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The Effect of Subject Characteristics and RespiratorFeatures on Respirator FitZiqing Zhuang a , Christopher C. Coffey b & Roland Berry Ann aa National Personal Protective Technology Laboratory, National Institute for OccupationalSafety and Health , Pittsburgh , Pennsylvaniab Division of Respiratory Disease Studies , National Institute for Occupational Safety andHealth , Morgantown , West VirginiaPublished online: 24 Oct 2007.

To cite this article: Ziqing Zhuang , Christopher C. Coffey & Roland Berry Ann (2005) The Effect of Subject Characteristicsand Respirator Features on Respirator Fit, Journal of Occupational and Environmental Hygiene, 2:12, 641-649, DOI:10.1080/15459620500391668

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Journal of Occupational and Environmental Hygiene, 2: 641–649ISSN: 1545-9624 print / 1545-9632 onlineDOI: 10.1080/15459620500391668

The Effect of Subject Characteristics and RespiratorFeatures on Respirator Fit

Ziqing Zhuang,1 Christopher C. Coffey,2 and Roland Berry Ann1

1National Personal Protective Technology Laboratory, National Institute for Occupational Safetyand Health, Pittsburgh, Pennsylvania2Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health,Morgantown, West Virginia

A recent study was conducted to compare five fit testmethods for screening out poor-fitting N95 filtering-facepiecerespirators. Eighteen models of NIOSH-certified, N95 filtering-facepiece respirators were used to assess the fit test methodsby using a simulated workplace protection factor (SWPF) test.The purpose of this companion study was to investigate theeffect of subject characteristics (gender and face dimensions)and respirator features on respirator fit. The respirator featuresstudied were design style (folding and cup style) and numberof sizes available (one size fits all, two sizes, and three sizes).Thirty-three subjects participated in this study. Each wasmeasured for 12 face dimensions using traditional calipersand tape. From this group, 25 subjects with face size categories1 to 10 tested each respirator. The SWPF test protocol entailedusing the PortaCount Plus to determine a SWPF based on totalpenetration (face-seal leakage plus filter penetration) whilethe subject performed six simulated workplace movements.Six tests were conducted for each subject/respirator modelcombination with redonning between tests. The respiratordesign style (folding style and cup style) did not have asignificant effect on respirator fit in this study. The numberof respirator sizes available for a model had significant impacton respirator fit on the panel for cup-style respirators with oneand two sizes available. There was no significant differencein the geometric mean fit factor between male and femalesubjects for 16 of the 18 respirator models. Subsets of one to sixface dimensions were found to be significantly correlated withSWPFs (p < 0.05) in 16 of the 33 respirator model/respiratorsize combinations. Bigonial breadth, face width, face length,and nose protrusion appeared the most in subsets (five orsix) of face dimensions and their multiple linear regressioncoefficients were significantly different from zero (p < 0.05).Lip length was found in only one subset. The use of facelength and lip length as the criteria to define the current half-facepiece respirator fit test panel may need to be reconsideredwhen revising the panel. Based on the findings from this andprevious studies, face length and face width are recommendedmeasurements that should be used for defining the panel forhalf-facepiece respirators.

Keywords face dimensions, filtering-facepiece respirators, fit testpanels, respirator sizing, simulated workplace protec-tion factors

Address correspondence to: Ziqing Zhuang, National PersonalProtective Technology Laboratory, National Institute for Occupa-tional Safety and Health, P.O. Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236; e-mail: zaz3@cdc.gov.

The findings and conclusions in this report are those of the authorsand do not necessarily represent the views of the National Institute forOccupational Safety and Health. Mention of commercial product ortrade name does not constitute endorsement by the National Institutefor occupational Safety and Health.

Respiratory protection has become a more promi-nent issue in recent years and has received moreattention due to emerging pathogens and chemi-cal, biological, radiological, and nuclear (CBRN)

agents. Ill-fitting respirators may compromise the protectionoffered to emergency responders in hazardous situations. Res-pirator certification standards for the United States, Australia,and New Zealand, and many European countries requirefit testing during respirator certification.(1−3) The NationalInstitute for Occupational Safety and Health (NIOSH) hasalso incorporated laboratory protection-level fit testing intothe certification standards for respirators for use by emergencyworkers for CBRN protection.(4−6)

The respirator fit test panels used in the United Statesfor NIOSH certification are based on the 25-subject panelsdeveloped by the Los Alamos National Laboratory (LANL) in1974.(7−8) The NIOSH CBRN standards require that respira-tors fit 95% of the LANL test panel. The LANL panels were de-veloped based on the data from the 1967–1968 U.S. Air ForceAnthropometry Survey. The panel for full-facepiece respiratorsis defined by face length (menton-sellion length) and face width(bizygomatic breadth). Panel members were divided into 10different categories to assure representation of all differentcombinations of face length and width. The panel for half-facepiece respirators is defined by face length and lip length.

