44 JANUARY 2014 Mınıng engıneerıng www.miningengineeringmagazine.com

Technical Papers

Key components for an effective 

filtration and pressurization system 

for mobile mining equipment

by A.B. Cecala, J.A. Organiscak, J.D. Noll and J.P. Rider

A.B. Cecala, J.A. Organiscak, 

members SME, and J.D. Noll are 

mining engineer, mining engineer, 

research chemist, and J.P. Rider, 

member SME, is acting team leader 

at the National Institute for 

Occupational Safety and Health, 

Pittsburgh Research Laboratory, 

Pittsburgh, PA. Paper number 

TP-12-067. Original manuscript 

submitted November 2012. Revised 

manuscript accepted for publication 

August 2013. Discussion of this 

peer-reviewed and approved paper 

is invited and must be submitted to 

SME Publications by April 30, 2014.

Abstract n Enclosed cabs have been used for many years to isolate workers on mobile

equipment in the mining industry for health and safety reasons. These enclosed cabs create

a microenvironment for workers where they can be either more protected or more vulnerable

to contaminants. Over the past decade, the U.S. National Institute for Occupational Safety

and Health (NIOSH) has performed substantial research efforts to improve the air quality

inside enclosed cabs of underground and surface mobile mining equipment. In these efforts,

NIOSH has partnered with mining companies, original equipment manufacturers (OEMs) and

manufacturers of filtration and pressurization systems in a synergistic effort to reduce respirable

dust and improve the air quality inside these enclosed cabs. Various field studies over this time

have shown an array of results ranging from very minor to very significant reductions (protection

factor: 3-89) in respirable dust levels inside these enclosed cabs. In addition to and concurrent

with the field work, NIOSH also performed a comprehensive laboratory study to evaluate all the

factors involved in cab filtration and pressurization systems and identified those factors that

were most significant for an effective system. From this comprehensive research effort, the key

components for an effective filtration and pressurization system have been identified in an effort

to provide the best air quality to equipment operators inside of enclosed cabs of mobile mining

equipment, thus minimizing respirable dust exposure.

Mining Engineering, 2014, Vol. 66, No. 1, pp. 44-50.	

Official publication of the Society for Mining, Metallurgy & Exploration Inc.

Introduction

Enclosed cabs have been used on 

mobile mining equipment for many 

years to protect operators from health 

and safety hazards. Enclosed cabs provide fall protection to the equipment 

operator and protect the mobile equipment operator from noise, dust and 

diesel contaminants. Protection of the 

operator from respirable dust inhalation was the primary focus of this research. The primary evaluation method 

used to determine the effectiveness of 

the pressurization and filtration system 

is to compare the respirable dust concentration inside the enclosed cab to 

those levels outside the cab. One would 

assume that without any protection in 

place, dust levels inside and outside the 

cab would be somewhat comparable. 

Even with an enclosure in place, this 

would also be the case when equipment operators leave the door and/or 

the windows open.

Throughout the past decade, the 

U.S. National Institute for Occupational Safety and Health (NIOSH) has 

partnered in a number of cooperative 

studies to determine the effectiveness 

of new filtration and pressurization systems installed on mobile mining equipment in an attempt to improve the air 

quality inside these enclosed cabs (Organiscak et al., 2004; Chekan and Colinet, 2003; Cecala et al., 2004; Cecala et 

al., 2005; Cecala et al., 2012). In all of 

these studies, pre- and post-evaluations 

of respirable dust concentrations using 

instantaneous and gravimetric sampling 

instrumentation, as well as airflow and 

pressurization measurements, were performed on filtration and pressurization 

systems installed on the enclosed cabs. 

These studies highlighted some very 

important factors, such as cab filtration, cab integrity and work practices 

and their impact on improving the air 

quality and ultimately protecting the 

workers with protection factors ranging 

from 3 to 89.

Laboratory study

From the various cooperative re-
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search efforts performed to lower silica and other respirable 

dust contaminants inside enclosed cabs, a number of different 

factors appear to be most significant in an effective system. 

