiencies for respirable dust are much higher than the specified filter efficiency. This is because the specified filter efficiencies are measured using the size of particles 

that are most likely to get through the filters—about 0.3 μm in diameter. Most respirable dust is 

larger than this, which makes it easier to filter. Thus, a filter that is 95% efficient for 0.3 μm particles will exhibit a much greater efficiency for respirable dust. 

The most commonly purchased filter types are N95s and P100s. Type 95 filters usually have a 

lower cost and lower breathing resistance than type 100 filters. 

While filter efficiencies may be very high, it does not follow that workers are protected with the 

same degree of efficiency.92

92Keep in mind that efficiency numbers quoted in respirator catalogs only refer to filter efficiency. 

 For instance, the rule-of-thumb efficiency for half-mask respirators 

is 90% for respirators that give a good fit. This is lower than the filter efficiency because some 

leakage at the seal against the wearer’s face usually occurs. For example, during one respirator 
 

123 

evaluation program [Cole 1984], half-mask respirators were tested on four longwall sections. 

The dust exposure of workers was reduced by 92%. 

Dust masks. Dust masks (also known as 

filtering facepiece respirators) (figure 9-2) 

have a lighter and simpler design than halfmask respirators.

 Figure 9-2.—Dust mask, also called a filtering facepiece. 

 The entire mask is fabricated from filter material and covers the 

mouth and nose, similar to a surgical mask. 

Dust masks offer some advantages compared to the replaceable-filter respirators. 

In particular, they are more comfortable and 

require no maintenance. However, dust 

masks usually do not form as tight a seal 

against the wearer’s face as half-masks with 

soft rubber seals, which allows more leakage. As a result, they are often much less 

effective than half-masks. 

Dust masks are certified by NIOSH under 

the 42 CFR 84 respirator certification tests. 

These standards only require a test of the 

filter material and do not assess how well 

the mask seals against the wearer’s face. 

As a result, this certification is no guarantee 

that the mask will perform well. In a recent 

study of dust masks [CDC 1998], the average dust reduction was only 67%.93 

93The study got much better results after fit-testing was performed, and individuals who failed the fit-test were 

dropped from the study. The authors of the study then concluded that fit-testing was necessary if dust masks were to 

be used. Nevertheless, any organization that goes to the trouble and expense of fit-testing its workers is better off 

with half-mask replaceable-filter respirators. 

 The 67% figure for dust masks is low compared to other types of respirators, but it is still better than the dust 

reduction produced by many engineering controls. 

In the mining industry, half-mask respirators are used far 

more than dust masks because their dust reduction efficiencies are much higher. 

Air helmets. The air helmet (figure 9-3) is a redesigned hard hat equipped with a batterypowered fan, filtering system, and face visor, thus providing protection for the head, lungs, and 
124 

eyes within one unit. Other advantages are a lack of breathing resistance, the ability to accommodate facial hair, and no fit-testing requirement for their use. 

Figure 9-3.—Air helmet. 

Although air helmets are slightly larger and 

heavier than conventional hard hats (they 

typically weigh about 3 lb), wearer acceptance has been favorable in high coal seams 

(particularly at longwalls) and in many hardrock mines. 

A small fan is mounted in the rear of the helmet to draw dust-laden air through a filtering 

system. The filtered air is directed behind a 

full-face visor and over the wearer’s face. 

Exhaled air and excess clean air exit the helmet at the bottom of the face visor. Face 

seals are provided along both sides of the 

visor to limit contamination from outside air. 

The fan is externally powered by a rechargeable battery worn on the miner’s belt. Filter 

life varies from one to eight shifts depending 

on the dust level at the worksite [Parobeck 

et al. 1989]. 

The effectiveness of the air helmet depends in part on the mine air velocity outside of the helmet 

and the direction of air impact on the helmet [Cecala et al. 1981], because high air velocities 

push dust particles past the face seals. For example, at a longwall face with an air velocity of 

less than 400 ft/min, air helmets reduced respirable dust by an average of 84%. However, at 

another longwall with an air velocity of 1,200 ft/min, the air helmet was not as effective; dust 

reduction averaged 49%. In both cases, the sampling included some periods when the face visor 

was raised. Raising the visor reduces the helmet’s effectiveness. 

