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.     

Health care workers and respiratory protection: is the user seal check a surrogate for respirator fit-testing?

Many agencies recommend that health care workers wear N95 filtering facepiece respirators (N95-FFR) to minimize occupational exposure to bioaerosols, such as tuberculosis and pandemic influenza. Published standards outline procedures for the proper selection of an N95-FFR model, including user seal checks and respirator fit-testing. Some health officials have argued that the respirator fit-test step should be eliminated altogether, given its additional time and cost factors, and that only a user seal check be utilized to ensure that an adequate face seal has been achieved. One of the aims of the current study is to examine whether a user seal check is an appropriate surrogate for respirator fit-testing. Subjects were assigned an N95-FFR and asked to perform a user seal check (as per manufacturer's instructions) after which they immediately underwent a respirator fit-test. Successfully passing a respirator fit-test was based on not detecting a leakage through the face seal (either qualitatively with a test agent or quantitatively with a particulate counter). The sample population consisted of 647 subjects who had never been previously fit-tested (naive), while the remaining 137 participants were experienced respirator users. Only four of the 647 naive subjects (0.62%) identified an inadequate seal during their user seal check. Of the 643 remaining naive subjects who indicated that they had an adequate face seal prior to fit-testing, 158 (25%) failed the subsequent quantitative fit-test and 92 (14%) failed the qualitative fit-test. All 137 experienced users indicated that they had an adequate seal after performing the user seal check; however, 41 (30%) failed the subsequent quantitative fit-test, and 30 (22%) failed the qualitative fit-test. These findings contradict the argument to eliminate fit-testing and rely strictly on a user seal check to evaluate face seal.     

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.     

Respirator donning in post-hurricane New Orleans

We evaluated correctness of N95 filtering facepiece respirator donning by the public in post-hurricane New Orleans, where respirators were recommended for mold remediation. We randomly selected, interviewed, and observed 538 participants, using multiple logistic regression for analysis. Only 129 (24%) participants demonstrated proper donning. Errors included nose clip not tightened (71%) and straps incorrectly placed (52%); 22% put on the respirator upside down. Factors independently associated with proper donning were as follows: ever having used a mask or respirator (odds ratio [OR] 5.28; 95% confidence interval [CI], 1.79-22.64); ever having had a respirator fit test (OR 4.40; 95% CI, 2.52-7.81); being male (OR 2.44; 95% CI, 1.50-4.03); Caucasian race (OR 2.09; 95% CI, 1.32-3.33); having a certified respirator (OR 1.99, 95% CI, 1.20-3.28); and having participated in mold clean-up (OR 1.82; 95% CI,1.00-3.41). Interventions to improve respirator donning should be considered in planning for influenza epidemics and disasters.     

Analysis of forces generated by n95 filtering facepiece respirator tethering devices: a pilot study

The restorative forces of elasticized tethering devices on N95 filtering facepiece respirators (N95 FFR), that occur in response to the application of a load (applied force) during donning, create the requisite pressure to effectively seal the respirator against the face and prevent excessive inward migration of harmful elements. Many workers don and doff the same N95 FFR multiple times in the course of a single workday, yet little is known regarding the possible degradation of these restorative loads and, by implication, protection with multiple donnings. This laboratory pilot study evaluated the degradation in loads of tethering devices of three models of N95 FFRs subjected to the strain of five wear periods of 15?min interspersed with 15-min periods without wear. Data indicate that there were load degradations at each donning that differed significantly with the FFR model (p = <0.001), the greatest of which occurred with the first donning. The N95 FFR model with the lowest restorative loads was able to pass fit testing in a previous study, indicating that lower loads, perhaps coupled with FFR model-specific features, are sufficient to provide an adequate face/FFR interface seal. Tethering devices are importantly related to issues of comfort and protection afforded by N95 FFR and additional research is warranted.     

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.     

