Key Design Factors of 

Enclosed Cab 

Dust Filtration Systems 

RI 9677 

REPORT OF INVESTIGATIONS/2008 

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Report of Investigations 9677 

Key Design Factors of Enclosed Cab Dust Filtration Systems 

By John A. Organiscak and Andrew B. Cecala 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

November 2008 
This document is in the public domain and may be freely copied 

or reprinted. 

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DHHS (NIOSH) Publication No. 2009–103 

November 2008 

SAFER • HEALTHIER • PEOPLETM 
CONTENTS
 

Page 

Abstract............................................................................................................................................1 

Introduction......................................................................................................................................2 

Test apparatus and measurement methods.......................................................................................3 

Experimental cab test factors...........................................................................................................6 

Experimental design.........................................................................................................................8 

Experimental results.........................................................................................................................9 

Statistical analysis..........................................................................................................................14 

Mathematical model for cab penetration .......................................................................................15
 

Discussion......................................................................................................................................18 

Conclusions....................................................................................................................................21 

Acknowledgment ...........................................................................................................................22 

References......................................................................................................................................22 

Appendix A.—Half-fraction experimental design.........................................................................24 

Appendix B.—Experimental test data ...........................................................................................25
 

Appendix C.—Stepwise regression analysis of filtration system without pressurizer ..................34 

Appendix D.—Stepwise regression analysis of filtration system with and without pressurizer......37 

Appendix E.—Mathematical model for cab filtration system.......................................................40 

ILLUSTRATIONS 

1. Experimental cab test apparatus..............................................................................................3 

2. Air pressure-quantity characteristic curves of fans on experimental cab apparatus...............4 

3. Laboratory cab test apparatus used in PRL’s longwall test gallery........................................5 

4. Box-and-whisker plot of cab Pen for filter combinations without pressurizer.......................9 

5. Box-and-whisker plot of cab Pen for filter combinations with pressurizer..........................10 

6. Relationship between intake filter differential pressure and intake airflow .........................12 

7. Relationship between cab differential pressure and intake airflow ......................................13 

8. Relationship between intake leakage and intake filter differential pressure.........................13 

9. Mathematically modeled cab Pen versus experimentally measured cab Pen.......................18 

10. Ambient air size classified particle count concentrations.....................................................19 

C-1. Standardized predicted values for regression model without pressurizer.............................35 

C-2. Normal probability plot of standardized residuals without pressurizer................................35 

C-3. Standardized residuals versus standardized predicted values without pressurizer ...............36 

D-1. Standardized predicted values for regression model with and without pressurizer..............38 

D-2. Normal probability plot of standardized residuals with and without pressurizer.................38 

D-3. Standardized residuals versus standardized predicted values with and without pressurizer...39 

E-1. Schematic of basic cab filtration system ..............................................................................41 

TABLES 

1. Experimental cab test factors..................................................................................................6 

2. Cab testing results without pressurizer .................................................................................11 

3. Cab testing results with pressurizer ......................................................................................11 

4. List of statistically significant regression factors affecting cab Pen.....................................14 
CONTENTS—Continued 

Page 

5. Recirculation filter efficiency results for 0.3- to 1.0-μm-sized particles..............................16 

6. Summary of NIOSH enclosed cab field studies ...................................................................20 

A-1. Half-fraction experimental design ........................................................................................24 

B-1. First-half fraction test data without intake pressurizer (I = +ABCDE) ................................25 

B-2. Second-half fraction test data without intake pressurizer (I = −ABCDE)............................28 

B-3. Pressurizer test data...............................................................................................................31 

C-1. Stepwise regression model without pressurizer....................................................................34 

C-2. ANOVA for stepwise regression model without pressurizer ...............................................34 

D-1. Stepwise regression model with and without pressurizer.....................................................37 

D-2. ANOVA for stepwise regression model with and without pressurizer ................................37 

ACRONYMS AND ABBREVIATIONS USED IN THIS REPORT 

AAF American Air Filter 

ANOVA analysis of variance 

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

 Engineers, Inc. 

CFR Code of Federal Regulations 

HVAC heating, ventilation, and air conditioning 

MERV minimum efficiency reporting value 

MSHA Mine Safety and Health Administration 

NIOSH National Institute for Occupational Safety and Health 

PRL Pittsburgh Research Laboratory (NIOSH) 

PVC polyvinyl chloride 

STP standard temperature and pressure 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

ft foot 

ft2

 square foot 

 ft3

 cubic foot 

 ft/min foot per minute 

ft3

/min cubic foot per minute 

hr hour 

in inch 

in2

 square inch 

 in Hg inches of mercury 

in w.g. inches of water gauge 

L liter 

 L/min liter per minute 

 mA milliampere 

 min minute 

 mg/m3 milligram per cubic meter 

 mph miles per hour 

V volt 

V dc volt, direct current 

 μm micrometer 

°F degree Fahrenheit 

 

 

KEY DESIGN FACTORS OF ENCLOSED CAB 

DUST FILTRATION SYSTEMS 

By John A. Organiscak1 and Andrew B. Cecala1 

1

Mining engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

ABSTRACT 

Enclosed cabs are a primary means of reducing equipment operators’ silica dust exposure 

at surface mines. The National Institute for Occupational Safety and Health experimentally 

investigated various factor effects on cab air filtration system performance. The factors investigated were intake filter efficiency, intake air leakage, intake filter loading (filter flow resistance), 

recirculation filter use, and wind effects on cab particulate penetration. Adding an intake pressurizer fan to the filtration system was also investigated. 

Results indicate that intake filter efficiency and recirculation filter use were the two most 

influential factors on cab penetration performance. Use of the recirculation filter reduced cab 

penetration by usually an order of magnitude over the intake air filter alone because of the multiplicative filtration of the cab interior air. Intake air leakage and filter loading affected the cab 

penetration to a lesser extent, while wind had the least impact on cab penetration between the 

calm and 10-mph wind velocities tested. Adding an intake pressurizer fan notably increased 

intake airflow and cab pressure with only minor changes to cab penetration. A mathematical 

model was developed that describes cab penetration in terms of intake filter efficiency, intake air 

quantity, intake air leakage, recirculation filter efficiency, recirculation filter quantity, and wind 

penetration. 
 

2
 

INTRODUCTION 

Overexposure to airborne respirable crystalline silica (or quartz) dust can cause silicosis, 

a serious or fatal respiratory lung disease. Mining has some of the highest incidences of workerrelated silicosis, and mining machine operators constitute the occupation most commonly associated with the disease [NIOSH 2003]. The 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 2.0 mg/m3 of airborne respirable dust for 

coal mine workers as defined by the U.K. Mining Research Establishment (MRE) criteria 

[30 CFR2

2

Code of Federal Regulations. See CFR in references. 

 70–72, 74 (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 sample. MSHA’s nuisance dust limit (total dust) for metal/nonmetal miners is 

10 mg/m3 as defined by the American Conference of Governmental Industrial Hygienists 

[ACGIH 1973; 30 CFR 56–58 (2007)]. If more than 1% quartz mass is determined to be in the 

metal/nonmetal mine worker dust sample using the National Institute for Occupational Safety 

and Health (NIOSH) 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 the shift. 

Mine worker overexposure to quartz dust continues to be a problem at U.S. mining operations. 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 2008]. 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 have shown that rock drill dust generation was one order of 

magnitude higher than bulldozer dust generation and that enclosed cab dust reduction efficiency 

for this equipment varied from 44% to nearly 100% [Organiscak and Page 1999]. This study 

further showed a wide variability in dust concentration and silica content within the same 

enclosed cab measured intermittently over an 8-month period [Organiscak and Page 1999]. 

Additional NIOSH field studies of retrofitting five older enclosed cabs with air filtration system 

improvements also showed their cab dust reduction efficiency varied from 64% to 99% [Chekan 

and Colinet 2003; Organiscak et al. 2003; Cecala et al. 2003, 2005]. These studies indicate that 

cab air filtration system design and operational factors influence dust control effectiveness and 

the 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 the NIOSH 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 performance. 
The dependent cab performance variables measured included cab particulate penetration, intake 

airflow, recirculation airflow, intake filter pressure, cab pressure, and intake air leakage. 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 cab filtration system features 

similar to those of existing equipment cabs. The cab test apparatus was a 72-ft3 painted plywood 

enclosure 6 ft high by 3 ft wide by 4 ft deep on rolling casters (Figure 1). 

Figure 1.—Experimental cab test apparatus. 

The front side was a 

hinged door with a Plexiglas window to observe the interior of the enclosure. The enclosure 

joints were sealed with silicon, and the entry door was sealed with high-density foam tape to 

ensure good cab integrity. Three 1-in-diam holes were uniformly spaced in the Plexiglas window 

on the front door and on the opposing back side wall of the cab to allow intake air to uniformly 

exit the cab at positive pressure. 

A 27.6-V dc, variable-speed, Ametek RTP1400 brushless dual-fan blower was mounted 

on the front half of the enclosure roof with discharge vents located through the cab ceiling near 

the front door. The dual-fan blower’s air pressure-quantity characteristic curve at maximum 

speed is shown in Figure 2. A mockup roof-mounted HVAC Plexiglas housing encased the dualfan blower, and a 1-ft by 2-ft cab recirculation air inlet was placed through the opposing back 

side of the roof/ceiling. A frame and holding bracket were incorporated around the ceiling inlet 

for installing a pleated panel filter. Another 1-ft by 2-ft cab inlet was placed near the back floor 

of the cab and was connected to the back side of the mockup HVAC enclosure on the cab roof 

3
 
with a transition, two 90° PVC elbows, and 6-in-diam PVC pipe. An inlet cover panel with highdensity foam on the perimeter was used to close either inlet during testing. During this testing, 

the cab recirculation air was drawn only through the ceiling inlet, which is similar to many of the 

roof-mounted retrofit HVAC systems. PRESSURE, in w.g. 

Figure 2.—Air pressure-quantity characteristic curves of fans on experimental cab apparatus. 

Outside makeup air was brought into the side of the mockup HVAC system housing 

through either of two 3-in-diam PVC pipes connected to an exterior Plexiglas filter box. One of 

the pipes drew air from the filter box with only the recirculation fans. The other pipe could be 

pressurized with intake air from a 15- to 27.6-V dc, variable-speed, Ametek ECDC brushless 

single-fan blower located inside the filter box. The single-fan blower’s air pressure-quantity 

characteristic curve at maximum speed is shown in Figure 2. Both PVC intake air pipes were 

fitted with ball valves so 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 1⁄2-in-inside-diam barbed hose fitting opening 

for leakage testing around the intake filter. 

Several of the cab’s operating parameters were measured during testing with static air 

pressure gauges and airflow monitors, electronically recording to a Telog R-3307 seven-channel 

data acquisition system (Telog Instruments, Inc., Victor, NY). The negative differential pressure 

across the exterior to interior of the intake filter box was measured with a 0- to 2-in w.g. 

Magnehelic pressure instrument with a 4- to 20-mA output (Dwyer Instruments, Inc., Michigan 

City, IN). Cab enclosure positive-pressure differential was measured with a 0.0- to 0.5-in w.g. 

Magnehelic pressure instrument with a 4- to 20-mA output (Dwyer 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 

speed was measured on the top left corner of the cab with a 0- to 6,000-ft/min AIRFLOW AV6 

Digital Handheld Vane Anemometer with a 0- to 1-V analog output to verify consistent airflow 

conditions during the test (AIRFLOW, Buckinghamshire, U.K.). 

4
 
Other cab operating data measured before and after each test were intake airflow, recirculation airflow, average wind speed, and atmospheric conditions. Intake airflow velocity was 

centerline measured inside the 3-in-diam PVC intake pipe with a 0- to 6,000-ft/min TSI Model 

8346 VelociCALC Hot Wire Anemometer (TSI, Inc., Shoreview, MN). The recirculation airflow 

was measured with a 0- to 2,000-ft3

/min Alnor Standard Balometer Capture Hood placed over 

the ceiling inlet/filter (TSI, Inc., Alnor Products, Shoreview, MN). Wind speed measurements 

were made with a Davis handheld vane anemometer for 1-min periods on each side and top of 

the cab (Figure 3). 

Figure 3.—Laboratory cab test apparatus used in PRL’s longwall test gallery. 

Atmospheric wet- and dry-bulb temperatures were taken with a Davis Inotek 

battery-operated psychrometer (Davis Inotek, Baltimore, MD). Barometric pressure was measured with a Pretel AltiPlus K2 Electronic Altimeter (France). 

The cab particulate penetration performance was measured by relative comparisons of 

particle count concentrations inside (C1) and outside (C3) the cab test stand, challenged with 

ambient air particles (see Figure 3). Portable handheld HHPC-6 particle counters with six custom 

channel sizes of 0.3, 0.5, 0.7, 1.0, 3.0, and 5.0 μm were operated at 2.83 L/min (0.1 ft3

/min) 

(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 1-min sampling periods. The instruments were mounted inside the enclosure and sampled at the designated locations remotely 

through 18-in lengths of 1/8-in-inside-diam Tygon tubing with isokinetic inlet probes. The 

manufacturer’s 0.45-in-diam isokinetic inlet probes were used at all locations except on the 

outside sampling location during the wind tests. For these tests, a 1/8-in-diam isokinetic probe 

inlet was used to more closely match up the inlet sampling velocity to the incoming wind velocity. Particle counts per liter were recorded for 1-min time periods in the instruments’ internal 

buffer/memory. Since the largest measurable fraction of ambient air particles was in the submicron size range, the three smaller particle counter channels were summed to determine the 

submicron (0.3- to 1.0-μm) respirable particle count concentrations inside (C1) and outside (C3) 

the cab enclosure for each minute of the test. Also, cab intake air particle count concentrations 

5
 
(C2) were measured with another HHPC-6 inside the filter box to determine intake filter efficiency under no leakage conditions around the intake filter. 

