USING MINE PLANNING AND OTHER TECHNIQUES TO IMPROVE VENTILATION IN LARGE-OPENING MINES 

R. H. Grau, III, NIOSH, Pittsburgh, PA

R. Krog, NIOSH, Pittsburgh, PA 

Abstract 

The National Institute for Occupational Safety and Health

(NIOSH) has conducted research to improve the ventilation of largeopening mines. The research has demonstrated that the ventilation of

large-opening mines improves significantly by including ventilation

requirements in the mine planning process and implementing some

practical techniques during mining. Planning the location of long pillars

to reduce the number of crosscuts between intake airways and return

airways, positioning auxiliary fans in their proper locations, and

establishing ventilation stoppings with minimal leakage all significantly

improve the ventilation of large-opening mines. Mine operators that

adopt these techniques in the mine ventilation plan will reduce

mineworkers’ exposure to airborne contaminants. 

Introduction 

This paper discusses methods to improve ventilation in largeopening mines. Utilizing engineering controls is the primary strategy

many operators use to reduce workers’ exposure to contaminants.

The controls include increasing the air quantity entering the mine,

using stoppings and auxiliary fans to direct airflow to faces, and

improving mine planning layouts (Grau et al., 2004a, 2006a, 2006b;

Krog et al., 2004) to direct airflow to the face areas. 

The ventilation demands of a fleet of diesel powered equipment

that is to be operated in an underground stone mine should be

incorporated into the mining plans (Head, 2001; Grau, et al., 2002;

Krog, et al., 2004). During this planning session, special thought

should be given to the length and orientation of stone pillars and to a

plan to divide the mine into smaller units such that the ventilation flow

to active face areas is increased by eliminating the need to ventilate

old works. The ventilation plan should also include the type and

location of main mine fans, auxiliary fans, and stoppings as well as

considerations for face areas, maintenance shops, crusher areas, and

truck haulage routes. 

Ventilation plans must be developed on the premise of the mine

fan developing enough air to adequately dilute airborne contaminants

and delivering sufficient air to the face to dilute and render harmless

airborne contaminates. In previous studies, NIOSH has shown that a

large percentage of air that is produced by the main mine fan can

reach the face best by using long stone pillars that form walls and

reduce crosscuts between intake and return airways (Grau et al.,

2006a). However, even with large air quantities reaching the face

area, the methods that are used to distribute the air within the face

area can significantly improve ventilating the working areas. 

The Application of Long Stone Pillars 

The rectangular stone pillars, shown in figure 1, are named “long

pillars” because they are over 10 times longer than wide. The long

pillars create a continuous wall that separates intake airways from

return airways as well as course and direct the intake airflow. Air is

delivered to the face area which is located beyond the last open

crosscut of a long pillar, as shown in figure 1. Long stone pillars

provide more resistance to leakage between adjacent entries than

fabric stoppings. Using long stone pillars significantly increases airflow

 

to face areas by reducing the number of crosscuts between intake and 

return airways. 

The mine illustrated in Figure 1 incorporates a blowing ventilation 

system utilizing long stone pillars to direct the ventilation air to the face 

area. The mine advanced about 550 m (1,800 ft) while having only 

four crosscuts between intake and return entries that were separated 

by fabric stoppings. Using this technique, about 74% of the air 

produced by the main mine fans was delivered to the face area. From 

observations of the stoppings in the mine, an even greater air quantity 

could be delivered to the face area by improving the four stoppings and 

thus reducing leakage. 

Figure 1. Using long pillars to maintain a high percentage of air

reaching the last open crosscut. 

Although using long pillars enables a high percentage of main 

mine air to reach the last open crosscut, a disadvantage is that at 

times, the last open crosscut may be 150 m (500 ft) or more from the 

face. This distance can create difficulty to adequately ventilate the 

face. Without using a properly positioned auxiliary fan, the ventilation 

air will short circuit the face and feed directly into the return entry 

through the last open crosscut in the long pillar. A strategically 

positioned auxiliary fan located outby the last open crosscut that blows 

fresh air to the face will reduce the air quantity that is short circuited. 

Various factors affect how much air quantity is moved to the face, and 

include the mine entry grade at the face, the amount of equipment 

moving in the face area, and most importantly, the auxiliary fan type, 

fan nozzle, location and orientation (Dunn et al, 1983). 
 

Moving More Fresh Air to the Face 

Although using a long pillar air wall will deliver large air quantities 

to the last open crosscut, the correct placement of auxiliary fans plays 

a vital role in moving the air from the last open crosscut to the face. 

