METHODS TO IMPROVE MINE VENTILATION SYSTEM EFFICIENCY 

C. Pritchard, NIOSH, Spokane, WA 

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 

often spend much of the time trying to find enough air to keep the 

operation running. With examination there are some things that can be 

done to make the best use of ventilation systems. Should there be 

surplus air, in which some of these options may result - financial and 

other benefits can be obtained. 

Some of the issues mine operators have needed to address 

recently are increased airflow requirements to dilute diesel particulates 

in metal and non-metal mines. Also, operations are faced with 

demands from reserves that are deeper, hotter and further away from 

fans and shafts, not to mention increased production demands. 

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. 

Most of the options presented in this paper are useful for metal 

non-metal operations but some may be applicable to coal too. 

OPTIONS FOR IMPROVEMENT 

Some of the areas to be addressed are shop ventilation methods, 

auxiliary equipment areas, dedicated intakes and returns, optimizing 

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 some potential 

to better utilize this, in most cases, relatively contaminant free air. 

Research the legal options for ventilating mine shops. 

MSHA regulations in 30CFR 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 

This regulation gives some operators flexibility in ventilating 

underground shop facilities. If shop air is to be coursed through the 

work area, and then 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. 

Clearly, regulations are a minimum standard, and can be 

exceeded. Metal non-metal mine regulations are not as specific 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 and 

solvents, etc. Survey the area and determine exposures. MSHA 

requires exposure monitoring in 30 CFR 57.5002 (1) of dust, gasses 

mists and fumes to assure air quality is being met. Perform surveys 

and examine existing data to quantify personal and area 

concentrations of contaminants. Often there is adequate circulation 

such that exposure levels in shop work areas are low. After sending 

shop air back into the system any contaminants would be further 

lowered by dilution with other mine intake air downstream. 

Look at the shop work schedule. If only on day shift, the other two 

shifts and possibly weekends have no activity or source of 

contamination to affect the ventilation system. 

The worst case planning scenario would be a shop fire. Study 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 further away from the mine shaft with deteriorated 

returns and leakage having 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) (see Figure 1A). No additional 

capacity was available at the main surface fan. A solution was to utilize 

the shop air then send it to the mine areas instead of directly to the 

return. 

Considerable information on shop air quality and exposures from 

many years of operation was examined and no negative data was 

discovered. A risk analysis determined that moving forward with a shop 

air reuse program was desirable. A plan was developed, analyzed and 

decision to proceed approved by mine management. 

The change was simulated on the computer with the USBM/MTU 

MFire program before being implemented. This included utilizing fire 

scenarios to examine potential exposures to inby mining sections and 

plan escape routes. A monitoring system was designed and installed in 

cooperation with the US Bureau of Mines to monitor carbon monoxide 
levels at three locations: in the shop intake, end of the shop bay and at 

the mixing point of the shop and east mine intake split. 

Figure 1. A & B Shop Ventilation. 

Additional work done to accomplish the change was to install a 

sprinkler system to the shop bay from the mine fresh water line with 

thermal links to actuate sprays. Considerable work was done designing 

the system per NFPA standards on pressure, flow and sprinkler 

spacing. System water pressure was monitored and checked on a 

weekly basis. The north shop return to the regulator was closed off by 

a stopping with 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 door was opened to let intake air flow through the shop, 

effectively reversing airflow direction, then joining the main intake split 

further inby the shop (see Figure 1B). 

Result 

Of the 24 m3

/s (50,000 cfm) previously utilized in the shop, 19 

m3

/s (40,000 cfm) was 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 opened up as a parallel intake, providing a more 

efficient route for intake air to flow. 

AUXILIARY EQUIPMENT STATIONS 

Another area to examine is where miners install equipment in a 

crosscut and knock a hole/regulator in the stopping for ventilation. This 

airflow loss includes worker lunch rooms, compressors, pump stations, 

etc. All mine facilities need ventilation, it is how that is best 

accomplished is in question. 