In order to evaluate these factors, a controlled laboratory experiment was performed at NIOSH’s Pittsburgh laboratory 

(Organiscak and Cecala, 2008; NIOSH, 2008). Figure 1 shows 

the cab filtration system setup used for this laboratory study 

and indicates the various parameters evaluated. 

In Fig. 1, the parameter definitions are as follows: Co = 

outside cab concentration; Ci = inside cab concentration; ηi

= intake filter efficiency, fractional; QI = intake air quantity; 

QL = leakage air quantity; l = intake air leakage; ηR = recirculation filter efficiency, fractional; QR = recirculation air 

quantity; QW = wind quantity infiltration; Vo = air velocity 

through an orifice; Ao = area of orifice; and VC = cab volume. 

Airborne particle counting measurements were conducted 

inside and outside the laboratory cab test stand while using 

different levels of experimental test parameters. 

Design drawing showing various components of test setup to 

evaluate various operational parameters on a filtration and 

pressurization system for an enclosed cab.

Figure 1

The results of this laboratory study indicate that intake 

filter efficiency and the use of a recirculation filter had the 

greatest impact on improving the air quality inside the enclosed cab. When considering the use of an intake air filter, 

the addition of the recirculation component significantly 

improved the air quality due to the repeated filtration of 

the cab’s interior air. The addition of an intake pressurizer 

fan to the filtration system increased intake airflow and cab 

pressure significantly. The cab air quality was also affected by 

intake filter loading and air leakage.

Mathematical model to determine enclosure protection 

factor. In the course of the laboratory study, the significance 

of the filtration system parameters was evaluated and the 

following mathematical model was developed. Equation (1) 

was formulated from a basic time-dependent mass balance 

model of airborne substances within a control volume with 

steady-state conditions. The equation determines the protection factor (PF) in terms of intake air filter efficiency, intake 

air quantity, intake air leakage, recirculation filter efficiency, 

recirculation filter quantity and outside wind quantity infiltration into the cab. This model’s applicability to determining 

cab filtration system performance was verified with the protection factor measurements and cab test parameters studied 

during the laboratory experiments.

 (1)

Equation (1) allows for a comparison of how changes in 

the various parameters and components in the system impact 

the PF. The wind quantity infiltration (QW) can be assumed 

to be zero if the cab pressure exceeds the wind velocity (Fig. 

1). By using Eq. (1), operations have the ability to determine 

the desired parameters necessary to systematically achieve a 

desired PF in an enclosed cab to improve the air quality for 

the equipment operator.

Key components for an effective enclosed cab system

Based on the knowledge gained from NIOSH’s laboratory and numerous cooperative field studies, the two most 

significant components necessary for an effective system 

for enclosed cabs in the mining industry are: 1) a competent 

filtration system comprised of a pressurized intake and a 

recirculation component and 2) an enclosed cab with structural integrity to achieve pressurization. These two keys components will be addressed, along with numerous secondary 

design considerations that should be considered for an effective system.

1. Effective filtration system

An effective filtration system is composed of a pressurized intake component as well as a recirculation component.

Effective pressurized intake air. An effective pressurized 

intake air component provides numerous important functions in an optimized system. First, it provides the required 

amount of outside air to ensure the equipment operator does 

not become asphyxiated from being in an enclosed area. A 

minimum quantity of at least 0.71 m3/min (25 cfm) of intake/

outside air per person is necessary to dilute CO2 quantities 

exhaled by each worker (ASABE, 2003). Since almost all 

enclosed cabs for mobile equipment in the mining industry 

are designed for a single operator, a recommended lower 

limit for pressurized intake air would be somewhere around 

the 1.13 m3/min (40 cfm) level range in order to achieve a 

minimal cab pressurization, while also ensuring a level of 

safety in regards to the CO2

 issue. A good rule of thumb for 

an acceptable pressurized intake air range derived from the 

various field testing would be between 1.13 and 3.96 m3/min 

(40 and 140 cfm).