RESPIRATORS FOR DIESEL EXHAUST 

Diesel exhaust, both the particulate and the organic vapors, have become more of a concern in 

recent years. Half-mask respirators will filter both the diesel particulate and the organic vapors 

when equipped with the proper cartridge or cartridge combination. A common cartridge designnation is Organic Vapor/P100, or OV/P100. Half-mask respirators will not protect the eyes from 

irritating fumes. Eye-irritating fumes are best handled by installing a catalytic converter on the 

engine [Schnakenberg and Bugarski 2002]. 

DONNING, SEAL CHECKING, AND MAINTENANCE 

When putting on the respirator, the wearer should follow the manufacturer’s instructions. 

Comfort is as important as a tight seal. The wearer may need to try different size respirators or 
 

125 

respirators from different manufacturers before finding one that conforms to his or her facial 

structure. 

Once a respirator is donned, a seal check is necessary to ensure there are no leaks that would 

degrade the respirator’s effectiveness. Either the positive- or negative-pressure check described 

below94

94From OSHA regulations at 29 CFR 1910.134 appendix B-1: User Seal Check Procedures. 

 or the respirator manufacturer’s recommended user seal check method must 

be performed. 

Seal checking is important for a respirator to be effective. 

Positive-pressure seal check. To perform a positive-pressure seal check, the wearer closes off 

the exhalation valve and blows gently into the facepiece. The face fit is satisfactory if a slight 

positive pressure can be built up inside the facepiece without any evidence of outward leakage 

of air at the seal. For most respirators, this method of leak testing requires the wearer to first 

remove the exhalation valve cover before closing off the exhalation valve. 

Negative-pressure seal check. To perform a negative-pressure seal check, the wearer closes off 

the inlet opening of the canister or cartridge by covering it with the palm of the hand or by 

replacing the filter seal. Next, the wearer inhales gently so that the facepiece collapses slightly, 

then the breath is held for 10 sec. If the facepiece remains in its slightly collapsed condition and 

no inward leakage of air is detected, the tightness of the respirator is satisfactory. However, the 

inlet opening of some filter cartridges cannot be sealed with the palm of the hand. In such cases, 

the test can be done by covering the inlet opening of the cartridge with a thin latex glove. 

During the seal check, the respirator wearer should pay the most attention to the region around 

his or her nose because it is the most likely place for leaks. Also, there should be no interference 

with eyeglasses. 

Respirator maintenance. Basic respirator maintenance is simple. The wearer should check to 

ensure that the filter cartridges are undamaged, the inhalation and exhalation valves are in working order, no straps are slipping or broken, there are no tears or deformities in the facepiece, and 

the respirator is reasonably clean. 

FILTER SERVICE LIFE 

Regular replacement of filters is an important part of respirator use [NIOSH 1997]. Normally, 

filters should be replaced when breathing resistance increases. Another approach is to replace 

filters when the filter loading reaches 200 mg of dust. Using this filter loading approach, if a 
126 

worker breathes 10 m3 per shift and the dust concentration is 5 mg/m3, the loading is 50 mg per 

shift, or 25 mg per filter if there are two filters. The two filters would then be good for eight 

shifts. 

If oil mist is present, N-series filters should not be used. R-series filters should be used for 

one shift, and P-series filters should be changed in accordance with the manufacturer’s 

recommendations. 

RESPIRATOR RESOURCES 

Many organizations on the Internet are good sources of 

information on respirators and respiratory protection 

programs. 

NIOSH has respirator publications at www.cdc.gov/niosh/respinfo.html. The two most useful 

are the NIOSH Guide to the Selection and Use of Particulate Respirators Certified Under 

42 CFR 84 [NIOSH 1996] at www.cdc.gov/niosh/userguid.html and the NIOSH Guide to Industrial Respiratory Protection [Bollinger and Schutz 1987] at www.cdc.gov/niosh/87-116.html. 

