Main belt entry

oO Crosseut
Q
a 2
3
fro
= 4
=) 5
m2
me 7 KEY
ro « RAM
8 « — Impactor
— Stopping
aR 9 c= Curtain
10. = Airflow direction
H © Sampling station
z 4 ft 19
20
. 32
3
1 { 33
“Stageloader- 34
Y crusher Cat" 35
{ 36
\
7O 37
+ 4
Longwall face ee

Figure 5.—Sampling station locations and equipment used for
longwall mining section survey. RAM = Instantaneous respirable
dust samper.

entry before crosscut 8. The same arrangement was used
at stations 2 and 3, which were 1,700 and 3,000 ft inby the
belt head, respectively. Two impactors and a RAM were
placed downwind of the stageloader-crusher at station 4 on
days 2 and 3 of the survey. Dust generated by the
stageloader-crusher could not be isolated on day 1 because
of its position in the entry, Face return air was sweeping
over most of the stageloader-crusher during day 1. Two
impactors were used to sample air in the adjacent entry at
station 5 on days 2 and 3 of the study. Table 6 shows
average gravimetric respirable dust levels collected in the
belt entry and the adjacent entry.

Table 6.—Results of longwall section survey

Measurement Day1 Day2 ODay3
Respirable dust levels at stations, !
mg/m?
1. : 067 «1.05 0.47
2 : 0.61 057 0.35
3. . 0.67 0.64 0.30
4. . a) 1.10 1.18
5. . Q 060 0.22
Production . seve tf. 315 205 325
Air velocity at stations, fpm:
To. on ce) 75 45
2. 55 5 70
3. 110 150 85

TStations 1, 2, and 3 were located 800, 1,700, and 3,000 ft

inby the belt head, respectively. Station 4 was downwind of the

stageloader-crusher, and station 5 was in an adjacent intake entry.
Station not used on day 1.

Air Leakage Into Belt Entry

The effect of belt entry length on respirable dust levels
could not be measured on this section because of airflow
patterns. Table 6 shows air velocities measured at the
sampling stations for each day of the study and daily
average production rates. Air from the adjacent entry was
leaking into the belt entry throughout its length. This air
may have acted to dilute the dust being generated by the
conveyor belt, This certainly appears to be the case on
day 3 of the study, because belt entry dust levels were
lower at station 3 than levels at station 1, and dust levels
in the adjacent entry were significantly lower than dust
levels in the belt entry.

Effect of Production Rate on Belt Entry Dust Levels

Daily fluctuations in production rates did not produce
an obvious trend in belt entry respirable dust levels upwind
of the crusher at this mine. However, the difference in
production rates between the longwall section and the
continuous miner section did appear to affect belt dust
levels, The daily average production rate on the longwall
section was about 280 st/h, while the daily average pro-
duction rate on the miner section was about 100 st/h.
Therefore, the longwall section produced about 1,440 st
per shift more than the miner section did. Using the
rough estimate of a 0.1-mg/m: increase in dust levels with
a 200-st-per-shift increase in production developed from
the continuous miner survey, one would expect belt entry
dust levels to be about 0.7 mg/m? higher on the longwall


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cfm

fpm

m/min

mg/m?

cubic foot per minute
foot per minute

foot

inch

cubic meter per minute

milligram per cubic meter

mg/min
min

pet

st

st/h

milligram per minute
minute

percent

short ton

short ton per hour



instrument scale during survey 1. Maximum RAM voltage
output corresponds to a 20-mg/m? dust level using this
setting. However, since dust levels never exceeded
2 mg/m? in the belt entry during survey 1, the more
sensitive 0-to-2-mg/m? setting was used during survey 2 in
an effort to isolate the possible effect of airflow on belt
entry dust levels. The air quantity in the belt entry was
changed at least once during the shift. RAM?’s were used
to compare dust levels during different levels of airflow at
each sampling station.

Figure 3 shows airflow and belt entry respirable dust
levels at station 3 during the time period from 14:41 to
17:11 on day 2. Production began at 14:41 and continued
through 16:06. This production period was followed by a
15-min break in production from 16:06 to 16:21 to move
the continuous miner. Mining operations started again at
16:21 and continued through 16:44. The period from 16:44
to 17:11 was downtime. Data collected during this time
period were similar to data collected during previous
shifts, The dust levels appeared initially to rise as mining
operations commenced. After a certain time period, about
45 min in this case, the dust levels appeared to stabilize
and remain consistent throughout the shift, independent of
airflow. Air velocity (airflow) was increased from 130 to
180 fpm during the time period from 14:41 to 16:05. Dust
levels also increased from about 0.18 to 0.30 mg/m? during
the time period from 14:41 to 15:26. However, dust levels
appeared to be independent of airflow, because when air
velocity was decreased to 105 fpm between 16:05 and
17:11, the dust levels remained consistent.

Dilution benefits from increased airflow may have been
offset by an increase in entrainment in the belt entry, re-
sulting from high relative air velocities. Since air velocity
in the belt entry was between 105 and 180 fpm and the
conveyor belt speed was maintained at 400 fpm during this
survey, coal on the belt was subjected to relative velocities
between 505 and 580 fpm. Past research conducted on
longwall faces indicates (5) that entrainment effects can
prevail over dilution effects at air velocities above 500 fpm.

