Laboratory and field evaluation of dust
 

collector bags for reducing dust exposure 


of roof bolter operators


J.M. LISTAK AND T.W. BECK 

J.M. Listak and T.W. Beck, member SME, are research 

engineers with the National Institute for Occupational Safety 

and Health (NIOSH), Pittsburgh, PA. Paper number TP-07-047. 

Original manuscript submitted December 2007. Revised 

manuscript accepted for publication March 2008. Discussion of 

this peer-reviewed and approved paper is invited and must be 

submitted to SME Publications Dept. prior to October 31, 2008. 

Abstract

The National Institute for Occupational Safety and Health 

conducted laboratory and fi eld tests to evaluate the effectiveness of dust collector bags for reducing dust liberation 

and operator exposure from a roof bolter’s dust collection 

system.The laboratory tests evaluated the bag’s effectiveness 

to contain dust and the effect on canister filter loading in 

both a bag and bagless condition.The dust emissions from 

the collector’s exhaust were also measured in each condition during laboratory testing. Laboratory results show that 

nearly 100 percent of the test dust fed into the collector was 

captured by the dust bags. Loading and pressure drop on 

the dust collector’s canister filter is greatly decreased when 

using the bags, enabling longer periods of drilling without 

filter removal/cleaning. The field results showed that, even 

though dust standards were met, respirable dust in exhausted emissions was reduced around the bolter. Laboratory 

and field results show that benefits from use of the bags are 

realized in all areas of operator exposure. 

Introduction

Respirable dust samples taken 

by the Mine Safety and Health Administration (MSHA) show that roof 

bolter operators are still at high risk 

for overexposure. From 2000 to 2004, 

MSHA inspectors collected nearly 

5,000 respirable dust samples at roof 

bolting occupations (MSHA, 2004). 

Of these samples, 20 percent exceeded a respirable silica dust concentration of 100 μg/m3

, a 

level that MSHA considers excessive. Previous studies 

have shown that the contents of the roof bolter dust box 

can contain high amounts of respirable silica dust (Colinet et al., 1985; Kok et al., 1985).A study by Ondrey et al. 

showed that mining downwind of the continuous miner 

was the major source of dust on roof bolting operations 

(Ondrey et al.). However, improper ventilation and poor 

dust-box cleaning procedures can add to the overexposure of bolter operators. 

Most roof bolting machines use an MSHA accepted 

(30CFR, Part 33) vacuum dust collection system to capture dust as holes are drilled.The drill steel, bit, dust box, 

fi lter and hoses together form a single unit approved by 

MSHA for use in underground coal mines. It is not possible to modify or change any part of this dust-control 

system without violating approval from MSHA. 

The system uses a vacuum pump on the machine to 

create negative pressure at the drill bit and draw the drill 

cuttings through the bit and drill steel. Many of these dust 

collection systems are equipped

with a precleaner that collects the 

larger drill cuttings before they enter the dust box. These cuttings are 

deposited onto the mine fl oor, while 

the remaining, fi ner, dust proceeds 

to the collector box. The dust box 

itself has several compartments and 

functions as a rough size classifi er 

allowing the coarser dust sizes to 

settle out of the dust stream in the main chamber (about 

95 percent of all the dust entering the box).A fi eld sample 

showed that 36 percent of the dust in the main chamber is 

<10 μm.The dust that passes through the main chamber is 

routed through cyclones and then into the fi lter chamber 

for deposition on a paper canister fi lter. The fi ltered air 

flows through the vacuum pump, a noise-reducing muffler and then into the mine environment. Figure 1 shows 

a schematic of the dust-collector system. Normally, the 

dust box is emptied at the end of every cut. As the fi lter 

accumulates fine particles of dust, the resistance increases 

and the flow through the system decreases. This requires 

the removal and cleaning of the filter, usually after several cuts. 

