Respiratory protection against Mycobacterium tuberculosis: quantitative fit test outcomes for five type N95 filtering-facepiece respirators

In preparing to fit test a large workforce, a respirator program manager needs to initially choose respirators that will fit the greatest proportion of employees and achieve the best fits. This article discusses our strategy in selecting respirators from an initial array of seven NIOSH-certified Type N95 filtering-facepiece devices for a respiratory protection program against Mycobacterium tuberculosis (M. tb) aerosol. The seven respirators were screened based on manufacturer-provided fit test data, comfort, and cost. From these 7 devices, 5 were chosen for quantitative fit testing on 40 subjects who were a convenience sample from a cohort of approximately 30,000 workers scheduled to undergo fit testing. Across the five brands, medium/regular-size respirators fit from 8% to 95% of the subjects; providing another size of the same brand improved the pass rates slightly. Gender was not found to significantly affect fit test pass rates for any respirator brand. Among test panel members, an Aearo Corporation respirator (TC 84A-2630) and a 3M Company respirator (TC 84A-0006) provided the highest overall pass rates of 98% and 90%, respectively. We selected these two brands for fit testing in the larger worker cohort. To date, these two respirators have provided overall pass rates of 98% (1793/1830) and 88% (50/57), respectively, which are similar to the test panel results. Among 1850 individuals who have been fit tested, 1843 (99.6%) have been successfully fitted with one or the other brand. In a separate analysis, we used the test panel pass rates to estimate the reduction in M. tb infection risk afforded by the medium/regular-size of five filtering-facepiece respirators. We posed a low-exposure versus a high-exposure scenario for health care workers and assumed that respirators could be assigned without conducting fit testing, as proposed by many hospital infection control practitioners. Among those who would pass versus fail the fit test, we assumed an average respirator penetration (primarily due to faceseal leakage) of .04 and 0.3, respectively. The respirator with the highest overall pass rate (95%) reduced M. tb infection risk by 95%, while the respirator with the lowest pass rate (8%) reduced M. tb infection risk by only 70%. To promote the marketing of respirators that will successfully fit the highest proportion of wearers, and to increase protection for workers who might use respirators without the benefit of being fit tested, we recommend that fit testing be part of the NIOSH certification process for negative-pressure air-purifying respirators with tightly fitting facepieces. At a minimum, we recommend that respirator manufacturers generate and provide pass rate data to assist in selecting candidate respirators. In any event, program managers can initially select candidate respirators by comparing quantitative fit tests for a representative sample of their employee population.     

Reducing respirator fit test errors: a multi-donning approach

As a continuation of recent studies to assess the accuracy of existing fit test methods, a multi-donning approach to fit testing is presented. As an example of that approach, a multi-donning quantitative fit test for filtering-facepiece respirators is presented and analyzed by comparing its error rates with those of the single-donning approach of current fit test methods. That analysis indicates the multi-donning fit test has the potential to reduce both the alpha error and the beta error to half that of single-donning fit tests. The alpha error is the error of failing a respirator that should pass; the beta error is the error of passing a respirator that should fail. Lowering fit test error rates for filtering-facepiece respirators is important because fit testing is an essential means of helping assure that an individual has selected an adequately fitting respirator. To reduce the alpha and beta error inherent in current fit test methods, the proposed fit test for filtering-facepiece respirators incorporates five donnings of the facepiece, unlike the single donning of existing fit test methods. The analysis presented here indicates that the multiple-donning approach reduces the element of chance in the fit test result and thereby increases the consistency and accuracy of the fit tests. The time to conduct the multi-donning test can approximate the time for current, single-donning tests by shortening the time the respirator is worn after each donning to about 10 sec. And, unlike current fit tests for filtering-facepieces that measure only faceseal leakage, the example multiple-donning fit test considered here is based on a measurement of total leakage (faceseal plus filter). Utilizing total respirator leakage can result in simpler quantitative fit test instrumentation and a fit test that is more relevant to the workplace. Further trials with human subjects are recommended in order to validate the proposed multi-donning approach.     

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.     

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.     

