Abstract

A series of laboratory evaluations examined the impact of

water spray pressure, curtain setback distance, and external and underboom spray use for controlling respirable

dust levels and sulfur hexafluoride tracer gas concentrations around a continuous mining machine. This mining

machine was equipped with a flooded-bed dust scrubber

and was positioned in the box or slab cut. Exhaust line brattice was used for all tests.

Dust levels were measured in the return airway and at

locations representing the operators of the continuous mining machine and the standard and off-standard shuttle cars.

Increasing water pressure or using the underboom sprays

produced no significant impacts on dust levels, although

their interactions did produce some significant impacts.

Increasing curtain setback distance often elevated dust levels, likely by reducing the amount of airflow reaching the

face. Use of the external sprays created additional airflow

around the mining machine that pushed the dust cloud

past the scrubber inlets. This significantly increased dust

levels at all sampling locations. 

Tracer gas levels were measured on the off-curtain and

curtain sides of the cutter head and in the return airway.

Increasing water pressure generally led to significantly

increased gas levels on the curtain side, although a slight

decrease was observed on the off-curtain side with the

machine in the box cut. Increasing setback distance elevated gas levels on both sides of the cutter head and in the

return by limiting the quantity of ventilation airflow reaching

the face. Use of the external sprays provided additional airflow along the off-curtain side of the machine, significantly

reducing gas levels in this region. These sprays adversely

impacted the dilution and removal of gas on the curtain

side of the cutter head. Use of the underboom sprays

adversely impacted gas levels on both sides of the cutter

head.

Use of the external sprays provided the best control of

respirable dust and face gas concentrations. The smaller

increases in miner operator dust levels produced by these

sprays were offset by larger reductions in face gas levels on

the off-curtain side of the cutter head. Although the underboom sprays minimally impacted respirable dust levels, use

of these sprays was not recommended because they

increased face gas levels.

1. Introduction 

Federal coal mine regulations in the United States limit

exposures to respirable coal dust to 2.0 mg/m3 for a working shift (Mineral Resources, 1999). This level is measured

gravimetrically using a nylon classifying cyclone and a sampling rate of 2.0 L/min. If the quartz content of the dust

exceeds 5% by weight, a new exposure limit is calculated

using the formula 10/(% quartz). Compliance with the 2.0

mg/m3 standard or a reduced standard maintains quartz

dust levels at or below 100 μg/m3. Federal regulations also

limit concentrations of methane gas at the face area to 1%.

Methane readings are typically taken with a machinemounted methanometer or a hand-held detector and usually taken as close to the face as practical, although they cannot be taken closer than 0.3 m from the roof, floor, face, or

ribs (Mineral Resources, 1999).

Many factors affect the ability of a dust scrubber to control respirable dust exposures and methane gas concentrations during coal mining. These include face ventilation airflow quantity, water spray pressure, and ventilation curtain

setback distance, among others. Past work showed that

increased curtain airflow reduced both respirable dust and

face gas concentrations (Colinet, McClelland & Jankowski,

1991). Increased water pressure created turbulence that

could improve the dilution of face gas (Foster-Miller Inc.,

1985). However, excessive turbulence created dust rollback

that pushed the dust cloud toward the machine operator

(Jankowski, Jayaraman & Babbit, 1987). Shorter setback

distances directed more airflow to the face, which could

improve control of dust and gas. 

Control and confinement of the dust cloud is necessary to

improve suppression and capture of these dust particles. To

control face gas levels, however, turbulence is needed to

promote dilution of the gas cloud. This suggests that ventilation airflows, spray pressures, and setback distances needed for optimal control of respirable dust concentrations may

not be as effective for control of methane gas at the face.

The effects of water spray placement 

for controlling respirable dust and face

methane concentrations

by G.V.R. Goodman, T.W. Beck & D.E. Pollock Pittsburgh

Research Laboratory National Institute for Occupational

Safety and Health Pittsburgh, PA 15236 USA

 
A series of laboratory tests evaluated the impacts of face

ventilation flow rate, water spray pressure, curtain setback

distance, and the uses of external and underboom sprays

on respirable dust levels measured at the miner operator,

shuttle car operators, and in the return airway.

