STUDYING INTAKE AIRWAY PRESSURIZATION BY VENTILATION 

MODELING AND LEAKAGE EVALUATION 

Anu Martikainen, National Institute for Occupational Safety and Health, PRL, Pittsburgh, PA 

Charles Taylor, National Institute for Occupational Safety and Health, PRL, Pittsburgh, PA 

Roy Grau, National Institute for Occupational Safety and Health, PRL, Pittsburgh, PA 

Abstract 

Utilization of belt air in underground coal mines has 

been discussed extensively during the last decade. The Final 

Report of the Technical Study Panel on the Utilization of 

Belt Air and the Composition and Fire Retardant Properties 

of Belt Materials in Underground Coal Mining formed by 

the Miner Act of 2006 recommends research on leakage, 

use of booster fans, and escapeway safety. 

This paper discusses the role of ventilation modeling in 

evaluating primary escapeway pressurization in a threeentry development system to improve emergency escape in 

a coal mine using belt air. The intake entry of the NIOSH 

Bruceton Experimental Mine was pressurized using a 1.1 m 

(42 in) diameter, 37 kW (50 hp) fan. The work details air 

movement in the simulated three-entry system and the resulting leakage patterns. Three mine ventilation software 

packages were compared to analyze their performance in 

predicting the airflows and leakage conditions with different 

fan settings. NIOSH researchers found that the measurement results correlated well with the results of modeling. 

Introduction 

The MINER Act of 2006 (Public Law 109-236) established 

a Technical Study Panel on the Utilization of Belt Air and 

the Composition of Fire Retardant Properties of Belt Materials in Underground Coal Mines. The report published by 

the Panel in 2007 (Mutmansky et al, 2007) included recommendations to conduct research on improving escapeway 

design in various ventilation situations, reducing air leakage 

through ventilation controls, and use of booster fans in underground coal mining operations. This research primarily 

studies ventilation in intake airways that are adjacent to belt 

entries and provide intake air to the working section. The 

purpose of the research is to assure that workers can safely 

use the intake airway to escape a section in the event of a 

fire or other emergency in which hazardous contaminants 

are produced in the belt entry. The Panel recommended that 

research utilizing ventilation modeling, engineering design 

and risk analysis be performed. 

Leakage through stoppings from the belt entry to the 

intake escapeway endangers escaping miners. Escapeway 

safety can be improved by pressurizing the intake entry to 

prevent influx of contaminants from the belt entry. MSHA 

shares the Panel’s view that the primary escapeway should 

have a higher pressure than the belt entry (Federal Register, 

2008). 

The objective of this research is to evaluate the role of 

ventilation modeling as a tool for planning the pressurization of an intake entry. Ventilation models created with different software packages are compared to define their feasibility for planning and implementation as well as predicting 

the leakage and airflow directions in the intake and belt entries. Different intake airway pressurization scenarios are 

modeled and the performance of three software packages is 

evaluated based on the comparison of measurement and 

modeling results. 

Test site 

General 

The NIOSH Pittsburgh Research Laboratory Experimental 

Mine was used to evaluate pressurization of an intake entry 

in a three-entry system and provide data for validating 

simulation models. The experimental mine is part of a complex of mines used to support research for the development 

and evaluation of new health and safety interventions for 

mine workers (NIOSH, 2008). The Experimental Mine consists of multiple drift entries and cross cuts driven approximately 430 m (1400 ft) into the Pittsburgh coal seam (Figure 1). The cross-sectional area of the entries is roughly 2 m 

(7ft) high and 3 m (10 ft) wide. 

The ‘main entry’ of the mine was used as an intake, the 

‘air course’ was defined as a belt entry, and the ‘east air 

course’ acted as an exhaust. The east and west entries on the 

1 
sides are separated from the main entries with bulkheads. 

The mine is ventilated with one exhausting main fan, which 

circulates approximately 14 m3

/s (30,000 cfm) of air 

through the mine when operating on its highest setting. The 

main fan is located on top of a shaft in the end of the east air 

course as shown in Figure 1. 

Figure 1. Map of the PRL Bruceton Experimental Mine. 

Fan set-up 

The intake entry was pressurized for leakage testing using a 1.1 m (42 in) diameter, 37 kW (50 hp) fan shown in 

Figure 2. The maximum theoretical airflow based on the fan 

curve is 26.4 m3

/s (56,000 cfm). 

