EFFECTS OF WATER SPRAYS AND SCRUBBER EXHAUST ON FACE METHANE 

CONCENTRATIONS 

Ch.D. Taylor J.A. Zimmer 

NIOSH/Pittsburgh Research Laboratory 

Pittsburgh, PA 

NIOSH/Pittsburgh Research Laboratory 

Pittsburgh, PA 

ABSTRACT 

Past studies with blowing face ventilation systems have shown that using a machine-mounted scrubber and water 

sprays can reduced methane levels at the face. The current research was conducted to determine how the sprays and 

scrubber interact to reduce methane levels, and what spray configurations provide the best face ventilation when used 

with a scrubber. Testing was conducted in a ventilation test gallery designed to simulate a full-scale mine entry. In 

the entry, a model mining machine, equipped with a simulated dust scrubber and water spray systems, was located at 

the face of a 6.1 m (20 ft) box cut. Face ventilation was provided by a blowing curtain located 12.2 m (40 ft) from 

the face. Methane released from a manifold at the face was measured at six locations near the face to compare the 

ventilation effectiveness of the spray systems while operating with and without the scrubber. Airflow movement 

across the face was affected by the spray configuration and scrubber operation. Average face concentrations were 

lowest when directed sprays were used with the scrubber. Varying the direction of the scrubber exhaust affected face 

methane levels. 

KEYWORDS 

Ventilation, water sprays, methane, coal mining, dust scrubber 

INTRODUCTION 

Effective face ventilation requires that the intake air 

delivered to the end of the tubing or brattice reach the 

face. Studies have shown that often only a small 

fraction of the intake air actually reaches the face 

(Thimons, 1999). The amount of air reaching the face 

usually decreases with increasing tubing or curtain 

setback distance. Research conducted during the 

development of extended cut mining methods 

demonstrated that machine-mounted water sprays and 

scrubbers could be used to help direct additional intake 

air to the mining face when setback distances exceeded 

6.1 m (20 ft) (Volkwein, 1985). 

Although designed primarily for dust control, 

machine-mounted water sprays and scrubbers play an 

important role in increasing the amount of intake air that 

reaches an extended cut mining face. A water spray 

moves air like a small fan. When used with exhaust 

ventilation, groups of sprays directed 30° toward the 

return side of the entry create airflow patterns that help 

clear methane from the face. On sections with blowing 

ventilation, the large quantities of air moved by 

machine-mounted dust scrubbers effect face airflow 

patterns. Tests using scrubbers with both blowing and 

exhausting ventilation showed that operation of a 

scrubber always reduces face methane concentrations 

unless the scrubber exhaust flow interferes with the 

movement of the intake air toward the face (Taylor, 

1996). 

All mining sections use water sprays for dust control, 

but most sections with exhaust ventilation do not use 

scrubbers. Scrubbers and water sprays are used on most 

sections that have blowing ventilation. Past research to 

evaluate the effects of scrubber use on face methane 

levels has been conducted with the spray systems 

operating. Using a scrubber and sprays together reduced 

face methane levels for a range of setback distances, 

scrubber flows, and intake flows (Taylor, 1996). 

Another study showed that water spray systems, 

regardless of design, improved methane control when 

used with scrubbers. However, ventilation improved 

most when the spray system was directed toward the 

return side of the face (Volkwein and Wellman, 1989). 

The current research is a continuation of earlier 

studies to evaluate how the combined use of scrubbers 

and water sprays affect face methane levels while using 

blowing ventilation. Tests were conducted for a range 

of operating conditions that included multiple drum 

heights and the use of side and underboom sprays. 
 

 

TEST FACILITY 

Gallery

Testing was conducted in the National Institute for 

Occupational Safety and Health’s (NIOSH) Pittsburgh 

Research Laboratory Ventilation Test Gallery. One side 

of the „L” shaped building is designed to model an 

underground mining entry which is 5 m (16.5 ft) wide 

by 2.1 m (7 ft) high (Figure 1). An exhaust fan draws 

approximately 5.9 m3

/sec (12,500 cfm) of air into the 

gallery. For these tests a brattice and wood curtain, 

constructed 0.6 m (2 ft) from the left side of the entry, 

directed 3.3 m3

/sec (7,000 cfm) of intake air toward the 

face. Curtain setback distance for all tests was 12.2 m 

(40 ft). The return air was pulled from the gallery 

behind a brattice and wood wall built along the right 

side of the entry. A 1.2 m wide by 6.1 m long (4 ft by 

20 ft) box was built along the right side of the face to 

simulate an uncut slab of coal. A box cut, rather than a 

slab cut configuration, was selected because changes in 

methane levels inby the cutting head are easier to detect 

in the more confined area of the box cut. 