190 T T T T 032

RESPIRABLE DUST CONCENTRATION,

&
=
z Py
§ 143 are
ro g
= Air velocity
« yi Dust level
= 1 ZZZZz Production

95 , ; : : 16

1411S S416 1641 ITAL

TIME

Figure 3.—Air velocity and dust level profiles collected in belt
entry.

SURVEY 3—EFFECT OF USING BELT ENTRY
TO VENTILATE FACE ON DUST LEVELS
AT VARIOUS SECTION LOCATIONS

The third miner section survey was designed to deter-
mine how using belt entry air to ventilate work areas
affected the respirable dust exposure levels of various
section occupations. The belt entry was used as an intake
entry on days 1 and 2 of the survey, and it was used to
draw air away from the face areas on days 3 and 4. About
6,000 cfm of air was measured in the belt entry for both
conditions. Gravimetric and instantaneous dust sampling
techniques were used to compare respirable dust levels at
various locations when the belt entry was used as an intake
entry with dust levels in the same locations when the belt
entry was used to draw air away from the face.

Sampling Equipment and Procedures

The survey was conducted with 10 personal impactors,
3 cyclone respirable dust samplers, and 4 RAM’s. Daily
average respirable dust concentrations were calculated
from the cyclone and impactor data. The RAM’s were
used to determine dust concentrations at various positions
during individual cuts. Airflow measurements were also
made throughout the 4-day survey. Airflow was measured
with smoke tubes in entries 2, 3, 4, 5, and 6. A ball-
bearing-type vane anemometer (continuous traverse tech-
nique) was used to measure airflows in entries 1 and 7.

Figure 4 shows sampling station locations and the
equipment used at each station. Sampling stations were
located in the belt entry (station 1), mouth of the belt
entry (station 2), right-side shuttle car cab (station 3), left-
side shuttle car cab (station 4), upwind of shuttle car
loading (station 5), and in the miner cab (station 6). Two
impactors were placed at all stations but station 6. Miner
cab dust levels were expected to be much higher than dust
levels at other positions; therefore, cyclone respirable dust
samplers were used at station 6 instead of impactors.
Cyclones can handle greater dust loads than impactors
before overloading occurs. A RAM was placed in stations
3, 4, 5, and 6.

Dust Measurement Results

Daily average respirable dust concentrations measured
with the cyclones and impactors at stations 3 through 6 are
shown in table 2. These values were used to calibrate the
RAM’s located in the shuttle car cabs, miner cab, and
upwind miner positions. The RAM’s allowed isolation of
the average dust levels at these positions for each cut.
The cut-by-cut dust levels are shown in table 3. The top
portion of table 3 shows respirable dust concentrations at
each RAM sampling station for each cut during days 1 and


INTRODUCTION

An increasing number of mines are either using or peti-
tioning to use belt entry air to ventilate active work areas.
Operators believe that using the belt entry as an intake
entry will allow them to deliver more air to the face,
providing better dust and methane dilution. However, this
technique results in an increased number of outby dust
sources, The conveyor belt itself is a source of dust
generation, and the stageloader-crusher or feeder-breaker
is always in intake air if belt entry air is used to ventilate
the face. Application of the dilution formula shows that if
belt entry air represents additional air brought to the face
and if belt entry dust levels including the stageloader-
crusher or feeder-breaker source can be maintained below
the average dust level measured at the designated occupa-
tion, it is beneficial from a dust compliance perspective for
the mine to use belt entry air to ventilate work areas. This
example is demonstrated in the appendix.

Compliance data analyzed (1)? by the Mine Safety and
Health Administration showed that mines using belt entry
air to ventilate work areas did not have significantly dif-
ferent respirable dust levels at the designated occupation
than mines not using belt air. For one district, mines
using belt entry air had a significantly lower mean dust
concentration than mines not using belt entry air.

However, these findings are not based on individual case
studies. The U.S. Bureau of Mines, as part of its goal to
improve the health of the Nation’s miners, recently con-
ducted four underground dust surveys to further explore
this topic, The objectives of this study were twofold: first,
to identify the variables affecting belt entry dust levels,
since the dilution formula indicates that the belt entry dust
concentration is critical for successful use of belt entry air,
and second, to determine how using belt entry air affected
the dust exposure levels of face workers at one mine.

The Bureau conducted three underground dust surveys
on a continuous miner section and one on a longwall min-
ing section for this study. The first two surveys conducted
at the continuous miner section were designed to evaluate
the effects of belt entry length, production rate, and air
velocity (quantity) on dust levels in the belt entry and to
determine how much dust the feeder-breaker operations
contributed to belt air. The third continuous miner section
survey compared dust exposure levels when the belt entry
was used as an intake entry with exposure levels when the
belt entry was used to draw air away from the face. The
longwall survey was conducted to compare longwall belt
entry dust levels with belt entry dust levels collected on the
miner section.

