REDUCING ENCLOSED CAB DRILL OPERATOR’S RESPIRABLE DUST EXPOSURE AT SURFACE COAL OPERATION 

WITH A RETROFITTED FILTRATION AND PRESSURIZATION SYSTEM

A.B. Cecala and J.A. Organiscak 

Natl Inst for Occuptnl Sfty and Health 

Pittsburgh, PA 

W.A. Heitbrink 

Natl Inst for Occuptnl Sfty and Health 

Cincinnati, OH 

J.A. Zimmer 

Natl Inst for Occuptnl Sfty and Health 

Pittsburgh, PA 

T. Fisher 

Air Intrntl Transit/Sigma Air Conditioning 

Addison, IL 

R.E. Gresh 

Mine Sfty & Health Admn 

Arlington, VA 

J.D. Ashley, ll 

Lodestar Energy, Inc. 

Pikeville, KY 

ABSTRACT 

Many different types of mobile equipment used in surface 

coal mining utilize enclosed cabs to protect equipment operators. 

The overburden removal process is extremely dusty and can 

cause excessive exposure to respirable dust, especially 

crystalline silica. After equipment is used for years, many 

components of the enclosure deteriorate and its effectiveness is 

greatly reduced. This report discusses a cooperative research 

study performed on an Ingersoll Rand DM45E surface drill, 

retrofitted with a new Sigma pressurization and filtration system. 

Respirable dust concentrations were substantially reduced from 

0.64 mg/m3

 during pre-testing to 0.05 mg/m3 during post-testing 

with the new system, representing a 92% reduction in dust levels 

in the drill cab. This new system appears to be a very well-built 

and sturdy device, well-suited for the mining industry. 

INTRODUCTION 

Surface coal miners are often exposed to high levels of 

respirable dust. Since much of the overburden at these 

operations contains silica-bearing strata, the health effects of this 

dust are even more hazardous (Silicosis and Silicate Committee, 

1988; Ng and Chan, 1994; Nnizdo and Sluis-Cremer, 1991). In 

an effort to lower the respirable dust exposure of surface miners, 

the National Institute for Occupational Safety and Health (NIOSH) 

has been conducting research in a number of different areas. 

Recently, one of the major thrusts has been improving the 

protection to workers operating surface mining equipment inside 

enclosed cabs. Normally, when this equipment is new, the cabs 

are fairly airtight and the filtrations systems are in good working 

order. However, most mining equipment is older, and as aging 

occurs, many components of the enclosure deteriorate. This 

causes the structural integrity of the cab to diminish and the 

effectiveness of the air filtration system is considerably lessened. 

The cab then does not adequately protect the worker from 

harmful contaminants, including respirable dust. Compounding 

the problem, dust sampling records indicate that drill operators 

and drill helpers have some of the highest dust exposures of all 

workers at surface mining operations (Tomb et al, 1995). 

In an effort to improve the protection to workers exposed in 

older mining equipment, NIOSH entered into a number of 

cooperative research efforts with mining companies, heating and 

air conditioning companies, and cab filtration manufacturers 

(Organiscak et al, 2000; Heitbrink et al, 2000). The research 

discussed in this report is one such study. This work was a 

cooperative research effort involving NIOSH, Air International 

Transit/Sigma Air Conditioning Inc., Lodestar Energy, Inc. 

(surface coal operation), and the Mine Safety and Health 

Administration (MSHA).1

NIOSH and Sigma Air Conditioning Inc. established a 

cooperative cost- sharing agreement to determine the impact of 

retrofitting an older piece of mining equipment with a new 

pressurization and filtration system. In the spring of 2000, NIOSH 

and MSHA visited Lodestar Energy’s Gooseneck Operation in 

eastern Kentucky to pursue the possibility of performing this 

evaluation at its surface coal operation. One objective of this 

study was to perform a worst-case scenario to determine the 

 

1.Mention of any company name or product does not constitute 

endorsement by the National Institute for Occupational Safety and 

Health. 
2 

degree of improvement when retrofitting the poorest quality 

enclosed cab with a new pressurization and filtration system. 

Lodestar Energy, Inc. also agreed to participate in this study and 

after many different pieces of mining equipment were considered, 

it was decided to perform this study on an Ingersoll Rand DM45E 

surface drill. Initially, baseline dust measurements were taken on 

the drill before any changes or modifications were made to it. 

After this was completed, a new filtration and pressurization 

system was installed, followed by an identical dust analysis to 

determine the changes in the drill operator’s respirable dust 

exposure with the new system in operation. 

