Development of a canopy 


air curtain to reduce roof bolters’ dust exposure
 

by J.M. Listak and T.W. Beck 

Abstract The U.S. National Institute for Occupational Safety and Health (NIOSH) conducted

a study to determine the effectiveness of a filtered air delivery system to reduce respirable dust

exposure of roof bolter operators in underground coal mines. When performing roof bolting

operations, roof bolter operators may experience exposure to high levels of respirable dust

during a working shift, especially when working downwind of the continuous mining machine.

While drilling and installing roof bolts, this filtered air system supplies a clean curtain of

air over the roof bolter operator by means of a plenum mounted beneath the canopy. This

experimentally designed air curtain, adapted for roof bolting machines used in this study, is

based upon previous design prototypes, computational fluid dynamics (CFD) simulations and

trial-and-error testing. Both the prototype and final designs were tested in the full-scale mining

galleries at the Office of Mine Safety and Health Research (OMSHR) in Pittsburgh, PA before

being taken underground for field testing. Test results of the system in both laboratory and

field studies show reductions in operator exposure to respirable dust when the operator is

positioned directly under the protected zone of the canopy.

Introduction 

Underground coal mine roof bolter 

operators are at risk of excessive exposure to respirable coal and silica dust, 

second only to continuous miner operators, based upon the U.S. Mine Safety 

and Health Administration (MSHA) 

personal dust samples (MSHA, 2009). 

Dust collectors on roof bolting machines, if maintained properly, effectively minimize dust exposures during 

drilling and bolting activities. However, 

due to mining sequencing, there may 

be times during a working shift when 

roof bolter operators must work downwind of the continuous mining operation.When this scenario occurs,the dust 

from the continuous miner enters the 

roof bolting workplace, potentially exposing the operators to high levels of 

respirable dust. In addition, the bolting operation itself can contribute to 

higher respirable dust concentrations 

in the worker’s area if dust collectors 

are not maintained, adding to operator exposure. To lessen the operator’s 

dust exposure when these conditions 

occur, a plenum mounted under the 

roof bolter’s protective canopy has 

been developed to supply filtered air 

over the operator as bolting duties are 

performed. This filtered air is delivered 

to the plenum via tubing connected to 

a blower that is mounted on the roof 

bolting machine. 

The roof bolting procedure requires 

the operator to stand under a support 

canopy for protection from loose roof 

rock as holes are drilled into the mine 

roof for the installation of roof bolts 

(Fig. 1). 

This canopy is fixed to the drill 

boom and continually offers the operator protection from loose debris as the 

boom is repositioned for each new hole. 

Based upon time studies conducted for 

this study, nearly 66% of the operator’s 

drilling time is spent under this canopy 

during a complete cycle of bolting. The 

canopy, therefore, provides an ideal location for installing a device to protect 

the operator from respirable dust. The 

underside of the roof canopy serves as 

a mount for such a device to deliver a 

filtered air supply over the operator 

during drilling activities. This device or 

canopy air curtain (CAC) serves as a 

plenum to blow a constant stream of 

fresh air over the breathing zone of 

the operator. The air supply will act 

as a “curtain” of fresh air for a zone of 

protection from the contaminated air 

around the bolter, regardless of the dust 

source (Fig. 2). 

Although a new application for roof 

bolting machines, air curtain technology 
 

for continuous miner operator cabs was originally developed 

under a U.S. Bureau of Mines contract in the 1970s by the 

Donaldson Company Inc. (1975). Before the advent of radio 

remotes for controlling the operation of continuous mining 

machines, the operators were located in an onboard control 

cab at the rear of the continuous miner. Close proximity of 

the cab to the cutter head subjected the operators to high 

levels of respirable dust during mining. In an attempt to reduce dust exposure to the operator, a contract was awarded 

to develop a device to provide a source of fresh air for these 

operators. This device was designed to be compatible with 

the mining equipment and offer protection from dust exposure while minimally affecting operator safety, comfort 

and mobility within the cab area. The final working design 

consisted of a square plenum, blower and filter, and connective tubing. The plenum housing was made from fiberglass 

and used perforated plate and screen mesh as an air diffuser. 