Submicron particle cab penetration (Pen = C1/C3) performance was determined from 

corresponding 15-min averages at reasonably stable interior cab concentrations. The time for the 

cab enclosure concentrations to decay and reach interior stability depended on several factors 

such as intake filter efficiency, intake airflow, recirculation filter use, initial inside particle count 

concentration, and outside particle count concentration. One presumption for interior cab 

concentration stability is a constant or stable outside concentration. Preliminary cab testing indicated that after closing the enclosure door most of the interior concentration decay occurred 

within 15 and 30 min with and without the recirculation filter, respectively. Ambient air concentrations were also found to be reasonably stable during these preliminary tests. Therefore, experimental cab tests were conducted for 30- and 45-min periods with and without the recirculation 

filter, respectively, to achieve a reasonably steady concentration averaging period for the last 

15 min of a test. A cab decay time for each test was estimated by the number of 1-min time 

periods it took to reach the average inside concentration for the last 15 min of the test. Finally, 

it must be noted that cab penetration (Pen) will be reported throughout this report, but can be 

easily converted to a cab reduction efficiency (% cab reduction efficiency = (1 – Pen) × 100%) 

or a cab protection factor (cab protection factor = 1/Pen) [Organiscak et al. 2003]. 

EXPERIMENTAL CAB TEST FACTORS 

Experiments were conducted on the cab test apparatus to study multiple filtration system 

factors on cab penetration. Table 1 shows these experimental test factors for cab filtration systems without and with an intake pressurizer fan (referred to as “pressurizer”). 

6
 

Table 1.—Experimental cab test factors 

Filtration system without Filtration system with 

Test factors intake pressurizer fan intake pressurizer fan 

Low-level (−1) High-level (+1) Low-level (−1) High-level (+1) 

(A) Intake filter efficiency Single-stage Multistage (a) Single-stage Multistage (a) 

(B) Intake filter loading Unloaded Loaded (b) Unloaded Loaded (b) 

(C) Intake air leakage Sealed 1⁄2-in hole (c) Sealed 1⁄2-in hole (c) 

(D) Recirculation filter None Panel filter (d) None Panel filter (d) 

(E) Wind Calm 10 mph (e) Calm Calm

The test factors 

studied on the cab filtration system without the pressurizer were intake filter efficiency, intake 

filter loading (airflow resistance), intake air leakage around the filter, recirculation filter use, and 

wind. This series of testing was conducted in PRL’s longwall test gallery with the cab’s front 

door and three air exit holes oriented into the wind direction, as shown in Figure 3. The cab was 

positioned in the cross-section of the gallery so as to achieve reasonably equal air velocities on 

both sides and top of the cab. The maximum wind velocity that could be reached inside the longwall gallery was 10 mph. Wind infiltration into the cab was previously shown to occur when cab 

pressure is exceeded by wind velocity pressure [Heitbrink et al. 2000]. 
Identical experimental test factors were studied on the cab filtration system with the 

pressurizer, except for wind. Wind was excluded from the pressurizer tests since the cab pressure 

was certain to be above the 0.05-in w.g. velocity pressure generated by the 10-mph wind velocity 

inside the longwall test gallery. This series of testing was conducted in the high bay area outside 

the gallery, as shown in Figure 1. 

The experimental cab test factors shown in Table 1 are described below. The low- and 

high-level conditions are mathematically represented by −1 and +1, respectively, for subsequent 

linear regression modeling of the test levels. The high level of cab test factors A, B, C, D, and E 

in Table 1 are also coded by lower-case letters a, b, c, d, and e, respectively, to conveniently 

describe test conditions. For example, the test condition ade without the pressurizer represents a 

multistage intake filter (a), an unloaded intake filter, a sealed intake leakage, a recirculation 

panel filter (d), and a 10-mph wind velocity (e) test. 

(A) Intake Filter Efficiency 

• Low-level (−1): A single-stage, round pleated cellulose filter cartridge (7-in-diam by 

13-in-long, Donaldson Co., Inc., Minneapolis, MN) with lower submicron particle size filter 

efficiency. 

• High-level (+1) (a): A multistage, round microglass and electrostatic contiguous 

layered filter cartridge (7-in-diam by 12-in-long, Clean Air Filter, Defiance, IA) with higher 

submicron particle size filter efficiency. 

(B) Intake Filter Loading 

 • Low-level (−1): An unloaded intake filter was tested in what was considered as new 

condition (without any exposure to heavy or coarse dust loading). 

• High-level (+1) (b): A loaded intake filter was simulated by placing a round cut piece 

of 14-gauge perforated plate (3/32-in-diam holes staggered 3/16 in center to center) fitted 

flush within the interior of the filter gasket area and outlet hole of the filter cartridge. A 2-inwide strip of duct tape was also placed down the center of the perforated plate to help 

noticeably increase filter resistance. Increasing intake filter resistance is used to simulate 

dust-loading effects on the cab filtration system. 

(C) Intake Air Leakage 

• Low-level (−1): The 1⁄2-in-inside-diam hole in the filter box was sealed or closed. 

• High-level (+1) (c): The 1⁄2-in-inside-diam hole in the filter box was open. The TSI 

Model 4040 Thermal Mass Flowmeter was connected with tubing to this hole for measuring 

the quantity of the leak. 

(D) Recirculation Filter 

• Low-level (−1): None used. A 12-in-wide by 24-in-long by 4-in-deep 2×4 woodconstructed open-filter frame blank was inserted into the aluminum frame filter holding 

bracket with a rectangular perforated restrictor plate (same material used for loading the 

intake filter) covering the inlet area side of the bracket. The restrictor plate had equally 

spaced 2-in-wide duct tape strips across it to achieve a targeted balance of 25 ft3

/min of 

intake air for the unloaded and more restrictive Clean Air Filter intake filter when used 

7
 
without the recirculation filter and pressurizer. The HVAC dual-fan blower had to be run at 

maximum speed to achieve this target intake airflow. 

• High-level (+1) (d): The recirculation filter used was an American Air Filter (AAF) 

pleated microglass panel filter (12-in-width by 24 in-length by 4-in-depth nominal size). 

It had an American Society of Heating, Refrigerating and Air-Conditioning Engineers 

(ASHRAE) minimum efficiency reporting value (MERV) of 15, or 85%–94.9% in the 

0.3- to 1.0-μm size range at a rated airflow capacity of 1,000 ft3

/min. This filter was inserted 

into the aluminum frame holding bracket with the perforated restrictor plate. 

(E) Wind (only tested on the cab filtration system without pressurizer) 

• Low-level (−1): Cab was tested at a calm air velocity condition inside the longwall test 

gallery. 

• High-level (+1) (e): Cab was tested at a 10-mph wind velocity condition inside the 

longwall gallery. 

Cab filtration system fan speeds were kept constant throughout experiments to examine 

the test factor effects on cab performance. All of the tests were conducted with the HVAC dualfan blower set to maximum speed. The intake pressurizer testing was conducted with its fan 

speed set in the middle of its operating range so the cab pressure instrumentation would not 

exceed its maximum of 0.5 in w.g. 

EXPERIMENTAL DESIGN 

Experiments were conducted on all of the cab test factor combinations shown in Table 1 

for each filtration system. These cab factor test combinations were conducted in several series or 

blocks of experiments. The first series of experiments was conducted on the cab filtration system 

without the intake pressurizer. Laboratory testing of this filtration system configuration was 

based on a five-factor, two-level factorial experimental design [Myers and Montgomery 1995]. 

This design was split into two blocks of half-fraction experiments (see Appendix A) [Myers and 

Montgomery 1995]. Each half-fraction is a full two-level factorial design for the four cab factor 

configurations (ABCD) with wind velocity (E) testing split equally between the half-fraction 

blocks of experiments. This design permits screening of a half-fraction block of data for the 

significant single factor and two factor interactions [Myers and Montgomery 1995]. 

The experimental run conditions were randomized, but testing was conducted by running 

a test period with one HHPC-6 instrument sampling inside and another HHPC-6 instrument 

sampling outside the cab enclosure and then switching these instruments for a subsequent second 

test period under the same experimental run conditions. Each experimental run condition was 

randomly conducted twice, providing four enclosed cab testing periods. Although the particle 

counting instruments were individually factory-calibrated, they were switched for the subsequent 

test periods to average out any instrument biases. Experimental runs were usually repeated more 

than two times if the ambient test concentration exceeded 100,000 counts/L or if there was 

noticeable cab penetration variation (standard deviation > 0.035). Since preliminary statistical 

analysis on the first half-fraction block of the experimental design indicated significance for all 

factors either individually or as interactions, the second half-fraction block of the experimental 

design was subsequently conducted to complete the full five-factor, two-level factorial experimental design. A total of 74 randomized conditional runs or 148 tests were conducted for the 

8
 
 

complete two-level factorial experimentation. The first and second half-fraction of experimental 

data are shown in Tables B-1 and B-2, respectively, in Appendix B. 

Lastly, another series or block of experiments was conducted on the cab test apparatus 

configured with the pressurizer fan. These tests were conducted without wind and in similar 

fashion as described above. This testing followed the four-factor, two-level factorial experimental design (ABCD) shown in Table A-1. A total of 34 randomized conditional runs or 68 tests 

were completed during these experiments. Table B-3 shows the pressurizer block of experimental data. 

EXPERIMENTAL RESULTS 

The two largest test factors that influenced cab penetration (Pen) for all of the experiments were intake filter efficiency and recirculation filter. Figures 4 and 5 show box-and-whisker 

plots of the cab penetration data classified by the intake filter and recirculation filter use for the 

first series of experiments without the pressurizer and for the second series of experiments with 

the pressurizer, respectively. Each box-and-whisker section represents 25% of the data collected, 

with the median displayed in the middle of the boxes. The open point shown outside the whisker 

in Figure 4 is an outlying data point.

9
 

Figure 4.—Box-and-whisker plot of cab Pen for filter combinations without pressurizer. 

 Figures 4 and 5 illustrate significant differences in cab Pen 

between the intake filters by themselves and with a recirculation filter. Using the recirculation 

filter made a significant reduction in cab Pen compared to the intake filter by itself. The figures 

also show that the cab Pen performance of the lower-efficiency intake filter in combination with 

the recirculation filter was similar to the cab performance of the higher-efficiency intake filter by 

itself. The effects of the other experimental test factors can be seen in the spread of Pen data in 

both of these figures. 
Figure 5.—Box-and-whisker plot of cab Pen for filter combinations with pressurizer. 

Cab Pen and other cab performance statistics were also computed and examined with 

respect to the experimental test factors. Table 2 shows the cab performance statistics (average 

and minimum-maximum) for three key test factors (intake filter efficiency (A), intake filter 

loading (B), and recirculation filter (D)) for the first series of experiments on the filtration system 

without a pressurizer. Average intake filter efficiencies measured for submicron size particles 

(0.3–1.0 μm) are also reported in this table. The wind velocity conditions were not differentiated 

in this table since this factor did not exhibit noticeable differences in cab Pen compared to the 

other experimental factors. Table 3 shows similar cab performance statistics for the second series 

of cab experiments on the filtration system with a pressurizer. 

Table 2 again shows that the largest reductions in cab Pen without the pressurizer 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 higherefficiency 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 min without the 

recirculation filter and from 7 to 9 min with the recirculation filter. 

Table 3 similarly shows that the largest reductions in cab Pen with the pressurizer 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 higherefficiency 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 min without the 

recirculation filter and from 6 to 11 min with the recirculation filter. 

10
 
Table 2.—Cab testing results without pressurizer 

(Top number is average; bottom italicized numbers are minimum-maximum range) 

Intake filter 

and efficiency, % 

(A) 

Intake 

filter 

loading 

(B) 

Recirculation 

filter 

(D) 

Pen 

C1 /C3 

QI , 

ft3

/min 

−Δpf , 

in w.g. 

l 

% of QI 

QR , 

ft3

/min 

+Δpc , 

in w.g. 

Decay 

time, 

min 

Single-stage 

35% 

Single-stage 

32% 

Single-stage 

44% 

Single-stage 

42% 

Multistage 

>99% 

Multistage 

>99% 

Multistage 

>99% 

Multistage 

>99% 

Unloaded 

Unloaded

Loaded 

Loaded

Unloaded 

Unloaded

Loaded 

Loaded

None 

 Panel filter 

None 

 Panel filter 

None 

 Panel filter 

None 

 Panel filter 

0.635 

0.557-0.690 

0.134 

0.122-0.148 

0.569 

0.426-0.637 

0.054 

0.045-0.059 

0.072 

0.027-0.132 

0.007 

0.002-0.012 

0.131 

0.040-0.211 

0.009 

0.003-0.014 

48.8 

45.4-50.6 

58.7 

56.0-61.0 

21.5 

20.5-22.3 

25.2 

23.6-27.2 

22.8 

21.0-25.0 

28.7 

26.2-30.2 

14.9 

13.8-16.2 

18.8 

17.2-20.2 

0.16 

0.14-0.18 

0.22 

0.19-0.23 

0.50 

0.46-0.53 

0.69 

0.67-0.72 

0.48 

0.45-0.51 

0.64 

0.62-0.67 

0.54 

0.50-0.58 

0.74 

0.71-0.77 

0.8 

0.0-1.7 

0.8 

0.0-1.8 

3.7 

0.0-7.8 

4.3 

0.0-7.9 

3.4 

0.0-7.1 

3.2 

0.0-6.5 

3.7 

0.1-11.6 

6.3 

0.1-10.8 

358 

338-368 

318 

300-328 

378 

368-390 

337 

332-345 

383 

370-390 

332 

318-345 

388 

365-398 

344 

330-350 

0.24 

0.21-0.28 

0.31 

0.28-0.37 

0.08 

0.05-0.12 

0.09 

0.06-0.10 

0.09 

0.06-0.12 

0.10 

0.07-0.12 

0.06 

0.03-0.09 

0.06 

0.04-0.09 

16 

1-38 

7 

1-21 

18 

3-38 

9 

1-23 

27 

15-36 

7 

2-20 

29 

12-39 

9 

1-23 

11
 

Table 3.—Cab testing results with pressurizer 

(Top number is average; bottom italicized numbers are minimum-maximum range) 

Intake filter 

and efficiency, % 

(A) 

Intake 

filter 

loading 

(B) 

Recirculation 

filter 

(D) 

Pen 

C1 /C3 

QI , 

ft3

/min 

−Δpf , 

in w.g. 

l 

% of QI 

QR , 

ft3

/min 

+Δpc , 

in w.g. 