The second important aspect in relation to an intake air 

component is to create enough positive pressurization to 

eliminate the wind from blowing dust and contaminants into 

the enclosed cab (discussed in the “Cab integrity” section). 

The amount of intake air delivered to create this pressurization must be carefully controlled and optimized. Optimal 

intake air quantity is relative to the size of the cab, number 

of occupants, capacity of the cab to hold pressure and the 

efficiency of the intake and recirculation filtration. Maintain-
46 JANUARY 2014 Mınıng engıneerıng www.miningengineeringmagazine.com

ing the correct balance between these factors over extended 

periods is the goal of an optimized system. Increasing the air 

volume beyond this point degrades the system by increasing 

particle penetration and decreasing filter efficiency by allowing more contaminants to flow through the filter media. As 

the intake air volume increases, it creates higher demands on 

the HVAC system to either heat or cool the air for operator 

comfort, which is another reason to optimize the intake air 

volume.

Figure 2

Design drawing showing two types of powered intake systems (A & B) as compared to static design (C).

High-efficiency intake filters are a necessity for an effective design. For the majority of enclosed cabs for mining 

applications, a MERV-16 intake filter using mechanical filter 

media would be the optimal design. When using a mechanical filter media, the filter becomes more efficient as it loads 

with dust and develops a filter cake. A nonloaded MERV-16 

media would have a greater than 95% filtering efficiency 

on particles in the respirable size range, being from 0.3 to 

10 μm. The MERV-16 filter is the highest rated type below 

the HEPA rating. As this filter media loads with dust, it then 

becomes even more efficient at removing particles from the 

intake airflow. It is a common trend today to immediately 

want to use a HEPA quality filter, which has an efficiency 

rating of 99.97% for particles greater than 0.3 μm in size. 

However, this filter is obviously more costly and restrictive 

than the MERV-16, which places additional demands on the 

entire system including the intake fan. In a recent NIOSH 

laboratory study to evaluate a number of different MERV 

rated filters, including a HEPA filter, on diesel particulate, 

it was believed that the MERV-16 rated filter would be the 

optimal design (Noll et al., 2011). In mining applications, a 

HEPA filter would load much more quickly with dust and 

diesel contaminants and this is thought to be more of a detriment than a benefit for filtration and pressurization systems 

for enclosed cabs in mining. NIOSH is currently performing 

a field study to compare MERV-16 to HEPA quality filters on 

the systems of two pieces of mobile equipment at an underground stone mine which will provide additional information 

on this comparison.

The last critical aspect is our recommendation that the 

intake be a powered unit versus a static (non-powered) system. On a powered unit, the intake air has its own fan, so the 

air is delivered at positive pressure through ductwork to the 

main HVAC unit. In this case, a known quantity of intake 

air is always being blown into the enclosed cab. Obviously, 

as the intake filter loads with dust, the intake air quantity 

will decrease, but there is a known air quantity range from a 

clean to a fully loaded filter. In addition, there are two proven 

techniques that can be used to minimize dust loading on the 

intake filter: 1) the use of a self-cleaning filter technique or 

2) the use of a centrifugal design that spins out the over-sized 

dust particles (>5.0 μm) before the intake filter. A common 

self-cleaning method is to use a reverse-pulse or back-flushing technique that uses a compressed air system to blow the 

dust cake off the filter. This reverse-pulse can be set up on a 

regular time interval or based upon a differential pressure 

across the filter. With the centrifugal design, the system spins 

the oversized particles out of the system back into the atmosphere to minimize the number of particles being deposited 

on the intake filter. This system has an approximately 90% 

efficiency with particles greater than 5 μm. Both of these 

techniques have been tested by NIOSH during cooperative research studies and were shown to be very effective at 

providing a known quantity of intake air to the enclosed cab 

while minimizing dust loading on the intake filter (Cecala 

et al., 2004; Cecala et al., 2012). In a static design, the actual 

intake air quantity is dependent on the loading rate of all of 

the filters used in the system, and it is difficult to determine 

or control the intake to recirculation air ratio. It also becomes 

much more difficult to ensure that the minimal air quantity 

of 1.13 m3

/min (40 cfm) is being maintained. Figure 2 shows 

the two types of recommended powered intake systems as 

compared to the static design.

