An overview of fundamental and emerging technologies to monitor 

and control respirable dust in underground coal mines in the 

United States 

James P. Rider1

1

Corresponding Author. National Institute for Occupational Safety and Health, 

Pittsburgh Research Laboratory, PO Box 18070, Pittsburgh, PA 15236, 

jrider@cdc.gov Telephone: 412.386.4727 FAX: 412.386.4917 

and Jay F. Colinet2 

2

 National Institute for Occupational Safety and Health, Pittsburgh Research 

Laboratory, PO Box 18070, Pittsburgh, PA 15236, jcolinet@cdc.gov 

ABSTRACT 

As production levels continue to increase in underground coal operations in the 

United States, greater quantities of respirable dust are generated with the potential to 

increase worker exposure. Ventilating air and water spray systems continue to be the 

primary means of controlling respirable dust for both continuous mining and 

longwall mining operations. Mine operators are applying these fundamental control 

technologies at elevated levels and are looking to new and emerging control 

technologies to better control respirable dust. New monitoring technologies are also 

being developed to improve the real-time measurement of worker dust exposure; so 

that corrective action can be taken before workers' become overexposed. 

The Pittsburgh Research Laboratory of the National Institute for Occupational Safety 

and Health (NIOSH) conducts research to develop and improve control technologies 

and monitoring instrumentation that can be used to reduce the respirable dust 

exposure of mine workers. An overview of fundamental dust controls technologies 

being utilized in underground US coal mines will be presented. Also, updates on 

emerging technologies such as the personal dust monitor (PDM), wet head spray 

technology for continuous miners, and a roof bolter canopy air curtain will be 

provided. 

 

1. INTRODUCTION 

In an effort to prevent lung disease, the Mine Safety and Health Administration 

(MSHA) enforces a respirable dust standard of 2.0 mg/m3 averaged over five 8-hour 

shifts for the underground coal mining industry in the United States (US). If the 

silica content of the collected sample exceeds 5%, the 2.0 mg/m3 dust standard is 

reduced according to the equation of 10 ÷ % silica. For example, if the sample 
contains 10% silica, the reduced dust standard would be 1.0 mg/m3

 (10÷10% silica). 

Currently, mine operators are required to collected dust samples on a bimonthly basis 

and MSHA samples each mechanized mining unit (MMU) four times a year. 

Improvements in longwall mining equipment and mining practices have led to 

substantial gains in longwall production levels, resulting in longwall mining 

accounting for 51% of the coal produced underground in the US (EIA, 2006). 

Average longwall production as reported by mine operators during compliance dust 

sampling in 2008 was 5,000 tons (5,500 short tons) per shift (Lindahl 2009). 

Although significant gains in longwall dust control have been made, they have been 

challenged by these increases in production. In 2006, 11.1% and 8.8% of 

compliance samples exceeded the applicable dust standard for the tailgate shearer 

operators and jacksetters, respectively. 

Along with major changes on longwalls in the US, continuous mining operations 

have also seen dramatic changes. Average production on the approximately 850 

continuous miner sections during compliance sampling reached 700 tons (770 short 

tons) per shift in 2008 (Lindahl 2009). The majority of continuous miners are 

operating with flooded bed scrubbers and taking extended cuts greater than 6.1 

meters (20 feet). The number of mines utilizing super-sections (sections with two 

continuous miners) has increased in recent years. This has resulted in the potential 

for roof bolter operators to work downwind of a continuous miner and be exposed to 

increased amounts of respirable dust. Another significant change that has occurred is 

an increase in the quantity of rock that is being mined as seam conditions have 

deteriorated. Cutting of this rock has the potential to add significant quantities of 

silica dust in the mine environment. In 2008, 17.9% of continuous miner operator 

and 7.1% of roof bolter operator samples exceeded their reduced dust standard. 

Medical studies have shown that prolonged exposure to excessive levels of airborne 

respirable coal dust can lead to coal workers’ pneumoconiosis (CWP), progressive 

massive fibrosis (PMF), and chronic obstructive pulmonary disease (COPD). These 

diseases are irreversible and can be debilitating, progressive, and potentially fatal. 