Corresponding tracer gas concentrations were measured

on the curtain and off-curtain sides of the cutter head and in

the return airway. Recommendations were made regarding

the best use of the external and underboom sprays for controlling respirable dust and face gas levels.

2. Experimental design

This laboratory work was conducted at a full-scale surface test gallery simulating a cut 12.2 meters deep, 5.5 m

wide, and roughly 2.0 m high. A full-scale mockup of a continuous mining machine used for this testing featured a 0.9-

m diameter cutting drum rotating at 50 rpm. The machine

was positioned at the end of the box cut or slab cut for testing. While in the box cut, a coal slab measuring 2.4 m by

6.1 m remained to the right of the machine (Figure 1).

Exhaust curtain ventilation was created in the laboratory by

drawing air via a main gallery fan through a curtain positioned on the left side of the test gallery. Airflow was measured at the mouth of the curtain using a conventional vane

anemometer. 

The mining machine was equipped with a flooded bed

dust scrubber rated at 3.3 m3/s. The scrubber included a

30-layer stainless steel filter screen. The machine used a

standard water spray system as offered by the manufacturer of 24 BD3-3 hollow cone sprays (Spraying Systems,

Wheaton, IL, USA) positioned above, below, and along the

sides of the cutting head.

Figure 1. Plan view of full-scale test gallery

Past work showed that high methane gas levels could

occur at the face when using exhaust curtain ventilation,

evidence that fresh airflow was not reaching the face, but,

instead, was flowing directly behind the curtain (Luxner,

1969). This testing showed that the corner of the face on

the off-curtain side of the entry often showed the highest

gas levels. 

Preliminary testing of the dust scrubber with the standard

water spray system showed relatively high gas levels in this

corner. To clear this area of gas, external spray manifolds

were placed on the right side of the machine frame 2.4 m

outby the hinge point of the cutting boom and on top of the

cutting head at the hinge point. Each manifold consisted of

two BD 20-2 hollow cone sprays oriented to “flush out” this

corner of the face. These external manifolds were plumbed

separately from the standard spray system to evaluate the

effect of these added sprays on controlling respirable dust

and face gas (Figure 2).

Figure 2. Water spray designs used with dust scrubber (Topplan view, Bottom-side view)

Two additional spray manifolds were placed under the

cutting boom, each manifold consisting of three BD3-3 hollow cone sprays oriented toward the cutting drum. These

underboom manifolds also were plumbed separately to

assess their effects on dust and gas levels.

A 10% mixture of quartz dust in coal dust was introduced

into the gallery at the miner cutting head via a compressed

air/eductor system. Two LH-1⁄2 brass eductors (Penberthy,

Prophetstown, IL, USA) were connected to a 34.5 kPa compressed air source. These eductors mixed the dust mixture

with the compressed air to deliver the dust to the cutting

head at a rate of 25 grams/minute. One eductor discharged

along the left front side of the cutting drum while the other

discharged along the right front of the drum. The rotating

cutting drum ensured mixing of the dust with the ventilation

airflow. 

For dust sampling, constant airflow pumps pulled dustladen air through 10-mm nylon cyclone separators at a rate

of 2 L/min as specified by 30 CFR 70.205 (Mineral

Resources, 1999). The respirable mass was deposited onto

pre-weighed 37-mm filters that were subsequently post

weighed and dust levels calculated. Selected filters with a

minimum weight gain of 0.30 mg were sent to an independent laboratory for x-ray diffraction analysis of respirable

quartz using NIOSH Method Number 7500 (NIOSH, 1994). 

A pair of gravimetric samplers placed on the off-curtain

(right) side of the entry, outby the mouth of the exhaust curtain, represented the location of the remote mining machine

operator, which moved with curtain setback distance. Two

pairs of samplers placed 7.6 m outby the rear of the mining

machine on the left and right sides represented locations of

the standard and off-standard shuttle car operators, respectively. Finally, gravimetric samplers placed in the return airway monitored dust levels in that location (Figure 1). 

This testing also evaluated the impact of face ventilation

flow rate, water spray pressure, and setback distance on

the removal and dilution of hazardous gas concentrations.

