Raising the Bar of Ventilation for Large-Opening Stone Mines 

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

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

1 INTRODUCTION 

The National Institute for Occupational Safety and 

Health (NIOSH) is the primary agency responsible 

for conducting health and safety research pertaining 

to the mining industry. A portion of this research is 

concerned with developing methods and technologies to improve the ventilation technology of largeopening mines. Historically, the ventilation techniques used in large-opening stone mines have often 

been the result of trial-and-error methodology. In 

many cases the ventilation system consists of axialvane fans being used as either auxiliary fans or main 

mine fans without the use of stoppings to direct the 

air. The research results presented in this report describe how the ventilation of large-opening drift 

mines can be dramatically improved by using largediameter main mine propeller fans in bulkheads in 

combination with a stopping line. Also discussed are 

methods for estimating the air quantity requirements 

for effective dilution of diesel particulate matter 

(DPM), choosing appropriate fans, air coursing 

methods, and mine layouts. 

2 CONCERNS AND LIMITS FOR WORKER 

EXPOSURE TO DPM 

Legislation was proposed by the Mine Safety and 

Health Administration (MSHA) to limit DPM concentrations in underground metal/nonmetal mines. 

Provisions of this health standard are found in “Diesel Particulate Matter Exposure of Underground 

Metal and Nonmetal Mines” published in the Federal Register on January 19, 2001 and amended on 

February 27, 2002 (MSHA 2001). An interim DPM 

standard of 400 μg/m3

of total carbon took effect on 

July 20, 2002 and it’s proposed that the DPM limit

be reduced to 160 μg/m3

 of total carbon by July 19, 

2006. 

To satisfy the requirements of the DPM standard, 

most operators will find it necessary to employ several engineering controls: increasing the air quantity 

entering the mine; directing air to the face areas by

the use of stoppings and auxiliary fans; and decreasing DPM emissions from engines by using catalytic 

converters, filters, and cleaner-burning engines 

(Schnakenberg 2001, Grau et al. 2002a, Grau et al. 

2002b). In addition to the general improvements in 

current ventilation methods, mine planners must also 

consider ventilation requirements when planning future mine layouts – until now, ventilation has been 

overlooked in most underground stone mine planning processes (Head 2001, Grau et al. 2002a, Grau 

et al. 2002b, Mucho et al. 2001). 

ABSTRACT: Due to the difficulties of ventilating large opening stone mines, the effective dilution of diesel

particulate matter and noxious gases has often been problematic. Since stone mines have large openings that 

develop low air resistances, and propeller fans are designed for low pressure-high volume applications, main 

mine propeller fans may be a feasible option for ventilating underground stone mines. This paper describes

the results of a case study where researchers from the National Institute for Occupational Safety and Health 

have demonstrated that significant increases in total mine airflow can be achieved and the ventilation improved in a large-opening stone mine by replacing an axial-vane mine fan with two 12-ft diameter propeller 

fans and adding a line of stoppings. In this study, the use of the propeller fans more than doubled the air quantity from 300,000 cfm to 750,000 cfm, while operating at 50 horsepower less than the original axial-vane fan. 
3 MINE PLANNING CONSIDERATIONS FOR 

EFFECTIVE VENTILATION 

A large-opening stone mine ventilation system 

must be designed to effectively dilute all airborne 

contaminants by supplying sufficient ventilation air 

to locations where it is needed the most, i.e., working faces, worker locations, etc. In order to accomplish that goal, the ventilation plan must include a 

main mine fan to develop the airflow, stoppings to 

control the airflow, and auxiliary fans to direct air 

where equipment and personnel are located. Invariably, all underground stone mines use diesel equipment that emits substantial amounts of DPM and 

noxious gases such as NOx, SO2, and CO. In mines 

that use older diesel engines, the overriding factor 

for determining ventilation air requirements is 

probably the dilution of DPM and not the noxious 

gases. A previous study has shown that significant 

ventilation air quantities are necessary to meet DPM 

compliance concentration levels (Grau et al. 2002a). 