Coal workers’ pneumoconiosis contributed to the deaths of 10,406 miners during the 

period of 1995 through 2004 (NIOSH 2008). Pneumoconiosis continues to be a very 

serious health threat to underground coal mine workers. Recent x-ray surveillance 

data have uncovered cases of rapidly progressing CWP and also revealed an upturn 

in the prevalence rate (CDC 2006). 

The continued development of CWP in underground coal mine workers and the 

magnitude of respirable dust over exposures in the US illustrate the need for NIOSH 

and the US mining industry to improve existing dust control technology and develop 

new control methods. 
2. LONGWALL MINING DUST CONTROL 

Outby dust sources can contribute significantly to worker dust exposure at the 

longwall face. Dust generated by these sources enters the ventilating airstream and 

remains airborne across the entire face, which can have a significant impact on the 

dust exposure of all face personnel. Efforts must be made to maximize the quantity 

and quality of ventilating air that reach the face area. Outby dust sources such as 

vehicle movement, removing stoppings, and delivering/unloading supplies can 

elevate intake dust levels. If at all possible, these activities should be limited during 

production shifts. Operators must be diligent in monitoring moisture content of the 

dust on intake roadways. The moisture content of the haulage floor should be 

approximately 10% (Kissell 2003) to minimize dust entrainment. Properly 

maintaining the belts is one of many vital components needed to keep respirable dust 

levels low along the belt entry. Dry belts could become a major source of dust in 

ventilation airstream. Missing rollers, belt slippage, and worn belts can cause belt 

misalignment and create spillage. With the substantial increase in airflow, rewetting 

of the coal may be necessary at intervals along the belt. Flat fan sprays and full-cone 

nozzles are typically used for coal wetting along the belt. Water application usually 

ranges from 3.8 to 15.1 lpm (1 to 4 gpm) at operating pressures at or greater than 348 

kPa (50 psi) (Bituminous Coal Research Inc). 

The stageloader/crusher is the most significant source of respirable dust in the 

headgate area. The breaking action of the crusher on the coal and rock generates 

large quantities of dust, which can mix with the ventilating airstream and be carried 

the entire length of the longwall face. In the US, all stageloader/crushers are fully 

enclosed; however, there is not a universally applied technique for enclosing the 

stageloader/crusher. The common practice is to enclose the stageloader and crusher 

through a combination of steel plates, strips of conveyor belting, and/or brattice. 

With the quantity of coal being transported through the stageloader/crusher, it is 

imperative that all seals and skirts be carefully maintained to ensure that dust stays 

confined within the enclosure. At a minimum, water sprays should be placed on both 

sides of the crusher and at the stageloader-to-section-belt transfer (figure 1A). 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. In an effort to keep fugitive dust from escaping from 

the stageloader/crusher area, fan-powered scrubbers located close to the crusher 

discharge and/or stageloader to belt transfer area are being utilized more often, 

according to the latest longwall surveys (Rider and Colinet, 2007). 

Adequate ventilation of the longwall panel involves supplying the required volume of 

air to the headgate and maintaining that airflow along the face. Often, loss of air into 
the gob in the headgate area prevents the maximum utilization of the intake air. A 

gob curtain (figure 1B) installed between the first support and the rib in the headgate 

entry, can force the ventilating airstream to make a 90 degree turn down the longwall 

entry, rather than leaking into the gob (Jankowski and Colinet 2000). The brattice 

curtain can be extended behind hydraulic support legs along the first five to ten 

shields to further reduce leakage into the gob area and thus increase airflow down the 

face. 

Figure 1: Dust control practices to reduce respirable dust in the headgate area 

A B 

To accurately assess face airflow, ventilation measurements should be taken at every 

10th support. The resulting profile could be used to determine the “average” face 

airflow, along with the effective utilization of the primary intake air, and the loss of 

air into the gob. Higher air velocities provide greater air quantities for better dust 

dilution, improved diffusion of dust from stagnant areas, and rapidly removes dust 

from the breathing zones of the face workers. 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). 