The effect of subject characteristics and respirator features on respirator fit

A recent study was conducted to compare five fit test methods for screening out poor-fitting N95 filtering-facepiece respirators. Eighteen models of NIOSH-certified, N95 filtering-facepiece respirators were used to assess the fit test methods by using a simulated workplace protection factor (SWPF) test. The purpose of this companion study was to investigate the effect of subject characteristics (gender and face dimensions) and respirator features on respirator fit. The respirator features studied were design style (folding and cup style) and number of sizes available (one size fits all, two sizes, and three sizes). Thirty-three subjects participated in this study. Each was measured for 12 face dimensions using traditional calipers and tape. From this group, 25 subjects with face size categories 1 to 10 tested each respirator. The SWPF test protocol entailed using the PortaCount Plus to determine a SWPF based on total penetration (face-seal leakage plus filter penetration) while the subject performed six simulated workplace movements. Six tests were conducted for each subject/respirator model combination with redonning between tests. The respirator design style (folding style and cup style) 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 panel for cup-style respirators with one and two sizes available. There was no significant difference in the geometric mean fit factor between male and female subjects for 16 of the 18 respirator models. Subsets of one to six face dimensions were found to be significantly correlated with SWPFs (p < 0.05) in 16 of the 33 respirator model/respirator size combinations. Bigonial breadth, face width, face length, and nose protrusion appeared the most in subsets (five or six) of face dimensions and their multiple linear regression coefficients were significantly different from zero (p < 0.05). Lip length was found in only one subset. The use of face length and lip length as the criteria to define the current half-facepiece respirator fit test panel may need to be reconsidered when revising the panel. Based on the findings from this and previous studies, face length and face width are recommended measurements that should be used for defining the panel for half-facepiece respirators.     

Facial anthropometric dimensions of Koreans and their associations with fit of quarter-mask respirators

Past studies on respirator fit or performance have mostly been done for Whites or male subjects, and little attention has been paid to minorities and Asians. To fill this gap, this study was designed to provide facial anthropometric data for Koreans and to analyze the association between facial dimensions and respirator fit factors for three brands of quarter-mask respirators, two domestic and one imported brand, using a Portacount 8020. A total of 110 university student subjects, 70 males and 40 females volunteered for participation in the study. The results of this study showed that Korean males and females have different facial dimensions as compared with those of White males and females. Unexpectedly, the imported respirator performed better than the domestic respirators. Males were found to achieve better respirator fit than females regardless of respirator brands tested. The regression analysis found no common prognostic variables with the three respirator brands studied. A stepwise logistic regression analysis was conducted to find predictive facial dimensions with respirator fits. Some facial dimensions were found to be statistically significant, but these dimensions are different from the traditionally recommended facial dimensions of face length and lip width for quarter mask. To improve respirator fit for Koreans, these different facial characteristics need to be considered in the design of quarter mask respirators.     

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.     

Correlations between workplace protection factors and fit factors for filtering facepieces in the welding workplace

Workplace protection factor (WPF) means a measure of the actual protection of respirator provided in the workplace when correctly worn. While fit factor (FF) represents a quantitative measure of the fit of a particular respirator to an individual and it is determined in the laboratory. To evaluate the relationship between WPF and FF is very important since FF may or may not be taken advantage of estimating WPF. Outside and inside Fe concentrations for three brand N95 filtering facepieces were collected on 14 workers/three respirator combinations in the welding workplace. The WPF measurements on the samples of the three respirator brands worn by 14 workers were observed to range from 2.2 to 132.9 with a geometric mean of 15.9 and a geometric standard deviation of 2.63. Respirator performances as measured by the WPF differed significantly among different respirator brands (p<0.05). In this study, correlations were found between the WPF measurements and the FF data for all samples of the three respirators (R2=0.38). The percentage of Fe particles having a smaller fraction than 1.1 microm diameter was observed as 71.6% of the total.     

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.     

Comparison of performance of three different types of respiratory protection devices

Respiratory protection is offered to American workers in a variety of ways to guard against potential inhalation hazards. Two of the most common ways are elastomeric N95 respirators and N95 filtering-facepiece respirators. Some in the health care industry feel that surgical masks provide an acceptable level of protection in certain situations against particular hazards. This study compared the performance of these types of respiratory protection during a simulated workplace test that measured both filter penetration and face-seal leakage. A panel of 25 test subjects with varying face sizes tested 15 models of elastomeric N95 respirators, 15 models of N95 filtering-facepiece respirators, and 6 models of surgical masks. Simulated workplace testing was conducted using a TSI PORTACOUNT Plus model 8020, and consisted of a series of seven exercises. Six simulated workplace tests were performed with redonning of the respirator/mask occurring between each test. The results of these tests produced a simulated workplace protection factor (SWPF). The geometric mean (GM) and the 5th percentile values of the SWPFs were computed by category of respiratory protection using the six overall SWPF values. The level of protection provided by each of the three respiratory protection types was compared. The GM and 5th percentile SWPF values without fit testing were used for the comparison, as surgical masks were not intended to be fit tested. The GM values were 36 for elastomeric N95 respirators, 21 for N95 filtering-facepiece respirators, and 3 for surgical masks. An analysis of variance demonstrated a statistically significant difference between all three. Elastomeric N95 respirators had the highest 5th percentile SWPF of 7. N95 filtering-facepiece respirators and surgical masks had 5th percentile SWPFs of 3 and 1, respectively. A Fisher Exact Test revealed that the 5th percentile SWPFs for all three types of respiratory protection were statistically different. In addition, both qualitative (Bitrex and saccharin) and quantitative (N95-Companion) fit testing were performed on the N95 filtering- and elastomeric-facepiece respirators. It was found that passing a fit test generally improves the protection afforded the wearer. Passing the Bitrex fit test resulted in 5th percentile SWPFs of 11.1 and 7.9 for elastomeric and filtering-facepiece respirators, respectively. After passing the saccharin tests, the elastomeric respirators provided a 5th percentile of 11.7, and the filtering-facepiece respirators provided a 5th percentile of 11.0. The 5th percentiles after passing the N95-Companion were 13.0 for the elastomeric respirators and 20.5 for the filtering-facepiece respirators. The data supports fit testing as an essential element of a complete respiratory protection program.     