These panels have been widely utilized to determinehow respirators fit the general working population. Most

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manufacturers supply half- and full-facepiece respirators inmultiple sizes that cover these 10 facial categories.(9) However,face length, face width, and lip length have not been shown to beconsistently correlated with fit factor while other dimensionssuch as nasal root breadth have been shown to correlate withfit factor.(10−16)

Oestenstad and Perkins(12−14) concluded that menton-subnasale (lower face) length alone was consistently indicatedas being correlated or associated with the fit of each brandof half-facepiece respirator rather than face length and liplength. These results imply that face length and lip length maynot be good criteria for designing respirators or predictingrespirator face-seal leakage. Brazile et al.(15) concluded thatrespirator fit was not associated with face dimensions basedon race/ethnicity or gender and seemed to be associated withindividual facial characteristics.

Because the LANL panels were based on military data,concern has been raised about applicability with civilianpopulations.(10) Military anthropometric data may not repre-sent civilian data because of stringent recruitment standards.

A large-scale anthropometric survey of U.S. respiratorusers was recently completed by NIOSH.(17) The LANLfull-facepiece panel excluded 15.3 percent of NIOSH surveysubjects.(18) It can be concluded that the LANL respirator fit-test panels do not represent the current U.S. civilian workforce well. The newly available NIOSH data are being usedto revise respirator fit test panels. Further study is needed toinvestigate the appropriateness of face dimensions for definingfit test panels including a systematic review of the literature onrespirator fit and face dimensions.

There were two objectives of this study: (1) to investigatethe effect of subject gender and respirator features on respirator

TABLE I. Features of Respirators Used in This Study

Manufacturer Model Number(s) Size(s) Type

3M 1860S/1860 Small, regular Cup3M 8110S/8210 Small, medium/large Cup3M 8212 One size fits all Cup3M 8512 One size fits all CupAearoSafety Pleats Small/medium, medium/large FoldingGerson 2737 One size fits all CupMoldex 2201N95/2200N95 Small, medium/large CupMoldex 2207N95 One size fits all CupMoldex 2301N95/2300N95 Small, medium/large CupMoldex 2701N95/2700N95 Small, medium/large CupMSA Affinity Plus Small/medium, medium/large CupMSA Affinity Ultra Small, medium, large CupNorth 7175N95 One size fits all CupSurvivair 1930 Small, medium, large FoldingUS Safety ADN95 One size fits all CupWillson 1410N95 One size fits all CupWillson N9510F Small, medium, large FoldingWillson N9520F Small, medium, large Folding

fit, and (2) to determine the appropriate face dimensions fordefining a half-facepiece respirator fit test panel. The studyreported in this article is a companion study of a recent NIOSHN95 filtering-facepiece respirator study that was conductedto evaluate five fit test methods for screening out improperlyfitting N95 filtering-facepiece respirators.(19) The fit of 18models of NIOSH-certified, N95 filtering-facepiece respiratorswas assessed by using a simulated workplace protection factor(SWPF) test.(20)

MATERIALS AND METHODS

SubjectsThirty-three people (18 females and 15 males) participated

in this study. Twenty-five subjects tested one respirator model.Some subjects did not test all respirator models because theywere substituted with other subjects with similar face sizecategories to speed up data collection.(8) Panel members wereselected to provide a variety of facial sizes without regard to anyparticular facial size distribution. All test subjects who weresmokers refrained from smoking for at least 30 min before thetests since it is known that smokers may exhale particles up to30 min after smoking a cigarette or cigar. The PortaCount Plus(TSI Inc., St. Paul, Minn.) can detect these exhaled particlesand count them as face seal leakage causing erroneous results.