Effective recirculation filtration. The use of the recircula-
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tion system is a very important component for any filtration 

and pressurization system design and there is a range of operating parameters that can be used in an effective system. 

The first parameter to consider is the filtration efficiency of 

the recirculation filter and the recommended range should 

be between a MERV-14 (greater than 90% filtering efficiency 

on particles in the respirable size range, being from 0.3 to 10 

μm) and a MERV-16 filter. The actual mining conditions in 

which the mobile equipment operates should dictate the actual filter efficiency rating chosen and should be based upon 

such things as the dust type, the silica content, the in-cab 

dust sources and dust levels, and the frequency that the mobile equipment operator enters or exits the enclosed cab, or 

even opens the door to perform a task or communicate with 

coworkers. It must be remembered that the ultimate effectiveness of the recirculation system is measured by the reductions that can be achieved through multiple cycles through 

the recirculation filter of the interior cab air (Organiscak 

and Cecala, 2009). The other consideration with the recirculation component is the volume of air recirculated and its 

proportion to the amount of intake air. The optimal amount 

of recirculation air derived from the laboratory and field 

research would be in the range of 3 to 4 times greater than 

the quantity of intake air, thus normally being in the range of 

6-8 m3

/min (200 to 300 cfm) for a typical enclosed cab. When 

the recirculated air is in this range, it can quickly remove incab dust sources, such as dust brought in from the operator’s 

work boots or clothing or dust allowed in when entering or 

exiting the enclosed cab. Obviously, even a 1 to 1 ratio of 

intake to recirculation air could be used, but this is not as 

effective because it requires more tempering of the air for 

heating or air-conditioning needs. Laboratory experiments 

showed a 10-times increase in protection factors when using a 

MERV-15 filter, which is 85 to 94.9% efficient on 0.3-to-1-μm 

particles, as compared to no recirculation filter. Laboratory 

testing also showed that the time for the interior to stabilize 

after the door was closed (decay time) was reduced by more 

than 50% when using the recirculation filter. The average 

decay times were between 16 and 29 minutes without the 

recirculation filter and between 6 and 11 minutes with the recirculation filter. Thus, the use of a recirculation filter greatly 

improved the air quality and reduced the exposure time after the cab door was closed (Organiscak and Cecala, 2008; 

NIOSH, 2008). An additional benefit of using a recirculation 

filter is that it allows cleaner air to be circulated through the 

HVAC system, thus providing better thermal efficiency and 

less maintenance, as stated above. 

2. Cab integrity

Cab integrity is the second key component for an enclosed cab system and is necessary in order to achieve pressurization, which is critical for an effective system. To prevent 

dust-laden air from infiltrating into the enclosure, the enclosure’s static pressure must be higher than the wind’s velocity pressure (Heitbrink et al., 2000). Equation (2) is used to 

determine the wind velocity equivalent for an enclosure (the 

wind velocity at which the cab is protected from outside infiltration as determined by the static pressure):

Wind velocity equivalent = ( )Pa 

x 4.48 @ standard air temperature and pressure (2)

where ∆p = cab static pressure in Pa.

In addition to maintaining an effective static pressure 

inside enclosed cabs as stated above, structural integrity is 

also important in regard to the filtration and pressurization 

system. Testing has shown that the installation of new door 

gaskets and seals, as well as plugging and sealing cracks and 

holes in the shell of the enclosure, has a major impact on 

increasing the enclosure pressurization. Gaskets and seals 

also need to be monitored and changed when signs of age 

(cracking or wear) or damage occur, because this could cause 

dust-laden air to be drawn into the unit, bypass the filtration 

component and be blown directly into the cab. In addition, it 

is also beneficial during inspection of the system to determine 

the cleanliness of the unit’s ductwork. Dust seen inside the 

ductwork on the clean air side of the system is a good indication of a system failure.