CONTINUOUS MINER SECTION BELT DUST STUDY

THE MINE

Three independent respirable dust surveys were con-
ducted on a continuous miner section located in the Lower
Kittanning Seam, West Virginia. Mining height was be-
tween 78 and 90 in, and entries were 20 ft wide. Double-
split ventilation was used to ventilate the section’s seven
entries. Entries 1 and 7 were returns. Entries 2 through
6 were intakes. A row of permanent concrete block stop-
pings was constructed between entries 3 and 4 to separate
intake entries 2 and 3 from the other intake entries. The
panel conveyor belt was located in entry 4. This particular
mine was in operation before law required mines to isolate
conveyor belts; therefore, entry 4 was open to intake
entries 5 and 6. In order to isolate dust generation in the
belt entry, the mine constructed a row of temporary
stoppings between entries 4 and 5 from the belt head to
the first crosscut inby the feeder-breaker. Isolating the
belt entry also allowed reversal of the airflow in the belt
entry for the third survey. The stoppings were framed

3Italic numbers in parentheses refer to items in the list of references
preceding the appendix at the end of this report.

with lumber and sealed with brattice cloth and instant
insulation. Airflow readings taken at opposite ends of the
belt entry were always within 10 pct of each other,
indicating that these temporary stoppings were quite tight.

SURVEY 1—EFFECT OF BELT ENTRY LENGTH,
PRODUCTION RATE, AND FEEDER-BREAKER
OPERATIONS ON DUST LEVELS

The first survey conducted on the continuous miner sec-
tion focused on determining how belt entry length, produc-
tivity, air velocity (quantity) and dust generation at the
feeder-breaker affected belt entry respirable dust levels.
The belt entry was used as an intake entry throughout this
3-day survey. A series of sampling stations were placed
throughout the entire length of the panel belt entry to
determine if belt entry air became increasingly dusty as it
moved toward the face. A production time study was con-
ducted at the feeder-breaker to determine how production
rate affected belt entry dust levels. The quantity of air in
the belt entry was changed at least once during the shift to
determine how air quantity affected belt entry dust levels.
Airflow entering the belt entry was regulated immediately


DUST CONSIDERATIONS WHEN USING BELT ENTRY AIR
TO VENTILATE WORK AREAS

By J. Drew Potts! and Robert A. Jankowski?

ABSTRACT

In this U.S. Bureau of Mines study, four underground respirable dust surveys were conducted to
determine factors affecting belt entry dust levels and how using belt air to ventilate work areas affected
dust exposures. Belt entry dust levels on the surveyed longwall and continuous miner sections averaged
0.59 and 0.26 mg/m’, respectively. The stageloader-crusher contributed an additional 0.5 to 0.9 mg/m?
of dust to belt air, while the feeder-breaker contributed 0 to 0.2 mg/m? of dust. A 1,000-ft increase in
belt entry length or a 200- to 500-st-per-shift increase in production resulted in roughly a 0.1-mg/m?
increase in dust. Using the belt entry as an intake entry on the continuous miner section appeared to
reduce dust levels by 0.1 to 0.3 mg/m? during cutting, Belt air was not used to ventilate the face on the
longwall section.

4Mining engineer.
?Supervisory physical scientist.
Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.


production rate from day to day. Table 1 shows average
production rates calculated over the entire sampling period
for each day. The daily average production rate for day 3
of the study was 75 st/h, and there was no measured dif-
ference in the gravimetric data collected at stations 4 and
5. However, the average production rate on day 1 was
115 st/h, and the feeder-breaker operations appeared to
generate about 0.2 mg/m’ of respirable dust.

The RAM data collected at station 5 showed how res-
pirable dust levels downwind of the feeder-breaker fluc-
tuated during the shuttle car dumping cycle. Figure 2
shows a profile of dust levels measured at station 5 during
the sampling period from 13:30 to 13:50 on day 1. During
this time, eight shuttle cars unloaded at the feeder,
equating to a production rate of about 240 st/h, which was
110 pet greater than the daily average production rate of
115 st/h. Eight distinct peaks corresponding to each
dumping cycle can be seen on the graph. Dust levels dur-
ing this high-production-rate period averaged 0.93 mg/m,
which was 40 pet greater than the daily average dust level
of 0.66 mg/m*. The peaks ranged in height from about 0.8
to 1.44 mg/m*, These data indicate that feeder-breaker
operations can contribute a significant amount of dust to
belt entry air, emphasizing the need for dust control at this
location.

Dust Control at Feeder-Breaker

This mine used several dust control techniques at the
feeder-breaker to control dust generation. Three auto-
matic sprays were used at the mouth of the feeder-breaker
to wet the coal before it was crushed. The feeder-breaker
was equipped with shelved sides that acted as muck
shelves, Skirt boards were used to properly load the coal
onto the section belt. The mine also used a belt scraper
to clean the inside surface of the belt before it entered
the feeder-breaker. All of these techniques are recom-
mended (3-4) to reduce dust generation, and they ap-
peared to do a good job for the production rates and
conditions encountered at this particular mine.

