Dust Control Practices for Underground Coal Mining 

Jay F. Colinet and Edward D. Thimons 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

626 Cochrans Mill Road 

Pittsburgh, PA 15236

Abstract

Underground coal mining operations in the United States continue to increase productivity as 

mining equipment and practices are improved. Unfortunately, increased production also results 

in the potential for increased respirable dust generation and worker exposure. In response, US 

operations are applying basic controls at elevated levels and looking to emerging technologies in 

an effort to better control respirable dust levels. 

Ventilating air and water sprays remain the basis of dust control strategies for both longwall and 

continuous mining operations, and the level of application for these controls continues to 

increase. In addition, new technologies are emerging that have the potential to further reduce 

dust levels. The National Institute for Occupational Safety and Health (NIOSH) has been 

conducting research into methods to optimize existing control technologies and evaluate 

emerging control technologies. This paper will summarize control technologies routinely being 

used in underground coal mine operations, as well as provide a review of new controls that are 

being pursued. 

Introduction

The Mine Safety and Health Administration (MSHA) establishes and enforces regulations for the 

mining industry in the United States. Since 1973, a respirable dust standard of 2.0 mg/m3

 over 

an 8-hour shift has been enforced. However, if silica in the collected sample exceeds 5%, a 

reduced dust standard is established by dividing 10 by the percent silica. For example, if the 

sample contains 10% silica, a reduced dust standard of 1 mg/m3 (10/10% silica) is enforced. 

Periodic occupational, personal and area sampling is conducted by MSHA and the mine 

operators to measure compliance with the applicable dust standard. 

Underground coal mining accounts for 33% of the coal production in the United States. Of this, 

51% of the production is produced by longwall mines (EIA, 2006). Approximately 45 longwalls 

are in operation at a given time. Average longwall production as reported by mine operators 

during compliance dust sampling in 2006 was 4,800 tons (5,300 short tons) per shift 

(Niewiadomski, 2007). This production has been achieved through improved machine reliability 

and improved operating practices. Average longwall panel size in 2002 was 287 m (940 ft) wide 

and nearly 3050 m (10,000 ft) long (Rider and Colinet, 2007). These improvements in longwalls 

challenge dust control efforts. In 2006, 16% and 14% of compliance samples exceeded the 

applicable dust standard for the tailgate shearer operators and jacksetters, respectively. 
In addition to improvements and changes being realized on US longwalls, continuous mining 

operations have also seen dramatic changes. Average production on the approximately 780 

continuous miner sections during compliance sampling reached 690 tons (760 short tons) per 

shift in 2006 (Niewiadomski, 2007). The vast majority of continuous miners are now operating 

with flooded bed scrubbers and taking extended cuts that are greater than 6 m (20 ft). An 

increase in the number of mines utilizing supersections (sections with two continuous miners) 

has also occurred. However, utilization of super sections has increased the potential for roof 

bolter operators to work downwind of a continuous miner, resulting in increased dust exposure. 

A negative change that has occurred has been an increase in the quantity of rock that is being cut 

as seam conditions deteriorate. Cutting of this rock has the potential to add significant quantities 

of silica dust to the mine environment, resulting in 51% of mines operating on reduced dust 

standards. In 2005, 11% of continuous miner operator and 12% of roof bolter operator samples 

exceeded their applicable dust standard. 

Since the initiation of the x-ray surveillance program in the US coal mining industry in 1970, the 

prevalence of Coal Workers’ Pneumoconiosis (CWP) in the workforce has been declining. For 

mine workers with 25 or more years of experience, the prevalence rate of CWP has dropped 

from 28.2 % in 1973 to 3.3 % in 1999 (NIOSH, 2003). However, recent x-ray surveillance data 

have uncovered cases of rapidly progressing CWP and also revealed an upturn in the prevalence 

rate (CDC, 2006). 

As a result of changes that have been occurring in the underground coal industry in the US, the 

continued overexposure of workers to respirable dust, and recent x-ray findings, the need to 

improve existing dust control technology and develop new control methods remains a major 

focus for NIOSH and the US mining industry. 

