1 INTRODUCTION 

Large-opening, room-and-pillar mines (i.e., those 

with openings larger than about 92.9 m2

 (1000 ft2), 

or 12.2 m (40 ft) wide and 7.6 m (25 ft) high) accounted for 135 of the 230 metal/nonmetal mines 

operating in the United States in 2004, and they employed about 2600 underground workers (MSHA 

2004). The commodities produced from these largeopening mines and the corresponding number of 

mines include: limestone for aggregate (103), 

lead/zinc (15), salt (14), marble (7), lime (6), stone 

(4), and sandstone (1) (MSHA 2004). Virtually all 

large-opening mining operations use a fleet of diesel-powered equipment that typically includes several large haulage trucks, one or more front-end 

loaders, drills, scalers, dozers, and various utility vehicles. A typical diesel-powered fleet frequently approaches 3730 kW (5000 hp), necessitating ventilation airflows of more than 354 m3

/s (750,000 

ft3

/min) to dilute diesel particulate matter (DPM) 

and diesel exhaust gases. A stone production blast 

will commonly use 454 kg (1000 lb) or more of high 

explosives and will liberate about 425 m3

 (15,000 

ft3

) of blasting gases and fumes, thereby imposing 

additional ventilation airflow requirements. 

2 VENTILATION CHALLENGES IN LARGEOPENING MINES 

Large-opening mines face ventilation challenges in 

the following areas: 

− moving adequate ventilation airflow volumes to 

dilute airborne contaminants to statutory levels 

− controlling and directing the airflow to where it is 

needed the most 

− planning ventilation systems to integrate with 

production requirements 

2.1 Moving adequate ventilation airflow volumes 

Large-opening mines pose unique ventilation challenges simply to move sufficient air quantities for 

dilution of all airborne contaminants. In mature 

stone mines, the total open-space volume can reach 

7,079,200 m3

 (250 MMft3). With these large openspace volumes, even fans capable of moving 472 

m3

/s (1.0 MMft3/min), take hours to complete a total 

air change. Therefore, ventilation air should be directed and coursed to the production face areas to 

concentrate and minimize the ventilation airflow 

volumes necessary to provide sufficient fresh air to 

the active working areas. 

Maximizing the ventilation of large-opening mines 

R. H. Grau III, R. B. Krog, and S. B. Robertson 

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 PA, USA 

ABSTRACT: The National Institute for Occupational Safety and Health (NIOSH) has conducted research to 

improve the ventilation of large-opening mines. Large-opening mine ventilation is unique for the following 

reasons: (1) it is challenging to keep airflow velocities high enough to effectively remove or dilute airborne 

contaminants, (2) large air volumes can be moved through the mines with little static pressure drop, and 

(3) stoppings to direct ventilation airflows are costly to construct and maintain. The research results suggest 

that by incorporating ventilation planning into the mine planning process, using propeller fans, developing 

new stopping materials and construction methods, and using long pillars to eliminate crosscuts where possible, the ventilation of large-opening mines can be significantly improved. The ventilation improvements created by incorporating these various techniques into the ventilation plan will help reduce the exposure of mine 

workers to airborne contaminants in underground large-opening mines. 
2.2 Controlling and directing the airflow 

The size of large-opening underground stone mines 

creates problems for controlling and directing ventilation airflows. Stopping designs and techniques 

suitable for use in coal mines generally cannot be 

applied in stone mines because of the entry sizes and 

the associated cost of construction. Ventilation curtain materials, such as mine brattice, can be problematic because of significant air leakage due to its 

deterioration caused by repetitive flapping (especially near the main mine fan) and blast pressures. 

2.3 Planning ventilation systems 

Stone production from most large-opening, roomand-pillar underground stone mines comes from 

multiple working faces located on the perimeter of 

the mine. In the initial mine development stages 

when few operating faces are present, it is relatively 

simple to provide adequate ventilation airflow across 

the production faces. Natural ventilation and an auxiliary fan may be sufficient to reduce airborne contaminants to acceptable levels at this stage of mine 

development. However, as a mine expands, ventilating all the working areas becomes more difficult as 

the number of working faces and the distances between the main mine fan and the working faces increase. 

