Laboratory investigation of enclosed cab 


filtration system performance factors
 

j.a. organiscak and a.b. cecala 

J.A. Organiscak and A.B. Cecala, members sMe, are senior 

research engineers with the national institute for occupational 

safety and Health (niosH), Pittsburgh, Pa. 

Abstract 

Enclosed cabs are a primary means of reducing the silica 

dust exposure of equipment operators at surface mines. 

The National Institute for Occupational Safety and Health 

(NIOSH) has investigated various factor effects on enclosed 

cab air filtration system performance. Factors experimentally investigated were intake filter efficiency, intake air 

leakage, intake filter loading (filter flow resistance), recirculation filter use and wind velocity effects on cab penetration (inside to outside cab concentration ratio). Adding 

an intake pressurizer fan to the filtration system was also 

investigated. Results indicate that the intake filter efficiency 

and recirculation filter were the two most influential factors 

on cab penetration.Use of a recirculation filter significantly 

reduced cab penetration over the intake air filter by itself 

due to the multiplicable filtration of the cab interior air.Cab 

penetration was also affected to a lesser extent by intake 

filter loading and air leakage.Adding an intake pressurizer 

fan notably increased intake airflow and cab pressure while 

providing only minor changes to cab penetration. 

Introduction 

Overexposure to airborne respirable crystalline silica (quartz) dust 

can cause silicosis, a serious or fatal 

respiratory lung disease. Mining has 

some of the highest incidences of 

worker-related silicosis, with mining 

machine operators being the occupation most commonly associated with 

the disease (NIOSH, 2003). The U.S. 

Mine Safety and Health Administration (MSHA) enacts 

and enforces mine worker safety and health standards 

to mitigate mine worker injuries and occupational diseases. 

MSHA’s permissible exposure limit is 2 mg/m3 of airborne respirable dust for coal mine workers (U.S. Code 

of Federal Regulations, 2007). If more than 5% quartz 

mass is determined to be in the coal mine worker dust 

sample using MSHA’s P7 infrared method (Parobeck and 

Tomb, 2000), the applicable respirable dust standard is 

reduced to the quotient of 10 divided by the percentage 

of quartz in the dust. MSHA’s nuisance dust limit (total 

dust) for noncoal miners is 10 mg/m3, as defined by the 

American Conference of Governmental Industrial Hygienists (ACGIH, 1973; U.S. Code of Federal Regulations, 

2007). If more than 1% quartz mass is determined to be 

in the noncoal mine worker dust sample using NIOSH’s 

X-ray method (Parobeck and Tomb, 2000), the applicable 

standard is then a respirable dust standard of 10 divided 

by the sum of the quartz percentage plus 2. Both of these 

dust standards are intended to limit 

worker respirable crystalline silica 

(quartz) exposure to 0.1 mg/m3 or 

less for a shift.

Mineworker overexposure to 

quartz dust continues to be a prob

lem at mining operations in the 

United States. The percentages of 

MSHA dust samples from 2000 to 

2004 that exceeded the respirable 

dust standard due to quartz were 

­

11% for sand and gravel mines, 11% for stone mines, 19% 

for nonmetal mines, 17% for metal operations and 17% 

for coal mines (NIOSH, 2006). At surface mining operations, the occupations that have the highest frequency of 

exceeding the respirable dust standard are usually operators of mechanized excavation equipment, such as drills, 

bulldozers, scrapers, front-end loaders, haul trucks and 

crushers (Tomb et al., 1995). 

A primary means of dust control on mechanized surface mining equipment is enclosed operator cabs with an 

air filtration system. Field assessment of six surface coal 

mine rock drills and five bulldozers by NIOSH has shown 

that enclosed cab dust reduction efficiency for this equipment varied from 44% to nearly 100% (Organiscak and 

Page, 1999).Additional NIOSH field studies involving the 

retrofitting of five older enclosed cabs with air filtration 

system improvements also showed that their cab dust reduction efficiency varied from 64% to 99% (Chekan and 

Colinet, 2003; Cecala et al., 2004; Organiscak et al., 2004; 

Cecala et al., 2005). These field studies indicate that cab 

air filtration system design and operational factors highly 

influence dust control effectiveness and ability to control 

operator dust exposure. 