The dust that is collected in the main chamber of the 

collector box is removed by opening the door and pulling 

a rake toward the opening to drag the dust out, allowing 

it to dump onto the mine floor. If cleaned improperly or 

in poorly ventilated workings, exposure can occur as the 

operator drags the dust from the box, entraining it into 

the air as it falls to the floor. A study by Goodman and 

Organiscak (2002) showed that using open containers 

constructed of either steel or line brattice helped contain 

dust in the main chamber for disposal against the rib, 

thus reducing operator exposure during cleaning. The 

four-sided reusable containers are fitted into the bottom 

of the main chamber and contained the dust as it settled. 

The containers are then removed, carefully dumped near 

the rib and then replaced. 

Another source of operator exposure comes from the 

canister fi lter. Dust that is too fi ne to be captured in the 

main and subsequent dust box chambers passes through 

to the filter. When the filter is removed for cleaning, it 

is shaken or tapped against the rubber tire of the bolter 

or a hard surface to dislodge the dust. This method of 

cleaning often creates a respirable dust cloud that contaminates the breathing area of the operator if he or she 

is not upwind of the dust. The operator must take care 

not to damage the filter or filter seal while cleaning, as 

dust not captured by the fi lter or that bypasses the fi lter 

seal is exhausted into the mine air. Care must be taken 
 

 

 

 

 

 

to stay upwind of the dust box during cleaning. At times, 

roof-bolting machines operate in areas with minimal 

fresh airflow. Any dust liberated through cleaning of the 

dust box or filter will remain around the bolting machine, 

increasing silica exposures for the machine operators 

(Colinet et al., 1985). 

A collector bag (Wildwood Industries, Bloomington, 

IL) was developed to capture and contain the collector 

dust and prevent it from contaminating the air around 

the roof bolter during cleaning. The dust collector bags 

are placed in the main chamber of the dust collector box 

to contain the dust that enters the boxes’ main chamber. 

The bags are installed on a bracket and hose retrofi t kit 

(J.H. Fletcher Co., Huntington,WV) in the main chamber 

of the collector box. Figure 2 shows (a) a collector bag, 

(b) the collector box without a bag installed and (c) the 

collector box with a collector bag installed. 

This study evaluated the performance of the collector box and the effectiveness of the collector bags to reduce respirable dust exposure of bolter operators during 

the bolting process. These bags are installed in the main 

chamber of the dust box to contain the majority of dust 

and allow operators to empty the box without being exposed to entrained dust. Both laboratory and fi eld investigations were conducted to determine dust capture, fi lter 

loading and dust concentrations around the bolter while 

operating in both bag and bagless conditions. 

Experimental design 

The laboratory test apparatus consisted of a dust collector system representative of the type and size found 

on many roof bolting machines used in underground coal 

mines (Fig. 3). The test protocol consisted of comparing 

two operational conditions of the collector and testing 

both with and without a collector bag. A total of 60 tests 

were conducted, 30 with the bag installed and 30 without. 

To avoid the potential health risks of working with quartz 

dust, ground limestone dust was used as feed material (ρ 

= 2.75 g/cc). Each test used 22.7 kg (50 lbs) of the limestone material as feed dust.This amount was determined 

by assuming that five 2.4 m (8 ft) holes are drilled in material with a density of 2,403 kg/m3

 (150 lb/cu ft). The 

duration of each test was 90 seconds. The particle size 

distribution of the limestone dust was compared to the 

distribution of dust obtained from a bolter dust box during an underground study. The results show that ground 

limestone dust has a bulk size distribution very similar to 

that of the dust from the roof bolter.The dust was stored 

at ambient temperature and humidity.The bag condition 

tests took place over the course of seven days at an average humidity of 69 percent. The bagless tests also took 

seven days at an average humidity of 71 percent. 

Under typical operating conditions (without a dust 

bag), the dust enters the collector at the top of the box 

and the heavier particles fall to the bottom of the main 

chamber. Due to the high velocities within the box, the 

smaller, lighter dust particles are carried to two cyclones 

that further classify the aerosol with the oversized fraction falling out to a compartment below. The fi nest size 

fraction then flows to the filter chamber where it collects 

on a single final canister filter (Model 123990, Donaldson, 

Inc., Minneapolis, MN). The filtered air then fl ows from 

the dust box as exhaust. 