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

liberation during longwall mining. In the US, all shearer cutting drums are equipped 

with drum-mounted water sprays. The intent is to apply water directly at the point of 

coal fracture to maximize dust suppression and add moisture to the product to 

minimize dust liberation during the transport of the coal off of the longwall face. 

Once respirable dust becomes airborne and is entrained by the primary airstream, it is 

then carried throughout the entire cross-sectional area of the longwall face. 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 or jet sprays are the most 

effective type of spray patterns to use in the shearer drums. These sprays increase 

wetting without inducing substantial air movement around the drum. 
Water sprays are very effective air-moving devices and when mounted on the shearer 

body can act very much like small fans that move air and entrain dust in the direction 

of the spray. Poorly designed shearer-mounted spray systems with the water sprays 

oriented upwind into the primary ventilation can cause high levels of dust to be 

transported away from the face area and into the walkway. If applied properly, water 

sprays can be used to augment the primary airflow and reduce the amount of shearergenerated dust. A technique used on longwall operations in the US is to hold the 

dust-laden air near the face by splitting the ventilating air as it reaches the headgate 

side of the shearer. 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 in 

the direction of the airflow and angled toward the face. A section of conveyor belting 

is also hung from the splitter arm to form a physical barrier between the face 

conveyor and walkway. Additional spray manifolds are mounted along the body of 

the shearer to further promote the movement of the dust-laden air along the face. 

Figure 2 illustrates a directional spray system operating on a shearer.

Figure 2: Directional spray system on a longwall shearer. 

 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. 
3. CONTINUOUS MINER DUST CONTROL 

The greatest source of respirable dust at continuous mining operations is generated 

by the continuous mining machine. Continuous miner dust affects the operator as 

well as anyone working downwind of the active mining area. In the US, two types of 

ventilation systems are used to supply fresh air to the face of a continuous mining 

section. Typically, the most effective method from a dust control standpoint is 

exhaust ventilation. 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 

keeps the continuous miner operator and shuttle car operators in clean air. The 

second system is blowing ventilation, where clean air is brought to the face behind 

the brattice or in tubing 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. From a dust 

control standpoint, the miner operator can position himself at the discharge of the line 

curtain/tubing and work in clean air. However, the shuttle car operators are exposed 

to dust-laden return air. 

In the US, water spray manifolds are typically mounted on top of the miner boom 

within 30-38 cm (12-15 inches) of the cutting drums. These sprays wet the coal as it 

is being cut and prevent dust from becoming airborne. High volume, cone sprays or 

flat-fan sprays operating at less than 690 kPa (100 psi) should be located across the 

boom as close to the cutter head as possible to provide uniform coal wetting across 

the cutter head during mining while limiting rollback (figure 3A). Dust rollback can 

occur when cone type sprays are used at higher pressures and force dust back over 

the continuous miner (Jayaraman, et al., 1984). Large-orifice, low-pressure sprays 

should be utilized under the boom of the miner and in the conveyor throat area. 

These sprays usually operate at 412 kPa (60 psi) or less with a flow rate of 

approximately 18.9 lpm (5 gpm). Broken material is wetted as it is gathered and 

conveyed (figure 3C). For dust containment under the boom, flat-fan sprays with a 

vertical orientation at 30 degrees are mounted 0.3 meters (1 foot) back from the 

cutter head outby the scrubber inlets on both sides of body of the machine (figure 

3B). Because sprays are oriented vertically they act as a water barrier along side of 

the miner boom and give the scrubber and external sprays an improved opportunity 

of capturing the dust. The operating pressure of these sprays can be higher than 690 

kPa (100 psi) to increase the impact zone of the sprays.
Figure 3: Orientation of sprays to prevent dust rollback 

Currently, most mining operators are using fan-powered, flooded bed scrubbers to 

assist in moving fresh air toward the face and to capture dust-laden air generated by 

the miner’s cutter heads. Airborne dust is pulled through one to three inlets located 

on the miner’s boom and passes through a wetted filter panel. Water sprays impact 

the filter panel and the dust mixes with the water droplets. The dust is removed from 

the airstream when the droplets are captured by a demister located behind the filter 

panel. The cleaned air is discharged from the back of the miner and is directed 

toward the return. If operated properly, over 90% of the respirable dust can be 

removed by a scrubber. It is critical that sufficient water is applied to the entire filter 

panel area to extend the effectiveness and performance of the scrubber. Usually, full 

cone sprays operated at 415 kPa (60 psi) are used to wet the scrubber filter. Periodic 

removal and cleaning of the filter and demister are 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 filter) can be utilized to maximize dust capture (Colinet and Jankowski, 2000). 
4. ROOF BOLTER DUST CONTROL 