To better qualify air filtration system design and 

operational factor effects on enclosed cab dust control 

performance, controlled laboratory experiments were 

performed on an enclosed cab test stand at NIOSH’s 

Pittsburgh Research Laboratory (PRL). These experiments examined the independent factor effects of intake 

filter efficiency, intake filter loading (airflow resistance), 

intake air leakage around the filter, recirculation filter 

use and wind on cab penetration.Additional experiments 

were also conducted on the enclosed cab test stand to 

investigate the effects of adding an intake pressurizer to 

the filtration system. 

Test apparatus and measurement methods 

An experimental cab test apparatus was constructed 

having similar cab filtration system features to existing 

equipment cabs. It was a painted plywood enclosure 

1.83 m high x 0.915 m wide x 1.22 m deep (6 x 3 x 4 ft) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

mounted on rolling casters (Fig. 1). Figure 1 

Experimental cab test apparatus. 

 A mock-up Plexiglas 

roof-mounted heating, ventilation and air-conditioning 

(HVAC) system was located on the roof with a 27.6-V dc, 

variable-speed, dual fan blower discharging air through 

ceiling vents into the enclosure near the door entry. One 

HVAC recirculation air inlet was a 305- x 610-mm (12- x 

24-in.) opening located on the opposite side of the ceiling with a holding bracket for mounting a pleated panel 

filter. Another 305- x 610-mm (12- x 24-in.) recirculation 

inlet was located on the wall near the floor, opposite the 

door. This recirculation inlet was exteriorly connected to 

the mock-up HVAC system by an inlet transition, two 90° 

PVC elbows, and 152-mm- (6-in.-) diameter PVC pipe.A 

cover panel was used to seal the floor inlet during these 

experiments, so recirculation air would be drawn through 

the ceiling inlet as with most roof-mounted HVAC systems. 

Outside makeup air was supplied into the mock-up 

HVAC system through either of two 76-mm- (3-in.-) diameter PVC pipes connected to an exterior Plexiglas filter box. One of the PVC pipes drew air from the filter box 

with the recirculation fans only, while the other PVC pipe 

could be pressurized with intake air from a 15- to 27.6-V 

dc, variable-speed, single-fan blower located inside the 

filter box. Both PVC intake air pipes were fitted with ball 

valves so that either intake delivery system could be individually tested. The filter-sampling box had an inlet hole 

and bracket to accommodate an intake cylindrical filter 

cartridge on the exterior of the box. The filter box also 

had a 12.7-mm- (1/2-in.-) inside diameter barbed hose 

fitting opening for leak testing around the intake filter. 

Three 25.4-mm- (1-in.-) diameter holes were uniformly 

spaced in the Plexiglas window on the front door and on 

the opposing back side wall of the cab to allow for the 

intake makeup air to uniformly escape the cab under 

positive pressure. 

The cab test stand operating parameters were continuously measured with several static air pressure gages 

and airflow monitors that were electronically recorded 

with a Telog R-3307 seven-channel data acquisition system (Telog Instruments Inc., Victor, NY).1 The negative 

pressure differential across the exterior to interior of the 

intake filter box was measured with a 0- to 498-Pa Dwyer 

Magnehelic air pressure instrument, having a 4 to 20­

mAmp output (Dwyer Instruments Inc., Michigan City, 

IN). The cab enclosure positive pressure differential was 

measured with a 0- to 124-Pa Dwyer Magnehelic air pres

sure instrument, having a 4- to 20-mAmp output (Dw

yer Instruments Inc., Michigan City, IN). Leakage into 

the filter box was measured with a 0- to 300-L/min TSI 

model 4040 thermal mass flowmeter, with a 0- to 10-V 

analog output (TSI Inc., Shoreview, MN). Wind velocity 

was measured on the top left corner of the cab with a 0 

to 1,830-m/min AIRFLOW AV6 digital handheld vane 

anemometer with a 0-1 V analog output (AIRFLOW, 

Buckinghamshire, England) to verify consistent airflow 

conditions during the wind tests. 

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­

Figure 2 

Laboratory cab test apparatus used in longwall test gallery. 

