The effect of gender and respirator brand on the association of respirator fit with facial dimensions

This study examined the association of facial dimensions with respirator fit considering the effect of gender and respirator brand. Forty-one subjects (20 white females and 21 white males) participated in the study. Each subject was measured for 12 facial dimensions using anthropometric sliding and spreading calipers and a steel measuring tape. Three quantitative fit tests were conducted with the same subject wearing one size of three different brands of half-mask respirators resulting in a total of nine fit tests. Linear mixed model analysis was used to model respirator fit as a function of gender and respirator brand while controlling for facial dimensions. Results indicated that the gender by respirator brand interaction was not statistically significant (p = 0.794), and there was no significant difference in respirator fit between males and females (p = 0.356). There was a significant difference in respirator fit among respirator brands (p < 0.001). Because correlations between facial dimensions and respirator fit differed across gender and respirator brand, six separate linear mixed models were fit to assess which facial dimensions most strongly relate to respirator fit using a "one variable at a step" backward elimination procedure. None of the 12 facial dimensions were significantly associated with respirator fit in all six models. However, bigonial breadth and menton-nasion length were significantly associated with respirator fit in five of the six models, and biectoorbitale breadth, bizygomatic breadth, and lip width were significantly associated with respirator fit in four of the six models. Although this study resulted in significant findings related to the correlation of respirator fit with menton-nasion length and lip width (the dimensions currently used to define the half-mask respirator test panel), other facial dimensions were also shown to be significantly associated with respirator fit. Based on these findings and findings from previous studies, it is suggested that other facial dimensions including bigonial breadth, biectoorbitale breadth, and bizygomatic breadth be considered when designing half-mask respirators, and that face length and lip width alone may not be appropriate in defining test groups whose fit is intended to be representative of worker populations.     

Correlation between respirator fit and respirator fit test panel cells by respirator size

The National Institute for Occupational Safety and Health (NIOSH), recognizing the difficulties inherent in using old military data to define modern industrial respirator fit test panels, recently completed a study to develop an anthropometric database of the measurements of heads and faces of civilian respirator users. Based on the data collected, NIOSH researchers developed two new panels for fit testing half-facepiece and full-facepiece respirators. One of the new panels (NIOSH bivariate panel) uses face length and face width. The other panel is based on principal component analysis (PCA) to identify the linear combination of facial dimensions that best explains facial variations. The objective of this study was to investigate the correlation between respirator fit and the new NIOSH respirator fit test panel cells for various respirator sizes. This study was carried out on 30 subjects that were selected in part using the new NIOSH bivariate panel. Fit tests were conducted on the test subjects using a PORTACOUNT device and three exercises. Each subject was tested with three replications of four models of P-100 half-facepiece respirators in three sizes. This study found that respirator size significantly influenced fit within a given panel cell. Face size categories also matched the respirator sizing reasonably well, in that the small, medium, and large face size categories achieved the highest geometric mean fit factors in the small, medium, and large respirator sizes, respectively. The same pattern holds for fit test passing rate. Therefore, a correlation was found between respirator fit and the new NIOSH bivariate fit test panel cells for various respirator sizes. Face sizes classified by the PCA panel also followed a similar pattern with respirator fit although not quite as consistently. For the LANL panel, however, both small and medium faces achieved best fit in small size respirators, and large faces achieved best fit in medium respirators. These findings support the selection of the facial dimensions for developing the new NIOSH bivariate respirator fit test panel.     

The effect of aerosol size distribution and measurement method on respirator fit

The particle size-dependent leakage into a respirator was examined by measuring the leakage of particle sizes between 0.07 to 4.4 microns through three hole sizes in a negative-pressure half-mask respirator worn by a human subject. This investigation showed that the size distribution of an aerosol test agent and the measurement method have an effect on the leakage measured in a quantitative fit test. For instance, the ratio of percent leakage measured by light scattering between test aerosols with count median diameters of 2.2 and 0.28 microns can be as large at 5:1. Likewise, the ratio of the percent leakage measured by a particle count method vs. a mass method of detection of the same polydisperse aerosol with a count median diameter equal to 2.2 microns can be as high as 4:1. The mass leakage into a mask with a leak is also greater for an exposure aerosol with a count median diameter between 0.15 to 0.30 micron compared to exposure aerosols with larger count median diameters for aerosols with the same mass concentration.     

