RESEARCH BY NIOSH FOR CONTROLLING RESPIRABLE DUST 

AND METHANE GAS ON CONTINUOUS MINER FACES

G.V.R. Goodman 

National Institute for Occupational Safety 

and Health 

C.D. Taylor 

J.F. Colinet 

E.D. Thimons 

Pittsburgh Research Laboratory 

Dust and Toxic Substances Control Branch 

Pittsburgh, PA 15236 USA 

National Institute for Occupational Safety 

and Health 

Pittsburgh Research Laboratory 

Dust and Toxic Substances Control Branch 

Pittsburgh, PA 15236 USA 

ABSTRACT 

The importance of controlling respirable dust and methane gas levels in underground coal mining cannot be 

underestimated. While respirable dust can significantly affect the occupational health of underground coal miners, 

methane gas accumulations pose significant safety concerns for these same workers. Water sprays and machine 

mounted dust scrubbers offer effective control of respirable dust exposures and methane gas accumulations. Water 

must not only be applied carefully to avoid dust rollback to the machine operator but must create sufficient turbulence 

to remove dead zones that could contain high concentrations of methane gas. While the flooded-bed dust scrubber 

has been generally responsible for decreased worker exposures to respirable dusts, this device has proved effective in 

controlling methane levels at the face. This paper reviews practical applications of water sprays and dust scrubbers to 

control respirable dust and methane gas on continuous miner faces.

KEYWORDS 

Coal mining, water sprays, coal dust, silica dust, engineering controls 

INTRODUCTION 

The United States Federal Coal Mine Health and Safety 

Act of 1969 limits personal exposure to respirable dust to 

2.0 mg/m3

. This limit is measured gravimetrically as an 

8-hour time weighted average concentration of the 

respirable coal dust (NIOSH, 1995). If the respirable dust 

sample contains more than 5 percent silica by weight, the 

respirable dust standard is reduced according to the 

formula 10 / (percent silica). Compliance with either the 

2.0 mg/m3

 respirable dust standard or reduced dust 

standard maintain silica percentages at or below 100 

Fg/m3

. Because the continuous miner operator is on or 

near the continuous mining machine, this person is 

frequently exposed to the greatest levels of respirable 

dust. According to data supplied by the Federal Mine 

Safety and Health Administration (MSHA), over 3100 

samples were collected at the continuous mining machine 

operator in 1998. Nearly 60 percent of the occupational 

samples contained more than 5 percent respirable silica 

dust while forty percent of these contained silica 

concentrations in excess of 100 μg/m3

. 

NIOSH RESEARCH TO CONTROL RESPIRABLE 

DUST EXPOSURES 

 Water sprays remain the most widely used 

technology for limiting exposures to respirable dust. 

Water sprays control dust exposure by suppressing 

airborne dust, inducing airflow to drive dust clouds 

away from personnel, and preventing generation of 

airborne dust (Goodman and Jankowski, 1998). Much 

research by NIOSH and its predecessor, the U.S. Bureau 

of Mines, dealt with balancing these attributes to 

provide effective control of respirable coal and silica 

dusts. 

The earliest water sprays on a continuous miner were 

used for bit lubrication, bit cooling, and dust control. 

Although these sprays controlled respirable dust 

exposure to a limited extent, they created large 

quantities of dust rollback. 

To control rollback, sprays were situated atop and 

beneath the cutting drum (Figure 1). The sprays operated 

at a pressure of approximately 690 kPa (100 psi) and a 

flow rate of 3.6 lpm (0.95 gpm) per spray. Two large 
 

 

orifice, deluge-type, sprays were mounted on the left and 

right underside of the boom and directed to spray into the 

cutting bits. These sprays operated at a low pressure of 

roughly 48 kPa (7 psi) and a higher flow rate of 18.9 lpm 

(5 gpm) per spray (Foster-Miller, 1986). Dust rollback 

decreased because the spray droplets moved only a short 

distance before impacting on the cutting bits. The short 

distance also increased coal surface wetting capabilities 

while minimizing turbulence. In-mine evaluations of 

these boom sprays showed that miner operator dust 

exposures were reduced 40 percent compared to the 

factory-issued spray system. 