Figure 1. Ventilation test gallery 

Mining Machine

A full-scale model mining machine was located at the 

center of the 3.8 m (12.5 ft) wide box cut face 

(Figure 2). During testing the cutting head rotated at 

40 rpm and the center of the drum was positioned 

approximately 0.5, 1.0, 1.5 m (20, 40 or 60 in.) above 

the floor (Figure 3). These locations are referred to as 

the „down,” „middle,” and „up” drum heights. 

The mining machine was equipped with a simulated 

dust scrubber. A fan mounted in the machine drew air 

into the two 25 by 36 cm (10 by 14 in.) inlets located on 

both sides, below and just behind, the machine boom. 

An orifice plate was placed in the scrubber duct to limit 

flow to approximately 3.3 m3

/sec (7,000 cfm) for all 

tests where the scrubber was operating. Air from the 

scrubber was exhausted through a 38 by 38 cm (15 by 

15 in.) opening at the right rear of the machine. Nine 

horizontal and 9 vertical louvers, each 4 cm (1.4 in.) 

wide were located at the exhaust opening (see Figure 2). 

By adjusting the louver direction, scrubber exhaust 

could be directed, up or down, right or left, and straight. 

For all tests of the spray systems and scrubber, the 

louvers were directed so that the scrubber exhaust was 

directed straight back the entry toward the return. Tests 

were also conducted to determine if the direction of the 

scrubber exhaust had an effect on face methane levels. 

For these tests exhaust flow direction was varied while 

using only one spray configuration. 

Figure 2. Model mining machine at face of box cut 

Figure 3. Drum test heights 
 

Water Spray Systems

The water spray system included manifolds located on 

the top, on the side, and under the boom (Figure 4). 

Figure 4. Spray locations on model mining machine 

Top spray manifold: Ten BD-3 hollow jet nozzles were 

mounted approximately 0.3 m (1 ft) apart in each of two 

3 m (10 ft) long plastic pipes located on top of the miner 

boom. The sprays in one pipe were directed straight 

toward the face. In the other pipe, they were directed 

30° to the right. All spray nozzles were approximately 

0.75 m (30 in.) from the face. 

Side spray manifold: Four Vee-jet nozzles were 

positioned 0.15 m (6 in.) apart in a 0.7 m (28 in.) plastic 

pipe that was mounted vertically on the left side of the 

mining machine. The flat spray nozzles were aligned so 

that the spray pattern was vertical and directed toward 

the face. 

Underboom spray manifold: Four BD-3 hollow jet 

nozzles were positioned 0.15 m (6 in.) apart in a 0.7 m 

(28 in.) plastic pipe that was attached to the underside of 

the cutting boom. The nozzles were mounted so that 

they were directed toward the face. 

Water flow and pressure: A centrifugal pump was used 

to provide the desired water pressure which was 

measured with a gauge mounted near the front of the 

model mining machine. Flows and pressures varied 

depending on the number of operating sprays. For all 

tests using water sprays, pressures were maintained 

between 758 and 896 kPA (110 and 130 psi) and the 

flow was allowed to vary depending on the number of 

sprays operating. Pressure at the gauge was adjusted by 

redirecting part of the water flow at the pump. 

METHANE RELEASE AND INSTRUMENTATION 

Methane gas was released into the gallery through 

four horizontal copper pipes that were drilled on top and 

bottom with 2 mm (1/16 in.) diameter holes. The pipes 

were equally spaced horizontally, and located 0.1 m 

(4 in.) away from the face to provide a relatively 

uniform release of gas. Locations 1, 2, and 3 are 0.3 m 

(1 ft) from the roof and face, evenly spaced across the 

face; Locations 4, 5, and 6 are 1.2 m (4 ft) below. 

Methane was released at a flow rate of approximately 

1,300 lpm (45 cfm). For some tests, however, the gas 

flow was reduced to prevent concentrations in the 

gallery from exceeding 2 pct. 

A vacuum pump was used to draw an air sample at 0.5 

lpm (0.02 cfm) from each of the six sampling locations. 

