Methods to improve efficiency of mine 

ventilation systems
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C. Pritchard 

National Institute for Occupational Safety and Health (NIOSH), 

Spokane Research Laboratory (SRL), Spokane, Washington
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Introduction 

John Marks said in his acceptance of the Hartman Award 

in 2008, “I guess that without the occasional complaint, your 

mine is probably over-ventilated” (Marks, 2008). Miners are 

seldom in this situation and spend much of the time trying to 

find enough air to keep an operation running. With examination, there are usually changes that can be made to increase 

the efficiency of ventilation systems. Mine ventilation air is 

a costly commodity, especially by the time it has been heated 

or cooled and moved to the bottom of the shaft and through 

the mine airways. Modifications that result in surplus mine 

ventilationair couldbringfinancial andenvironmentalbenefits.

Some issues mine operators have needed to address recently 

are increased airflow requirements to dilute diesel particulates 

in metal and nonmetal mines, to ventilate reserves that are 

deeper, hotter, and further away from fans and shafts, and to 

meetdemands fromincreasedproduction.Thispaperdiscusses 

successful methods to find additional usable air when there is 

no extra ventilation capacity. Most of the options presented in 

this paper are useful for metal/ nonmetal operations but some 

may be applicable to coal as well. 

Options for improvement. Areas that can be exploited to 

improve mine airflow are shop ventilation methods, auxiliary 

equipment areas, dedicated intakes and returns, optimizing 

mine development, examination of mine airway utilization 

and alternative ventilation methods. 

Underground shops

First, examine what is being done with the underground 

shop air. If it is being coursed directly to the returns, there 

may be potential to better utilize this relatively contaminantfree air. MSHA regulations in 30 CFR 57.4761 (1) allow the 

following options: 

To confine or prevent the spread of toxic gases from a fire 

originating in an underground shop where maintenance work 

is routinely done on mobile equipment, one of the following 

measures shall be taken: use of control doors or bulkheads, 

routing of the mine shop air directly to an exhaust system, 

reversal of mechanical ventilation, or use of an automatic fire 

suppression system in conjunction with an alternate escape 

route. The alternative used shall at all times provide at least 

the same degree of safety as control doors or bulkheads. 

Discussion. Thisregulationgives operatorssomeflexibility 

in ventilating underground shop facilities. If shop air is coursed 

through the work area and directly to the mine return, the question should be asked: is the quality of air good enough to be 

reused in the mine, and if so, what are the risks? Can the risks 

be accommodated and managed to accomplish the change? 

If so, a considerable increase in mine level airflow could be 

attained by reusing shop air.

Regulations set a minimum standard that can be exceeded. 

Metal/nonmetalmine regulations arenot asspecific as coal,due 

to the multitude of different mining methods and conditions 

utilized. Risks must be thoroughly examined and addressed 

to assure a safe environment. 

Issues. Determine what contaminants are being produced 

in the work area – welding fumes, diesel exhaust, paint fumes, 

chemicals, lubricants, hydrogen from battery chargers and 

solvents, etc. The mine operator should survey the area and 

determine exposures. In 30 CFR 57.5002 (1), MSHA requires 

exposure monitoring of dust, gases, mists and fumes to assure 

air quality is being met. Surveys need to be performed and 

existing data examined to quantify personal and area concentrations of contaminants. Often there is adequate circulation to 

maintain low exposure levels in shop work areas. When shop 

air is returned to the intake system, any contaminants would 

be further diluted downstream. 

Also consider the shop work schedule. If the shop works 

the day shift, there may be no activity or source of contamination to affect the ventilation system on the other two shifts 

and the weekend. 

A shop fire would be the worst-case planning scenario. 
The operator must study potential fire scenarios and simulate 

how this would affect the mine and shop area. MSHA regulations require an escape route and a fire suppression system be 

installed and maintained as follows in 30 CFR 57.4671 (1): 

(d) Automatic fire suppression system and escape route. If 

used as an alternative, the automatic fire suppression system 

and alternate escape route shall meet the following requirements: (1) The suppression system shall be--(d)(1)(i) Located 

in the shop area;(d)(1)(ii) The appropriate size and type for 

the particular fire hazards involved; and (d)(1)(iii) Inspected 

at weekly intervals and properly maintained. (2) The escape 

route shall bypass the shop area so that the route will not be 

affected by a fire in the shop area. 