TOP SIDE

 Underboom

deluge sprays

Upper spray

 manifold

Figure 1. Water sprays to control dust rollback 

Additional sprays were installed to improve dust 

control in the underboom area. Two hollow cone sprays 

were positioned on the rear corner of the shovel on the 

side opposite from the ventilation curtain. These sprays 

were used with exhaust ventilation only. Each spray 

operated at 1,206 kPa (175 psi) with a flow rate of 

8.5 lpm (2.3 gpm). Due to the high spray pressure and 

flow rate, these sprays induced significant airflow 

beneath the cutting boom. This not only swept the 

underboom area dust into the return airway, but also 

improved suppression of this dust. 

Extensive underground testing of these sprays was 

conducted with the operator located on the mining 

machine. Dust reductions of 60 percent at the 

continuous miner operator’s location were noted. 

Subsequent analyses showed that these shovel sprays 

also were quite effective in controlling respirable silica 

dust produced by the continuous miner. In fact, silica 

dust was virtually eliminated at the miner operator’s 

location (Figure 2). 

Cutting boom sprays

Deluge-type underboom sprays

 Shovel-mounted sprays

(assuming right-hand curtain)

Figure 2. Shovel mounted sprays control 

underboom dust 

Half the respirable silica generated in underground 

coal mining has a size between 1.0 and 3.5 microns. 

Due to the relatively small size of these particles, their 

capture is difficult with larger water droplets produced 

by conventional water sprays. Higher pressure sprays 

can generate the smaller water droplet sizes and 

increased spray velocities required to capture smallersized particles. 

High pressure sprays operating at 17,250 kPa (2,500 

psi) were installed under the cutting boom and directed 

toward the face. Dust levels were reduced nearly 60 

percent with the most dramatic dust reductions 

occurring in the size range below 2.9 microns. In fact, 

the reduction more than doubled for 1.8 micron particles 

with the addition of high pressure sprays (Jayaraman 

and Jankowski, 1988). 

Past work showed that flooded-bed scrubbers 

effectively controlled occupational dust exposures when 

used with either blowing or exhausting face ventilation 

schemes. As of 1997, approximately 60 percent of the 

operating continuous mining machines used a floodedbed dust scrubber to control occupational dust levels. 

MSHA typically requires air quantities measured at the 

curtain mouth to be equal to or slightly greater than the 

rated capacity of the dust scrubber (Schultz and Fields, 

1999). Excessive air flow at the mouth of a blowing 

curtain is thought to overpower the scrubber and blow 

dust by the scrubber inlets. However, excessive air flow 

at the mouth of an exhausting curtain does not appear to 

significantly affect dust capture (Colinet and Jankowski, 

1996). 

Increased emphasis on controlling occupational dust 

exposures led to increases in face airflow and scrubber 

airflow. Although physical constraints limit scrubber 

performance, scrubber airflow was increased by 

reducing the density of the scrubber filter. However, this 

reduction suggested lower dust collection efficiencies 

and thus increased occupational exposures to respirable 

coal and silica dusts. Recent work investigated silica 

collection efficiencies of filters containing 10, 15, 20, 

and 30 layers of stainless steel meshing (Colinet and 

Jankowski, 2000). The 20-layer scrubber filter is the 

most common filter in use in the U.S. mining industry. 

Also investigated was a filter panel containing a nonwoven synthetic fiber and one containing an array of 

nylon brushes. Multiple scrubber duct velocities of 11.1 

and 17.8 m/s were tested. 

Over the range of velocities tested, respirable silica 

collection efficiencies ranged from 69 percent to 84 

percent for the standard 20-layer scrubber filter. 

Efficiencies for the denser 30-layer and synthetic fiber 

filters varied from 91 to 95 percent. The 10-layer filter 

panel had the lowest collection efficiencies ranging 

from 58 percent to 76 percent. All filter panels showed 

improved silica collection at higher scrubber velocities 

(Figure 3). 