Other data measured and recorded for each test were 

intake airflow, recirculation airflow and wind velocity 

around the cab. Intake airflow was centerline measured 

inside the 76-mm- (3-in.-) diameter PVC intake pipe before and after test with a 0- to 1,830-m/min TSI model 

8346 VelociCALC hot wire anemometer (TSI Inc., Shoreview, MN). The recirculation airflow was measured before and after each test with a 0- to 3,400-m3

/hr ALNOR 

Standard Balometer capture hood placed over the ceiling 

inlet/filter (TSI Inc., Alnor Products, Shoreview, MN). 

Air velocity around the cab before and after each wind 

test was determined by averaging Davis handheld vane 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

anemometer measurements (Davis Instrumentation, Baltimore, MD) on both sides and top of the cab (Fig. 2).All 

pre- and post-test airflow measurements were averaged 

for each test. 

Cab particulate protection performance was determined by relative comparisons of particle count concentrations inside (C1

) and outside (C3) the cab test stand that 

was challenged with ambient air particles (Fig. 2). Cab intake air particle concentrations (C2

) were also measured 

inside the filter box, allowing the intake filter efficiency 

to be determined without leaks around the filter. Handheld HHPC-6 particle counters with six custom channel 

sizes of 0.3, 0.5, 0.7, 1.0, 3 and 5 μm were operated at 

2.83 L/min (0.1 cfm) (Hach Ultra Analytics, Grants Pass, 

OR). Differential size particle counting was conducted 

in concentration mode over a sample volume of 2.83 L 

or for one-minute sampling periods and recorded in the 

instrument’s internal buffer/memory. Because the largest measurable fraction of ambient air particles counted 

were found to be in the submicrometer size ranges (0.3 

to 0.5 μm, 0.5 to 0.7 μm and 0.7 to 1 μm), these channels 

were summed into cumulative (0.3 to 1 μm) submicron 

respirable particle count concentrations for cab and filter 

particulate performance determinations. 

Three particle-counting instruments were mounted 

inside the enclosure and remotely sampled the designated 

locations through 457-mm- (18-in.-) lengths of 3.18-mm- 

(0.125-in.-) inside diameter Tygon tubing with isokinetic 

inlet probes. The manufacturer’s 11.4-mm- (0.45-in.) diameter isokinetic inlet probes were used at all locations 

except on the outside sampling location during the wind 

tests. For these tests, a 3.18-mm- (1/8-in.-) diameter isokinetic probe inlet was used to more closely match wind 

velocity to the inlet velocity. 

Submicrometer particle cab penetrations (C1/C3) were 

determined from the corresponding 15-minute concentration averages under stable interior concentrations. After 

closing the enclosure door, preliminary laboratory tests 

indicated that the interior concentrations predominantly 

reached stability within 15 and 30 minutes, respectively, 

with and without the recirculation filter. Therefore, experimental cab testing periods were conducted for 30 

and 45 minutes, respectively, with and without the recirculation filter to achieve a reasonably 

steady concentration averaging period 

for the last 15 minutes of a test. A cab 

concentration decay time for each test 

was estimated by the number of oneminute time periods it took to reach 

the average inside concentration for 

the last 15 minutes of the test. Finally, 

submicrometer particle intake filter efficiencies ((C3

− C2)/C3) × 100%) were 

determined for tests without intake 

leakage during the same last 15-minute 

time period as the cab penetration. 

Figure 3 

Cab intake airflow and differential pressure relationships. 

Experimental testing 

The first set of experiments examined the independent factor effects 

of intake filter efficiency, intake filter 

loading (airflow resistance), intake air 

leakage around the filter, recirculation filter use and wind. A Donaldson, 

single-stage, round pleated cellulose filter cartridge, 178­

mm- (7-in.-) diameter x 330-mm- (13-in.-) long, was used 

as the lower efficiency intake filter tested (Donaldson 

Company Inc., Minneapolis, MN). A Clean Air Filter, 

multi-stage, round microglass and electrostatic contiguous layered filter cartridge, 178-mm- (7-in.-) diameter x 

305-mm- (12-in.-) long, was used as the higher efficiency 

intake filter tested (Clean Air Filter, Defiance, IA). Each 

filter was tested in new condition (without any exposure 

to heavy or coarse dust loading) and a simulated loaded 

condition with a round cut piece of 14 GA perforated 

plate, 2.38-mm- (3/32-in.-) diameter holes staggered 4.76­

mm- (3/16-in.-) center-to-center, fitted flush within the 

interior of the filter gasket area and outlet hole. This 

perforated plate also had a 50.8-mm- (2-in.-) wide strip 

of duct tape down the center to further increase filter 

resistance. The intake filter and loading test conditions 

were also conducted with the 12.7-mm- (1/2-in.-) inside 

diameter hole closed or opened into the filter box to examine leakage effects around the intake filter. 