Each air sample was drawn through 9 m (30 ft) of 0.6 cm 

(1/4 in.) plastic tubing and passed over an individual 

catalytic heat of combustion type sensor head. 

TEST PROCEDURE 

Prior to the start of each test the desired operating 

conditions were set. Next, methane gas was introduced 

into the gallery for 5 min to allow the gas and air to mix. 

After the mixture reached a relatively steady state 

concentration, data was collected at each location for 

5 minutes. 

Data from each methanometer was down-loaded 

every two seconds to a personal computer via an analog 

to digital conversion board. For each of the locations 

sampled, the average methane concentration for each 

five minute sampling period was calculated using an 

electronic spreadsheet file. Most tests were repeated 

once and the results averaged. 

RESULTS 

Tests were conducted with either the 30° or top sprays 

operating and the scrubber on. The average face 

concentrations for the six sampling locations were 

obtained for each of the three drum heights (Figure 5). 

For either spray system the highest concentrations were 

measured when the drum was up and the lowest when 

the drum was in the middle position. All additional 

tests to evaluate the water spray systems were 

conducted with the drum in the up position. Figure 6 

shows the concentrations at the left, center, and right 

side of the face with the drum up and only the straight 

or 30° top sprays operating. 

Tests were conducted to evaluate the top spray 

systems with underboom sprays (Figure 7), side sprays 

(Figure 8), and underboom and side sprays together 

(Figure 9). With the addition of side and/or underboom 

sprays, methane concentrations decreased or remained 

about the same except: 
 

Figure 5. Effect of drum heights and top mounted 

sprays on methane levels 

Figure 6. Effects of top strays at face sampling 

locations 

Figure 7. Using underboom sprays with the top sprays 

− When using top 30° sprays and underboom sprays 

methane levels increased on the left side of the face 

42 pct (see Figures 7 and 6). When the underboom 

and side sprays were used with the top 30° sprays, 

concentrations on the left side were 14 pct less than 

when only top sprays were used (see Figures 9 and 6). 

− When using top straight sprays with the side sprays 

methane levels increased 66 pct on the right side of 

the face (see Figures 8 and 6). When the underboom 

and side sprays were used with the top straight sprays, 

concentrations on the right side were about 17 pct less 

than when only top sprays were used (see Figures 9 

and 6). 

Figure 8. Using side sprays with the top sprays 

Figure 9. Combined use of underboom and side sprays 

with top sprays 

Tests were conducted to determine how changing the 

direction of the scrubber exhaust would affect face 

methane concentrations. For these tests the top 30°, 

side, and underboom sprays were operating, and the 

drum was in the middle position. Face methane 

concentrations were reduced as the scrubber exhaust 

direction was moved from left to right (Figure 10). 

Changing the horizontal exhaust flow direction, up and 

down, had less of an effect on face methane levels. 

DISCUSSION AND CONCLUSION 

Operation of either water sprays or machine-mounted 

scrubber affects face airflow patterns. Using smoke 

tubes, airflow patterns were drawn with the scrubber 

and sprays on and off (Figure 11). Curtain setback 

distance was 12.2 m (40 ft) and intake flow quantity 

was 3.3 m3

/sec (7,000 cfm). With only the blowing 

curtain, the ventilation flow created a „Figure 8” pattern 

that moved from the return to the intake side of the face. 

Operation of either the scrubber or water sprays 

reversed the direction of the face airflow, resulting in 

movement from the intake to the return side of the face. 

Based on observations of the smoke flow, which 

indicated straighter and better defined flow with the 

scrubber, more intake air reached the face with the 

scrubber operating than with the sprays operating. 

Establishing a face airflow that moves from the intake 
 

to return side of the entry is an important factor in 

reducing face methane levels. 

Figure 10. Effect of scrubber flow direction on face 

methane levels 

Figure 11. Face airflow patterns for (A) no water 

sprays or scrubber, (B) scrubber only, and (C) water 

sprays only 

When both the sprays and scrubber were operating, 

flow turbulence inby the miner cutting boom made it 

difficult to observe the direction of the air movement. 

The distribution of methane measured during testing 

indicates that flow did move from the intake to the 

return side of the face, and the use of the top 30° sprays 

improved that flow direction. 