Often auxiliary facilities need to be ventilated, and the main

travelway right next to the facility has plenty of available air. An option 

is to utilize a split of travelway air to accomplish the task instead of 

sending it directly into the return. 

This may be done by the use of an auxiliary fan and ducting, 

either blowing (shown Figure 2) or exhausting can ventilate the back 

end of the drift and send the warm air out of the crosscut to the 

travelway. A wing curtain can also do this, but often blocks access for 

inspection or maintenance. Although a fan will require continuous 

power, if 9.4 m3

/s (20,000 cfm) is otherwise vented to the return and 

system efficiency is 50%, this saves 19 m3

/s 40,000 cfm at the main 

fan! 

Figure 2. Auxiliary Equipment Ventilation. 

Should fire be a concern at the installation, a thermal or carbon 

monoxide sensor could be installed and provisions made to 

automatically stop the fan and open a regulator at the back end should 

it be activated. This would prevent fumes from entering the intake 

airway or escapeway. 

What about the heat being put back into the mine intake system? 

In some applications this is an important consideration if mine cooling 

is involved. Many auxiliary facilities can be situated in a place not of 

concern to face or district cooling. Looking at most mines, heat or 

cooling source air has damped back to natural rock temperatures in a 

short distance. The effect of the source is localized. Think of a room 

and pillar system as a big heat sink at rock temperature. 

Case Study 

While planning for a longwall block, the subject of ventilating the 

longwall hydraulic pump bank and compressor station came up. In the 

past this required 14 m3

/s (30,000 cfm) for each installation depending 

on the panel layout. In the previous longwall block the situation was 

brought to management’s attention and the compressor was placed 

next to the secondary travelway and not back against the stopping, 

utilizing travelway flowby air for cooling instead of sending air to the 

return, saving 14 m3

/s (30,000) cfm. The new block was a semipermanent installation for four longwall panels and both pumps and 

compressors were going to be installed in separate crosscuts up 

against the stopping, requiring cooling ventilation directly to the 

returns. Since this was 8 miles from the shaft at the end of the 

ventilation circuit it was pointed out during the planning meeting the 

ventilation system could not afford loosing 28 m3

/s (60,000 cfm) here. 

The longwall district airflow requirements were: 94 m3

/s (200,000 

cfm) longwall, and 57 m3

/s (120,000 cfm) for two development sections 

plus 14 m3

/s (30,000) cfm for a setup panel, totaling 165 m3/s (350,000 

cfm). Ventilation intake air available would be 189m3

/s (400,000 cfm). 

Resources would be stretched to handle the additional 28 m3

/s (60,000 

cfm) for two auxiliary facilities. 

Plans were drawn up to modify the auxiliary installations to allow 

placement adjacent to the travelway to utilize flow-by intake air for 

cooling and minimize air wasted to the return. A regulator was installed 

at the back end of each facility but utilized at a reduced rate of 2.3 m3

/s 

each (5,000 cfm).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 remaining vigilant. 

MINE PLANNING AND SYSTEM ANALYSIS 

Discussion 

Better utilization of shop and auxiliary equipment air are the two 

big hitters in finding additional air for the mine. Other options are also 

available to make mine airflow more efficient short and long term. 
Eliminating Stoppings through Long Pillars 

Every installed ventilation structure leaks, and will also deteriorate 

over time depending on ground movement and stability. The best 

solution is to minimize the number of ventilation structures and 

resultant leakage by having less. This can be aided by lengthening 

crosscuts to minimize stoppings per unit of development (Grau et al 

2008). Much of this depends on the mining equipment used, number of 

entries and cable lengths, etc. Work with mine production to maximize 

crosscut length. This will also save ventilation material cost, and 

possibly reduce the number of belt and power moves. Make sure the 

auxiliary ventilation system can handle the increased distahce to 

provide adequate face airflow. 

