1 INTRODUCTION 

Moving adequate fresh air volumes in large-opening, 

room-and-pillar mines presents several challenges 

due to the large open-space volume of the mine and 

the extremely low airflow resistance 0.0005 N·s2

/m8

(4.5 x 10-13 in·min2

/ft6). The low mine resistance is 

caused by the large 12 m × 8 m (40 ft × 27 ft) entries. A well developed underground stone mine can 

have a void volume of several million cubic meters 

(100 million cubic feet) and require many hours to 

effect a complete air change. Unlike most underground coal mines and many metal mines, the resistance to flow in these large-opening mines is very 

low. Recognizing this fact, NIOSH demonstrated the 

use of low-pressure propeller fans for whole mine 

ventilation (Grau et al. 2004, Krog et al. 2004). Several large-opening mines have subsequently installed 

propeller fans for main mine ventilation instead of 

relying on changing natural ventilation. Mine operators are responsible to meet any federal guidelines 

(Title 30 U.S. Code of Federal Regulations Part 57) 

regarding placement and installation of fans. 

NIOSH has since focused on the application of 

propeller fans to regional and face ventilation applications in large-opening mines. Previous research on 

ventilating large-opening oil shale mines conducted 

by the U.S. Bureau of Mines (USBM) in the 1970s 

and 1980s tested free-standing vane-axial fans as regional and face fans, Brechtel et al. (1985) and Dunn 

et al. (1983). The researchers examined vane-axial 

fan placement for efficient face ventilation; however, similar investigations using propeller fans for 

auxiliary face and regional ventilation were required 

and are discussed in this paper. 

2 FAN AIRFLOW ENTRAINMENT 

CHARACTERISTICS 

NIOSH researchers conducted studies of auxiliary, 

free-standing vane-axial and propeller fans, showing 

that each type has different airflow distribution patterns around the fan. An electronic vane anemometer 

mounted on an adjustable pole was used to measure 

average airflow readings on a grid pattern. A propeller fan tends to draw air from behind, and entrains 

the airflow only up to 30 m (100 ft) or to the first 

crosscut, as the resultant medium-speed airflow expands rapidly. Conversely, a vane-axial fan, with its 

lower air quantity and higher fan exit speed, draws 

minimal air from behind the fan. However, the vaneaxial fan entrains the airflow for a distance of up to 

three crosscuts ahead of the fan because the highspeed airflow takes over 90 m (300 ft) to fully expand. Therefore, propeller and vane-axial fans have 

different placement criteria when used as auxiliary 

fans. 

Fan selection for large-opening mines: vane-axial or propeller fans – 

which to choose? 

R.B. Krog, R.H. Grau III 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, Pennsylvania, 

USA 

ABSTRACT: The National Institute for Occupational Safety and Health (NIOSH) has investigated the unique 

ventilation requirements of large-opening mines to help identify and evaluate the effectiveness of various fan 

types to improve the ventilation and air quality in the underground workplace. Large-opening mines, with 

their low airflow resistance factors, can be ventilated with free-standing auxiliary fans because airflow patterns in these mines are primarily controlled by airflow momentum. The flow characteristics of both vaneaxial and propeller fans were investigated and tested at four large-opening mines to assess the effects of fan 

location on recirculation and entrainment. Each fan type has its own airflow, entrainment and penetrating airflow characteristics, and operating costs that are advantageous for specific applications. Either fan type can be 

used for most auxiliary applications. However, this research has shown that the optimum placement and use 

criteria for propeller fans differ from those promulgated by the U.S. Bureau of Mines (USBM) for vane-axial 

fans Brechtel et al. (1985). 
2.1 Vane-Axial Fan 

Figure 1 shows the vane-axial fan used in the study. 

