UNITED STATES BUREAU OF MINES

UNITED STATES DEPARTMENT OF THE INTERIOR

RI 9616 REPORT OF INVESTIGATIONS/1995

Assessment of Airborne Dust Generated

From Small Truck-Mounted Rock Drills

By J. A. Organiscak and S. J. Page
U.S. Department of the Interior

Mission Statement

As the Nation’s principal conservation agency, the Department of the

Interior has responsibility for most of our nationally-owned public

lands and natural resources. This includes fostering sound use of our

land and water resources; protecting our fish, wildlife, and biological

diversity; preserving the environmental and cultural values of our

national parks and historical places; and providing for the enjoyment

of life through outdoor recreation. The Department assesses our

energy and mineral resources and works to ensure that their

development is in the best interests of all our people by encouraging

stewardship and citizen participation in their care. The Department

also has a major responsibility for American Indian reservation

communities and for people who live in island territories under U.S.

administration.
Report of Investigations 9616

Assessment of Airborne Dust Generated From

Small Truck-Mounted Rock Drills

By J. A. Organiscak and S. J. Page 

UNITED STATES DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

BUREAU OF MINES

Rhea Lydia Graham, Director
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract ........................................................................................... 1

Introduction ........................................................................................ 2

Dust survey of small rock drills ........................................................................ 2

Sampling strategy and precision ..................................................................... 2

Dust emission sources ............................................................................. 5

Improved dust controls for small truck-mounted drills ...................................................... 7

Abatement dust controls ........................................................................... 7

Wet dust suppression of Rotoclone exhaust ......................................................... 7

Improved dust capture at the drill deck shroud ....................................................... 8

Shrouded Rotoclone hopper discharge ............................................................. 9

Wet drilling ................................................................................... 9

Dust avoidance techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Extended rotoclone exhaust port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Worker positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

ILLUSTRATIONS

1. Plan view of dust sampling strategy ................................................................ 3

2. Plan view of cyclone sampling orientation with respect to wind .......................................... 4

3. Plot of regression models for air velocity effects on dust sampler orientation ............................... 4

4. Drill with dust emissions around the drill deck shroud and the exhaust of the Rotoclone dust collector .......... 5

5. Dust cloud generated during Rotoclone dust-collector dumping .......................................... 6

6. Graph of instantaneous dust levels during a typical dust-collector dumping ................................ 6

7. Visible dust in the Rotoclone exhaust of a coal mine drill ............................................... 8

8. No visible dust in the exhaust from a drill equipped with the water-trickle system ........................... 8

9. An improved drill deck shroud arrangement .......................................................... 9

10. No visible dust with the shrouded collector dumping operation and field installation of Rotoclone exhaust extender

10

TABLES

1. Dust sampling data from small highwall drills ........................................................ 3

2. Drill area dust sample averages .................................................................... 6

3. Dust control evaluation data for small highwall drills .................................................. 7
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

Metric Units

L liter mg millligram

Lpm liter per minute mg/m milligram per cubic meter 3

m meter mm millimeter

m/s meter per second

U.S. Customary Units

fpm foot per minute min minute

ft feet mph mile per hour

gal gallon pct percent

gpm gallon per minute RPM revolution per minute

h hour s second

in inch

Reference to specific products does not imply endorsement by the U.S. Bureau of Mines.
Mining engineer. 1

Research physicist. 2

 Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh PA.

ASSESSMENT OF AIRBORNE DUST GENERATED FROM SMALL

 TRUCK-MOUNTED ROCK DRILLS

By J. A. Organiscak and S. J. Page 1 2

ABSTRACT

Dust surveys were conducted around small truck-mounted rock drills operating at surface coal mines to assess

their airborne respirable dust generation and in-service dust control methods. Of four out of seven drills

sampled, respirable dust concentrations measured around the drill deck ranged from 8.68 to 95.15 mg/m with 3

concentrations ranging from 1.37 to 2.69 mg/m at distances 12.2 to 30.5 m downwind of these drills. The other 3

drills had noticeably lower respirable dust concentrations measured around the drill deck at or below 1.30 mg/m .3

Rotoclone-type dry dust collectors were commonly used with dust being emitted from around the drill deck

shroud, collector exhaust, and collector fines dumping. Wind speed and direction was also a factor in the dust

concentrations measured on the bench.

Dust control modifications were made to three rock drills to reduce their airborne dust emissions. Dust

controls tested included water injection into the Rotoclone exhaust, Rotoclone exhaust extension, improved

sealing of drilling deck shroud, shrouding the Rotoclone hopper dump process, and wet drilling. These control

techniques showed noticeable improvement in dust concentrations measured around the drills. Finally,

repositioning the drill operator showed that operator dust exposure can be improved by avoiding the dust cloud

around the drill.
2

INTRODUCTION

Silica dust continues to be an ongoing health concern in the significant variable affecting the degree of dust control

coal mining industry. Exposure to crystalline silica dust can appeared to be operation of the systems (4). Dry dust

cause serious or fatal respiratory disease. The three types of

silicosis, depending on the airborne concentration of crystalline

silica and length of exposure are: chronic, occurring after 10 or

more years of exposure to relatively low concentrations; degradation and bit wear from operating in an abrasive rock

accelerated, occurring 5 to 10 years of exposure to high dust-slurry environment. To improve the effectiveness of these

concentrations; and acute, occurring after a few weeks to 5

years exposure to extremely high concentrations.