NIOSH performed in-mine tests to determine how face ventilation is 

affected by the placement of an auxiliary fan. The percentage of air at 

the last open crosscut that is used at the face represents face 

ventilation efficiency and is calculated by dividing the airflow at the face 

by the airflow at the last open crosscut and multiplying by 100. 

Ventilation efficiency is a means to normalize results obtained for 

different mines having different air quantities. The ventilation efficiency 

represents how much air at the last open crosscut is effectively being 

used at the face. The results in this report present the face ventilation 

efficiency at a set distance from the last open crosscut for comparing 

one system to another. 

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

Distance, m

Face Ventilation Effeciency, (%)

0 50 100 150 200 250 300 350 400 450

Distance, ft

No Auxiliary Fan

Auxiliary fan outby last open crosscut

Auxiliary fan inby last open crosscut

Figure 2. Face ventilation efficiencies of fan locations and distances

from last opening in pillar. 

Figure 2 shows graphically how air at the last open crosscut was 

found to be effectively used at the face for three different scenarios. 

The scenarios include ventilating with no auxiliary fan, positioning the 

auxiliary fan inby the last open crosscut, and positioning the fan outby 

the last open crosscut blowing through the intake air stream. Different 

results were found with each scenario, but the best results were found 

when the auxiliary fan is positioned in the intake blowing through the 

main air flow. 

Figure 3 shows the least efficient face ventilation scenario of the 

three scenarios with the face being ventilated without using an auxiliary 

fan. With this scheme, about seven percent of the intake air that was 

available at the last open crosscut was measured at a distance of 

about 73 m (240 ft) inby from the last open crosscut. A small amount 

of face ventilation is achieved because the air mass moving down the 

intake entries carries momentum which pushes it a short distance into 

the face area before eventually being turned and moving through the 

last open cross cut. Also, a small amount of ventilation arises from the 

motion of both the loader and trucks at the face. However, even with 

these factors, the face ventilation in this scheme is minimal. 

Using Fan Airflow Characteristics to 

Improve Face Ventilation Efficiency 

Fan characteristics such as entrainment and intake air velocity 

common to most fans can impact the fresh air quantity moved to the 

face. The fan used in the scenarios shown in Figures 4 and 5 is a freestanding vane-axial fan with a diameter of 0.91 m (36 in). It was 

powered by a 19kW (25 hp) motor, and mounted with a reducer at the 

outlet with discharge diameter of 0.58 m (23 in). Figure 6 shows 

comparisons of air quantities flowing through an entry from the 3-ft 

vane-axial fan as well as a 8-ft propeller fan (Krog et al., 2006). For 

both fans, due to the fan entrainment properties, the maximum air 

quantity produced occurs some distance away from the fan. The total 

flow produced by these free-standing fans is the sum total of the air 

produced by the fan, the air entrained around the fan and by the air 

plume leaving the fan. Figure 6 shows that the vane axial fan's high 

exit velocity causes air entrainment for a distance slightly less than 90 

m (300 ft) from the fan. The actual volume passing through the fan 

was 10.4 m3

/s (22,000 cfm) however due to entrainment and air 

moving around the fan, the fan eventually moved about fifteen times 

the original air volume that passed through the fan. The ability of the 

fan to entrain such large amounts is partly due to momentum. The 19 

kW (25 hp) fan by itself is not well suited to move large amounts of air 

and without a reducer it would operate at a very low efficiency. The 

reducer forces the fan’s airflow to pass through a small 0.58 m (23 in) 

diameter nozzle, which creates the higher exit velocity and therefore a 

higher momentum. Entrainment by free-standing fans in other cases 

has been documented to be quite high. Dunn et al, (1983) found an 

entrainment ratio ranging from 9 to 15. Also, Kissell (2006) reported 

several studies that showed ventilation efficiencies in dead head 

entries were improved when jet fans were equipped with a nozzle and 

were tilted slightly to the roof. 

Figure 3. Least efficient face ventilation with no fan. 

The other fan characteristic to consider is the fan intake. For all 

practical purposes, as shown in Table 1, air motion is negligible only a 

few distances away from a fan intake. A free standing fan placed a 

few crosscuts inby the last open crosscut will only intake air that is 

recirculating from the face and will not pull in fresh intake air from 

several crosscuts away. Since the face ventilation efficiency is a 

percentage of air at the last open crosscut that is moved to the face, 

with a 100 pct recirculation, no airflow at the last open crosscut is 

moved to the face area; consequently, the face ventilation efficiency is 

zero. 

Figure 2 shows that an improperly placed fan inby the last pillar 

opening provides only marginal improved ventilation than if an auxiliary 

fan is not present. Figure 4 shows a plan view of this scenario where a 

fan is positioned inby the last opening in the long pillar resulting in poor 

face ventilation. In this scenario, only about five percent of the air 

available at the last opening in the long pillar was measured 120 m 

(400 ft) from the last open crosscut. 