Case study. In an underground room and pillar mine, active mine workings were advancing away from the mine shaft 

with deteriorated return airways and leakage had a negative 

effect on ventilation airflows to the face. Mine level airflows 

were 236 m3/s (500,000 cfm) and shop airflows were 24 m3/s

(50,000 cfm) (Fig. 1A). No additional capacity was available 

at the main surface fan. A solution was to ventilate the shop, 

then send the air on to the mine production areas instead of 

directly to the return.

Data on shop air quality and exposures from many years of 

operation was examined and no overexposures were discovered. A risk analysis determined that moving forward with a 

shop air reuse program was desirable. A ventilation plan was 

developedandanalyzedandadecisiontoproceedwas approved 

by mine management.

The ventilation change was simulated on the computer with 

the United States Bureau of Mines / Michigan Tech MFire 

program before implementation. This simulation included developing fire scenarios to examine potential exposures to inby 

mining sections and planning escape routes. An atmospheric 

monitoring system was designed and installed in cooperation 

with the U.S. Bureau of Mines to monitor carbon monoxide 

levels at three locations: in the shop intake, at the end of the 

shop bay and at the mixing point of the shop and east mine 

intake split.

In addition, a sprinkler system was installed in the shop 

work bay fed from the mine fresh water line with thermal links 

to actuate sprays. The system was designed per National Fire 

ProtectionAssociationstandardsonpressure,flowandsprinkler 

spacing. System water pressure was monitored and checked 

on a weekly basis. The north shop return regulator was closed 

off by a stopping with an access mandoor. Airflow through the 

shop battery charging station was isolated and sent directly out 

of the mine as required by state law, utilizing 4.7 m3/s (10,000 

cfm). The existing shop access drive-through door was opened 

to let intake air flow through the shop, effectively reversing 

airflow direction, which re-joined the main intake split further 

inby the shop (Fig. 1B). 

Figure1 —Casestudy:reusingshopairformineventilation. 

A: original shop airflow. B: intake air flows through shop. 

Result. Ofthe24m3/s(50,000cfm)of airpreviouslyutilized 

in the shop, 19 m3/s (40,000 cfm) were saved and sent to the 

mine production areas. Actual shop airflow volume increased 

from 24 to 38 m3/s (50,000 to 80,000 cfm) when the shop 

was opened up as a parallel intake, providing a more efficient 

route for intake air. 

Auxiliary equipment stations

Examine where dead end stub worker lunch rooms, compressors, pump stations, etc., need to be specially ventilated by 

cutting a hole or regulator into the stopping. Because all such 

facilities require ventilation, it is necessary to plan efficiently. 

When these auxiliary facilities need to be ventilated and the 

main travelway next to the facility has available air, one option 

is to redirect a parallel split of travelway air to ventilate the 

auxiliary station instead of venting directly into the return.

This may be accomplished by an auxiliary fan and ducting, 

either blowing (Fig. 2) or exhausting, to ventilate the back end 

of the drift and send the exhaust air from the crosscut back into 

the travelway. A wing curtain can also be used, but this often 

blocks access for inspection or maintenance. If left on, a small 

auxiliary fan will require continuous power. Should 9.4 m3/s

(20,000cfm)of airbe ventedtothe return andsystem efficiency 

is 50%, 19 m3/s (40,000 cfm) of air is saved at the main fan, 

more than compensating for the additional power use.

Should fire be a concern at the installation, an effective 

fire sensor system should be installed and provisions made 

to automatically stop the fan and open a regulator at the back 

end if activated. This would prevent fumes from entering the 

intake airway or escapeway. 
Figure 2 – Increasing mine ventilation by efficiently 

venting auxiliary equipment stations.
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Mine operators may have concerns about the heat being put 

back into the mine intake system. Many auxiliary facilities can 

be located where face or district cooling is not a concern. Often, 

heated or cooled air reverts back to natural rock temperature 

after a short distance, not affecting face air quality. 