The Mine Safety and Health Administration's (MSHA)

permissible dust standard for coal mine workers is a shift

average of 2.0 mg of airborne respirable coal mine dust per

cubic meter of air (2.0 mg/m as defined by the Mining 3

Research Establishment (MRE) Criteria)(1). If the airborne 3

respirable dust (ARD) sample contains more than 5 pct quartz

(crystalline silica), the dust standard is reduced to the quotient

of 10 divided by the percentage of quartz in the dust, limiting

the respirable crystalline silica exposure to a maximum of 0.1

mg/m (MRE equivalent). These respirable dust standards are 3

expected to significantly reduce a worker's risk to occupational

lung disease throughout an average life expectancy. The

Occupational Safety and Health Administration (OSHA) also

reduces their dust standards for crystalline silica in mineral

dusts in nonmining occupations (2).

In the late 1980's, surface mine highwall drill operators

accounted for about 20 pct of the more stringent dust standards

issued by MSHA in the coal industry, and this occupation had

the lowest average reduced standard at 0.8 mg/m (3). Many of 3

the highwall drill operators were on reduced standards below

0.5 mg/m , indicating that this occupation had silica exposure 3

risks. U.S. Bureau of Mines (USBM) research on surface mine

overburden drills in the late 1980's showed that dust controls

typically used on large track-mounted surface drills are either

a dry cyclone-filter type or a wet suppression system that

injects small quantities of water into the bailing air. Both dry

and wet dust collection systems were capable of achieving dust

reductions of 95 pct, but the most

collectors usually had emission problems with collector

dumping and cleaning, and dust leakage around the drill deck.

Wet drilling had problems with reduced bit life due to bearing

dust control systems, the USBM identified several concepts to

rectify the problem areas identified with the existing systems

(5). Dust control methods that improved the effectiveness of

dry collection systems include a pin-type agglomerator for

dumping the collector cuttings and an air ring seal to contain

dust from escaping the drill deck. Water quantity guidelines

and a water separator inside the bit stabilizer were found to

improve dust capture and increase bit life for wet drilling

systems. USBM research established that viable dust control

technology is available to control dust on large track-mounted

surface drills.

The National Institute for Occupational Safety and Health

(NIOSH) has recently issued an NIOSH Alert: Request for

Assistance in Preventing Silicosis and Deaths in Rock Drillers

(6). In this report, NIOSH documented cases of acute,

accelerated, and chronic silicosis in surface mine drill

operators. The age of these workers start as low as 25 with

cases of workers in their 30's. Since many of these personnel

worked on small rotary rock drills, NIOSH concluded that

inadequate dust controls are being used on many small mobile

rock drills and requested that the USBM investigate these types

of rock drills.

The USBM dust research program, in response to the

NIOSH Alert and request for investigation, recently studied

small surface mine drills to assess their dust generation hazards

and the effect of dust control technologies implemented. Most

of these drills were truck-mounted and used Rotoclone dry-dust

collection systems. This report describes the initial dust source

surveys and assessment of dust control enhancements for small

mobile rock drills.

DUST SURVEY OF SMALL ROCK DRILLS

SAMPLING STRATEGY AND PRECISION drill deck and on the surface mine bench downstream of the

The USBM conducted dust sampling around seven truck- they could be positioned 0.6 to 1.5 m (2 to 5 ft) off the ground.

mounted rock drills operating at small surface coal mines. The Each tripod had a real-time aerosol monitor, a RAM-1, (with a

dust sampling strategy encompassed sampling in the visible data logger) and two personal respirable dust gravimetric

dust clouds around the samplers. Initially two sampling stations (tripods) were

Italic numbers in parentheses refer to items in the list of references at the 3

end of this report.

drill (see figure 1). Dust samplers were placed on tripods so

positioned on each side of the drill deck and one sampling

station on the bench. Depending on the wind
3

Figure 1

Plan view of dust sampling strategy.

direction, only one sampling station around the drill deck was

exposed to the dust cloud, so only one sampling station was

positioned on the immediate downstream side of the drill deck

with two sampling stations positioned downstream 12.2 to 30.5

m (40 to 100 ft) of the drill on the mine bench. Sampling

stations were moved with the drill, and sampling times ranged

from 2 to 4 h. The bench sampling stations were positioned at

varying distances from the drill to accommodate the bench

terrain and sample the Rotoclone exhaust dust cloud

descending onto the bench. Momentary RAM sampling was

also conducted in the dust cloud generated by dumping the

cuttings from the dust collector every few holes drilled. All the

dust concentrations measured are not worker dust exposures,

but indicate the respirable dust concentrations in the visible

dust clouds around the drill. Also, all airborne respirable dust

concentrations measured by personal dust samplers (Atomic

Energy Commission (AEC) Criteria (2)) in this study are not

reported as MRE equivalent concentrations. A MRE equivalent

concentration is a personal sampler concentration multiplied

by a constant factor prescribed by the Secretary of Labor (1).