Due to safety concerns, however, methane gas could not
be used in this testing. Instead, sulfur hexafluoride (SF6)

was used as a surrogate or tracer gas. This gas is tasteless,

odourless, not found naturally in the atmosphere, and is

nontoxic in the amounts used in this testing. It is also

detectable in the parts per million (ppm) concentration

level. This substance was introduced at the cutting drum

where its rotation mixed the gas with the face airflow. 

A model 1303 multipoint gas doser (California Analytical

Instruments, Orange, CA, USA) metered the gas into the

gallery at a rate of 6 milliliters/sec for four 20-minute periods. Each period consisted of an initial 3-minute period of

sampling with no dosing, a 14-minute period of dosing and

sampling, and a final 3-minute period of sampling with no

dosing. Real-time measurement of the sulfur hexafluoride

gas levels was made with a California Analytical Instruments

model 1312 photoacoustic gas monitor. Gas sampling was

conducted at locations representing typical methanometer

locations on a continuous mining machine: on the left and

right sides of the cutting boom approximately 0.6 m outby

the cutting drum. Gas levels also were measured in the

return airway (Figure 1). Tracer gas dosing and sampling

ran concurrently with dust sampling. Disposable filters,

placed at the ends of the gas sampling tubes, prevented

dust from entering the gas monitoring equipment.

Only a single curtain flow rate of 3.8 m3/s was used to

minimize the size of the test matrix. Curtain setback distance was either 9.1 m or 12.2 m and water pressure was

either 620 kPa or 1172 kPa. This testing also evaluated the

impacts of the external spray manifolds and the underboom

spray manifolds. Measured water flow rates for the various

spray combination ranged from 76.6 to 145.9 liters per

minute (Table 1.). Each test ran 90 minutes.

Table 1. Water flow rates (L/min) measured for different

spray system designs.

For this analysis, only the effects of the four independent

variables and six two-way interactions were considered;

three-way and four-way interactions were not evaluated.

Two replicates of each test were made to obtain a measure

of the error associated with each combination. We also randomized the order in which tests were run.

The dust concentration at each sampling location was

calculated using the average of the concentrations for each

group of samplers. The tracer gas concentration at each

location was the average of the concentrations recorded for

the four pulses. Respirable dust and tracer gas concentrations for each series of test conditions were calculated

using the average concentration for each test comprising

that set of conditions.

3 Effects on respirable dust exposures

Analyses of variance (ANOVA) were used to define the

impact of the independent variables (water pressure, curtain

setback distance, external spray usage, underboom spray

usage) on respirable dust exposures measured at the miner

operator, standard and off-standard shuttle car operators,

and in the return airway. A significance level of 0.05 was set

for all analyses. 

The data collected did not typically exhibit normal distributions. To improve normality of the data and equality of the

variances, square root transformations were used on the

respirable dust concentrations. Although some transformed

data showed departures from normality, the F-tests used in

these analyses are robust and little affected by such departures. Also, the balanced design of this analysis minimizes

the impact of unequal variances (Neter, Wasserman, Kutner,

1985). The untransformed data in Table 2 show the mean

and standard deviation for each operator and return sampling location with the machine in the box and slab cut

position. Results in the following sections are based upon

square root transformed data.

3.1 Continuous Miner in Box Cut

Curtain setback distance and external spray use significantly impacted dust levels for the miner operator (Table 3).

Increasing curtain setback distance significantly increased

dust levels for the mining machine operator likely by reducing the amount of fresh air reaching the cutting face. Use of

the external sprays also significantly increased these dust

levels, likely by increasing air velocity along the machine

that pushed the dust cloud past the scrubber inlets. Similar

effects of increased air velocity have been reported by others (Hole & Von Glehn, 1998; Schultz & Fields, 1999). The

interaction of water pressure and underboom spray use significantly impacted miner operator dust levels. Increasing

water pressure led to higher dust levels with use of the

underboom sprays and lower levels without these sprays.

An interaction of curtain setback distance and external

spray use was noted.

The use of the external sprays increased dust levels for

the standard shuttle car operator by pushing the dust cloud

past the scrubber inlets where it could flow to outby locations. Changing curtain setback distance produced significant changes in dust levels for the off-standard shuttle car

operator by placing the mouth of the curtain near this location. Dust entering the curtain mouth likely contaminated

these samples. Use of external sprays significantly

increased dust levels at this location with the greatest

impact occurring at high pressure. 