All the intake filter and leakage configurations were 

further tested in combination with and without an inside 

cab recirculation filter. An American Air Filter (AAF) 

rectangular pleated microglass panel filter, 305-mm- (12­

in.-) wide x 610-mm- (24-in.-) long x 102-mm- (4-in.-) 

deep nominal size, was the recirculation filter used. The 

filter had an American Society of Heating, Refrigerating 

and Air-Conditioning Engineers (ASHRAE) Minimum 

Efficiency Reporting Value (MERV) of 15, which is 85% 

to 94.9% in the 0.3- to 1-μm size range.When no recirculation filter was used, a 305-mm- (12-in.-) wide x 610-mm- 

(24-in.-) long x 102-mm- (4-in.-) deep two-by-four wood 

constructed filter frame blank was used.The recirculation 

filter and filter blank fit into an aluminum frame holding 

bracket with a perforated restrictor plate (same plate 

material used with intake filter) on the outside area of the 

bracket. This restrictor plate was used to achieve at least 

42.5 m3

/h of intake airflow for an unloaded intake filter 

without the recirculation filter in place. 

The first series of cab filtration system testing was 

conducted without the intake pressurizer within PRL’s 

longwall gallery under calm and 16 km/h (10 mph) wind 

conditions.This cab configuration was only tested against 
 

wind in the mine gallery because its positive interior cab 

pressure could have possibly been exceeded by the 16-

km/h (10 mph) wind velocity pressure of 12 Pa during 

some of the tests (Heitbrink et al., 2000). Figure 2 shows 

the cab test position in the cross-section of the gallery 

with three of the cab air exit holes facing into the wind. 

Experimental test conditions were randomized, but testing was conducted by running a test period with one 

HHPC-6 inside and outside the cab enclosure and then 

switching these instruments for a subsequent second test 

period under the same experimental conditions. Each 

experimental test condition was randomly conducted 

twice, providing four enclosed-cab testing periods. The 

instruments were switched for subsequent test periods to 

average out instrument bias. 

A second series of cab filtration system testing was 

conducted with an intake pressurizing fan and no wind 

in the high bay area outside the gallery.The experimental 

test conditions were randomized as described above with 

two subsequent testing periods conducted by switching 

inside and outside particle counters. 

Experimental results 

Cab filtration performance statistics were computed 

and examined for the experimental conditions tested. 

Table 1 shows the key summary statistics (average, with 

minimum and maximum values shown in parenthesis) 

for the intake filter, intake filter loading and recirculation filter use in the first series of cab experiments with 

and without wind and with no intake pressurizer.Table 2 

shows similar key summary statistics in the second series 

of cab experiments with no wind and with the intake 

pressurizer. Intake air leakage is quantified as the per

cent of intake air quantity.Wind test conditions were not 

differentiated in Table 1 because the 16-km/h (10-mph) 

wind condition did not exhibit noticeable differences in 

cab penetration as compared to the other experimental 

factors. The 16-km/h (10-mph) equivalent wind velocity 

pressure of 12 Pa never exceeded the cab pressure dur

ing the wind tests, minimizing its cab penetration effect 

in the first series of experiments (Heitbrink et al., 2000). 

Submicrometer intake filter efficiencies (EI, 0.3 to 1.0 

μm size range) were measured without leakage and are 

shown for the intake filter test condition. The recirculation filter used had an ASHRAE MERV rating of 15, or 

85% to 94.9% for the 0.3 to 1 μm size range, and could 

not be directly measured in these experiments due to its 

multiplicable filtration effect. 

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­

Table 1 

Cab testing without pressurizer. 