Effect of Production Rate on Belt Entry Dust Levels

The impactor data were also examined to determine if
production rates affected belt entry respirable dust levels
upwind of the feeder-breaker operations. Production rates
appeared to be positively correlated with belt entry dust
levels (table 1). The highest belt entry dust levels and the
highest production rate occurred on day 1, while the low-
est belt entry dust levels and lowest production rate
occurred on day 3. The average production rate decreased
35 pet from day 1 to day 3, and the average belt entry dust
level decreased 45 pet. This effect equated roughly to a
0.1-mg/m: increase in belt entry dust levels for a 200-st-
per-shift increase in production.

Le 104

SE 126

uz 1.08

| i

BE .90

zE 72

ae

Q8 .s4

a2 36 A fl i
8 "1330 13:35 ——«13:40~—~=«1345—~—~=«S'SO

TIME

Figure 2.—Profile of dust levels in belt entry measured down-
wind of feeder-breaker operations.

Dust Controls at Belt Head

Dust controls used at the belt head helped to maintain
low dust levels in the belt entry. Three automatic sprays
were used to suppress dust at the section-to-main transfer
point. The mine also used a scraper equipped with sprays
to clean the outside surface of the belt after the coal had
been transferred to the main belt.

Effect of Entry Length on Belt Entry Dust Levels

Impactor data collected at stations 1 through 4 (table 1)
were used to determine if cumulative belt entry length
affected belt entry respirable dust levels. Belt entry air did
appear to get dustier as it traveled through the entry, be-
cause dust levels were slightly higher at stations 3 and 4
than dust levels at stations 1 and 2. This effect equated
to roughly a 0.1-mg/m® increase in the dust level for a
1,000-ft increase in belt entry length. Although the length
effect was irrelevant on this section, it may prove to be
important on longer panel development sections.

Need for Survey 2

The previous data analyses ignore airflow levels. Daily
average airflows measured in survey 1 are shown in the
form of air velocities in table 1. Airflow levels were
ignored because no relationship between airflow and res-
pirable dust levels in the belt entry was observed from
cither the gravimetric data or the RAM data collected dur-
ing survey 1. A more sensitive RAM setting was used in
survey 2 in an attempt to isolate the potential effect of
airflow on dust levels.

SURVEY 2—EFFECT OF AIRFLOW
ON DUST LEVELS

Survey 2 was conducted to isolate the possible effect of
airflow on belt entry respirable dust levels. Sampling sta-
tions and procedures used in survey 1 were duplicated for
survey 2; however, a more sensitive RAM setting was used
for survey 2. RAM’s were set on the 0-to-20-mg/m?*


Reiter,

e
1992

Dust Considerations When Using Belt Entry
Air To Ventilate Work Areas

By J. Drew Potts and Robert A. Jankowski



Table 3.—Respirable dust levols (milligrams per cuble meter)

measured at each RAM sampling station for each cut
Orien-Left-side Right-side  Upwind Normalized for production
Cut Entry tation car car miner Miner ~—Left-sideRight-side  Upwind Miner
car car miner

BELT ENTRY USED AS INTAKE ENTRY

4 SA 0.29 0.92 0.23 9.93 0.32 1.03 0.26 © 11.07
5 RC 22 07 aT 1.86 25 .08 13 216
5 SA 25 36 19 462 23 33 a7 419
6 RC 13 4B 34 2.31 a7 87 45 3.04
6 SA a7 A 59 2.50 15 36 52 2.20
3 Lc 12 07 12 1.35 14 08 140 157
6 SA 09 10 C) 83 08 09 ° 73
4 SA 23 St 09 9.20 23 51 09 9.20
3 SA 12 18 22 2.89 aT 16 20 © 262
2 SA 16 22 0) 4.43 26 35 ) 7.14
BELT ENTRY USED TO DRAW AIR AWAY FROM FACE
4 RC 0.32 0.20 0.07 3.86 052 0.32 O11 6.22
4 tc a 17 08 3.27 23 18 09 (3.51
5 SA 64 A2 a“ 5.89 66 M4 A1 6.10
6 SA 3t 28 18 2.42 22 20 1300 1.75
7 SA 34 32 7 1.40 26 24 13° 1,07
4 tc 30 2 14 1.84 24 16 At 1.44
3 tc 45 7 08 «17.91 35 2 06 14.04
1 SA 56 (0) 01 6.73 54 (e) 01 5.54
4 SA 67 () 01 5.16 AT () 01 3.65
4 Le 48 te) 01 2.55 AB 10) 01 2.55
: 6 SA 36 i) 01 427 55 ¢) 02 6.52

Left crosscut.

Instantaneous respirable dust sampler.

Right crosscut.

Straight ahead.

All dust samples collected from right-side shuttle car on day 4 were lost when sampling equipment was pinched between car
and rib.

Table 4.—Average respirable dust levels, Ventilation Mode Changes
milligrams per cubic meter!