Decay 

time, 

min 

Single-stage 

29% 

Single-stage 

29% 

Single-stage 

39% 

Single-stage 

39% 

Multistage 

>99% 

Multistage 

>99% 

Multistage 

>99% 

Multistage 

>99% 

Unloaded 

Unloaded

Loaded 

Loaded

Unloaded 

Unloaded

Loaded 

Loaded

None 

 Panel filter 

None 

 Panel filter 

None 

 Panel filter 

None 

 Panel filter 

0.693 

0.636-0.720 

0.194 

0.179-0.211 

0.609 

0.596-0.620 

0.073 

0.064-0.079 

0.071 

0.030-0.107 

0.009 

0.004 -0.012 

0.108 

0.037-0.178 

0.010 

0.003–0.018 

80.1 

78.2-82.0 

91.8 

89.4-93.4 

30.2 

29.2-31.4 

33.2 

31.9-34.8 

39.2 

38.0-40.8 

44.8 

43.4-46.0 

23.1 

21.4-25.0 

26.4 

24.6-28.6 

0.31 

0.31-0.33 

0.39 

0.38-0.40 

0.96 

0.94-1.01 

1.16 

1.13-1.21 

0.87 

0.84-0.88 

249 

0.99-1.02 

1.04 

1.02-1.06 

1.24 

1.23-1.25 

0.8 

0.0-1.6 

0.9 

0.0-1.6 

3.8 

0.0-7.7 

3.8 

0.0-7.7 

2.8 

0.0-5.7 

2.7 

0.0-5.4 

4.0 

0.1-10.0 

4.9 

0.1-9.8 

342 

340-348 

310 

305-315 

383 

370-395 

338 

332-345 

370 

358-378 

335 

325-342 

387 

380-395 

341 

330-350 

0.44 

0.42-0.45 

0.47 

0.44-0.49 

0.10 

0.09-0.11 

0.12 

27-32 

0.16 

0.14-0.17 

0.20 

0.18-0.21 

0.07 

0.06-0.08 

0.08 

0.07-0.09 

22 

0-36 

8 

1-26 

17 

3-40 

11 

1-21 

25 

12-36 

8 

 2-21 

20 

 13-32 

6 

1-16 
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 2 and 3 

shows the cab Pen for the lower-efficiency intake filter tests perceptibly increased with the addition of the pressurizer. This corresponded to higher intake airflows and decreased intake filter 

efficiency with the pressurizer versus without the pressurizer. Cab Pen change was negligible for 

the higher-efficiency 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 (−Δpf ), cab intake airflow quantity (QI), cab differential pressure (+Δpc), and intake air leakage (l) all noticeably changed for the filter test factor 

combinations and pressurizer as shown in Tables 2 and 3. Figure 6 illustrates the indirect 

relationships between intake filter differential pressure (−Δpf ) and cab intake airflow quantity 

(QI) for these experiments. 

Figure 6.—Relationship between intake filter differential pressure and intake airflow. 

The intake filter differential pressure and airflow quantity data are 

grouped by recirculation filter and pressurizer use, with group associations indicated by dashed 

lines. The data show that the differential pressure across the intake filter was inversely related to 

intake air quantity for all data groups. Adding a recirculation filter increased both the intake airflow and intake filter differential pressure, shifting the associated relationship to the top right of 

the graph. The pressurizer additionally increased the intake airflow and filter differential pressure, further shifting these associated relationships to the top right of the graph. 

Figure 7 shows the direct cab differential pressure (+Δpc) relationship with respect to 

intake air quantity (QI), with points classified by wind and pressurizer use. This figure clearly 

indicates the direct relationship between cab pressure and intake air quantity. It also shows that 

wind increased cab differential pressure by roughly the wind velocity pressure. The pressurizer 

further increased the intake air quantity and cab pressure. 

12
 
Figure 7.—Relationship between cab differential pressure and intake airflow. 

The relationship between leakage (l) and intake filter differential pressure (−Δpf ) with the 

1⁄2-in-diam leakage hole open is shown in Figure 8.

13
 

Figure 8.—Relationship between intake leakage and intake filter differential pressure. 

 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 the 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. 
STATISTICAL ANALYSIS 

Linear regression analysis was conducted to statistically quantify the relationship 

between the cab testing factors (considered independent variables) and cab penetration (dependent variable). Since the box-and-whisker plots of Figures 4 and 5 illustrate an extensive data 

range, nonnormality, and unequal variance in the dependent cab penetration variable, it was 

transformed by using natural logarithms (ln Pen) to stabilize regression modeling variance 

[Myers and Montgomery 1995]. Linear regression analysis was conducted on comparative sets 

of experimental data. Both half-fractions of the cab filtration configuration without the pressurizer were analyzed together for the five experimental test factors (intake filter efficiency (A), 

intake filter loading (B), intake air leakage (C), recirculation filter (D), and wind (E)). A stepwise 

regression analysis of the dependent variable (ln Pen) with respect to the single factors and twofactor interactions was conducted and is shown in Appendix C. The cab filtration system with 

and without the intake pressurizer configurations were also comparatively analyzed excluding 

the 10-mph wind tests. Appendix D shows this stepwise regression model and analysis for the 

dependent variable (ln Pen) with respect to the single factors, two-factor interactions, and 

pressurizer (a blocking factor). All stepwise regression model factors and interactions were 

successively selected by the highest level of significance on cab Pen with no factor removal 

during the analysis. Table 4 shows the statistically significant experimental factors and interactions, listed in descending order of significance for both regression analyses. 

Table 4.—List of statistically significant regression factors affecting cab Pen 

Regression 

selection 

order 

Filtration system tests without 

intake pressurizer fan 

Filtration system tests with and without 

intake pressurizer fan, excluding wind 

1 Recirculation filter (D) Intake filter efficiency (A) 

2 Intake filter efficiency (A) Recirculation filter (D) 

3 Intake filter efficiency × loading (AB) Leakage (C) 

4 Leakage (C) Intake filter efficiency × loading (AB) 

5 Intake filter efficiency × leakage (AC) Intake filter efficiency × leakage (AC) 

6 Intake filter efficiency × recirculation filter (AD) Loading × recirculation filter (BD) 

7 Loading × recirculation filter (BD) Intake filter efficiency × recirculation filter (AD) 

8 Loading × wind (BE) Loading (B) 

9 Loading × leakage (BC) Pressurizer (P) 

Analysis of both filtration systems showed comparable top seven regression factors, 

selected in a somewhat different order. Table 4 again illustrates that the top two experimental 

factors were the intake filter efficiency and the recirculation filter for both filtration systems 

tested. It also shows that leakage had a significant effect on cab Pen for both systems. Furthermore, cab Pen was significantly affected by intake filter efficiency interactions with loading, 

leakage, and recirculation filter use. Wind (eighth, as an interaction) and the pressurizer (ninth, 

as a blocking factor) were some of the least significant factors selected by regression analyses. 

The analyses clearly reveal the multifaceted experimental factor effects on cab Pen, with interactions suggesting factor codependence with other cab operating variables. 

14
 
MATHEMATICAL MODEL FOR CAB PENETRATION 

The cab test factor codependence with several other cab operating variables can be 

observed in Tables 2 and 3 and Figures 6 through 8. The air pressure and quantity relationships 

for the cab filtration system indicate that air quantity balance of contaminants within the system 

may better describe cab penetration. This cab filtration mathematical model is developed in 

Appendix E. It was formulated from a basic time-dependent mass balance model of airborne substances within a control volume. This mathematical model was particularly formulated for 

steady-state conditions in Appendix E and is shown below. It describes cab penetration in terms 

of intake filter efficiency, intake air quantity, intake air leakage, recirculation filter efficiency, 

recirculation filter quantity, and outside wind quantity infiltration into the cab. 

x QI (1−η I + lη I )+ Q Pen =	 = w (E-12) C Q I + Q Rη R 

This equation can also be expressed in other useful forms: 

Q 1−η w

I + lη I + 

Q Pen = 

I (E-13) Q 1+ R η Q R

I 

Q Q 1−η + L w

I η I +

Q Q

or Pen = 

I	 I (E-14) Q 1+ R η Q R

I 

where x = inside cab contaminant concentration, 

 C = outside cab contaminant concentration, 

Pen = ratio of inside to outside contaminant concentration, or x/C, 

QI = intake air quantity into the cab, 

 ηI = intake filter efficiency, fractional, 

QL = air leakage quantity around the intake filter, 

l = fractional portion of intake air leakage, or QL /QI , 

QR = recirculation filter airflow, 

 ηR = recirculation filter efficiency, fractional, 

and Qw = wind quantity infiltration into the cab. 

NOTE: The above equations are dimensionless, so air quantities used in these equations 

must have equivalent units. Also, filter efficiencies and intake air leakage used must be fractional 

values (not percentage values). 

15
 
Verification of this model was examined using the experimental data. Many of the above 

model variables were directly measured during experimental testing, except for the recirculation 

filter efficiency and wind quantity infiltration into the cab. To determine the experimental 

recirculation filter efficiency for validating this model, additional particle counting testing was 

conducted upstream and downstream of the recirculation filter to measure its filter efficiency. 

The AAF recirculation filter panel was tested at the cab floor inlet with the ceiling inlet blocked, 

intake air ducts closed, and cab door opened. A sealed horizontal plywood barrier was installed 

inside the cab, 1.5 ft parallel and above the floor, to create a separate intake sampling duct 

section to the recirculation filter. A particle counter sampled the ambient air in the intake section 

to the filter, and a particle counter sampled the filtered air inside the middle straight section of 

the 6-in-diam PVC recirculation duct (see PVC tube on the outside of the cab shown in 

Figure 1). Isokinetic sampling inlets were used to match sampler inlet velocities to air duct 

velocities. A VelociCalc Hot Wire Anemometer was used to measure the airflow in the PVC 

recirculation duct, and the HVAC dual-fan blower was operated at full speed during these tests to 

achieve recirculation filter airflow comparable with the experiments. Filter tests were conducted 

over a 15-min sampling period with the particle counting instruments switched between successive tests. 

Table 5 shows the filter efficiency results for eight filter tests. 

Table 5.—Recirculation filter efficiency results 

for 0.3- to 1.0-μm-sized particles 

Filter 

test 

Test 

time, 

min 

Filter 

airflow, 

ft3

/min 

Upstream 

concentration, 

counts/L 

Downstream 

concentration, 

counts/L 

Filter 

efficiency,1 

% 

1 15 346 11,296 2,859 74.7 

2 15 346 10,912 2,738 74.9 

3 15 348 24,934 7,007 71.9 

4 15 347 24,020 6,723 72.0 

5 15 344 28,718 8,216 71.4 

6 15 346 39,395 11,382 71.1 

7 15 344 36,635 10,427 71.5 

8 15 346 30,505 8,702 71.5 

Average 15 346 25,802 7,257 72.4 1

Filter efficiency = ((upstream conc. – downstream conc.) /upstream conc.) × 100%. 

Average recirculation filter 

efficiency measured with ambient air was 72.4% for 346 ft3

/min of airflow. Another similar AAF 

filter panel (not used in the experiments) was tested and showed a comparable filter efficiency of 

71.1% for 347 ft3/min of airflow. These filter efficiencies were observed to be less than their 

MERV 15 rating of 85%–94.9% in the 0.3- to 1.0-μm size range. The lower filter efficiencies 

found in these particular tests are most likely due to a relatively larger portion of 0.3- to 0.5-μmsized particles measured in ambient air compared to a more balanced aerosol size range used in 

the MERV test procedure. 

Wind quantity infiltration into the cab during these experiments could not be directly 

measured, but could be estimated for the three orifice openings facing directly into the wind by 

applying the general orifice flow equation described in Appendix E (Equation E-15) and shown 

below [Streeter and Wylie 1979]. The particular orifice flow equation when the wind velocity 

16
 
Q

vo = o Δp= 2 o (E-15) Ao Cd ρ air 

where vo = air velocity through an orifice, 

 Qo = airflow quantity through an orifice, 

 Cd = orifice discharge coefficient, 

Ao = area of orifice, 

 Δpo = air pressure differential across orifice, 

and ρair = air density. 

Wind infiltration into the cab was presumed to occur when wind velocity exceeded the 

cab exit air velocity out of the three orifices opposed to the wind. Cab exit air velocity was 

initially calculated by assuming that the measured intake air quantity into the cab would exit 

equally through the six 1-in-diam holes with a discharge coefficient of 0.61 (a reasonable circular orifice coefficient [Streeter and Wylie 1979], also used in the wind penetration Equation E-16 

[Heitbrink et al. 2000]). When wind velocity exceeded this cab exit air velocity, the difference 

was anticipated to be the wind velocity penetration through the opposing front three holes in the 

cab door, with all of the cab airflow exiting out the back three holes. Equation E-15 was used to 

estimate this wind air quantity forced into the front three holes. Wind quantity infiltration into 

the cab was estimated to vary from 0.8 to 1.8 ft3

/min only for 10 tests under wind test conditions 

abe and abce. The high-efficiency intake filter (a) under loaded conditions (b) had some of the 

lowest cab intake airflows that could be overcome by the 10-mph wind (e) in these particular 

experiments, confirming the loading (B) and wind (E) regression factor interaction with cab Pen 

in Table 4. The increase in cab pressures measured for tests with wind versus without wind (see 

Figure 7) supports the premise that more airflow is disproportionately discharged out a smaller 

area through the back three holes of the cab. 

