Summary

Millions of Americans use respirators in their places of work to protect themselves from exposures to such respiratory hazards as toxic vapors and gases, harmful particulate matter, and airborne pathogens. Some respirators filter the ambient air, while others employ a separate air supply; but in either case the respirator will protect its user only if it fits properly. It must mold to the user’s face in such a way that no air from the outside can leak in, even when the user is moving or speaking.

It is the responsibility of the National Institute for Occupational Safety and Health (NIOSH) to certify that respirators from manufacturers meet certain minimum performance levels. NIOSH performs this task with the help of fit-test panels, each of them a group of about 25 people who have been chosen because, collectively, their facial dimensions are assumed to be representative of the respirator-wearing workforce as a whole. A respirator will be certified only if it performs effectively on the members of the panel—or at least on an appropriate subset of them. If, for example, a line of respirators in various sizes is being certified, it is not necessary that any one size fits all 25 panel members, but each of the test subjects should be able to be fitted suitably with at least one of the respirators.

If such a fit-test face panel is to function effectively, the faces of its members must accurately represent the faces of the entire diverse U.S. respirator-wearing workforce. This, in turn, demands having good anthropometric data—particularly data on facial dimensions—from a representative sample of the respirator-wearing workforce. Once such data have been collected and analyzed, an appropriate fit-test panel can be designed from them.



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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users Summary Millions of Americans use respirators in their places of work to protect themselves from exposures to such respiratory hazards as toxic vapors and gases, harmful particulate matter, and airborne pathogens. Some respirators filter the ambient air, while others employ a separate air supply; but in either case the respirator will protect its user only if it fits properly. It must mold to the user’s face in such a way that no air from the outside can leak in, even when the user is moving or speaking. It is the responsibility of the National Institute for Occupational Safety and Health (NIOSH) to certify that respirators from manufacturers meet certain minimum performance levels. NIOSH performs this task with the help of fit-test panels, each of them a group of about 25 people who have been chosen because, collectively, their facial dimensions are assumed to be representative of the respirator-wearing workforce as a whole. A respirator will be certified only if it performs effectively on the members of the panel—or at least on an appropriate subset of them. If, for example, a line of respirators in various sizes is being certified, it is not necessary that any one size fits all 25 panel members, but each of the test subjects should be able to be fitted suitably with at least one of the respirators. If such a fit-test face panel is to function effectively, the faces of its members must accurately represent the faces of the entire diverse U.S. respirator-wearing workforce. This, in turn, demands having good anthropometric data—particularly data on facial dimensions—from a representative sample of the respirator-wearing workforce. Once such data have been collected and analyzed, an appropriate fit-test panel can be designed from them.

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users In short, certification fit testing of respirators depends upon two main factors: a well-conducted anthropometric survey of a representative sample of the respirator-wearing workforce, and a fit-test panel based on these anthropometric data that accurately represents the facial shapes and sizes of the millions of workers who use—or who should be using— respirators in their jobs. For many years NIOSH has been using the fit-test panels developed in 1972 by researchers at Los Alamos National Laboratory (LANL) based upon anthropometric data available from a U.S. Air Force study. The population sample used by the LANL researchers was a group of men and women serving in the U.S. Air Force. It is unlikely that this sample was ever representative of the broader U.S. workforce—Air Force personnel are generally young and in good health, for instance, and the U.S. Air Force has height and weight requirements as well—but in the intervening years the U.S. workforce has become much more diverse, with more women workers and more minorities. Furthermore, the growing obesity problem in the United States means that workers are, on average, much heavier than they were two or three decades ago. In addition, the ethnic composition of the U.S. workforce had changed over the 30 years. So fit-test panels based on physical characteristics of Air Force personnel from the early 1970s are unlikely to accurately represent the broad U.S. workforce today. Because of this situation, in 2001 NIOSH contracted with Anthrotech, Inc., to collect new anthropometric data that would be representative of today’s respirator-wearing workforce and to use those data to design new fit-test panels. After Anthrotech finished that task, NIOSH contracted with the Institute of Medicine (IOM) to establish an ad hoc committee to review the NIOSH-sponsored Anthrotech study. This report contains the findings, conclusions, and recommendations of that IOM committee (Box S-1). THREE OVERARCHING THEMES The various elements of the NIOSH-sponsored Anthrotech study— anthropometric measurements, statistical sampling techniques, fit testing, and so on—are complicated, and this review must necessarily wade into them in some detail; but the basic message of this report can be summarized with the following three broad statements:

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users the results of the NIOSH-sponsored Anthrotech study represent a clear improvement over the anthropometric data and corresponding LANL fit-test face panels that have been used since the 1970s; nonetheless, the NIOSH-sponsored Anthrotech study has a number of weaknesses that limit its effectiveness and reliability; and, therefore, there are certain steps that should be taken to address the weaknesses, in order to move toward more effective testing and certification of respirators in the future. These three statements can also be seen as the report’s overarching themes, themes that are touched upon again and again throughout the course of the review. ANTHROPOMETRIC MEASUREMENTS The field of anthropometry is a well-established one, with measuring techniques that have been honed over decades of practice. In their survey, the Anthrotech researchers used traditional tools such as calipers and measuring tapes to take 18 facial and head dimensions from the 4,026 subjects in their survey. They also recorded height and weight for comparison to other similar datasets, and neck circumference was added partway through data collection when it was learned that this measurement plays a role in some national and international respirator standards. Taking such anthropometric measurements requires a researcher to first identify and mark a series of landmarks on the subject’s face. Both the placement of these landmarks and the measurement of the distance between pairs of landmarks are potential sources of error. Measurement Error Ideally, in a large field study on anthropometric measurement, a pilot study is conducted to check how accurately landmarks are placed and distances measured by the technicians who will perform the study and to determine how closely the measurements taken by different technicians agree. This makes it possible to assess how much error can be expected

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users in the study and to determine the sources of error, thereby offering a means for improvement. The Anthrotech researchers did make special efforts to reduce human errors in landmark placement and dimension measurements, having the field technicians practice on each other until an allowable level of accuracy was achieved. However, data that could be used to independently assess the precision of measurements—that is, how closely measurements made by different technicians agreed and how closely measurements agreed when made by the same technician on different occasions—were not reported. There was also no apparent record of an attempt to measure the relationship between individual differences in facial shape and the level of measurement error. For these reasons, the committee concluded that the NIOSH-sponsored Anthrotech report did not adequately address the potential effects of measurement error on the validity and quality of its anthropometric measurements and makes the following recommendation: Recommendation 2-1: Analyze Measurement Error. In future studies NIOSH should perform additional analyses of the impact of measurement error, including the effects of intraobserver and interobserver variations in measurement. Use of Three-Dimensional Scan Data In addition to the traditional anthropometric measurements, the Anthrotech researchers also performed three-dimensional (3D) scans on approximately a quarter of the subjects in an effort to develop a set of standard head forms. Although the datasets from these 3D scans were archived, the data were not used in the development of the proposed fit-test panels. NIOSH informed the committee that this was because there were discrepancies between the 3D data and the traditional measures. This decision not to use the 3D data concerned the committee because 3D data have a number of advantages over the traditional, manually collected data, such as providing a more accurate and complete summary of the facial geometry, and providing information about the localized variation around a landmark. The use of 3D scans in anthropometry is still a developing area, and it is necessary to test any newly acquired scans (or scanning devices) against already validated means of

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users collecting data. Though no uniform, evidence-based, best-practice standards exist against which measures collected from 3D image data can be compared, an appropriate test must be defined for every study until such standards are developed. In light of the potential advantages, the committee recommends the following: Recommendation 2-2: Consider Utilizing Three-Dimensional Scan Data. NIOSH should consider collecting and utilizing data from 3D scans, alone, or in combination with traditional manually collected data, to ensure the most robust set of data are used to develop future anthropometric face panels. DATA SAMPLING To create a population sample that reflected the race, ethnicity, age, and gender diversity of the respirator-wearing workforce in the United States, NIOSH developed a plan that called for approximately 4,000 subjects divided, evenly into men and women, three age categories (18-29, 30-44, and 45-65), and four racial/ethnic categories (white, African-American, Hispanic, and Other). Unfortunately, the NIOSH-sponsored Anthrotech study did not appropriately subdivide the sample population based on race and ethnicity. The Other category was overly diverse, including Asian, American Indian, and Alaskan Native subjects, while not including other groups that might be designated as “Other.” Given the diversity of the respirator wearing workforce, it is important that the Other group be included in analyses of the entire target population. However, its small sample size and limited diversity may make it difficult, if not impossible, to perform useful analysis of the Other category as a distinct subgroup. For logistical reasons, the Anthrotech researchers decided to limit their sample population to workers from eight states: California, Illinois, Kentucky, New York, Ohio, Pennsylvania, Texas, and Virginia. Within each state, the researchers selected work sites that were deemed representative and contacted the work sites to see if they were willing to participate in the survey. There are no details in the report on the criteria Anthrotech used to select the various establishments, the response rate