Location With belt air? Without belt air? An analysis of airflow levels measured during this
- survey may explain why respirable dust levels were lower
Left-side car... 0.19 0.41 when the belt ed intak. “All ai
Right-side car’. "35 25 en entry was used as an intake entry. air
Upwind miner . 12 07 passing through the face areas exited through return
Miner 44 48 entries 1 and 7. Airflows in entries 1 and 7 were moni-
Values calculated from data in table 3; represent tored throughout the 4-day study. The average total air-
Production time only. flow in these two entries was 58,800 cfm when the belt
Belt entry used as intake entry. d intake d 52,900 cfm when the
3Belt entry used to draw air away from face areas. entry was used as an intake entry and 52,900 cfm when
‘All dust samples collected from right-side shuttle belt entry was used to draw air away from the face areas.
car on a Navas lost when. sampling equipment When the belt entry was used to draw air away from work
was pinches jen car and rib, i: i
SUpwind dust levels for cuts 4 and 5 on day 1 not areas, air drawn into the belt entry never reached the face.
included in data because instruments were improp- Therefore, about 10 pct more air was available for dust
erly placed inby shuttle car operators’ positions dilution when the belt entry was used as an intake entry.

during loading.


KEY

«= RAM
— 4 Impactor
¢ Cyclone

— Intake
| + Return

© Sampling
{ station

|

Figure 4.—Sampling station locations and equipment used for continuous miner section survey 3. RAM = In-

stantaneous respirable dust sampler.
2 of the study, when the belt entry was used as an intake
entry. The bottom portion of table 3 shows similar data
for days 3 and 4, when the belt entry was used to draw air
away from the face areas. Since production rates changed
between cuts, the dust levels were normalized for an
average cut production rate (not daily rate) of 290 st/h.
The normalized levels are shown in the last four columns
of table 3. All data analyses were conducted with the
normalized levels. Daily average dust levels are lower
than the levels shown in table 3, because daily average
levels include downtime.

Table 2.Respirable dust levels (milligrams per cubic meter)
used to calibrate RAM’s

Day Leftside _Right-side Upwind Miner
car car miner

Toe 0.14 0.23 024 196

12 19 12 2.92

33 22 14 3.38

46 ¢) 0 2.92

RAM Instantaneous respirable dust sampler.

TAIl dust samples collected from right-side shuttle car on day 4
were lost when sampling equipment was pinched between car and
fib,

Table 4 lists the average respirable dust concentrations
calculated from RAM data in table 3. The upwind dust
levels for cuts 4 and 5 on day 1 were not included in this
analysis because instruments were improperly placed inby
the shuttle car operators’ positions during loading. This
inby position exposed the upwind samplers to loading dust.
The significance of each of the differences shown in
table 4 was checked using the t-test statistic. Only the
difference in respirable dust levels for the left-side shuttle
car was significant at a 95-pct confidence level. The
significance of this difference indicates that using belt entry
air to ventilate the section at this particular mine reduced.
dust levels by 0.1 to 0.3 mg/m? during cutting. This
analysis is based on the assumption that the RAM
sampling techniques were precise enough to measure a
difference this small. The RAM’s were calibrated with
impactor data. Two impactor samples were collected at
each location. An analysis of the data collected in both
shuttle cars for each day of the survey showed that the
mean difference in con-centrations measured with side-by-
side impactors was 0.05 mg/m? and the standard deviation
was 0.06 mg/m*. Therefore, it is possible that the
reported reduction in dust levels measured when using the
belt entry as an intake was the product of sample error;
however, it is more likely the product of a real difference
in dust levels.


inby the belt head by opening or closing gaps in the
brattice cloth between entries 4 and 5. Instantaneous
respirable dust samplers (RAM’s) were used to isolate
respirable dust levels at each sampling station during
different production rates and air quantities. Sampling
stations located upwind and downwind of the feeder-
breaker were used to calculate the feeder-breaker’s
contribution to belt entry dust levels.

Sampling Equipment and Procedures

This survey was conducted with 12 gravimetric dust
samplers (personal impactors), 5 RAM’s, and 2 recording
anemometers. Impactors collect a total dust sample and
fractionate the sample by particle diameter. Average
respirable dust concentrations for the sampling period
were calculated (2) from the gravimetric impactor data.
Gravimetric data were used to calibrate the RAM’s.
RAM’s yield a respirable dust profile of the sampling
period. Recording anemometers yield an air velocity
profile. A ball-bearing-type vane anemometer was used
(continuous traverse technique) to calibrate the recording
anemometers,

Figure 1 shows sampling station locations and the
equipment used at each station. Stations 1, 2, 3, and 4
were 100, 340, 580, and 820 ft inby the belt head, re-
spectively. Station 5 was immediately downwind of shuttle
car dumping operations at the feeder-breaker, and sta-
tion 6 was in an adjacent intake entry. Two impactors
were placed at each station. A RAM was placed at each
station except station 6. A recording anemometer was
placed at stations 1 and 4. Table 1 shows average gravi-
metric respirable dust levels collected at each station
for each day of the survey as well as 3-day average
concentrations.

Table 1.—Results of continuous miner section survey 1

Measurement

Respirable dust levels at
stations,! mg/m?:

Day1 Day2 Day Average

1 0.32 0.22 0.18 0.24
2 0.28 0.23 0.16 0.22
3 0.36 0.24 0.23 0.28
4 0.46 0.21 0.21 0.29
5 0.66 025 0.20 0.37
6.. 0.14 0.15 0.18 0.16
Production st/h.. 115, 100 75 NAp
Air velocity .... fpm.. 105 125 55 NAp

NAp Not applicable.