Water pressure interacted with underboom spray use to

significantly impact off-standard car dust levels. Increasing

water pressure reduced dust levels when using underboom

sprays and increased dust levels without these sprays. The

interaction of water pressure and the external sprays produced the opposite effect. Increasing water pressure led to

higher dust levels with use of the external sprays and lower

dust levels without these sprays. Use of the external sprays

led to greater increases in dust levels with the underboom

sprays off than with these sprays on. 

Use of the external sprays led to significant increases in

dust levels measured in the return airway. A mechanism

similar to that described for the off-standard shuttle car

operator likely applied in this case. Interactions between

Spray system design Spray pressure

620kPa 1172 kPa

Standard sprays 76.6 98.5

Standard+externals 89.4 120.9

Standard+underbooms 94.4 127.7

Standard+externals+underbooms 145.9 106.5
water pressure and use of either the underboom or external

sprays and an interaction between the uses of the underboom and external sprays produced variations similar to

those seen for the off-standard shuttle car operator.

3.2 Continuous Miner in Slab Cut

As with the box cut data, changing curtain setback distance and use of the external sprays produced significant

changes in dust levels for the miner operator. The interaction of curtain setback distance and external spray use produced significant increases in dust concentrations. 

At the two shuttle car sampling locations and in the

return airway, dust levels were significantly affected by use

of the external sprays and by the interaction of these sprays

with curtain setback distance. This interaction increased

dust levels at the off-standard car location with use of the

external sprays and reduced dust levels without these

sprays. At the standard shuttle car location and in the return

airway, increasing setback distance elevated dust levels.

Use of external sprays produced higher dust levels at the

larger curtain setback distance for all sampling locations.

Use of the external sprays significantly increased dust levels

with the underboom sprays off and slightly reduced these

levels with the underboom sprays on.

Low dust concentrations were measured at the miner

operator and shuttle car operator sampling locations. The

required filter weight gain of 0.30 mg could not be obtained

for quartz analysis, even when combining filters from multiple tests. However, dust concentrations were higher in the

return, allowing us to obtain sufficient weight by combining

filters according to box or slab position and use of either the

external or underboom sprays. Respirable quartz contents

on the filters varied from less than 1.1% by weight to nearly

4.6% with an average of 2.9%. ANOVA analyses showed no

impact on quartz percentages with changes in machine

position (box cut versus slab cut) or with use of either the

external or underboom sprays.

4. Effects of SF6 tracer gas levels

Gas concentration data collected at the off-curtain side,

curtain side, and return sampling locations also were

square root transformed to improve normality of the data

and equality of the variances. The original untransformed

data is given in Table 4, while the following analyses are

based upon transformed data.

Water Curtain External Underboom

spray setback sprays Dust levels in box cut, mg/m3 (standard deviation)

pressure distance Dust levels in slab cut, mg/m3 (standard deviation)

Mining machine Standard Off-standard Return

operator shuttle car shuttle car

(kPa) (m) (on/off) (on/off) operator operator

620 9.1 off off 0.03 (0.00) 0.05 (0.02) 0.07 (0.02) 0.63 (0.04)

0.11 (0.09) 0.09 (0.02) 0.11 (0.00) 1.24 (0.20)

1172 9.1 off off 0.04 (0.02) 0.06 (0.04) 0.07 (0.02) 0.46 (0.07)

0.04 (0.02) 0.06 (0.03) 0.12 (0.01) 0.94 (0.26)

620 12.2 off off 0.15 (0.01) 0.06 (0.02) 0.16 (0.08) 0.72 (0.03)

0.09 (0.02) 0.04 (0.02) 0.10 (0.07) 1.11 (0.05)

1172 12.2 off off 0.11 (0.01) 0.04 (0.03) 0.11 (0.06) 0.52 (0.12)

0.20 (0.04) 0.09 (0.01) 0.09 (0.01) 0.96 (0.13)

620 9.1 off on 0.04 (0.03) 0.03 (0.03) 0.14 (0.02) 1.08 (0.13)