The inlet port was tapered, as well as the area over the air 

diffuser. The surface of the air diffuser had dimensions of 

43.2 x 43.2 cm (17 x 17 in.). Figure 3 shows the Donaldson air 

curtain design. Field testing of the air curtain in continuous 

miner cabs showed reductions in dust exposure from 30% to 

75% depending upon the amount of time the operator spent 

in the protected zone. 

Figure 1 

Roof bolter operator under roof canopy during roof drilling. 

Figure 2 

Roof bolter operator protected by clean airflow provided by canopy air curtain. 

Figure 3 

Original square air curtain design, by Donaldson Company, 

Inc. 

In the early 1980s, the Mining Research and Development Establishment (MRDE) of the National Coal Board 

in Great Britain (NCB) (MRDE, 1981) tested Donaldson’s 

air curtain design in the cabs of heading/ripping machines to 

determine its effectiveness in reducing operator exposure 

to respirable dust. The MRDE research found that entry 

velocities in excess of 0.51 m/s (100 fpm) could infiltrate the 

protected area under the cab, “pushing” dust into the operator’s breathing zone. Through design modifications, the 

MRDE produced an air curtain that reduced dust by up to 

70% in an entry airflow velocity of nearly 1.5 m/s (300 fpm). 

Another study (Volkwein et al., 1982) showed that the 

Donaldson air curtain was applicable for dust reductions on 

equipment other than continuous mining machines. Volkwein showed dust reductions of up to 50% on a gatheringarm loader operator in a salt mine. However, as with other 

studies, results showed that higher entry velocities reduced 

the effectiveness of the air curtain. 

Although Donaldson proved that the air curtain concept 

could be an effective means to reduce operator dust exposure, the 10.2 cm (4 in.) thickness of the original design did 

not allow adequate headroom beneath some operator’s canopies. In response to this problem, Donaldson was awarded 

another contract in 1983 (Donaldson Company Inc., 1987) 

to design an air canopy that would be thinner, yet provide 

the necessary airflow to be as effective as the original design. 

The newer design had the same-sized diffuser, but the smaller 

thickness required different inlet geometry. The newly designed air curtain performed as well as the original and gave 

impetus for investigating air curtain use under the canopies 

of roof bolting machines. NIOSH researchers (Goodman 

and Organiscak, 2001) conducted tests on the new design 

to determine its effectiveness to reduce respirable dust for 

roof bolter operators under various simulated mine conditions. The unit was tested at different distances below the 

diffuser plate, as well as in different entry air velocities. The 

environment in which the unit was tested 

had respirable dust concentrations of approximately 4 mg/m3

. The results of this 

study showed respirable dust reductions 

of up to 62%. A smaller air curtain with 

a rectangular shape, 61 x 25.4 cm (24 x 10 

in.), was subsequently field tested to determine the feasibility of installing, operating 

and maintaining the complete system on a 

roof bolting production cycle (Goodman 

et al., 2006). Although the plenum was too 

small to offer dust reduction to the operators, the tests showed that the system could 

function on a roof bolting machine in an 

underground environment. 

The Donaldson design proved that dust 

reductions can be achieved using a filtered 

air delivery system. However, the square 
 

geometry of the plenum, if used 

on a standard roof bolter canopy, 

would only provide partial coverage of the worker’s operating area 

while under the canopy. Therefore, 

a new prototype was developed that 

would offer greater coverage of filtered air beneath any area of the 

roof canopy. 

Prototype design and testing 

Parameters for the newly designed unit began with the shape 

of the plenum. The typical canopy 

dimensions of roof bolters sized for 

coal seam heights up to 1.83 m (6 

ft) are 101.6 x 50.8 cm (40 x 20 in.). 

The dimensions also include a tapered angle reducing the outermost 

dimension to 25.4 cm (10 in.). These 

dimensions were used to define the 

geometry of a newly developed plenum. A height restriction of 5.1 cm (2 in.) was required to 

provide head clearance for operators beneath the canopy. 