Impact of time and assisted donning on respirator fit

The goal of this study was to examine the impact of assistance with donning and time on quantitative fit factors (FF) and pass rates for subjects wearing an N95 filtering facepiece respirator (FFR) and a non-certified adhesive mask. Fit factors were measured using two side-by-side TSI Portacount instruments sampling second-by-second simultaneous inside- and outside-facepiece concentrations. Naïve subjects made two visits at least one week apart. At each visit subjects first donned either the respirator or adhesive mask without assistance and performed a five-exercise fast fit test. They then donned a new respirator or mask with assistance in proper donning (e.g., proper forming of the nosepiece, strap placement, etc.) and performed a second five-exercise fast fit test. The same sequence of unassisted and assisted donning was then repeated with the other facepiece. Fifteen subjects participated in the study; time between visits ranged from 7–29 days (average 12 days). On visit 1 the respirator FFs were significantly higher (GM = 88) than for the adhesive mask (GM = 14); with assistance these FFs showed significant improvements to 116 and 124, respectively. At visit 1 almost half of subjects donning the respirator without assistance achieved a passing FF of 100 or greater, while only one-fifth of subjects were able to pass the fit test wearing an adhesive mask without assistance. Pass rates improved for both groups with assistance, but more so for the adhesive mask wearers. On visit 2 the pass rates for both groups had decreased, with the adhesive mask group showing a greater decrease. With assistance, pass rates improved for both groups, but again more so for those wearing the adhesive mask. Results suggest that wearers would benefit from assistance and re-training every time they don a respirator, even if the time between donnings is as short as one or two weeks.     

Effect of test exercises and mask donning on measured respirator fit

Quantitative respirator fit test protocols are typically defined by a series of fit test exercises. A rationale for the protocols that have been developed is generally not available. There also is little information available that describes the effect or effectiveness of the fit test exercises currently specified in respiratory protection standards. This study was designed to assess the relative impact of fit test exercises and mask donning on respirator fit as measured by a controlled negative pressure and an ambient aerosol fit test system. Multiple donnings of two different sizes of identical respirator models by each of 14 test subjects showed that donning affects respirator fit to a greater degree than fit test exercises. Currently specified fit test protocols emphasize test exercises, and the determination of fit is based on a single mask donning. A rationale for a modified fit test protocol based on fewer, more targeted test exercises and multiple mask donnings is presented. The modified protocol identified inadequately fitting respirators as effectively as the currently specified Occupational Safety and Health Administration (OSHA) quantitative fit test protocol. The controlled negative pressure system measured significantly (p < 0.0001) more respirator leakage than the ambient aerosol fit test system. The bend over fit test exercise was found to be predictive of poor respirator fit by both fit test systems. For the better fitting respirators, only the talking exercise generated aerosol fit factors that were significantly lower (p < 0.0001) than corresponding donning fit factors.     

Correlation of qualitative and quantitative results from testing respirator fit

Three qualitative respirator fit tests were evaluated for their ability to adequately measure respiratory protection. The evaluated methods were the negative pressure test, the isoamyl acetate test, and the irritant smoke test. Each test was performed concurrently with a single quantitative fit test, the dioctylphthalate (DOP) test, during 274 half-mask and 274 full facepiece wearings. The quantitative values of DOP penetration obtained after passing or failing each qualitative fit test were lognormally distributed. For each qualitative test performed on each mask type, the average log penetration values obtained after passing and failing each test were statistically different from each other. The mean of the log penetration values associated with the failed qualitative test was always larger than the mean of the log penetration values associated with passed qualitative tests for all three qualitative methods. Most (95%) of the tested study had adequately fitting respirators as determined by quantitative testing. Of these subjects, 96% to 100% passed the qualitative fit tests. Of the 5% of the study subjects with inadequately fitting half mask respirators, 93% to 100% of the inadequate fits were detected by qualitative methods. Twenty three to 46% of the poorly fitting full face masks were detected by qualitative methods. The probability of passing or failing a qualitative test with an inadequately fitting respirator can be estimated; however, the uncertainty associated with each estimate is large due to the small number of study subjects with poorly fitting respirators.     