The results of the dust surveys are shown in table 1. Initial

dust sampling results from the first two drills sampled (A and

B) showed a large variation between dust concentrations

measured by the two personal dust samplers on each tripod (see

table 1). Sampling at these two drills was conducted under

high gusty wind conditions with the personal sampler cyclones

(respirable dust classifiers) placed on each side of the RAM not

necessarily oriented (cyclone inlets)

Table 1.—Dust sampling data from small highwall drills

Drill Sample location

Sampler orientation

Air

velocity

Random Parallel Perpendicular

Dust conc.,

 mg/m var. mg/m var. mg/m var. 3

Coef. of Dust conc., 3Coef. of Dust conc., 3Coef. of

A . . Downstream drill on bench . .

Left side of drill ............

Right side of drill ...........

0.33 ± 0.48

1.03 ± 0.67 0.67 (20 mph)

1.58 ± 1.32 1.32

1.07 ND ND ND ND Est. @ >8.9 m/s

B . . Downstream drill on bench . .

Downstream drill on bench . .

Left side of drill ............

1.79 ± 3.18 1.28 ND ND ND ND Est. @ >8.9 m/s

0.18 ± 0.09 0.36 (20 mph)

0.54 ± 0.31 0.42

C . . Downstream drill on bench . .

Downstream drill on bench . .

Next to drill shroud .........

ND ND 2.86 ±0.17 0.04 2.26 ±0.03 0.01 4.1-7.6 m/s

2.98 ±0.65 0.16 2.69 ±0.01 0.00 (800-1,500 fpm)

11.44 ±1.30 0.08 8.30 ±1.22 0.11 

D . . Downstream drill on bench . .

Downstream drill on bench . .

Next to drill shroud .........

ND ND 1.35 ±0.09 0.05 1.78 ±0.37 0.15 1.5-2.0 m/s

2.21 ±0.59 0.19 2.02 ±0.76 0.27 (290-400 fpm)

118.03 ±30.89 0.19 72.28 ±6.01 0.06 

E . . Next to drill shroud . . . . . . . . . ND ND 1.23 ±0.29 0.17 ND ND ND 1.5-2.0 m/s

 (290-400 fpm)

F . . Downstream drill on bench . .

Downstream drill on bench . .

Next to drill shroud .........

ND ND 2.47 0.26 1.0-1.7 m/s

1.47 ±0.26 0.13 2.50 ±1.31 0.38 (200-326 fpm)

13.44 ±0.25 0.01 10.09 ±0.25 0.02 

G . Downstream drill on bench . .

Downstream drill on bench . .

Next to drill shroud .........

ND ND 0.90 ±0.30 0.24 0.83 ±0.05 0.04 1.6-1.8 m/s

3.02 ±4.32 1.03 0.76 ±0.10 0.09 (320-345 fpm)

8.62 ±0.84 0.07 8.74 ±0.74 0.48 

Average 0.91 0.85 14.07 0.20 9.38 0.15 1 1

ND No data.

Drill E not in average because sampler orientation comparisons were not made at this drill. 1

NOTE:—Bold numbers identify significant differences between dust concentrations measured with different sampler orientations.
4

Figure 2

Figure 3

in the same direction with the wind. The average coefficient of analysis showed a similar good fit with a model of Y = X (R

variation for these sampler pairs was 85 pct. When sampling = 0.90 (see figure 3). The fitted curve is shown with a dashed

drills C through G, two more personal samplers were added to line up to 10 mg/m and the dotted line is the model extrapolation

each tripod, and a pair of cyclone inlets were oriented reasonably above the regression data range. Also shown on figure 3 is the

into the wind (parallel) and 90E (perpendicular) to the wind in an unity curve Y = X , assuming equal dust concentrations for

attempt to improve precision and identify a wind effect on different sampler orientations. Both regression curves were

sampler orientation (see figure 2). Several 1-min air velocity found to be significantly different from the unity line (at a 95-pct

measurements were taken with a vane anemometer during dust confidence level) and these curves both bend toward the Y axis

sampling (reported in table 1). Results of this sampling (parallel sampler), indicating that higher dust concentrations

modification showed that sampling error was notably reduced were measured with the parallel orientation. This sampling

with consistent sampler orientation and four of the sampler pairs difference is noticeable at higher dust concentrations. However,

had significant differences (at the 95 pct confidence level) in smaller differences in dust concentrations for sampler orientadust concentrations measured with the different sampler tions are predicted by both regression models at lower dust

orientations (shown in bold print in table 1). Nine out of the concentrations. For example, if the perpendicular oriented dust

eleven sampler pairs had higher concentrations oriented into the sampler measured 2.0 mg/m , the regression models predict that

wind. The average concentrations measured into the wind the parallel concentrations would be between 2.1 and 2.2 mg/m