RespiratorsThe 18 models of NIOSH-certified, N95 filtering-facepiece

respirators used in this study are listed in Table I. Therespirators were selected at random prior to the beginning ofthe study from the approximately 70 models commerciallyavailable. The random process was that each respirator was

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assigned a number and then a random number generator wasused to pick the ones tested. The number of respirator sizesavailable were 1 (one size fits all), 2 (small/medium andmedium/large), and 3 (small, medium, and large). Respiratorsavailable in multiple sizes did not have instructions describinghow to choose the appropriate size. Therefore, test subjectswere given a respirator based on their face and lip lengthmeasurements as previously reported.(19) The respirator sizesfor the corresponding face and lip length were based onrecommendations by the Los Alamos National Laboratory.(8)

Simulated Workplace Protection Factor TestingThe SWPF testing using the PortaCount Plus was used

to determine whether an acceptable level of protection wasobtained. The six-donning, six-exercise SWPF procedureused in this study has been demonstrated, in a simulatedhealthcare workplace test, to provide fit factors that have a highcorrelation with a wearer’s actual exposure.(21) Before startingan SWPF test, a subject donned the respirator per the respiratormanufacturer’s instructions including performing and passinga user-seal check. After the respirator was donned, SWPFtesting began.

An SWPF test consisted of a test subject performing thefollowing six exercises for one minute each: (1) normalbreathing, (2) deep breathing, (3) moving head side to side,(4) moving head up and down, (5) reading the rainbow passageout loud, and (6) normal breathing.(19) An overall SWPF wasobtained using the harmonic mean. An SWPF is a measureof the protection received from a respirator and includes bothfilter penetration and face seal leakage. After completing thefirst test, a subject removed the respirator and gave it to thetest operator. The test operator returned the respirator to itsoriginal configuration that included loosening the head strapsand flattening the nosepiece. The subject then donned and user-seal checked the same respirator again per the manufacturer’sinstructions. A second test, identical to the first, was conducted.This procedure was repeated four additional times for a totalof six SWPF tests for each subject and respirator combination.

Measurement of Face DimensionsThirty-two of the 33 subjects were measured for 12 face

dimensions with the traditional sliding calipers (GPM Instru-ments, SiberHegner, Zurich, Switzerland), spreading calipers,and Lufkin Executive Diameter Steel Tape 16 mm × 2 m(Cooper Tools, Apex, NC). The face measurements wereconducted after SWPF data collection was completed. Onesubject left the area and could not be measured. The facedimensions were measured once by an engineering technicianwho had been trained by Anthrotech, Inc. (Yellow Springs,Ohio) to ensure that measuring accuracy (±1 or 2 mm)was achieved based on repeated measurements of anothertrainee during the training. All measurements were made inmillimeters to one decimal point. Dimensions were selectedto maximize the information that could be obtained from eachsubject for respirator design and testing.

Statistical AnalysisFor presenting and analyzing facial anthropometric data,

descriptive statistics were calculated. Measured SWPFs wereright-skewed, which is consistent with the lognormal dis-tribution, and the log-transformed SWPFs (referred to asLSWPFs) did not differ significantly from the normal distri-bution based on Shapiro-Wilk test. Since each subject donnedeach respirator model six times, the mean LSWPF data foreach respirator model/respirator size/subject combination werecalculated and used as the dependent variable. LSWPFs wereused for subsequent statistical analyses.

All face dimensions were found to be normally distributedbased on Shapiro-Wilk test. Thus, a student’s t-test wasused to determine if there was any gender difference in facedimensions. To see if the face dimensions are correlated amongthemselves, Pearson’s correlation analysis was performed.Since the correlation coefficients are similar to those reportedby Han and Choi,(16) they are not reported in this article.

One-way analysis of variance (ANOVA) was conducted todetermine if the number of respirator sizes available, respiratorstyle, and gender affect respirator fit. One-way ANOVA wasalso conducted for number of respirator sizes available for eachrespirator style separately. The cup-style respirator had one tothree respirator sizes available and folding-style respirator hadtwo and three respirator sizes available. These five groups ofrespirators were also analyzed by one-way ANOVA model.

The relationship between LSWPF and face dimensions wasanalyzed using multiple regression analysis. To test if any of thevariation in the SWPF data may be explained by the facial data,a stepwise procedure in SAS for Windows (SAS Institute Inc.,Cary, NC) was used to identify a best subset multiple regressionmodel for each respirator model/size combination. In thisanalysis, a standardized transformation of the independentvariables in our multiple regression analysis was performedto permit the relative comparisons of the estimated regressioncoefficients in common units. Another reason for using astandardized predictor variable in the multiple regressionmodel is that the standardized transformation of the predictorvariables often reduces the multicollinearity substantially andtends to avoid computational difficulties.(22)

RESULTS

T able II summarizes the mean and standard deviation forall 12 face dimensions based on gender and all subjects.