Errors associated with three methods of assessing respirator fit

Three fit test methods (Bitrex, saccharin, and TSI PortaCount Plus with the N95-Companion) were evaluated for their ability to identify wearers of respirators that do not provide adequate protection during a simulated workplace test. Thirty models of NIOSH-certified N95 half-facepiece respirators (15 filtering-facepiece models and 15 elastomeric models) were tested by a panel of 25 subjects using each of the three fit testing methods. Fit testing results were compared to 5th percentiles of simulated workplace protection factors. Alpha errors (the chance of failing a fit test in error) for all 30 respirators were 71% for the Bitrex method, 68% for the saccharin method, and 40% for the Companion method. Beta errors (the chance of passing a fit test in error) for all 30 respirator models combined were 8% for the Bitrex method, 8% for the saccharin method, and 9% for the Companion method. The three fit test methods had different error rates when assessed with filtering facepieces and when assessed with elastomeric respirators. For example, beta errors for the three fit test methods assessed with the 15 filtering facepiece respirators were < or = 5% but ranged from 14% to 21% when assessed with the 15 elastomeric respirators. To predict what happens in a realistic fit testing program, the data were also used to estimate the alpha and beta errors for a simulated respiratory protection program in which a wearer is given up to three trials with one respirator model to pass a fit test before moving onto another model. A subject passing with any of the three methods was considered to have passed the fit test program. The alpha and beta errors for the fit testing in this simulated respiratory protection program were 29% and 19%, respectively. Thus, it is estimated, under the conditions of the simulation, that roughly one in three respirator wearers receiving the expected reduction in exposure (with a particular model) will fail to pass (with that particular model), and that roughly one in five wearers receiving less reduction in exposure than expected will pass the fit testing program in error.     

Comparison of simulated respirator fit factors using aerosol and vapor challenges

Although not well established, mask leakage measured using submicron aerosol challenges is generally accepted as being representative of vapor challenges. The purpose of this study was to compare simulated respirator fit factors (FFs) measured using vapor challenges to those measured using an aerosol challenge. A full-facepiece respirator was mounted on a headform inside a small enclosure and modified with controlled leaks (laser-drilled orifices) to produce FFs ranging from about 300 to 30,000. A breathing machine was used to simulate breathing conditions of 1.0 L tidal volume and 25 breaths/min. A monodisperse aerosol consisting of 0.72 micron polystyrene latex spheres (PSL) was used for the reference test aerosol, and FFs were measured using a laser aerosol spectrometer. An inert gas, sulfur hexafluoride (SF6), and an organic vapor, isoamyl acetate (IAA), were used as the vapor challenges. The in-mask concentration of SF6 was measured using a gas chromatograph (GC). A GC was also used to quantify in-mask IAA concentration samples actively collected with sorbent tubes. FF measurements made with the PSL aerosol challenge were conducted in sequence with the SF6 and IAA challenges, without disturbing the mask, to yield matched data pairs for regression analysis. FFs measured using the PSL reference aerosol were found to correlate well with those measured with the SF6 (r2 = 0.99) and IAA (r2 = 0.98) vapor challenges. FFs measured using IAA tended to be higher at values below 10,000. The best agreement was observed with the inert gas, SF6. The results of this study suggest that submicron aerosols are suitable as quantitative fit test challenges for assessing the performance of respirators against inert vapors.     

Facial hair and respirator fit: a review of the literature

The effect of facial hair on the quality of fit obtained while wearing a tight-fitting respirator has been and continues to be a controversial subject. Many people hold strong opinions on both sides of the issue, but it is not opinion that is needed. Rather what is needed is quantitative study of the situation to determine precisely what effect facial hair has on respirator fit. The results of fourteen studies of the facial hair leakage question have been summarized. All but two of the fourteen studies found that in the presence of facial hair, face seal leakage increases from 20 times to 1000 times. In addition both intersubject and interrespirator face seal leakage variability increased when facial hair was present. In the other two studies, one completed with positive pressure SCBAs and the other completed in the workplace, no statistically significant leakage differences were found.     

The effect of pressure drop on respirator faceseal leakage

Users of particulate air-purifying respirators are typically told to change their filters when breathing resistance becomes uncomfortable. It has been proposed that a noticeable increase in breathing resistance (pressure drop) may increase airflow through respirator faceseal leaks. This logic has been extended to suggest that respirator user exposure to contaminants may increase because of this theoretical increase in air leakage. Procedures similar to those of previous investigators were used to study this issue. Repeated faceseal leak rate measurements were made at -5.6 through -20.1 mm water pressure drops across the faceseal. Subjects were divided into two groups, representing acceptable fit or unacceptable fit, based on leak rate criteria prescribed by the Occupational Safety and Health Administration (OSHA). Subjects with acceptable fit did not experience an increase in faceseal leak rate with increased pressure drop. Leak rates for subjects with unacceptable fit were highly variable and did not show an association with pressure drop. Results of this study do not support the concept of increased faceseal leakage with increased pressure drop. The evidence does not suggest increased risk of contaminant exposure through the face seal as pressure drop increases.     