The remaining components consisted of a centrifugal fan 

(American Fan, model AF-10), sized for delivering air to 

the plenum, and a filter. The fan used in laboratory testing 

provided 0.165 m3 at 0.25 kPa (350 CFM at 1 in WC). A filter 

(P12-3990, Donaldson Co., Inc., Minneapolis, MN) was used 

to clean the air before it passed through the fan. Tubing with 

a diameter of 10.2 cm (4 in.) connected the fan/filter assembly 

to the plenum. As with the Donaldson design, the success of 

the system depends on a uniform distribution of air flowing 

over the operator to provide a protected area beneath the 

entire canopy. Therefore, the initial plenum design was based 

upon the Donaldson units. A perforated plate with a 13% 

open area, backed by 180-μm (80-mesh) screen, was used 

as the outflow air diffuser, covering the entire underside of 

the plenum. The inlet portal shape and location had to be 

changed to allow for canopy movement and to conform to 

the mast location on the roof bolting machine. Figure 4 shows 

the first prototype unit. The figure shows two distinct areas 

that will be referenced throughout the paper, the trapezoidal 

area and the square area. Although these regions are contiguous, the distinction is shown in Fig. 4 to better direct the 

reader when references are made to plenum performance. 

Figure 4
	

Original air curtain designed for a roof bolter canopy. 

To evaluate the plenum design, air velocity exiting the 

diffuser was measured to determine airflow uniformity. A 

10.2-x-10.2-cm (4-x-4-in.) grid was constructed and mounted 

beneath the plenum to perform repetitive velocity measurements of the new and subsequent designs. The grid was located 25.4 cm (10 in.) below the plenum, which falls within 

the breathing zone range of a worker wearing a hardhat. The 

velocity measurements beneath the unit were taken using 

a hotwire anemometer (TSI Inc., Model 8346) as shown in 

Fig. 5. 

Figure 5 

Velocity measurement grid 25.4 cm (10 in.) beneath the 

plenum. 

Figure 6
	

Velocity profile of original CAC design.
	

Using the 136-point velocity values from each grid traverse, velocity profiles were created to show the distribution of air exiting the plenum. On the early plenum designs, 

velocity profiles showed that the air flowing from the perforated plate was very uneven. As an example, Fig. 6 shows 
 

the velocity profile of the original plenum design. As shown 

in the figure, most of the airflow was concentrated to the 

square area of the plenum. A maximum velocity of 1.12 m/s 

(220 fpm) was measured. In the trapezoidal area of the plenum, the airflow exited on an angle out beyond the outer 

perimeter of the unit. Little to no flow was measured directly 

beneath the trapezoidal area of the plenum. 

Testing also included dust measurements in the area 

where an operator would perform drilling duties. Although 

there was poor clearance overall, point measurements consistently showed that an air velocity from the plenum of 0.51 

m/s (100 fpm) would provide dust clearance (> 50%) at an 

entry velocity of 0.31 m/s (60 fpm). As can be seen in Fig. 6, 

the velocity contour area greater than 0.51 m/s (100 fpm) is 

limited to a small area under the plenum. 

To try to improve airflow distribution, the unit was disassembled and various baffles, inflow vanes and flow straighteners were added in attempts to direct the air through the 

device for better distribution. All initial modifications failed 

to produce uniform airflow. Therefore, to better determine 

the dynamics of the airflow within the plenum and make 

the necessary changes, the unit was assessed by a ventilation 

computer simulation company using computational fluid 

dynamics (CFD) evaluation. The initial CFD results showed 

deficiencies in the original design. Based on these results, 

CFD modifications were made to the prototype in an attempt 

to provide even flow from the unit. Several iterations were 

performed until the computer model showed that the modifications inside the plenum would provide the best flow from 

the unit. After the design changes were made (Fig. 7), the 

unit was retested in the laboratory to determine the velocity 

profile beneath the unit. 

Figure 7 

Prototype modified based upon CFD analysis. 

Although there was improvement 

over the original design, the distribution of air beneath some 

areas of the unit was still too low in velocity to be effective 

for protection against dust infiltration.To improve flow, CFD 

simulators suggested a design change to the unit that would 

increase the vertical height of the plenum. This change was 

not an acceptable modification, due to the overhead clearance requirement for operator comfort. 

After incorporating some of the CFD modifications, an 

angled plate with an adjustable louver was installed inside 

the square area of the unit to regulate airflow. The perforated plate over the square was removable, allowing for adjustment of the louver. The trapezoidal section was also tapered 

externally to force airflow downward. This design resulted 

in better flow, and preliminary in-mine tests were planned. 

Operational problems at the mine proved problematic, and 

the field testing was inconclusive. However, the field testing 

provided information that led to another positive change. 