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users from these establishments, or how participating sites may have differed from nonparticipating sites. The committee found that the 41 work sites listed in the final report were more often larger establishments, but it is not clear whether this was a choice made by the Anthrotech investigators or was due to larger companies being more willing to participate. Once a work site was identified, Anthrotech investigators worked with a single individual who provided access to test subjects and assisted with both scheduling and recruitment. Unfortunately, the criteria for selection of the test subjects are ill defined in the report, so it is difficult to ascertain if the selection process was random or if issues that arose during the selection of subjects biased the sample. The final sample consisted of 3,998 subjects, which was very close to the original target number. The final distribution, however, did not follow the original plan of having equal numbers of subjects per category, but instead ended up being closer to the actual demographic makeup of the U.S. workforce. Nor was the distribution even across geographic region, as originally planned. Instead, the final distribution was more heavily weighted toward Texas, Ohio, and Illinois. It is not clear what difference either of these factors may have made to the sample, but since race and ethnicity are not evenly distributed across the United States, the limited geographic distribution may have unintentionally introduced a racial and ethnic bias into the sample. Defining the Target Population Although a clear definition of the target population is critical to survey design, the Anthrotech report does not provide such a definition. In addition, although the survey intends to reflect “respirator users,” it was unclear if that included anyone who may ever need to use a respirator, or simply those who use or should be using respirators. Finally, another problem is that the selection of the subjects in this survey did not seem to be random, while a well-designed survey will have random sampling. Unfortunately, the committee could not determine exactly how the subjects were selected, and this left many questions unanswered. Did the sample include overrepresentation of workers whom the management knew had adapted well to the respirators they wore? Conversely, did workers volunteer for the study because they recognized they had problems? Either situation would have seriously biased the population sample.

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users Because of these and other shortcomings in the creation of the sample, the committee recommends the following: Recommendation 3-1: Define Target Populations More Precisely. Future anthropometric face panel studies undertaken by, or on behalf of, NIOSH should have a statistically rigorous and valid sampling plan and implementation strategy that precisely define the target population and also ensure that the samples of selected subjects included in the studies are representative of the predefined sample population (e.g., the current workforce that wears respirators, workers who should be using respirators, the general United States workforce). DATA ANALYSIS AND FIT-TEST FACE PANELS When the 4,000 subjects in the population sample were divided into groups according to sex, age, and race/ethnicity, the sizes of the groups in the sample were not in the same proportions as those groups are in the general U.S. workforce. Therefore, the first step in Anthrotech’s data analysis was to weight each sample cell to adjust for that disparity. This is a workable strategy, but it raises the issue of which population to use as a reference when calculating the weights. Ideally that population would be the target population of the survey—those in the U.S. workforce who should use respirators, for example—but the Anthrotech researchers were apparently unable to find data on this population, so they defaulted to the entire U.S. workforce. The committee was unable to tell if this was an appropriate tactic, but it is at least conceivable that there is a difference in anthropometric measurements between the entire U.S. workforce and the subset of workers who should routinely wear or who should wear respirators in an emergency. Benchmarking the Target Population Perhaps the most important consideration in this weighting, however, is to make sure that it is done in such a way as to capture the true demo-