The free-standing vane-axial fan had a diameter of 

0.91 m (36 in). It was powered by a 19 kW (25 hp) 

motor, and mounted with a reducer at the outlet with 

a discharge diameter of 0.58 m (23 in). The airflow 

characteristics generated by the vane-axial fan are 

shown in Figure 2. The patterns indicate that the 

high exit velocity of the fan’s reducer [39 m/s (7600 

ft/min)] causes air turbulence and entrainment for a 

distance of over 90 m (300 ft) in front of the fan. 

The venturi effect of the reducer was observed up to 

3 meters (10 ft) in front of the fan, where little air interaction was observed surrounding the fan’s highspeed airflow. 

Figure 1. 0.91 m (36 in) vane-axial fan with 0.58 m (23 in) reducer. 

186 163 185

50 41 21

51

16

A

A

B

B

175

= Defected Airflow = Main Airflow

= Minor Airflow = Airflow m3 186 /s

13

18

Benched Area Fan location Cross Sections

= Benched Area

= Stopping

50 m

186 163 185

50 41 21

51

16

A

A

B

B

175

= Defected Airflow = Main Airflow

= Minor Airflow = Airflow m3 186 /s

13

18

Benched Area Fan location Cross Sections

= Benched Area

= Stopping

50 m

Figure 2. Airflow characteristics for a 0.91 m (36 in) vane-axial 

fan with reducer, note recirculation patterns generated around 

the second to forth intersections. 

The airflow through the fan was 10.4 m3

/s 

(22,000 cfm). However, due to entrainment effects, 

the total airflow 83 m (272 ft) downstream of the fan 

was over 17 times greater, at 183 m3

/s (388,000 

cfm). The airflow patterns in the cross-cuts at the 2nd

to 4th intersections in front of the fan were bidirectional (Fig. 2). High velocity air moving down 

the main entry would catch the corners of the pillars 

and be directed perpendicularly down the cross-cuts. 

An eddy formed behind the pillars of the cross-cuts, 

pulling air into the main ventilation drift. The net result was little change in the total airflow moving 

down the main entry for the first three intersections, 

downstream from the fan (Fig. 2). However, because 

of the high-speed of the expanding airflow, there 

was recirculation with the surrounding air. 

Figure 3 shows the cross-sectional velocity profile 28 meters (92 ft) in front of the vane-axial fan’s 

outlet. The airflow is concentrated at the lower half 

of the 12.5 m × 8.4 m (41.1 ft × 27.4 ft) opening in 

the center of the drift as the high-speed air starts to 

expand. The peak air velocity was 6.56 m/s (1290 

ft/min), and the air velocity approaches zero in the 

upper third of the cross section. Airflow in the top 

corners was below recordable levels. 

Figure 4 shows a similar air profile as in Figure 3 

recorded 27 m (88 ft) further down the drift. The air 

stream is still predominantly flowing along the 

ground, and very little airflow was recorded in the 

upper half of the drift. The peak velocity was 3.68 

m/s (725 ft/min). 

0.6 1.8 3.0 4.3 5.5 6.7 7.9 9.1 10.4 11.6

7.3

6.7

5.5

4.3

3.0

1.8

0.6

Velocity (m/s)

Width (m)

Height (m)

6.0-7.0

5.0-6.0

4.0-5.0

3.0-4.0

2.0-3.0

1.0-2.0

0.0-1.0

0-1

1-2

2-3 3-4 4-5 5-6

6-7

Figure 3. Vertical cross-section A of airflow 28 m (92 ft) in 

front of 0.91 m (36 in) vane-axial fan, flow out of page. 

0.3 1.5 2.7 4.0 5.2 6.4 7.6 8.8 10.1 11.3 12.5

7.3

6.7

5.5

4.3

3.0

1.2

0.6

Velocity (m/s)

Width (m)

Height (m)

6.0-7.0

5.0-6.0

4.0-5.0

3.0-4.0

2.0-3.0

1.0-2.0

0.0-1.0

0-1

1-2

2-3

3-4

Figure 4. Vertical cross-section B of airflow 55 m (180 ft) in 

front of 0.91 m (36 in) vane-axial fan, flow out of page. 