Case Studies 

Crosscuts spacing was increased from 30 to 37m (100 to 120 ft), 

saving 8 stoppings in a 1500m (5000 ft) panel. Installation costs and 

leakage were reduced. This 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 to the above concept, a multi entry mains 

development intake and returns were mined separately for three 

breaks, then connected, with only one of three crosscuts mined 

through between the two, saving two stoppings per three crosscuts. 

This eliminated 32 stoppings in 1500m (5000 ft) based on 33m (100 ft) 

crosscut centers! (See Figure 3) 

Figure 3. Eliminating Stoppings by Not Mining Crosscuts. 

Long term development options 

Long term airways need to be planned to maximize efficiency. 

That goal is challenging if ground conditions are difficult, requiring

considerable ventilation structure maintenance or the location of main 

intake and returns are next to each other, continually leaking. 

Case Study 

A trona mine’s difficult ground conditions utilized yield pillars for 

ground control. Floor heaved, roof sheared and sagged, and ribs 

failed, causing stoppings to deteriorate, increasing leakage. Anytime 

high extraction mining occurred nearby, the higher pillar loading would 

intensify ground movement, further causing leakage and decreasing 

the entry opening area for airflow, a terrible combination (see Figure 

4). 

Figure 4. Poor Ground Conditions. 

Solution: original main developments (see Figure 5A) were 

ultimately turned into dedicated intake or return airways, away from 

high extraction mining,. This eliminated or greatly reduced the amount 

of stoppings and stabilized airways to minimize floor heave which 

reduced loss of airway area and maximized district airflow. 

Figure 5. Dedicated Intake/Returns. 

The main intake was up the center of the orebody and two 

dedicated returns/bleeders were mined parallel north and south, 

remote from extractive mining (see Figure 5B). This eliminated many 

leaking stoppings and isolated areas from high extraction mining which 

minimized floor heave and resultant airflow area reduction, maximizing 

long term airflow to production areas. 
DAY TO DAY SYSTEM EXAMINATION/OPTIMIZATION 

As the mine expands or changes, there is a need to examine the 

system utilization and analyze overall efficiency regularly. Often mine 

plans change from those envisioned years ago and implementation 

has not been optimal. Personnel changes over time result in losing 

track of those efficiency goals. 

The key to ventilation is having adequate cross sectional area to 

support the required airflow. Pressure required is proportional to 

velocity squared, so the goal is to economically minimize velocity. 

Some airways may be better utilized by changing “gender” – from 

intake to return or vice versa. 

Consider if some of the old returns could be opened to intake and 

better utilized. When intake velocities are dropped there is less dust 

generated from conveyor belts and travelways. What procedure should 

be followed to determine if the change is beneficial? First, verify 

assumptions by simulations on the computer model. If favorable, then 

test the hypothesis by temporarily isolating the old return with curtains 

and check if it makes any difference to inby airflow. If not, open it up to 

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

up for the increased system resistance. 

Case Studies 

Longwall block mains were developed with three center intakes 

and three returns, two west and one east (see Figure 6).

Figure 6. Main Entry Optimization. 

 Three intakes 

would be adequate for development ventilation and 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 identified by mine planning, when the longwall 

moved inby, the east return would be changed to intake, allowing 

increased intake capacity necessary for future longwall mining. 

Longwall return air will be routed away from the mains so the return 

capacity needed here would be less. A long stopping line will be 

eliminated, saving about 9.4 m3

/s (20,000 cfm) leakage. 

Next, underutilized airways should also be examined. Further 

outby in an older development, a return carries 9.4 m3

/s (20,000 cfm) 

and if taken out of the circuit will have no negative effect on airflows 

inby. Intake airways next to this return have high velocities and 

pressure losses coming from the main shaft. Opening up this 

underutilized return to intake will lower system resistance, increase 

main fan airflow, and lower total system leakage due to reduced 

pressure differentials. The mine is a big pipe system: make sure it is 

utilized efficiently. 

Changes made to intake and return airways should be done with 

consideration of mine escapeways and the existing emergency plan for 

ventilation and evacuation routes. 