FIGURE 1 

Schematic of roof bolter dry dust collector system. 

FIGURE 2 

Dust collector bag. 

FIGURE 3 

Laboratory dust box simulator. 

Airflow through the box is provided by a Roots DVJ 

Whispair vacuum pump (Airtek Inc., Irwin, PA) rated at 

0.03 m3

/s (60 cfm) at a pressure of 508 mm (20 in.) mercury column.To simulate the drilling process, dust is fed into 

the collector box using an “Accu-rate” bulk dust feeder 

with a 57 mm (2.25 in.) screw (Schenck Inc., Whitewater, 

WI). The dust feed rate for each test was 22.7 kg/min (50 
 

 

lbs/min). An additional 30 seconds were added to assure 

that all the dust had cleared the hopper and feed tube. 

When testing in the bag condition, the collector bags 

were weighed after each test to determine the amount 

of dust contained by the bags compared to the amount 

of dust fed into the system. Likewise, the feed dust bags 

were weighed before loading the feeder and then the 

empty bags were weighed to determine the net amount 

of dust fed.The canister filter was weighed after each test 

to determine filter loading and to make comparisons between the bag and bagless test conditions.The exhaust air 

was sampled to determine the dust concentration and the 

amount of particles that escape the collector and is subsequently reintroduced into the air. Because the exhaust 

air exits at a velocity that is too high to sample, the air is 

routed through a short length of 51-mm- (2-in.-) diameter hose and then into a 3.1-m (10-ft) length of 152-mm-

(6-in.-) diameter PVC pipe. Particle 

sizes were measured in the 152-mm-

(6-in.-) diameter pipe, 2.4 m (8 ft) away 

from the entry of the 51-mm (2-in.) 

hose into the PVC pipe.Aerodynamic 

particle sizes were measured using 

a TSI Aerodynamic Particle Sizer 

(APS) (Model 3310, TSI Inc., Minneapolis, MN) with a TSI diluter (Model 

3302) (100:1 diluter nozzle). A laptop 

computer was interfaced with the APS 

and data acquired using the available 

TSI software. The theory and operation of the APS and diluter are available in other publications (Chen et al., 

1985; Baron, 1986; Cheng et al., 1993). 

Aerosol was drawn isokinetically into 

the diluter at 5 L/m through a 1.2-m 

(4-ft) length of 7.9-mm- (0.31-in.-) ID 

conductive tubing. Calibration of the 3310 analyzer was 

checked periodically using PSL spheres with mean diameters of 1.020 ± 0.022 μm, 5.010 ± 0.035 μm and 10.03 

± 0.05 μm (Duke Scientific, Palo Alto, CA). Samples of 

each were placed in small Petri dishes and allowed to dry 

overnight. The dried particles were brushed into the diluter inlet with a small artist brush (Maynard and Kenny, 

1995). Dust concentrations were recorded continuously 

in the 152-mm- (6-in.-) diameter pipe using a RAM-1 

(Realtime Aerosol Monitor) instantaneous dust monitor 

(Thermo Andersen Inc., Smyrna, GA).Vacuum pressures 

within the box and across the filter were also recorded 

continuously during each test. Figure 4 shows a schematic 

of the laboratory setup. 

FIGURE 4	 

Schematic of laboratory test apparatus. 

FIGURE 5 

(a) Canister filter weight gain and (b) pressure across 

fi lter. 

Laboratory results 

The collected data were analyzed to determine the 

effectiveness of the collector bags to collect and contain 

the dust within the box, to reduce dust accumulation on 

the canister filter and to reduce emissions in the collectors’ exhaust. In addition, the pressure drop within the 

system was monitored to determine the resistance of 

filter loading over the course of testing in both bag and 

bagless conditions. 

To determine the amount of dust the bag collected 

and contained, the net weights of the feed dust and collector bag dust were measured before and after each test. 