The area of the canopy nearest the mast hung over the 

machine and observation showed that when the plenum was 

mounted beneath the canopy, air was not flowing over the 

operator, but rather onto the tool tray of the machine. As a 

result, this area of the perforated plate was blocked off, shifting all flow forward and, thus, creating a smaller area from 

which to flow, resulting in higher velocity. Figure 8 shows all 

the modifications made to the final design. 

Figure 8 

The final CAC design.
	

After the modifications were made, velocity measurements were taken and 

are shown in Fig. 9. 

Figure 9 

Velocity profile of the final design. 

In the new design, the velocity contours 

greater than 0.51 m/s (100 fpm) cover an area of approximately 70%. An area of low-velocity contours is obvious 

in the transition zone between the square and trapezoidal 

areas. Dust samples were measured in this zone and will be 

discussed in a subsequent section of this paper. 

The final prototype was the result of an evolutionary 

experimental design process. The modifications were based 

upon previously designed prototypes (USBM contracts pre-
 

viously cited), CFD simulations and trial-and-error testing. 

Changes included perforated plate percentage open, air inlet 

location and geometry, internal baffles and vanes, and flow 

straighteners (fine mesh screen and honeycomb cell). 

Experimental design 

Laboratory tests were conducted on the final plenum design to determine the zone of protection and the amount of 

respirable dust that was reduced. These tests were conducted 

in the full-scale mine simulation gallery at NIOSH Pittsburgh. The tests measured respirable dust concentrations 

at locations under the filtered air supplied by the plenum 

and outside the plenum in the gallery entry. Three entry velocities were also examined to determine whether 

faster entry air moving into the plenum’s downward airstream would reduce the effectiveness of 

the system. The NIOSH test gallery simulates inmine parameters including entry size, airflow, air 

velocity and dust concentrations. To simulate the 

use of the air curtain under a roof bolter canopy 

operating in a 1.83-m (6-ft) coal seam, a wooden 

test frame was constructed in the gallery. The test 

frame’s mount for the air curtain was 1.7 m (67 

in.) from the gallery floor, 0.58 m (23 in.) from the 

roof and 1.27 (50 in.) from the left side of the entry. The dimensions of the gallery in this location 

are 2.29 m (90 in.) high by 1.98 m (78 in.) wide. 

The plenum was mounted to the underside of the 

test frame for the tests. 

The frame was positioned in the return airway 

of the gallery approximately 24.4 m (80 ft) downwind of a vibratory dust feeder (Vibra Screw Inc., 

Totowa, NJ). The respirable dust (Keystone Mineral Black, 325BA, Keystone Filler and Manufacturing Co., Muncy, PA) was fed into the airstream 

upwind of the test stand using the dust feeder.An 

auxiliary fan was also used in the entry to facilitate mixing of 

the dust before it reached the sampling instruments. A dust 

concentration of approximately 6 mg/m3 was maintained for 

each test velocity. The use of this concentration was based 

upon a previous NIOSH study showing return concentrations 

of continuous miners using scrubbers (Listak et al., 2010). 

The test setup is shown in Fig. 10. 

Figure 10 

NIOSH mine gallery test setup configuration. 

Figure 11 

Dust sampling instrument locations under plenum. 

The dust sampling instruments consisted of gravimetric samplers and a personal DataRam (pDR 1000, Thermo 

Fisher, Franklin, MA). To measure dust levels beneath the 

canopy, six gravimetric samplers were positioned in spatial 

locations, 25.4 cm (10 in.) beneath the plenum. Physically, 

25.4 cm (10 in.) is in the range of the typical breathing zone 
 

of an operator wearing a hardhat. The samplers were spaced 

laterally to measure dust at locations within an operator’s 

range of motion while performing drilling duties (Fig. 11). 

The entry dust was measured using two gravimetric samplers and a personal DataRam (pDR). This sampling array 

was positioned 1.52 m (5 ft) upwind of the plenum.Tests were 

conducted prior to introducing plenum airflow to ensure that 

dust concentration in both sampling positions (under the 

plenum and outside in the entry) were the same. The pDR 

was used to continually monitor dust feeder concentrations. 

The feeder was adjusted to keep concentrations at approximately 6 mg/m3 throughout the testing of the three different 

entry velocities. 