Dust scrubbers are very effective when the dust is 

contained beneath the cutting head. Movement of the 
 

continuous mining machine at the face sometimes can 

cause this dust to escape from under the cutting head. 

Placing water sprays on the left and right sides of the 

cutting head induces additional airflow in these areas. 

This increases containment of the dust cloud under the 

cutting head and can improve the capture of this dust by 

the scrubber. This, in turn, reduces both dust rollback 

and dust exposure for the machine operator. 

50

60

70

80

90

100

10-L15-L20-L30-L

Brush

Synthetic

Filter type

Collection efficiency, %

11.1 m/s 17.8 m/s

Figure 3. Silica collection efficiencies 

for various filters 

These sprays were tested at an underground operation. 

One manifold, each containing two flat fan sprays, was 

mounted on each side of the continuous miner, near the 

scrubber inlets. Each spray delivered 6.1 lpm (1.61 

gpm). Dust levels were measured at the left and right 

rear corners of the continuous miner and at the remote 

miner operator location, with and without the additional 

side sprays in operation (Goodman, 2000). 

Respirable dust exposures decreased 20% for the 

mining machine operator. Similar reductions were seen 

at the left and right rear corner sampling locations. It is 

likely that the decreases in dust concentrations arose 

from a combination of improved suppression and 

improved capture by the dust scrubber (Figure 4). 

0

2

4

6

8

10

12

Left rear corner Right rear corner Operator

Sampling location

Dust concentration (mg/m3)

Sprays off

Sprays on

Figure 4. Effects of additional sprays on measured dust 

levels 

NIOSH RESEARCH TO CONTROL METHANE GAS 

Federal regulations require that methane levels in the 

face area be maintained below one percent. Methane 

readings obtained with a hand held methane monitor are 

usually taken as close to the face as practical although 

they cannot be taken closer than 0.3 m (12 in) from the 

roof, face, ribs, and floor. Machine-mounted methane 

monitors are used to continuously monitor methane 

levels on the mining machine. Whenever methane 

readings are one percent or higher mining must stop 

until concentrations are reduced below one percent. 

Methane gas released at or near the mining face is 

controlled by providing sufficient intake air to the face 

to maintain methane levels below one percent. Although 

air delivered to the end of the tubing or curtain must be 

directed to the face, most of this intake air never reaches 

the face. Generally, the quantity of air reaching the face 

decreases as tubing or curtain setback distance 

increases. Although water sprays and scrubbers are 

designed primarily for dust control, research has shown 

that they can also be used to reduce methane levels by 

increasing the amount of intake air that reaches the face. 

Exhaust face ventilation systems are generally 

preferred over blowing face ventilation systems for dust 

control because the dust is removed from the face area 

before it passes over the machine operator’s location 

(Shultz and Fields, 1999). However, for a given setback 

distance, airflow quantities reaching the face with 

exhaust ventilation are often less, and face methane 

concentrations higher. 

Water sprays systems can be designed for use with 

exhaust ventilation to maintain and improve face 

airflow at longer setback distances (Foster-Miller, 

1985). The nozzles in the spray system are oriented to 

move air from the intake to return side of the entry. 

Each of the spray nozzles acts as a small fan and the 

system is referred to as a spray fan system. Tests 

showed that increasing water pressure and flow rate 

increased the air moved by the sprays. Although typical 

flow pressure for the spray fan system was at least 689 

KPa (100 psi), high water pressure created turbulence 

that led to dust roll back. 

The orientation and location of spray nozzles on the 

mining machine are also important factors in 

determining face airflow. Nozzles on the mining 

machine boom should be directed toward the return side 

to maintain airflow across the face while nozzles on the 

intake side of the machine maintain intake airflow to the 

face. The best design for a particular mining face is the 

one that provides the greatest air flow quantity with 

consistent flow patterns (intake to return) at the face. 