 

 

 

 

 

 

 

 

 

Test factors: average (minimum-maximum)

 Filter conditions Pen Q -∆p L Q +∆p , Decay time, I f R c

Intake Loaded Recirculation C1

/C3 m3/hr Pa % of QI m3/hr Pa min 

Lower EI No No 0.635 82.9 39 0.8 608 60 16
 

35% (0.557-0.690) (77.1-86.0) (35-45) (0.0-1.7) (574-625) (52-70) (1-38)
 

Lower EI No Yes 0.134 99.7 54 0.8 540 78 7
 

32% (0.122-0.148) (95.2-103.7) (47-57) (0.0-1.8) (510-557) (70-92) (1-21)
 

Lower EI Yes No 0.569 36.5 124 3.7 642 20 18
 

44% (0.426-0.637) (34.8-37.9) (114-132) (0.0-7.8) (625-663) (12-30) (3-38)
 

Lower EI Yes Yes 0.054 42.8 172 4.3 573 22 9
 

42% (0.045-0.059) (40.1-46.2) (167-179) (0.0-7.9) (564-586) (15-25) (1-23)
 

Higher EI No No 0.072 38.8 119 3.4 651 21 27
 

>99% (0.027-0.132) (35.7-42.5) (112-127) (0.0-7.1) (629-663) (15-30) (15-36)
 

Higher EI No Yes 0.007 48.7 160 3.2 564 25 7
 

>99% (0.002-0.012) (44.5-51.3) (154-167) (0.0-6.5) (540-586) (17-30) (2-20)
 

Higher EI Yes No 0.131 25.3 135 3.7 660 14 29
 

>99% (0.040-0.211) (23.4-27.5) (124-144) (0.1-11.6) (620-676) (7-22) (12-39)
 

Higher EI Yes Yes 0.009 31.9 184 6.3 584 15 9
 

>99% (0.003-0.014) (29.2-34.3) (177-192) (0.1-10.8) (561-595) (10-22) (1-23)
 

The two largest factors that influenced cab penetration (Pen) for both series of experiments were intake 

filter efficiency and recirculation filter use.Table 1 shows 

that the largest reductions in cab Pen were achieved 

with an increase in intake filter efficiency and the use of 

a recirculation filter.The lower efficiency filter provided 

an average cab Pen of 0.635 and 0.569 for the unloaded 

and loaded intake filter, respectively, without the recirculation filter. These average cab Pens significantly 

decreased to 0.134 and 0.054, respectively, with the recirculation filter.The higher efficiency filter provided an 

average cab Pen of 0.072 and 0.131 for the unloaded and 

loaded intake filter, respectively, without the recirculation filter.These average Pens significantly decreased to 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.007 and 0.009, respectively, with the recirculation filter. 

The recirculation filter also decreased the decay time 

needed for the cab interior concentrations to go down 

and stabilize after the cab door was closed. The average 

decay times ranged from 16 to 29 minutes without the 

recirculation filter, and from 7 to 9 minutes with the 

recirculation filter. 

Similar results were seen in the second series of experiments with the pressurizer. Table 2 shows that the 

largest reductions in cab Pen were achieved with an 

increase in intake filter efficiency and the use of a recirculation filter. The lower efficiency filter provided an 

average cab Pen of 0.693 and 0.609 for the unloaded and 

loaded intake filter, respectively, without the recirculation filter.These average Pens significantly decreased to 

0.194 and 0.073, respectively, with the recirculation filter. 

The higher efficiency filter provided an average cab Pen 

of 0.071 and 0.108 for the unloaded and loaded intake 

filter, respectively, without the recirculation filter.These 

average Pens significantly decreased to 0.009 and 0.010, 

respectively, with the recirculation filter. The recirculation filter also decreased the decay time needed for the 

cab interior concentrations to go down and stabilize 

after the cab door was closed. The average decay times 

ranged from 17 to 25 minutes without the recirculation 

filter and were 6 to 11 minutes with the recirculation 

filter. 

Adding the intake pressurizer fan to the cab filtration system resulted in minor changes to the cab Pen 

from the increased airflow through the intake filter. A 

comparison of Tables 1 and 2 shows that the cab Pen for 

the lower EI intake air filter tests perceptibly increased 

with the addition of the pressurizer. This corresponded 

to higher intake airflows and decreased intake filter efficiency with the pressurizer compared to without the 

pressurizer. Cab Pen change was negligible for the higher EI filter with the addition of the pressurizer, corresponding to negligible changes in intake filter efficiency 

over the range of airflows achieved with and without the 

pressurizer. The pressurizer did not significantly change 

the recirculation airflow quantity (QR) for identical filter 

combinations. 