To help determine the ventilation air quantity requirements to dilute DPM concentrations to statutory 

levels in the main mine air stream, NIOSH has developed an air quantity estimator (AQE) (Robertson 

2001, Robertson et al. 2003). The AQE is a userfriendly computer program that comes as a standalone package. It will run on most personal computers and is not dependent on the installation of 

spreadsheet programs. 

4 HISTORICAL PHYSICAL 

CHARACTERISTICS OF UNDERGROUND 

STONE MINES THAT INFLUENCE 

VENTILATION 

Many underground large-opening stone mines 

have common physical characteristics that influence 

ventilation airflow. Multiple portal entries are common, with the portals ranging from fully open to almost completely closed due to highwall rock falls or 

icing during winter months. Typically, in stone drift 

mines, the differences in elevation between entries 

are small in terms of creating natural ventilation. 

Nevertheless, these mines do have some natural ventilation. In addition, numerous openings, truck 

movements, outside wind conditions, and freestanding fans provide some ventilation in the mine. Finally, the large mine void volume acts as a sizable 

sink of available air for diesel exhaust dilution. 

Many of these mines do not utilize stoppings, and 

thus air moves randomly resulting in unpredictable 

and haphazard ventilation. It is common for freestanding auxiliary fans to move ventilation air along 

designated routes and to push the ventilation air to 

where it is needed. Generally these fan locations are 

determined by trial-and-error methods. The auxiliary 

fans, blowing in this manner, provide better ventilation than natural ventilation alone, but bulkheaded 

main mine fans are superior for providing consistent 

ventilation. 

5 LARGE-OPENING MINE VENTILATION 

CASE STUDY 

At the onset of this research effort, NIOSH engineers visited several underground stone mines to 

conduct ventilation surveys and observe baseline operating conditions. It was concluded from these initial surveys that the ventilation of many underground 

stone mines could be greatly improved by using two 

synchronized approaches: installing main mine propeller fans to produce the air quantity needed to sufficiently dilute the airborne contaminants to statutory 

levels and constructing stoppings in conjunction 

with auxiliary fans to direct the ventilation airflow. 

Propeller fans are used for a variety of circumstances; however, documentation of propeller fans 

being used in large-opening mines was not available. 

Therefore, a case study was necessary to determine 

whether propeller fans are truly applicable for use in 

underground large-opening mines. The study ran for 

21 months and included monitoring the mine ventilation prior to and after the installation of a brattice 

stopping line and two main mine propeller fans. 

The case study mine had a physical extent of approximately 0.75 square miles and entries that are 

about 1,125 ft2 in cross-sectional area. However, 

more than one-half of the mine is benched and those 

entries are considerably larger, often exceeding 

2,200 ft2 in cross-sectional area. The propeller fans 

used for this study were selected on the basis of the 

parameters measured during ventilation surveys 

made at various stone mines (Grau et al. 2002a). 

Those surveys suggested that for large-entry drift 

stone mines, and even for some mines with shallow 

air shafts, propeller fans would be a good choice for 

improving ventilation airflow because they are designed to deliver large air quantities at pressures of 

less than one-inch w.g. (Grau et al. 2002a, Grau et 

al. 2002b). 

6 VENTILATION CHARACTERISTICS 

PRIOR TO STUDY 

Figure 1 shows the ventilation airflow patterns 

and fan locations before any ventilation improvements were installed. The mine exhibited noticeable 

air movement at various locations; but recirculation 

was a predominant factor. In conjunction with the 

fans, other factors that impacted the ventilation air-
flow direction included the outside air temperature, 

the outside wind condition, and the movement of 

haul trucks in the mine. During this time, one main 

mine fan and two auxiliary fans were all freestanding and operating without the use of stoppings. The 

main mine fan was a Pope1

 250-hp, 1,750-rpm,

350,000-cfm, 72-in-diameter axial-vane fan that was 

located in the central portion of the mine. The two 

booster fans were a Joy1

 100-hp, 1,770-rpm,

150,000-cfm, 60-in-diameter axial-vane fan and a 

Buffalo1

 125-hp, 1,770-rpm, 90,000-cfm, 54-indiameter axial-vane fan. 