The cab operating variables for these experiments were applied in the above mathematical penetration model to examine its agreement with the actual cab penetration measured by 

the particle counters. Intake filter efficiencies measured without leakage for the particular filter 

and loading conditions (shown in Tables 2 and 3) were used in the model, as well as the 72.4% 

recirculation filter efficiency determined above. The other model variables (intake air quantity, 

intake air leakage, recirculation air quantity, and wind quantity penetration) were obtained from 

the experimental data in Appendix B. 

Figure 9 shows the graph for the mathematically modeled cab Pen results compared to 

the experimentally measured cab Pen for all test conditions. A unity line is drawn on the graph to 

visually inspect how well the model compared to the measurements. This figure illustrates that 

the model provides a reasonable estimate of the cab Pen using the cab filtration system operating 

variables. The open points in the lower left of the graph illustrate some of the ab tests conducted 

at lower outside particle count concentrations (<15,400 particle counts/L), noticeably increasing 

the measured cab Pen. Additional ab experimental tests were conducted to measure cab Pen at 

pressure exceeds cab static pressure (Equation E-16) described in Appendix E could not be 

applied in these particular experiments because the wind velocity pressure never exceeded the 

cab pressure during the 10-mph wind tests [Heitbrink et al. 2000]. 

17
 
higher outside particle count concentrations (see Tables B-2 and B-3 in Appendix B). Others 

have also reported unreliable cab Pen measurements if outside cab particle counts are too low to 

show measurable differences with respect to those inside the cab [Heitbrink et al. 1998]. Given 

these experimental variations, the mathematical model seems to provide a reasonable estimate of 

the cab penetrations. 

Figure 9.—Mathematically modeled cab Pen versus experimentally measured cab Pen. 

DISCUSSION 

The cab Pen measured in these laboratory experiments was conducted by counting 

particles found in ambient air. Figure 10 shows the size composition of ambient air particle 

concentrations measured for determining cab Pen during the last 15 min of all the tests. The 

three lines on the graph illustrate the 10th, 50th, and 90th percentiles for all of the experimental 

test data. Most of the particles were found in the submicron range, with a median (50thpercentile) submicron (0.3- to 1.0-μm) particle count concentration of 32,394 counts/L. These 

submicron particle count concentrations in the ambient air were found to remain reasonably 

constant during the cab test periods, but changed noticeably from day to day. Tables B-1, B-2, 

and B-3 in Appendix B illustrate this by the smaller differences observed in the average outside 

particle count concentrations (C3) for the last 15 min of the test compared to the complete test 

and by the noticeably larger outside particle count concentrations between tests. This particle 

count variation is part of the experimental error. 

The submicron particles in the ambient air were found to be a convenient and reasonable 

cab Pen test medium in these experiments. Only several particular run conditions were repeated 

because of higher cab Pen variability (standard deviation > 0.035) observed from lower ambient 

air particle count concentrations. Furthermore, coincidence error from high ambient particle 

concentrations (uncounted particles hidden behind other particles) seemed to be negligible in 

these experiments. The particle counter instrument coincidence error is specified at 5% for 

2,000,000 particle counts/ft3, or 70,670 particle counts/L. Only 25 of the 216 tests exceeded this 

concentration, with 7 tests exceeding 100,000 particle counts/L. Since most of the experimental 

18
 
runs having some of the higher ambient air concentration tests resulted in cab Pen standard 

deviations below 0.035, coincidence error was considered inconsequential. 

Figure 10.—Ambient air size classified particle count concentrations. 

The experimental results and mathematical model developed have several limitations. 

First, the intake air leakage was placed in the negative air pressure plenum of the filtration system. Leakage into a negative air pressure plenum can be estimated by using the general orifice 

flow equation. If the leak is on the positive air pressure plenum of the filtration system, air leakage into the filtration system is very unlikely unless air velocity pressure is extremely high near 

the leak to induce air suction (venture effect) into the system. Secondly, experimental wind 

infiltration was more readily estimated from the general orifice equation because a portion of exit 

air was discharged directly into the wind. Wind infiltration through other cab exit air discharge 

configurations is much more difficult to determine and model. Wind infiltration into the cab for 

various discharge configurations can be minimized by maintaining cab pressure higher than wind 

velocity pressure. Finally, the mathematical model does not account for any internal cab 

contamination sources, such as transporting and dispersing contaminants inside the cab by 

the operator. 

In addition, examining various levels of cab enclosure integrity was not part of this 

experimentation. These experiments were conducted on a laboratory cab test stand with reasonably tight, consistent, and well-controlled enclosure integrity. Exhaust air was discharged 

through three 1-in-diam holes on the front and rear of the cab test stand for a combined area of 

0.033 ft2

, or 4.7 in2. It was able to be pressurized to 0.10 in w.g. with 30 ft3/min of intake air and 

had a minimum pressurization of 0.03 in w.g. with 13.8 ft3

/min of intake air under calm wind 

conditions (see Figure 7). Therefore, the cab pressure and exit air velocity were only low enough 

to be affected by the 10-mph wind velocity for a small subset of tests, when the higher-efficiency 

intake filter was under loaded conditions. 

In previous NIOSH field studies, cabs were found to have varying degrees of enclosure 

integrity, indicated by their differences in cab pressures. In these field studies, five older 

19
 
 

enclosed cabs were retrofitted with air filtration system improvements, and their cab dust reduction efficiencies varied from 64% to 99% or cab penetrations of 0.36 to 0.01, respectively 

[Chekan and Colinet 2003; Organiscak et al. 2003; Cecala et al. 2003, 2005]. Table 6 

summarizes these results in ascending order of performance achieved with these retrofitted 

installations. 

Table 6.—Summary of NIOSH enclosed cab field studies 

 

 

Average Average Wind velocity Cab pressure, inside cab outside cab Penetration, Cab evaluation equivalent,1 

in w.g. dust level, dust level, in/out mph mg/m3 mg/m3 

Davey M8B drill None detected 0 0.08 0.22 0.36 

Euclid R-50 truck 0.01 4.5 0.32 1.01 0.32 

CAT 980B loader 0.015 5.6 0.03 0.30 0.10 

IR DM45E drill 0.20–0.40 20.3–28.7 0.05 2.80 0.02 

DrillTech DK40 drill 0.07–0.12 12.0–15.7 0.07 6.25 0.01 

1

Wind velocity equivalent = (4000 √ Δpcab) ft/min × 0.011364 miles · min/ft · hr @ STP. 

All of these cabs had a new roof-mounted HVAC unit installed with a pressurizer 

and filtration system. The Davey M8B drill, CAT 980B loader, and DrillTech DK40 drill had 

Red Dot roof-mounted HVAC systems and a Clean Air Filter intake filter pressurizer. The 

Euclid R-50 and IR DM45E drill had International Transit/Sigma HVAC systems with a singlestage fan pressurizer and a dual-fan pressurizer, respectively. Intake and recirculation filter 

efficiency performance specifications on the retrofitted cab systems were at least 95% on 

respirable-size dust. Pressurizer airflow specifications for these systems were equal or greater 

than 70 ft3

/min. 

During these retrofits, any reasonably repairable cab enclosure cracks, gaps, or openings 

were sealed with silicon and closed-cell foam tape. The cabs had varying degrees of enclosure 

integrity, indicated by their differences in cab pressures. A wind velocity equivalent for the 

measured cab pressures was also calculated using the velocity pressure relationship of the 

general orifice equation (Equation E-15), assuming air density at standard temperature and 

pressure (STP, 70 °F and 29.92 in Hg). These wind velocity equivalents are also shown in 

Table 6 and generally indicate the wind velocity resistance of the cab. Field evaluation of these 

cab systems were conducted with personal gravimetric respirable samplers during three to seven 

operating shifts. 

These field study results show that all of the cab filtration systems reduced outside dust 

penetration into the enclosure, but suggest that enclosed cab integrity was a factor for their range 

of penetration performance. Lower respirable dust cab penetration was observed for two tighter 

cabs that operated from 0.07 to 0.40 in w.g., or wind velocity equivalents of 12 to 28.7 mph, 

respectively. The three cabs that operated from 0 to 0.015 in w.g. or wind velocity equivalents of 

0 to 5.6 mph, respectively, had higher respirable dust penetrations. Since these three cabs had 

achieved cab pressures ≤0.015 in w.g. with 70 ft3

/min or more of intake airflow, one can infer 

that these cabs had significantly larger leakage areas than the laboratory cab test stand. These 

leakage areas comprised tough-to-seal enclosure openings around movable mechanical control 

linkages, behind control panels and from other unidentifiable openings on the cab, which are 

susceptible to penetrating air velocities by wind or the equipment itself such as engine fans 

20
 
and/or tire movement. Also, the Euclid R-50 tr uck could easily exceed the wind velocity 

equivalent of the cab pressure during its traveling operation. Although all of these field studies 

showed that enclosed cab filtration systems reduced outside dust penetration, they also imply that 

better enclosure integrity ensures increased pressurization and resistance to outside penetration 

from wind or high air velocity sources during field operations. 

CONCLUSIONS 

Cab air filtration system factors were experimentally studied in the laboratory for submicron 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 (from 29% to 44% capture efficiency). Using a recirculation filter (72.4% capture efficiency) further reduced cab 

penetration, usually by an order of magnitude over the intake air filter alone. 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 to 

29 min without the recirculation filter and from 6 to 11 min with the recirculation filter. Thus, 

a recirculation filter mutually reduced cab penetration and exposure time to higher peak concentrations after the cab door was closed. 

Air leakage around the intake filter was another significant factor on cab Pen and was 

directly related to the pressure differential across the leak. Loading and leakage interactions 

with the intake filter efficiency were also found to be statistically significant with cab Pen. Wind 

had the least impact on cab Pen between the calm and 10-mph wind velocities tested and was 

only found to be significant as an interaction with intake filter loading without the intake pressurizer fan. 

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 Pen. The lower-efficiency intake filter showed decreased capture efficiency at 

higher intake airflow rates, slightly increasing cab penetration with the pressurizer. The higherefficiency 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 negative differential pressure across the intake filter and increased the positive differential 

pressure inside the cab. Although cab pressure was directly related to intake air quantity, it does 

not necessarily reflect the intake air quality and overall cab penetration. 

Regression analyses of the laboratory cab test stand results corroborated the significance 

of these experimental test factors on cab Pen, but a more general mathematical penetration 

model was formulated with respect to the cab’s filtration system operating variables. It models 

cab Pen in terms of intake filter efficiency, intake air quantity, intake air leakage, recirculation 

filter efficiency, recirculation filter quantity, and outside wind infiltration. This mathematical 

model was validated by the experimental test data and can be used to assess cab filtration penetration based on these cab filtration design variables. 

21
 
ACKNOWLEDGMENT 

The authors express their appreciation to Thomas Mal, Engineering Technician, 

NIOSH-PRL, for his assistance with the setup and execution of these experiments. 

REFERENCES 

ACGIH [1973]. Threshold limit values for chemical substances in workroom air adopted 

by the ACGIH for 1973. Cincinnati, OH: American Conference of Governmental Industrial 

Hygienists. 

Cecala AB, Organiscak JA, Heitbrink WA, Zimmer JA, Fisher T, Gresh RE, Ashley JD 

[2003]. Reducing enclosed cab drill operator’s respirable dust exposure at a surface coal operation using a retrofitted filtration and pressurization system. In: Yernberg WR, ed. Transactions of 

Society for Mining, Metallurgy, and Exploration, Inc. Vol. 314. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 31–36. 

Cecala AB, Organiscak JA, Zimmer JA, Heitbrink WA, Moyer ES, Schmitz M, 

Ahrenholtz E, Coppock CC, Andrews EH [2005]. Reducing enclosed cab drill operator’s respirable dust exposure with effective filtration and pressurization techniques. J Occup Environ Hyg 

2(1):54–63. 

CFR. Code of Federal regulations. Washington, DC: U.S. Government Printing Office, 

Office of the Federal Register. 

Chekan GJ, Colinet JF [2003]. Retrofit options for better dust control. Aggregates Manag 

8(9):9–12. 

Hartman HL [1961]. Mine ventilation and air conditioning. New York: John Wiley & 

Sons, pp. 37–38. 

Heitbrink WA, Hall RM, Reed LD, Gibbons D [1998]. Review of ambient aerosol test 

procedures in ASAE standard S525. J Agric Saf Health 4(4):255–266. 

Heitbrink WA, Thimons ED, Organiscak JA, Cecala AB, Schmitz M, Ahrenholtz E 

[2000]. Static pressure requirements for ventilated enclosures. In: Proceedings of the Sixth International Symposium on Ventilation for Contaminant Control (Helsinki, Finland, June 4–7, 

2000), pp. 97–99. 

Myers RH, Montgomery DC [1995]. Response surface methodology: process and product 

optimization using designed experiments. New York: John Wiley & Sons, Inc. 

NIOSH [2003]. Work-related lung disease surveillance report, 2002. Morgantown, WV: 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, 

National Institute for Occupational Safety and Health, Division of Respiratory Disease Studies, 

DHHS (NIOSH) Publication No. 2003–111. 

NIOSH [2008]. Reducing silica exposures in mining through improved control technologies. [http://www.cdc.gov/niosh/nas/mining/strategicoutcome2.htm]. Date accessed: 

August 2008. 

Organiscak JA, Page SJ [1999]. Field assessment of control techniques and long-term 

dust variability for surface coal mine rock drills and bulldozers. Int J Surf Min Reclam Env 

13:165–172. 

Organiscak JA, Cecala AB, Thimons ED, Heitbrink WA, Schmitz M, Ahrenholtz E 

[2003]. NIOSH/industry collaborative efforts show improved mining equipment cab dust 

protection. In: Yernberg WR, ed. Transactions of Society for Mining, Metallurgy, and 

22
 
Exploration, Inc. Vol. 314. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., 

pp. 145–152. 

Parobeck PS, Tomb TF [2000]. MSHA’s programs to quantify the crystalline silica content of respirable mine dust samples. SME preprint 00-159. Littleton, CO: Society for Mining, 

Metallurgy, and Exploration, Inc. 