The fan is equipped with a variable frequency drive for 

easy control of the flow. Three fan settings were used in 

testing, high, medium, and low. The measured flows for 

these settings were 24 m3

/s (52,000 cfm), 16 m3/s (33,000 

cfm) and 12 m3

/s (26,000 cfm). The fan curve information 

showing all speed adjustments is presented in Figure 3. 

The fan was sized so that it could be installed freestanding close to the portal to provide a positive pressurization of the entire intake entry. Air recirculation around the 

fan was expected due to the lack of enclosure and a 1.1 m 

diameter (3.6 ft) regulator located at the end of the intake 

entry. Similar pressurization of the intake entry would have 

resulted from the installation of a smaller fan into a bulkhead. Bulkhead construction was not feasible in the Experimental Mine at this location due to access requirements 

inby the fan. 

The intake entry is separated from the other entries by 

stoppings and bulkheads. In the 430 m (1400 ft) entry the 

velocity pressure produced by the fan transforms into static 

pressure. 

Figure 2. Fan at the installation location.

2 
0

200

400

600

800

1000

1200

1400

1600

1800

2000

7 12 17 22 2

Q (m3/s)

p (Pa)

Figure 3. Fan curves for the free-standing fan.

7

Data Acquisition 

Ventilation survey 

Prior to the fan installation a ventilation survey was 

performed in the mine to define the airflows. The crosssectional areas were measured throughout the mine for 

planning purposes by taking three vertical and horizontal 

measurements. Several air velocity measurements were taken and the roughness of the walls was evaluated to estimate 

friction factors. Airflow directions and pressures were 

measured with the main fan only to evaluate leakage in the 

baseline operation situation. 

Airflow study 

Davis vane anemometers were used to measure air velocities at the locations A through G shown on Figure 4. 

Green arrows are used in the figure to determine airflow direction in the intake, blue arrows in the belt entry, and red 

arrows in the exhaust. 

Airflow measurements at each sampling location were 

made during each of four fan states, with only the main fan 

operating, and with the free-standing fan operating at three 

flow rates. Each air velocity measurement result was an average of two one-minute traverse readings, and the crosssectional areas were measured with high accuracy. A grid of 

1 ft was used for cross-sectional area measurements. Air velocity readings were taken simultaneously in the two entries 

to minimize the effect of the changing surface conditions 

and to ensure accurate results that can be used to compare 

the simulation models. 

Leakage study 

Leakage between the intake and belt entries was minimal due to thick, gunite-coated, concrete block stoppings 

constructed between the entries. Three pipes running 

through the stoppings (Locations 1, 2 and 4) were opened to 

act as leakage points (Figure 4). The leakage point at location 3 was a 0.5 m2

 (5.4 ft2) square hole in the stopping. 

Figure 4. Air velocity and leakage measurement 

locations. 

Plastic tubing was extended through the three metal 

pipes and one hole. These tubes were used for measuring 

pressure differentials across the stoppings. Numbers from 1 

to 4 and two-headed arrows are used to identify the leakage 

locations. 

Pressure differentials were measured with a DP-Calc

micromanometer with an accuracy of ±1 % of the reading 

or ±1 Pa (0.004 in wg) and a resolution of 0.1 Pa (0.0004 in 

wg). At each location the measurements were averaged over 

15 seconds. Airflow direction at each leakage location was 

confirmed using a smoke tube. 

3 
Ventilation modeling 

Modeling software 

Three different software packages referred to as Program A, Program B, and Program C were used in ventilation modeling. The input parameters required in these software packages differed from each other, so differences were 

expected in the results as well. 

Two of the software packages, Programs A and B, were 

based on incompressible flow and did not take into account 

thermodynamic behavior. One of the software packages, 

Program C takes into account thermodynamics and compressibility of airflow. 

Four scenarios were simulated with all three programs. 

The first scenario was the basic network model with main 

fan only, the other scenarios were fan on low, medium, and 

high setting, respectively. 

Baseline model 

The basic network model was created based on the information gathered by a ventilation survey prior to the installation of the free-standing fan. This model, created by 

Program A and validated by the measurement data, was 

used to size the fan. 