(parallel) was 14.07 mg/m and perpendicular to the wind was under the air velocity conditions measured in this study, 1.0 to 3

9.38 mg/m . The average coefficient of variations for parallel 7.6 m/s (200 to 1,500 fpm). 3

and perpendicular orientation pairs were 20 and 15 pct, Prior USBM research has shown that respirable dust

respectively. It must be noted that some inconsistencies or errors concentrations can be affected by cyclone orientation (7).

in the orientation study were introduced by some wind direction

variations, but samplers were reasonably operated for a majority

of the time in the indicated sampler orientations.

Regression analysis of the sampler inlet orientation data also

indicates that the samples oriented into the wind tend to have

higher concentrations, particularly at high dust levels.

Regression analysis of the perpendicular sampler (X) and

parallel sampler (Y) data showed the model Y = X (R = 0.99) || z

1.11 2

to be a good fit (see figure 3). Since one data point in this

analysis is significantly higher than the other point and can

notably influence the regression model, another regression analysis was conducted with the highest data point removed. This 

Plan view of cyclone sampling orientation with respect to

wind.

|| z

1.09 2

3

|| z

3

3

Cyclone orientation into the airstream showed 20 pct

Plot of regression models for air velocity effects on dust

sampler orientation.
5

Figure 4

over-sampling at air velocities of 6.1 m/s (1,200 fpm) and in- ambient wind on the drill bench will carry away the emitted dust.

creased to over 30 pct at 10.2 m/s (2,000 fpm). Cyclone The dust cuttings removed by the collector are accumulated in

orientation perpendicular to the airstream showed 20 pct hoppers and have to be manually dumped or emptied

undersampling at air velocities as low as 2.0 m/s (400 fpm) and periodically. One of the seven drills studied (drill E) used a

increased to 30 pct at 6.1 m/s (1,200 fpm) and 40 pct at 10.2 m/s Donaldson filter-type dust collector instead of the Rotoclone that

(2,000 fpm). These results indicate that cyclone orientation eliminated the dust emission source from its collector exhaust.

sampling error, depending on air velocity, can produce either This type of dust collector also had an automated dump port

over sampling or under sampling when the cyclone orientations close to the bench surface, eliminating the dust cloud generated

vary by 90E. Since most of the air velocities measured in the from emptying the collector cuttings.

above study were under 6.1 m/s (1,200 fpm), the most influential The two primary and constant dust emission sources from the

effect was probably undersampling with the samplers oriented Rotoclone collector were from the drill deck shroud and the dust

perpendicular to the wind. However, air velocities above 10.2 collector discharge exhaust. Figure 4 visibly shows these two

m/s (2,000 fpm) may impact lower dust concentration emission sources when a drill is operating. Table 2 shows the

measurements as theorized from the poor sampling precision average dust concentration and quartz content of all the samplers

measured under high gusty wind conditions observed at drills A (oriented parallel and perpendicular to the wind) located around

and B. the shroud and on the drill bench for each drill sampled. As can

DUST EMISSION SOURCES were usually around the drilling deck with lower dust

The dust generated at these drills was a result of poor from the drill. Four of the seven drills had average dust

containment of the dust by the collector. These drills typically concentrations greater than or equal to 8.68 mg/m around the

use a Rotoclone dust collector. This dust collector is basically a drill deck shroud. These drills usually had a shroud with gaps

dry centrifugal fan separator, equipped with a pre-separator. along the adjoining seams of each side or a large gap between the

The intake of the Rotoclone is ducted from the drill deck which ground and shroud, allowing dust to escape the collector inlet.

is enclosed or shrouded with belting material. Although the Also, some of the operators would leave one side of the shroud

Rotoclone is effective in removing total airborne dust material pulled up to shovel cuttings. Drills A, B, and E had wellfrom the intake, it still discharges significant quantities of constructed shrouds with smaller gaps, contributing to the lower

respirable dust to the atmosphere. The exhaust of the Rotoclone dust concentrations measured around the drill deck (#1.30

is usually directed vertically upwards with the intention that the mg/m ).

be seen from this table, the highest dust concentrations measured

concentrations measured 12.2 m to 30.5 m (40 to 100 ft) away

3

3

 Drill with dust emissions arround the drill deck shroud and the exhaust of the Rotoclone dust collector.
6

Table 2.—Drill area dust sample averages

Drill Sampler location Mean conc.,

mg/m3

Mean 

quartz, pct

A . . Downstream drill on bench .