Streeter VL, Wylie EB [1979]. Fluid mechanics. 7th ed. New York: McGraw-Hill Book 

Co., pp. 342–349. 

Tomb TF, Gero AJ, Kogut J [1995]. Analysis of quartz exposure data obtained from 

underground and surface coal mining operations. Appl Occup Environ Hyg 10(12):1019–1026. 

23
 
APPENDIX A.—HALF-FRACTION EXPERIMENTAL DESIGN 

Table A-1 shows the construction of two experimental half-fractions. 

24
 

Table A-1.—Half-fraction experimental design 

Run 

Experimental 

condition 

Factor level Block 1 I = +ABCDE Block 2 I = −ABCDE 

A 

Intake 

filter 

efficiency 

B C 

Intake Intake 

filter air 

loading leakage 

D 

Recirculation 

filter 

E 

Wind

Treatment 

 Combination 

E 

Wind 

Treatment 

Combination 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

1 

a 

b 

ab 

c 

ac 

bc 

abc 

d 

ad 

bd 

abd 

cd 

acd 

bcd 

abcd 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

+1 

−1 

−1 

+1 

+1 

−1 

−1 

+1 

+1 

−1 

-1 

+1 

+1 

−1 

−1 

+1 

+1 

−1 

−1 

−1 

−1 

+1 

+1 

+1 

+1 

−1 

−1 

−1 

−1 

+1 

+1 

+1 

+1 

−1 

−1 

−1 

−1 

−1 

−1 

−1 

−1 

+1 

+1 

+1 

+1 

+1 

+1 

+1 

+1 

+1 

−1 

−1 

+1 

−1 

+1 

+1 

−1 

−1 

+1 

+1 

−1 

+1 

−1 

−1 

+1 

e 

a 

b 

abe 

c 

ace 

bce 

abc 

d 

ade 

bde 

abd 

cde 

acd 

bcd 

abcde 

−1 

+1 

+1 

−1 

+1 

−1 

−1 

+1 

+1 

−1 

−1 

+1 

−1 

+1 

+1 

−1 

1 

ae 

be 

ab 

ce 

ac 

bc 

abce 

de 

ad 

bd 

abde 

cd 

acde 

bcde 

abcd 

The lower intake 

filter efficiency, unloaded intake filter, no intake leak, no recirculation filter, and no wind factor 

levels were coded with −1. The higher intake filter efficiency (a), loaded intake filter (b), intake 

leak (c), recirculation filter (d), and wind (e) factor levels were coded with +1. Each half-fraction 

has a full two-level factorial design for the four cab factor configurations (ABCD), with the plus 

and minus wind factor (E) levels in each half-fraction identified by the plus and minus sign of 

the highest-order interaction (identity (I) = +ABCDE and –ABCDE). This partitioned the experimental runs into two identity test blocks with the highest-order interaction (ABCDE) confounded 

[Myers and Montgomery 1995]. 
25 

25

APPENDIX B.—EXPERIMENTAL TEST DATA

ABCDE) + I = er (z est data without intake pressuri

)nioitdno cntalperime ber or ex num

Table B-1.—First half-fraction of t

 run by (Tests sorted 

Test Cab operating parameters Wet- Dry- Baro- Last 15-min test average Test Test and Wind Decay Start Cab Run bulb bulb metric average period † QL time, condition +Δpc ‡ C1 ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen No. QI −Δpf QR vw temp., temp., press., Nos. min ft3/min in w.g. L/min in w.g. ft3/min ft/min °F °F in Hg counts/L counts/L counts/L counts/L counts/L C1 /C3 

T2.P1 1 e 47.9 0.14 0.3 0.28 355 877 44.2 56.5 29.14 1 36,350 30,383 NA 48,760 46,027 0.623 

T2.P2 1 e 48.9 0.14 0.3 0.28 355 904 42.0 53.5 29.14 4 49,244 33,545 NA 52,633 51,773 0.637 

T18.P1 1 e 45.4 0.15 0.3 0.26 368 878 54.5 66.8 29.09 2 19,738 14,126 15,231 22,916 21,432 0.616T18.P2 1 e 46.0 0.15 0.3 0.26 362 886 53.5 65.8 29.09 2 23,008 18,485 19,371 29,287 26,930 0.631T35.P1 1 e 46.8 0.15 0.3 0.25 360 883 44.5 50.0 28.98 37 26,179 10,791 11,479 17,224 20,929 0.627T35.P2 1 e 48.0 0.15 0.2 0.25 358 876 41.5 48.5 29.00 2 12,758 10,367 11,622 17,534 14,098 0.591T27.P1 2 a 23.0 0.51 0.4 0.07 378 Calm 53.5 63.8 29.03 32 68,013 2,067 117 75,368 76,331 0.027

T27.P2 2 a 23.0 0.51 0.5 0.07 385 Calm 52.5 64.2 29.01 25 55,231 1,656 67 45,682 48,045 0.036

T28.P1 2 a 22.7 0.51 0.4 0.07 385 Calm 54.0 65.8 28.93 34 38,838 1,597 64 42,482 49,953 0.038

T28.P2 2 a 22.7 0.51 0.4 0.07 388 Calm 53.5 66.0 28.92 27 34,351 1,747 59 38,713 38,641 0.045

T6.P1 3 b 20.5 0.53 0.4 0.07 368 Calm 52.0 66.5 28.98 37 23,502 10,710 11,433 19,563 21,699 0.547T6.P2 3 b 20.6 0.53 0.4 0.07 378 Calm 51.5 66.5 29.00 13 17,700 10,008 10,453 18,272 17,992 0.548T12.P1 3 b 20.8 0.52 0.4 0.06 370 Calm 60.0 74.8 28.96 10 28,949 16,920 17,815 31,492 31,050 0.537T12.P2 3 b 21.0 0.52 0.4 0.06 372 Calm 60.0 75.0 28.94 38 30,752 17,653 18,363 32,866 33,226 0.537T19.P1 4 abe 14.1 0.52 0.3 0.09 385 888 47.5 56.8 29.26 15 108,789 19,914 374 140,665 133,737 0.142 

T19.P2 4 abe 14.4 0.52 0.3 0.09 382 878 46.5 57.2 29.24 39 124,576 15,767 287 113,173 120,995 0.139 

T20.P1 4 abe 14.0 0.52 0.3 0.08 382 881 49.8 65.0 29.16 36 61,142 6,452 111 53,636 57,970 0.120

T20.P2 4 abe 13.8 0.52 0.3 0.08 385 869 49.0 64.0 29.14 38 45,947 5,456 96 45,597 46,830 0.120

T33.P1 4 abe 14.8 0.52 0.3 0.09 390 876 47.0 56.0 29.26 19 68,911 9,846 153 76,538 71,388 0.129

T33.P2 4 abe 14.6 0.53 0.3 0.08 390 894 44.8 55.5 29.24 39 62,273 7,191 111 56,837 59,971 0.127

T9.P1 5 c 49.6 0.16 24.5 0.25 360 Calm 55.5 73.2 29.33 32 21,208 14,829 14,951 22,763 23,046 0.651

T9.P2 5 c 49.8 0.16 24.6 0.26 360 Calm 55.0 74.0 29.32 16 20,580 14,638 14,726 22,350 22,347 0.655

T10.P1 5 c 49.8 0.16 24.3 0.26 362 Calm 56.5 76.5 29.26 27 20,229 13,777 13,772 21,444 21,786 0.642

T10.P2 5 c 50.0 0.16 24.3 0.26 362 Calm 56.0 76.5 29.26 6 19,198 14,024 13,866 21,509 21,570 0.652

T8.P1 6 ace 23.5 0.45 44.1 0.12 375 913 41.5 52.8 29.28 24 19,999 2,215 267 24,905 24,468 0.089

T8.P2 6 ace 24.0 0.45 44.5 0.12 370 900 38.5 47.0 29.26 20 22,644 2,111 268 24,047 24,318 0.088NA Not available. 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 
Table B-1.—First half-fraction of test data without intake pressurizer (I = +ABCDE) —Continued

(Tests sorted by run number or experimental condition)

Cab oper tinga rameters pa tWe - Dry- Wind Baro- in tes Last 15-m e t averag Test Start Cab Test and y Deca Run Test † Q bulb bulb metric ‡ C ‡ C e averag period QI −Δpf L +Δpc QR w v e, tim ‡ C1 1 ‡ C2 3 ‡ C3 Pen No. condition tem ., p tem ., p ess., pr Nos. min in Hg in ft3/m in w.g. n L/mi in w.g. ft in 3/m in ft/m °F F ° counts/L counts/L counts/L counts/L counts/L C1 /C3 

T16.P1 6 ace 21.6 0.45 42.9 0.10 385 900 53.8 69.0 28.60 16 20,820 2,671 329 20,187 21,033 0.132

T16.P2 6 ace 21.6 0.45 42.8 0.10 385 901 53.5 69.0 28.58 26 16,619 1,760 285 17,849 17,898 0.099

1 T3.P 7 bce 22.2 0.46 44.5 0.12 390 882 46.0 61.0 28.91 5 25,426 17,595 19,271 31,207 29,124 0.564 

2 T3.P 7 bce 22.3 0.46 44.7 0.12 390 871 46.0 59.0 28.86 4 35,720 26,094 27,982 43,519 43,433 0.600 

T15.P1 7 bce 21.9 0.46 43.5 0.10 388 881 54.8 66.2 28.66 24 42,535 25,569 27,777 45,624 46,160 0.560 

T15.P2 7 bce 22.2 0.46 43.5 0.10 390 902 53.8 66.2 28.64 28 43,403 24,521 25,326 41,143 42,649 0.596 

1 T4.P 8 abc 16.2 0.56 50.4 0.05 385 Calm 41.5 52.8 29.28 19 20,064 2,632 1,803 19,666 19,697 0.134 2 T4.P 8 abc 16.2 0.56 50.2 0.05 385 Calm 38.5 47.0 29.26 15 17,437 3,005 1,810 19,318 19,174 0.156 

T31.P1 8 abc 15.5 0.56 50.7 0.04 390 Calm 46.0 55.8 28.68 34 51,404 4,534 2,660 29,908 37,297 0.152 T31.P2 8 abc 15.6 0.56 50.8 0.04 388 Calm 43.2 54.2 28.68 37 33,377 9,734 6,072 54,894 70,390 0.177 T23.P1 9 d 57.8 0.22 0.5 0.32 322 Calm 60.8 74.5 28.98 13 18,256 6,693 34,396 51,091 51,358 0.131 

T23.P2 9 d 57.7 0.22 0.4 0.33 322 Calm 61.0 75.2 28.98 8 20,983 6,445 32,841 48,277 48,340 0.134 

T32.P1 9 d 59.5 0.22 0.4 0.31 315 Calm 42.8 51.8 28.64 5 9,415 3,734 20,757 30,552 30,288 0.122 

T32.P2 9 d 58.4 0.22 0.4 0.32 315 Calm 41.8 51.8 28.65 12 9,656 3,219 17,478 26,358 26,968 0.122 

T13.P1 10 ade 26.8 0.62 0.3 0.12 332 881 56.5 76.5 29.26 3 17,792 127 42 56,133 54,626 0.002

T13.P2 10 ade 27.1 0.63 0.3 0.12 338 881 56.0 76.5 29.26 13 21,105 114 43 55,910 56,304 0.002T24.P1 10 ade 26.2 0.62 0.4 0.12 340 878 60.2 70.8 28.86 4 18,351 133 50 47,345 50,721 0.003T24.P2 10 ade 26.5 0.62 0.3 0.12 345 877 59.2 69.5 28.84 2 14,981 135 42 43,717 43,800 0.003T11.P1 11 bde 23.7 0.67 0.4 0.10 335 880 55.2 66.5 01 29. 2 19,025 2,363 28,462 47,442 46,644 0.050 

T11.P2 11 bde 24.0 0.67 0.3 0.10 335 888 54.8 66.0 00 29. 2 17,402 2,366 27,955 46,420 46,796 0.051 

T30.P1 11 bde 23.6 0.67 0.3 0.10 338 886 62.0 66.2 67 28. 1 17,662 2,836 34,800 62,857 62,629 0.045 

T30.P2 11 bde 23.9 0.67 0.3 0.10 338 894 62.2 66.5 65 28. 10 26,015 2,251 26,580 47,826 50,150 0.047 

T14.P1 12 abd 17.3 0.76 0.4 0.04 348 Calm 62.0 75.8 28.82 18 8,568 93 32 25,012 25,509 0.004

T14.P2 12 abd 17.2 0.76 0.3 0.05 350 Calm 61.0 76.0 28.78 5 7,496 116 29 23,280 23,499 0.005 

T17.P1 12 abd 17.8 0.76 0.5 0.04 345 Calm 63.5 78.0 29.06 8 15,870 166 71 48,640 50,329 0.003 

T17.P2 12 abd 17.8 0.76 0.6 0.05 348 Calm 62.0 78.0 29.08 13 11,806 158 54 37,561 39,369 0.004 

T5.P1 13 cde 56.0 0.19 25.2 0.37 325 904 46.0 55.8 92 28. 1 25,003 7,964 43,622 60,761 59,146 0.131 

T5.P2 13 cde 56.8 0.19 25.5 0.37 320 920 43.2 54.8 28.92 1 32,682 9,475 50,781 69,687 68,893 0.136 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

26

26
 
27

Table B-1.—First half-fraction of test data without intake pressurizer (I = +ABCDE) —Continued

(Tests sorted by run number or experimental condition)

Cab operating parameters Wet- Dry- Test Wind Baro- Start Last 15-min test average Cab Test and Decay Run Test bulb bulb metric average period † QL ‡ C1 ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen QI −Δpf +Δpc QR vw time, No. condition temp., temp., press., Nos. min in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min °F °F counts/L counts/L counts/L counts/L counts/L C1 /C3 