The challenges of the modeling included varying 

weather conditions affecting airflows in the mine and immeasurable changes in pressures due to the small size of the 

mine at the baseline situation. The Experimental Mine has 

three surface connections and due to the size of the mine the 

surface conditions affect the conditions underground, especially close to the portals. All tests were performed when 

the weather was rather stable with little temperature or wind 

variation. Also, the measurements were taken simultaneously in the intake and belt entries to minimize effects of 

weather changes. The temperature data was included in the 

input of Program C. Improved pressure analysis was 

achieved by acquiring a more accurate measurement instrument that was used throughout the rest of the study. 

Modeling expectations 

Pressurizing the intake was expected to result in increased airflow between the entries, as there was originally 

very little difference in the pressures of the simulated belt 

and intake entries. The air velocity in the intake and belt entries at the time of the ventilation survey was around 1 m/s 

(200 fpm). The fan was sized to provide approximately 2 

m/s (400 fpm) for the intake and 0.5 m/s (100 fpm) for the 

belt entry. The simulations showed that these values would 

result in pressurization of the intake all the way up to the 

simulated face. If the air velocity in the intake would have 

been above 2.5 m/s (500 fpm), the airflow direction in the 

belt entry would have changed based on modeling results. 

The minimum accepted air velocity in the belt entry is currently 0.5 m/s (100 fpm). 

Results 

Leakage study 

As previously noted, with only the main fan operating, 

the air velocities are very close in the two entries. The freestanding fan increased the air velocity in the intake as expected. In the belt entry the air velocity decreased. The lowest air velocities were measured in the belt entry with the 

fan on high. The opposite was true for the intake. The expected values in both the intake and belt entries agreed quite 

well with the measured values of 1.9 m/s and 0.6 m/s when 

the fan was on the high setting. The airflows calculated 

based on the measurement results are presented in Table 1. 

Table 1. Calculated airflows with and without the freestanding fan. 

Airflow (m3

/s)

Location 

Main fan 

only Fan low 

Fan 

medium Fan high 

A 7.3 8.6 10.9 11.8 

B 7.5 8.9 9.9 11.7 

C 7.9 9.4 10.0 11.8 

D 7.5 8.0 8.5 10.1 

E 6.4 5.8 4.9 3.9 

F 6.3 5.3 4.6 3.5 

G 5.7 4.9 4.4 3.4 

For the baseline condition, flow at all leakage locations 

was toward the intake, but the measured pressure differentials were small, ranging from 3.6 Pa (0.014 in wg) to 9.1 

Pa (0.037 in wg). This shows that the barometric pressures 

in the entries were almost identical without the effect of the 

free-standing fan. 

Using the low setting of the fan resulted in leakage towards the belt entry in locations 1 through 3, and leakage 

towards the intake in location 4. The medium and high settings pressurized the intake enough to cause the air to flow 

from intake to the belt entry in all four measurement locations. The smoke tube confirmed the airflow directions 

shown by the pressure readings. The measured pressure differentials and leakage directions are shown in Table 2. 

 

Table 2. Measured pressure differentials. 

P Pressure differential (Pa)

o

i

n

t 

Main fan 

only 

Fan 

low 

Fan 

medium 

Fan 

high 

1 3.6 to intake 11.5 to belt 47.9 to belt 98.4 to belt 

2 3.6 to intake 12.5 to belt 46.6 to belt 91.8 to belt 

3 4.9 to intake 6.5 to belt 43.1 to belt 92.3 to belt 

4 9.1 to intake 8.5 to intake 36.7 to belt 78.1 to belt 

4 
Comparison of mine data and computer simulation data 

The results of the modeling were compared with the 

four airflow measurements made in the intake and the three 

made in the belt entry. The compared model values and 

measurement values are referred to as value pairs. 

The baseline models created by Programs A, B, and C 

correlated well with the measured and calculated values. A 

comparison of the measurement information and network 

model values is shown in Table 3. Most of the model values 

are within 5 % of the airflow values calculated from the 

measurement results. Out of all of the simulated scenarios, 

all three programs gave their best performance with the 

baseline. 

A leakage recirculation branch (Figure 5) was added to 

every fan scenario to enable simulation of recirculation 

around the free-standing fan with each of the different settings. Measurements were taken at the fan outlet and 30 ft 

downstream from the fan in order to define the amount of 

recirculation around the fan. The recirculation with the 

highest fan setting was about 50 %, with the medium setting 

about 40 % and with the low setting only 25 %. This information was used in modeling. 