Evaluation of a quantitative fit testing method for N95 filtering facepiece respirators

A method for performing quantitative fit tests (QNFT) with N95 filtering facepiece respirators was developed by earlier investigators. The method employs a simple clamping device to allow the penetration of submicron aerosols through N95 filter media to be measured. The measured value is subtracted from total penetration, with the assumption that the remaining penetration represents faceseal leakage. The developers have used the clamp to assess respirator performance. This study evaluated the clamp's ability to measure filter penetration and determine fit factors. In Phase 1, subjects were quantitatively fit-tested with elastomeric half-facepiece respirators using both generated and ambient aerosols. QNFT were done with each aerosol with both P100 and N95 filters without disturbing the facepiece. In Phase 2 of the study elastomeric half facepieces were sealed to subjects' faces to eliminate faceseal leakage. Ambient aerosol QNFT were performed with P100 and N95 filters without disturbing the facepiece. In both phases the clamp was used to measure N95 filter penetration, which was then subtracted from total penetration for the N95 QNFT. It was hypothesized that N95 fit factors corrected for filter penetration would equal the P100 fit factors. Mean corrected N95 fit factors were significantly different from the P100 fit factors in each phase of the study. In addition, there was essentially no correlation between corrected N95 fit factors and P100 fit factors. It was concluded that the clamp method should not be used to fit-test N95 filtering facepieces or otherwise assess respirator performance.     

Respiratory protection provided by N95 filtering facepiece respirators against airborne dust and microorganisms in agricultural farms

A new system was used to determine the workplace protection factors (WPF) for dust and bioaerosols in agricultural environments. The field study was performed with a subject wearing an N95 filtering facepiece respirator while performing animal feeding, grain harvesting and unloading, and routine investigation of facilities. As expected, the geometric means (GM) of the WPFs increased with increasing particle size ranging from 21 for 0.7-1 microm particles to 270 for 5-10 microm particles (p < 0.001). The WPF for total culturable fungi (GM = 35) was significantly greater than for total culturable bacteria (GM = 9) (p = 0.01). Among the different microorganism groups, the WPFs of Cladosporium, culturable fungi, and total fungi were significantly correlated with the WPFs of particles of the same sizes. As compared with the WPFs for dust particles, the WPFs for bioaerosols were found more frequently below 10, which is a recommended assigned protection factor (APF) for N95 filtering facepiece respirators. More than 50% of the WPFs for microorganisms (mean aerodynamic diameter < 5 microm) were less than the proposed APF of 10. Even lower WPFs were calculated after correcting for dead space and lung deposition. Thus, the APF of 10 for N95 filtering facepiece respirators seems inadequate against microorganisms (mean aerodynamic size < 5 microm). These results provide useful pilot data to establish guidelines for respiratory protection against airborne dust and microorganisms on agricultural farms. The method is a promising tool for further epidemiological and intervention studies in agricultural and other similar occupational and nonoccupational environments.     

Speech intelligibility assessment of protective facemasks and air-purifying respirators

Speech Intelligibility (SI) is the perceived quality of sound transmission. In healthcare settings, the ability to communicate clearly with coworkers, patients, etc., is crucial to quality patient care and safety. The objectives of this study were to: (1) assess the suitability of the Speech Transmission Index (STI) methods for testing reusable and disposable facial and respiratory personal protective equipment (protective facemasks [PF], N95 filtering facepiece respirators [N95 FFR], and elastomeric half-mask air-purifying respirators [EAPR]) commonly worn by healthcare workers; (2) quantify STI levels of these devices; and (3) contribute to the scientific body of knowledge in the area of SI. SI was assessed using the STI under two experimental conditions: (1) a modified version of the National Fire Protection Association 1981 Supplementary Voice Communications System Performance Test at a Signal to Noise Ratio (SNR) of ?15 (66 dBA) and (2) STI measurements utilizing a range of modified pink noise levels (52.5 dBA (?2 SNR) – 72.5 dBA (+7 SNR)) in 5.0 dBA increments. The PF models (Kimberly Clark 49214 and 3 M 1818) had the least effect on SI interference, typically deviating from the STI baseline (no-mask condition) by 3% and 4% STI, respectively. The N95FFR (3 M 1870, 3 M 1860) had more effect on SI interference, typically differing from baseline by 13% and 17%, respectively, for models tested. The EAPR models (Scott Xcel and North 5500) had the most significant impact on SI, differing from baseline by 42% for models tested. This data offers insight into the performance of these apparatus with respect to STI and may serve as a reference point for future respirator design considerations, standards development, testing and certification activities.     

Comparison of qualitative and quantitative fit-testing results for three commonly used respirators in the healthcare sector

N95 filtering facepiece respirators are used by healthcare workers when there is a risk of exposure to airborne hazards during aerosol-generating procedures. Respirator fit-testing is required prior to use to ensure that the selected respirator provides an adequate face seal. Two common fit-test methods can be employed: qualitative fit-test (QLFT) or quantitative fit-test (QNFT). Respiratory protection standards deem both fit-tests to be acceptable. However, previous studies have indicated that fit-test results may differ between QLFT and QNFT and that the outcomes may also be influenced by the type of respirator model. The aim of this study was to determine if there is a difference in fit-test outcomes with our suite of respirators, 3M - 1860S, 1860, AND 1870, and whether the model impacts the fit-test results.