0.05 (0.03) 0.08 (0.05) 0.13 (0.10) 1.29 (0.91)

1172 9.1 off on 0.02 (0.02) 0.03 (0.02) 0.11 (0.03) 0.98 (0.08)

0.06 (0.06) 0.04 (0.05) 0.16 (0.03) 1.39 (0.08)

620 12.2 off on 0.17 (0.03) 0.07 (0.03) 0.22 (0.08) 0.88 (0.13)

0.30 (0.20) 0.11 (0.07) 0.16 (0.03) 1.89 (0.70)

1172 12.2 off on 0.14 (0.03) 0.06 (0.05) 0.20 (0.06) 0.82 (0.11)

0.24 (0.20) 0.09 (0.08) 0.08 (0.03) 1.57 (0.79)

620 9.1 on off 0.04 (0.04) 0.06 (0.04) 0.15 (0.07) 1.30 (0.16)

0.07 (0.02) 0.10 (0.06) 0.18 (0.05) 1.72 (0.60)

1172 9.1 on off 0.10 (0.05) 0.08 (0.04) 0.26 (0.06) 2.39 (0.16)

0.05 (0.03) 0.07 (0.03) 0.16 (0.06) 1.34 (0.15)

620 12.2 on off 0.28 (0.06) 0.09 (0.04) 0.27 (0.05) 1.33 (0.33)

0.44 (0.12) 0.15 (0.03) 0.23 (0.09) 2.44 (0.25)

1172 12.2 on off 0.32 (0.03) 0.08 (0.02) 0.45 (0.07) 1.87 (0.22)

0.35 (0.16) 0.14 (0.06) 0.24 (0.12) 2.38 (0.33)

620 9.1 on on 0.06 (0.05) 0.07 (0.06) 0.19 (0.09) 1.65 (0.22)

0.03 (0.03) 0.05 (0.04) 0.13 (0.03) 1.10 (0.21)

1172 9.1 on on 0.05 (0.01) 0.05 (0.03) 0.15 (0.02) 1.22 (0.08)

0.02 (0.01) 0.05 (0.03) 0.11 (0.02) 0.91 (0.13)

620 12.2 on on 0.30 (0.01) 0.12 (0.09) 0.32 (0.06) 1.43 (0.17)

0.50 (0.20) 0.17 (0.04) 0.31 (0.11) 2.03 (0.43)

1172 12.2 on on 0.21 (0.07) 0.05 (0.05) 0.30 (0.01) 1.24 (0.09)

0.31 (0.14) 0.13 (0.04) 0.16 (0.10) 1.73 (0.57)

Table 2. Untransformed gravimetric dust levels measured in box and slab cuts (mg/m3)
4.1 Continuous Miner in Box Cut

Gas concentrations on the off-curtain (right) side of the

cutter head significantly decreased with higher water pressure and use of the external sprays, indicating improved

ventilation and dilution at this site (Table 5). The external

sprays were more effective in reducing gas levels at the

higher water pressure. Increasing curtain setback distance

led to elevated gas levels. The underboom sprays

increased gas levels, likely by trapping the gas on the offcurtain side of the face or restricting the flow of dilution airflow to this area. 

Higher gas levels on the curtain (left) side arose from

increasing water pressure, possibly a result of the higher

pressure forcing the gas to this side. These levels also

increased with use of either external or underboom sprays.

The increase in water pressure led to higher gas levels at

the smaller setback distance. 

Increasing curtain setback distance led to a statistically

significant increase in return airway gas level, although the

increase was minimal. No interactions were noted among

the independent variables. 

4.2 Continuous Miner in Slab Cut

Tracer gas levels on the off-curtain (right) side increased

significantly with curtain setback indicating less dilution airflow in this area (Table 5). Levels increased with use of

underboom sprays, suggesting that these sprays were

impeding the flow of air to this area. Use of external sprays

significantly reduced gas levels on the off-curtain side, a

result of increasing air velocity around the cutter head. 

Gas levels on the curtain (left) side increased with water

pressure. Use of external or underboom sprays also

increased gas levels, likely by creating airflow patterns that

hindered removal and dilution of the gas cloud. Increases

in setback distance reduced airflow reaching the curtain

side of the cutting head. Use of the external sprays produced greater increases in face gas levels with the underboom sprays off than with use of these sprays. Return gas

levels were not significantly impacted by changes in any

independent variable or interaction of these variables. 