Longwall Mining Dust Control 

Ventilating air and water sprays are the primary controls used for protecting workers from 

overexposure to respirable dust. Ventilation provides reduced dust levels through dilution of 

generated dust and through transporting dust away before it can migrate to the breathing zones of 

miners. As a result, efforts must be made to maximize the quantity and quality of ventilating air 

that reaches the face. This is achieved by ensuring that dust levels in the intake air steam are 

low, that stoppings and curtains are tight, and that as much of the intake air is directed down the 

face as possible. Outby dust sources can be controlled by wetting roadways, minimizing outby 

dust-producing activities (unloading supplies, removing stoppings), and ensuring that sufficient 

coal wetting occurs before being transported out the belt entry. In recent surveys of US 

longwalls, the average face airflow was found to be 3.4 m/sec (665 fpm) with an estimated 

average air quantity of 31.6 m3

/sec (67,000 cfm). This air quantity represents a 65% increase in 

airflow from 10 years ago (Rider and Colinet, 2007). 

As clean intake air is brought onto the face, the potential exists for this air to be contaminated by 

dust generated at the crusher/stageloader. In response, water sprays should be placed on both 

sides of the crusher and at the stageloader-to-section belt transfer (Jayaraman et al., 1992). The 

objective of these sprays is to wet the coal product and prevent respirable dust from becoming 

airborne. Consequently, water quantity is more critical than water pressure, so larger orifice, 
full-cone sprays operating at water pressures below 414 kPa (60 psi) are recommended. Also, 

the entire crusher/stageloader unit should be completely enclosed to prevent dust that is 

generated within the unit from escaping into the ventilating air. Mines have successfully utilized 

steel plating, conveyor belting, expanding foam, and line brattice to seal these units. Belting can 

also be hung at the inlet to the crusher and brattice can be used to enclose the transfer point from 

the stageloader-to-section belt. Figure 1 shows two enclosed stageloaders and conveyor belting 

hung at the crusher inlet. 

Figure 1. Enclosed stageloaders and crusher 

In order to maximize the quantity of intake air that reaches the face, a gob curtain can be hung in 

the headgate entry (Jankowski et al., 1993). This is simply a section of line brattice that is hung 

between the rib and first shield in the headgate entry to turn intake air down the face. Several 

longwalls have expanded on this technique by extending brattice behind the shield legs on the 

first 5-10 shields to further improve the seal around the headgate and turn as much air down the 

face as possible. 

 

Water spray application is the other primary control being used to substantially reduce the dust 

exposure of longwall face workers. The first attempt to control dust generation from the shearer 

occurs as the shearer bits cut the coal. All shearers in the US are equipped with water sprays in 

the cutting drums. In general, water spray pressure to the shearer drums should be limited to a 

maximum of 690 kPa (100 psi) to prevent dust from being blown into the walkway by the sprays. 

Also, past research has shown that full-cone sprays are the most effective type of spray pattern to 

use in the shearer drums. These sprays increase wetting without inducing substantial air 

movement around the drum. 

In recent surveys of nine US longwalls, all operations were using directional spray systems on 

their shearers (Rider and Colinet, 2007). The exact type, number, and location of these sprays 

varied significantly between mines, but all were operating on the principle of splitting the 

ventilating air as it reaches the headgate side of the shearer and holding the dust-laden air near 

the face. This air split is facilitated through the use of a “splitter arm,” which is a steel arm that 

extends from the headgate side of the shearer body parallel to the headgate ranging arm. Sprays 

are mounted on this splitter arm and oriented at an angle to the face in the direction of the airflow 

coming from the headgate. Additional spray manifolds are located along the body of the shearer 

to further enhance the movement of the ventilating air along the face. Typically, a section of 
conveyor belting is also hung from the splitter arm as a physical barrier between the face 

conveyor and walkway. Figure 2 illustrates a directional spray system operating on a shearer. 

The physical structure of the splitter arm and water sprays on the arm force the dust-laden 

portion of the ventilating air toward the face, while the “clean” split of air travels down the 

walkway. Spray manifolds on the back side of the shearer help to maintain this dust near the 

face and move the dust cloud past the shearer. Since the sprays in these directional spray 

systems are attempting to move air, the operating pressure is critical and pressures of at least 

1035 kPa (150 psi) should be utilized. Hollow cone sprays and/or venturi sprays are effective in 

this application. 

Figure 2. Headgate side splitter arm and directional sprays on shearer 

To assist in protecting the tailgate side shearer operator, companies have started using spray 

manifolds mounted at the tailgate end of the shearer. Typically, these sprays are located directly 

above the panline and oriented parallel to the tailgate ranging arm. The water spray pattern and 

induced airflow help move dust-laden air past the tailgate side operator before the dust reaches 

the walkway. Figure 3 illustrates a manifold of these sprays mounted on the shearer body. 