TESTING 

Since the ultimate objective of this research was to 

determine the reduction in the drill operator’s dust exposure with 

the Sigma pressurization and air filtration system, the sampling 

strategy was designed to provide a quantitative analysis of the 

change in the operator’s respirable dust exposure. Data collected 

included gravimetric respirable dust sampling, impactor dust size 

distribution, instantaneous respirable dust monitoring through 

Mini-RAM and Data-RAM measurements, instantaneous GRIMM 

particle counter size distributions, weather conditions (wind 

speed, direction, temperature, and humidity), and documentation 

of equipment operation. During post-testing, temperature 

recording devices were also located inside and outside the 

enclosed cab to perform a comparison of temperature levels. 

Three main sampling areas were chosen for this evaluation: 

1) Inside operator’s cab; 2) Outside on drill cab; and 3) Outside on 

sampling tripod. The first sample unit inside the operator’s cab 

monitored conditions that the drill operator would be exposed to 

during time spent in the cab over the work day. All in-cab 

sampling instrumentation was placed on a sampling rack located 

directly behind the drill operator’s chair (Figure 1). This sample 

unit was composed of three gravimetric samplers, a cascade 

personal impactor, and an instantaneous respirable dust monitor. 

Also during post-testing, a temperature recording device was 

used both inside and outside the operator’s cab to give a 

continuous recording of temperature levels at both locations. 

Figure 1. Interior cab sampling instrumentation on 

Ingersoll Rand drill. 

All instrumentation on the outside cab sampling unit was 

located on a sampling rack attached to the back of the drill. This 

sampling unit was composed of three gravimetric samplers, one 

personal cascade impactor, and a temperature recording device 

for post-testing. The cascade impactor device was only operated 

for a short period of time (usually 60 to 90 min), because of the 

high dust concentrations recorded at this outside location. Finally, 

the tripod sampling location was composed of three gravimetric 

samplers and was manually moved during testing by NIOSH 

personnel to be positioned at the windward side of the drill unit in 

the dust cloud. 

Baseline dust measurements were performed on this drill in 

May of 2000 for three consecutive 10-hour daylight shifts. After 

the completion of this baseline testing, a Sigma Air Conditioning, 

Inc. representative traveled to the operation to obtain all 

necessary design specifications, then the new pressurization and 

filtration unit was fabricated and installed in September of 2000. 

This Sigma system was made up of the following components: 

FFR6 filter/heater/air conditioning main unit; TFC6 condensor for 

air conditioning unit; and FVW100 pressurizer unit. 

The FFR6 filter/heater/air conditioning main unit is designed 

for rooftop mounting on the cabs of heavy duty off-highway 

machinery. The system has high heating and cooling capacity to 

suit large equipment, such as drills, shovels, dozers, and trucks. 

Sigma also uses a modular approach for the pressurization and 

filtration systems, which provides flexibility to the end user to 

customize a system to fit user needs and cost. A system can be 

designed to accept either a standard pressurizer or a selfcleaning pressurizer; the self-cleaning type was used in this 

study. The FFR6 filter/heater/air conditioning unit is equipped 

with a two-stage filter design. The first stage is a Farr 33/30 filter, 

which has a 95% efficiency rating for particles 5 μm. This filter is 

designed to remove the larger particles and reduce the loading of 

the second and final stage filter, a pleated spun polyester 

washable medium, which is 99% efficient on particles > 0.5 μm. 

This system uses 134a environmentally friendly refrigerant 

for air conditioning. The maximum airflow capacity delivered to 

the enclosed cab with this system is 450 cfm. The self-cleaner 

filter medium on the FVW 100 pressurizer unit also uses the final 

stage filter medium. Outside air is drawn through the filter before 

entering the pressurizer system, then mixed with the enclosed 

cab return air in the main unit (FFR6). This mixed air then flows 

through the evaporator section of the A/C system, where either 

heating or cooling is applied. The cab operator manually adjusts 

a solid state control that sets the fan speed. The fan speed 

mainly deals with operator comfort and has a very minor effect on 

cab pressurization. The pressurizer system operates for a set 

time period then automatically provides a back-flushing cycle to 

clean the filter using the reverse pulse technique. 