Table 1

Average respirable dust concentrations (mg/m3

) inside 

enclosed cab for three days of testing with cab door closed 

and open.

Door closed Door open

Day 1 0.08 0.84

Day 2 0.17 0.39

Day 3 0.03 1.21

Secondary design considerations

The following are other secondary design considerations 

for an effective filtration and pressurization system on mobile 

mining equipment.

Intake air inlet location. The intake air inlet pickup location needs to be considered in the system design. Locating 

the cab air inlet near major dust sources causes unnecessary 

high dust loading on the air filtration system. This high dust 

loading burdens the filtration system and reduces its effectiveness by increasing the pressure drop across the loaded filter and decreasing the quantity of air and cab pressurization. 

In addition, the increased pressure drop across the loaded 

filter also increases the potential for dust leakage around 

the filter cartridge. This requires that the filter cartridge be 

cleaned or changed more frequently, which also increases the 

filter cost. Finally, air filtration is based on relative dust capture efficiency, so filtering higher outside dust levels creates 

higher inside cab dust concentrations.

In an effort to minimize these effects, it is recommended 

to place the enclosure’s air inlet strategically away from dust 

sources to reduce dust loading of the filter cartridge (NIOSH, 

2001). This can usually be accomplished by locating the outside air intake inlet at higher levels, away from the ground, 

and on the opposite side of the enclosed cab and away from 

dust sources. This location also enables the cab to shield some 

of the dust from the inlet.

Keeping doors and windows closed. In order to achieve 

and maintain enclosed cab pressurization, doors and windows 

must be closed at all times except while the operator is enter-
48 JANUARY 2014 Mınıng engıneerıng www.miningengineeringmagazine.com

ing or exiting the cab. This problem was noted during a field 

study on a surface drill, when the operator repeatedly opened 

the cab door to manually guide the drill steel into place each 

time an additional section was needed (Cecala et al., 2007; 

Organiscak and Cecala, 2008). The cab door was usually open 

somewhere between 20 and 45 seconds each time this process 

took place before being closed again. Because no drilling 

was occurring and no dust cloud was visible as the cab door 

was opened, the impact to the drill operator’s respirable dust 

exposure was initially thought to be insignificant. However, 

when dust data from inside the enclosed cab were analyzed, 

a substantial increase in respirable dust concentrations was 

noted during the periods when the door was open. This significant increase was unexpected when one considers that 

drilling had ceased approximately two minutes before the 

door was opened. Table 1 shows average concentrations for 

each of the three days of testing for the time period when the 

cab door was closed and open. The average concentration for 

all three days was 0.09 mg/m3

 with the cab door closed and 

0.81 mg/m3 with the door open. Despite no visible dust cloud 

during the time when the cab door was open, respirable dust 

concentrations inside the cab were nine times higher than 

when the door was closed and drilling was being performed.

The results of this testing clearly stress the importance of 

keeping doors and windows closed at all times in an effort 

to keep the compartment pressurized and working properly. 

Again, the only exception to keeping the door closed should 

be when the equipment operator enters or exits the cab. It 

also needs to be stressed that even when dust clouds are 

not visible outside, respirable dust levels can be significantly 

higher than filtered levels inside cabs.

Problem created by heater stirring up dust from the floor 

and blowing dust off of the worker’s clothing.

Figure 3

Floor heaters. Any type of floor heater or fan located low

in the enclosed cab that can stir up dust should be eliminated 

for an effective design. During a field study, it was found that 

a floor heater fan used during the winter months to provide 

heat to an operator of a surface drill greatly increased the 

respirable dust concentrations inside the enclosed cab (Fig. 