OSHA has a downloadable Small Entity Compliance Guide for the Revised Respiratory Protection Standard at www.osha.gov/Publications/secgrev-current.pdf. Also, OSHA has a series of

photographs that can be used for training at 

www.osha.gov/RespiratorOutreach/Powerpoint/Html/RespStd/sld001.htm. 

The International Safety Equipment Association provides a useful buyer’s guide at 

www.safetyequipment.org. The International Society for Respiratory Protection 

(www.isrp.com.au) provides information on respiratory protection. The society publishes a 

quarterly journal and convenes periodic conferences. 

In addition to publications on the Internet, the American Conference of Governmental Industrial 

Hygienists (www.acgih.org) sells a Respiratory Protection Program and Record Keeping Kit as 

publication No. 9278CB. The American Industrial Hygiene Association (www.aiha.org) sells 

Respiratory Protection: A Manual and Guideline as stock No. 439-PC-01. 

Respirator fit-testing and other respirator-related services are readily available for hire. 

REFERENCES 

ANSI [1969]. ANSI Z-88.2-1969: Practices for respiratory protection. Triangle Park, NC: 

American National Standards Institute. Available from Global Engineering Documents, Englewood, CO. 

‌

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127 

Bollinger NJ, Schutz RH [1987]. NIOSH guide to industrial respiratory protection. Cincinnati, 

OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) 

Publication No. 87-116. Available at www.cdc.gov/niosh/87-116.html. 

CDC (Centers for Disease Control and Prevention) [1998]. Laboratory performance evaluation 

of N95 filtering facepiece respirators, 1996. MMWR 47(48):1045-1049. 

Cecala AB, Volkwein JC, Thimons ED, Urban CW [1981]. Protection factors of the airstream 

helmet. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 8591. NTIS 

No. PB 82-135575. 

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, Office 

of the Federal Register. 

Cole DE [1984]. Longwall dust control: respirators. In: Proceedings of the Coal Mine Dust 

Conference (Morgantown, WV, Oct. 8-10, 1984), pp. 61-64. 

MSHA [1995]. Program information bulletin No. P95-3. Available at 

www.msha.gov/regs/complian/pib/1995/pib95%2D03.htm. 

NIOSH [1996]. NIOSH guide to the selection and use of particulate respirators certified under 

42 CFR 84. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health 

Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety 

and Health, DHHS (NIOSH) Publication No. 96-101. Available at 

www.cdc.gov/niosh/userguid.html. 

NIOSH [1997]. NIOSH respirator user notice, May 2, 1997. Available at 

www.cdc.gov/niosh/respupdt.html. 

OSHA [1998a]. Small entity compliance guide for the revised respiratory protection standard. 

Section (c): Respiratory protection program. Washington, DC: U.S. Department of Labor, 

Occupational Safety and Health Administration. Available at 

www.osha.gov/Publications/secgrev-current.pdf. 

OSHA [1998b]. Small entity compliance guide for the revised respiratory protection standard. 

Section (c)(2): Voluntary respirator use. Washington, DC: U.S. Department of Labor, Occupational Safety and Health Administration. Available at www.osha.gov/Publications/secgrevcurrent.pdf. 

OSHA [1998c]. Small entity compliance guide for the revised respiratory protection standard. 

Section (f)(1): Respirators that require fit testing. Washington, DC: U.S. Department of Labor, 

Occupational Safety and Health Administration. Available at 

www.osha.gov/Publications/secgrev-current.pdf. 

Parobeck PS, Francart WJ, Ondrey RS, Stoltz RT, Atchison DJ, Gerbec EJ [1989]. Application 

of the Racal airstream helmet in four underground coal mines. Appl Ind Hyg 4(5):126-133. 