The intake filter differential pressure, cab intake airflow quantity and 

cab differential pressure all significantly changed with the experimental 

filter combinations and pressurizer. 

Figure 3 presents the cab intake airflow quantity (QI

) relationships with 

intake filter differential pressure (∆pf) 

and cab differential pressure (∆pc). 

The intake filter differential pressure 

data are categorized by recirculation 

filter and pressurizer use with dashed 

lines drawn through these data 

groups to illustrate their associations. 

The data show that intake air quantity was inversely related to the negative differential pressure across the 

intake filter for all data groups. Also, 

the recirculation filter increased both 

the intake airflow and filter differential pressure, shifting the associated 

relationship to the lower right. The 

pressurizer additionally increased the intake airflow 

and filter differential pressure, further shifting these 

associated relationships to the lower right. 

Figure 3 also shows the direct relationship between 

the cab’s differential pressure (∆pc

) and intake air quantity (QI

). A solid line is drawn through these points to 

illustrate the direct relationship. Intake airflow increases from filter combinations and pressurizer use were 

subsequently translated into higher positive cab differential pressures. 

Cab Pen to a lesser extent was also influenced by 

intake filter loading and air leakage. Figure 4 shows 

the relationship between leakage (L) and intake filter 

differential pressure (-∆pf), with the 12.7-mm- (1/2-in.­

) diameter leakage hole open. The leakage data are 

categorized by recirculation filter and pressurizer use 

with dashed lines drawn through these data groups to 

illustrate their associations. This figure shows a direct 

relationship between intake leakage and filter differential pressure for all of the data groups. The higher efficiency intake filter and loading conditions increased the 

differential pressure and leakage across all data groups. 

The corresponding minimum and maximum leakage 

(L) and penetration (Pen) ranges shown in Tables 1 

and 2 are reflective of this effect. Pen for no leakage 

conditions was commonly between the minimum and 

the average value and Pen for leakage was commonly 

between the average and maximum value. 

Figure 4 

Intake leakage and filter differential pressure relationship. 

Conclusions 

Cab air filtration system factors were experimentally 

studied in the laboratory for submicrometer particulate penetration into the cab enclosure. Both series of 

experiments indicated that the intake filter efficiency 

and recirculation filter were the two most influential 

factors on cab penetration. The higher efficiency intake filter (>99% capture efficiency) changed the cab 

penetration by an order of magnitude over the lower 

efficiency intake filter (between 29% and 44% capture 

efficiency). Using a recirculation filter (~90% capture 

efficiency) further reduced cab penetration, usually by 

an order of magnitude over the intake air filter by itself. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The recirculation filter also significantly decreased the 

decay time needed for the cab interior concentrations 

to go down and stabilize after the cab door was closed. 

The average decay times ranged from 16 and 29 minutes without the recirculation filter and were from 6 to 

11 minutes with the recirculation filter. Thus, a recirculation filter mutually reduced cab penetration and 

exposure time to higher peak concentrations after the 

cab door is closed. 

Cab penetration was also affected to a lesser extent 

by intake filter loading and air leakage. Intake filter 

efficiency and filter loading increased the pressure differential across the filter and on the 12.7-mm- (1/2-in.-) 

diameter leak opening on the downstream side of the 

filter. This higher pressure differential increased the 

percentage of intake air leakage bypassing the filter, 

thus increasing cab penetration. 

Adding an intake pressurizer fan to the cab filtration system increased intake airflow and cab pressure 

significantly with negligible changes to recirculation 

airflow and only small changes to cab penetration. The 

lower efficiency intake filter showed decreased capture 

efficiency at higher intake airflow rates, slightly increasing cab penetration with the pressurizer. The higher 

efficiency intake filter showed negligible changes in 

filter efficiency and cab penetration at higher intake 

airflows with the pressurizer. Higher intake airflows 

from the pressurizer increased the differential pressure 

across the intake filter and increased the cab pressure. 

Although cab pressure was directly related to intake air 

quantity, it did not reflect the quality of the intake air 

supply and cab penetration performance. 

Acknowledgments 

The authors express their appreciation to Thomas 

Mal, engineering technician, for assistance with the setup 

and execution of these experiments. 

Footnote: 1

Mention of any company name or product does not 

constitute endorsement by the National Institute for Occupational Safety and Health. 

Disclaimer 

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. 

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