\Stations 1 through 4 were located 100, 340, 580, and 820 ft inby
the belt head, respectively. Station 5 was immediately downwind
of shuttle car operations at the feeder-breaker, and station 6 was
in the adjacent intake entry.

Feeder - breaker

iced

—

Intake air

| KEY
+ Recording anemometer
« RAM
« Impactor

— Permanent stopping
-- Temporary stopping
¢ Curtain

O Sampling station

GocoUOOCCOOO

<_—
O Intake air

o

Belt
head

Figure 1.—Sampling station locations and equipment used for
continuous miner section surveys 1 and. RAM = Instantaneous
resplrable dust sampler.

Dust From Feeder-Breaker

Impactor data collected at stations 4 and 5 were used
to determine how much respirable dust was being gener-
ated by feeder-breaker operations. Subtracting the dust
levels measured at station 4 from the dust levels at sta-
tion 5 indicated that feeder-breaker operations contributed
an average 0 to 0.2 mg/m? of dust to the belt entry air.
These fluctuations most likely resulted from changes in the


CONTENTS

Abstract
Introduction
Continuous miner section belt dust study .
The mine
Survey 1—Effect of belt entry length, production rate, ‘and feeder- breaker operations on dust levels
Sampling equipment and procedures .
Dust from feeder-breaker ......
Dust control at feeder-breaker ..
Effect of production rate on belt entry dust levels .
Dust controls at belt head ..............05
Effect of entry length on belt entry dust levels ... .
Need for survey 2
Survey 2~Effect of airflow on dust levels .
Survey 3—Effect of using belt entry to ventilate face on dust levels at various section locations .
Sampling equipment and procedures
Dust measurement results .....
Ventilation mode changes
Other dust measurements
Longwall panel belt dust study
The mine
The survey—Effect of production rate and stageloader- crusher operations on dust levels .
Sampling equipment and procedures
Air leakage into belt entry
Effect of production rate on belt entry dust levels .
Dust controls in use
Dust from stageloader-crusher ..
Conclusions
References

ILLUSTRATIONS

Sampling station locations and equipment used for continuous miner section surveys 1 and 2
Profile of dust levels in belt entry measured downwind of feeder-breaker operations . .

Air velocity and dust level profiles collected in belt entry . . sees
Sampling station locations and equipment used for continuous miner section survey 3.
Sampling station locations and equipment used for longwall mining section survey ... .

WFP Ynr

TABLES

Results of continuous miner section survey 1 .
Respirable dust levels used to calibrate RAM’s . .
Respirable dust levels measured at each RAM sampling station for each cut
Average respirable dust levels
Respirable dust levels at belt entry and mouth of belt eatty stations .
Results of longwall section survey

AWwP ENP

CANEYW

CoOIADY


10

section, In fact, dust levels were only about 0.3 mg/m?
higher on the longwall section. However, the positive
correlation between production rates and belt entry dust
levels is reinforced by these findings. For the two mines
surveyed during this study, a 200- to 500-st-per-shift in-
crease in production corresponded to a 0.1-mg/m? increase
in belt entry dust levels.

Dust Controls in Use

Low conveyor belt dust generation on the longwall
section probably resulted from the implementation of dust
control techniques that were similar to those used by the
continuous miner section. One spray was used at the
stageloader-crusher to wet the coal before it was crushed.
Two sprays were used to wet and suppress dust at the
discharge to the panel belt. Two sprays were used at the
belt head to reduce dust generation at the panel-to-main

transfer point. Belt scrapers used at both ends of the
panel belt also helped reduce dust generation.

Dust From Stageloader-Crusher

Stageloader-crusher operations generated 0.5 to
0.9 mg/m? of respirable dust. (These values were calcu-
lated by subtracting dust levels collected at station 3 from
dust levels collected at station 4.) Different levels of
generation probably resulted from different production
tates. The production rate on day 2 of the study was
205 st/h, and the stageloader-crusher generated about
0.5 mg/m? of respirable dust. On day 3, the production
rate was 325 st/h and the stageloader-crusher generated
about 0.9 mg/m: of dust; production increased 60 pet and
dust generation increased 80 pet over day 2 levels. Even
so, dust levels in the headgate area averaged less than
1.2 mg/m: for both days.

CONCLUSIONS

On the continuous miner section, the average respirable
dust level in the belt entry upwind of the feeder-breaker
was 0.26 mg/m*. Feeder-breaker operations generated an
additional 0 to 0.2 mg/m? of dust. These low dust levels
resulted from controls implemented by the mine. Three
automatic sprays were used at the mouth of the feeder-
breaker to wet the coal before it was crushed. The feeder-
breaker was equipped with shelved sides that acted as
muck shelves. Skirt boards were used to properly load the
coal onto the section belt. The mine also used a belt
scraper to clean the inside surface of the belt before it
entered the feeder-breaker. Similar controls were used at
the belt head. Three automatic sprays were used to
suppress dust at the section-to-main transfer point. The
mine also used a scraper equipped with sprays to clean the
outside surface of the belt after the coal had been
transferred to the main belt.