Ventilation airflow is needed predominantly

where vehicles are most active, i.e., at the active 

production faces. The active faces in this mine are 

located in two primary areas: in the bench area located in the central portion of the mine and at the 

development sections in the south and southeast portion of the mine as shown in Figure 1. From observations and discussions with various mine operators, 

sufficient ventilation for dilution of noxious gases is 

often of lesser concern in the bench areas. The large 

volumetric size of the entries in the bench areas 

sometimes provides adequate air volume for the dilution of those exhaust gases. In the study mine, as is 

common with many underground stone mines, the 

active production faces can generally utilize as much 

air as the most efficient ventilation system can provide, i.e., for practical purposes, they can never have

too much air. Therefore, the ventilation improvements in this case study focused on the southern portion of the mine where the active production faces 

were located and where the air was most needed. 

 1

 Product mention does not imply endorsement by NIOSH. 

7 OVERHAULING THE VENTILATION 

SYSTEM 

The mine ventilation overhaul for this case study 

consisted of two phases: constructing a stopping 

line, and installing and replacing the main mine axial-vane fan with two high-volume, low-pressure, 

propeller exhausting fans mounted in a bulkhead. 

The stopping line was oriented perpendicular to the 

directions of face advance and several breaks outby 

the working faces. This type of ventilation is typical 

of a perimeter mining ventilation plan (Grau et al. 

2002a). Ventilation surveys were periodically taken 

during the construction of the stopping line to determine if the stopping line, in combination with 

auxiliary fans, had sufficient impact to negate the 

addition of a main mine propeller fan. Before completion, the stopping line which was a series of brattice curtains, initially improved the airflow, but at 

the end of the brattice line the air movement quickly 

dissipated as shown in Figure 2. Substantial air recirculation was also present at all times. It was clear

that additional ventilation improvements such as 

completion of the stopping line and the installation 

of large-volume main mine fans were necessary to 

effectively ventilate the working faces. 

Upon completion of the stopping line, two 

twelve-foot diameter propeller fans (Figure 3), were 

installed in the exhausting mode replacing the Pope1

main mine fan. The propeller fans were Series 10S 

12-ft-diameter high-volume, low-pressure fans 

manufactured by Hartzell Fan Co1 mounting 100 hp 

motors each. After the propeller fans were operated

for several weeks, it was observed that the standard 

brattice stoppings would not withstand the pressure 

and continuous flapping created by the fans, especially at locations near the fans. Brattices were 

pulled from the roof and rib as shown in Figure 4, or 

the constant flapping of the brattices near the faces

caused them to shred. Other significant forces damFigure 1. Ventilation airflow patterns prior to

modifications.

Figure 2. Airflow patterns with partial stopping

lines and original fans.
aging the brattices were face blast pressures and flyrock impacts. 

The brattices used for this study were a one-piece

design and were sized for the entries that were 45 ft

wide and 25 ft high for a total cross-sectional area of 

1,125 ft2

. Metal grommets were spaced every 3 ft on 

the perimeter of the brattice for added support. A 

base for attaching the brattice to the rib and roof was

made by bolting 2-in x 6-in wood planks to the roof 

and rib. On the roof, the brattice was wrapped 

around the wood to make a secure holding for the 

brattice. Along the rib and roof, the brattice was attached to the wood by 1.5-in common roof nails with 

a fender washer to account for the grommet hole. 

Within a few months, many of the roof nails pulled 

away from the wood, suggesting that some type of a 

screw would be a better anchor. 

8 PROPELLER FAN INSTALLATION 

Fan installation techniques vary and depend upon 

the physical attributes at the fan site. The fans for 

this case study were installed in entries that were 25 

ft high and 45 ft wide. The two 12-ft-diameter fans

displace a combined area of 226 ft2

. Therefore, for 

practical purposes, a difference of about 900 ft2

needed to be bulkheaded. The most convenient way 

to create the bulkhead was to first construct a ramp 

from waste rock across the entry to set the fan on as

shown in Figure 5. This tactic effectively reduced 

the size of the bulkheaded area from 900 ft2

 to about 

630 ft2 (not including fan area). The ramp consisted

of large boulders which were covered with smaller

2A modified gravel. The bulkhead was secured by 4-

ft long split set bolts into the boulders. 