A feasibility study of quantitative respirator fit testing by controlled negative pressure

The feasibility of using a direct measure of respirator leakage flow rate as a quantitative index of respirator face seal fit has been explored through the use of a new controlled negative pressure method. The method is based on exhausting air from a temporarily sealed respirator facepiece at a rate sufficient to generate and then sustain a constant negative pressure inside the facepiece while the wearer holds his breath. The magnitude of the negative pressure is preselected to replicate the mean inspiratory pressure inside the mask during normal wear. With the air-purifying paths into the respirator temporarily blocked, measurement of the exhaust flow rate yields a synonymous measure of the leakage flow rate into the mask during inspiration under normal use conditions. The feasibility of using the new method to quantify respirator fit was assessed in a preliminary study that compared its performance with a quantitative fit test method based on the use of dichlorodifluoromethane as a challenge agent. Study data exhibit a high degree of correlation (r greater than 0.99) and no significant difference between the two methods over a range of controlled mask leakage rates. A major advantage of the new method is that a worker can be fit tested with his assigned respirator because the method does not require a destructive sampling probe. Other significant benefits compared to current methods used to quantify respirator fit appear to include (1) ease of test administration, (2) simplicity of test components, (3) lack of a potentially toxic challenge agent, (4) a straightforward calibration procedure, (5) multiple test capability, (6) immediacy of test results, and (7) field portability of the test system.     

Predictive value of the user seal check in determining half-face respirator fit

Guidelines issued by the Centers for Disease Control and Prevention and the World Health Organization state that healthcare workers should wear N95 masks or higher-level protection during all contact with suspected cases of severe acute respiratory syndrome. Before use, the manufacturer recommends performing a user seal check to ensure that the mask is fitted correctly. This study aimed to test the ability of the user seal check to detect poorly fitting masks. This study is a retrospective review of a mask-fitting programme carried out in the intensive care unit of the Prince of Wales Hospital in Hong Kong. In this programme, all staff were tested with two types of N95 mask and one type of N100 mask. The results of the documented user seal check were then compared with the formal fit-test results from a PortaCount. Using a PortaCount reading of 100 as the criterion for a correctly fitted mask, the user seal check wrongly indicated that the mask fitted on 18-31% of occasions, and wrongly indicated that it did not fit on 21-40% of occasions. These data indicate that the user seal check should not be used as a surrogate fit test. Its usefulness as a pre-use test must also be questioned.     

Experiments supporting the use of ambient aerosols for quantitative respirator fit testing

Most methods for testing facial seal leakage on subjects undergoing respirator fit tests involve comparing the generated aerosol particulate concentration inside the subject's respirator to the concentration in a test chamber. These aerosols are produced by fogging substances such as corn oil, dioctyl sebacate, or dioctyl phthalate (DOP) into the test chamber. The health effects of these substances and of their aerosols on respiratory systems are uncertain. The proposed alternate method uses as a test medium ambient particles which exist in most room atmospheres. The proposed method eliminates the need for a test chamber and for an intentionally produced aerosol. The subject is tested for respirator inleakage by comparing the particulate count concentration inside the subject's respirator to that of the room atmosphere outside the respirator. This method is less expensive and simpler to administer than the use of oil or other deliberately produced aerosols because it uses an existing ambient test medium. Statistical analysis of the test data indicates favorable comparison with the conventional chamber-aerosol method.     