An average feed dust of 22.9 ± 0.34 kg (50.54 ± 0.75 lbs) 

was fed into the box over the entire testing period. The 

average dust in the collector bags after all tests were conducted was 22.8 ± 0.39 kg (50.38 ± 0.85 lbs). The results 

show that more than 99 percent of the feed dust entering 

the dust collector was contained by the dust bags. 

Before each testing condition, a new canister fi lter 

was installed in the collector box. The filter was carefully removed, weighed and reinstalled after each test. 

To determine the cumulative dust accumulation on the 

paper media over the course of testing, the filter was not 

cleaned between tests. As dust accumulates on the fi lter, resistance within the system increases.Therefore, the 

pressure drop in the collector was also monitored to determine the effect the collector bag had on the systems’ 

ability to maintain vacuum pressure. Figure 5 shows the 

nearly linear progression of weight gain on the fi lter and 

the associated pressure drop in the collector box during 
 

 

 

 

testing in both conditions. The data show that the fi lter 

weight gain is more than fi ve times higher when the bag 

is not used and that the pressure drop across the fi lter for 

all tests ranged from 76.2 to 83.8 mm (3 to 3.3 in.) WG 

when the bag was used compared to 101.6 to 213.4 mm (4 

to 8.4 in.) WG without the bag. Figure 6 shows the total 

weight gain of the filter after testing was completed for 

both conditions. 

Dust emissions from the collector box exhaust were 

monitored for dust concentration levels during testing 

by the RAM-1 and APS. The RAM-1 is not a dust- compliance instrument. Therefore, RAM-1 concentration 

measurements are only used for direct comparison purposes and will be referred to as RAM-1 Units. Figure 7 

shows the dust concentration levels from the RAM-1 in 

the collector box emissions over the course of testing. 

A high concentration reading was measured during the 

first test for both bag and bagless tests. This initial high 

reading was caused by the installation of a new fi lter for 

the testing condition. The newly installed filter allows a 

momentary passage of fi ne particles before the dust can 

load and clog openings in the paper media. This event 

is recorded as a high dust concentration for a relatively 

brief period of time.After the first test, the dust measurements became more consistent, and they showed that the 

dust levels are higher when testing in the bagless condition.The APS measured particles in the collector exhaust 

from 30 to <0.487 μm. However, more than 80 percent of 

all particles measured were less that 2 μm.Therefore, the 

range from 2 to <0.487 μm was examined for this analysis. 

Figure 8 shows the particle counts per cubic centimeter 

over the duration of each test. The graph shows similar 

results to what was seen by the RAM-1. 

FIGURE 6 

Total weight gain on canister filter for east test condition. 

FIGURE 7 

Dust levels recorded by RAM-1 in bolter exhaust. 

FIGURE 8 

Field study Particle counts in bolter exhaust. 

Dust sampling took place on a Fletcher dual boom 

bolter Model DDR-13. The bolter was equipped with 

dust collector boxes with vacuum bags on either side of 

the machine. The original sampling strategy called for 

sampling the exhaust of the collectors for one shift using 

bags in both collectors and for one shift without bags in 

the collectors. However, due to operational constraints 

and at the request of mine officials, sampling without bags 

in both collectors was not conducted. Exhaust emissions 

were sampled for one shift from both collectors while 

using a bag in the right collector and without a bag in 

the left collector. Then sampling was conducted for one 

shift using a bag in both collectors. As a result, the study 

involved sampling a shift without the bag in one of the 

collectors for a shift (this will be considered the bagless 

condition) and then with the bag in both collectors for 

a shift (the bag condition) to determine the difference 

in dust concentration under the two conditions. Therefore, any dust levels seen while in the bagless condition 

are assumed to be greater than the measured levels. The 

bolter’s exhaust ports for the collectors were situated 

side by side on the left rear side (from the rear of the 

machine) of the bolter. 

Exhausting ventilation was used in the bolted places, 

which provided intake air over the bolter from rear to 

front.Two bolted places were sampled in the bagless condition and three places were sampled with the bags in 

place. Air velocity in Places 1 and 2 during the bagless 

tests were 0.96 and 0.34 m/s (188 and 66 fpm) respectively. 