Think Out of the Box 

It’s tough these days to find time to do serious analysis of the 

ventilation system, but doing so could have big payoffs in air quality for 

miners and cost savings for the operation. 

If certain areas are difficult to ventilate consider a booster fan 

installation. A little extra horsepower in the right place could make a big 

difference and a lot less horsepower required than at the main fan! 

Another possibility to consider is controlled district recirculation. 

(Pritchard 1995, Robinson 1989) Examine the air quality in the mine 

return. Sometimes, it’s equivalent or better than the intake. Mine 

returns can act as a big “bag house” system helping dust settle out. 

Even diesel soot settles out in time. Contaminants from face areas are 

also diluted by leakage. Reheating this air isn’t necessary as it’s 

already at rock temperature. Blasting fumes, cooling requirements and 

methane may be issues with this option in some mines. 

The main fan may be operating at low pressures and off the 

efficiency curve. Talk to your fan manufacturer about de-blading or 

removing fan blades (Loring 2007) – this can drastically improve 

efficiency, especially at high altitudes. 

With multiple main mine fans, behavior is not always as expected. 

When one of three main fan’s blades were reduced, total mine airflow 

went down but mine section airflow went up. Airflow increased 

because the fans didn’t have to fight each other and mine pressure 

differential went down, reducing leakage. Operating cost was reduced 

and airflow to the working areas went up – the ideal outcome. 

Look to flexibility in mine ventilation. Investigate applying 

Ventilation on Demand (VOD) principles. Apply air where it is needed, 

when needed instead of fixed airflow quantities at all times. There is 

considerable monitoring and control capability in the industry, use it to 

your advantage (Allen, 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. What is needed is to look around, inquire, measure and 

understand. Actions to dilute contaminants and improve the working 

environment will result in a healthier, happier workforce and most likely 

improved production and lower turnover. 

This paper has discussed some ways to find extra usable air 

when there is no extra ventilation capacity. If there is adequate air, 

then the option is to implement some of these changes and reduce 

expenditures through lowering operating costs. Since airflow power is 
proportional to velocity cubed (Marx 2008) the first fan blade setting 

reduction is the biggest savings. Don’t forget, each cfm saved doesn’t 

have to be heated or cooled either (Hall, 1985). 

Remember to take the entire system into account. Develop and 

utilize a good computer model. All changes have consequences, so be 

sure to perform a risk analysis and determine the effects on 

emergency and evacuation planning.

So – after this, I hope you only get “the occasional complaint”! 

REFERENCES 

1. US Code of Regulations, 30 CFR Part 57, 2008. 

2. Allen C, Keen B, (2008) “Ventilation on Demand (VOD) Project – 

Vale Inco Ltd. Coleman Mine”, 12th US/North American Mine 

Ventilation Symposium, Reno, NV. 

3. Grau, R, Krog R, (2008) “Using Mine Planning and other 

Techniques to improve Ventilation in Large-Opening Mines”, SME 

Annual Meeting , Salt Lake City, UT. 

4. Hall, A E, (1985) “The use of recirculation ventilation to conserve 

energy”, 2nd US Mine Ventilation Symposium, Reno, NV. 

5. Loring D, (2007) “Development of a Tool to Predict Performance 

of Debladed Mine Fans at Henderson Mine”, SME Annual 

Meeting, Denver, CO. 

6. Marks J, (2008) “Acceptance Speech 2008 Howard Hartman 

Award”, 12th US/North American Mine Ventilation Symposium, 

2008, Reno, NV. 

7. Marx WM et al, (2008) “Development of Energy Efficient Mine 

Ventilation and Cooling Systems”, Mine Ventilation of South Africa 

Society Journal, April/June. 

8. Pritchard C J, (1995) “Preparatory Work Required for a LongTerm District Recirculation Test in a Gassy Underground Metal 

Non-Metal Mine”, Proceedings of the 7th US Mine Ventilation 

Symposium, Louisville, KY. 

9. 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, Berkely, 

CA.