中国成年人呼吸防护用品适合性检验新型头面分栏研究

目的 为满足呼吸防护用品的适配性设计和测试需求,根据目前我国成年人头面测量数据提出2种新的分类(栏)方式:二元分栏和主成分分栏,并分析2种分栏对我国成人头面划分的适用性.方法 以近期我国3000名成年人头面尺寸测量数据为基础建立头面尺寸数据库,根据头面尺寸指标脸长-脸宽的二维分布提出我国成年人头面二元分栏.采用主成分分析对10项稳定的头面尺寸指标(最小额宽、脸宽、鄂宽、脸长、瞳孔间距、头宽、鼻突长、鼻宽、鼻梁宽、鼻长)分析后提出我国成年人头面主成分分栏.通过我国成年人头面数据在不同分栏的分布比例分析两类分栏对成人头面划分的适用性.结果 我国成年人头面二元分栏和主成分分栏分别将脸型分为10个型号和8个型号.总覆盖率分别为96.9%(男性95.4%,女性98.4%)和96.5%(男性95.1%,女性98.1%).各型号覆盖比例较为均匀,二元分栏各型号覆盖率在4.6%～21.7%之间,主成分分栏各型号覆盖率在10.4%～14.6%之间.对比分析国外头面分栏方法,美国洛斯阿拉莫斯实验室(LANL)全面罩分栏只能覆盖我国70.9%的人群,且各型号覆盖极不均匀,其中3个型号的覆盖率之和不足1%;美国国家职业安全卫生研究所(NIOSH)研制的二元分栏和主成分分栏能覆盖我国96.4%和95.9%的人群,但各型号分布不均匀,其二元分栏中5个型号仅覆盖6.3%的人群,主成分分栏中3个型号的覆盖率之和为7.2%.结论 根据我国成人头面数据提出的二元分栏和主成分分栏能代表国人头面尺寸分布,比国外分栏更适用.     

Study of respirator effect on nasal-oral flow partition

Factors affecting worker tolerance of respiratory personal protective devices are inadequately understood. This study evaluates whether respirator-type loads affected the switch from nasal to oral breathing. Eleven healthy subjects were studied under progressive exercise conditions, using a respirator full-face mask with inspiratory resistance (I), pressure breathing (P) (10 cm H₂O end-expiratory pressure), or no load (N). A rapid-response thermistor was used to determine whether flow was predominantly oral or nasal. Both P and I increased the percentage of time that breathing was predominantly oral. The effect was most pronounced at higher exercise levels. The percentage of mouth breathing appeared to be closely related to the expiratory time. This study suggests that nasal-oral flow partitioning should be considered as a possible determinant of respirator tolerance. Am. J. Ind. Med. 32:408–412, 1997. © 1997 Wiley-Liss, Inc.     

Racial differences in respirator fit testing: a pilot study of whether American fit panels are representative of Chinese faces

The current respirator fit test panels (RFTPs) developed by Los Alamos National Laboratory or improved by the National Institute for Occupational Safety and Health were based on facial anthropometric survey of American groups including few Chinese examples. Facial anthropometric dimensions for other race/ethnic groups are different. Despite the fact that China has been the largest national source of industrial labor supply, and Chinese is one of top 10 races for immigration to America and Britain, there have been few related facial anthropometric studies on RFTPs for Chinese. This pilot study was conducted to investigate the difference of facial anthropometric dimensions between Chinese and Americans, and whether American RFTPs are applicable to Chinese. The results show that facial anthropometric measurements of 461 Chinese subjects are different from those of American groups described in the literature. About 12-35% of the Chinese subjects fall outside the ranges derived from American panels. Chinese may have shorter and wider facial character than American groups. Current RFTPs, which are based on American facial anthropometric surveys, may not fairly represent the facial anthropometric characteristics of Chinese groups. The results can also help to construct new RFTPs for Chinese in the future. Further studies are needed to verify whether the results in this study would be in agreement with those of facial anthropometric survey in wider samples.     

Evaluation of the benefit of the user seal check on N95 filtering facepiece respirator fit

The objective of this study was to better understand the benefit of the user seal check step for respirator test subjects in the N95 filtering facepiece respirator donning process. To qualify for the study, subjects were required to pass a standard quantitative fit test on at least one of the three N95 filtering facepiece respirator models: 3M 1860 (cup), 3M 1870 (flat-fold), and Kimberly Clark PFR95-270 (duckbill). Eleven subjects were enrolled and performed a series of abbreviated, quantitative fit tests where they were randomly asked either to perform or not perform a user seal check with 20 different respirator samples of each model. The experimental design included 3 respirator models × 10 subjects × 2 treatment levels with 10 replications. Geometric mean (GM) fit factors and percentages of times a fit factor ≥ 100 was achieved for a donning were compared for each subject with and without the user seal check across all models and for each model. Higher GM fit factors and smaller geometric standard deviations across all models were achieved for 10 of the 11 subjects when performing a user seal check compared with not performing a user seal check. Geometric mean fit factors of 148, 184, and 156, compared with 126, 187, and 115, respectively, were obtained for the 3M 1860, 3M 1870, and Kimberly Clark PFR95-270 models when the user seal check was performed vs. not performed. Differences in the GM fit factors for the 3M 1860 and Kimberly Clark PFR95-270 models were statistically significant (p < 0.05) when performing a user seal check vs. not performing a user seal check. These data suggest that there may be some benefit to performing the user seal check for at least some models during the filtering facepiece respirator donning process for workers who have previously passed a fit test for those respirator models. Additional research is needed with larger groups of subjects and respirator models/types.     