Air velocity in Places, 1, 2 and 3 in the bag condition were 

0.9, 0.37 and 0.1 m/s (177, 72 and 33 fpm), respectively. 

Sampling took place only when the bolter was upwind of 

the continuous miner. 

Before sampling began, the left collector box was 

cleaned, the bag was removed and the filter replaced. 

The right collector box was cleaned and a new bag was 

installed. Sampling began at approximately 11:00 a.m. 

and continued until about 2:10 p.m. on the first day of 

sampling.Two places were bolted during that time period. 

On the second day of sampling, bags were used in both 

collector boxes.Three places were bolted over a time period of 4 hours and 40 minutes (9:20 a.m. to 2:00 p.m.). 

Three sampling packages were used to measure dust 

levels around the bolter. Area samples were taken each 

day of testing with three different instruments in each 

sampling package.Two gravimetric samplers and one Per­
 

sonal Data Ram (pDR) (ThermoFisher Scientifi c) were 

used in each package. One of these packages was hung 

in the intake air and the other was hung in the return air 

to isolate the bolter section from other dust sources. The 

other package was placed on a tripod 1.5 m (5 ft) behind 

the bolter in the collector box exhaust to sample the air 

passing through the dust collection system. Personal dust 

monitors (PDMs) were worn by NIOSH researchers to 

collect personal samples on either side of the bolter. Figure 9 shows the instrument arrangement, locations and 

sampled areas. 

Like the RAM-1, the pDRs are instantaneous samplers that provide a profile of dust levels over the entire sampling period. Unlike gravimetric samplers that 

provide a single mass sample over the entire sampling 

period, pDR samplers use light-scattering technology to 

measure and record ambient air. Although not a compliance sampling instrument, the pDR is very good for 

direct comparison measurements.The measurements are 

recorded in 10-second intervals so that changes in dust 

levels can be compared to mining activities to determine 

sources of dust. The data collected are then downloaded 

to a computer for graphical representation and analysis. 

In addition to the gravimetric and pDRs, personal dust 

monitors were worn by two NIOSH personnel to gather 

exposure data from either side of the bolter during the 

bolting and collector box cleaning cycles. Like gravimetric samplers, the PDMs provide the personal dust exposure over the course of the shift of the person wearing it. 

Although NIOSH personnel could not be in the same position as the bolter operators, positions that approximate 

their positions on either side of the bolter were assumed. 

NIOSH personnel also cleaned the collector boxes when 

needed to measure the exposure from that activity. 

FIGURE 9 

Instrument and sampling locations. 

Table 1 

Average dust concentrations for each test condition. 

 Gravimetric averages, mg/m3 

Location Bagless test Bag test 

Intake 0.23 0.17 

Bolter exhaust 1.19 0.31 

Return 0.33 0.23 

FIGURE 10 

Gravimetric sampler data from dust collector exhaust. 

Data analysis and results 

The intake and return samplers were used as a control to ensure that the dust sampled at the bolter is not 

confounded by other sources. Gravimetric samplers 

were used to sample the areas in the intake, return and 

bolter exhaust. The pDR graphs show the changes in 

dust levels in the exhaust during bolting with and without the bag in place. The PDM data show a personal 

sample of the total concentration of dust exposure for 

each person for bag versus bagless operation. It should 

be noted that on the first day of sampling, while in Place 

2, rock dusting took place outby, which elevated dust 

concentrations over a 10-minute period. This period 

of elevated dust concentration is taken into account, 

as will be shown in the data analysis. The time taken to 

clean the dust from the box and the canister fi lter when 

required was also recorded. 