Because of stresses from blast pressures, the fan

bulkhead and associated framework needed to be designed carefully. Incidents have occurred where face 

blast pressures have blown out bulkheads or damaged fans. However, over design of bulkheads can 

be costly. The entire framework for the fan bulkhead 

used in this case study sits atop a 12-in x 24-in I 

beam. The framework consists of 8-in x 8-in beams

as shown in Figure 6. The beams were oriented in a 

square/triangle pattern to enhance the strength of the

bulkhead. The fan was bolted to the bulkhead frame

through tabs available on the fan’s exterior shell. 

Smaller sections of I-beam were positioned to increase the bearing support of the circular fans that 

were positioned in the square box frame. The entire 

frame, excluding the opening for the fan, was covered with a 3/8-in steel plate to act as a barrier to 

prevent short-circuiting of air. To further minimize 

leakage, a U-shaped rubber seal was positioned between the fan frame and the mine roof. The bulkhead 

framework was prefabricated in a machine shop and 

shipped to the mine in two sections; the bottom half 

with beams only, and the top half with beams and 

plate attached. After securing the base half, the top 

half was simply set on top of the base half, as shown 

in figure 7, and welded in place. The final step was 

welding the bottom plate in place. 

Figure 3. Two propeller fans installed for this study.

Figure 5. Cross-sectional view of propeller fan installation.

Figure 4. Typical common example of brattice being

pulled from rib.
Mine fans are required to have a guarding grid 

that is less than 1 in2

. The manufacturer reports that 

the pressure loss on the flat fan guarding that is normally used in these applications ranges from oneeighth to one-quarter of an inch of w.g., not including the resistance caused by the build up of soot deposits on the grid (Atkinson 2002). This resistance 

could be detrimental to the performance of a low 

pressure propeller fan. One alternative to flat fan 

guarding is area guarding. Area guarding is a fence 

enclosure installed several feet from the fan, and was 

utilized for the fan in this study. The fan area guarding consisted of a 10-ft high chain link fence with 

locked access doors, as shown in Figure 8. MSHA 

required that the guards used for this fan be at least 5

ft away from the fan. This distance not only satisfied 

the necessary safety requirements but also prevented 

any air-flow resistance. 

9 MEASURED VENTILATION 

IMPROVEMENTS 

The combination of a stopping line and propeller 

fans resulted in dramatic ventilation improvements 

at the case study mine, as shown in Table 1 and Figure 9. The most important improvement was the 

more than doubling of the quantity of fresh airflow 

into the mine; from 300,000 cfm to 750,000 cfm. After the addition of the two propeller fans, the total 

number of fans increased from three fans to four 

fans, while the total rated horsepower of the fans decreased from 475 hp to 425 hp. 

Rubber Seal

12 x 24 Beam 8 x 8 Beam

4’ Split set

Roof Bolts

3/8” Steel Plate

Figure 6. Plan view of propeller installation.

Figure 8. Fan installation with perimeter guarding during maintenance. 

Table 1. Ventilation fan criteria before and after ventilation

changes 

Ventilation Stage Number 

of Fans 

Available 

Total Horsepower 

Air Volume; 

1,000 cfm

Original Ventilation 3 475 300

Improved Ventilation 4 425 750

 Difference +1 -50 +450

Figure 7. Installation of prefabricated fan bulkhead

Figure 9. Airflow patterns after installation of stopping line and propeller fans. 

A graphical representation of the airflow measured along the stopping line after the propeller fans 

were installed is shown in Figure 10. The first airflow measurement was made after the first stopping 

closest to the fans and was 725,000 cfm (an estimated 25,000 cfm had already been lost); the last 

measurement was taken 3,200 ft from the fan and 
was only 250,000 cfm. The 475,000 cfm loss of 

ventilation airflow was due to air leakage across the 

stopping line. The air quantity reaching the working 

faces, when compared to the air exhausted by the 

fans represents the mine ventilation efficiency. The 

ventilation efficiency calculated for the mine after

the propeller fan and brattice installation was about 

34 pct (Scenario 1, Table 2). The ventilation efficiency could have been further improved by two 

means; using stone pillars or permanent stoppings 

and/or upgrading the remaining stoppings as will be 

discussed latter. 