The females had lip lengths ranging from 43 to 55 mm andface lengths ranging from 104 to 124 mm. The males had liplengths of 44 to 59 and face lengths of 112 to 135 mm. With theexception of lip length, nasal root breadth, and nose protrusion,all other face dimensions were significantly different betweenmale and female (p < 0.05).

Table III summarizes the geometric mean (GM) SWPF andgeometric standard deviation by the number of respirator sizesand styles available. There were significant differences in theGM SWPF among all three groups (42 for three respiratorsizes available, 25 for two respirator sizes available, and 14 for

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TABLE II. Statistical Summary of Face Dimensions

Face Dimension Male (n = 14) Female (n = 18) All (n = 32)

1. Bigonial breadth 117.8 ± 9.5 1089 ± 7.5 112.8 ± 9.42. Bitragion-chin arc 312.1 ± 14.8 282.9 ± 14.6 295.7 ± 20.63. Bitragion-frontal arc 314.7 ± 11.2 300.6 ± 9.5 306.8 ± 12.44. Bitragion-subnasale arc 282.8 ± 10.1 265.3 ± 12.9 272.9 ± 14.65. Face width 69.1 ± 3.0 65.1 ± 4.2 66.9 ± 4.26. Interpupillary breadth 65.1 ± 2.9 62.4 ± 3.0 63.6 ± 3.27. Lip length 51.5 ± 4.6 49.5 ± 3.8 50.4 ± 4.28. Face length 124.0 ± 6.8 113.3 ± 5.3 118.0 ± 8.09. Menton-subnasale length 70.5 ± 5.7 63.9 ± 3.5 66.8 ± 5.6

10. Nasal root breadth 18.1 ± 2.6 17.3 ± 2.1 17.7 ± 2.411. Nose width 34.9 ± 2.1 31.9 ± 2.8 33.2 ± 2.912. Nose protrusion 23.4 ± 3.0 21.9 ± 1.2 22.5 ± 2.3

Note: With the exception of lip length, nasal root breadth, and nose protrusion, all other measurements were significantly different between gender based on t-test(p < 0.05).

one respirator size available) for combined data for cup andfolding styles (p < 0.05). There was no significant differencein the GM SWPF between cup style (25) and folding style (22)for combined data from all number of respirator sizes available(p > 0.05). There were significant differences in the GM SWPFamong all three groups for the cup-style respirators (p < 0.05).There was significant difference in the GM SWPF between tworespirator sizes available and three respirator sizes available forthe folding-style respirators (p < 0.05).

When all five groups were analyzed with a one-wayANOVA, the cup-style respirator model with three respiratorsizes available had the largest GM SWPF (240) which wassignificantly larger than all other GM SWPF values. The cup-

TABLE III. Summary of SWPF by Number of Respi-rator Sizes and Styles

Cup Style Folding Style Both StylesNo. ofRespiratorSizesAvailable n

GMA

SWPFB

(GSD)C n

GMA

SWPFB

(GSD)C n

GMA

SWPFB

(GSD)C

3 25 240 (2.3) 75 24 (3.1) 100 42 (4.3)2 149 25 (2.8) 25 28 (2.9) 174 25 (2.8)1 180 14 (2.6) 180 14 (2.6)All Sizes 354 25 (3.1) 100 22 (3.4)

Notes: One of the seven one-size-fits-all (OSFA) models had 31 tests (datapoints) and another of them had only 24 tests; thus, the total number of testsfor the seven OSFA models was 180. One of the six models with two sizesavailable had only 24 tests; thus, the total number of tests for these six modelswas 149. One-way analysis of variance was conducted and number of respiratorsizes available was found to have significiant impact on the fit of cup stylerespirators (p < 0.05).AGM = geometric mean.B SWPF = simulated workplace protection factor.C GSD = geometric standard deviation.

style respirator models with one respirator size available hadthe smallest GM SWPF (14), which was significant smallerthan all other GM SWPF values. There was no significantdifference among the other three groups (cup style respiratorswith two sizes available and folding style respirators with twoand three size available). Since the cup-style respirator modelwith three sizes available was the only model in the group, thenumber of respirator sizes available had significant impact onrespirator fit on the panel for cup-style respirators only (onesize versus two sizes available).