3) (Cecala et al., 2001). The floor heater can be a serious

problem because the floor is the dirtiest part of the cab due to 

the operator bringing dirt in on his or her work boots. Then, 

as the operator moves his or her feet around, dust is created 

and is then blown throughout the cab by the fan on the floor 

heater. This fan also tends to stir up dust that may be on the 

drill operator’s clothes.

Because of the significant increase in dust levels with 

floor heaters, it is recommended that they not be used. If 

removal is not an option, they should be repositioned to a 

higher area in the enclosure where they are less prone to pick 

up dust from the floor and operator’s clothing. Also, no type 

of fan should be used low in the cab because of the potential 

to stir up in-cab dust sources. Ideally, the heater unit should 

be tied into the filtration and pressurization unit to deliver 

the heated air at the roof of the cab.

Good housekeeping (cab cleanliness). To maintain pressurization and filtration systems, good housekeeping practices 

are essential in that systems need to be cleaned periodically 

and filters need to be changed when necessary. In addition, 

the enclosed cab must also be inspected for integrity to ensure that pressurization is maintained by replacing gaskets 

and seals when wear appears, and by plugging and sealing 

holes and cracks in the wall, ceiling, and cab floor. It must be 

understood that a system that is not properly maintained will 

deteriorate over time to a point where it is no longer providing an acceptable level of protection, thus causing workers to 

be exposed to respirable dusts.

During the field studies, a number of filtration units were 

found in all forms of disarray and had deteriorated to a condition where they were no longer providing acceptable levels 

of protection to the worker. In some cases, it appeared that 

the air quality or the protection provided to the worker was 

not a priority as long as the operator remained comfortable 

in regard to temperature controls. Although many cabs used 

standard heaters and air conditioners to control temperatures, in some instances workers resorted to just opening 

windows in an effort to be comfortable, thus bypassing the 

protection provided by the enclosed cab. With a little time, 

effort and finances, effective maintenance can be performed 

on filtration and pressurization systems to transition them 

from poor systems to ones that will again provide clean and 

acceptable air quality to workers.

Enclosure floors are commonly soiled from workers 

tracking dirt and product inside the enclosure upon entering 

from the mine site. In almost all cases, a substantial amount of 

dust and product gets tracked into the cab and housekeeping 

should be performed on a daily or shift basis. It is critical that 

the inside of an enclosed cab be maintained in a manner that 

minimizes the worker’s respirable dust exposure.

Ease of filter change. When designing filtration and pressurization systems, one key component is the ease with which 

filters can be replaced when necessary. It defeats the purpose 
www.miningengineeringmagazine.com	 Mınıng engıneerıng JANUARY 2014 49

of a good system if a filter to be changed is so difficult to access that the operator or maintenance workers do not want 

to take the time to perform the task. Another consideration 

is dust contamination during the filter change. It also should 

be noted that, in many cases, this dust-laden filter will have 

some percentage of silica mixed in with the other types of 

dust; therefore, extreme care should be taken to minimize 

the exposure to the worker changing the filter. The easier 

a filter is to change, the less contamination should occur to 

the worker performing the task and to the work area. When 

changing a canister filter, a common and effective technique 

is to remove the new filter from the cardboard box and then 

insert the old dust-laden filter into the box, tape it closed, 

and dispose of it.

Mechanical filter media. It is highly recommended that 

the outside air and recirculation filters be a mechanical type 

filter media, as compared to an electrostatic media. Mechanical filters become more effective as they load with product. 

This occurs because, as the filter loads with dust, a dust cake 

forms on the filter media and captures additional dust particles, which further improves the filter efficiency. Increased 

filter efficiency occurs with enhanced loading until the point 

where the air flow through the filter drops to an unacceptable 

level and the system effectiveness is compromised. At this 

point, the filter needs to be cleaned or replaced. Filtration 

and pressurization systems can use a reverse pulse air jet to 

clean the dust cake from the filter media based on a preset 

time sequence or when a predetermined pressure loss occurs 

across the filter to effectively deal with this situation.