Figure 5. A close-up of a ventilation network showing 

airflows, fans, recirculation branch and leakage location 1. 

Concerning the other three fan scenarios, all three programs showed more fluctuation compared with the baseline. 

The difference between the simulated and calculated values 

is shown in Tables 4-6 as a percentage. 

For each fan scenario Program A had four out of seven 

measured values within 5 % of the calculated values, and 

over 75 % of compared values were within 10 % overall. 

However, two of the simulated values were over 20 % different from the calculated values. 

Program B performed better with the low and medium 

fan settings where five out of seven sample locations had 

calculated values within 5 % of simulated values. At the 

high fan setting, however, only three out of seven values 

were within 5 % of each other. At the 10 % comparison level, Program B showed a marked decrease in performance as 

the fan speed increased. There were seven out of seven, six 

out of seven, and five out of seven value pairs within 10 % 

of each other for the low, medium and high fan settings, respectively. For Program B, the only value pair not within 20 

% was found with the high fan setting. 

Program C gave the same results as Program A for the 

low and medium fan settings, each with four out of seven 

value pairs being within 5 %. At the high setting the results 

were the same as with Program B, three out of seven within 

5 %. However, Program C had seven out of seven comparisons within 10 % with the fan set on low (Table 4, Figure 6) 

and five out of seven with the fan set on medium. On the 

high setting, Program C had six out of seven occasions 

when the calculated values were within 10 % of the simulated values (Figure 5, Table 6). Out of all three programs, 

Program C was the only one that had no results where the 

calculated and simulated values were greater than 20 % different. In fact, the greatest difference was found on the medium fan setting and was only 14.0 %. These results showed 

that Program C was more consistent than the other programs. 

Even if Program A did not perform as well as Program 

B in giving comparison values with the fan scenarios, it 

gave a good estimate of the functionality of the fan in installation planning. Air velocity values aimed for realized quite 

well with the high setting of the fan (Table 1). 

Discussion 

The free-standing fan increased the total airflow, 

changed the pressure balance of the entries, and changed the 

direction of the leakage flows towards the belt entry in 

every leakage location with the medium and high fan settings. The pressure differentials of up to almost 100 Pa with 

the high setting of the fan resulted in a properly pressurized 

escapeway with no risk of contaminant leakage from the 

belt entry. 

5 
 

6 

Table 3. Computer simulation comparison – Baseline

Location Program A Program B Program C 

Airflow (m3

/s) Difference (%) Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%)

A 7.5 2.3 7.62 3.8 7.7 4.8 

B 7.5 0.4 7.58 1.5 7.5 0.4 

C 7.5 -4.7 7.59 -3.4 7.5 -4.7 

D 7.6 1.8 7.79 4.2 7.8 4.3 

E 6.6 2.7 6.55 1.9 6.3 -1.9 

F 6.3 -0.2 6.19 -2.0 5.9 -7.0 

G 6.2 7.4 6.21 7.6 5.8 1.0 

Table 4. Computer simulation comparison – Fan on low setting 

Location Program A Program B Program C 

Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%)

A 8.9 3.7 8.95 4.2 8.9 3.7 

B 8.6 -3.5 8.67 -2.7 8.8 -1.2 

C 8.5 -11.0 8.60 -9.7 8.7 -8.5 

D 6.3 -27.1 7.93 -1.0 8.1 1.1 

E 5.6 -3.7 5.53 -5.0 5.3 -9.6 

F 5.3 -0.1 5.24 -1.2 5.0 -6.1 

G 5.4 10.0 5.33 8.8 5.0 2.8 

Figure 6. An example of the mine ventilation network with fan on low, Program C. 
Table 5. Computer simulation comparison – Fan on medium setting 

Location Program A Program B Program C 

Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%)

A 10.8 -0.7 10.41 -4.5 10.5 -3.6 

B 10.4 4.7 10.02 1.1 10.2 2.8 

C 10.4 3.6 9.89 -1.4 10.2 1.7 

D 7.1 -19.2 8.45 -0.1 8.7 2.7 

E 4.4 -11.0 4.37 -11.8 4.3 -13.6 

F 4.3 -6.0 4.26 -7.0 4.0 -14.0 

G 4.4 0.5 4.35 -0.7 4.1 -6.8 

Table 6. Computer simulation comparison – Fan on high setting 

Location Program A Program B Program C 

Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%) Airflow (m3/s) Difference (%)