3 NIOSH LARGE-OPENING MINE VENTILATION RESEARCH 

NIOSH is conducting a research effort to improve 

the ventilation airflow quantity and quality in largeopening underground mines. Investigations have focused on a four-point approach: 

− Developing techniques to estimate the required 

air quantity to dilute airborne contaminants. 

− Identifying alternative fans capable of efficiently 

moving the required air quantity to dilute airborne 

contaminants to statutory levels 

− Developing improved stoppings to direct and 

control the ventilation airflow to the production 

faces 

− Evaluating improved mine designs to deliver and 

distribute the required ventilation airflows without interfering with production requirements 

3.1 The Air Quantity Estimator 

Mine ventilation planners must determine the air 

quantity needed to meet the statutory DPM concentration limits by taking into account the emissions 

characteristics of the site-specific fleet of engines at 

their operation. To meet this challenge, NIOSH developed the Air Quantity Estimator (AQE) to assist 

mine operators with ventilation planning (Robertson 

et al. 2004). The AQE provides an initial estimate of 

the required air quantity needed to dilute DPM contaminates to statutory levels in the main air stream of 

the mine. The AQE is a user-friendly, stand-alone 

computer program that uses diesel engine performance test data from both the Environmental Protection Agency (EPA 2002) and the Mine Safety and 

Health Administration (MSHA 2002). The AQE is 

available upon request to NIOSH at: http://www.cdc.gov/

niosh/mining/products/analysissoftware.htm#AQE. 

3.2 Improving ventilation airflow volumes with 

propeller fans 

Due to the opening size, the resistance to flow in 

large-opening drift mines is minimal. Low-pressure 

propeller fans can efficiently move large airflow 

volumes in such mines as demonstrated by NIOSH 

(Grau et al. 2002, 2004, Krog et al. 2004). Grau 

(2002, 2004) found that historically, large-opening 

drift mines almost exclusively used vane-axial fans 

for main mine fans, where in most cases, a better 

choice would have been propeller fans. The difference in the air quantity-pressure loss relationship between a large-opening mine and a typical coal mine 

is significant, as shown in Figure 1. In both cases, 

the mine resistance pressure increases as the square 

of the ventilation airflow volume. The required ventilation pressure for an underground stone drift mine 

rarely exceeds 249 Pa (1 in w.g.) (Grau et al. 2004a) 

since the resistance is so small. 

Figure 1 also shows the fan curves for a typical 

high-pressure, vane-axial fan commonly used to 

ventilate a coal mine and the fan curve for a typical 

3.66-m (12-ft) propeller fan. The operating point for 

the coal mine (Point A, Fig. 1), occurs at a flow volume of 118 m3

/s (250,000 ft3/min) and a static pressure of 1.77 kPa (7.1 in w.g.). The same coal mine 

vane-axial fan used in a large-opening mine would 

operate at 153 m3

/s (325,000 ft3/min) and 52 Pa 

(0.21 in w.g.) (Point B, Fig. 1). However, at that operating point, the static fan efficiency is less than 

6%, well outside the manufacturer’s normal operating envelope. 

The operating point for the 3.66-m (12-ft) propeller fan (Point C, Fig. 1) occurs at 175 m3

/s (370,000 

ft3

/min) and 67 Pa (0.27 in w.g.) however, the static 

fan efficiency is much higher at 14%. Although this 

efficiency is low for the propeller fan, it is 2.3 times 

more effective than the axial-axial fan used in the 

same 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 1. Pressure and quantity curves for two fans and corresponding resistance curves. 

3.3 Improving stoppings for directing ventilation 

airflows 

Using stoppings to direct ventilation airflows in 

large-opening mines has been limited due to their 

high capital cost and construction and maintenance 

difficulty. The most challenging problems exist in 

older, extensive mines that have never incorporated 

stoppings into the mining plan. Retrofitting an older 

mine with stoppings requires considerable labor, material, and maintenance costs (Grau 2004). Major design criteria for stoppings are: 

− withstanding fan pressure differentials 

− withstanding production blast pressures 

− minimizing leakage between the intake and return 

air courses 

− having high durability and requiring minimal 

maintenance 

The relative importance of these design criteria is 

associated with three distinct areas of a mine, the 

main entries, intermediate entries, and the face areas. 