The fan position located inby the main ventilation air stream 

increases recirculation while providing minimal fresh intake air to the 

face. Furthermore, the position of the fan in the middle entry as shown 

tends to promote excessive recirculation as the air reverses both in 

entry “A” and “B” and the recirculated air acts as a substitute for fresh 

air. It should be noted that not all recirculation is detrimental, as 
previous studies have shown that recirculation is a problem only when 

it is substituted for fresh air rather than be added to fresh air (Kissell et 

al., 1975). 

Figure 4. An improperly located fan reduces ventilation efficiency and

increases recirculation. 

able 1. Diminishing air velocity with distance from end of ventilation 

ity, percent at fan 

T

pipe, 0.30-m (1-ft) diameter (Hartman, 1961). 

Distance, diameters Veloc

0.25 60

0.50 27

0.75 14

1 7

Figure 5. A properly located auxiliary fan increases ventilation

efficiencies. 

The correct auxiliary fan location, as shown in figure 5, should be 

outby the last open crosscut where it can entrain and blow fresh air 

into the face area. The fan should also be positioned in the furthest 

upstream entry (in this case left) to create air movement that is moving 

in the same general direction as the air being moved by the main mine 

fan. Being in the left most entry, recirculation is reduced and the air 

sweeps along the face. Using this configuration, virtually all of the air 

that was moved by the fan was intake air and 57 pct of the air at the 

last open cross cut was available at 120 m (400 ft) from the last open 

 

crosscut as described in Figures 2 and 5. There are two positive 

factors at work in this scenario. First, with the fan blowing down the 

left entry, the air recirculation is reduced and the energy is used to 

deliver air to the face rather than creating recirculation. Second, the 

fan is positioned properly to maximize intake air to the fan and 

maximize the entrainment of fresh air. It should be considered that 

moving the fan further from the face, outby the last open in the long 

pillar, does not increase the airflow at the face, but increases the 

percentage of air available at the last open cross cut to be moved to 

the face. 

Figure 6. Air flow at center of entry compared to distance from fan fo

-

50

100

150

200

250

300

0 50 100 150 200 250 300

Distance From Fan (m)

Air Quantity (m3/s)

-

100,000

200,000

300,000

400,000

500,000

600,000

0 100 200 300 400 500 600 700 800 900

Distance From Fan (feet)

Air Quantity (cfm)

2.44 m (8') Propeller

0.91 m (3') Axial Vane

r 

two fan types. 

Considering the Floor Grade 

In some instances, the floor grade has an influence on the 

ventilation and air quality in the face areas (figure 7). Mining 

downgrade has a tendency to improve ventilation and air quality. From 

observation alone, a slight increase in efficiency was observed while 

mining downgrade with no auxiliary fan. Generally, from observations 

and discussions with mine operators, mining up grade, as shown in 

Figure 7, is more difficult to ventilate since the hot exhaust fumes rise 

and accumulate in the upper face corner. Conversely, mining down 

grade enhances air quality as hot exhaust fumes rise and follow the 

roofline to the return entry. Fans blowing into a face with an upslope 

would have less efficiency as fans blowing downgrade into a face. 

Summary 

This paper discusses methods to improve the ventilation in largeopening mines such as utilizing mine planning layouts that use long 

stone pillars along with using stoppings and auxiliary fans to direct 

airflow to the face areas. The use of long stone pillars is particularly 

effective in reducing leakage between intake airways and return 

airways, thus allowing the maximum amount of air produced by the 

main mine fan to reach the face area. Although, various factors can 

impact the effectiveness of the face ventilation, the best method to 

ventilate the face is to position an auxiliary fan outby the last open 

crosscut, in the furthest upstream entry, such that it blows through the 

intake entry. Auxiliary fans blowing through an entry entrain 

considerably more air quantity than the actual rated air quantity of the 

fan. This entrainment leads to larger fresh air quantities moving 

toward the face. The fan should be positioned so all entrainment 

occurs in intake air. To reduce recirculation, the fan should also be 

located in the furthest upstream entry to create air movement that is 

moving in the same general direction as the air being moved by the 

main mine fan. Using this method, 57 pct of the available air reaching 

the last open crosscut was moved 120 m (400 ft) inby the last open 

crosscut. 
Figure 7. Air quality variations when mining up and down dip. 

Disclaimer 

The findings and conclusions in this report have not been formally 

disseminated by the National Institute for Occupational Safety and 

Health and should not be construed to represent any agency 

determination or policy. 

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