Figure 4 shows that entrainment will still occur 

further down the drift. The airflow interaction with 
the corners of the pillars varies with the height off 

the floor because of the different velocities along the 

ribs. Airflow interactions in the crosscuts at the intersections were bi-directional with airflow leaving 

the main drift along the lower half and airflow entering the main drift in the upper half of the crosscuts. 

This was due to the difference in airflow velocities 

in the main drift (Fig 3-4 ribs). 

2.2 Propeller Fan 

Figure 5 shows the 2.44 m (8 ft) diameter propeller 

fan, powered by a 22.3 kW (30 hp) motor, used in 

the study. Both the vane-axial and propeller fans 

were operating at close to 17.2 kW (23 hp) during 

the field investigations. The propeller fan moves a 

larger quantity [58.5 m3

/s (124,000 cfm)] of slower 

moving air that interacts differently with the surrounding air than the airflow from the vane-axial 

fan. The air leaving the propeller fan outlet is moving at 13 m/s (2500 ft/min), and expands rapidly to 

cover the entire cross-section of the drift. Figure 6 

shows the airflow patterns generated by the propeller 

fan. Note that, compared to the vane-axial fan, a 

higher airflow quantity, 253 m3

/s (536,000 cfm) was 

achieved initially with the propeller fan. The airflow 

quantity progressively diminishes after each intersection. Also, the airflow does not leave the propeller fan in a straight uniform direction, but spreads 

out over the entire cross section of the drift. 

Figure 5. 2.4 m (8 ft) propeller fan used in study. 

Figure 7 shows the cross-sectional velocity profile 25 meters (82 ft) in front of the propeller fan’s 

outlet. The airflow is quickly being dispersed across 

the entire drift. The peak air velocity was 4.40 m/s 

(866 ft/min), and the minimum air velocity was 1.12 

m/s (221 ft/min). All grid sections of the drift had 

positive measurable airflow down the drift, with no 

airflow roll back being observed. 

201 149 158

50 43 31

69 A

A

B

B

253

15 28

26

25

Benched Area Fan location Cross Sections

= Defected Airflow = Main Airflow

= Minor Airflow = Airflow m3 186 /s

= Benched Area

= Stopping

50 m

201 149 158

50 43 31

69 A

A

B

B

253

15 28

26

25

Benched Area Fan location Cross Sections

= Defected Airflow = Main Airflow

= Minor Airflow = Airflow m3 186 /s

= Benched Area

= Stopping

50 m

Figure 6. Airflow characteristics for a 2.44 m (8 ft) propeller 

fan, note recirculation patterns generated at the second intersection. 

0.6 1.8 3.0 4.3 5.5 6.7 7.9 9.1 10.4 11.6

7.3

6.1

4.9

4.3

3.0

1.8

0.6

Velocity (m/s)

Width (m)

Height (m)

4.0-5.0

3.0-4.0

2.0-3.0

1.0-2.0

0.0-1.0

1-2 2-3 3-4

3-4

4-5

1-2

Figure 7. Vertical cross-section A of airflow 25 m (82 ft) in 

front of 2.44 m (8 ft) propeller fan, flow out of page. 

Figure 8 shows the airflow 52 m (171 ft) in front 

of the propeller fan. The air stream completely enveloped the drift, with a peak air velocity of 2.84 

m/s (559 ft/min) and minimum air velocity of 1.26 

m/s (249 ft/min). The velocity profile is much closer 

to uniform (i.e. being more evenly distributed across 

the drift) than was observed with the vane-axial fan 

shown in Figure 4. Recirculation is only observed in 

the second intersection, and it is less than with the 

vane-axial fan. It appears that some of the airflow is 

leaving the main drift after the first intersection. 