Qualitative fitting characteristics of elastomeric half face-piece respirators using Isoamyl acetate agent

To examine the fit testing of elastomeric half face-piece respirators (EHRs), a total of 41 candidates were randomly assigned into seven EHRs equipped with organic vapor (OV) cartridges which were commonly used in the Iranian industrial workplaces. The qualitative fitting into the facial dimensions was assessed using the Allegro Isoamyl Acetate fit test kit. While the studied EHRs showed very low passing fit testing rates, the 3M, AoSafety (Medium), and AoSafety (Large) had the highest passing rates with 22.0%, 14.60%, and 9.76%, respectively. The AoSafety (All sizes) delivered a higher passing fit test rate than the 3M brand (29.30 vs. 22.0%). The one size fits all respirators including the DUO and Climax showed lower proportions of passing fit tests compared with AoSafety three-size system brands (2.40% and 4.90% vs. 29.30%). Low fit test passing rates were determined among different respirators. The respirators with various sizes and styles had more opportunities for different wearers to pass the fit test than single size models. The initial and annual fit testing requirements shall be developed by local government. Also, the manufacturers are required to pay attention to respirator features and subject characteristics during the production to obtain satisfactory protection for the end-users.     

Fit factors for quarter masks and facial size categories

Respirator fit testing is necessary before entering hazardous working environments to ensure that the respirator, when worn, satisfies a minimum fit and that the wearer knows when the respirator fits properly. In the many countries that do not have fit testing or total inward leakage regulations (including Korea), however, many workers wearing respirators may be potentially exposed to hazardous environments. It is necessary to suggest a useful tool to provide an alternative for fit testing in these countries. This study was conducted to evaluate fitting performance for quarter-mask respirators, and fit factors in facial size categories based on face lengths and lip lengths of the wearers. A total of 778 subjects (408 males, 370 females) were fit tested for three quarter masks: Sejin Co. SK-6 (Ulsan, Korea), Yongsung Co. YS-2010 S (Seoul, Korea), and 3 M Co. Series 7500 Medium (MN, USA) masks with a PortaCount 8020 (TSI Co., USA). A facial dimension survey of the subjects was conducted to develop facial size categories, on the basis of face length and lip length. Geometric mean fit factors (GMFFs) of Series 7500 Medium were found to be the highest of the three respirators. All of the respirators were more suitable for males than females in fitting performance. The Series 7500 Medium fitted a large number of the males tested, since the GMFFs for males were above 100 for every box of facial size categories, and high pass proportion rates were shown at an individual fit factor level of 100. The YS-2010 S provides an adequate fit for males in a limited range of facial dimensions. The Series 7500 Medium is more limited in providing adequate fit for females at specific facial dimensions than for males. For adequate fitting performance, the SK-6 is not preferentially recommended for Korean male and female workers due to low GMFFs and pass proportions. The result of this study indicates that after more accurate studies are performed, facial size categories, on the basis of facial dimensions, could be a useful tool to assist in the selection of adequately fitting respirators for workers in the countries having no fit testing requirements.     

An evaluation of an air-supplied blouse and an air hood

Fit factor studies for an air-supplied blouse (blouse) and an air hood respirator (air hood) were conducted by Lawrence Livermore National Laboratory. Nine test subjects were used to test the blouse. Three subjects were used to test the air hood. Exercises conducted in the test chamber included touching toes, raising both arms overhead, squatting, twisting at the torso while holding a rod, and running in place. Both the air hood and blouse were tested with 8 ft3/min air supply. Both respirators were worn in a test chamber. The blouse provided a fit factor of greater than 40,000. The air hood, for nearly all tests, also provided a fit factor greater than 40,000 when worn correctly. Fit factors were also measured for improperly worn air hoods.     