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users graphic makeup of the U.S. respirator-using workforce. That workforce has become more and more diverse over the past several decades, resulting in an increased range of facial dimensions, and that trend can only be expected to continue in the next few decades. Thus the committee makes the following recommendation: Recommendation 4-1: Ensure Appropriate Representation of Demographics Groups. NIOSH should benchmark its sample population against the current and future United States workforce that should be wearing respirators to ensure adequate representation of demographic groups on the panel (e.g., age, gender, race, and ethnicity). To develop those fit-test panels from their survey data, the Anthrotech researchers used methods similar to those employed by the original LANL face panel designers. In particular, they chose to rely on the same facial dimensions as in the LANL face panels. Anthrotech’s rationale for this choice was not clear to the committee, as there is no evidence that these parameters lead to the most effective fit-test panels. Expanding Face Panels There were two clear differences between the fit-test face panels offered in the NIOSH-sponsored Anthrotech report and those created in the 1972 LANL study. First, the proposed face panels were not confined to a strictly rectangular arrangement of cells as had been the case earlier. The Anthrotech investigators found that, in offsetting some of the cells, they were able to achieve a greater coverage of the target population. And, second, there was a clear shift of the cells to the upper-right quadrant, where the larger faces reside. This was the result of a major difference in facial dimensions between the earlier LANL sample and the current one—of the individuals surveyed in the current sample, 15.3 percent would not have been covered by the LANL face panel, most of them because of having larger faces. Thus the shift in the face panel was necessary to provide coverage for the larger faces in the current survey; but the committee noted that the shift came at the expense of smaller-faced individuals, including many in minority populations, even though small faces still make up a

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users considerable proportion of the workforce. Thus the committee recommends the following: Recommendation 4-2: Include Large and Small Faces in Panel. NIOSH should develop an expanded anthropometric face panel that includes the larger-sized faces described in the NIOSH-sponsored Anthrotech study, while retaining the small-sized subjects from the LANL face panel. This may require adjusting the total number of subjects in the face panel. Facial Dimensions and Fit The proposed face panel based on Anthrotech survey is more representative of the current U.S. workforce than the LANL face panel. A recent study found that the LANL face panels, expected to accommodate more than 95 percent of the civilian population, only accommodate 84 percent of civilian population. However, this in itself does not mean that the updated panel will result in better fitting respirators. Because of an absence of fit-test data comparing the two face panels, the committee was unable to determine the extent to which the new panel is an improvement. Thus the committee recommends the following: Recommendation 4-3: Perform Studies to Compare the Proposed Face Panel to the LANL Face Panel. NIOSH should perform a study in which it compares the range of quantitative fit provided for specified respirators on subjects representing the LANL face panel and subjects representing the proposed NIOSH-sponsored Anthrotech bivariate face panel (adjusted in accordance with recommendation 4-2). And, indeed, the ultimate test of the usefulness of the new fit-test face panels will be determined not by how representative they are of the facial dimensions of the respirator-wearing workforce, but rather by how good a job they do in identifying respirators that will fit a substantial portion of that workforce. Unfortunately, at the present time there is no good understanding of how various facial dimensions affect the fit of a respira-

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users tor. Thus, although the fit-test panels proposed in the NIOSH-sponsored Anthrotech study cover well over 95 percent of the workforce in terms of including workers with a certain range of facial dimensions, this does not translate clearly into statements about respirator fit. In particular, the present state of knowledge does not permit one to conclude with any degree of confidence that respirators that fit members of the proposed fit-test panels will also fit 95 percent of the population of workers who should be using respirators. Thus the committee recommends the following: Recommendation 4-4: Analyze an Appropriate Proportion of the Respirator-Using Population That Can Be Fitted to Respirators. NIOSH should perform a statistical analysis of the proportion of workers who should be using respirators to determine the proportion of that population that is included in the proposed NIOSH face panels. Based on that analysis, NIOSH should either adjust the proposed face panel to meet a 95 percent confidence level and some appropriate margin of error, or state the confidence metric as it stands. This recommendation assumes that NIOSH will take into account Recommendation 4-1 in the design of its future face panel(s). More generally, since there is not currently a good understanding of the relationship between various facial dimensions and fit, it would have made sense for the Anthrotech researchers to have performed fit testing as part of their survey. The failure to include fit testing with anthropometric facial measurements limited the ultimate utility of the data collected in the NIOSH-sponsored Anthrotech study. Further, half-face respirators in particular have not had proper analyses performed on the relationship between facial dimensions and fit. For that reason the committee makes the following recommendations: Recommendation 4-5: Determine Key Features Related to Fit Using Quantitative Fit Measures. NIOSH should perform research to determine which facial features have the greatest impact on the respiratory protection of face masks in the workplace, us-