After the Sigma system was installed and working properly, 

the post-dust evaluation was performed in September 2000 for 

three consecutive days. All monitoring equipment and 

procedures were identical to pre-testing, with two minor 

exceptions. Additional temperature recording devices were used 

to monitor the air temperature inside and outside the enclosed 

cab to account for the operator’s ability to self-control temperature 

inside the enclosed cab. The second variation was a change in 

the instantaneous dust monitor used inside the operator’s cab. 

During pre-testing, a Mini-RAM unit connected to a solid state 

data-logger device was used to record instantaneous respirable 

dust concentrations. At the end of each day of testing, the dataloggers were dumped to a personal computer for permanent data 

storage and data analysis. For post-testing, a Data-RAM unit was 

used, which has a built-in datalogger unit. Since both instruments 

were built by the same company, all aspects excluding the data 

storage capability on the Data-RAM, were either identical or very 

similar. 

One final analysis was performed during the beginning of 

November for one day using GRIMM particle counting 

instruments. This was used to measure the number of dust 

particles in various size spectrums both inside and outside the 

enclosed cab. This information was used to compare and confirm 

the results of other dust sampling instrumentation and provided a 

data base of other similar analysis performed at other operations. 

RESULTS 

The main objective of this research effort was to determine 

the impact on the drill operator’s dust exposure by the 

implementation of the new Sigma pressurization and filtration 

system. Table I shows the average respirable dust concentration 

as measured by gravimetric sampling for the three sample 

locations for both pre- and post-installation testing of the Sigma 

unit. The most important detail to note from this table is the 

extremely low respirable dust concentrations measured inside the 

cab during post-testing. The average concentration for the entire 

three days of post-testing was 0.05 mg/m3

. 
3 

TABLE I. Average Respirable Dust Concentration 

Measured by Gravimetric Samplers 

Location Pre-Test (mg/m3

) Post-Test (mg/m3) 

Average Tripod 7.69 2.69 

Average Outside 7.30 2.82 

Average Inside 0.64 0.05 

Figure 2 shows the calculated protection factors for preand post-testing of the enclosed operator cab on this Ingersoll 

Rand drill. The protection factor values shown in this graph are 

calculated from average gravimetric dust data. The cab 

protection factor is the average outside respirable dust 

concentration (average outside cab and tripod) divided by the 

inside cab dust concentration. As shown in the graph, the 

average pre- and post- protection factors are values of 12 and 52, 

respectively. One interesting point was the change in outside 

respirable dust concentrations between pre- and post-testing. For 

pre-testing, respirable dust levels were in the seven milligram per 

cubic meter range, whereas for post-testing, these values were in 

the two milligram per cubic meter range. We believe the main 

reason for this change can be associated with the depth of 

drilling. During pre-testing, the Ingersol Rand drill was drilling two 

drill steels, which was approximately 40-foot holes. During posttesting, the drill was only drilling roughly 15-foot holes, thus 

generating less dust. 

Considering the information presented in Table I, it must be 

noted that inside the enclosed cab, respirable dust concentrations 

obtained for pre-testing analysis provided reasonable protection 

to the drill operator with the original Ingersoll Rand dust control 

system. The average inside respirable dust concentration was 

0.64 mg/m3

 with a protection factor of 12. This is a respectable 

value when one considers the age of the drill and that the filter 

unit had not been actively maintained over the life of the drill. 

Figure 2. Protection Factors during testing of Sigma unit 

on Ingersoll Rand DM45E drill. 

Table II presents the silica analysis of the gravimetric 

samples analyzed at the analytical lab at the Pittsburgh Research 

Laboratory. The first part of this table lists the silica content of the 

respirable dust collected on the sampling filters. The silica 

content ranged from 3.7 to 18% for all samples with a mean and 

standard deviation of 12.46% and 3.04%, respectively. The first 

part of the table indicates the consistency in the silica content for 

both pre- and post-testing. It is important from a comparability 

standpoint that this value remain very similar. For pre-testing, the 

silica content mean and standard deviation were 12.8 and 1.1, 

respectively. For post-testing, the silica content mean and 

standard deviation were 12.1 and 4.2, respectively. Hence, the 

silica content of the overburden being drilled between the two 

weeks of testing was very similar. The second part of the table 

lists the micrograms of crystalline silica on the gravimetric filters. 

An area of prime interest is silica levels inside the operator cab, 

which the drill operator is exposed to. MSHA’s standard for silica 

(Permissible Exposure Limit - PEL) is based upon a 100- 

microgram standard. NIOSH’s Recommended Exposure Limit 

(REL) is 50- micrograms. For pre-testing, the average silica 

weight was 57 micrograms; this compares to an average of 3.5 

micrograms for post-testing, which is a 94% reduction. 