In general, the lower the intake air velocity moving 

toward the face, the greater the effect water sprays will 

have on face airflow patterns. Sprays have a greater 

effect on face airflow when exhausting rather than 

blowing face ventilation is used. With blowing face 

ventilation, sprays primarily affect face airflow within 1 

or 1.2 m (3 or 4 ft) of the face. They can have a 

significant effect on re-distributing the gas at the face, 

but the sprays have less effect on moving methane out 

of the face area. 

For the conditions tested, which included a uniform 

release of methane at the face, methane levels were 

highest when the drum was up and lowest when the 

drum was in the middle position. In the up position 

most of the water from the top mounted sprays hit the 

roof before it could have a significant impact on face 

airflow. In the middle position most of the spray 

reached the face and had a greater effect on face 

airflow. 

Underboom sprays are often used on mining machines 

for dust control. The effect of underboom sprays used 

in combination with top and side sprays was evaluated. 

When used with the top 30° sprays, underboom sprays 

created turbulence that interfered with the movement of 

air across the face. The result was increased methane 

levels on the left side of the face. Addition of the side 

sprays directed more air flow to the left side of the face 

and reduced face methane levels at that location. Using 

the side sprays only with the top straight sprays 

increased methane levels on the right side of the face 

because the top straight sprays are less effective for 

moving gas out of the face area. Addition of 

underboom sprays to the top and side sprays increased 

turbulence enough to reduce methane levels on the right 

side of the face. 

The direction of the exhaust flow had an effect on 

face methane concentrations. Face methane 

concentrations were highest when the vertical direction 

of the exhaust flow was toward the left or intake side of 

the face. Directing the exhaust to the left interfered 

with and reduced airflow toward the face. Directing 

scrubber flow to the right or return side of the entry had 

the least effect on intake flow and methane 

concentrations were lowest. Changing the horizontal, or 

up and down direction of the scrubber exhaust flow had 

less of an effect on face methane levels, although the 

gas concentrations were lower when the exhaust was 

directed downward. Scrubber exhaust should be 

directed so that it has the least effect on intake air 

moving toward the face. If the exhaust velocity over 

any worker is too high, the flow can be directed 

downward. 

The conditions tested were designed to simulate face 

ventilation during mining of a box cut using blowing 

ventilation. Methane concentrations measured in an 

operating mine will vary depending on the actual 

operating conditions and the methane liberation rate in 

the face area. The results obtained provide guidelines 

for selection and use of water spray systems for use in 

improving face airflow and reducing methane 

concentrations at the face. 

The guidelines are designed to reduce methane in the 

face area using water sprays and scrubbers, but will 

not necessarily reduce dust generated at the face by the 

mining operation. Water sprays increase turbulent 

airflow at the face that can improve dilution of 

methane with available intake air. Turbulent flow can 

increase dust levels if it creates excessive dust 

rollback. In some situations the use of a particular 

water spray system can reduce the collection 

efficiency of scrubbers by causing the dust to bypass 

the scrubber inlets. Studies to evaluate the effect of 

water sprays on dust and water for the same range of 

operating conditions are planned. 
 

REFERENCES 

Taylor CD, Rider JP, and Thimons ED [1996]. 

„Changes in Face Methane Concentrations Using 

High Capacity Scrubbers with Exhausting and 

Blowing Ventilation," Proceedings of the SME

Annual Meeting, Preprint 96-167, Phoenix, AZ, 

March 11-14, 5 pp 

Thimons ED, Taylor CD, and Zimmer JA [1999]. 

„Ventilating the Box Cut of a Two-Pass 40 ft 

Extended Cut,” Journal of the Mine Ventilation 

Society of South Africa, Vol. 52, No.3, July/Sept., 

108-115 pp 

Volkwein JC, Ruggieri SK, McGlothlin C and Kissell 

FN [1985]. „Exhaust Ventilation of Deep Cuts Using 

a Continuous-Mining Machine,” Bureau of Mines 

Report of Investigation No. 8992, 16 pp 

Volkwein JC, Thimons ED, and Hallfinger G [1985]. 

„Extended Advance of Continuous Miner 

Successfully Ventilated With a Scrubber in a Blowing 

Section,” 2nd U.S. Mine Ventilation Symposium, 

Reno, NV, Sept 23-25, pp. 741 

Volkwein JC, and Wellman TS [1989]. „Impact of 

Water Sprays on Scrubber Ventilation Effectiveness,” 

Bureau of Mines Report of Investigation No. 9259, 

12 pp