A 11.7 -1.2 11.92 0.6 11.6 -2.1 

B 11.3 -3.8 11.45 -2.4 11.3 -3.8 

C 11.2 -5.5 11.23 -5.2 11.2 -5.5 

D 8.2 -22.6 9.14 -10.0 9.3 -8.1 

E 3.7 -6.4 3.24 -21.5 3.5 -12.5 

F 3.5 -1.0 3.25 -8.8 3.3 -7.2 

G 3.5 3.5 3.38 0.1 3.5 3.5 

Intake entry pressurization as described in this paper 

can be achieved in an operational mine to improve escapeway safety. A main fan or a free-standing fan can be 

used to pressurize the intake entry, depending on where 

the use of one is applicable. Future research will include 

feasibility evaluation for installing a pressurizing fan for 

emergency use only. 

Buoyancy induced by fire affects airflows and may 

change leakage directions. Evaluation of buoyancy effects 

would require a fire simulation. This would be beneficial 

in defining the pressurization requirements of an intake in 

an operational mine. 

Conclusions 

The fan operation was well predicted by the simulations prior to installation. The air velocities in the entries 

as well as leakage directions changed as expected based 

on the simulation results. 

Ventilation modeling with three different simulation 

software packages provided similar results in the case of 

the baseline model. The programs performed well at the 

baseline, giving results within 5 % of the airflows observed in the mine. The other fan scenarios were further 

off from the measurement results, but still most simulated 

values fell within 10 %. 

All three software packages were able to predict the 

pressurization of the intake entry with a reasonably good 

accuracy. In this case a small mine, in which surface conditions affect the conditions inside the mine, was analyzed. Program C, with the thermodynamic input, was 

considered to have performed best, as its results were the 

most consistent with the calculated values. 

The software packages mostly underestimated the 

airflow in comparison with the measured values in the fan 

scenarios. This is an advantage as slightly higher pressurization than planned was acquired in this application 

and might act as a safety factor in future ventilation planning exercises. 

Based on the underground study and modeling it can 

be concluded that ventilation modeling software can be 

used as a tool for planning to study intake airway pressurization and leakage directions with good accuracy. In 

the future a larger network with more complicated structures will be modeled and optimal locations for underground fans will be sought. Also, pressure differentials 

and contamination outby the fan will be studied in the larger network. 

Acknowledgements 

The authors would like to recognize and thank Paul 

Stefko, Joseph Sabo, Jack Teatino, Heather Dougherty, 

and Andrew Mazzella (all from NIOSH) for their valuable 

assistance during the set up and conduct of the tests at the 

NIOSH Experimental Mine. The authors also thank Pro7 
fessor Andrzej Wala from the University of Kentucky for 

his help and support with ventilation modeling. 

Disclaimer 

The findings and conclusions in this manuscript are 

those of the authors and do not necessarily represent the 

views of the National Institute for Occupational Safety 

and Health (NIOSH). Mention of any company or product does not constitute endorsement by NIOSH. 

References 

1. Federal Register, (2008), “Flame-Resistant Conveyor 

Belt, Fire Prevention and Detection, and Use of Air 

from the Belt Entry; Final Rule” Mine Safety and 

Health Administration 30 CFR Parts 6, 14, 18, et al., 

http://www.msha.gov/REGS/FEDREG/FINAL/2008f

inl/E8-30639.pdf. 

2. Mutmansky, Jan M., Brune, Jürgen F., Calizaya, Felipe, Mucho, Thomas P., Tien, Jerry C., and James L. 

Weeks, (2007), “Final report of the technical study 

panel on the utilization of the belt air and the composition and fire retardant properties of belt materials in 

underground coal mining”, December, 132 pp. 

3. National Institute for Occupational Safety and 

Health, (2008), “NIOSH Mining Facility; Safety Research and Experimental Coal Mines”, 

http://www.cdc.gov/niosh/mining/aboutus/facilitydet

ails1.htm

4. Public Law 109-236, (2006), Mine Improvement and 

New Emergency Response Act of 2006, (MINER 

Act). 

8