The airflow quantities moving down the main 

drift for both fans is shown in Figure 9. The vaneaxial fan with its high exit velocity maintains a level 

of entrainment as far as 79.5 m (261 ft) in front of 

the fan, whereas the propeller fan only maintains entrainment for about 52 m (170 ft). Both fans have 

similar exponential (natural decay) reductions in airflow quantities beyond the effects of entrainment. 

The propeller fan acts like a large single source of 

airflow that quickly settles into a long natural decay 

trend after the first intersection, with an exponential 

curve of best fit (R2

 = 0.997). The vane-axial fan 

does not experience the natural decay trend until af-
ter 79.5 m (261 ft) because of ongoing entrainment. 

The vane-axial fan does not act as a single source of 

airflow, but covers a larger area of entrainment. The 

propeller fan pulls air from behind the fan and only 

up to the first crosscut. The vane-axial fan pulls air 

from behind the fan and the first three crosscuts. 

 

0.3 1.5 2.7 4.0 5.2 6.4 7.6 8.8 10.1 11.3 12.5

7.3

6.7

5.5

4.3

3.0

1.2

0.6

Velocity (m/s)

Width (m)

Height (m)

2.0-3.0

1.0-2.0

0.0-1.0

2-3

1-2 2-3

Figure 8. Vertical cross-section B of airflow 52 m (171 ft) in 

front of 2.44 m (8 ft) propeller fan, flow out of page. 

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Distance From Fan (m)

Air Quantity (m3/s)

0

100,000

200,000

300,000

400,000

500,000

600,000

0 200 400 600 800

Distance From Fan (feet)

Air Quantity (cfm)

2.44 m Propeller

0.91 m Vane-Axial

Figure 9. Airflow characteristics for free-standing vane-axial 

and propeller fans. 

Statistical data for the velocity profiles of the 

cross-sections in front of the fans (Figs. 3-4 and 6-7) 

are given in Table 1. The level of possible entrainment is a function of the non-uniformity in the velocity profiles across the drift. A uniform distribution of velocities across the drift will not induce 

entrainment, but non-uniform velocity distributions 

can. As can be seen in Table 1, the vane-axial fan 

standard deviation is high, when compared to the 

mean velocity for both cross-sectional locations, indicating that entrainment will occur further down the 

drift and work against the natural decay of airflow 

quantities. Data from the propeller fan have a much 

lower standard deviation, indicating that additional 

airflow cannot be entrained beyond the first crosscut, as shown in Figure 9. 

Table 1 Mean velocity and standard deviation of crosssectional airflow in front of the fans. 

Distance to fan (m) 28 55 25 52

Mean Velocity (m/s) 1.80 1.86 2.46 1.97

Standard Deviation (m/s) 1.60 0.94 0.81 0.40

Distance to fan (ft) 92 180 81 169

Mean Velocity (ft/min) 354 366 485 388

Standard Deviation (ft/min) 315 185 158 80

Vane-Axial Propeller

2.3 Use of large propellers fans for regional-area 

ventilation 

The use of propeller fans for ventilating a large regional area was investigated. One mine operator has 

successfully used a 3.66 m (12 ft) free-standing propeller fan for this purpose (Fig. 10). The induced airflow for the 3.66 m (12 ft) fan in this application had 

a similar pattern to that of the previously discussed 

2.44 m (8 ft) propeller fan application, i.e. all of the 

air was pulled from behind the fan or from the first 

intersection in front of the fan. Flow rates measured 

in front of the fan 216 m (710 ft) down the main 

drift were over 250 m3

/s (530,000 cfm) (Fig. 11). 

After the first intersection, the airflow traveling 

down the main drift exhibits the same natural decay 

as the 2.44 m (8 ft) propeller fan. 

Figure 10. 3.65 m (12 ft) propeller fan used for regional airflow 

studies. 