Right side of drill .........

0.33

1.30

( )1

( )1

B . . Downstream drill on bench .

Left side of drill ..........

0.98

0.54

( )1

( )1

C . . Downstream drill on bench .

Next to drill shroud ........

2.69

9.87

12.3

10.4

D . . Downstream drill on bench .

Next to drill shroud ........

1.84

95.15

11.4

13.7

E . . Next to drill shroud ........ 1.23 8.1

F . . Downstream drill on bench .

Next to drill shroud ........

1.98

11.76

7.1

5.3

G . . Downstream drill on bench .

Next to drill shroud ........

1.37

8.68

6.5

6.9

or quartz analysis. Not enough weight f 1

Figure 5

Figure 6

The Rotoclone exhaust stream is directed vertically upwards dispersion by wind creates a substantial airborne dust problem.

above the drill so the wind will dilute and/or carry away the Figure 5 visibly shows the dust cloud that can be generated from

emitted dust. However, on small drill benches in the hilly terrain emptying the Rotoclone hopper and figure 6 shows a graph of

of the Appalachian Mountains, the wind commonly hugs the the typical respirable dust concentrations while emptying the

terrain, passing over the drill and swirling back onto the drill dust collector. As can be seen in these two figures, the airborne

bench. The bench sampler locations downstream of the drill dust concentrations are high but occur during short intervals (a

were positioned in the visible dust swirling from the Rotoclone few minutes) every couple of holes. Although the total portion

exhaust back onto the bench, measuring its contribution to dust of time exposed to this dust source is small, the high level of dust

concentrations on the bench. These bench dust concentrations, concentration generated can still influence dust exposure.

12.2 m to 30.5 m (40 to 100 ft) downstream of the drill, ranged

Dust cloud generated during Rotoclone dust collector

dumping.

 from 0.33 to 2.69 mg/m , averaging 1.53 mg/m . Although 3 3

these dust concentrations are a lot lower than around some of the

drill decks sampled, they are not insignificant when the quartz

content of the dust is high. Quartz content or the dust clouds

sampled at each drill were similar at the bench and drill deck

location, indicating that the quartz content of the dust is similar

regardless of where it is emitted by the drill. The measurable

quartz content of all the dust clouds sampled in this study were

between 5.3 to 13.7 pct, which would reduce the dust standard

for mine workers exposed to these dust clouds to somewhere

between 2.0 and 0.8 mg/m .3

A less frequent, although still significant, third source of dust

is the dumping of the Rotoclone hopper(s). The hoppers retain

the dust removed by the Rotoclone and must be periodically and

manually emptied. This is accomplished by opening two trap

doors and letting the material fall out to the ground, a distance of

0.9 to 1.2 m (3 to 4 ft). Impact of the material and subsequent

Graph of instantaneous dust levels during a typical dust

collector dumping.
7

IMPROVED DUST CONTROLS FOR SMALL TRUCK-MOUNTED DRILLS

Poor containment of the dust by the Rotoclone collector ABATEMENT DUST CONTROLS

system was the most common problem associated with small

truck-mounted rock drills. The USBM evaluated several drill Abatement dust control techniques that were studied included

modifications and operating practices to identify improved dust water injected (trickled) into the Rotoclone exhaust, improved

control techniques for these small truck-mounted rock drills. dust capture at the drill deck shroud, shrouded Rotoclone hopper

The dust control methods studied were either abatement or discharge, and wet drilling. These techniques were evaluated at

avoidance techniques. Abatement techniques contain or capture two drilling sites on three different drills. Evaluation of each

the dust before it becomes airborne in the worker's environment, control technique was conducted on the same drilling bench

avoidance techniques involve keeping the worker out of the dust during one operating shift, half of shift with the baseline

cloud that is emitted. condition(s) and the other half of the shift with controlled

Assessment of dust control techniques was conducted at three condition(s). Results of these field studies are shown in table 3.

different drill operations. Some of these controls were studied

individually and some were studied in combination. Dust Wet Dust Suppression of Rotoclone Exhaust

sampling was conducted with RAM and gravimetric samplers

mounted on a tripod, similar to the source identification study, Wet suppression of the dust in the Rotoclone exhaust was

except that three gravimetric samplers were oriented into or conducted by injecting small quantities of water into an extended

parallel to the airflow on the bench. Prior USBM research Rotoclone discharge duct on drill H. The Rotoclone discharge

concluded that this sampler orientation is less susceptible to air port was rotated so that the discharge is horizontal or

velocity effects, especially under 10.2 m/s (2,000 fpm) air downward. Approximately 6.1 m (20 ft) of flexible tubing that

speeds. These samplers were placed downwind of the emission is approximately the same diameter as the discharge port, was

source before and after the modifications were made to the drill coupled to the port. Although not tested, a shorter length may

during the same operating shift. Again, these samplers were possibly work as well. The duct was mounted at a downwardmoved with the drill and commonly operated for 1 to 3.5 h of sloping angle along the side of the drill so that the exit remains

sampling during each test condition, and cannot be used for above the ground approximately 0.3 m (1 ft).

compliance purposes. Quartz analyses were conducted on the

samples that contained enough weight for analysis.