The largest source of roof bolter operator’s dust exposure can occur when working 

downwind of the continuous miner. The mining pattern should be designed to 

eliminate or at least minimize the need for the bolter to work downwind of the 

continuous miner. Other sources of dust exposure for the bolter operators are the 

drilling process and maintaining the dust collector. The majority of the roof bolters 

in the US utilize a dry vacuum dust collector system that pulls dust through the drill 

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. Properly maintaining 

the dust collector system is critical; checks should be made for loose hose 

connections and damaged compartment door gaskets. Vacuum pressure at the drill 

head should be checked periodically by using an approved pressure gauge to 

maintain manufacturer’s vacuum specifications for proper airflow. Frequent cleaning 

of the main dust compartment is necessary to ensure proper operation of the dust 

collection system. As the collector box fills, it is necessary for the operator to empty 

the box and change the filter cartridge. The operator should maintain an upwind 

position when removing dust from the dust box to reduce exposure. 

Utilization of a collector bag has shown to reduce dust exposures to bolter operators 

when emptying the dust box. These collector bags contain the dust and reduce 

loading on the filter cartridge. Operators can easily remove the filled bags from the 

dust box and deposit the bag against the rib. Dust loading on the filter cartridge is 

significantly reduced and the filter does not need to be replaced as often. 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). It should be noted 

that the dust collector must be fitted with an automated pre-cleaner that separates and 

captures larger particles prior to the material reaching the collector. This minimizes 

the loading of the collector bag and extends its usable time. If the bolting machine’s 

dry dust collector is properly maintained, and if the bolter is not working downwind 

of the continuous miner, very little dust should be measured in the air around the 

bolter (Goodman and Organiscak, 2002). 

5. WET HEAD SPRAY TECHNOLOGY 

Continuous miner manufacturers in the United States have started offering a miner 

that is equipped with water sprays in the cutting drums. Spray nozzles are located 

directly behind each cutting bit on the drum, while conventional technology places 

the water sprays on the boom approximately 30-38 cm (12-15 inches) away from the 

cutting bits. The initial intent of locating spray directly behind the cutting bit was to 

offer improved control of frictional ignition with the potential to reduce dust levels. 
This allows water to be introduced at point of coal fracture and immediately adds 

moisture to minimize dust where the dust cloud forms. Figure 4 illustrates the wet 

head miner and spray nozzle location. 

Figure 4: Wet head miner and spray location behind bit.

Currently, NIOSH is evaluating this technology to determine the effectiveness of the 

wet head cutting drum for limiting respirable dust exposures for miner operator and 

downwind personnel. Two studies conducted by Goodman, et al. (2006) compared 

dust levels around continuous miners that were operated with either a conventional 

spray system located on top of the miner’s boom or a wet head spray system. One 

study was conducted with exhaust ventilation, while the second study used blowing 

ventilation. Measured dust reductions at the miner operator ranged from 0.2 to 0.5 

mg/m3. During these studies, each wet head spray was limited to 1.5 lpm (0.4 gpm) 

in order to maintain overall water flow to the miner at an acceptable level. Additional 

work is planned to further explore the dust reduction potential of the wet head design. 

6. CANOPY AIR CURTAIN 

NIOSH is currently developing and testing a canopy air curtain for installation on a 

roof bolter to deliver filtered air over the operator’s breathing area. This device is 

mounted on the underside of the bolter canopy and consists of a hollow metal plenum 

with a perforated plate on the bottom. A fan located at the rear of the bolter draws in 

ventilating air from the entry and passes it through a filter. Tubing carries the air 

from the fan to the plenum. A stream of filtered air is discharged from the perforated 

plate and passes over the operator. This filtered air 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 and was followed by 

an underground study (Goodman, et al., 2006). Data collected during this study 

showed promise and suggested several ways to improve the efficiency of the canopy 
air curtain, such as increasing air curtain size to increase coverage area. A 

computational fluid dynamics (CFD) model has been utilized to optimize the flow of 

air underneath the canopy as it relates to the position of the operator. NIOSH is 

currently evaluating a second generation air curtain in the laboratory. Figure 5 shows 

the canopy air curtain being test underground and a CFD model illustrating airflow 

patterns of the redesigned air curtain. 