160

67

144

148

181

399 329 365 346 286 259

87

162

Flow (m3/s)

32.0 m 

centers

18.3 m pillars

7.6 m height

= Fan = Main Airflow = Airflow m 399 3/s

160

67

144

148

181

399 329 365 346 286 259

87

162

Flow (m3/s)

32.0 m 

centers

18.3 m pillars

7.6 m height

= Fan = Main Airflow = Airflow m 399 3/s

Figure 11. Regional airflow distribution for a 3.66 m (12 ft) 

propeller fan. 
2.4 Propeller fans used on single entry drifts 

NIOSH tested a trailer mounted, diesel powered 1.37 

m (54 in) propeller fan to be used for regional and 

face ventilation (Fig. 12). The diesel power propeller 

fan performed well in inducing airflow at the last 

open crosscut, but performed poorly when ventilating a single-entry heading. Figure 13 demonstrates 

the effect that an incorrect placement of an inappropriate fan can have on ventilation efficiency. The 

low exit velocity of 10.0 m/s (1970 ft/min) from the 

propeller fan has a poor penetrating distance, which 

could not sufficiently remove the airborne contaminants at the mucking location located 55 m (180 ft) 

in front of the fan. Very little airflow mixing was 

observed at the intersection used for loading, and a 

build up of diesel contaminants soon caused a shut 

down of production. Based on previous USBM studies a better result would have been achieved with a 

vane-axial fan equipped with a reducer to create a 

high-speed jet airflow capable of penetrating completely into the single entry drift, as shown in Figure 

3. This would have resulted in more air mixing and 

dilution at the loading site. Propeller fans, because 

of their low speed and quickly expanding airflow 

patterns, are poor choices for ventilating single entry 

drifts. 

Figure 12. 1.37 m (54 in) diesel powered propeller fan used for 

face and regional mine ventilation. 

A good application using a propeller fan to ventilate an underground crusher site was demonstrated 

by Chekan (2006). The low-speed, wide airflow pattern generated by the propeller fan completely engulfed the entry and pushed the dust towards the return airway drift, without disturbing the dust lying 

on the ground. 

 

Mucking Area

94 22

98

100

Recommended 

Location for 

Propeller Fan

Loading Area

98 = Airflow m3/s

= Airflow Direction

= Fan

Propeller Fan 

Test Location

Vane-Axial 

Regional Fan

50 m

Mucking Area

94 22

98

100

Recommended 

Location for 

Propeller Fan

Loading Area

98 = Airflow m3/s

= Airflow Direction

= Fan

Propeller Fan 

Test Location

Vane-Axial 

Regional Fan

50 m

Figure 13. Test of a diesel powered propeller fan in a dead end 

drift, airflows in m3

/s. 

2.5 Fan placement recommendations 

Vane-axial fans should be positioned in such a way 

that they can entrain a maximum amount of fresh 

air. In some cases it is best to have the fan blowing 

across a fresh air stream because these fans entrain 

little airflow from behind the fan yet have entrainment for 90 m (300 ft) after the fan before airflow is 

lost from the main drift (Fig 4). Propeller fans 

should be located with in the fresh air stream because propeller fans entrain airflow from behind the 

fan and from the first crosscut after which airflow is 

lost from the main drift (Fig 6). The following recommendations are also important: 

− Propeller fans should be situated in the fresh air 

stream. 

− Vane-axial fans should be placed one entry behind the fresh air stream. 

− Propeller fans work best in regional ventilation 

applications. 

− Vane-axial fans work best (better penetration, 

greater mobility) in face and dead end ventilation 

applications while propeller fans are not well 

suited for these applications. 

3 REPLACEMENT OF VANE-AXIAL MAIN 

MINE FANS WITH PROPELLER FANS 

As main mine fans for large-opening mines (fans 

mounted in a bulkhead), propeller fans are the preferred choice (based on lower noise levels, capital 

and operating costs), so long as the pressure requirements are low [less than 185 Pa (0.75 in w.g.)]. 