Another result that underscores the efficiency of the Sigma 

filtration and pressurization system is the data obtained from the 

impactor size distribution measurements. Figure 3 identifies the 

highlights of the measurements from inside the operator cab for 

both pre- and post-testing. This graph shows the improvement 

with the new system. Percentage of efficiency represents a 

collection efficiency of 100% (points at the top of the graph). As 

shown, the collection efficiency is almost at the 100% level for the 

various size ranges of particles collected with the impactor 

devices. 

TABLE II. Silica Content and Weight for Analysis of Sample 

Gravimetric Filters Silica Analysis - Content, (percentage) 

Location Day 

1 

Day 

1 

Day 

2 

Day 

2 

Day 

3 

Day 

3 

 PreTest PostTest PreTest PostTest PreTest PostTest 

Tripod 13.7 13.8 12.5 9.3 12.2 8.9 

Outside 12.7 15.3 12.2 14.5 12.4 18.0 

Inside 15.4 13.7 12.3 11.9 11.8 3.7 

Silica Analysis - Weight, (micrograms) 

Location 

Day 

1 

Day 

 1 

Day 

 2 

Day 

 2 

Day 

3 

Day 

 3 

 PreTest PostTest PreTest PostTest PreTest PostTest 

Tripod 823.

8 

75.3 280.

2 

672.

8 

627.

9 

252.

0 

Outside 825.

4 

139.

7 

330.

4 

763.

6 

673.

0 

137.

4 

Inside 86.3 1.8 24.6 6.1 60.9 2.5 

From information obtained with the instantaneous 

respirable dust monitor inside the cab and testing performed with 

the GRIMM particle-counting instrumentation, a significant portion 

of the dust measured inside the cab resulted from periods when 

the door was opened on the drill so that the drill operator or test 

personnel could enter or exit the enclosed cab. The Data-RAM 

data showed very low respirable dust levels except for periods 

when spikes were recorded. We believe these periods represent 

times when the door on the enclosed cab was opened. For 

approximately a one-hour period during the afternoon of 

September 26, the drill operator was actually operating the drill 

with the drill-stem side door open, allowing for better visibility of 

the necessary drill depth. 

The GRIMM particle counting instrument testing on 

November 8 also indicated significantly higher levels inside the 

enclosed cab immediately after the door had been opened. 

Particle size data of the GRIMM instruments indicate that it took 

approximately 7 minutes for dust levels to stabilize inside the 

enclosed cab after the door was opened. Once the system 

operated for this time period, dust levels remained at very low 

levels. The GRIMM instruments also provide a protection factor 
4 

calculation for the various size range distributions of dusts as 

measured by the instrument. The protection factor ranges from a 

low of approximately 40s to a high in the low 70s (Figure 4). The 

average from all particle size ranges is a protection factor in the 

low 50s range. These protection factors correlate closely with the 

average protection factor of 52 which was obtained with the 

gravimetric samplers. 

Figure 3. Improvement in cab collection efficiency with 

new Sigma system in operation. 

The cost for this Sigma unit was approximately $10,000 

plus the cost of installation. The components used for this 

research study were the upper-level components to indicate the 

greatest levels of protection possible for the enclosed cab 

operator. Choosing smaller components would lower the cost of 

the system. 

One last area that was monitored and has an impact on 

reduced respirable dust levels inside the operator cab is the 

amount of pressurization, or static pressure, from the dust filtering 

and pressurization system. During pre-testing, air pressure inside 

the cab relative to outside was measured using a magnehelic 

pressure gauge and a Solomat PDM205 pressure meter. When 

just the pressurizer unit was operated, there was no 

pressurization detected with either device. When the air 

conditioner was turned on, a reading of 0.03 inches of water 

gauge was detected. This was checked periodically during the 

three days of testing with the same values being recorded. 

During post-testing with the new Sigma filtration and 

pressurization system, good pressurization was achieved for all 

three days of testing. The pressurization ranged from 

approximately 0.20 inches water gauge to approximately 0.40 

inches water gauge. There are three fan speed settings: Low, 

Medium, and High. A few hundredths (0.02-0.04) difference was 

evident between the low and high setting. 

Cab pressurization is a very important factor affecting 

protection inside the operator cab under all weather conditions. 

For pre-test conditions, high wind speeds or currents would have 

been able to blow dust from the outside into the operator’s cab. 