5. Controlling full-cut dust and gas concentrations

The best use of either the external or underboom sprays

should ideally result in the lowest dust and gas concentrations. This study showed that use of these sprays often produced opposite effects on respirable dust and tracer gas

levels. The practical use of these sprays, therefore, should

lead to minimal negative impact on dust or gas concentrations. We made a final analysis by assuming that the continuous miner spends 60% of the cut time in the box cut and

40% mining the slab cut. We computed equivalent full-cut

concentrations for respirable dust and tracer gas by using

these weightings (Table 6). 

For these tests, full-cut dust concentrations measured at

the miner operator locations varied from 0.04 to 0.38

mg/m3. Variations in full-cut dust levels were similar at the

two shuttle car operator locations and in the return. Full-cut

tracer gas levels ranged from 0.65 to 6.49 ppm on the offcurtain (right) side of the cutter head from 0.97 to 3.18 ppm

on the curtain (left) side. Little variation was seen in return

gas levels. Tracer gas levels around the machine were

impacted more than respirable dust levels by changes in

water pressure, setback distance, and spray manifold use.

The best application of these sprays should provide control

of full-cut tracer gas levels.

Based upon the data collected, use of the external sprays

reduced gas concentrations on the off-curtain side of the

cutter head by a factor of ten (Table 6). These sprays, however, increased gas levels on the curtain side of the cutter

head by a factor of slightly more than three. This increase

was minimised by turning off the underboom sprays, which

did not effectively control face gas levels anyway.

Use of the external sprays (without the underboom

sprays) increased full-cut miner operator dust levels approximately 0.10 mg/m3 (Figure 3). Similar effects were noted at

the standard and off-standard shuttle car operators sampling locations. While the external sprays produced only a

small increase in miner operator dust exposure, they created larger reductions in full-cut gas levels on the off-curtain

side of the cutter head. A smaller increase in gas levels

occurred on the curtain side of the cutter head, especially at

the lower pressure of 620 kPa. The external sprays should

be used while the underboom sprays need not be used

(Figure 4).

Table 3. F-ratios from ANOVA analyses of square root transformed gravimetric data, box and slab cuts (n=3)

Source of Mining Standard shuttle Off-standard Return

variation machine car operator shuttle

(box-cut) operator car operator

A: water pressure 0.33 1.76 0.23 0.03

B: curtain setback 231.43* 1.99 44.40* 2.02

distance

C: external spray 40.99* 5.34* 55.59* 150.52*

use

D: underboom 0.52 1.28 1.87 1.76

spray use

Interaction: AB 3.30 1.94 0.00 0.11

Interaction: AC 2.05 0.05 6.08* 8.16*

Interaction: AD 6.71* 0.94 4.68* 8.86*

Interaction: BC 6.43* 0.07 1.81 0.39

Interaction: BD 0.05 1.89 0.00 0.61

Interaction: CD 1.44 0.00 11.01* 29.74*

Source of Mining Standard shuttle Off-standard Return

variation machine car operator shuttle

(box-cut) operator car operator

A: water pressure 1.59 1.35 1.68 2.57

B: curtain setback 89.62* 10.85* 1.54 16.30*

distance

C: external spray 4.93* 5.64* 13.23* 10.37*

use

D: underboom 0.05 0.55 0.02 0.05

spray use

Interaction: AB 0.09 1.31 2.94 0.02

Interaction: AC 1.17 0.11 0.51 0.06

Interaction: AD 0.16 1.17 1.70 0.11

Interaction: BC 12.20* 4.76* 8.10* 7.35*

Interaction: BD 3.49 4.08 0.56 1.11

Interaction: CD 1.48 0.54 1.88 15.10*

Critical F-value = F0.95,1,37= 4.11

* = significant at 0.95 level of confidence
Water Curtain External Underboom

spray setback sprays sprays Tracer gas levels in box cut, ppm (standard deviation)

pressure distance Tracer gas levels in slab cut, ppm (standard deviation)