The effects of sprays on face airflow can be compared 

by using smoke or the discharge from a fire extinguisher 

to draw face airflow patterns. Test results show that, 

when compared to a 3-m (10-ft) primary ventilation 

brattice, the spray fan system consistently provided 

better face ventilation up to and including a 12-m (40-ft) 
brattice setback (Volkwein, et al., 1985). Use of the 

spray fan system allowed curtain setback distance to be 

increased while maintaining the effectiveness of the 

face ventilation system. 

Blowing face ventilation systems are usually 

preferred over exhausting face ventilation systems for 

methane control because, for a given curtain or tubing 

setback distance, the former provides more air to the 

mining face (Luxner, 1969). Scrubbers are used with 

most blowing systems to reduce the amount of dust that 

passes over the operator’s work location. Dust control 

and ventilation plans approved by MSHA typically 

permit blowing curtain ventilation flows to exceed the 

rated capacity of the dust scrubber by no more than 

0.50 m3

/sec (1,000 cfm). This additional face airflow 

helps control face methane levels. 

Early studies indicated that water spray systems used 

with a dust scrubber and blowing ventilation had little 

effect on face methane levels (Gillies, 1982). Spray 

systems used with scrubbers usually were directed 

toward the face and were not intended, as with the spray 

fan system, to direct air from the intake to return side of 

the face. Test results showed that the scrubber 

maintained the intake airflow reaching the face as 

curtain setback distance increased from 7.5 m to 15 m 

(25 ft to 50 ft) (Ingersoll Rand Research, 1984). 

Releasing smoke near the face showed how face 

airflow patterns changed and indicated that, with the 

scrubber operating, intake airflow was present on the 

curtain side of the entry (Figure 5). Intake air velocities, 

measured at the end of the blowing curtain, increased 

with the scrubber operating. These increases were 

greater at the higher scrubber flows and lower intake 

flows. Face methane levels decreased with increasing 

scrubber flow, even when scrubber flow was greater 

than intake flow (Figure 6) (Taylor et al., 1996a). 

S c ru bbe r, 3 .3 m 3/s

No scrub ber

12m

FACE AIRFLOW PATTERNS

KEY

Airf low

Turbulence

Figure 5. Face airflow patterns with and without 

scrubber 

Using a scrubber with exhaust ventilation also 

reduced face methane levels. The methane levels were 

lower with blowing than exhausting due to the higher 

velocities created by the blowing system (Taylor, et al., 

1996b). However, for both types of face ventilation the 

methane concentrations decreased as scrubber flow 

increased. When using a dust scrubber, the mouth of the 

exhaust curtain must be positioned outby the exhaust of 

the scrubber. With the curtain mouth inby the scrubber 

exhaust, air recirculation to the face increases and, 

more importantly, intake air reaching the face is 

reduced. 

0.00

0.10

0.20

0.30

0.40

2.8 4.7 6.6

Intake flow, m3/s

Methane, %

2.8 cu. m/s scrubber

4.7 cu. m/s scrubber

6.6 cu. m/s scrubber

Figure 6. Face methane levels with varying intake and 

scrubber flows 

SUMMARY 

Water sprays remain the most widely used method for 

controlling respirable dust exposures. NIOSH research 

has evaluated sprays to reduce dust rollback from the 

cutting head, high pressure sprays to control exposures 

to respirable silica dust, and sprays to improve 

performance of a flooded-bed dust scrubber. The dust 

capture properties of various wetted screens used in the 

dust scrubber have been evaluated. 

Face methane concentrations at the cutting face have 

been reduced using water sprays and flooded-bed 

scrubbers. NIOSH research has shown that water sprays 

can be used to maintain and improve face airflow at 

longer setback distances with exhaust face ventilation 

systems. This work has also shown that dust scrubbers 

increase intake airflow with either blowing or 

exhausting face ventilation systems. Higher face 

ventilation flows are needed to control face methane 

concentrations. 