Generally, the pressure requirements are low for 

large-opening drift mines with several portals. Figure 14 shows typical pressure versus flow curves for 

a high-resistance coal mine and a low-resistance, 
large-opening mine. Fan curves are shown for a 

high-pressure vane-axial fan and a low-pressure 

propeller fan. Points A and B represent the operating 

points for the high-pressure vane-axial fan with a 

high-resistance coal mine and the low resistance of a 

large-opening mine, respectively. Point C is the operating point for the propeller fan and the largeopening mine. 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 20 40 60 80 100 120 140 160 180 200

Fan Flowrate (m3/s)

Fan Static Pressure (kPa)

0

2

4

6

8

10

12

0 50 100 150 200 250 300 350 400

Fan Flowrate (x 1000 cfm)

Fan Static Pressure (in. w.g.)

3.66 m Propeller

Large Mine Resistance

2.13 m Vane-Axial

Coal Mine Resistance

A

B C

Figure 14. Pressure and quantity curves for vane-axial and propeller fans in a large opening mine. 

3.1 Case study 

A mature large-opening mine made a direct replacement of a 2.44 m (8 ft) vane-axial fan with a 

3.66 m (12 ft) propeller fan for main mine ventilation. The original bulkhead mounted vane-axial fan 

shown in Figure 15 was operating at 119 kW (160 

hp) and exhausting 127 m3

/s (270,000 cfm) of ventilation airflow. The replacement 3.66 m (12 ft) propeller fan is operating at 25 kW (34 hp) and exhausting 132 m3

/s (280,000 cfm) of ventilation airflow. 

Figure 16 shows a 3.66 m (12 ft) propeller fan installation. Table 2 compares the operating conditions for 

the two fans along with their operating costs. The 

replacement of the vane-axial fan with the propeller 

fan saves the mine about $155 per day in operating 

costs at $0.07/kWh, which results in a payback period of less than three months for the propeller fan 

purchase. The mine operates approximately 300 

days a year, so the expected annual cost saving is 

over $47,000, an obvious economic advantage for 

the use of propeller fans as main mine fans in this 

case. The total ventilation airflow of the mine could 

be increased by the installation of two 3.66 m (12 ft) 

propeller fans operating together to exhaust 368 m3

/s 

(780,000 cfm) and operating at the same power cost 

as the original vane-axial fan, 119 kW (160 hp). This 

would represent an increase of approximately 190% 

more airflow in the mine for the same operating 

costs as the original vane-axial fan (Table 2). 

Figure 15. 2.44 m (8 ft) vane-axial main mine fan mounted in a 

sheet metal bulkhead. 

Table 2. Engineering comparison and cost analysis of replacing 

a vane-axial main mine fan with a propeller fan. 

Vane-Axial Propeller 2 Propeller 

Fan Fan Fans

Diameter (m) 2.44 3.66 3.66

Diameter (ft) 8 12 12

Capital cost 14,000 $ 28,000 $ 

Airflow (m3

/s) 127 132 368

Airflow (cfm) 270,000 280,000 780,000 

Brake kW 119 25 119

Brake horsepower 160 34 160

Cost per kWh 0.07 $ 0.07 $ 0.07 $ 

Cost per day 200 $ 43 $ 200 $ 

Cost savings per day 157 $ - $ 

Airflow increase (%) 4% 189%

Payback (days) 89 

Annual cost savings* 47,222 $ 

* Assumed 300 day of operation per year

3.2 Parallel fans 

The addition of a second parallel fan to a bulkhead 

of a large-opening mine will create a significant improvement over the original fan due to the little interference between the parallel fans. Placing two 

high-pressure fans in parallel normally causes the 

two fans to work against each other, reducing the individual fan’s airflow quantity. However, with the 

low resistance of the large-opening mines, the parallel fans only have to overcome a small static pressure. The result is an almost free-flow discharge by 

fans operating in parallel, and the actual minor reduction in airflow quantity is within measurement 

errors. Further testing will be conducted to investigate the possibility of operating three or four fans in 

parallel. Figure 16 shows a propeller fan mounted in 

a steel bulkhead with room for a second fan to be installed in the future. 
Figure 16. 3.66 m (12 ft) propeller fan mounded in a steel 

bulkhead. 