Hollow cone sprays operated at pressures at or above 1035 kPa (150 psi) would be effective air 

movers in this application. 

Measurement of water usage on US longwall operations shows that an average of 495 lpm (130 

gpm) is being supplied to the shearer, with an additional 285 lpm (75 gpm) being added with 

stageloader/crusher sprays (Rider and Colinet, 2007). One operator reported using 850 lpm (225 

gpm) on their shearer (Dezeuuw, 2007). 

Continuous Miner Dust Control 

Ventilation for continuous mining operations in the US is supplied either through exhaust or 

blowing ventilation systems. For the exhaust system, fresh air is brought to the face in the 

working entry and line brattice or tubing is installed within the entry to create an air separation. 

Dust-laden air is then drawn from the face through the tubing or behind the curtain. This method 
Figure 3. Spray manifold on tailgate end of shearer 

of ventilation is typically the most effective from a dust control viewpoint since it keeps the main 

working entry and the continuous miner and shuttle car operators exposed to fresh air. 

For blowing ventilation, the clean air is brought to the face through tubing or behind brattice and 

discharged toward the face. Dust-laden air is then carried out of the face through the entry. This 

type of ventilation typically penetrates deeper toward the face and is more effective for methane 

control. Ideally, the miner operator can position himself at the discharge of the brattice/tubing 

and work in fresh air. However, the shuttle car operators are positioned in the dust-laden return 

air. 

Most operations in the US are taking extended cuts of more than 6m (20 ft) in depth and use 

continuous miners equipped with fan-powered, flooded-bed scrubbers. These scrubbers assist in 

moving air toward the face and in capturing airborne dust generated by the miner cutter heads. 

They typically pull dust-laden air through one to three inlets on the miner boom and pass the air 

through a filter panel being wetted with water sprays. The dust mixes with the water droplets 

and is removed from the airstream when the droplets are captured by a demister located behind 

the filter panel. Over 90% of respirable dust can be removed by a scrubber. The cleaned air is 

then discharged from the back of the miner and directed toward the return. It is critical that 

sufficient water is applied to the entire filter panel area to extend the effectiveness and 

performance of the scrubber. Typically, full-cone sprays operated at 415 kPa (60 psi) are used to 

wet the scrubber filter. Periodic removal and cleaning of the filter is also necessary to maintain 

optimum performance of these dust collectors. 

Research has shown that the selection of the scrubber filter can have a significant impact on dust 

collection efficiency. If dust control is a concern, the more efficient filters (30-layer stainless 

steel or bottle brush filters) can be utilized to maximize dust capture (Colinet and Jankowski, 

2000). 

In addition to the scrubber, all miners are equipped with an external spray system. These sprays 

are typically located on top of the miner boom behind the cutting drum and oriented toward the 

bits on the miner cutting drums. These sprays wet the coal as it is being cut and prevent dust 
from becoming airborne. Research has shown that flat fan sprays that are operated at less than 

690 kPa (100 psi) are most effective at reducing dust while preventing rollback (Jayaraman et al., 

1984). Rollback occurs when cone type sprays are used at higher pressures. The air-moving 

action of the cone sprays can force dust back toward the operator, particularly as spray pressures 

are increased. 

In addition to scrubbers and boom sprays, it is important to utilize low-pressure, high-volume 

sprays under the boom of the miner and in the conveyor throat. These sprays are designed to wet 

the coal under the boom and prevent dust liberation as the coal is loaded and transported to the 

shuttle cars. These sprays are typically limited to 415 kPa (60 psi) or less. 

NIOSH research has also shown that “blocking sprays” can be mounted on the sides of the miner 

outby the scrubber inlets to help contain dust near the face. These blocking sprays give the 

scrubber and external sprays an improved opportunity of capturing this dust. The blocking 

sprays are also fan sprays that are mounted with a vertical orientation to develop a water barrier 

along the side of the miner boom. The operating pressure of these sprays can be higher than 690 

kPa (100 psi) to increase the impact zone of the sprays. 

Within the last two years, the leading continuous miner manufacturer in the US has been offering 

a miner that is equipped with water sprays in the cutting drums. These “wet head” miners place 

the spray directly behind the cutting bit and offer improved control of frictional ignition with the 

potential to reduce dust levels. Figure 4 illustrates the wet head miner and spray nozzle location. 

NIOSH has evaluated two wet head miners and measured dust reductions at the mine operator 

ranging from 0.2 to 0.5 mg/m3

 (Goodman et al., 2006). 