Table 3.—Dust control evaluation data for small highwall drills

Drill Dust control method Sampler location

Controls OFF Controls ON Efficiency

 Dust

 conc., content, conc., content, conc., content,

mg/m pct mg/m pct mg/m pct 3

Quartz Dust

3

Quartz Dust

3

Quartz 

H.... Wet dust suppression of Roto-

 clone exhaust. haust.

Next to Rotoclone ex- 27.20 21.1 2.14 18.5 -92.1 -12.3

I..... Extended Rotoclone exhaust and Downstream drill on 1.22 9.9 0.46 7.8 -62.3 -21.1

 closed drill shroud. bench.

Extended Rotoclone exhaust and Next to drill shroud. 2.34 10.0 0.86 11.0 -63.2 10.2

 closed drill shroud.

Rotoclone discharge hopper en- Next to discharge hop- 25.42 ( ) 4.94 ( ) -80.6 ( )

 closed. per.

Sampler location—on drill vs on Drill control panel and 1.56 14.0 1.51 11.6 -3.2 -17.1

 operator. operator.

Operator location—standing back Next to and away from 1.51 11.6 0.47 ( ) -68.9 ( )

 from drill. shroud.

1 1

1

1

1

J .... Wet drilling .................... 2 Next to drill shroud. 1.18 12.1 0.84 10.1 -28.8 -16.8

or quartz analysis. Not enough weight f 1

Efficiency is a comparison with drill I using all controls operating on the same drilling bench. 2
8

Figure 7 Figure 8

A water tank of approximately 378 L (100 gal) capacity was airflows that can be obtained on a given size of Rotoclone due to

mounted at a location and elevation that is suitable for gravity- the RPM of operation, the amount of water used must be

feeding a small amount of water into the Rotoclone discharge determined individually for each application. One simple

port. The drill operator using this system used an old truck fuel guideline is to slowly increase the trickle flowrate until the

saddle tank. It is estimated that 378 L (100 gal) or less will be visible emissions are significantly reduced. It will be found that

sufficient for 8 h of continuous drilling, using 0.76 Lpm (0.2 as the duct interior becomes wetted, the dust reduction will

gpm) flowrate for most Rotoclone sizes typically used on small improve with time.

drills. Due to the low flowrate, the water from the tank was Also, the down-sloping of the discharge duct is important to

supplied through 6.35-mm (1/4-in) tubing. Any variety of allow excess water to drain from the line. Actual extended

fittings suitable can be mounted in the metal discharge port of operation of the system showed that some material

the Rotoclone. It is recommended that two valves be used to agglomeration will occur within the first foot of duct length

control the water flow, one as a flow regulator and the second during an 8-h drilling period. However, this material is easily

valve as the on/off control. removed by disconnecting the duct from the Rotoclone exit. If

In tests to compare the effectiveness of the water trickle in the duct is connected with a standard hose clamp, cleaning can

reducing dust emissions from the Rotoclone discharge, tests be performed in a few minutes.

were performed on the same drill bench with and without the use

of water. The results of dust sampling approximately 3.0 m (10

ft) directly downwind of the Rotoclone discharge, showed 92 pct

reduction of respirable dust and the elimination of all visible dust

emissions. Analysis of the dust samples showed that the quartz

content of the respirable samples decreased slightly from 21 pct

quartz without using water to 18 pct quartz with the water trickle

system (a negligible difference). Figures 7 and 8 show the

effectiveness of the trickle system on eliminating visible

emissions from the Rotoclone discharge. First-hand visual

observation of the discharge while using water could not detect

any emissions.

Operationally, it is critical not to use too much water to

prevent clogging problems. Because of the wide range of

Visible dust in the Rotoclone exhaust of a coal mine drill.

Improved Dust Capture at the Drill Deck Shroud

The existing drill deck shroud on the drill tested (drill I) was

generally found to be in good condition. In order to simulate an

inferior shroud, one lower corner of the front shroud flap was

fixed to a chain and hooked in the "up" position for the duration

of the test segment labeled "controls off". This practice was

employed by the drillers occasionally so that they could shovel

out some of the cuttings. However, during the "controls on" test

segment the flap was immediately lowered after shoveling.

Testing showed that reducing the leakage of the shroud area

simply by maintaining a shroud in good condition reduced the

dust emissions by approximately 63 pct. Leakage would still 

No visible dust in the exhaust from a drill equipped with the

water-trickle system.
9

Figure 9

occur along the seams occasionally, resulting in the measured calculated to determine the speed of operation or measured

dust concentration of 0.86 mg/m during the "controls on" test. directly with a strobe tachometer. 3

The changes in quartz content in the dust between the control

condition was negligible (10 pct with open shroud, 11 pct with Shrouded Rotoclone Hopper Discharge

closed shroud).