Six 30-min tests were conducted at velocities of 0.05, 0.3 

and 0.61 m/s (10, 60 and 120 fpm) at the test area. These velocities were selected to reflect velocities that may be experienced in a typical roof bolter’s workplace. Test velocities in 

the gallery at the test stand were established, measured and 

maintained using an ultrasonic anemometer (WindSonic, Gill 

Instruments Ltd.,Lymington, U.K.).As previously described, 

the air canopy system uses filtered air to flow over the operator beneath the plenum. The same filter remained in the 

dust-laden entry air during all testing. To ensure the filter 

continued to remove dust from the supply air, an isokinetic 

orifice, connected to a gravimetric sampler, was placed in 

the tubing that supplies air to the plenum. The air supply 

was monitored throughout five hours of testing (in one air 

velocity test) to ensure that the airflow from the plenum 

was uncontaminated. After a total of five hours of testing, 

the concentration of dust in the filtered air was 0.035 mg/m3

. 

Figure 12 shows the sampler locations relative to the 

velocity contours. 

Figure 12 

Dust samplers relative to air velocity under plenum. 

There is a distinct drop in velocity at the 

transition zone between the square and trapezoidal areas of 

the perforated plate. Samplers D and E were located in this 

area to measure dust concentrations. The dust measurements 

verified that this area provided less protection than the areas 

where the other samplers were located. For instance, for the 

test velocity of 0.61 m/s (120 fpm), the dust levels from samplers D and E were 4.5 times greater than those measured at 

samplers A through C. The authors believe this low-flow area 

was created partially by the metal seam in the perforated 

plate. Another cause may be the transition zone inside the 

plenum from the square to the trapezoidal region. 

Data analysis 

Dust concentrations in the entry were compared to the 

dust levels measured under the plenum for all three velocities. For comparative purposes of this part of the analysis, 

the six samplers under the plenum were analyzed collectively, 

based on the fact that the operators are constantly moving 

under the entire area of the canopy throughout the drilling 

cycle. Dust concentrations measured beneath the plenum 

were averaged and compared to the two average concentrations measured on the entry samplers. Table 1 shows data 

collected from the 0.3 m/s (60 fpm) velocity test. 

Figure 13 shows a graph of the average concentrations 

from the six test replications for the 0.3 m/s (60 fpm) velocity test from Table 1. 

Figure 13
	

Relative dust concentrations, showing standard error bars, 

under the plenum versus outside the plenum (i.e., entry). 

Table 1
	

Dust concentration averages from the two test locations at 

0.3 (60 fpm). 

Velocity test dust averages, mg/m3 

Test Plenum Entry 

1 1.62 4.48 

2 1.41 4.57 

3 1.70 5.13 

4 1.63 4.78 

5 1.36 4.56 

6 2.42 6.52 

To illustrate the degree of uncertainty 

between the tests, the graph is shown with standard error 

bars (standard error of the mean). As can be seen on the 

graph, the tests have low standard deviations from the mean 

in the entry measurements and higher variability under the 

plenum. The higher variability under the plenum is a result 

of the higher dust measurements at samplers D and E. The 
 

graph also visually shows a distinct difference in average dust 

concentrations at the plenum and entry sampling locations. 

A test for significance at 95% confidence using a statistical t-test was also performed on the two sampling locations. 

The t-test shows that there is a significant difference (p < 

0.05) between measurements taken in the entry and measurements taken under the plenum.A 67% reduction in dust 

concentration is shown under the plenum at this test velocity. 

This graph and the tests for confidence are representative of 

all three test velocity results when comparing dust concentrations under the plenum versus outside the plenum. 

The data were also summarized to show dust concentration comparisons at each of the test velocities. The measured 

dust levels under and outside the plenum at the different 

test velocities are shown with associated dust reductions in 

Table 2. 

Table 2 

Six-test average of all tested velocities. 

Six-test average concentration, mg/m3 

Entry 

(outside 

plenum) 

Velocity 

m/s (fpm) 

Under 

plenum 

Reduction, 

% 

0.05 (10) 1.95 6.90 72 

0.03 (60) 1.68 5.01 67 

0.61 (120) 1.50 6.07 75 

Statistical t-tests show that a significant difference 

in dust concentration is measured for each test velocity when 

comparing levels under the plenum and in the entry. Figure 

14 shows the three average dust concentrations (1.5 to 1.95 

mg/m3

Figure 14 ) under the plenum at each velocity. 

Dust concentration averages for three test velocities 

showing standard error bars. 