The stoppings in the main entries will typically see 

low blast pressures. However, due to their close 

proximity to the main mine fan, they experience the 

highest pressure differential and thus have the greatest potential for leakage. The stoppings in the main 

entries must last throughout the life of the mine with 

little maintenance, and thus have the highest durability requirement. If curtain stoppings are installed 

close to the main fan, they must have sufficient durability to withstand repetitive flapping (Krog et al. 

2004). Grau et al. (2002) measured pressure differentials generally less than 62 Pa (0.25 in w.g.) at the 

main mine fan in large-opening stone drift mines 

with multiple entries. Pressures from face production 

blasts can far exceed these ventilation pressures and 

from observation, depending on the mine layout, 

stoppings may be located near face blasts for several 

years. Mucho et al. (2001) measured blast pressures 

from two different production-face shots, ranging 

from 8.27 kPa (1.20 psi) to 9.38 kPa (1.36 psi) at 

distances of 61 m (200 ft) to 152 m (500 ft) from the 

shot. Both test shots were similar to typical production blasts in underground stone mines, and they 

each consisted of 181 kg (400 lb) of ANFO, 77 kg 

(169 lb) of dynamite, and 23 kg (50 lb) of Detagel. 

Stoppings located close to face areas or even in 

intermediate areas may require a blast pressure relief 

mechanism to prevent damage from production 

blasts. Timko and Thimons (1987) discussed a 

method to provide blast relief using VELCROTM fasteners on typical brattice stoppings. NIOSH recently 

performed tests where twelve 23-kg (50-lb) sandbags were placed on the bottom of a curtain stopping 

that was laying on the mine floor. It was found that 

this method held the stopping in place for lower 
pressure shots, but allowed for pressure relief during 

higher pressure shots by allowing the curtain to slip 

out from under the sandbags. Experimentation on a 

site-specific basis may be necessary to determine the 

appropriate sandbag pressure relief weight for stoppings in intermediate areas of the mine. 

The most efficient ventilation barrier separating 

intake from return air is a long stone pillar. These 

barriers are created by eliminating at least the last 

face shot that would normally break through two adjoining entries, thus keeping a natural connection between the pillars. A series of these connected pillars 

creates a long stone air wall that is an effective and 

practical method for directing ventilation air. This 

technique reduces maintenance and the expense of 

building stoppings. The pillars can eventually be 

mined when the barrier is no longer needed, such as 

just prior to mine closure. 

Since stone stoppings cannot always be used, 

NIOSH has developed and tested two new stopping 

types, the “Super Stopping” and the “EZ-Up Stopping” (Figures 2 and 3) for use in large-opening 

mines (Grau et al. 2006). The Super Stopping is a 

long-term or permanent ventilation control structure, 

and is constructed from low density, composite cement and fly ash blocks measuring 1.22 m (48 in) 

wide by 1.22 m (48 in) high by 0.81 m (32 in) thick, 

and weighing approximately 544 kg (1200 lb) each. 

The blocks are laid and positioned using an extended 

reach fork lift. The EZ-Up stopping is a temporary, 

portable, curtain stopping which is raised to the mine 

roof using a winch system. In-mine tests at NIOSH’s 

Lake Lynn Laboratory have demonstrated the viability of the proposed construction methods and materials. 

Figure 2. Schematic of Super Stopping. 

Figure 3. Schematic of EZ-Up Stopping. 

3.4 Mine design considerations for improving 

ventilation airflows 

Three improved mine designs and associated ventilation plans have been identified for large-opening 

mines: perimeter, unit, and split. Selecting the appropriate mine design and associated ventilation 

plan is a factor of mine size. Grau et al. (2002, 

2004), Mucho et al. (2001), and Krog et al. (2004) 

discuss the applications of these proposed mine designs for improving the ventilation of large-opening 

mines. Perimeter ventilation is best suited for older 

mines with little previous ventilation planning. New 

mines are generally more readily adaptable to split 

and unit mine ventilation practices. Achieving an 

optimal ventilation system layout that works well 

with production is relatively easy for a newer operation. However, retrofitting the new concepts into extensive existing operations may present unique challenges. NIOSH research has identified key 

considerations for selecting the best mine design for 

optimal ventilation while meeting basic production 

requirements (Krog et al. 2004). These considerations include: 