Figure 9 shows a conceptual diagram of an improved shroud Figure 10 shows a temporary installation of a shroud around

design that may provide significantly better sealing of the corner the hopper discharge doors on drill I used for test purposes. The

seams while maintaining the necessary flexibility. This design shroud consisted of brattice material and was mounted by large

has not been tested nor has it been found to be previously used magnets for ease of installation and removal during testing. Two

or described in the literature. However, it is the opinion of the flaps were cut in the shroud to allow the operator access to the

authors that it may be a design suitable for reducing dust hopper doors for opening and closing. ARD concentrations

emissions from the shroud used on both dry and wet drilling were reduced by an average of 80 pct during the testing. Since

operations. gravimetric dust samples were collected over short periods of

Important to the testing of the shroud is the fact that prior to time (minutes) during the Rotoclone dumping, not enough

testing, the drill operator increased the operating speed of the weight was collected for quartz analysis. The sole reason for the

Rotoclone close to the maximum recommended value of 3,000 measurement of any dust present while using the shroud was

RPM. According to the operator, the Rotoclone had been leakage at the open vertical seam in the shroud. Although

running significantly slower and the increased speed made a leakage was minimized by overlapping the shroud ends after the

noticeable difference to dust capture in the shroud. This fact is wrap-around, it could not be eliminated. A more permanent

important if many existing Rotoclones in operation are running installation would have a sealed seam and would certainly be

slower in comparison, resulting in a preferential increase in the expected to provide better control of the dust.

amount of dust escaping a shroud that is not in very good

condition. Thus, maintaining good shroud condition is more Wet Drilling

important at slower collector operating speeds. Previous

research on larger track-mounted rock drills show that as dust During the testing of dust controls on drill I, another identical

collector airflow to bailing airflow ratio increases from 2:1 to truck-mounted drill (drill J) operating on the same mining bench

8:1, the dust leakage from the shroud is significantly reduced used water injection down-the-hole instead of a Rotoclone

(5). Therefore, increasing the speed of the Rotoclone should be collector. This drill was also dust sampled downstream of the

advantageous to reducing dust leakage from the shroud. Since

they are usually belt-driven with pulleys, it can either be

drill deck shroud, thereby providing identical test conditions for

an ideal comparison between wet drilling and the modified

An improved drill deck shroud arrangement.
10

Figure 10

Rotoclone system. Compared to the Rotoclone collector with bench (figure 10). Testing was performed with and without this

the multiple improvements discussed above, wet drilling was 29 exhaust extension during the evaluation period. At a downwind

pct better in reducing ARD levels in the immediate drill vicinity distance of approximately 30.5 m (100 ft), the exhaust extension

where the operator would typically be located. In addition, the lowered ARD concentrations by an average of 62 pct. This

dust emission problem of the Rotoclone exhaust was eliminated. reduction was visually observed to be due to the effect of

DUST AVOIDANCE TECHNIQUES this, the air currents were not able to downdraft the dust

Avoidance dust control techniques that were studied included higher above bench level for a much longer distance. Although

extended Rotoclone exhaust port and worker positioning. These this technique does not "clean" the dust from the exhaust, it

techniques were also evaluated at drill I, concurrently with the appears to significantly reduce dust levels on the drill bench and

other controls being evaluated. Evaluation of each control may possibly be suitable for use when other mine personnel are

technique was conducted on the same drilling bench during one not located downwind of the drilling bench.

operating shift, half of the shift with the baseline condition(s)

and the other half of the shift with controlled condition(s). Worker Positioning

Results of these field studies are shown in table 3.

Extended Rotoclone Exhaust Port distances from the drilling deck of drill I to identify the

The exhaust port of the Rotoclone was fitted with a 2.4 m (8 its operation. One set of samplers (three gravimetric personal

ft) vertical section of 1.52-mm (6-in) PVC pipe to test the samplers) were mounted on the drill near the operator control

effectiveness in lowering the dust concentrations on the drill panel. Two other sets of samplers (two gravimetric samplers)

discharging the visibly emitted dust higher in the air. Because of

significantly with the result that the dust remained airborne

Dust sampling was conducted at several locations at various

significance of worker positioning around the drill deck during

No visible dust with the shrouded collector dumping operation and field installation of Rotoclone exhaust extended.
11

were worn by two USBM personnel standing at two different operator (1.51 mg/m ). However, a 69 pct lower dust conlocations away from the drill deck shroud. One mobile location centration was observed for the employee standing further back

was positioned near the drill operator close to the drill deck from the drilling deck (0.47 mg/m ). These results indicate that

shroud. The other location was about 3.0 m (10 ft) further away a conscientious drill operator can notably reduce his dust

from the drill with the USBM employee trying to avoid the dust exposure by standing away from the drill and only getting near

cloud. The dust sampling results showed that negligible the drill when shoveling cuttings, making drill adjustments, or

difference was observed between the samplers mounted on the changing drill steel.

drill (1.56 mg/m ) and the samplers worn next to the drill 3

3

3

CONCLUSIONS

Dust surveys conducted around small truck-mounted rock similar drilling conditions. Since drilling operations were

drills operating at surface coal mines showed that a significant constant during the shift, these evaluations are expected to be

amount of airborne respirable dust is emitted from the fairly representative measurements of dust control effectiveness.