Figure 4. Wet head miner and spray location behind bit 

Each miner in these surveys was equipped with approximately 70 sprays on the cutting heads. 

As designed, the cooling water for these miners was not utilized through the wet head sprays. 

Consequently, the manufacturer and mine operator wanted to limit the water supplied to the 

cutting head. Each spray was limited to 1.5 lpm (0.4 gpm) in order to maintain overall water 

flow to the miner at an acceptable level. The restricted flow to the wet head sprays may have 

limited the dust reductions to the range observed in these surveys. Additional work with the 

manufacturer is planned to further explore the dust reduction potential of the wet head design. 
Roof Bolter Dust Control 

Roof bolter operators are often exposed to respirable silica dust during drilling. This dust can 

come from drilling into the roof strata or from operating downwind of the continuous miners. 

Most roof bolters in the US are utilizing a dry vacuum dust collection system that pulls dust 

through the drill steel back to a dust collector box. The dust is removed from the airstream and 

deposited in chambers of the collector box or captured by a filter cartridge. When operated and 

maintained properly, this system can be very effective in capturing and removing dust generated 

by drilling. 

As the collector box fills, it is necessary for the bolter operator to empty the box and clean the 

filter cartridge. Both of these tasks can expose the bolter operators to elevated levels of silica. 

One method of minimizing the dust exposure of workers when cleaning the box is through the 

use of collector bags that contain the dust and reduce loading on the filter cartridge. These bags 

fill with dust and can be removed without significant dust exposure to the workers. The bag is 

then discarded without the potential for further contamination. Since the dust loading on the 

filter cartridge is reduced, the filter does not need to be cleaned or replaced as often. This also 

reduces the potential for dust getting beyond the seal of the cartridge, where it can be discharged 

through the muffler back into the mine atmosphere. It should be noted that the dust collector 

must be fitted with an automated pre-dump that separates larger particles prior to reaching the 

collector. This minimizes the loading of the collector bag and extends its usable time. 

Laboratory and field testing of the collector bags has shown that they reduce dust loading on the 

filter cartridge by approximately 80 % (Listak and Beck, 2007). Figure 5 illustrates the 

difference in dust deposition within the collector when the bag is utilized. It is much easier for 

the bolter operator to service the collector box when the collector bag is used, and far less dust 

exposure results. 

Figure 5. Dust as normally deposited in the collector box (left) and the collector box with bag utilized (right) 

Another recent control that has shown promise is a canopy air curtain. The canopy air curtain is 

mounted on the underside of the bolter canopy and blows air down over the bolter operator. This 

air is drawn from the ventilating air in the entry and passes through a filter prior to being blown 

over the operator. Consequently, a stream of filtered air is passing over the operator, which 
prevents dust from drilling or dust generated upwind by the miner from reaching the bolter 

operator. 

Laboratory testing has shown a 50% reduction of dust under the air curtain. An underground 

survey confirms that the air curtain has the potential to reduce operator dust and was well 

received by the operator (Goodman et al., 2006). Figure 6 illustrates the principle of operation 

for the canopy air curtain and also shows the air curtain being tested underground. This testing 

also identified modifications that could be made to the air curtain to improve its effectiveness. 

NIOSH is currently evaluating a second generation air curtain in the laboratory. 

Figure 6. Canopy air curtain for roof bolting machines 

Discussion 

A number of basic control technologies for longwall and continuous miner operations have been 

discussed in this paper. Information on several emerging control technologies has also been 

presented. However, this paper only touched upon a limited number of controls. A more 

comprehensive summary of dust control principles and technologies is summarized in a NIOSH 

handbook (Kissell, 2003). This handbook provides a concise discussion of multiple control 

technologies and includes references that can be accessed for greater detail on individual 

controls. 

In order for any and all of these dust controls to realize their maximum potential, it is critical that 

maintenance of the controls becomes a routine part of operating practices. Management must 

encourage mine workers to regularly examine the installed dust controls and provide the 

opportunity for control technologies to be maintained. An effective program for reducing the 

respirable dust exposure of mine workers must also contain an education and training component 

along with appropriate control technologies. Workers must be made aware of the potential 

health risks associated with breathing excess respirable dust. Also, the importance of proper 

utilization of the dust control technologies must be stressed and supported by mine management. 

In the US, mine management must post the approved ventilation plan at the mine. This plan 

includes the types of controls to be used and approved operating levels for these controls. 

 
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