Table IV summarizes the GM SWPF and geometric stan-dard deviation by model and gender. There was no significantdifference in the GM SWPF between male and female subjectsfor 16 of the 18 respirator models. For two respirator models(Moldex 2301N95/2300N95 and Wilson N9520F), the GMSWPF values for females were significantly larger than thecorresponding GM SWPF values for male (p < 0.05).

Table V summarizes regression coefficients for the best sub-set multiple linear regression models between face dimensionsand GM SWPF. An example of a multiple linear regressionequation is given for Wilson (N9510F, small size) as follows(R2 = 0.96, adjusted R2 = 0.92, p < 0.05).

Log(SWPF) = 1.54 + 0.18 × Face Width + 0.17

× LipLength − 0.41 × Face Length + 0.15

× Menton S. Length

Subsets of one to six face dimensions were identified frommultiple linear regression analysis between face dimensionsand fit factors at significance level of 0.15 in 28 of the 33respirator model/size combinations. Of these 28 multiple linearregression models, 16 models were statistically significant(p < 0.05).

Table VI summarizes the frequency of face dimensionswhich were included in subsets and were significantlycorrelated to GM SWPF. Bigonial breadth appeared the

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TABLE IV. Summary of GM SWPF by Respirator Model and Gender

Male Female

Manufacturer Model NGMA

SWPFB GSDC nGMA

SWPFB GSDC

3M 1860S/1860 10 52 2.3 15 51 2.13M 8110S/8200 10 51 1.4 15 47 1.93M 8212 11 18 3.6 14 18 5.23M 8512 11 20 2.4 14 30 3.3AeroSafety Pleats 10 27 3.5 15 29 2.7Gerson 2737 10 16 1.7 15 14 2.0Moldex 2201N95/2200N95 10 24 2.7 15 22 1.9Moldex 2207N95 11 7 2.5 14 13 2.4Moldex 2301N95/2300N95 11 7 2.8 14 16 2.3Moldex 2701N95/2700N95 10 14 2.5 14 16 4.1MSA Affinity Plus 9 23 2.9 16 24 2.1MSA Affinity Ultra 10 214 1.8 15 264 2.7North 7175N95 14 17 1.6 17 17 1.6Survivair 1930 10 14 3.1 15 23 3.6US Safety ADN95 10 7 2.0 14 7 2.1Wilson 1410N95 10 18 1.8 15 13 2.0Wilson N9510F 11 29 2.6 14 35 2.4Wilson N9520F 11 12 4.1 14 36 2.2

Note: For two respirator models (Moldex 2301N95/2300N95 and Wilson N9520F), the GM SWPF values for female were statistically significantly larger than thecorresponding GM SWPF values for male based on one-way analysis of variance (p < 0.05).AGM = geometric mean.B SWPF = simulated workplace protection factor.C GSD = geometric standard deviation.

most in subsets (6) with regression coefficients significantlydifferent from zero at a significance level of 0.05. Facewidth, face length, and nose protrusion each appeared in fivesubsets.

DISCUSSION

F acial measurements have long been a subject of investi-gation for purposes of respirator fit testing. Hughes and

Lomaev(23) conducted an anthropometric survey of males inAustralia, for the purpose of designing half-facepiece respi-rators in 1972. The study measured faces of 538 Australianmales, and recommended a panel of 10 individuals fallingwithin dimensional criteria described by two dimensions, facelength and face width.

McConville et al.(24) reported that studies of militarypopulations, including a 1967 Air Force study, provided themost useful data relevant to respirator fit, but noted that themilitary population studies are not necessarily representativeof the civilian work force. Nonetheless, McConville et al.concluded the military data could be used for the design andsizing of respirators. Subsequently, Hack et al.(7) developedfacial size specifications for a panel of subjects that could beused by NIOSH for respirator fit testing in 1974. That workselected subjects using face length and face width as the criteriafor wearing full-face masks. For half-facepiece respirators,

face length and lip length were used. These dimensions wereselected because they were felt to be (a) relative to facepiecefit, (b) capable of being measured with reproducibility, and(c) independent of other measurements.(7) Using the previouslymentioned 1967 data for Air Force men and a subsequent studyof Air Force women,(25) Hack et al. identified the combinationsof facial length and width that would include 95% of the U.S.population. The upper limits were set as the mean of malemeasurements plus two standard deviations. The lower limitswere set as the mean of the female measurements minus twostandard deviations.