Subjects were recruited from residential care facilities. Each participant was assigned a respirator and underwent sequential QLFT and QNFT fit-tests and the results (either pass or fail) were recorded. To ascertain the degree of agreement between the two fit-tests, a Kappa (Κ) statistic was conducted as per the American National Standards Institute (ANSI) respiratory protection standard. The pass-fail rates were stratified by respirator model and a Kappa statistic was calculated for each to determine effect of model on fit-test outcomes.

We had 619 participants and the aggregate Κ statistic for all respirators was 0.63 which is below the suggested ANSI threshold of 0.70. There was no statistically significant difference in results when stratified by respirator model.

QNFT and QLFT produced different fit-test outcomes for the three respirator models examined. The disagreement in outcomes between the two fit-test methods with our suite of N95 filtering facepiece respirators was approximately 12%. Our findings may benefit other healthcare organizations that use these three respirators.     

Effect of Upper Strap Downward Displacement on N95 Filtering Facepiece Respirator Fit Factors: A Pilot Study

Fifteen subjects underwent three replicates of quantitative respirator fit-testing with N95 filtering facepiece respirators that were donned with the upper strap high on the occiput, as per the manufacturers’ donning instructions. Each fit-test was immediately followed by repeat fit-testing with the upper strap downwardly displaced to the level of the ear sulcus to determine any change in fit factors that might occur with upper strap downward slippage. A total of 35/45 (78%) initial fit-tests had a passing score (fit factor ≥100) with the top strap high on the occiput and 33/35 (94%) of these passed subsequent fit-testing after the top strap was displaced downward to the ear sulcus. Geometric mean fit factors for the initial passed fit-tests, and following downward strap displacement, were 217±1.6 and 207±1.9, respectively (p = 0.64). Downward displacement of the top strap did not significantly impact fit factors of N95 FFRs that had previously passed fit-testing.     

Assessing real-time performances of N95 respirators for health care workers by simulated workplace protection factors

To assess performances of N95 respirators for Health Care Workers (HCWs) in a simulated health-care setting, we measured the Simulated Workplace Protection Factors (SWPFs) in real-time from the volunteers. A total of 49 study subjects, wearing 3 M respirator Model N95 1860 and 1860S, were fit tested using the OSHA Exercise Regimen. The test subjects were asked to perform simulated scenarios, including patient assessments, suction, and intravenous injection (IV) treatment. Two TSI PortaCount instruments continuously measured concentrations in the respirator and the room concentration. For Quantitative Fit Testing (QNFT), 36 out of 49 (73.5%) passed the fit factor (FF) criteria set at 100 and 13 (26.5%) failed. The results of QNFT were found to have a low correlation with SWPF, with R²=0.32. The geometric means (GM) and geometric standard deviations (GSD) of SWPF were 68.8 (1.1) for those subjects who passed and 39.6 (1.3) for those who failed. Real-time assessments of SWPF showed that lower SWPFs were; moving head up and down, and bending at the waist. This study identifies the needs for providing different sizes of respirators for HCWs and the importance of performing fit tests for HCWs regularly. And particular movements were identified as attributing factors affecting more on SWPFs.     

Filter and leak penetration characteristics of a dust and mist filtering facepiece

The filtering facepiece, also referred to as a disposable respirator, is an extensively used type of respirator without an officially accepted fit testing method. This study describes an aerosol generator and a sampling train, which have been developed for investigating the aerosol penetration characteristics through the filter element and the face seal. Electrostatic attraction and impaction are the two primary filtration mechanisms for micrometer- and supermicrometer-sized aerosols, respectively. Filtration and flow dynamics were found to affect aerosol penetration in distinct ways that allow for the differentiation of the face seal leakage from the filter penetration. The slope of the aerosol size-dependent penetration curve potentially may differentiate the face seal leakage from filter penetration.     