Gravimetric samples. These data include the two places bolted without the bag in place on the left collector box 

and the three places bolted with both bags in place on the 

second day of sampling. To determine the dust coming 

into the bolter entry, the two intake gravimetric samples 

were averaged. The two gravimetric samples collected 

in the proximity of the bolter were also averaged. Average dust concentrations of the two gravimetric samplers 

taken at each position are shown in Table 1. The higher 

concentration in the intake air during the bagless test is 

attributed to the rock dusting outby during testing. The 

net average concentration of the bolter exhaust when 

operating without the bag was 0.96 mg/m3

 as opposed to 

0.14 mg/m3 when sampling with the bag installed. Figure 

10 shows a graph of the gravimetric sampler data taken 

at the collector exhaust position over the sampling period 

for each collector box condition. The gravimetric results 

show an improvement in dust concentration of nearly 

seven times when the bag is used. This difference would 

be greater if neither collector had the benefit of a collector bag during the test. 

Personal dust monitors (PDMs). Typically, the downwind bolter operator will experience the highest exposures on a dual boom bolter. The PDMs were worn by 

NIOSH personnel to measure personal dust concentrations on the left and right rear (exhaust versus non exhaust side) of the bolter to differentiate between test 

conditions. Figure 11 illustrates the dust concentrations 

recorded by the PDMs from the two test conditions. The 

graph shows that during the bagless condition, dust con­
 

 

centration was more than two times higher on the left 

side (exhaust side) of the bolter than on the right. PDM 

data for the bag condition shows little difference in dust 

concentration from the left to the right side of the bolter. 

The time period during which the collector box was emptied in a bagless condition was isolated in the PDM data 

file and showed no increase in dust levels. 

Personal DataRams (pDRs). The pDRs show variation in dust levels during the shift at 10-second intervals 

and show how the dust levels fluctuate over the course 

of the sampling period. Figures 12 and 13 show the dust 

profiles of a place bolted each day without and with 

the collector bag, respectively. These two bolted places 

were in Entries 5 and 6 and had similar entry velocities of 0.96 and 0.9 m/s (188 and 177 fpm), respectively. 

Entry 5 had seven rows of 2.7 m (9 ft) bolts installed 

and 1.2 m (4 ft) rib bolts installed each row for a total 

of 42 holes. Entry 6 had six rows of 2.7 m (9 ft) bolts 

installed and 1.2 m (4 ft) rib bolts installed every other 

row for a total of 33 holes. Figure 12 shows the bagless 

test results. Although these dust levels are higher than 

the bag test, the levels are consistently low for most of 

the 63-minute time interval. However, the graph shows 

brief elevated levels of dust at irregular intervals occurring throughout the bolting cycle. Figure 13, the bag 

test, shows low consistent dust levels with elevated levels occurring similar to those in Fig. 12. The elevated 

levels in Entry 6 are fewer in frequency than those in 

Entry 5, possibly due to the number of holes drilled in 

each place. The elevated levels in both bag and bagless 

tests show that dust is bypassing the canister fi lter and 

escaping the collector system during the bolting cycle. 

Based on the limited testing performed, the reason for 

this occurrence cannot be determined. 

Table 2 shows a summary of the average bolter exhaust dust levels recorded by the pDRs for the places 

that were sampled during bolting. The averages were 

calculated by extracting the data interval recorded by 

the pDR while the bolter was bolting each place to 

arrive at an average dust level while bolting. On the 

bagless day of operation, rock dusting took place outby 

for a 10-minute period while sampling in Place 2. The 

rock dust raised the dust levels during the bolting of 

this place.The table shows two values for Place 2 for the 

bagless test condition. The value in parentheses is the 

dust level with the 10-minute rock-dusting interval removed.The average value in parentheses is the average 

of Place 1 and Place 2 without the rock-dusting interval. 

With the rock dusting time period removed, the collector operating without the bag during bolting of two 

places is more than two times the dust level recorded 

with the bag during bolting of three places. 

The time required to clean the bagless collector side 

and filter was 4 minutes, as opposed to 30 seconds to 

remove and replace the bag from the other collector. 

Table 2 

Dust level averages from pDRs at the bolter exhaust 

during bolting of each place. 

 

 

 

Average pDR dust levels at the bolter, pDR units 

Location Bagless1 Bag 

Place one 0.77 0.32 

Place two 2.78 (1.13) 0.19 

Place three – 0.75 

Average 1.78 (0.95) 0.42 

1

Dust levels in parentheses are with 10-minute rock-dusting period removed. 