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users ing quantitative measures. These research findings should be utilized in the design of future anthropometric face panel studies. Recommendation 4-6: Perform Facial Dimension Analyses for Half-Face Respirators. NIOSH should perform additional facial dimension analysis when developing anthropometric face panels for half-facepiece respirators, including at least one nasal dimension. Recommendation 4-7: Utilize Multiple Features in the Development of Face Panels. NIOSH should examine the potential effects of a nonlinear relationship between respirator fit and facial dimensions. Alternative Face Panel Approaches In addition to creating new fit-test panels using the same methods as the earlier LANL panels (but with a new population survey), the Anthrotech investigators also created fit-test panels based on a principal component analysis (PCA) of the facial measurements obtained from their survey. The investigators identified a group of 10 facial measurements as being best correlated with fit and then did a PCA on those 10 variables to come up with 2 new variables that were linear combinations of those 10. The 2 new variables can be described as the overall size of the face (from small to large) and the general shape of the face (from a small face with a short, wide nose to a long face with a long, narrow nose). Working with those two new variables, the Anthrotech investigators proposed a fit-test panel that would be based on a new system of five facial groups defined by a combination of size and shape instead of the traditional face length and face width. The committee, however, was unable to determine whether the PCA-based fit-test panel would be an improvement over the proposed panel that Anthrotech constructed using the same approach as the LANL panel but with new data. The committee did suggest another nontraditional approach to panel design that NIOSH might consider. Traditionally, the cells in a fit-test panel have had members in proportion to how the broader target popula-

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users tion is distributed across the panel. That is, if 20 percent of the respiratorusing workforce had facial dimensions that put them in a particular cell, then 20 percent of the panel members come from that cell as well. In the committee’s suggested approach, NIOSH might investigate creating fittest panels that are populated in proportion to variance, thus making it more likely that workers in those facial regions with greater variability have as much protection as those workers in the regions with less variability. If, for example, the 20 percent of the population in one cell all have facial dimensions similar to one another, they can be represented effectively by fewer panel members, while cells with more highly variable populations need—and with this approach will have—larger numbers of panel members to be representative. FUTURE DIRECTIONS Finally, the committee has a number of suggestions for future directions that NIOSH should take to best ensure the safety of respirator-using workers. The committee concluded that the proposed NIOSH-sponsored Anthrotech face panel represents an improvement over the LANL face panel, and its application is likely to improve the availability of respirators that fit a broader segment of the workforce. However, the Committee also found that this study could have been greatly improved. In addition, the NIOSH face panels require periodic updates. Recommendation 5-1: Update the Panel More Often, Using a Scientifically Valid Design. NIOSH should plan to update the face panel more often to reflect the rapidly changing demographic structure of the U.S. workforce. To do so, it should (1) establish a valid sample of the target population for its respirator certification, (2) assure that the sample that is selected to establish a valid panel is representative of the target population, (3) apply 3D measures to describe the essential fit characteristics of the panel, and (4) rely on quantitative fit testing to determine the extent to which a respirator covers the fit characteristics of the face panel.

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users The current use of isoamyl acetate for fit testing is a qualitative and subjective process that does not provide NIOSH certification personnel with a specific value to analyze leakage around the facepiece. Therefore the committee makes the following recommendation: Recommendation 5-2: Replace Isoamyl Acetate with Quantitative Measures. NIOSH should use quantitative measures for respirator fit-test certification. The current use of qualitative measures as a fit-test agent for certification—for example, isoamyl acetate—should be discontinued. The committee is concerned that filtering facepiece respirators are not currently certified against a fit-test panel. This failure may result in families of respirators that do not adequately fit some of the population of workers who should be using respirators. Recommendation 5-3: Utilize the Revised Anthropometric Face Panel for Filtering Facepiece Respirators. NIOSH should include filtering facepiece respirators in the revised anthropometric face panel used for certification of half-facepiece respirators. Plans for any additional data gathering should be developed in consultation with experts in statistical sampling and measurement. The committee noted that certification requirements for single-size facepieces (“one size fits all”) are different from those for facepieces that are available in multiple sizes (e.g., small, medium, large), which can make it difficult for manufacturers of multiple-sized facepieces to obtain certification for each individually sized facepiece. Thus the committee recommends Recommendation 5-4: Modify Certification Requirements. NIOSH should modify its certification requirements to encourage manufacturers to develop specific sizes designed to fit underrepresented anthropometric categories. Certification requirements should be