Real-Time Fit of a Respirator during Simulated Health Care Tasks

Fit is an important but difficult-to-predict feature of respirator performance. This study examined a new approach to measuring respirator performance using two continuous direct-reading particle-counting instruments in a simulated health care workplace. A pilot test was conducted with eight experienced health care professionals who passed a traditional quantitative fit test before performing three randomized 10-min health care scenarios (patient assessment [PA], IV treatment [IV], and wound care [WC]). Two TSI Portacount Plus (Model 8020) with N95 Companion (Model 8095) instruments were used to continuously measure 1-sec ambient particle concentrations inside and outside the respirator facepiece. A simulated workplace protection factor (SWPF) was calculated by dividing outside by inside concentrations. Data were log transformed and examined using analysis of variance (ANOVA) between subjects, scenario types, and scenario order. The GM SWPF for the eight subjects, three scenarios per subject, ranged from 172 to 1073 (GSD 1.7 to 3.5) and was significantly different for each subject. A multi-way analysis of variance showed no difference between the three scenario types (PA, IV, WC). There were differences by the order in which scenarios were performed: the third scenario SWPF was significantly different and higher than that of the first and second scenarios. All subjects passed the initial quantitative fit test with a fit factor of at least 100. Five subjects had fit factors greater than 200 and GM scenario SWPFs greater than 400. Three participants with initial fit factors less than 200 had GM scenario SWPFs ranging from 132 to 326. This pilot test demonstrates that it is possible to evaluate instantaneous respirator fit using two quantitative fit test instruments in a simulated health care environment. Results suggest that an initial fit test may be predictive of fit during simulated tasks and that one scenario may be adequate for measuring a simulated workplace protection factor. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a video for subject D activities overlaid with simulated workplace protection factor data.].     

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.     

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.     

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.     

Persistence of Respirator Use Learning

Although retraining and repeat fit-testing are needed for respirator users, the optimal frequency is uncertain. The persistence of proper respirator donning/doffing techniques and changes in quantitative fit factor over 6 months after initial training were measured in this study. Initial training was designed for rapid rollout situations in which direct contact with well-trained occupational health professionals may be infeasible. Subjects (n = 175) were assigned randomly to use either a filtering facepiece N95 (FFR) or dual cartridge half facemask (HFM) respirator. Each was assigned randomly to one of three training methods—printed brochure, video, or computer-based training. Soon after initial training, quantitative fit and measures of proper technique were determined. These measurements were repeated 6 months later. In the six-month followup, subjects were randomized to receive either a brief reminder card or a placebo card. Total performance score, major errors, and quantitative fit all became significantly worse at 6 months. An individual's result soon after training was the most important predictor of performance 6 months later. There was a marginal not statistically significant tendency for those initially trained by video to have better protection 6 months later. The study suggests that persons who use respirators intermittently should be thoroughly retrained and reevaluated periodically.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Additional statistical analyses.     

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.     

Development of an Advanced Respirator Fit-Test Headform

Improved respirator test headforms are needed to measure the fit of N95 filtering facepiece respirators (FFRs) for protection studies against viable airborne particles. A Static (i.e., non-moving, non-speaking) Advanced Headform (StAH) was developed for evaluating the fit of N95 FFRs. The StAH was developed based on the anthropometric dimensions of a digital headform reported by the National Institute for Occupational Safety and Health (NIOSH) and has a silicone polymer skin with defined local tissue thicknesses. Quantitative fit factor evaluations were performed on seven N95 FFR models of various sizes and designs. Donnings were performed with and without a pre-test leak checking method. For each method, four replicate FFR samples of each of the seven models were tested with two donnings per replicate, resulting in a total of 56 tests per donning method. Each fit factor evaluation was comprised of three 86-sec exercises: “Normal Breathing” (NB, 11.2 liters per min (lpm)), “Deep Breathing” (DB, 20.4 lpm), then NB again. A fit factor for each exercise and an overall test fit factor were obtained. Analysis of variance methods were used to identify statistical differences among fit factors (analyzed as logarithms) for different FFR models, exercises, and testing methods. For each FFR model and for each testing method, the NB and DB fit factor data were not significantly different (P > 0.05). Significant differences were seen in the overall exercise fit factor data for the two donning methods among all FFR models (pooled data) and in the overall exercise fit factor data for the two testing methods within certain models. Utilization of the leak checking method improved the rate of obtaining overall exercise fit factors ≥100. The FFR models, which are expected to achieve overall fit factors ≥ 100 on human subjects, achieved overall exercise fit factors ≥ 100 on the StAH. Further research is needed to evaluate the correlation of FFRs fitted on the StAH to FFRs fitted on people.

[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a file providing detailed information on the advanced head form design and fabrication process.]