Since the development of the LANL respirator fit testpanels, there have been a few studies evaluating the appropri-ateness of the face dimensions used to define the panels.(10−16)

Liau et al.(10) collected face dimensions of 190 white malesubjects, using direct measurements and measurements fromphotographs. In this study, face dimensions were “normal-ized” by dividing each dimension by a comparable measure-ment of a respirator. The normalized data were correlatedwith quantitative fit test data via linear regression. Theseinvestigators found that the correlations with the normal-ized dimensions were rather low: mouth width produced anr = 0.22 (p = 0.02) and face width produced an r-value = 0.30(p = 0.001). The authors noted that the use of polynomialregression models did not improve the correlations whencompared to the linear regression model.

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TAB

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TABLE VI. Frequency of Face Dimensions in Subsets

No. of Subsets No. of Subsets No. of SubsetsNo. Face Dimensions (p < 0.15) (p < 0.05) (p < 0.01)

1 Bigonial breadth 8 6 22 Bitragion chin arc 4 3 13 Bitragion frontal arc 3 2 04 Bitragion subnasale arc 5 3 05 Face width 11 5 26 Interpupillary breadth 3 3 27 Lip length 2 1 08 Face Length 5 5 19 Menton-subnasale length 3 1 010 Nasal root breadth 3 1 011 Nose breadth 3 2 012 Nose protrusion 8 5 3

Note: The total number of unique subsets is 22.

Gross and Horstman(11) compared facial measurements for121 (60 female and 61 male) civilian workers to quantitative fittest data for three different brands of respirators. They foundno significant correlations between the facial measurementsand respirator fit. However, when the fit test data weredichotomized to passing or failing (greater or less than 10), theinvestigators found the men who failed the fit test generallyhad larger face dimensions than those who passed the fit test.Women who failed the fit test generally had smaller noses andface lengths and longer lips than the women who passed the fittest.

Oestenstad et al.(12) studied the location and shape of face-seal leak sites for a single brand of half-mask respirator wornby 73 subjects, and compared those observations to facialmeasurements, subject gender, and quantitative fit factor. Theydetermined that 89% of the leak sites were near the nose orchin. Males were more likely to have the diffusely shapedleaks. Chin-related fit factors were significantly lower thanother categories, indicating that chin leaks are generally largerin terms of amount of leakage. Significant correlations werefound for three face dimensions (menton-subnasale, biocularbreadth, nasal root breadth), none of which are used to definethe traditional fit test panels described by Hack et al.(7)

The authors suggested that consideration be given to nasaldimensions when defining a respirator test panel and selectinga respirator for an individual wearer.

Oestenstad and Perkins(13) reported on another set ofcomparisons of facial measurements to quantitative fit test data.They found that the fit of a half-facepiece respirator could bereasonably predicted by selected wearers’ face dimensions.The face dimensions that were found to have significantcorrelation coefficients with fit factors were menton-subnasalelength, biocular breadth, nasal root breadth, and nose width.However, those correlation coefficients were in the range of0.26–0.37. This finding was similar to that described abovefor Liau et al.(10) In an attempt to determine the predictive

potential of facial measurements, Oestenstad and Perkins(13)

conducted a stepwise multiple linear regression for twelvefacial measurements as the independent variables and thenatural log of fit factor as the dependent variable. In that study,it was determined that dimensions with significant regressioncoefficients in four or more models were face length, menton-subnasale length, subnasale-sellion length, binocular breadth,and nasal root breadth. Face length is included in the LANLfit test panel.(7)

In a subsequent report attempting to relate face dimensionsto respirator fit, Oestenstad(14) reported that seven facialmeasurements (including face width and face length) werecorrelated to fit for females, whereas one measurement wascorrelated for males. The author concluded that dimensionsother than those currently used may be more appropriate todefine test panels whose fit is intended to be representative ofworker populations.

Brazile et al.(15) reported on 14 face dimensions andtheir impact on respirator fit among three ethnic groups:White, African American, and Mexican American. Significantdifferences were found in the facial measurements amongthe ethnic groups. The only face dimension found to besomewhat correlated with fit was nose protrusion (R2 =0.1596, p = 0.0296). The authors conducted a backward-elimination stepwise regression, and found that nose widthand nose protrusion had significance, but they could onlyaccount for 4.45% of the variation found in the fit test data.The authors concluded that racially influenced nose width andnose protrusion are not good predictors of respirator fit.