− maximizing ventilation system efficiencies 

− determine the maximum distance between the 

face area and a fresh air source while still providing adequate ventilation 

− locating truck haulage routes underground to 

minimize contamination of the fresh air supply 

− direct fresh air to the faces along the shortest path 

possible 

A mine ventilation system can be rated by calculating ventilation efficiency. Ventilation efficiency is 

the percent of useful ventilation air quantity passing 

a specific point compared to the total possible air 

quantity available. When evaluating different designs for large-opening, room-and-pillar mines, three 

related ventilation efficiency measures have been 

used by NIOSH: 
(1) Ed = Qlop ÷ Qm

(2) Ef = Qf ÷ Qlop

(3) Et = Qf ÷ Qm = Ed × Ef

Where: 

− Ed = delivery efficiency, air delivered to the 

working area 

− Ef = face ventilation efficiency, air available at 

the face 

− Et = total mine efficiency; 

− Qm = air quantity entering the mine 

− Qlop = air quantity exiting the face area at last 

opening at a pillar 

− Qf = air quantity at face. 

An example of increasing ventilation efficiency 

by incorporating long stone pillars in the design of a 

new mine is shown in figures 4 and 5. This example 

is a variant of a split-mining ventilation system 

where a propeller fan blows 143 m3

/s (303,000 

ft3

/min) into three dedicated intake airways located 

in the northwest portion of the mine. 

A long stone pillar separates these intake airways 

from the working areas. Two crosscuts within this 

pillar line have been sealed with permanent stoppings as the mine was developed. Of the 143 m3

/s 

(303,000 ft3

/min) entering the mine, about 122 m3/s 

(258,000 ft3

/min) ventilated the working area and 

was measured passing through the last opening in 

the stone pillar, giving a ventilation delivery efficiency of 85% (see Equation 1). 

S SSSS S S S

2 (4)

34 (72)

109 (231)

0 19 (41)

143 (303)

S S

122 (258)

S

Auxiliary Fan Working Areas

S = Brattice Stopping

= Airflow Direction

= Permanent Stopping

Second Stone Pillar

First Stone Pillar

Third Stone Pillar 

Being Developed

Permanent Stopping

= 50 m95 (202)

Propeller Fan

N

S SSSS S S S

2 (4)

34 (72)

109 (231)

0 19 (41)

143 (303)

S S

122 (258)

S

Auxiliary Fan Working Areas

S = Brattice Stopping

= Airflow Direction

= Permanent Stopping

Second Stone Pillar

First Stone Pillar

Third Stone Pillar 

Being Developed

Permanent Stopping

= 50 m95 (202)

Propeller Fan

N

Figure 4. Ventilation airflows of new mine with long stone pillars. (Bold numbers are ventilation airflow volumes, m3

/s, (x 

1000 cfm). 

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700 800 900

Distance from fans (m)

Air Quantity (m3/s)

0

100

200

300

400

500

600

700

800

0 500 1000 1500 2000 2500

Distance from fans (ft)

Air Quantity (x 1000 cfm)

Brattice stopping line

Long stone pillars

Future long stone pillars

Original axiliary fan

Required Airflow 108 m3/s (230,000 cfm) 80%

Revised Ventilation System

Long Stone Pillars

Future Long Stone Pillars

76%

87%

66%

53%

43%

33%

100%

88% 85%

83% 81%

100%

Original Auxiliary Fan

A G

F

E

D

C

B H

Figure 5. Ventilation delivery efficiencies of new mine using long stone pillars, and 15-year-old mine before and after ventilation 

improvements. 
About 95 m3

/s (202,000 ft3/min) of the ventilation 

airflow entering the working area was measured at 

the working faces, resulting in a calculated face efficiency of 78% (see Equation 2). Total mine efficiency (see Equation 3), is the working face ventilation airflow divided by the mine intake volume, or 

67% for this case. Alternatively, total mine efficiency is the product of delivery efficiency multiplied by the face ventilation efficiency (85% × 78% 

for this example), or again, 67%. 

Separating ventilation efficiency into its component parts provides a useful way to compare and 

evaluate alternative mine ventilation systems layouts 

for large-opening underground stone mines. Recent 

work by Grau et al. (2004) illustrates the utility of 

the ventilation efficiency concept for planning a ventilation system that delivers more air to the working 

faces. 