On the longwall-mining section, the average respirable
dust level in the belt entry upwind of the stageloader-
crusher was 0.59 mg/m*. Stageloader-crusher operations
generated an additional 0.5 to 0.9 mg/m? of dust. The
difference in dust levels measured between the continuous
miner section and longwall mining section most likely
resulted from differences in production rates. The aver-
age production rate on the longwall section was about
280 st/h, while the average production rate on the miner
section was about 100 st/h. Dust control techniques used
at the longwall section were similar to those used at the
miner section. One spray was used at the stageloader-
crusher to wet the coal before it was crushed. Two sprays
were used to wet and suppress dust at the discharge to the

panel belt. Two sprays were used at the belt head to
reduce dust generation at the panel-to-main transfer point.
Belt scrapers used at both ends of the panel belt also
helped reduce dust generation. Three Bureau publica-
tions (3-4, 6) explain in detail how belt entry dust levels
and stageloader-crusher dust generation can be minimized.
The stageloader-crusher controls may also be applicable as
feeder-breaker controls.

Belt entry length and production rate both appeared
to affect belt entry respirable dust levels. Conversely,
air quantities did not appear to affect belt entry dust
levels. Greater production rates and belt entry lengths
appeared to increase belt entry dust levels upwind of the
stageloader-crusher and feeder-breaker operations. The
entry length effect equated to roughly a 0.1-mg/m? in-
crease in dust for a 1,000-ft increase in length. The pro-
duction effect equated to roughly a 0.1-mg/m! increase in
dust for a 200- to 500-st-per-shift increase in production,

Using the belt entry as an intake entry results in
additional outby dust sources; however, it may also
increase the amount of air available for dust dilution. On
the continuous miner section surveyed for this study, the
benefits of increased dust dilution appeared to outweigh
the effects of additional dust sources. Data indicated that
using the belt entry as an intake entry on the miner section
reduced respirable dust levels by 0.1 to 0.3 mg/m? during
cutting. However, the magnitude of outby dust sources
and the dilution effect are mine specific. Therefore, any
decision to use the belt entry as an intake entry for dust
control should be supported with a field study similar to
the ones conducted for these mines.


12

APPENDIX.—IMPACT OF USING BELT AIR TO VENTILATE WORK AREAS

Case 1: No belt entry air is used to ventilate work
area X. Work area X is exposed to respirable dust gener-
ated by the bolter, miner, and shuttle cars, which generate
400, 1,000, and 400 mg/min, respectively. The section is
ventilated with 900 m3/min of intake air containing no
dust. The concentration in work area X (C,) is given by
the following formula, where D is the total dust generated
by all sources, in mg/min, and Q is the total quantity of
air, in m*/min, available for dilution.

c, = D/Q,

and C, = (400 + 1,000 + 400)/900 = 2.0 mg/m.

Case 2: Same as case 1, except belt entry air as well as
intake air is used to ventilate work area X. The conveyor
belt and feeder-breaker generate 600 mg/min of dust, and
using belt entry air provides the mine with 330 m?/min of
additional air for dilution. C, is the concentration of dust
in the belt entry.

C, = 600/330 = 1.82 mg/m’,

and

(400 + 1,000 + 400 + 600)/1,230 = 1.95
mg/m,

Case 3: Same as case 2, except the conveyor belt and
feeder-breaker generate 720 mg/min of dust.

C, = 720/330 = 2.18 mg/m,

0

and (400 + 1,000 + 400 + 720)/1,230 = 2.05

mg/m?,

It follows that using belt entry air may reduce face dust
levels if the following conditions exist:

1. Belt entry air represents additional air brought to
the face; and

2. Belt entry dust levels, including the stageloader-
crusher or feeder-breaker source, are lower than face dust
levels.


Library of Congress Cataloging in Publication Data:

Potts, J. Drew.
Dust considerations when using belt entry air to ventilate work areas / by LD.
Potts and RA. Jankowski.
P. _ em. — (Report of investigations; 9426)
Includes bibliographical references (p. 11).
Supt. of Docs. no.: I 28.22:9426.
1. Mine dusts. 2. Mine ventilation. 3. Belt conveyors. I. Jankowski, Robert A.

Il. Title. IL Series: Report of investigations (United States. Bureau of Mines);
9426.

TN23.U43 [TN312] 622 s—de20 [62283] 92-13942 CIP



Report of Investigations 9426

Dust Considerations When Using Belt Entry
Air To Ventilate Work Areas

By J. Drew Potts and Robert A. Jankowski

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
TS Ary, Director


Other Dust Measurements

Most of the gravimetric data were used to calibrate the
RAM’s. However, gravimetric data were also collected in
the belt entry (station 1) and at the mouth of the belt
entry (station 2). Measured and normalized respirable
dust levels at these two locations are shown in table 5. A
comparison of dust levels collected in the belt entry
verified that feeder-breaker-generated dust was being
drawn down the belt entry when the belt entry was used
to draw air away from the section. The average normal-
ized dust level in the belt entry was 0.11 mg/m? when the
belt entry was used as an intake and 0.23 mg/m? when the
belt entry was used to draw air away from the section.
These data are consistent with those from survey 1, which
showed that the feeder-breaker contributed between 0 and
0.2 mg/m? of respirable dust to the belt entry air. Airflow
in the belt entry was about 6,000 cfm for both ventilation
modes,

The mine conducted a belt move after day 2 of the
study. The belt move prevented maintenance of a con-
sistent sampling position at the mouth of the belt entry.