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users modified to allow families of respirators (e.g., small, medium, and large) to be certified against a fit-test panel and not specify what portion of the panel each individual size respirator must fit, provided that the family adequately covers the entire panel. Finally, the committee noted that the current respirator size designations of small, medium, and large are not adequately informative for wearers and fit testers. In particular, fit testers and respirator-wearing workers have difficulty determining which size and brand of facepiece is most likely to fit any given worker. This is largely due to inadequate details on the potential sizing of the facepieces on their packaging. To address this issue, the committee recommends Recommendation 5-5: Develop Improved Descriptions of Face Mask Sizes. NIOSH should encourage manufacturers to develop improved methods of describing facial sizes and shapes in product literature. For example, NIOSH and manufacturing companies should further explore the use of face panel images, and respirator containers should include corresponding pictures of small, medium, and large sizes, and long/narrow and small/wide face pictures.

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users BOX S-1 Summary of Conclusions and Recommendations Anthropometric Measurements Conclusion 2-1: The NIOSH-sponsored Anthrotech report did not adequately address the potential impact of measurement error on the validity and quality of the anthropometric face dimension data. Recommendation 2-1: Analyze Measurement Error. In future studies NIOSH should perform additional analyses of the impact of measurement error, including the effects of intraobserver and interobserver variations in measurement. Conclusion 2-2: Three-dimensional scan data may offer advantages over tradi-tional, manually collected anthropometric data; however, there is no evidence base of best practice against which 3D scans may be compared. Recommendation 2-2: Consider Utilizing Three-Dimensional Scan Data. NIOSH should consider collecting and utilizing data from 3D scans, alone or in combina-tion with traditional manually collected data, to ensure the most robust set of data are used to develop future anthropometric face panels. The NIOSH-Sponsored Anthrotech Study’s Sampling Strategy Conclusion 3-1: The proposal and NIOSH-sponsored Anthrotech Report did not adequately define or represent an appropriate target population. Recommendation 3-1: Define Target Populations More Precisely. Future anthro-pometric face panel studies undertaken by, or on behalf of, NIOSH should have a statistically rigorous and valid sampling plan and implementation strategy that precisely define the target population, and also ensure that the samples of se-lected subjects included in the studies are representative of the predefined sam-ple population (e.g., the current workforce that wears respirators, workers who should be using respirators, the general United States workforce). Data Analysis and Fit-Test Panels Conclusion 4-1: The demographic makeup of the United States workforce has been, and will continue to become, more diverse, resulting in an increased range of facial dimensions. Recommendation 4-1: Ensure Appropriate Representation of Demographics Groups. NIOSH should benchmark its sample population against the current and future U.S. workforce that should be wearing respirators to ensure adequate rep-resentation of demographic groups on the panel (e.g., age, gender, race, and ethnicity).

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users Conclusion 4-2: The proposed NIOSH-sponsored Anthrotech face panel selects larger-dimension faces at the expense of the smaller faces currently included in the LANL face panel, even though some of these small faces still make up a con-siderable proportion of the workforce. Recommendation 4-2: Include Large and Small Faces in Panel. NIOSH should develop an expanded anthropometric face panel that includes the larger faces described in the NIOSH-sponsored Anthrotech study, while retaining the smaller subjects from the LANL face panel. This may require adjusting the total number of subjects in the face panel. Conclusion 4-3: The proposed NIOSH-sponsored Anthrotech face panel is likely to be more representative of the current U.S. workforce than the LANL panel, but information is not available to determine the extent to which the new panel pro-vides a better fit for that workforce. Recommendation 4-3: Perform Studies to Compare the Proposed Face Panel to the LANL Face Panel. NIOSH should perform a study in which it compares the range of quantitative fit provided for specified respirators on subjects represent-ing the LANL face panel, and subjects representing the proposed NIOSH-sponsored Anthrotech bivariate face panel (adjusted in accordance with Recom-mendation 4-2). Conclusion 4-4: The present state of knowledge does not permit the committee to conclude with any degree of confidence that respirators that fit the proposed NIOSH-sponsored Anthrotech study face panel are likely to fit 95 percent of the population of workers who should be using respirators. Further, the committee was unable to determine a level of confidence or margin of error for the proposed face panel. However, the proposed panel, based on newer data, appears to be more representative of the population than the 30-year-old data used in the LANL face panel. Recommendation 4-4: Analyze an Appropriate Proportion of the Respirator-Using Population That Can Be Fitted to Respirators. NIOSH should perform a statistical analysis of the proportion of workers who should be using respirators to deter-mine the proportion of that population that is included in the proposed NIOSH face panels. Based on that analysis, NIOSH should either adjust the proposed face panel to meet a 95 percent confidence level and some appropriate margin of error, or state the confidence metric as it stands. This recommendation assumes that NIOSH will take into account Recommendation 4-1 in the design of its future face panel(s). Conclusion 4-5: The ultimate utility of the data collected in the NIOSH-sponsored Anthrotech study is limited because the study did not include the collection of fit-testing data along with facial measurements. Recommendation 4-5: Determine Key Features Related to Fit Using Quantitative Fit Measures. NIOSH should perform research to determine which facial features have the greatest impact on the respiratory protection of face masks in the work-place, using quantitative measures. These research findings should be utilized in the design of future anthropometric face panel studies.