Figure 6 shows a 15-year-old mine that relied 

primarily on natural ventilation supplemented with 

three auxiliary fans. The working faces required an 

air quantity of about 109 m3

/s (230,000 ft3/min) to 

dilute the expected DPM. An air quantity of 330 

m3

/s (700,000 ft3/min) was measured downwind of 

the second auxiliary fan. Unfortunately, only 116 

m3

/s (245,000 ft3/min) flowed to the turn in the 

stopping line (Location D), giving a ventilation efficiency of less than 35% (116/330) to that location. 

Less than 24 m3

/s (50,000 ft3/min) is available at the 

last stopping (Location E), implying a delivery efficiency of less than 7% (24/330), and a very low total 

mine efficiency, as evidenced by air velocities that 

were too low to measure at the production faces. 

330 (700) 330 (700)

116 (245) 116 (245)

24 (50) 24 (50) 0 0

330 (700) 330 (700) AIR QUANTITY, m AIR QUANTITY, m3/s (x 1,000 cfm) /s (x 1,000 cfm) AIRFLOW DIRECTION AIRFLOW DIRECTION

Active Sections

Active Sections

FAN

Benched Area

STOPPING STOPPING

100 m

E

D

C

330 (700) 330 (700)

116 (245) 116 (245)

24 (50) 24 (50) 0 0

330 (700) 330 (700) AIR QUANTITY, m AIR QUANTITY, m3/s (x 1,000 cfm) /s (x 1,000 cfm) AIRFLOW DIRECTION AIRFLOW DIRECTION

Active Sections

Active Sections

FAN

Benched Area

STOPPING STOPPING

100 m

E

D

C

Figure 6. Initial ventilation airflows for a 15-year-old mine 

with partial brattice curtain stopping line and auxiliary fans. 

Figure 7 shows the measured ventilation airflows 

for the same 15-year-old mine that is shown in Figure 6 after it has been upgraded with two exhausting 

propeller fans (Location F) and 23 additional brattice 

curtain stoppings. Figure 5 shows the calculated 

ventilation efficiencies for both the old auxiliary fan 

ventilation system and the improved revised ventilation systems in the 15-year-old mine, as well as the 

results of using long stone pillars in the new mine 

shown in Figure 4. At distances greater than 91 m 

(300 ft) from the fan, the original auxiliary fan ventilation system could not deliver the required air quantity of 108 m3

/s (230,000 ft3/min) to dilute the expected DPM in the 15-year-old mine, and the total 

efficiency decreased rapidly with increasing distances from the fan. As indicated on Figures 5 and 7, 

measured airflows for the upgraded ventilation system exceed the required airflow at the working 

faces, and uses less fan energy (Grau et al. 2004). 

However, total efficiency beyond about 305 m 

(1,000 ft) (Location G) from the propeller fans falls 

to less than 50% due to stopping leakage. This upgraded ventilation system was a significant improvement from the original auxiliary fan ventilation 

system, but as the mine expands, the loss of ventilation airflow due to leakage will result in inadequate 

fresh air being supplied to the working area. 

Active Sections

Active Sections

118 (250) 118 (250)

331 (660) 331 (660)

274 (580)

234 (500)

359 (760) 359 (760)

156 (330) 156 (330) 189 (400) 189 (400)

Benched Benched Area

330 (700) 330 (700) AIR QUANTITY, m AIR QUANTITY, m3/s (x 1,000 cfm) /s (x 1,000 cfm) AIRFLOW DIRECTION AIRFLOW DIRECTION

FAN STOPPING STOPPING

100 m

H

G

F

Active Sections

Active Sections

118 (250) 118 (250)

331 (660) 331 (660)

274 (580)

234 (500)

359 (760) 359 (760)

156 (330) 156 (330) 189 (400) 189 (400)

Benched Benched Area

330 (700) 330 (700) AIR QUANTITY, m AIR QUANTITY, m3/s (x 1,000 cfm) /s (x 1,000 cfm) AIRFLOW DIRECTION AIRFLOW DIRECTION

FAN STOPPING STOPPING

100 m

H

G

F

Figure 7. Improved ventilation airflows for a 15-year-old mine 

after installation of brattice curtain stopping line and propeller 

fans. 