T26.P1 13 cde 57.8 0.21 26.2 0.33 322 891 51.0 64.5 29.10 14 19,143 4,789 25,547 39,018 40,073 0.123 T26.P2 13 cde 58.1 0.21 26.2 0.33 320 908 51.2 65.5 29.10 21 14,223 4,308 22,122 32,998 33,961 0.131 

T7.P1 14 acd 30.1 0.65 55.2 0.11 335 Calm 51.5 66.8 29.30 5 4,792 153 168 14,782 14,327 0.010T7.P2 14 acd 30.2 0.65 55.3 0.11 338 Calm 50.5 67.0 29.32 2 4,966 176 169 14,713 14,341 0.012T25.P1 14 acd 30.0 0.64 54.8 0.10 332 Calm 53.5 66.0 29.20 3 25,024 849 1,203 96,535 92,181 0.009 T25.P2 14 acd 29.6 0.64 54.9 0.10 335 Calm 53.0 67.8 29.19 20 27,662 648 800 70,240 75,281 0.009T1.P1 15 bcd 26.5 0.71 57.0 0.09 340 Calm 54.2 71.2 29.16 1 7,037 1,127 12,350 20,027 19,791 0.056 

T1.P2 15 bcd 26.6 0.70 56.8 0.09 338 Calm 53.0 71.8 29.16 4 8,257 1,014 11,057 18,154 18,127 0.056 

T29.P1 15 bcd 25.6 0.69 56.4 0.08 338 Calm 62.0 67.5 28.77 2 13,415 2,218 24,288 42,218 40,740 0.053 

T29.P2 15 bcd 25.9 0.69 56.4 0.08 332 Calm 62.0 68.0 28.76 1 14,591 2,840 31,911 54,915 49,702 0.052 

T36.P1 15 bcd 27.2 0.70 58.0 0.08 338 Calm 49.8 61.2 29.05 23 19,350 2,094 21,870 35,137 41,814 0.060 

T36.P2 15 bcd 27.0 0.69 57.9 0.08 335 Calm 49.5 62.0 29.06 21 7,295 878 9,095 15,107 17,747 0.058 

T21.P1 16 abcde 18.6 0.72 56.7 0.09 348 882 51.5 62.5 29.20 2 38,797 1,080 9,515 110,525 104,355 0.010 

T21.P2 16 abcde 19.2 0.72 57.0 0.09 345 883 49.5 60.5 29.20 2 36,589 1,167 10,236 114,693 112,835 0.010 

T22.P1 16 abcde 18.8 0.71 56.1 0.09 345 884 51.2 64.0 29.14 16 26,952 601 5,032 63,261 65,637 0.010 T22.P2 16 abcde 18.9 0.72 56.3 0.08 348 854 49.2 61.5 29.14 2 18,984 664 5,334 66,037 62,081 0.010 T34.P1 16 abcde 20.2 0.72 57.0 0.09 332 883 43.8 56.2 29.16 23 16,087 541 4,930 52,772 58,905 0.010 T34.P2 16 abcde 20.1 0.72 57.6 0.09 338 878 43.0 55.5 29.14 4 8,405 288 2,172 23,865 23,568 0.012 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

27
 
Table B-2.—Second half-fraction of test data without intake pressurizer (I = −ABCDE) 

(Tests sorted by run number or experimental condition)

Cab operating parameters Wet- Dry- Test Test and Wind Baro- Decay Start Last 15-min test average Cab Run Test bulb bulb metric average period † QL QI −Δpf +Δpc QR time, ‡ C1 ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen No. condition vw press., temp., temp., Nos. min ft3/min in w.g. L/min in w.g. ft3/min °F °F in Hg ft/min counts/L counts/L counts/L Counts/L counts/L C1 /C3 

T56.P1 1 1 50.4 0.18 0.4 0.21 355 Calm 52.0 69.8 29.01 24 20,155 14,089 13,331 20,781 21,032 0.678 T56.P2 1 1 50.2 0.17 0.3 0.21 355 Calm 52.0 70.0 29.00 32 20,189 13,375 12,530 19,371 19,697 0.690 T69.P1 1 1 48.7 0.17 0.4 0.21 352 Calm 57.0 74.5 28.39 2 12,343 8,007 7,934 14,026 12,923 0.571

T69.P2 1 1 48.2 0.17 0.4 0.21 358 Calm 57.0 75.0 28.38 6 13,412 8,158 7,978 14,660 14,898 0.556

T75.P1 1 1 49.0 0.17 0.4 0.23 368 Calm 63.2 78.5 28.96 36 97,913 58,335 58,500 87,912 100,363 0.664 T75.P2 1 1 49.2 0.17 0.4 0.23 368 Calm 62.8 79.5 28.96 34 74,747 49,686 49,713 74,271 76,089 0.669 T41.P1 2 ae 21.3 0.46 0.3 0.10 390 872 41.8 49.5 28.71 34 23,484 1,239 34 28,772 28,632 0.043 T41.P2 2 ae 22.2 0.47 0.3 0.10 390 883 39.0 47.8 28.70 33 26,731 1,213 37 30,079 29,987 0.040 T47.P1 2 ae 21.0 0.47 0.3 0.08 385 862 47.8 50.8 28.52 30 147,368 2,660 116 96,816 113,274 0.027T47.P2 2 ae 21.8 0.46 0.2 0.10 388 850 42.5 50.0 28.50 36 83,022 3,211 98 81,250 80,983 0.040 T40.P1 3 be 20.8 0.48 0.3 0.10 368 885 41.8 52.0 28.76 31 19,510 8,834 9,384 15,889 16,900 0.556

T40.P2 3 be 21.2 0.49 0.2 0.09 375 873 39.8 49.8 28.77 3 15,726 11,553 12,699 27,120 23,105 0.426 

T61.P1 3 be 20.6 0.49 0.3 0.08 378 850 44.0 52.0 29.10 28 10,706 6,863 6,347 11,233 11,056 0.611

T61.P2 3 be 20.7 0.49 0.3 0.08 375 854 42.0 52.0 29.10 8 11,979 7,605 7,616 13,140 12,707 0.579

T45.P1 4 ab 14.8 0.57 0.4 0.03 398 Calm 50.5 66.5 28.77 37 24,612 1,817 27 26,876 26,569 0.068 

T45.P2 4 ab 14.7 0.56 0.4 0.03 395 Calm 48.5 64.0 28.77 26 42,633 2,280 NA 36,394 41,872 0.063 T48.P1 4 ab 14.6 0.56 0.5 0.03 390 Calm 52.2 66.0 28.48 37 48,610 2,138 65 51,517 52,842 0.042 

T48.P2 4 ab 14.5 0.56 0.4 0.03 392 Calm 53.5 68.0 28.48 31 45,221 1,857 53 45,952 47,447 0.040 

T70.P1 4 ab 14.0 0.56 0.4 0.03 398 Calm 56.5 76.0 28.35 30 14,366 1,725 26 12,324 12,829 0.140 

T70.P2 4 ab 14.0 0.56 0.3 0.03 392 Calm 57.5 77.0 28.36 30 11,637 2,140 29 15,365 12,563 0.139 

T73.P1 4 ab 15.2 0.58 0.4 0.03 365 Calm 54.5 71.0 29.34 25 14,967 2,160 36 11,924 12,184 0.181 

T73.P2 4 ab 15.2 0.58 0.4 0.03 375 Calm 53.5 72.0 29.32 37 12,375 2,007 38 12,323 12,127 0.163 

T74.P1 4 ab 15.1 0.57 0.5 0.03 388 Calm 60.8 75.0 29.02 29 113,185 6,379 263 121,196 120,629 0.053 

T74.P2 4 ab 14.7 0.57 0.6 0.03 390 Calm 61.2 77.0 29.02 22 107,085 8,642 257 116,388 116,036 0.074 

T39.P1 5 ce 47.2 0.14 21.9 0.25 355 870 44.2 49.0 28.79 2 93,959 73,832 81,208 116,720 113,966 0.633 T39.P2 5 ce 47.4 0.14 21.8 0.25 338 886 42.2 52.2 28.78 38 110,092 42,963 44,266 63,351 86,921 0.678 

NA Not available. 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

28

28
 
29

Table B-2.—Second half-fraction of test data without intake pressurizer (I = −ABCDE) —Continued

(Tests sorted by run number or experimental condition)

Test Wet- Dry- Cab operating parameters Wind Baro- Start Last 15-min test average Cab Test and Test Decay average Run bulb bulb metric period condition time, No. † QL ‡ C1 QI −Δpf +Δpc QR vw temp., temp., press., ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen Nos. min °F °F in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min counts/L counts/L counts/L counts/L counts/L C1 /C3 

T57.P1 5 ce 49.8 0.15 22.8 0.24 368 864 44.5 54.5 29.10 32 39,991 27,509 27,724 42,126 42,538 0.653 T57.P2 5 ce 50.6 0.15 22.9 0.24 355 860 41.5 53.0 29.08 6 40,984 28,776 28,960 43,224 42,182 0.666 T71.P1 5 ce 49.8 0.16 22.6 0.21 348 934 46.0 56.5 28.83 4 36,662 24,783 27,100 41,715 40,991 0.594 T71.P2 5 ce 50.6 0.16 22.5 0.21 352 941 45.2 55.2 28.83 4 39,445 25,827 27,796 41,850 40,911 0.617 T37.P1 6 ac 23.6 0.49 46.7 0.07 378 Calm 57.8 73.2 28.77 34 43,314 5,168 603 47,992 48,887 0.108 

T37.P2 6 ac 23.3 0.49 46.6 0.07 382 Calm 57.2 73.2 28.76 16 41,007 5,065 579 43,561 44,625 0.116 

T50.P1 6 ac 25.0 0.50 47.7 0.06 388 Calm 48.8 65.0 29.10 36 36,721 3,271 216 32,015 34,194 0.102 

T50.P2 6 ac 24.8 0.50 47.4 0.06 380 Calm 49.2 66.5 29.08 15 27,840 3,253 215 27,905 28,741 0.117 

T49.P1 7 bc 22.2 0.53 48.9 0.05 382 Calm 49.5 64.5 29.18 36 25,911 12,630 11,987 21,148 23,317 0.597 

T49.P2 7 bc 22.2 0.53 48.8 0.05 382 Calm 48.0 64.2 29.17 6 22,281 13,960 12,892 22,503 23,377 0.620 T63.P1 7 bc 22.3 0.51 47.3 0.06 368 Calm 56.5 73.0 28.67 8 16,412 9,860 9,366 16,898 16,362 0.584 

T63.P2 7 bc 22.0 0.51 47.3 0.06 370 Calm 56.5 73.5 28.67 6 17,996 11,855 10,868 18,622 17,977 0.637 

T42.P1 8 abce 15.6 0.51 46.9 0.08 395 887 42.5 50.5 28.67 37 25,057 5,216 2,748 27,919 28,724 0.187 

T42.P2 8 abce 15.9 0.51 47.2 0.08 390 881 41.2 48.8 28.68 36 23,150 4,381 2,150 20,745 22,342 0.211 T46.P1 8 abce 14.6 0.50 46.6 0.09 395 896 45.5 56.0 28.70 26 21,655 4,891 1,703 25,676 24,496 0.190 T46.P2 8 abce 15.6 0.50 46.8 0.09 392 903 46.0 54.5 28.68 12 26,044 6,610 2,390 35,440 32,832 0.187 T62.P1 9 de 60.4 0.23 0.3 0.29 318 854 43.0 54.0 29.08 1 6,325 2,389 12,131 18,113 17,617 0.132 

T62.P2 9 de 61.0 0.23 0.2 0.28 318 859 41.5 52.5 29.08 15 8,753 2,404 11,933 17,666 17,864 0.136 

T68.P1 9 de 57.2 0.22 0.3 0.29 300 916 52.0 66.0 28.64 2 37,260 12,558 60,775 87,910 87,437 0.143 

T68.P2 9 de 57.5 0.22 0.3 0.29 305 927 52.0 66.5 28.60 1 39,978 13,482 63,812 90,801 90,380 0.148 

T51.P1 10 ad 29.3 0.67 0.4 0.08 330 Calm 50.5 65.5 29.00 14 5,942 137 16 24,450 24,993 0.006 

T51.P2 10 ad 29.4 0.67 0.4 0.08 328 Calm 49.5 66.5 29.02 2 5,136 136 17 25,561 25,307 0.005 

T59.P1 10 ad 28.0 0.67 0.5 0.07 325 Calm 58.8 74.0 28.82 9 17,526 213 48 61,746 62,056 0.003 

T59.P2 10 ad 28.0 0.67 0.7 0.08 330 Calm 59.5 75.0 28.83 11 17,859 221 46 60,687 61,847 0.004 

T38.P1 11 bd 23.6 0.70 0.3 0.07 338 Calm 56.2 73.0 28.74 13 10,277 1,949 21,522 36,452 37,221 0.053 T38.P2 11 bd 23.6 0.70 0.4 0.07 335 Calm 56.0 73.0 28.72 17 9,805 1,758 19,451 32,804 33,228 0.054 T52.P1 11 bd 24.8 0.72 0.4 0.06 335 Calm 49.5 65.5 29.00 7 7,104 1,287 14,020 24,389 24,458 0.053 

T52.P2 11 bd 24.8 0.72 0.4 0.06 335 Calm 49.0 65.5 28.98 23 8,381 1,396 15,388 26,747 28,744 0.052 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

29 
30

Table B-2.—Second half-fraction of test data without intake pressurizer (I = −ABCDE) —Continued

(Tests sorted by run number or experimental condition)

Test Wet- Dry- Cab operating parameters Wind Baro- Start Last 15-min test average Cab Test and Decay average Run Test bulb bulb metric period time, No. condition † QL ‡ C1 QI −Δpf +Δpc QR vw temp., temp., press., ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen Nos. min °F °F in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min counts/L counts/L counts/L counts/L counts/L C1 /C3 