Monitoring cab system performance. An effective method to monitor a cab filtration and pressurization system’s 

performance is a pressure differential indicator that notifies 

the operator of pressure changes. With any new filtration 

and pressurization system, the starting pressure should be 

determined and the change in pressure should be monitored 

over time as the filters load with contaminants. The pressure monitor provides a real-time indication of the system’s 

performance. A magnehelic pressure gauge is one method 

to effectively monitor the cab filtration and pressurization 

system. In addition, a newly developed cab pressure monitor 

is currently available that uses an LED display to inform the 

equipment operator of the cab pressure. It also has an audible alarm that can be engaged to sound at a predetermined 

cab pressure to inform the operator of the need for service.

Since filter loading rates are different in all cases based 

on contaminant levels, using a filter cleaning or changing 

schedule based on time is not the preferred method because, 

as previously mentioned, a mechanical filter becomes more 

efficient as it loads with contaminants. The cab pressure indicator would inform the equipment operator or maintenance 

worker of the ideal filter changing time when the loss in cab 

pressure is such that it is detrimental to the overall system 

performance (maintaining positive pressure). On the other 

hand, based upon field experience, it is believed that the filter 

should be changed at 1,000 hours of use, and/or at least once 

a year for integrity issues, even if maintaining positive cab 

pressure does not become an issue. Conversely, a rapid increase in positive cab pressure also indicates a system failure. 

This could include such things as a hole or tear in the filter 

media, a clog in the recirculation system such as a plastic bag 

or a rag covering the recirculation inlet, or even a maintenance worker removing a used filter and then forgetting to 

replace it with a new one.

Unidirectional design. The use of a unidirectional airflow 

pattern should be considered whenever possible to maximize 

the air quality at the breathing zone of the operator inside 

the enclosure. In most systems, the intake and discharge for 

the recirculation air are located in the roof. Unfortunately, 

this location causes the dust-laden air within the enclosure to 

be pulled directly over the worker as it is drawn into the ventilation system. Further, in many designs, the contaminated 

return air and clean filtered air are ducted within inches of 

each other at the ceiling. This poor design allows for recirculated air to be short-circuited and allows dust-laden return 

air to be pulled directly back into the ventilation system and 

over the operator’s breathing zone. A more effective design is 

to draw the recirculated air from the bottom of the enclosure, 

away from the worker’s breathing zone (Cecala et al., 2009).

Conclusions

NIOSH has conducted a substantial effort during the 

past decade in an attempt to improve the air quality inside 

of enclosed cabs of mobile equipment in the mining industry. 

From many different cooperative field studies, along with an 

in-depth laboratory study, the key components for an effective filtration and pressurization system have been identified in an effort to minimize the respirable dust exposure 

and provide the best air quality to the equipment operator. 

The two most significant components necessary for an effective system are a competent filtration system comprised 

of a pressurized intake and a recirculation component, and 

an enclosed cab with structural integrity to achieve pressurization. Some other secondary considerations include: 

locating the intake air inlet at a point to minimize as much 

dust loading on the filter as possible; having the operator 

keep doors and windows closed; the elimination of any fans 

or heaters located on the floor of the cab, which stirs up dust 

from the operator’s clothing and the floor; performing good 

housekeeping techniques, including periodic filter changes 

on the filtration system and daily cleanings of the enclosed 

cab; using a system that allows for easy access for the filter 

changes; using mechanical filter media which becomes more 

efficient as it loads with dust; using some type of visual pressure indicator to inform the equipment operator of the cab 

pressure and when a filter is damaged or clogged; and considering a uni-directional design to minimize respirable dust 

flowing over the equipment operator’s breathing zone as it 

is drawn into the recirculation inlet duct. These components 

are necessary to provide an operator cab that minimizes respirable dust exposure and delivers the best air quality to the 

equipment operator. n

Acknowledgments

The authors acknowledge the following companies and 

organizations for their participation and cooperative efforts 

through the course of NIOSH’s research efforts: J.H. Fletcher 

Co., Clean Air Filter Co., MI Air Systems, LLC, Sy-Klone 

International, Red Dot Corp., Bergstrom Inc., Air International Transit, Sigma Air Condition, SCS-Frigette, Mine 
50 JANUARY 2014 Mınıng engıneerıng www.miningengineeringmagazine.com

Safety and Health Administration, California EPA, Sidwell 

Materials Inc., CEMEX, Vulcan Materials Co., U.S. Silica Co., 

Al Hamilton Contracting Co., Lodestar Energy Inc., Leslie 

Resources, Powder River Coal Company, John Deere Product Engineering and Nelson Manufacturing. 