Although dust reduction appears to be greater as entry velocity increases, the 

chart, shown with standard error bars from the six test measurements at each velocity, implies no significant difference 

related to change of velocity. Dust reductions were similar 

for all test velocities, and, therefore, the system is effective 

for reducing respirable dust concentrations for velocities 

common to roof bolting work areas. 

Field testing 

Field testing of the canopy air curtain system was attempted on two occasions to verify results obtained in the 

laboratory (Fig. 15). 

Figure 15 

NIOSH-designed air canopy system on a roof bolter in an 

underground coal mine. 

For each field test, the system was delivered to the mine site in advance for installation on the roof 

bolting machine. However, due to operational problems (fan 

seal damage) while integrating the centrifugal fan into the 

hydraulic system of the roof bolter, both of these studies 

ended prematurely and provided limited data for analysis. 

Despite the problems encountered, the studies were beneficial in that they identified the need for a dedicated hydraulic stage on the roof bolter to independently operate and 

regulate the fan speed. The machine manufacturer has since 

added additional hydraulics on the roof bolter to test another 

air canopy design. 

Although no significant results can be discerned from the 

limited field data, the two places that were sampled showed 

improvement under the plenum. Table 3 shows the two roof 

bolter places that were measured before damage to the fan 

occurred. These data were measured using Personal Dust 

Monitors (PDMs) (Thermo Fisher) worn by the roof bolter 

operators on either side of the dual boom machine. Time 

studies were conducted during the sampling, and it was found 

that during the bolting cycle (from tram in to tram out of a 

place) the operator is under the canopy about 66% of the 

time. From the few roof bolter places that were sampled, 

reductions in respirable dust were evident. 

The concentrations measured by PDMs worn by the operators during the entire sampling period (194 min) were 

compared and found to be 2.93 mg/m3 for the operator under 

the plenum and 4.46 mg/m3 for the operator under the unmodified canopy, a reduction of 34% when using the canopy 

air curtain. 

Conclusion 

Previous contract work and research studies have shown 

that air curtains can effectively provide protective zones of 

clean air in dusty mine environments. To successfully adapt 

this technology to a roof bolting machine, the air curtain 

plenum had to be modified to conform to the roof bolting 
 

machine’s canopy, in order to provide greater airflow coverage. However, this modification changed the airflow patterns, resulting in an uneven flow of air beneath the plenum. 

Through CFD simulation and trial-and-error testing, a unit 

was developed to provide filtered air under approximately 

70% of the canopy. Laboratory tests revealed that air velocity exiting the plenum in excess of 0.51 m/s (100 fpm), 25.4 cm 

(10 in.) below the unit, will provide an area of reduced dust 

exposure to operators in entry air velocity of up to 0.61 m/s 

(120 fpm). Statistical analysis of laboratory data show that, 

at each test velocity, a significant reduction in respirable dust 

was achieved under the plenum. Reductions of 72%, 67% 

and 75% were realized for 0.05, 0.3 and 0.61 m/s (10, 60 and 

120 fpm), respectively. 

Field testing of the system, while incomplete, showed that 

the air curtain can be successfully integrated into the canopies of roof bolting machines and that these machines can 

be modified and retrofitted with blower fans, filters and hydraulics. The limited field data that was available for analyses 

revealed reduced operator dust exposures. However, further 

field testing should be conducted. 

Table 3 

Respirable dust concentrations and reductions from field data. 

Bolter 

workplace 

1 

2 

Operator under plenum, mg/m3 

1.81 

4.73 

Operator under unmodified 

canopy, mg/m3 

3.88 

7.3 

Reduction, % 

53 

35 

Velocity at bolter 

Negligible* 

Negligible* 

*Not able to be detected on a vane anemometer. 

An equipment manufacturer is currently working with a 

mining company in Virginia to add air curtains on the mining 

company’s roof bolter canopies (Fig. 16). 

Figure 16 

Alternative designed air curtain based on mine/ 

manufacturer collaboration. 

Another company 

in Kentucky is retrofitting the cabs of its shuttle cars with air 

curtains to reduce operator dust exposure in blowing curtain 

ventilation schemes. Recent and continued advances in CFD 

modeling may result in improved air curtain designs for use 

on mining equipment. 

Disclaimer 

Mention of any company or product does not constitute endorsement by the National Institute for Occupational 

Safety and Health. The findings and conclusions in this paper 

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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