Case study.Whileplanningfor anewlongwallblock,provisions needed to be made for ventilating the longwall hydraulic 

pump bank and compressor station. Similar situations in the 

past had required 14 m3/s (30,000 cfm) for each installation, 

depending on the panel layout. In the previous longwall block, 

the compressor was placed next to the secondary travelway, not 

back against the stopping. Travelway flowby air was utilitzed 

for cooling instead of sending air to the return, saving 14 m3/s

(30,000 cfm). The new area was a semi-permanent installation 

of four longwall panels. Both pump and compressor installations were planned by management to be installed in separate 

crosscuts against the stopping, requiring ventilating air to go 

directly to the returns. Longwall district airflow requirements 

were: 94 m3/s (200,000 cfm) for the longwall, 57 m3/s (120,000 

cfm) for two development sections and 14 m3/s (30,000 cfm) 

for a setup panel, totaling 165 m3/s (350,000 cfm). Available 

ventilation intake air would be 189m3/s (400,000 cfm). Resources would be stretched to handle the additional 28 m3/s

(60,000 cfm) of air for two auxiliary facilities, with no allowance for unplanned system problems.

Upon investigation, and utilizing previous operating experience with the compressor station, the operator decided to 

modify the auxiliary installations to allow placement adjacent 

to the travelway. This utilized flow-by intake air for cooling 

and minimized the air diverted to the return. A regulator was 

installed at the back of each facility, but only 2.3 m3/s (5,000 

cfm) of air was coursed to the return in each case. This saved 

around 23 m3/s (50,000 cfm) of the 28 m3/s (60,000 cfm), 

and illustrates the importance of involving ventilation in the 

mine planning process and carefully monitoring the ventilation 

system to avoid any inefficiency. 

Figure 3 — Case study: eliminating stoppings 

by not mining crosscuts. 

Figure 4 — Case study: poor ground 

conditions at a trona mine. 

Mine planning and system analysis

Discussion. Althoughbetterutilizationofshopandauxiliary 

equipment air are the two most important methods for finding 

additional mine air, other short- and long-term options are also 

available for system improvement. 

Eliminating stoppings through long pillars. Every installed ventilation control structure leaks and will deteriorate 

over time, depending on ground stability. Leakage is best minimizedbyreducingthenumberofventilationstructures.Thiscan 

be accomplishedbylengtheningthedistancebetweencrosscuts 

to minimize the number of stoppings per unit of development 

(Grau and Krog, 2008). Much of this process depends on the 

mining equipment used and the number of entries and cable 

lengths, among other factors. Ventilation planners should work 

with mine production planners to maximize crosscut length. 

This will also save ventilation material and installation costs, 

and may reduce the number of belt and power moves. The 

operator must ensure that the auxiliary ventilation system can 

handle the increased distance to provide adequate face airflow. 

Case studies. Crosscut spacing was increased from 30 

to 37 m (100 to 120 ft), saving eight stoppings in a 1,500-m 

(5,000-ft) panel. Installation costs were reduced by $6,400 

and leakage was reduced by 1.8 m3/s (4,000 cfm) per panel. 

This reduction was especially helpful as ground deterioration 

took a toll on stoppings and required extensive resealing and 

maintenance over time. Changes were also required to the mine 
roof control plan to implement this change.

In a variation on the above concept, the intake and returns 

in a six-entry main development section were mined separately 

for three breaks then connected, saving two stoppings per three 

crosscuts (Fig. 3). This eliminated 32 stoppings in 1,500 m 

(5,000 ft) of development based on 33-m (100-ft) crosscut 

centers. Ultimately, when these entries were utilized as mains, 

ventilation savings were 13.8 m3/s (30,000 cfm). 