Rotoclone-type dust collector. At four out of seven drills The evaluation results indicate that—

sampled, respirable dust concentrations measured around the

drill deck ranged from 8.68 to 95.15 mg/m with concentrations • Adding a low flow of water 0.76 Lpm (0.2 gpm) to the 3

ranging from 1.37 to 2.69 mg/m at distances 12.2 to 30.5 m (40 collector exhaust can reduce the dust emitted by 92 pct. 3

to 100 ft) downwind of these drills. Dust was emitted from • Increasing drill deck shroud containment and increasing

around the drill deck shroud, collector exhaust, and collector the rotoclone speed may reduce respirable dust levels by 63 pct.

fines dumping. The other three of these seven drills had notice- • Vertically extending the Rotoclone exhaust may reduce

ably lower respirable dust concentrations measured around the downwind respirable dust levels by 62 pct.

drill deck at or below 1.30 mg/m . These drills had well • Enclosing the Rotoclone hopper discharge may reduce 3

constructed shrouds with smaller gaps, contributing to their respirable dust levels by 80 pct.

lower dust concentrations measured around the drill deck. • Wet drilling by injecting small amounts of water into the

Dust sampling around these drills also indicated that wind bailing air appears to be more effective than an improved

direction and speed were factors in the dust concentrations Rotoclone drill deck shroud by 29 pct.

measured on the bench. Cyclones of the gravimetric samplers • Operator repositioning away from the drill during most of

oriented into the wind and perpendicular to the wind showed that its operation can keep him/her out of the dust cloud and reduce

the dust concentrations measured into the wind tended to be dust levels by 69 pct.

higher than the perpendicular measurement, especially for very

high dust concentrations. Prior USBM laboratory research These improvements are inexpensive and showed measshows that this effect can be present with air speeds as low as 2.0 ureable reductions of airborne respirable dust measured at

m/s (400 fpm). several locations around the drill. In addition, this class of drill

Dust collector improvements were made on several drills to has a much more extensive use in the construction industry.

control dust from the emission sources. Dust measurements Therefore, the results of this study are of direct benefit in

were made for part of the drilling shift with and without these reducing dust exposure to not only a small segment of the

improvements to evaluate their control effectiveness under mining industry, but the construction work force as well.

REFERENCES

1. U.S. Code of Federal Regulations. Title 30—Mineral Resources; Chapter 4. Zimmer, R. A., and S. R. Lueck. Investigation of Quartz Dust Sources

I—Mine Safety and Health Administration, Dep. Labor; Subchapter O—Coal and Control Mechanisms on Surface Coal Mine Operations (contract J0348032,

Mine Safety and Health; Part 70—Mandatory Health Standards—Underground PEI Associates, Inc.). USBM OFR 61A-86, 1986, 72pp.; NTIS PB 86-215852.

Coal Mines, Subpart B, Section 70.101; and Part 71—Mandatory Health 5. Page, S. J. Respirable Dust Control on Overburden Drills at Surface

Standards—Surface Coal Mines and Surface Work Areas of Underground Coal Mines. Published in the Proceedings of the AMC Coal Convention '91,

Mines, Subpart B, Section 71.101, U.S. Gov. Print. Off., Off. Fed. Reg., July 1, Pittsburgh, PA, June 5, 1991, pp 523-539.

1994. 6. NIOSH Alert: Request for Assistance in Preventing Silicosis and Deaths

2. U. S. Code of Federal Regulations. Title 29—Labor; Chapter in Rock Drillers [DHHS (NIOSH) 92-107], Aug. 1992, 15 pp.

XVII—Occupational Safety and Health Administration, Dep. Labor; Part 7. Cecala, A. B., J. C. Volkwein, R. J. Timko, and K. L. Williams. Velocity

1910.1000, U. S. Gov. Print. Off., Off. Fed. Reg., July 1, 1994. and Orientation Effects on the 10-mm Dorr-Oliver Cyclone. USBM RI 8764,

3. Organiscak, J. A., S. J. Page, and R. A. Jankowski. Sources and 1983, 11 pp.

Characteristics of Quartz Dust in Coal Mines. USBM IC 9271, 1990, 21 pp.

INT.BU.OF MINES,PGH.,PA 30225