Disclosure

Mention of any company or product does not constitute endorsement by the National Institute for Occupational 

Safety and Health. 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.

References

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Schmitz, M., Ahrenholtz, E., Coppock, C.C., and Andrews, E.H., 2005, 

“Reducing enclosed cab drill operator’s respirable dust exposure with 

effective filtration and pressurization techniques,” Journal of Occupational and Environmental Hygiene, Vol. 2, pp. 54-63.

Cecala, A.B., Organiscak, J.A., Zimmer, J.A., Moredock, D., and Hillis, 

M.S., 2007, “Closing the door to dust when adding drill steels,” Rock 

Products, Vol. 110 No., 10 pp. 29-32.

Cecala, A.B., Organiscak, J.A., Zimmer, J.A., Hillis, M.S., and Moredock, 

D., 2009, “Maximizing air quality inside enclosed cabs with a unidirectional filtration and pressurization system,” Society for Mining, 

Metallurgy, and Exploration – 2009 Transactions, Vol. 326, pp.71-78.

Cecala, A.B., Organiscak, J.A., and Noll, J.D., 2012, “Long-term evaluation 

of cab particulate filtration and pressurization performance,” Society 

of Mining, Metallurgy and Exploration, Inc., Annual Meeting, Feb. 

19-22, 2012, Seattle, WA, Preprint 12-059, 9 pp. 

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silica dust exposures in older trucks,” Aggregates Manager, Vol. 8 No. 

9, pp. 9-12.

Heitbrink, W.A., Thimons, E.D., Organiscak, J.A., Cecala, A.B., Schmitz, 

M., and Ahrenholtz, E., 2000, “Static pressure requirements for ventilated enclosures,” Proceedings of the Sixth International Symposium 

on Ventilation for Contaminant Control, Helsinki, Finland, June 4-7.

NIOSH, 2001, Technology News 485: Improved Cab Air Inlet Location 

Reduces Dust Levels and Air Filter Loading Rates, J.A. Organiscak 

and S.J. Page, Pittsburgh, PA: U.S. Department of Health and Human 

Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health.

NIOSH, 2008, Key Design Factors of Enclosed Cab Dust Filtration Systems, 

J.A. Organiscak and A.B. Cecala, NIOSH Report of Investigations 

9677, Pittsburgh, PA: U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health.

Noll, J.D., Cecala, A.B., and Organiscak, J.A., 2011, “The effectiveness of 

several enclosed cab filters and systems for reducing diesel particulate 

matter,” Society of Mining, Metallurgy and Exploration, Inc., Transactions 2011, Vol. 328, pp. 408-415.

Organiscak, J.A., and Cecala, A.B., 2008, “Laboratory investigation of enclosed cab filtration system performance factors,” Mining Engineering, 

Vol. 60, No, 12, pp. 74-80.

Organiscak, J.A., and Cecala, A.B., 2009, “Doing the math–the effectiveness 

of enclosed-cab air–cleaning methods can be spelled out in mathematical equations,” Rock Products, October, pp. 20-22.

Organiscak, J.A., Cecala, A.B., Thimons, E.D., Heitbrink, W.A., Schmitz, 

M., and Ahrenholtz, E., 2004, “NIOSH/Industry collaborative efforts 

show improved mining equipment cab dust protection,” Society of 

Mining, Metallurgy and Exploration, Inc., Transactions 2003, Vol. 314, 

pp. 145-152.