4 VENTILATING A NEW MINE 

NIOSH collaborated with the operators of a new, 

dual-portal large-opening mine to determine suitable 

ventilation systems during the first few years of operation. Free-standing fans were recommended to 

ventilate the mine initially because at the early stage 

of mine development, bulkheads would not be able 

to stand up to nearby blast pressures. The same 

vane-axial and propeller fans (Figs. 1 and 5) used 

previously to determine underground airflow patterns were used for this study. The research approach consisted of varying the location and directions of the fans, and then evaluating the resultant 

airflows into and out of the dual portals (Fig. 17). 

Figure 17. Site one, 2.44 m (8 ft) propeller fan blowing into a 

dual-entry large-opening mine. 

4.1 Fans blowing into the mine 

The 2.44 m (8 ft) propeller fan (Fig. 17) was tested 

at three locations (Table 3) while blowing into the 

mine as shown in Figure 18. The experiment was repeated again using the vane-axial fan (Fig. 19) at the 

same three locations. Table 3 summarizes the site 

locations relative to the portal and the recorded airflow. 

Table 3. Fans blowing into mine. 

Distance Location Propeller Vane-Axial

m m3

/s m3/s

Site 1 19.2 Outside 153 80

Site 2 31.7 Outside 147 98

Site 3 25.9 Inside 134 93

ft cfm cfm

Site 1 63 Outside 325,000 169,000

Site 2 104 Outside 311,000 207,000

Site 3 85 Inside 283,000 198,000

Stopping

2 3 1

50 m

Fan Locations

Site 1 - 153 m3/s

Site 2 - 147 m3/s

Site 3 - 134 m3/s

Figure 18. 2.44 m (8 ft) propeller fan blowing into the mine. 

Stopping

2 3 1

Fan Locations

Site 1 - 80 m3/s

Site 2 - 98 m3/s

Site 3 - 93 m3/s

50 m

Figure 19. 0.91 m (3 ft) vane-axial fan blowing into the mine. 

4.2 Fans blowing out of the mine 

Tests were also performed with the fans exhausting 

from the mine, but resulted in less airflow the closer 

the fans were positioned to the portal entrance because of mixing and entrainment of the air. Site 3 

was used again, as well as an additional location 

(Site 4), located 14.0 m (46 ft) inside the portal. The 

results for the propeller fan are shown in Figure 20 

and Table 4. With the propeller fan blowing out of 

the mine, a maximum flow rate of 83 m3

/s (176,000 

cfm) was achieved, which is much less than that 
measured with the same fan blowing into the mine at 

any of the test sites (Fig. 18). 

The vane-axial fan was also tested at Sites 3 and 

4 inside the mine, but the airflows were below the 

vane anemometer’s detection limits of 19 m3

/s 

(40,000 cfm) at both locations. The poor performance of the vane-axial fan when used to exhaust 

from the mine was expected because the confined 

high-speed jet air stream would be outside the mine 

before it could expand and entrain any appreciable 

mine airflow. 

Stopping

4 3

Fan Locations

Site 3 - 83 m3/s

Site 4 - 52 m3/s

50 m

Figure 20. 2.44 m (8 ft) propeller fan blowing out of the mine. 

Table 4. Fans exhausting out of mine. 