(kPa) (m) (on/off) (on/off) Off-curtain side Curtain side Return

620 9.1 off off 4.34 (0.37) 0.58 (0.03) 1.48 (0.04)

3.48 (0.21) 2.05 (0.37) 1.52 (0.07)

1172 9.1 off off 4.35 (0.19) 1.17 (0.03) 1.49 (0.10)

3.95 (0.31) 2.06 (0.53) 1.49 (0.07)

620 12.2 off off 4.72 (0.20) 0.92 (0.02) 1.61 (0.06)

4.84 (0.40) 1.06 (0.11) 1.47 (0.01)

1172 12.2 off off 4.59 (0.24) 1.32 (0.17) 1.48 (0.02)

4.38 (0.31) 1.57 (0.24) 1.51 (0.16)

620 9.1 off on 5.72 (0.66) 0.77 (0.20) 1.52 (0.06)

5.59 (3.23) 2.96 (0.92) 1.51 (0.05)

1172 9.1 off on 5.43 (0.65) 1.39 (0.38) 1.42 (0.05)

4.49 (0.42) 3.17 (0.27)1.55 (0.09)

620 12.2 off on 6.74 (0.59) 1.13 (0.16) 1.51 (0.05)

6.12 (0.70) 1.63 (0.15)1.51 (0.05)

1172 12.2 off on 6.71 (0.27) 1.70 (0.20) 1.58 (0.05)

6.13 (0.57) 2.14 (0.21)1.48 (0.03)

620 9.1 on off 0.84 (0.10) 0.66 (0.14) 1.42 (0.05)

1.01 (0.06) 3.32 (0.24)1.48 (0.02)

1172 9.1 on off 0.48 (0.06) 2.59 (0.26) 1.54 (0.12)

0.91 (0.08) 4.05 (0.31)1.50 (0.08)

620 12.2 on off 1.57 (0.14) 1.33 (0.09) 1.59 (0.16)

1.16 (0.20) 2.08 (0.29)1.52 (0.04)

1172 12.2 on off 0.94 (0.06) 1.73 (0.21) 1.50 (0.04)

1.02 (0.12) 2.67 (0.28)1.50 (0.07)

620 9.1 on on 1.74 (0.03) 1.64 (0.17) 1.50 (0.07)

2.31 (0.46) 3.28 (0.43)1.46 (0.03)

1172 9.1 on on 1.17 (0.03) 2.28 (0.54) 1.46 (0.13)

1.90 (0.17) 3.46 (0.04)1.49 (0.07)

620 12.2 on on 2.35 (0.12) 1.46 (0.04) 1.54 (0.05)

2.81 (0.13) 2.28 (0.10)1.55 (0.06)

1172 12.2 on on 1.68 (0.14) 1.93 (0.14) 1.55 (0.10)

1.91 (0.29) 2.29 (0.04)1.57 (0.08)

Table 4. Untransformed tracer gas levels measured in box and slab cuts (ppm)

Figure 3. Impact of external and underboom sprays on

untransformed miner operator dust levels.
Source of Off-curtain side Curtain side Return

variation (box cut)

A: water pressure 35.79* 82.96* 0.61

B: curtain setback 86.00* 2.84 7.32*

distance

C: external spray 2716.20* 51.51* 0.00

use

D: underboom 248.86* 12.79* 0.02

spray use

Interaction: AB 0.05 10.85* 0.00

Interaction: AC 24.33* 1.36 0.56

Interaction: AD 0.00 3.95 0.02

Interaction: BC 5.82* 0.42 0.00

Interaction: BD 0.56 7.38* 0.02

Interaction: CD 0.02 0.02 0.02

Source of 

variation (slab cut) Off-curtain side Curtain side Return

A: water pressure 2.36 12.19* 0.20

B: curtain setback 7.94* 108.18* 0.46

distance

C: external spray 275.14* 73.37* 0.13

use

D: underboom 47.34* 11.14* 0.55

spray use

Interaction: AB 0.25 1.22 0.13

Interaction: AC 0.78 0.03 0.07

Interaction: AD 1.20 1.18 0.16

Interaction: BC 2.35 0.11 3.81

Interaction: BD 0.09 0.04 0.28

Interaction: CD 2.42 24.83* 0.00

Critical F-value = F0.95,1,37= 4.11

* = significant at 0.95 level of confidence

Table 5. F-ratios from ANOVA analyses of square root transformed SF6 data, box and slab cuts (n=3)