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Schnakenberg GH Jr., Bugarski AD [2002]. Review of technology available to the underground 

mining industry for control of diesel emissions. Pittsburgh, PA: U.S. Department of Health and 

Human Services, Public Health Service, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002-154, 

IC 9462. 
129 

INDEX 

A 

Accuracy of samplers ............................................110 

Air entrainment by sprays................... 9-11, 33, 42-43 

Air helmets .................................................... 123-124 

Airborne capture.................................................. 8-10 

Antirollback spray system .......................................33 

Atomized sprays ......................................................10 

Automation..............................................................49 

Avoidance of dust......................................................6 

B 

Belt dust............................................................. 86-88 

Belt scrapers ............................................................86 

Belt transfer point .......................................... 6, 88-89 

Belt washing ............................................................87 

Bit replacement........................................................34 

Blasting dust ................................................ 58, 85-86 

Blowing duct ...........................................................27 

Blowing ventilation ........................................... 26-28 

Bolter dust ...............................................................34 

Bolter dust collector........................................... 34-36 

C 

Cab filtration............................................................77 

Cab floors .......................................................... 77-78 

Cab protection factor ...............................................77 

Cabs, enclosed ................................................... 76-78 

Cabs, older...............................................................77 

Calcium chloride................................................ 78-79 

Chemical suppressants.............................................79 

Chlorides............................................................ 78-79 

Clogged sprays ........................................................46 

Continuous miner dust control........................... 23-38 

Conveyor belts................................................... 86-88 

 scrapers...............................................................86 

 washing systems .................................................87 

Crushers.................................................. 58-60, 89-90

Crystalline silica ......................................................12 

Cutting bits ..............................................................34 

D 

Damage-resistant brattice .................................. 68-69 

Design stage planning for tunnels.................. 105-106 

Diesel particulate control................................... 60-61 

Dilution ventilation ...................................................4 

Direct-reading instruments ............................ 110-111 

Displacement ventilation ...........................................4 

Dorr-Oliver cyclone....................................... 109-110 

Drill deck shroud ............................................... 74-76 

Drill dust................................................ 58, 73-76, 85

Drum sprays....................................................... 49-50 

Dry collection ........................................ 12, 14, 74-76 

Dust avoidance ..........................................................6 

Dust collectors ............................................. 12-13, 23 

 efficiency ............................................................24 

 filtration efficiency .............................................25 

 inlet capture efficiency .......................................24 

Dust deposition......................................................113 

Dust dilution .................................................. 113-114 

Dust masks.............................................................123 

Dust respirators.............................................. 119-127 

Dust source confinement ....................................... 5-6 

Dust source turbulence .......................................... 5-6 

Dust, blasting............................................... 58, 85-86 

Dust, generated .................................................. 13-15 

Dust-hog bits ...........................................................35 

E 

Electrically charged atomized sprays ......................10 

Enclosed cabs .................................................... 76-78 

Enclosed operator booth ..........................................59 

Evaporation of fine droplets ....................................10 

Exhaust ventilation ............................................ 29-31 

F 

Face partition...........................................................50 

Facepiece seal, respirator............................... 121-123 

Filter efficiency .......................................................25 

Filter materials, respirator .....................................122 

Filter panel......................................................... 24-25 

Filtration of water .............................................. 33-34 

Finding dust sources ................................................39 

Fit-testing....................................................... 120-121 

Flat fan sprays..........................................................10 

Flooded-bed panel ............................................. 24-25 

Foam..................................................................11, 50

Fog sprays................................................................10 

G 

Gob curtain ..............................................................44 

H 

Half-curtain.................................................... 6, 30-31 

Half-mask respirators .................................... 121-122 
130 

Hard-rock mines ................................................ 83-96 

Hard-rock tunnels ............................................ 97-108 

Haul road dust control ....................................... 78-80 

High-pressure sprays ...............................................11 

High-velocity air, sampling in ....................... 114-115 

Homotropal ventilation............................................51 

I 

Infusion of coal seams ....................................... 50-51 

Inlet capture efficiency ................................ 12, 24-25 

Instrumentation.............................................. 109-111 