Long-termdevelopmentoptions.Long-termairwaysmust 

be planned to maximize efficiency. Efficiency is especially 

challenging when ground conditions are difficult, requiring 

considerable ventilation structure maintenance to minimize 

leakage. 

Case study. Poor ground conditions required utilization of 

yield pillars for ground control at a trona mine. The floor had 

heaved, the roof sheared and sagged, and the ribs had failed, 

causing stoppings to deteriorate and increasing leakage. Where 

high-extraction mining approached, higher pillar loading 

would intensify ground movement, causing further leakage 

and decreasing the entry opening area for airflow, resulting in 

significant impact to the ventilation system (Fig. 4).

A solution to the problem was to turn the original main developments (Fig. 5A) into dedicated intake or return airways, 

away from high extraction mining. The main intake was in the 

center of the orebody and two remote dedicated returns were 

mined parallel north and south, remote from extractive mining as shown in Fig. 5B. This eliminated or greatly reduced 

the amount of stoppings required and stabilized airways to 

minimize floor heave, which reduced loss of airway area and 

maximized district airflow. 

Figure 5 — Case study: repurposing existing 

airways. A: original main development. B: Dedicated intake/returns. 

Day-to-day system examination/ optimization

Regularlyexamineventilationsystemutilizationandanalyze 

overall efficiency as a mine expands or changes. Operational

prioritiesmayalso changeovertime, andthe original efficiency 

goals are lost.

The key to mine ventilation is having adequate cross sectional area to support the required airflow. Air pressure and 

fan power required is proportional to velocity squared, so the 

economic goal is to minimize velocity. Some airways may be 

better utilized by changing “gender” – from intake to return 

or vice versa. 

The operator should consider if some of the old returns 

could be opened to intake for better utilization. When intake 

velocitiesareloweredthereislessdustgeneratedfromconveyor 

belts, haulage and travelways. To determine if the change is 

beneficial,theoperator should verifyassumptionsbycomputer 

modeling simulations. If favorable, the change should be fieldtested by temporarily isolating the old return with curtains and 

measuring the difference related to inby airflow. If there is no 

significant difference, the return should be opened up to the 

intake. The change will probably reduce leakage, too, which 

may make up for the increased system resistance. 

Case studies. Longwall block mains were developed in a 

mine with three center intakes and three returns, two west and 

one east (Fig. 6).

Figure 6 – Case study: main entry optimization. 

 Three intakes would be adequate for ventilation and would allow dual parallel travelways, one on each 

side of the belt entry. Returns on both sides were necessary for 

ventilating developments off each side as the mains advanced. 
As identifiedbymine planning, whenthe longwall movedinby, 

the east return would be changed to intake, allowing increased 

intake capacitynecessaryforfuture longwallmining.Longwall 

return air would be routed away from the mains so that the 

required return capacity would be less. A long stopping line 

would be eliminated by stopping off the ends and opening to 

intake, preventing about 9.4 m3/s (20,000 cfm) leakage and 

increasing intake airflow capacity.

Next, underutilized airways were examined. Further outby 

inanolderdevelopment, a return carried9.4m3/s(20,000 cfm). 

If taken out of the return circuit, it would have no negative 

effect on airflows inby. The intake airways next to this return 

had high velocities and pressure losses coming from the main 

shaft. Opening up this underutilized return to intake lowered 

system resistance, increased main fan airflow, and lowered 

total system leakage due to reduced pressure differentials. 

Changes to intake and return airways should be made with 

consideration of mine escapeways and the existing emergency 

plan for ventilation and evacuation routes. 

Think outside of the box. It is essential to conduct an 

in-depth analysis of the ventilation system—doing so has big 

payoffs in air quality for miners and in cost savings for the 

operation.

Consider a booster fan installation if certain areas are difficult to ventilate. A little extra horsepower in the right place 

can make a big difference and is a lot less costly than increasing 

power at a main fan.

Another possibility is controlled district recirculation. 

(Pritchard, 1995; Robinson, 1989) Often the air quality in the 

mine return is equivalent to or better than that of the intake. 