T65.P1 12 abde 17.4 0.72 0.3 0.07 348 840 47.5 58.0 28.80 6 26,445 507 110 77,348 78,349 0.007T65.P2 12 abde 17.7 0.73 0.3 0.07 348 834 45.5 57.0 28.80 5 26,385 435 97 66,400 67,559 0.007T66.P1 12 abde 17.4 0.72 0.3 0.07 345 854 48.0 61.0 28.82 6 17,227 290 64 46,709 46,849 0.006T66.P2 12 abde 17.6 0.73 0.3 0.07 348 851 46.8 59.8 28.82 10 16,139 284 62 45,013 45,445 0.006T43.P1 13 cd 61.0 0.23 30.0 0.30 328 Calm 50.0 65.0 29.04 4 7,667 3,266 15,842 24,051 23,767 0.136 

T43.P2 13 cd 60.6 0.23 30.1 0.30 325 Calm 49.5 65.8 29.04 9 7,070 3,018 14,694 21,744 21,869 0.139 T54.P1 13 cd 59.8 0.23 29.9 0.29 315 Calm 50.0 68.0 29.03 1 8,148 3,344 15,621 24,063 23,373 0.139 T54.P2 13 cd 59.2 0.23 29.9 0.28 312 Calm 50.5 68.0 29.02 1 8,059 3,413 15,848 23,727 22,943 0.144 T60.P1 14 acde 28.9 0.63 52.3 0.10 328 841 52.0 65.0 28.79 2 25,496 754 604 80,490 79,988 0.009

T60.P2 14 acde 29.0 0.63 52.3 0.11 328 846 51.0 64.0 28.77 7 26,992 702 536 74,034 74,746 0.009

T64.P1 14 acde 29.4 0.63 52.0 0.10 318 852 59.0 60.5 28.64 3 11,560 374 360 37,596 35,760 0.010

T64.P2 14 acde 30.0 0.63 52.2 0.11 325 848 47.5 59.0 28.63 4 13,778 437 409 42,793 42,304 0.010

T44.P1 15 bcde 25.0 0.68 55.5 0.10 342 881 39.8 50.0 28.99 2 14,111 2,232 25,092 39,348 39,135 0.057 T44.P2 15 bcde 25.3 0.69 56.0 0.10 340 885 37.8 47.5 28.98 3 12,294 2,211 24,700 38,523 38,612 0.057 T58.P1 15 bcde 26.0 0.67 54.6 0.10 345 840 45.5 58.0 29.02 22 14,119 1,945 20,433 34,134 37,462 0.057 T58.P2 15 bcde 26.6 0.67 54.8 0.10 335 856 44.5 57.0 29.00 7 9,735 1,603 17,180 28,102 28,362 0.057 

T53.P1 16 abcd 19.8 0.76 59.7 0.04 345 Calm 50.8 66.5 29.06 7 6,171 308 1,666 22,615 22,633 0.014 

T53.P2 16 abcd 19.6 0.76 59.8 0.05 342 Calm 50.2 67.2 29.06 2 5,596 309 1,690 22,302 22,214 0.014 

T67.P1 16 abcd 20.0 0.74 58.5 0.04 330 Calm 56.0 73.5 28.72 20 21,715 810 7,824 78,492 77,926 0.010 

T67.P2 16 abcd 19.8 0.74 58.4 0.04 340 Calm 55.5 74.8 28.76 1 21,670 1,261 12,870 92,369 85,440 0.014 

T72.P1 16 abcd 20.2 0.77 60.3 0.04 342 Calm 52.5 68.0 28.85 17 6,198 224 1,890 21,231 21,628 0.011 

T72.P2 16 abcd 20.0 0.77 60.0 0.04 338 Calm 52.5 69.5 28.86 3 6,212 232 1,776 19,579 19,751 0.012 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

30
 
31

Table B-3.—Pressurizer test data 

(Tests sorted by run number or experimental condition)

Test Cab operating parameters Wind Wet- Dry- Baro- Start Last 15-min test average Cab Test and Decay average Run Test bulb bulb metric period time, † QL ‡ C1 ‡ C3 No. condition QI −Δpf +Δpc QR vw temp., temp., press., ‡ C1 ‡ C2 ‡ C3 Pen Nos. min °F °F in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min counts/L counts/L counts/L counts/L counts/L C1 /C3 

T95.P1 1 1 78.5 0.31 0.4 0.45 340 Calm 57.5 74.5 28.96 17 37,506 29,958 30,474 42,916 43,014 0.698 T95.P2 1 1 78.2 0.31 0.4 0.45 342 Calm 57.0 77.0 28.94 1 39,291 35,225 35,502 48,911 49,714 0.720 T96.P1 1 1 80.2 0.31 0.4 0.45 340 Calm 55.0 71.5 28.79 30 58,901 46,101 46,447 67,065 67,121 0.687 T96.P2 1 1 79.6 0.31 0.4 0.45 342 Calm 54.5 72.5 28.77 32 59,566 44,698 44,452 62,239 63,533 0.718 T85.P1 2 a 38.6 0.88 0.4 0.16 362 Calm 58.0 77.0 29.33 31 9,752 591 14 8,147 8,103 0.073 

T85.P2 2 a 38.2 0.88 0.4 0.16 358 Calm 56.0 77.0 29.30 24 7,763 506 14 8,166 8,031 0.062 

T87.P1 2 a 38.2 0.88 0.4 0.15 372 Calm 59.5 79.0 29.14 12 17,215 835 34 21,177 20,806 0.039 

T87.P2 2 a 38.0 0.88 0.4 0.16 370 Calm 58.0 79.0 29.12 13 17,349 765 41 25,670 24,432 0.030 

T78.P1 3 b 29.3 1.01 0.5 0.09 380 Calm 60.0 74.5 29.06 8 45,618 31,271 31,235 52,222 50,169 0.599 T78.P2 3 b 29.2 1.00 0.5 0.10 382 Calm 60.5 75.0 29.04 4 53,277 37,982 38,031 62,221 58,483 0.610 T105.P1 3 b 29.2 0.96 0.4 0.10 382 Calm 58.5 75.0 28.74 36 24,232 13,529 13,799 22,683 24,848 0.596 T105.P2 3 b 29.2 0.96 0.4 0.10 395 Calm 58.5 77.0 28.74 5 21,800 14,739 15,097 24,053 22,459 0.613 T93.P1 4 ab 22.0 1.05 0.4 0.06 382 Calm 53.0 70.5 28.80 14 10,799 1,105 42 9,349 10,029 0.118 

T93.P2 4 ab 21.9 1.05 0.4 0.07 382 Calm 51.5 71.0 28.80 16 8,799 1,091 35 8,928 8,879 0.122 

T94.P1 4 ab 22.4 1.05 0.5 0.06 385 Calm 55.5 71.5 28.99 31 49,492 2,126 224 57,102 57,170 0.037 

T94.P2 4 ab 22.1 1.05 0.4 0.06 380 Calm 55.5 72.0 29.00 20 49,267 2,071 212 56,469 57,726 0.037 

T109.P1 4 ab 21.5 1.06 0.6 0.07 392 Calm 61.5 81.0 29.06 21 14,557 1,050 46 14,978 15,067 0.070 

T109.P2 4 ab 21.4 1.06 0.5 0.07 392 Calm 61.0 83.0 29.06 21 12,868 857 42 13,987 13,918 0.061 

T79.P1 5 c 81.9 0.33 36.1 0.42 348 Calm 64.5 78.5 29.00 34 72,557 55,407 56,148 80,123 81,464 0.692 

T79.P2 5 c 82.0 0.32 36.1 0.42 342 Calm 64.0 79.0 28.97 36 67,460 49,438 49,754 70,439 72,598 0.702 

T103.P1 5 c 80.2 0.31 35.4 0.44 342 Calm 58.0 73.0 28.74 0 13,130 43,669 42,549 68,716 44,010 0.635 

T103.P2 5 c 80.1 0.31 35.4 0.44 342 Calm 60.0 75.0 28.74 28 80,013 48,831 46,637 70,263 75,971 0.695 

T92.P1 6 ac 40.7 0.87 64.9 0.14 372 Calm 51.5 67.0 28.77 29 15,167 1,356 1,262 13,313 14,767 0.102 

T92.P2 6 ac 40.8 0.84 64.1 0.17 375 Calm 51.5 68.0 28.78 22 12,380 1,191 1,008 11,112 11,908 0.107 T107.P1 6 ac 39.6 0.85 63.4 0.16 370 Calm 60.0 79.0 28.80 34 21,398 1,977 2,082 24,922 25,793 0.079 T107.P2 6 ac 39.6 0.85 63.3 0.16 378 Calm 60.0 79.5 28.81 36 19,245 1,603 1,704 20,150 20,911 0.080 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

31 
32

Table B-3.—Pressurizer test data—Continued 

(Tests sorted by run number or experimental condition)

Test Wet- Dry- Cab operating parameters Wind Baro- Start Last 15-min test average Cab Test and Decay average Run Test bulb bulb metric period time, No. condition † QL ‡ C1 QI −Δpf +Δpc QR vw temp., temp., press., ‡ C1 ‡ C2 ‡ C3 ‡ C3 Pen Nos. min °F °F in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min counts/L counts/L counts/L counts/L counts/L C1 /C3 

T80.P1 7 bc 31.2 0.95 67.7 0.11 370 Calm 64.5 76.5 29.00 3 29,559 23,244 24,477 37,884 35,954 0.614 

T80.P2 7 bc 31.4 0.95 67.5 0.11 380 Calm 64.5 77.5 29.00 3 34,375 27,157 28,195 43,807 42,227 0.620 T81.P1 7 bc 31.2 0.94 66.4 0.11 390 Calm 67.5 81.0 29.00 40 55,285 38,898 41,466 64,509 66,815 0.603 T81.P2 7 bc 30.9 0.94 66.4 0.11 388 Calm 66.5 79.5 29.00 36 57,820 35,185 37,043 56,825 59,650 0.619 T101.P1 8 abc 24.8 1.03 70.2 0.07 395 Calm 58.0 75.0 28.99 32 30,194 3,373 2,922 23,470 26,640 0.144 

T101.P2 8 abc 25.0 1.02 69.9 0.07 395 Calm 58.0 77.5 28.98 19 23,078 3,328 2,890 23,251 23,006 0.143 

T104.P1 8 abc 24.7 1.03 69.8 0.07 380 Calm 58.0 74.0 28.74 15 16,413 2,829 2,263 15,885 16,539 0.178 

T104.P2 8 abc 25.0 1.03 69.6 0.08 382 Calm 58.0 76.0 28.74 13 14,430 2,140 1,746 12,273 12,280 0.174 

T99.P1 9 d 89.4 0.38 0.5 0.48 305 Calm 59.8 75.5 28.54 3 4,979 2,407 8,947 12,498 12,903 0.193 

T99.P2 9 d 89.4 0.38 0.4 0.49 305 Calm 58.8 75.8 28.54 1 5,168 2,455 9,128 12,848 12,455 0.191 

T100.P1 9 d 91.9 0.39 0.4 0.48 308 Calm 55.5 71.0 28.96 3 12,577 6,802 24,351 34,586 34,690 0.197 T100.P2 9 d 92.1 0.39 0.4 0.48 305 Calm 55.0 72.0 28.98 26 15,067 6,837 24,743 34,186 34,553 0.200 T76.P1 10 ad 44.6 1.02 0.6 0.18 342 Calm 63.5 75.0 29.04 2 11,026 170 60 41,169 41,700 0.004 

T76.P2 10 ad 44.4 1.02 0.4 0.18 342 Calm 63.8 75.0 29.03 9 11,909 145 56 39,353 39,877 0.004 

T98.P1 10 ad 44.0 1.01 0.4 0.18 325 Calm 58.0 72.5 28.49 5 1,916 51 12 6,646 6,864 0.008

T98.P2 10 ad 43.4 1.01 0.4 0.18 330 Calm 58.0 74.0 28.49 4 1,436 48 9 5,582 5,362 0.009 

T102.P1 11 bd 32.2 1.16 0.5 0.11 338 Calm 58.5 72.0 28.73 1 2,630 648 5,688 9,043 8,797 0.072 

T102.P2 11 bd 32.0 1.16 0.6 0.11 338 Calm 57.5 72.0 28.74 1 2,860 762 6,825 10,826 10,591 0.070 

T108.P1 11 bd 32.4 1.21 0.2 0.11 345 Calm 60.5 76.0 29.08 18 5,904 1,295 11,921 20,263 20,893 0.064 

T108.P2 11 bd 31.9 1.21 0.2 0.11 345 Calm 60.0 77.0 29.08 14 5,290 1,204 11,147 18,852 19,243 0.064 T89.P1 12 abd 24.6 1.25 0.4 0.08 345 Calm 59.5 76.5 28.84 16 8,061 91 73 24,205 30,688 0.004

T89.P2 12 abd 25.0 1.25 0.4 0.08 340 Calm 58.0 76.0 28.54 5 5,670 78 63 20,518 20,824 0.004

T106.P1 12 abd 24.6 1.24 0.4 0.07 340 Calm 59.0 74.5 28.80 7 6,586 65 68 22,031 22,337 0.003

T106.P2 12 abd 24.6 1.24 0.5 0.07 342 Calm 58.5 74.5 28.80 2 4,884 60 61 21,025 21,388 0.003

T77.P1 13 cd 92.2 0.40 40.1 0.45 312 Calm 63.2 75.0 29.04 22 9,644 4,143 15,289 22,342 23,276 0.185 T77.P2 13 cd 91.6 0.40 40.2 0.45 312 Calm 62.5 75.0 29.04 2 8,614 3,911 14,549 20,907 20,859 0.187 T83.P1 13 cd 93.0 0.40 40.9 0.44 312 Calm 65.0 77.5 29.12 7 27,267 14,755 51,099 71,685 71,790 0.206 

T83.P2 13 cd 93.4 0.40 40.9 0.44 310 Calm 65.0 78.0 29.12 1 31,608 15,275 52,470 72,480 71,371 0.211 

†The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

32 
33

Table B-3.—Pressurizer test data—Continued 

(Tests sorted by run number or experimental condition)