Table 2. Potential improvements in air distribution by upgrading stoppings 

One noteworthy observation from the case study 

was that when two parallel entries were available for

ventilation airflow, about 60 pct of the total airflow

traveled in the entry immediately adjacent to the 

stopping line. This percentage was slightly lower 

when more entries were present. In areas with four 

entries; the distribution of air from the first entry to 

the fourth entry was 43 pct, 29 pct, 20 pct, and 8 pct, 

respectfully. This indicates that when using the perimeter mining method, fresh air is being delivered 

near the working areas, but auxiliary fans become

necessary to push the air to the active faces. This becomes increasingly important as the production faces 

advance more than four entries away from the stopping line as described above. 

10 POTENTIAL ADDITIONAL 

VENTILATION IMPROVEMENTS 

NIOSH is researching methods to improve the 

performance of both permanent and flexible stoppings (i.e. brattice). The mine in the case study utilized brattice stoppings and from observations it appears that brattice stoppings can be improved by 

backing with cabling or geotechnical grid and by attaching the brattice to the roof and rib in a manner to 

minimize high stress points. During the case study, 

there were 28 stoppings along the 3,200 ft brattice 

line perimeter (Figure 9); however, 70 pct (333,000 

cfm) of the air loss occurred in the first 1,200 ft (8 

stoppings) from the fan. A significant decrease in air 

short circuiting could have been achieved if half of 

the first eight brattice stoppings would have been 

stone stoppings or permanent stoppings of some

type. If the remaining four brattice stoppings were 

improved to reduce losses by a conservative 25 pct, 

the total air loss in the first 1,200 ft of stopping line 

could be reduced to 125,000 cfm. The remaining 

2,000 ft of stopping line had a loss of about 143,000 

cfm through 20 stoppings for a total leakage of 

267,000 cfm and a ventilation efficiency of 63 pct 

for the first potential improvement, as shown in Scenario 2, Table 2. 

0

100

200

300

400

500

600

700

800

0 500 1000 1500 2000 2500 3000 3500

Distance from fan, ft

Air Quantity, cfm (x1,000)

Total Airflow

Attainable Airflow

Figure 10. Airflow along stopping line. 

Scenario Total Number

of Brattice 

Stoppings 

Total Leakage, 1,000 

cfm

Available 

Airflow at 

3,200 ft,

1,000 cfm

Ventilation 

Efficiency, 

Pct. 

1. Initial 

 Conditions 

28 475 250 34

2. Improving 

 first 8

 Stoppings 

 (4 Stone

 Stoppings)

24 267 458 63 

3. Improving 

 all stoppings 

 (14 stone 

 stoppings)

14 179 546 75 

If all stoppings were improved, i.e., if half of the 

remaining 20 brattice stoppings from the previous 

scenario were stone pillars and the remaining 10 

brattice stoppings were improved to reduce leakage 

by 25 pct, the total air loss in the remaining 2,000 ft 

would be reduced to about 54,000 cfm from 143,000 

cfm. This would represent a total air loss of only 

179,000 cfm (75 pct efficiency) at the end of the 

brattice stopping line (Scenario 3, Table 2). The 

available air at 3,200 ft would increase to 546,000 

cfm from the initial conditions of 250,000 cfm, and 

is shown as the attainable airflow in Figure 10. Repairing the brattice stoppings to reduce short circuiting by 25 pct is a conservative estimate since the observed stoppings had large gaps present as shown in 

Figure 11. 

11 OTHER BENEFITS OF PROPELLER FANS 

Improving ventilation is not the only benefit to 

using propeller fans. The two 12-ft-diameter propeller fans used in this case study are capable of producing about 750,000 cfm under loads that are less 
than one-quarter of an inch of w.g. with an actual 

130 combined total operating horsepower. As a feasibility comparison to using traditional axial-vane 

fans, three 84-in diameter fans would have been required in this study with each fan producing 250,000 

cfm to move a total air quantity of 750,000 cfm. 