In another study of half-facepiece respirators in 2003, Hanand Choi(16) concluded that face width, bitragion-menton arc,and nose protrusion should be preferentially considered whendesigning a half-facepiece respirator for Korean workers.

The key findings from previous studies and the current studyare summarized in Table VII. As can be found from the table,face length and/or face width were found to have significant

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TABLE VII. Summary of findings from Previous Studies and the Current Study

Researcher Respirator Models Number of Subjects Conclusions

Liau et al. (1982)(10) Four different brands of half-maskrespirators (no specifics given)

190 white males The two most important parametersare face width and mouth width.

Gross and Horstman(1990)(11)

MSA Comfo II, Survivair Blue 1,and Siebe Norton 7500 series

61 males60 females

Nose length, face length, and liplength were different betweensubjects passing fit test and thosefailing fit test.

Oestenstad et al.(1990)(12)

U.S. Safety Series 200 half-maskrespirators

39 males34 females

Significant correlations were foundfor three face dimensions(menton-subnasale, biocularbreadth, nasal root breadth).

Oestenstand and Perkins(1992)(13)

U.S. Safety Series 200 half-maskrespirators

38 males30 females

Face dimensions with significantregression coefficients in four ormore models were face length,menton-subnasale length,subnasale-sellion length, binocularbreadth, and nasal root breadth.

Oestenstad (1994)(14) AO 5-Star SeriesNorth 770 Series Survivair Series

2000

20 white males21 white females

Face length, face width, and otherfive face dimensions had significantpositive correlation coefficients withfit factors.

Brazile et al. (1998)(15) MSA Advantage half-maskrespirators

total = 186White AmericanAfrican AmericanMexican American

Respirator fit was not significantlyaffected by characteristic facedimensions influenced byrace/ethnicity;

The face dimensions correlated withrespirator fit were nose width andnose protrusion.

Han and Choi (2003)(16) Youngsung Co. YS1050DSSamgong Co. SG51213M Co. Series 6000

total = 150Korean112 males38 females

Face width, bitragion-menton arc,and nose protrusion should bepreferentially considered whendesigning a half-mask respirator forKorean workers.

Zhuang et al. 18 models of NIOSH-certified,N95 filtering-facepiecerespirators

15 males18 females

Subsets of one to six face dimensionswere found to be significantlycorrelated with SWPFs in 28 of the33 respirator model/respirator sizecombinations. Face width, bigonialbreadth, nose protrusion, and facelength were found in 11, 8, 8, and 5of the 28 subsets, respectively.

correlation with fit in six of the eight studies. Thus, it is rec-ommended that these two measurements be considered whendefining the panel for half-facepiece respirators. Correlationanalysis was also conducted between LSWPF and these twovariables (face width and face length). The correlation modelwas statistically significant (p < 0.01), but the R2 value wasonly 0.032.

CONCLUSIONS

T he respirator design style (both folding style and cupstyle) did not have a significant effect on respirator fit

in this study. The number of respirator sizes available for a

model had significant impact on respirator fit on the panelfor cup-style respirators with one and two sizes available.There was no significant difference in the GM SWPF betweenmale and female subjects for 16 of the 18 respirator models.Subsets of one to six face dimensions were found to besignificantly correlated with SWPFs in 16 of the 33 respiratormodel/respirator size combinations. Bigonial breadth, facewidth, face length, and nose protrusion appeared the most insubsets (five or six) of face dimensions where their multiplelinear regression coefficients were significantly different fromzero (p < 0.05). Lip length was found in only one subset. Facelength and lip length, which are used to define the current half-facepiece respirator fit test panel, may need to be reconsidered

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when revising the panel. Based on the findings from this andprevious studies, face length and face width are recommendedto be used for defining the panel for half-facepiece respirators.

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8. Hack, A.L., and J.T. McConville: Respirator protection factors: Part I—Development of an anthropometric test panel. Am. Ind. Hyg. Assoc. J.39:970–975 (1978).

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15. Brazile, W.J., R.M. Buchan, D.R. Sandfort, W. Melvin, J.A. Johnson,and M. Charney: Respirator fit and facial dimensions of two minoritygroups. Appl. Occup. Environ. Hyg. 13:233–237 (1998).

16. Han, D.H., and K.L. Choi: Facial dimensions and predictors of fit forhalf-mask respirators in Koreans. Am. Ind. Hyg. Assoc. J 64:815–822(2003).

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