FIGURE 11 

PDM sample data worn by NIOSH personnel on the left 

(exhaust) and right sides of the bolter. 

Summary 

Lab tests. The laboratory dust collector tests show 

that nearly 100 percent (99.6 percent) of the test dust 

fed into the collector was captured by the dust bags. Figure 14 shows the condition of the main chamber before 

and after testing for each test condition. Total weight 

gain on the canister filter was more than five times higher without use of the bag. The RAM-1 unit shows respirable dust levels in the collector exhaust to be more 

than two times higher when tests were conducted without the bags in place.The APS showed that the number 

of total dust particles emitted from the exhaust was two 

times greater when the tests were conducted without 

the bags. Because nearly all the dust is contained in the 

bag, operator exposure is improved when emptying the 

collector box’s main chamber. Filter loading is greatly 

decreased when using the bags, enabling longer periods 

of drilling without filter removal/cleaning. Pressure drop 

across the filter for all tests ranged from 76.2 to 83.8 mm 

(3 to 3.3 in.) WG when the bag was used and 101.6 to 

213.4 mm (4.0 to 8.4 in.) WG without the bag. Filtered 

air emitted from the collector has less respirable dust 

and fewer total dust particles when the bags are used. 

FIGURE 12 

Bagless test dust levels measured in the bolter exhaust 

in Entry 5 with a pDR. 
 

FIGURE 13	 

Bag test dust levels measured in the bolter exhaust in 

Entry 6 with a pDR). 

Field tests. Although limited data were collected, all 

sampling results show a similar trend. Dust reductions 

around the bolter were shown in both area and personal 

samplers when the bag was used in the dust-collector 

system. The following observations were made: 

• 	 Gravimetric samplers at the bolter showed a dust 

improvement of from 0.96 to 0.14 mg/m3 when the 

bag is in use. 

• 	 Personal samples from the PDMs show that the left 

side (exhaust side) of the bolter experienced two 

times the amount of respirable dust than the right 

side. NIOSH personnel cleaned the dust boxes when 

required so that the samplers would measure dust 

from the cleaning process. Depending on the amount 

of ventilation air, dust box cleaning and dust piles 

on the mine floor may add to operator exposure. 

However, PDM data show no increase from one side 

to the other.The time required to clean the bagless 

collector side and filter was 4 minutes, as opposed 

to 30 seconds to remove and replace the bag from 

the other collector. Use of the bag limited exposure 

time while cleaning the dust box and prevented dust 

from accumulating on the mine floor avoiding possible re-entrainment. 

•	 Overall dust level averages for the bolter as recorded 

by the pDRs were lower for each place when the 

bags are used. However, the recorded data also show 

unexplained elevated dust levels in short time periods over the course of both sampling conditions. 

Both laboratory and field results show that benefi ts 

from use of the bags are realized in all areas of operator exposure. To utilize these bags in underground coal 

mines, the dust bags must be accepted by MSHA as an 

optional item for the specifi c dust-collection system and 

machine model (CFR30, part 33). In addition, the collector must be equipped with a pre-cleaner option and a 

retrofit kit installed inside the collector to connect to the 

bag. Without the pre-cleaner option, the bags would fi ll 

too quickly and need replaced too often. 

FIGURE 14 

(a) Collector box conditions without use of a bag and (b) 

collector box conditions with use of bag. 

Disclaimer 

Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health (NIOSH). In addition, 

citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, 

NIOSH is not responsible for the content of these Web 

sites.

 The findings and conclusions of this report are those 

of the authors and do not necessarily represent the views 

of the National Institute for Occupational Safety and 

Health. 

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Available at U.S. Department of Labor, MSHA, Arlington, VA. 

Ondrey, R., Stoltz, R., Atchison, D., and Gerbec, E., “Dust sampling roof bolting operations,” Mine Safety and Health Administration, Available at MSHA Website: http://www.msha.gov/s&hinfo/ 

TECHRPT/dust/dustsamp.pdf.