With the new system installed, the pressurization was great 

enough that it would eliminate any wind-infiltrating dust into the 

cab under any reasonable weather conditions. 

0

10

20

30

40

50

60

70

80

0.10 1.00 10.00

 Diameter (μn)

Protection Factor

 Figure 4. Protection Factors as measured by as measured by GRIMMParticle Monitors. 
5 

DISCUSSION 

From this study, as well as others on filtration and 

pressurization systems, we believe that there are two key 

components necessary for an enclosed cab to be effective from a 

dust control standpoint: 1) effective filtration, and 2) cab integrity. 

Both of these components are important and must be properly 

addressed for the system to be effective. An effective filtration 

system should be composed of both a recirculation and outside 

(makeup) air system. The majority of air inside an enclosed cab 

should be recirculated through a high quality filter medium. This 

allows air to be conditioned to the cab operator’s comfort (heating 

or air conditioning) without major air changes that would 

significantly affect the size and capability requirements, and 

ultimately the cost for conditioning the cab air. Another 

consideration is to have separate fans for makeup and 

recirculating air. 

A major component in an effective system is to have the 

makeup air positively pressurize the enclosed cab. This results in 

any system leakage to travel from the inside of the cab to outside, 

preventing dusty air from entering the cab. It is also highly 

recommended that the makeup air be positively pressurized after 

being filtered to eliminate any possibility of dust- laden air being 

drawn into the system. Additionally, the makeup air should 

optimally be located on the cab the furthest practical distance 

from the dust sources (Technology News 485, 2001). This 

reduces the amount of loading on the filters and increases the 

time between cleaning or replacement. Finally, the discharge for 

makeup air into an enclosed cab should be located high in the 

enclosure, preferably at the roof. This allows the clean air to be 

blown down over the equipment operator’s breathing zone without 

becoming contaminated by any in-cab dust sources. The Sigma 

filtration and pressurization system met each of these design 

criteria as listed. 

One last design criteria that we recommend for the filtration 

component of an effective design is to use a top-down approach 

to the clean air flow pattern. In the Sigma design tested for this 

study, as well as in most other systems, the intake and discharge 

for the recirculation air is located in the roof unit. Although this is 

acceptable, we believe the most beneficial design would be to 

draw the recirculated air from the bottom of the cab instead of at 

the roof of the enclosure. This allows the dust- laden air to be 

drawn out the cab near the worker’s feet and away from the 

breathing zone. Again, the clean air would be blown in at the roof 

of the enclosure and the dust-laden recirculated air would be 

withdrawn from the floor of the cab. We would never recommend 

the discharge of clean air low in the cab because, as we 

observed, this can entrain a significant amount of dust from soiled 

work clothes, boots, and a dirty floor (Cecala, Organiscak, and 

Heitbrink, 2001). Figure 5 represents our ideal schematic for an 

effective filtration and pressurization system on an enclosure drill 

cab. Once again, we are unaware of any manufacturers who are 

currently pulling the recirculated air low within the cab. 

The second factor for dust control effectiveness is cab 

integrity. Cab integrity is necessary in order to achieve some 

level of pressurization. Field testing has shown that installing new 

door gaskets and plugging and sealing cracks and holes in the 

shell of the cab have a major impact on increasing cab 

pressurization. To prevent dust-laden air from infiltrating into the 

cab, the cab’s static pressure must be higher than the wind’s 

velocity pressure. Although higher static pressure requirements 

help overcome outside wind speeds, a major drawback is that this 

necessitates more air being delivered by the outside air unit, 

causing more loading on the filters. Higher air flows through 

filters can also decrease the filter’s efficiency by allowing more 

contaminants to flow through the filter media. Another drawback 

to higher airflows is that they create more air conditioning (heating 

and cooling) requirements for operator comfort, which increases 

the size and cost for this component. 

The Ingersoll Rand drill enclosure tested in this study was 

still adequate and did not require new door gaskets or repair to 

achieve positive pressurization. Although sealing the cab was not 

necessary during the time of installation in this particular case, we 

do recommend the use of some type of pressure gauge inside the 

enclosed cab. This indicates when cab integrity is marginal and 

maintenance needs to be performed. Loss of pressure indicates 

either a filter loading problem or a cab integrity failure. Filter 

maintenance should be performed periodically and when a predetermined pressure loss occurs over time. A sudden increase in 

pressure normally indicates a major failure in one of the filters and 

this problem should be corrected immediately. 