Table 6. Untransformed full-cut dust and gas levels

Full-cut dust levels, mg/m3 Full-cut tracer gas levels, ppm

Water Curtain Mining Standard Off standard Return Off Curtain Return

spray setback External Underboom machine shuttle car shuttle car curtain side

pressure distance sprays sprays operator operator operator side

(kPa) (m) (on/off) (on/off)

620 9.1 off off 0.06 0.07 0.09 0.88 3.99 1.17 1.50

1172 9.1 off off 0.04 0.06 0.09 0.65 4.19 1.53 1.49

620 12.2 off off 0.13 0.05 0.14 0.87 4.77 0.97 1.55

1172 12.2 off off 0.15 0.06 0.10 0.70 4.50 1.42 1.49

620 9.1 off on 0.04 0.05 0.14 1.16 5.67 1.64 1.52

1172 9.1 off on 0.04 0.03 0.13 1.14 5.05 2.10 1.47

620 12.2 off on 0.22 0.08 0.20 1.28 6.49 1.33 1.51

1172 12.2 off on 0.18 0.07 0.15 1.12 6.48 1.88 1.54

620 9.1 on off 0.05 0.08 0.16 1.47 0.91 1.72 1.44

1172 9.1 on off 0.08 0.08 0.22 1.97 0.65 3.18 1.52

620 12.2 on off 0.34 0.12 0.25 1.77 1.41 1.63 1.56

1172 12.2 on off 0.33 0.10 0.37 2.08 0.97 2.11 1.50

620 9.1 on on 0.05 0.06 0.16 1.43 1.97 2.29 1.48

1172 9.1 on on 0.04 0.05 0.13 1.10 1.46 2.75 1.47

620 12.2 on on 0.38 0.14 0.32 1.67 2.54 1.79 1.54

1172 12.2 on on 0.25 0.08 0.24 1.44 1.77 2.07 1.56

6 Conclusions

Miner operator dust exposures increased with increasing

curtain setback distance and use of the external sprays with

the machine in the box or slab cut. The interaction of these

variables also significantly impacted operator dust levels. In

the box cut, the interaction of water pressure and underboom spray use negatively affected dust levels. 

The external sprays increased dust levels for the standard and off-standard shuttle car operators and in the return

by blowing the dust cloud past the scrubber inlets. These

effects were similar with the mining machine in either the

box or slab cut. Curtain setback distance impacted the offstandard operator in the box cut and return airway dust levels with the miner in the slab cut. With the machine in the

box cut, interactions between water pressure and use of the

underboom or external sprays and interactions between the

underboom and external sprays significantly impacted dust

levels at the off-standard shuttle car location and in the

return airway. In the slab cut, an interaction between curtain

setback and external spray use significantly affected dust

levels at the two shuttle car locations and in the return airway. A final interaction between uses of the external and

underboom sprays impacted dust levels in the return.

The external sprays increased air velocity around the cutter head, decreasing gas levels on the off-curtain side and

elevating levels on the curtain side. The underboom sprays

increased gas levels on both sides. In general, increasing

water pressure reduced off-curtain side gas levels while

increasing curtain side gas levels. Increasing setback distance elevated gas levels on the off-curtain side of the cutter

head for all positions of the continuous miner and
increased gas levels on the curtain side with the machine in

the slab cut. In the box cut, interactions between water

pressure and external spray use and setback distance and

underboom spray use impacted off-curtain side gas levels.

Interactions between setback distance and water pressure

or underboom spray use significantly affected gas levels on

the curtain side of the cutter head. n the slab cut, external

spray use interacted significantly with underboom spray

use to increase gas levels on the curtain side of the cutter

head.

Use of the external sprays reduced full-cut gas levels

measured on the off-curtain side of the cutter head and

increased these levels on the curtain side, although the

increase was minimal at the lower spray pressure. These

sprays had minimal impact on full-cut dust levels at all sampling locations. The underboom sprays, which adversely

affected full-cut gas levels and provided little benefit on fullcut dust levels, are not recommended.

7 Rerences

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