Intake dust ...............................................................44 

Isokinetic sampling................................................115 

J 

Jet fan placement ............................................... 62-67 

L 

Light-scattering dust monitor ........................ 110-111 

Limestone mines................................................ 57-72 

Longwall dust control........................................ 39-55 

Longwall shields................................................ 47-48 

Low airflow, sampling in.......................................114 

M 

Maintenance ................................................23, 25, 83

Methane gas.......................................................27, 91 

Mismatched airflow directions ..............................101 

Modified cutting cycle.............................................32 

Muckpile stoppings..................................................68 

N 

Nozzle pressure, measuring.....................................33 

O 

Ore pass dust control ......................................... 84-85 

Overspray ................................................................33 

P 

Pinpointing dust sources.................................... 39-41 

Placement of dust samplers ........................... 111-115 

Propeller fans...........................................................70 

R 

Remote control ................................ 26-29, 32, 43, 92

Remote operator location................................... 26-29 

Respirators 

 filters.................................................................122 

 maintenance.............................................. 124-126 

 regulations ................................................ 119-121 

 resources...........................................................126 

 seal check..........................................................125 

 use............................................................. 119-126 

Respiratory protection program..................... 119-121 

Roadheaders ...................................................... 91-93 

Rollback...............................................................5, 33

Roof bolters .............................................................34 

S 

Salts ................................................................... 78-79 

Samplers ........................................................ 109-111 

Sampling........................................................ 109-117 

 concentration gradient .............................. 112-113 

 direct reading ............................................ 110-111 

 gravimetric................................................ 109-110 

 in low-velocity air.............................................114 

 in high-velocity air.................................... 114-115 

 to assess technology effectiveness....................116 

 to avoid deposition............................................113 

Scavenger systems......................................... 100-101 

Scrubbers – see Dust collectors
 

Seal check, respirator.............................................125 

Shank-type bits ........................................................35 

Sharp cutting bits.....................................................46 

Shearer concentration profile...................................45 

Shearer dust .............................................................39 

Shearer-clearer system.............................................45 

Shielded cyclone............................................ 114-115 

Shroud for surface drills 

 circular.......................................................... 75-76 

 drill deck....................................................... 74-75 

Silica........................................................................12 

Silt ...........................................................................80 

Soil cements....................................................... 78-79 

Solid-stream (jet) sprays..........................................50 

Source of dust..................................................39, 109

Spiral-wound duct..................................................105 

Sprays 

 atomizing ............................................................10 

 capture efficiency ...............................................10 

 charged ...............................................................10 

 clogging ..............................................................10 

 fog.......................................................................10 

 high-pressure ......................................................11 

 low-pressure .................................................33, 92 

 nozzles .......................................................... 10-11 

 number of........................................................8, 42

Stageloader/crusher dust..........................................43 

Stone mines ....................................................... 57-72 

Stoppings 

 brattice and wire mesh........................................68 

 damage-resistant brattice .............................. 68-69 

 leakage................................................................70 

 muckpile .............................................................68 

 pipe and sheeting ................................................68 
131 

Support dust....................................................... 47-48 

Surface mines .................................................... 73-82 

T 

Transfer points............................................... 6, 88-89 

Tunnels ............................................................ 97-106 

U 

Unidirectional cutting..............................................47 

Uniformity of wetting................................................8 

V 

Ventilation

 dilution..................................................................4 

 displacement .........................................................4 

Voluntary use, respirators......................................121 

W 

Water curtain .............................................................9 

Water filtration .................................................. 33-34 

Water infusion ................................................... 50-51 

Water proportioning ................................................51 

Water spray, air entrainment – See Air entrainment

 by sprays
 

Water sprays – see Sprays
 

Wet drilling..............................................................73 

Wetting agents .........................................................12 

Wetting, uniformity of........................................... 7-8 

Wing curtain ...................................................... 48-49