Distance Location Propeller Vane-Axial

m m3

/s m3/s

Site 3 25.9 Inside 83 <19

Site 4 14.0 Inside 52 <19

ft cfm cfm

Site 3 85 Inside 176,000 <40,000

Site 4 46 Inside 110,000 <40,000

5 SUMMARY 

NIOSH investigated the use of propeller fans in underground large-opening mines as an alternative to 

vane-axial fans. Free-standing propeller fans only 

pull airflow from behind the fan and from a distance 

of 30 m (100 ft) in front of the fan (first intersection). The propeller fan acts as a large single source 

to push the air in one direction, followed quickly by 

the natural decay of the airflow. 

Compared to a propeller fan, a free-standing, 

vane-axial fan mounted with a reducer pulls less airflow from behind the fan and from the first 30 m 

(100 ft), but it has a large area of entrainment and 

mixing for 90 m (300 ft) in front of the fan before 

the natural decay of the airflow occurs. Both freestanding vane-axial and propeller fans have the ability to effectively ventilate a region or to flush the 

working areas of a mine. However, propeller fans 

will have lower operating costs for the same total 

airflow. Propeller fans should be located in the fresh 

air stream, whereas vane-axial fans should be located so that they blow through the fresh air stream. 

Propeller fans clearly have a large advantage 

when mounted in a bulkhead for applications in the 

low mine resistances common to large-opening multiple-portal drift mines. Improvements in airflow 

quantities, operating costs, and ventilation efficiency 

can be achieved with the replacement of highpressure, vane-axial fans with low-pressure propeller 

fans, as shown in Table 2. For a new large-opening 

mine, the use of a propeller fan located just outby a 

portal and blowing into the mine generates a large 

and effective airflow for the mine. A vane-axial fan 

mounted with a reducer is far superior to a propeller 

fan for ventilation of a single development heading. 

For single-entry ventilation previous USBM work 

by Brechtel et al. (1985) and Dunn et al (1983) on 

free standing vane-axial fans is still valid, and is the 

preferred method. 

6 DISCLAIMER 

The findings and conclusions in this report are those 

of the authors and do not necessarily represent the 

views of the National Institute for Occupational 

Safety and Health. 

7 REFERENCES 

Brechtel C.E., Adam M.E., Agapito J.F. 1985. Development of 

effective face ventilation systems for oil shale mining. 

Pittsburgh, PA: U.S. Department of the Interior, Bureau of 

Mines, (BOM), OFR 14-1. 

CFR. U.S. Code of Federal Regulations Part 57. Washington, 

DC: U.S. Government Printing Office, Office of the Federal 

Register. 

Chekan G.J., Colinet J.F., Grau, R.H. 2006. Impact of Fan 

Type for Reducing Repairable Dust an Underground Limestone Crushing Facility. Proceedings of the 11th North 

American/Ninth US Ventilation Symposium, University 

Park, Pa., June 5-7, 2006 

Dunn M.F., Kendorski F.S., Rahim M.O., Mukherjee A. 1983. 

Using auxiliary “Jet Fans” in large underground metal/nonmetal mines. A handbook. Pittsburgh, PA: U.S. Department 

of the Interior, Bureau of Mines, (BOM), OFR 107-84. 

Grau III, R.H. et al 2002. NIOSH ventilation research addressing diesel emissions and other air quality issues in nonmetal 

mines. 2002 SME Annual Meeting, Preprint 02-187, Phoenix, Arizona, February 25-27. 

Grau III R.H., Robertson S.B., Krog R.B., Chekan G.J., Mucho 

T.P. 2004. Raising the bar of ventilation for large-opening 

stone mines. In: Ganguli R, Bandopadhyay S, eds. Mine 

ventilation: Proceedings of the 10th U.S./North American 

Mine Ventilation Symposium (Anchorage, AK, May 16–

19, 2004). Leiden, Netherlands: Balkema, pp. 349–355. 

Krog R.B., Grau III R.H., Mucho T.P., Robertson S.B. 2004. 

Ventilation planning layouts for large-opening mines. SME 

preprint 04-187. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 1-9.