Capability of respirator wearers to detect aerosolized qualitative fit test agents (sweetener and Bitrex) with known fixed leaks

This study was designed to evaluate and compare the ability of respirator wearers to detect qualitative respirator fit test agents (saccharin and Bitrex) when the respirators were modified to include fixed size leaks. In recent years the number of persons who require fit testing has increased, partly in response to the needs of health care workers with potential exposure to infectious bio-aerosols. Many health care providers have chosen qualitative respirator fit testing using saccharin and/or Bitrex for a variety of reasons, including (but not limited to) low initial equipment cost. Respirators were modified to include a mid-line sampling probe between the nose and mouth for quantitative fit testing with a TSI PortaCount. A second modification included the introduction of a shortened 14-gauge intravenous catheter at the bridge of the nose. The fixed leak was designed to produce fit factors < 100 when unplugged, with an average fit factor of 67 among 26 respirator wearers. A complete fit test was not performed, because one purpose of this study was to determine the ability of respirator wearers to detect a known fixed leak during a single normal breathing exercise, without introducing unknown and potentially variable size leaks. Sensitivity threshold screening included a placebo and requirement to correctly characterize the taste of the agent used. Quantitative fit factors without leaks ranged from 96 to > 20,000 and 22 to 160 with the leak present. Twenty four of 26 subjects had fit factors < 100 (92%) when fixed leaks were induced. All subjects correctly detected Bitrex with fixed leaks (sensitivity = 100%). Nine of 26 subjects (35%) were unable to detect saccharin in the presence of a known fixed leak even though the average fit factor for these subjects was 77. When the two subjects with fit factors > 100 were excluded, only 16 of 24 respirator wearers were able to detect saccharin with fixed leaks (sensitivity = 67%). There were several important aspects of our study design worth noting, including the introduction of a placebo during sensitivity threshold testing, limiting the subject response time to a single maneuver, using a higher concentration of Bitrex than commercially available, and requiring the subjects to correctly characterize the taste of the qualitative test agent. In conclusion, leak detection was correctly identified with Bitrex, but not saccharin.     

Simplified pressure method for respirator fit testing

A simplified pressure method has been developed for fit testing air-purifying respirators. In this method, the air-purifying cartridges are replaced by a pressure-sensing attachment and a valve. While wearers hold their breath, a small pump extracts air from the respirator cavity until a steady-state pressure is reached in 1 to 2 sec. The flow rate through the face seal leak is a unique function of this pressure, which is determined once for all respirators, regardless of the respirator's cavity volume or deformation because of pliability. The contaminant concentration inside the respirator depends on the degree of dilution by the flow through the cartridges. The cartridge flow varies among different brands and is measured once for each brand. The ratio of cartridge to leakflow is a measure of fit. This flow ratio has been measured on human subjects and has been compared to fit factors determined on the same subjects by means of photometric and particle count tests. The aerosol tests gave higher values of fit.     

Determination of known exhalation valve damage using a negative pressure user seal check method on full facepiece respirators

A negative pressure user seal check (NPUSC) method was evaluated for its ability to adequately detect known exhalation valve leakage into a respirator. Three valves with different types of damage were included. Twenty-six test subjects, wearing full facepiece respirators, were asked to perform a NPUSC. Their responses as to whether they passed or failed the user seal check were compared to fit testing results from two quantitative fit test methods: ambient aerosol and controlled negative pressure. In addition, equipment developed at the University of Cincinnati was used to measure in-mask pressures that are generated during the performance of NPUSCs. This technique was employed to assess the ability of respirator wearers to properly conduct user seal checks. The data were analyzed to determine if the user seal check procedure is an effective method for detecting known exhalation valve damage. All test subjects reported passing the user seal check with the undamaged valve. With the warped valve installed, 95 percent of test subjects reported passing the user seal check. With the slit valve installed, 73 percent of test subjects reported passing. With the dirty valve installed, 65 percent reported passing. All fit factors, measured with the damaged valves, were below the Occupational Safety and Health Administration-recognized pass/fail criteria except one fit test with the respirator equipped with the slit valve. Results from the in-mask pressure measurements confirmed whether or not the subject properly conducted a user seal check, but did not detect respirator leakage. In conclusion, the performance of a NPUSC rarely helped to identify damaged exhalation valves. These results support the need for respirator inspection prior to donning with periodic fit testing and the performance of user seal checks as necessary components of an adequate respiratory protection program.     