REFERENCES 

Colinet, J.F. and Jankowski, R.A., 1996, “Dust Control 

Considerations for Deep-Cut Mining When Utilizing 

Exhaust Ventilation and a Scrubber,” Report of 

Investigations 9615, U.S. Bureau of Mines, 

Pittsburgh, PA 

Colinet, J.F. and Jankowski, R.A., 2000, “Silica 

Collection Concerns When Using Flooded-Bed 
Scrubbers,” Mining Eng., Vol. 52, No. 4, April, pp. 

49-54 

Foster-Miller, Inc., 1985, “Improved Diffuser and 

Sprayfan Systems for Ventilation of Coal Mine 

Working Faces,” Contract Report No. JO113010, 

U.S. Bureau of Mines, Pittsburgh, PA 

Foster-Miller, Inc., 1986, “Development of Optimal 

Water Spray Systems for Dust Control in 

Underground Mines,” Contract Report No. 

H0199070, U.S. Bureau of Mines, Pittsburgh, PA 

Gillies, A.D.S., 1982, “Studies in Improvements to Coal 

Face Ventilation with Mining Machine Mounted Dust 

Scrubber Systems,” Preprint No. 82-24, Soc. Mining 

Eng. Ann. Mtg., Dallas, Texas 

Goodman, G.V.R. and Jankowski, R.A., 1998, “Using 

Water Sprays to Improve Control of Dust in 

Underground Coal Mining Operations,” Proceedings, 

9th Inter. Conf. Occupational Respiratory Diseases, 

Chiyotani K, Hosoda, Y, Aizawa Y (eds.), Kyoto, 

Japan, pp. 1081-1087 

Goodman, G.V.R., 2000, “Using Water Sprays to 

Improve Performance of a Flooded-Bed Dust 

Scrubber,” Applied Occupational Envir. Hygiene, 

Vol. 15, No. 7, July, pp. 550-560 

Ingersoll Rand Research, Inc., 1984, “Feasibility of a 

Machine Mounted Scrubber System for Ventilating 

Coal Mine Working Faces,” Contract Report No. 

JO199080, U.S. Bureau of Mines, Pittsburgh, PA 

Jayaraman, N.I. and Jankowski, R.A., 1988, 

“Atomization of Water Sprays for Quartz Dust 

Control,” Applied Ind. Hyg., Vol. 3, No. 12, Dec., pp. 

327-331 

Luxner, J.V.. 1969, “Face Ventilation in Underground 

Bituminous Coal Mines,” Report of Investigations 

7223, U.S. Bureau of Mines, Pittsburgh, PA 

National Institute for Occupational Safety and Health 

(NIOSH), 1995, “Occupational Exposure to 

Respirable Coal Mine Dust, Criteria for a 

Recommended Standard,” U.S. Dept. of Health and 

Human Services, Centers for Disease Control and 

Prevention, Atlanta, GA 

Schultz, M.J. and Fields, K.G., 1999, “Dust Control 

Considerations for Deep Cut Mining Sections,” 

Preprint 99-163, Society of Mining Eng. Ann. Mtg., 

Denver, CO 

Taylor, C.D., Rider, J.P., and Thimons, E.D., 1996a, 

“Changes in Face Methane Concentrations Using 

High Capacity Scrubbers with Exhausting and 

Blowing Ventilation,” Preprint 96-167, Soc. Mining 

Eng. Ann. Mtg., Phoenix, AZ 

Taylor, C.D., Rider, J.P., and Thimons, E.D., 1996b, 

“Impact of Unbalanced Intake and Scrubber Flows on 

Methane Concentrations,” Proceedings, 6th Inter. 

Mine Ventilation Congress, Ramani, R.V. (ed.), 

Pittsburgh, PA, pp. 169-172 

Volkwein, J.C., Ruggieri, S.K., McGlothlin, C., Kissell, 

F.N., 1985, “Exhaust Ventilation of Deep Cuts using 

a Continuous-Mining Machine,” Report of 

Investigations 8992, U.S. Bureau of Mines, 

Pittsburgh, PA