Figure 5: Underground testing of the canopy air curtain prototype and CFD model of 

the second generation air curtain. 

7. PERSONAL DUST MONITOR 

To date, dust monitoring in the US has relied upon collection of a gravimetric sample 

with a coal mine dust personal sampler unit (CMDPSU). The CMDPSU utilizes a 

pre-weighed 5 μm pore size polyvinyl chloride (PVC) filter preceded by a 10 mm 

Dorr-Oliver nylon cyclone operated at a flow rate of 2.0 lpm to collect a respirable 

sample of airborne coal mine dust. The CMDPSU is operated over an 8-hour (portal 

to portal) sampling period to determine the average dust exposure of the wearer. 

Unfortunately, the dust exposure can not determined until the filter has been mailed 

to MSHA and processed, which can take up to 10 days. In the interim, the mine 

worker may continue to be exposed to elevated dust levels. 

In an effort to provide real-time measurement of dust exposures, NIOSH developed 

the Personal Dust Monitor (PDM). The PDM utilizes the Tapered Element 

Oscillating Microbalance (TEOM) technology to convert a mass-based measurement 

into real-time dust concentrations (Volkwein et al., 2004). A data processor in the 

PDM utilizes these real time measurements to calculate and display a cumulative dust 

exposure to that point in the shift, as well as, a projected dust concentration for the 

end of the shift. The mine worker and management can monitor these levels 

throughout the shift and make improvements to the dust controls, if it appears that an 

overexposure will occur. The TEOM sensor is incorporated into a cap lamp housing, 
while the sampling inlet is mounted on the cap lamp light. Figure 6 presents a 

schematic identifying the key components of the PDM. 

Figure 6: Components of the Personal Dust Monitor 

Display 

and Buttons Power Takeoff 

Block with 

Flow Sensor Orifice 

Temp and RH Air heater 

Sample filter 

TEOM 

Mass Sensor 

Cap Lamp 

Battery (Left) 

TEOM System 

Battery (Right) 

Air/ Electrical 

Umbilical Cable 

Sample 

Inlet 

Cap Lamp Cyclone 

Pump 

NIOSH completed extensive laboratory and in-mine testing of the PDM and found 

that the PDM dust measurements closely correlate with the CMDPSU (Volkwein et 

al, 2006). PDM measurements are multiplied by 1.05 to be equivalent to dust 

concentrations measured with the CMDPSU (Page, 2008). A manufacturer is 

producing a commercial version of the PDM that is expected to be available by the 

summer of 2009. 

8. DISCUSSION 

Control technologies that maximize the potential to limit dust exposures to operators 

of continuous miners, roof bolters, and longwall operations were presented in this 

paper. Also discussed were emerging technologies and included a wet head miner, 

canopy air curtain and a person-wearable dust monitor that provides accurate realtime respirable dust concentration data to miners. However, this paper only touched 

upon a limited number of control technologies to reduce or eliminate harmful 

respirable dust. A more comprehensive discussion of dust control principles and 

possible solutions to respirable dust concerns is summarized in a NIOSH handbook 

(Kissell, 2003). 

Connector

Sensors HeaterHeater

Filter
It is imperative that maintenance of these dust control technologies become a routine 

part of operating practices to realize their maximum potential. Mine managers must 

encourage mine workers to routinely inspect the control technologies and provide the 

mechanism to properly maintain the installed dust control equipment. An effective 

dust control program must contain an education and training component along with 

appropriate control technologies. Also, workers must be made aware of the potential 

health risks associated with breathing excess respirable dust and be encouraged to 

suggest possible solutions to dust concerns. 

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