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users Conclusion 4-6: Proper analyses of facial dimensions have not been performed for half-face respirators; lip length and menton-sellion length may not be the most appropriate dimensions to use when developing anthropometric face panels. Recommendation 4-6: Perform Facial Dimension Analyses for Half-Face Respirators. NIOSH should perform additional facial dimension analysis when developing anthropometric face panels for half-face respirators, including at least one nasal dimension. Conclusion 4-7: The use of multiple features in the development of face panels is likely to be inherently better than the use of just facial height and width, but it is not yet well understood which features are directly relevant to fit and how they can best be combined. Recommendation 4-7: Utilize Multiple Features in the Development of Face Panels. NIOSH should examine the potential effects of a nonlinear relationship between respirator fit and facial dimensions. Future Directions: Additional Analyses and Research to Practice Conclusion 5-1: The proposed NIOSH-sponsored Anthrotech face panel repre-sents an improvement over the LANL face panel, and its application is likely to improve the availability of respirators that fit a broader segment of the workforce. However, the committee also found that this study could have been greatly im-proved. In addition, the NIOSH face panels require periodic updates. Recommendation 5-1: Update the Panel More Often, Using a Scientifically Valid Design. NIOSH should plan to update the face panel more often to reflect the rap-idly changing demographic structure of the U.S. workforce. To do so, it should (1) establish a valid sample of the target population for its respirator certification, (2) assure that the sample that is selected to establish a valid panel is representative of the target population, (3) apply three-dimensional measures to describe the essential fit characteristics of the panel, and (4) rely on quantitative fit testing to determine the extent to which a respirator covers the fit characteristics of the face panel. Conclusion 5-2: Qualitative fit testing is a subjective process and does not pro-vide NIOSH certification personnel with a specific value to analyze leakage around the facepiece. Recommendation 5-2: Replace Isoamyl Acetate with Quantitative Measures. NIOSH should use quantitative measures for respirator fit-test certification. The current use of qualitative measures as a fit-test agent for certification, for ex-ample isoamyl acetate, should be discontinued. Conclusion 5-3: The failure to use anthropometric face panels for certification of filtering facepiece respirators may result in families of respirators that do not ade-quately fit some of the population of workers who should be using respirators. Recommendation 5-3: Utilize the Revised Anthropometric Face Panel for Filtering FacePiece Respirators. NIOSH should include filtering facepiece respirators in the revised anthropometric face panel used for certification of half-face respira

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Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users tors. Plans for any additional data gathering should be developed in consultation with experts in statistical sampling and measurement. Conclusion 5-4: Manufacturers of multiple-sized facepieces often have difficulty obtaining certification for each individually sized facepiece. Recommendation 5-4: Modify Certification Requirements. NIOSH should modify its certification requirements to encourage manufacturers to develop specific sizes designed to fit underrepresented anthropometric categories. Certification requirements should be modified to allow families of respirators (e.g., small, me-dium, and large) to be certified against a fit-test panel and not specify what por-tion of the panel each individual size respirator must fit, provided that the family adequately covers the entire panel. Conclusion 5-5: The current size designations of small, medium, and large for respirators in product literature are not adequately informative for wearers and fit testers. Recommendation 5-5: Develop Improved Descriptions of Face Mask Sizes. NIOSH should encourage manufacturers to develop improved methods of de-scribing facial sizes and shapes in product literature. For example, NIOSH and manufacturing companies should further explore the use of face panel images, and respirator containers should include corresponding pictures of small, me-dium, and large sizes, and long/narrow and small/wide face pictures.