Each of these axial-vane fans would require an outlet 

cone and a 200-hp motor that would operate at 130-

hp for a total of 390-hp, as compared to the 130 hp 

of the two propeller fans. 

The capital cost for the two propeller fans is

about $25,000, as compared to about $90,000 for

three axial-vane fans with outlet cones. Both sets of

capital costs exclude the necessary starter motors.

Annual operating costs are dependent upon the 

number of hours operated and the electrical unit 

cost. However, assuming an electrical cost of 

$0.08/kWh with the fans operating for 50 hrs per 

week for 50 weeks, the annual operating cost for the 

two propeller fans would be about $20,000, while 

the operating cost for three axial-vane fans would be 

about $59,000. 

12 SUMMARY 

The results of this case study demonstrate that 

dramatic improvements in ventilation airflow in underground large-opening mines can be achieved by 

the addition of large-diameter propeller fans. This 

increase in ventilation airflow should be an effective, 

practical, and cost-saving answer for improving the 

air quality in many underground large-opening 

mines, particularly large-opening drift mines. Not

only do propeller fans produce large air quantities, 

they do so with relatively low initial capital cost, low 

operating cost, and at a higher mechanical efficiency 

than axial-vane fans under the typical low-pressure 

conditions. Additionally, a method to bulkhead propeller fans was documented and serves as an installation guide for other mine operators. The study also 

showed that a brattice stopping line and auxiliary 

fans used in conjunction with the propeller fans was

an important aspect of improving the ventilation efficiency in the mine. 

13 REFERENCES 

Atkinson, G. Personnel communication (2002). Vice 

President of Sales, Hartzell Fan, Inc.

Grau, III, R.H., Robertson, S.B., Mucho, T.P., Garcia, F., and Smith, A.C. (2002a). NIOSH research addressing diesel emissions and other air 

quality issues in nonmetal mines. In 2002 Society for Mining, Metallurgy and Exploration Annual Meeting, Phoenix AZ, Feb. 26-28, 2002. 

Figure 11. Leakage through brattice stopping

Grau, III, R.H., T.P. Mucho, S.B. Robertson, A.C. 

Smith and F. Garcia (2002b). Practical techniques to improve the air quality in underground

stone mine, North American/Ninth U.S. Mine 

Ventilation Symposium, Kingston, Ontario, 

Canada, pp.123-129, June 8-12, 2002. 

Haney, R., and Saseen, G. (1998). Estimation of 

diesel particulate concentrations in underground 

mines. Preprint 98-146, presented at the Society 

for Mining, Metallurgy and Exploration Annual 

Meeting March 9-11, Orlando, FL. 

Head, R. (2001). Calculating underground mine ventilation fan requirements. Aggregates Manager, 

April 2001: 6(3):17-19. 

Mucho, T.P., Grau III, R.H., Robertson, S.B. (2001). 

Practical mine ventilation. Presentation at the 

Safety Seminar for Underground Stone Mines, 

Louisville, KY, Dec. 5. 

Mine Safety and Health Administration (MSHA), 

U.S. Department of Labor, (2001a). MSHA Web 

Site, Nonpermissible diesel engines approved under Part7,

http://www.msha.gov/S&HINFO/DESLREG/190

9a.HTM

Mine Safety and Health Administration (MSHA), 

U.S. Department of Labor (2001). Final Rule 30 

CFR Part 57. 

Robertson, Susan, (2001). The NIOSH Air Estimator, Underground Stone Safety Seminar, Louisville, KY, Dec. 2001. 

Robertson, Susan, Grau III, R.H., Dolgos, J. (2003). 

A computer software program that estimates air 

quantity requirements in large opening mines. 

North American/Tenth U.S. Mine Ventilation 

Symposium, Anchorage, AL, May 16-19, 2004. 

Schnakenberg, Jr., G.H. (2001). Estimate of technically feasible DPM levels for underground metal 

and nonmetal mines, Mining Engineering, 

Sept.2001.