Figure 5. Ideal schematic for an effective filtration and 

pressurization system on an enclosed cab. 

CONCLUSION 

The field study on the Sigma air filtration and pressurization 

system showed this system to be very effective at reducing the 

drill operator’s dust exposure, as well as providing a working 

environment that is more controllable and comfortable to the drill 

operator. A number of different sampling strategies and 

equipment were used in this evaluation; in all cases, they showed 

the Sigma air filtration and pressurization to be a very effective 

system. 

When considering the gravimetric dust results, the unit 

reduced the drill operator’s respirable dust exposure from a pretest concentration of 0.64 mg/m3

 to a post-test concentration of 

0.05 mg/m3

. This represents a 79% reduction in respirable dust 

concentrations when outside dust measurements are normalized 

since pre-testing levels were significantly higher than post-testing. 

The protection factor provided by the system averaged a value of 

52 for the entire evaluation period. When considering the 

reduction in silica exposure, the drill operator had an average 

silica exposure of 57 micrograms per day for pre-testing, as 

compared to an average silica exposure of 3.5 micrograms for 

post-testing. When considering the data from the GRIMM particle 

counting instruments and the cascade impactor devices, the 

information also supports the effectiveness of the Sigma filtration 

and pressurization system at the various particle size ranges 

evaluated. This system was very effective in removing the 

respirable size range of dust particles (less than 10 μm) which are 

harmful to a worker’s lungs. The Sigma system also provided 

very good pressurization to the enclosed cab without requiring 

any changes to the enclosure by the sealing of cracks or leakage 

points. The pressurization of 0.2 to 0.40 inches of water gauge 

also ensured that the wind would not be blowing dust from outside 

into the cab. Allowing the drill operator to have the flexibility of 

controlling the temperature level inside the cab and the fan speed 

keeps the operator involved in the system. Both drill operators 

stated that they like the system very much. 

One last area that we were very impressed with is the 

ruggedness and mine-worthiness of the unit. The unit appears 

very suitable for a mine environment and should hold up as well 

as any unit could be expected. 
6 

REFERENCES 

Cecala, A. B., Organiscak, J. A., and Heitbrink, W. A., 2001, “Dust 

Underfoot - Enclosed Cab Floor Heaters Can Significantly 

Increase Operator’s Respirable Dust Exposure,” Rock 

Products, April, Vol. 104, No. 4, pp. 39-44. 

Heitbrink, W. A., Thimons, E. D., Organiscak, J. A., Cecala, A. B., 

Schmitz, M., and Ahrenholtz, E., 2000, “Static Pressure 

Requirement for Ventilated Enclosures,” Progress in 

Modern Ventilation Vol. 2, Proceedings of the Sixth 

International Symposium on Ventilation for Contaminant 

Control, Helsinki, Finland, June 4-7. 

Ng, T., and Chan, S., 1994, “Quantitative Relations Between 

Silica Exposure and Development of Radiological Small 

Opacities in Granite Workers,” Annals of Occupational 

Hygiene, Vol. 38, Suppl. 1, pp. 857-863. 

Nnizdo, E., and Sluis-Cremer, G. K., 1991, “Silica Exposure, 

Silicosis, and Lung Cancer: A Mortality Study of South 

African Gold Miners,” British Journal of Industrial Medicine, 

Vol. 48, pp. 53-60. 

Organiscak, J. A., Cecala, A. B., Heitbrink, W. A., Thimons, E. D., 

Schmitz, M., and Ahrenholtz, E., 2000, “Field Assessment 

of Retrofitting Surface Coal Mine Equipment Cabs with Air 

Filtration Systems,” Virginia Tech Conference, Blacksburg, 

Virginia, August 27-30. 

Silicosis and Silicate Committee, 1988, “Diseases Associated with 

Exposure to Silica and Nonfibrous Silicate Minerals,” 

Archives of Pathology and Laboratory Medicine, Vol. 112, 

July, pp. 673-720. 

Technology News 485, 2001 “Improved Cab Air Inlet Location 

Reduces Dust Levels and Air Filter Loading Rates,” 

National Institute for Occupational Safety and Health 

(NIOSH), February. 

Tomb, T. F., Gero, A. J., and Kogut J., 1995, “Analysis of Quartz 

Exposure Data Obtained from Underground and Surface 

Coal Mining Operations,” Applied Occupational and 

Environmental Hygiene, Vol. 10, No. 12, Dec., pp. 1019-

1026.