Preliminary research by NIOSH suggests that using long stone pillars instead of brattice curtain 

stoppings will maintain the total efficiency over 60% 

at distances greater than 305 m (1000 ft) from the 

propeller fans in similar mining situations as shown 

in Figures 4, 6, and 7. Long stone pillars eliminate 

the construction and maintenance costs associated 

with brattice curtain stoppings. Long stone pillars 

also eliminate leakage, resulting in both an increase 

in total mine, and delivery ventilation efficiencies, as 

illustrated for the new mine in Figure 5 by the long 

stone pillar curve. Using long stone pillars can be a 

key factor in maintaining adequate ventilation airflows at increasing distances from the fan to the active production faces where it is most critical. 

4 SUMMARY 

Improvements in ventilation efficiencies can be 

achieved in underground large-opening mines by 

utilizing a systematic four point approach to the 

problem. First, it is imperative to estimate the air 
quantity required for adequate dilution of airborne 

contaminants. A thorough understanding of the airborne contaminant sources such as DPM and fumes 

from diesel equipment and blasting is necessary for 

the selection of the appropriate fan for the sitespecific conditions. An air quantity estimator has 

been developed by NIOSH to perform that task. 

Second, appropriate fan selections should be 

based upon the most effective method to move the 

required ventilation air quantity for proper dilution. 

Propeller fans produce large air quantities at a higher 

mechanical efficiency than vane-axial fans for the 

typical low-pressure conditions of large-opening 

drift mines, and with relatively low initial capital 

and operating cost. 

The third component is the use of improved stopping designs to direct and control the ventilation airflow to where it is needed the most. Long stone pillars are recommended to reduce air leakage, and 

they also eliminate the stopping maintenance issue. 

In situations where long stone pillars are not feasible, proper stopping construction techniques are vital 

for the delivery of a high percentage of the ventilation airflow to the desired location. 

Fourth, improved mine designs should be used to 

deliver and distribute the required ventilation airflows without interfering with production requirements. 

When properly addressed, these four key ventilation factors will ultimately result in effective, practical, and cost effective increases in the ventilation 

airflows to improve the air quality in large-opening 

mines. 

5 DISCLAIMERS 

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. 

Mention of any company or product does not constitute endorsement by NIOSH. 

REFERENCES 

EPA 2002. U.S. Environmental Protection Agency. Web site at 

http://www.epa.gov/otaq/certdata.htm#largeng. 

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

Garcia, F. 2002. Practical techniques to improve the air 

quality in underground stone mines. In E. De Souza (ed.), 

North American/Ninth U.S. Mine Ventilation; Proc.intern.symp. 

Kingston, Ontario, Canada, June 8–12, 2002. Netherands: 

Balkema. 

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

Mucho T.P. 2004. Raising the bar of ventilation for largeopening 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, 349–355. 

Grau, III R.H., Robertson S.B., Mucho T.P., Garcia F. & Smith 

A.C. 2004a. NIOSH ventilation research addressing diesel 

emissions and other air quality issues in nonmetal mines. 

Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc. Transactions 2004, Vol. 316, 149–158. 

Grau, III R.H., Krog, R.B. & Robertson, S.B. 2006. Novel 

stopping designs for large-opening metal/nonmetal mines. 

Proceedings of the 11th U.S./North American Mine Ventilation Symp. University Park, PA, June 5–7, 2006. 

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., 1–9. 

MSHA 2002. Nonpermissible diesel engines approved under 

Part 7. U.S. Mine Safety and Health Administration. 

http://www.msha.gov/s&hinfo/deslreg/1909a.htm. 

MSHA 2004. Quarterly employment and coal production: accidents/injuries/illnesses reported to MSHA under 30 CFR 

Part 50. Denver, CO: U.S. Department of Labor, Mine 

Safety and Health Administration, Office of Injury and 

Employment Information. 

Mucho, T.P., Grau, R.H. & Robertson, S.B. 2001. Practical 

mine ventilation. Presentation at the Safety Seminar for 

Underground Stone Mines, Louisville, KY, Dec 5. 

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

2004. A computer software program that estimates air 

quantity requirements in large-opening stone mines. In: R. 

Ganguli, S. Bandopadhyay S, (eds.), Mine ventilation: Proc. 

of the 10th U.S./North American Mine Ventilation Symp., 

Anchorage, AK, May 16–19, 2004. Leiden, Netherlands: 

Balkema, 363–369. 

Timko, R.J. & Thimons E.D. 1987. Damage resistant brattice 

stoppings in mines with large entries. Eng. Min. J. ; 

Vol/Issue: 188:5