Test Wet- Dry- Cab operating parameters Wind Baro- Start Last 15-min test average Cab Test and Decay average Run Test bulb bulb metric period time, No. condition † QL ‡ C1 ‡ C3 QI −Δpf +Δpc QR vw temp., temp., press., ‡ C1 ‡ C2 ‡ C3 Pen Nos. min °F °F in Hg ft3/min in w.g. L/min in w.g. ft3/min ft/min counts/L counts/L counts/L counts/L counts/L C1 /C3 

T86.P1 13 cd 92.8 0.38 39.8 0.49 315 Calm 56.5 73.5 29.22 11 8,467 3,873 14,435 21,633 21,977 0.179 

T86.P2 13 cd 92.5 0.38 39.6 0.49 315 Calm 56.5 74.5 29.22 1 8,142 4,254 15,777 22,804 22,264 0.187 T90.P1 14 acd 46.0 0.99 69.0 0.21 340 Calm 60.5 74.5 28.96 21 18,848 611 6,391 57,668 61,294 0.011 

T90.P2 14 acd 45.8 0.99 68.7 0.21 338 Calm 59.5 75.0 28.94 17 11,406 445 4,424 40,842 42,917 0.011 T91.P1 14 acd 45.0 0.99 68.3 0.21 332 Calm 63.0 79.5 28.86 2 5,894 306 2,783 26,395 26,748 0.012 T91.P2 14 acd 44.8 0.99 68.1 0.21 330 Calm 61.5 80.0 28.84 4 5,600 291 2,634 25,086 24,960 0.012 T88.P1 15 bcd 34.8 1.13 73.5 0.13 332 Calm 61.0 75.0 28.84 21 4,449 969 8,149 12,759 13,219 0.076 T88.P2 15 bcd 34.7 1.13 73.5 0.13 335 Calm 60.0 75.5 28.84 16 3,867 871 7,302 11,316 11,691 0.077 T97.P1 15 bcd 33.8 1.13 73.7 0.12 335 Calm 57.0 75.5 28.69 14 21,084 4,766 40,289 60,301 62,843 0.079 

T97.P2 15 bcd 33.6 1.13 73.5 0.12 332 Calm 56.0 76.0 28.68 1 18,532 5,130 43,501 64,722 62,175 0.079 

T82.P1 16 abcd 28.0 1.23 77.0 0.09 330 Calm 63.5 75.0 29.11 2 7,680 511 5,207 35,108 32,679 0.015 

T82.P2 16 abcd 27.9 1.24 77.1 0.09 335 Calm 63.0 74.0 29.12 1 9,891 1,338 14,985 89,881 77,690 0.015 

T84.P1 16 abcd 28.6 1.25 77.6 0.09 348 Calm 55.8 73.2 29.36 13 1,695 117 836 6,507 6,562 0.018

T84.P2 16 abcd 28.1 1.25 77.4 0.09 350 Calm 55.0 73.8 29.38 1 1,875 131 1,085 8,188 7,758 0.016 †The mass flowmeter analog output had a several tenths of flow bias at 0.0 L/min on the display.‡The particle counter concentrations are for particle diameter sizes ranging from 0.3 to 1.0 μm. 

33 
APPENDIX C.—STEPWISE REGRESSION ANALYSIS OF FILTRATION SYSTEM 

WITHOUT PRESSURIZER 

A stepwise linear regression analysis of the dependent variable (ln Pen) with respect to 

the single factors and two-factor interactions was conducted using SPSS Version 15.0 for 

Windows. Table C-1 shows the regression model coefficients with their statistical significance, 

and Table C-2 shows the ANOVA model statistics. The stepwise regression model parameters or 

coefficients shown in Table C-1 were successively selected by the highest level of significance 

on cab penetration with no variable removal in the process. The stepwise regression analysis 

provided a very efficient model with coefficient of multiple determinations (standard and 

adjusted) above 0.98 for the cab filtration system configured without a pressurizer. Figure C-1 

illustrates the goodness of fit of the regression model to the observed response variables. 

Figures C-2 and C-3 illustrate that the normality and equal variance assumptions were 

reasonably met by the natural logarithm transformation of cab penetrations for the regression 

model. This regression model is considered reasonably good, but others could be formulated 

from these experiments. 

34
 

Table C-1.—Stepwise regression model without pressurizer 

R2 = 0.983, R2

adj = 0.982, n = 148 

Standard error of regression = 0.220, Durbin-Watson statistic = 1.173 

Regression model Standard Coefficient t-statistic ln Pen = error Significance 

level 

Intercept −2.598 0.018 −142.145 

Recirculation filter (D) −1.146 0.018 −62.349 

Intake filter efficiency (A) −1.108 0.018 −60.744 

Intake filter efficiency × loading (AB) 0.260 0.018 14.203 

Leakage (C) 0.230 0.018 12.578 

Intake filter efficiency × leakage (AC) 0.201 0.018 10.932 

Intake filter efficiency × recirculation filter (AD) −0.168 0.018 −9.136 

Loading × recirculation filter (BD) −0.162 0.018 −8.766 

Loading × wind (BE) 0.050 0.018 2.728 

Loading × leakage (BC) −0.040 0.018 −2.198 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.007 

0.030 

Table C-2.—ANOVA for stepwise regression model 

without pressurizer 

Regression 

model 

 Sum of 

 squares 

Degrees of 

freedom 

Mean 

square 

F-statistic Significance 

level 

Regression 396.161 9 44.018 906.988 0.000 

Residual 6.697 138 0.049 — — 

 Total402.858 147 — — — 
Figure C-1.—Standardized predicted values for regression model without pressurizer. 

35
 

Figure C-2.—Normal probability plot of standardized residuals without pressurizer. 
36
 

 Figure C-3.—Standardized residuals versus standardized predicted values 

without pressurizer. 
APPENDIX D.—STEPWISE REGRESSION ANALYSIS OF FILTRATION SYSTEM 

WITH AND WITHOUT PRESSURIZER 

Regression analysis was conducted with the additional pressurizer test data to statistically 

examine the effect on cab penetration. This regression analyzed the enclosed cab filtration 

system data with and without an intake pressurizer fan and no wind. The cab filtration tests without the pressurizer were considered one block of experiments coded with −1. The cab filtration 

tests with the pressurizer (P) were considered another block of experiments coded with +1. 

A stepwise linear regression analysis of the dependent variable (ln Pen) with respect to the intake 

pressurizer blocks, the single factors, and the two-factor interactions within the blocks was 

conducted using SPSS Version 15.0 for Windows. Table D-1 shows the regression model 

coefficients with their statistical significance, and Table D-2 shows the ANOVA model statistics. 

The stepwise regression model parameters or coefficients shown in Table D-1 were successively 

selected by the highest level of significance on cab penetration with no variable removal in the 

process. Figure D-1 shows the plot of the standardized predicted values for the regression model. 

Figure D-2 shows the normal probability plot of the standardized residuals, and Figure D-3 

shows the plot of standardized residuals versus standardized predicted values. This regression 

model is considered reasonably good, but others could be formulated from these experiments. 

37
 

Table D-1.—Stepwise regression model with and without pressurizer 

R2 = 0.988, R2

adj = 0.976, n = 144 

Standard error of regression = 0.260, Durbin-Watson statistic = 1.085 

Regression model Standard Coefficient t-statistic ln Pen = error Significance 

level 

Intercept −2.538 0.022 −116.028 

Intake filter efficiency (A) −1.156 0.022 −52.844 

Recirculation filter (D) −1.075 0.022 −49.057 

Leakage (C) 0.241 0.022 11.011 

Intake filter efficiency × loading (AB) 0.206 0.022 9.416 

Intake filter efficiency × leakage (AC) 0.217 0.022 9.890 

Loading × recirculation filter (BD) −0.176 0.022 −8.026 

Intake filter efficiency × recirculation filter (AD) −0.157 0.022 −7.172 

Loading (B) −0.067 0.022 −3.058 

Pressurizer (P) 0.051 0.022 2.329 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.000 

0.003 

0.021 

Table D-2.—ANOVA for stepwise regression model 

with and without pressurizer 

Regression 

model 

Sum of 

squares 

Degrees of 

freedom 

Mean 

square 

F-statistic Significance 

level 

Regression 364.014 9 40.446 597.659 0.000 

Residual 9.068 134 0.068 — — 

 Total373.082 143 — — — 
 

 

Figure D-1.—Standardized predicted values for regression model 

with and without pressurizer. 

38
 

 

 

Figure D-2.—Normal probability plot of standardized residuals 

with and without pressurizer. 
39
 

 

 

Figure D-3.—Standardized residuals versus standardized predicted values 

with and without pressurizer. 
APPENDIX E.—MATHEMATICAL MODEL FOR CAB FILTRATION SYSTEM 

40
 

Development of this cab filtration model is based on a time-dependent mass balance 

model of airborne substances within a control volume. Equation E-1 below is a differential equation describing the mass balance of an airborne substance in a cab filtration system control volume shown in Figure E-1. This is a reformulation of the basic equation for general dilution 

ventilation [Hartman 1961]. The left-hand part of the equation describes the mass of the 

contaminant in the control volume. The positive terms in the right-hand part of the equation 

describe the addition of contaminant mass into the control volume, including intake air leakage, 

intake filter penetration, and wind infiltration. The negative terms describe the removal of the 

contaminant mass from the control volume, including intake air dilution and recirculation filter 

removal. 

Mathematical model: 

Vc dx = QL Cdt + QF C(1−η I )dt + Qw Cdt − QI xdt − QR xη R dt (E-1) 

Model assumptions: 

(1) Outside contaminant concentration is constant. 

(2) Contaminant leakage into the filtration system is proportional to the air quantity leakage 

around the filter. 

(3) Wind penetration into the cab occurs when the wind velocity (vw) exceeds the opposing cab 

exit air velocity (vI). 

where Vc = cab volume, 

 x = inside cab contaminant concentration, 

 QF = filtered intake air quantity, 

 ηI = intake filter efficiency, fractional, 

QL = air leakage quantity around the intake filter, 

QI 	 = intake air quantity into the cab, 

l = portion of intake air leakage, or QL /QI , 

QR = recirculation filter airflow, 

 ηR = recirculation filter efficiency, fractional, 

C = outside cab contaminant concentration, 

Qw = wind quantity infiltration into the cab, 

t = time, 

vI = cab intake air exit velocity, 

and vw = wind velocity. 
Figure E-1.—Schematic of basic cab filtration system. 

Since: QI = QL + QF and QL = QI l; QF = QI (1− l) 

V c dx = Q I lCdt + QI ( 1−l)( 1−η I ) Cdt + Q w Cdt − ( Q I + QR η R )xdt (E-2) 

V c dx = Q I C( 1−η I +lη I )dt + Q w Cdt − ( QI + QR η R )xdt (E-3) 

x dx 1 t 2 

∫ = ∫ dt (E-4) 

x o 

Q I C (1 −η I + l η I ) +Q w C −(QI + Q R η R )x V c t 1 

Let: u = Q I C(1−η I + l η I ) +Q w C −(QI + Q Rη R )x and du = − (QI + Q Rη R )dx

1 u du 1 t 

( ) ∫ = ∫

2 

dt (E-5) − Q I + Q R η R uo 

u V c t 1 

Integrate and rearrange: 

− (Q I + Q 

u = R η R ) (t2 −t ) ln − ln uo

1 (E-6) V c 

u − + Q R η ln = (Q I R ) Δt

 (E-7) 

u o V c 

41
 
Substitute for u: 

QI C(1−η + lη )+ Q C −( ln I I w Q I + Q Rη R )x −(Q + Q η )Δt

= 

I R R (E-8) QI C(1−η I + lη I )+ Qw C −(Q I + Q Rη R )xo Vc 

) Q

⎛ − Q + η Δt ⎞ ⎜ ( I Q R R ⎟ ⎜ ⎟ I C(1−η I + lη I )+ Qw C −(Q I + Q Rη R )x

= e ⎝ V

( c ⎠ (E-9) QI C 1−η I + lη I )+ Qw C −(Q I + Q Rη R )xo 

The steady-state solution as Δt→∞; e

−∞→0 

QI C(1−η I + lη I ) + Qw C − (Q I + Q Rη R )x = 0 (E-10)

QI C(1−η I + lη 

x I ) + Qw C= (E-11) Q I + Q Rη R 

x Q (1−η + lη )+ Q Pen = = 

I I I w (E-12) C Q I + Q Rη R 

Rearrange into other useful forms: 

Q 1−η + w

I lη I + 

Q Pen = 

I (E-13) Q 1+ R η Q R

I 

Q 1−η I + L Q η w

Q I +Q Pen = 

I I (E-14) Q 1+ R η Q R

I 

The air quantity leakage around the filter (QL) and the wind quantity infiltration into the 

cab (Qw) in the above equations may be estimated by applying orifice flow equations derived 

from Bernoulli’s principle [Streeter and Wylie 1979; Heitbrink et al. 2000]. The orifice flow 

relationship for air at atmospheric and turbulent flow conditions is shown in Equation E-15 

[Streeter and Wylie 1979], assuming the air is incompressible with a Reynolds number ≥ 4000. 

A particularly developed wind infiltration relationship into cabs when the wind velocity pressure 

exceeds cab static pressure is also shown in Equation E-16 [Heitbrink et al. 2000]. 

42
 
Qo Δp

vo = = 2 o ; orifice flow from high to low pressure (E-15) Ao Cd ρ air 

Qo 0.5 ρ v 

2 − p 

vo =	 = 0.61 2	 

( air w c ) ; wind penetration when 0.5 ρ v

2 

air w > p c (E-16) Ao ρ air 

where vo = fluid velocity through an orifice, 

 Qo = airflow quantity through an orifice, 

 Cd = orifice discharge coefficient, 

Ao = area of orifice, 

 Δpo = air pressure differential across orifice, 

 ρair = air density, 

vw = wind velocity, 

and pc = cab pressure. 

43
 
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