An assessment of critical anthropometric dimensions for predicting the fit of a half-mask respirator.

The purpose of this study was to determine if facial dimensions for a group of subjects were predictive of the fit factors measured while one brand of half-mask respirator was worn. Fit factors and 12 facial dimensions measured on 30 female and 38 male subjects were analyzed by correlation coefficients; weighted, multiple linear regression; and discriminant analysis. Data were analyzed for all subjects, gender subgroups, a race subgroup (whites only), and race/gender subgroups. Significant correlation coefficients with the log-transformed fit factors were found for four dimensions; four dimensions had significant coefficients in four or more multiple linear regression models. Only two dimensions had significant coefficients in four or more discriminant analysis models. Menton-subnasale (lower face) length was the only dimension included in all three of these groups. Gender-specific regression models had very high coefficient of determination values (R2 > 0.85). Discriminant analysis of the data for all subjects and race/gender subgroups found very good predictive scores for statistical software-generated models and menton-subnasale length alone; these scores were significantly better than those for the model with the respirator test panel dimensions (face length and lip width). These analyses found that facial dimensions were good predictors of respirator fit for those subjects wearing one brand of half-mask respirator. Lower face length was consistently indicated as being correlated or associated with fit. These results would indicate that dimensions other than those currently used may be more appropriate to define a half-mask respirator test panel.     

Impact of three biological decontamination methods on filtering facepiece respirator fit, odor, comfort, and donning ease

The objective of this study was to determine if ultraviolet germicidal irradiation (UVGI), moist heat incubation (MHI), or microwave-generated steam (MGS) decontamination affects the fitting characteristics, odor, comfort, or donning ease of six N95 filtering facepiece respirator (FFR) models. For each model, 10 experienced test subjects qualified for the study by passing a standard OSHA quantitative fit test. Once qualified, each subject performed a series of fit tests to assess respirator fit and completed surveys to evaluate odor, comfort, and donning ease with FFRs that were not decontaminated (controls) and with FFRs of the same model that had been decontaminated. Respirator fit was quantitatively measured using a multidonning protocol with the TSI PORTACOUNT Plus and the N95 Companion accessory (designed to count only particles resulting from face to face-seal leakage). Participants' subjective appraisals of the respirator's odor, comfort, and donning ease were captured using a visual analog scale survey. Wilcoxon signed rank tests compared median values for fit, odor, comfort, and donning ease for each FFR and decontamination method against their respective controls for a given model. Two of the six FFRs demonstrated a statistically significant reduction (p < 0.05) in fit after MHI decontamination. However, for these two FFR models, post-decontamination mean fit factors were still ≥ 100. One of the other FFRs demonstrated a relatively small though statistically significant increase (p < 0.05) in median odor response after MHI decontamination. These data suggest that FFR users with characteristics similar to those in this study population would be unlikely to experience a clinically meaningful reduction in fit, increase in odor, increase in discomfort, or increased difficulty in donning with the six FFRs included in this study after UVGI, MHI, or MGS decontamination. Further research is needed before decontamination of N95 FFRs for purposes of reuse can be recommended.     

Study of contact characteristics between a respirator and a headform

This article presents a computational study on contact characteristics of contact pressure and resultant deformation between an N95 filtering facepiece respirator and a newly developed digital headform. The geometry of the headform model is obtained based on computed tomography scanning of a volunteer. The segmentation and reconstruction of the headform model is performed by Mimics v16.0 (Materialise, Leuven, Belgium), which is a medical image processing software. The respirator model is obtained by scanning the surface of a 3M 8210 N95 respirator using a 3D digitizer and then the model is transformed by Geomagic Studio v12.0 (3D system, Rock Hill, SC), a reverse engineering software. The headform model contains a soft tissue layer, a skull layer, and a separate nose. The respirator model contains two layers (an inner face sealing layer and an outer layer) and a nose clip. Both the headform and respirator are modeled as solid elements and are deformable. The commercial software, LS-DYNA (LSTC, Livermore, CA), is used to simulate the contact between the respirator and headform. Contact pressures and resultant deformation of the headform are investigated. Effects of respirator stiffness on contact characteristics are also studied. A Matlab (MathWorks, Natick, MA) program is developed to calculate local gaps between the headform and respirator in the stable wearing state.