Because of the new position of the feeder-breaker in the
entry, the sampling equipment was much closer to shuttle
car dumping operations on days 3 and 4 of the study. This
may have exposed the samplers to dust rollback when the
automatic feeder-breaker sprays were activated. It was
also necessary to move the sampling equipment from the
left-side rib to the right-side rib for days 3 and 4 of the
study. Therefore, the reliability of the data collected at
the mouth of the belt entry is questionable.

Table 5.—Respirable dust levels (milligrams per cuble meter)
at belt entry and mouth of belt entry stations

Normalized for

Day Belt entry vent- Belt Mouth of production
ilation mode entry belt entry “Bet Mouth of

entry _ belt entry

1. 1 009 «0.15 013 O21

2.. I 094 08 12

3 R 24 29 18 22

4. R 2322 28 a7

1 Intake,

R_ Return.

LONGWALL PANEL BELT DUST STUDY

THE MINE

One survey was conducted on a longwall mining section
located in the Wheatcroft No. 9 Seam, KY. Mining height
was about 60 in. This particular mine was using homotro-
pal ventilation; therefore, dust generated by the conveyor
belt and stageloader-crusher operations was directed into
the section return. This ventilation mode prevented direct
assessment of the impact of belt entry air on face dust
levels but it facilitated isolation of the conveyor belt and
stageloader-crusher dust sources. Crosscuts between the
belt entry and the adjacent entry were open from the belt
head to crosscut 7, as shown in figure 5. An airflow survey
indicated that the adjacent entry was contaminated with
dust generated at the belt head. Crosscuts were sealed
between crosscut 8 and the longwall face with concrete
block stoppings. Check curtains hung across the conveyor
belt were used to control airflow in the belt entry.

THE SURVEY—EFFECT OF PRODUCTION RATE
AND STAGELOADER-CRUSHER OPERATIONS
ON DUST LEVELS

A 3-day respirable dust survey was conducted on a
longwall mining section with a longer panel belt and
higher production rates than those of the continuous miner
section to determine if belt entry dust levels were different

between the two sections. Belt entry length and produc-
tion rates appeared to influence dust levels on the con-
tinuous miner section surveyed for this study. The sam-
pling strategy used for the longwall survey was similar to
that used for the first two continuous miner surveys. Sam-
pling stations were placed throughout the length of the
belt entry to determine how belt entry length affected belt
entry dust levels. Production-time studies were used to
determine how production rates affected belt entry dust
levels. Stageloader-crusher-generated dust was isolated by
sampling upwind and downwind of this equipment.

Sampling Equipment and Procedures

The survey was conducted with 10 gravimetric dust
samplers (impactors) and 4 RAM’s. Gravimetric respira-
ble dust concentrations were calculated from the impactor
data. The gravimetric dust data were used to calibrate the
RAM’s. RAM’s were used to generate respirable dust
profiles during the sampling period. A ball-bearing-type
vane anemometer was used (continuous traverse tech-
nique) to measure air velocities in the belt entry.

Figure 5 shows sampling station locations and the
equipment used at each station. Two impactors and a
RAM were placed at station 1 in the belt entry, 800 ft
inby the belt head. Station 1 was placed between crosscuts
9 and 10 because the belt entry was open to the adjacent


11

REFERENCES

1. Mine Safety and Health Administration (Dep. Labor). Belt Entry
Ventilation Review: Report of Findings and Recommendations. 1989,
42 pp.

2. Potts, J. D., M. A. McCawley, and R.A. Jankowski. Thoracic
Dust Exposures on Longwall and Continuous Mining Sections. Appl.
Occup. and Environ. Hyg, v. 5, No. 7, July 1990, pp. 440-447,

3. Organiscak, J. A., R. A. Jankowski, and J. S. Kelly. Dust Con-
trols To Improve Quality of Longwall Intake Air. BuMines IC 9114,
1986, 8 pp.

4. Mody, V., and R. Jakhete. Conveyor Belt Dust Control (contract
H0113007, Martin Marietta Lab.). BuMines OFR 31-86, 1984, 410 pp.

5. Mundell, RL, R.A. Jankowski, R. S. Ondrey, and T. Tomb.
Respirable Dust Control on Longwall Mining Operations in the United
States. MSHA IR 1151, 1984, 24 pp.

6. Grigal, D., G. Utken, J. Sandstedt, M. Blom, and D. Johnson,
Development of Improved Scrubbers for Coal Mine Applications (con-
tract 0199055, Donaldson Co, Inc.). BuMines OFR 91-83, 1982,
124 pp.; NTIS PB 83-205385.