Development of Medium-size Half-mask Facepiece for Male Workers at a Shipyard and Its Fit Performance in Korea

Ten years ago, three differently sized half-mask facepiece prototypes were constructed from silicon using computer graphics and statistical analysis to fit them according to Korean facial dimensions. The purpose of this study was to complete the medium-size half-mask respirator based on the prototype, which would provide an adequate fit performance for male workers at a shipyard, Hyundai Samho Heavy Industry Co., in Korea. The complete respirator—the hardness 55—was manufactured with existing accessories such as a filter, exhalation valve, and strap attached. The fit performance test was conducted by performing a quantitative fit-test on 48 male subjects: workers who usually wear half-mask respirators (Dobulife Tech Co., Model DM-911, Gwangju, Gyeonggi-do, Korea). The results showed that the hardness 55 provided male subject workers with much better fit performance than the existing mask constructed by the same company. Because softness of the material of the facepiece, in particular the inner part, influenced faceseal leakage, further research on developing better-fit respirator facepieces should consider carefully the fine control of material softness.     

Laboratory study to assess causative factors affecting temporal changes in filtering facepiece respirator fit: part I - pilot study

The National Institute for Occupational Safety and Health is conducting a first-of-its-kind study that will assess respirator fit and facial dimension changes as a function of time and improve the scientific basis for decisions on the periodicity of fit testing. A representative sample of 220 subjects wearing filtering-facepiece respirators (FFR) will be evaluated to investigate factors that affect changes in respirator fit over time. The objective of this pilot study (n = 10) was to investigate the variation in fit test data collected in accordance with the study protocol. Inward leakage (IL) and filter penetration were measured for each donned respirator, permitting the calculation of face seal leakage (FSL) and fit factor (FF). The study included only subjects who (a) passed one of the first three fit tests (FF ≥ 100), and (b) demonstrated through a series of nine donnings that they achieved adequate fit (90th percentile FSL was ≤ 0.05). Following the respirator fit tests, 3-D scans of subjects were captured, and height, weight, and 13 traditional anthropometric facial dimensions were measured. The same data were collected 2 and 4 weeks after baseline. The mean change in FSL for the 10 subjects was 0.044% between Visits 1 and 2, and was 0.229% between Visits 1 and 3. Technicians achieved at least moderate reliability for all manual measurements except nose protrusion. Filter penetration was generally less than 0.03%. Geometric mean fit factors were not statistically different among the three visits. The large variability was observed with different respirator samples for the same model, between subjects (inter), and within each subject (intra). Although variability was observed, adequate fit was maintained for all 10 subjects. Pilot scans collected show subject faces remained the same over the 4 weeks. The consistent results during the pilot study indicate that the methods and procedures are appropriate for the 3-year main study. In addition, this baseline fit change data will be compared with future fit changes to determine if the changes are meaningful.     

Recommended test methods and pass/fail criteria for a respirator fit capability test of half-mask air-purifying respirators

This study assessed key test parameters and pass/fail criteria options for developing a respirator fit capability (RFC) test for half-mask air-purifying particulate respirators. Using a 25-subject test panel, benchmark RFC data were collected for 101 National Institute for Occupational Safety and Health-certified respirator models. These models were further grouped into 61 one-, two-, or three-size families. Fit testing was done using a PortaCount® Plus with N95-Companion accessory and an Occupational Safety and Health Administration-accepted quantitative fit test protocol. Three repeated tests (donnings) per subject/respirator model combination were performed. The panel passing rate (PPR) (number or percentage of the 25-subject panel achieving acceptable fit) was determined for each model using five different alternative criteria for determining acceptable fit.

When the 101 models are evaluated individually (i.e., not grouped by families), the percentages of models capable of fitting >75% (19/25 subjects) of the panel were 29% and 32% for subjects achieving a fit factor ≥100 for at least one of the first two donnings and at least one of three donnings, respectively. When the models are evaluated grouped into families and using >75% of panel subjects achieving a fit factor ≥100 for at least one of two donnings as the PPR pass/fail criterion, 48% of all models can pass. When >50% (13/25 subjects) of panel subjects was the PPR criterion, the percentage of passing models increased to 70%.

Testing respirators grouped into families and evaluating the first two donnings for each of two respirator sizes provided the best balance between meeting end user expectations and creating a performance bar for manufacturers. Specifying the test criterion for a subject obtaining acceptable fit as achieving a fit factor ≥100 on at least one out of the two donnings is reasonable because a majority of existing respirator families can achieve an PPR of >50% using this criterion. The different test criteria can be considered by standards development organizations when developing standards.     

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.