Mine returns can act as a big “bag house” system by helping 

dust settle out. Even diesel particulate matter settles out in 

time. Contaminants from face areas are also diluted by leakage. Reheating of this “saved” air is not necessary because it 

is already at rock temperature, resulting in additional energy 

savings. Blasting fumes, cooling requirements, and methane 

may complicate this option in some mines.

The main fan may be operating at low pressure and not at 

maximum efficiency. The fan manufacturer may be able to 

modify the fan by deblading or removing fan blades (Loring, 

2007), which can significantly improve efficiency, especially 

at high altitudes.

With multiple main mine fans the ventilation system gets 

increasingly complex and behavior is not always as expected. 

It is possible that multiple fans work against one another. In 

one instance, when one of a mine’s three main fans had a blade 

pitch reduction, total mine airflow went down but mine section airflow went up. It increased because the fans no longer 

had to “fight” each other, causing the overall mine pressure 

differential to go down and reducing leakage. Operating cost 

was reduced and airflow to the working areas went up – a 

surprising yet beneficial outcome.

The operator should always look to flexibility in mine 

ventilation, including applying Ventilation on Demand (VOD) 

principles. VOD is designed to apply air where it is needed and 

when it is needed, instead of maintaining fixed airflow quantities at all times. Considerable air quality and flow monitoring 

and control equipment is available on the market and should 

be used to create a more efficient and economical ventilation 

system (Allen and Keen, 2008). A flexible ventilation system 

is a win-win for production and safety. 

Conclusion 

There are many things that can be done to improve airflow 

in the mine. Ventilation engineers must look around, inquire, 

measure and thoroughly understand the mine air flows and 

quality. Diluting contaminants and improving the working 

environment will result in a healthier, happier workforce and 

most likely in improved production and lower turnover. 

Several ways have been discussed to find more usable air 

when there is little additional ventilation capacity. If there is 

adequate air, one option is to implement some of these changes 

andreduceexpendituresthroughloweringoperatingcosts.Since 

airflow power is proportional to velocity cubed (Marx et al., 

2008), a fan blade setting reduction can result in significant 

savings. Also, saved air quantity does not have to be heated 

or cooled (Hall, 1985).

The operator should always consider the entire ventilation 

system and develop and utilize a good computer model. All 

systemchanges have consequences,sotheventilationengineer 

should perform a risk analysis and determine the effects on 

emergency and evacuation planning. 

References 

Allen, C., and Keen, B., 2008, “Ventilation on demand (VOD) project – Vale Inco 

Ltd. Coleman Mine,” 12th US/North American Mine Ventilation Symposium, 

Reno, NV. 

Grau,R.,andKrog,R.,2008,“Usingmineplanningandothertechniquestoimprove 

ventilation in large-opening mines,” SME Annual Meeting, Salt Lake City, UT. 

Hall, A. E., 1985, “The use of recirculation ventilation to conserve energy,” 2nd 

US Mine Ventilation Symposium, Reno, NV. 

Loring, D., 2007, “Development of a tool to predict performance of debladed 

mine fans at Henderson Mine,” SME Annual Meeting, Denver, CO. 

Marks, J., 2008, “Acceptance speech, 2008 Howard Hartman Award,” 12th US/ 

North American Mine Ventilation Symposium, 2008, Reno, NV. 

Marx, W. M., Von Glehn, F.H., and Wilson, R.W., 2008, “Development of energy 

efficient mine ventilation and cooling systems,” Mine Ventilation of South 

Africa Society Journal, April/June, Vol. 16, pp. 5-9. 

Pritchard, C. J., 1995, “Preparatory work required for a long-term district recirculation test in a gassy underground metal non-metal mine,” Proceedings 

of the 7th US Mine Ventilation Symposium, Louisville, KY. 

Robinson, R., 1989, “The use of booster fans and recirculation systems for environmental control in British coal mines,” Proceedings of the Fourth Mine 

Ventilation Symposium, Berkeley, CA. 

U.S. Code of Regulations, 30 CFR Part 57, 2008.