Dennis J. Viscusi

Digital 3-D headforms with facial features representative of the current US workforce.

Existing headforms are based on anthropometric data collected over 30 years ago. In 2003, the National Institute for Occupational Safety and Health conducted an anthropometric survey of 3997 respirator users, of which 1013 subjects were scanned with a Cyberware 3-D Rapid Digitizer. The objective of this study was to create headforms representative of the current US workforce. Ten facial dimensions relevant to respirator fit were chosen for defining a principal component analysis model, which divides the user population into five face-size categories. Mean facial dimensions were then computed to target the ideal facial dimensions for each size category. Five scans in each category were chosen and averaged to construct a representative headform for each size category. Five digital 3-D headforms were developed: small, medium, large, long/narrow and short/wide. All dimensions are within 3 mm of the computed means for the sample population in each size category. Statement of Relevance: This manuscript describes a new approach to constructing headforms that takes into account the facial form (size and shape) of the US workforce. These headforms could be incorporated into respirator research, certification standards and design in efforts to reduce the risk of injury or illness caused by inhalation hazards.

Head-and-Face Anthropometric Survey of Chinese Workers

Millions of workers in China rely on respirators and other personal protective equipment to reduce the risk of injury and occupational diseases. However, it has been >25 years since the first survey of facial dimensions for Chinese adults was published, and it has never been completely updated. Thus, an anthropometric survey of Chinese civilian workers was conducted in 2006. A total of 3000 subjects (2026 males and 974 females) between the ages of 18 and 66 years old was measured using traditional techniques. Nineteen facial dimensions, height, weight, neck circumference, waist circumference and hip circumference were measured. A stratified sampling plan of three age strata and two gender strata was implemented. Linear regression analysis was used to evaluate the possible effects of gender, age, occupation and body size on facial dimensions. The regression coefficients for gender indicated that for all anthropometric dimensions, males had significantly larger measurements than females. As body mass index increased, dimensions measured increased significantly. Construction workers and miners had significantly smaller measurements than individuals employed in healthcare or manufacturing for a majority of dimensions. Five representative indexes of facial dimension (face length, face width, nose protrusion, bigonial breadth and nasal root breadth) were selected based on correlation and cluster analysis of all dimensions. Through comparison with the facial dimensions of American subjects, this study indicated that Chinese civilian workers have shorter face length, smaller nose protrusion, larger face width and longer lip length.

Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators

Abstract Concerns have been raised regarding the availability of National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) during an influenza pandemic. One possible strategy to mitigate a respirator shortage is to reuse FFRs following a biological decontamination process to render infectious material on the FFR inactive. However, little data exist on the effects of decontamination methods on respirator integrity and performance. This study evaluated five decontamination methods [ultraviolet germicidal irradiation (UVGI), ethylene oxide, vaporized hydrogen peroxide (VHP), microwave oven irradiation, and bleach] using nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) to determine which methods should be considered for future research studies. Following treatment by each decontamination method, the FFRs were evaluated for changes in physical appearance, odor, and laboratory performance (filter aerosol penetration and filter airflow resistance). Additional experiments (dry heat laboratory oven exposures, off-gassing, and FFR hydrophobicity) were subsequently conducted to better understand material properties and possible health risks to the respirator user following decontamination. However, this study did not assess the efficiency of the decontamination methods to inactivate viable microorganisms. Microwave oven irradiation melted samples from two FFR models. The remainder of the FFR samples that had been decontaminated had expected levels of filter aerosol penetration and filter airflow resistance. The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.

Development of a Test System To Apply Virus-Containing Particles to Filtering Facepiece Respirators for the Evaluation of Decontamination Procedures

ABSTRACT A chamber to apply aerosolized virus-containing particles to air-permeable substrates (coupons) was constructed and validated as part of a method to assess the virucidal efficacy of decontamination procedures for filtering facepiece respirators. Coliphage MS2 was used as a surrogate for pathogenic viruses for confirmation of the efficacy of the bioaerosol respirator test system. The distribution of virus applied onto and within the coupons was characterized, and the repeatability of applying a targeted virus load was examined. The average viable virus loaded onto 90 coupons over the course of 5 days was found to be 5.09 ± 0.19 log10 PFU/coupon (relative standard deviation, 4%). To determine the ability to differentiate the effectiveness of disinfecting procedures with different levels of performance, sodium hypochlorite and steam treatments were tested in experiments by varying the dose and time, respectively. The role of protective factors was assessed by aerosolizing the virus with various concentrations of the aerosol-generating medium. A sodium hypochlorite (bleach) concentration of 0.6% and steam treatments of 45 s and longer resulted in log reductions (>4 logs) which reached the detection limits for both levels of protective factors. Organic matter (ATCC medium 271) as a protective factor afforded some protection to the virus in the sodium hypochlorite experiments but was not a factor in the steam experiments. The evaluation of the bioaerosol respirator test system demonstrated a repeatable method for applying a targeted viral load onto respirator coupons and provided insight into the properties of aerosols that are of importance to the development of disinfection assays for air-permeable materials.

Evaluation of the filtration performance of 21 N95 filtering face piece respirators after prolonged storage.

Background Organizations are stockpiling respirators to prepare for an influenza pandemic. To understand better the effects of prolonged storage, this investigation evaluated the filtration efficiency of 21 different models of National Institute for Occupational Safety and Health (NIOSH)-certified disposable N95 filtering face piece respirators. These respirators had been stored in their original packaging for a period of at least 6 years in research laboratories and dry warehouse facilities, ranging in temperature between 15°C and 32°C and relative humidity between 20% and 80%. Methods Filter penetration was measured using an abbreviated version of the NIOSH respirator certification test incorporating a polydisperse sodium chloride aerosol at 85 L/min. Results Of the 21 respirator models tested, 19 models had both average penetration results of less than 5%. Mean initial penetration values ranged from 0.39% to 5.83%, whereas mean maximum penetration values ranged from 0.95% to 5.83%. There did not appear to be any correlation between the length of storage and failure to pass the filtration test. Conclusion Results indicate that most N95 filtering face piece respirators stored for up to 10 years at warehouse conditions will likely have expected levels of filtration performance and that the degree of filtration efficiency degradation is likely model specific.

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 respirators 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.

New Respirator Fit Test Panels Representing the Current Chinese Civilian Workers

Respirator fit test panels provide an objective tool for selecting representative human test subjects based upon their facial characteristics for use in research, product development, testing and certification. Fit test panels were typically based upon anthropometric data such as the 1967-1968 survey of American military personnel. In this study, the objectives were to: (i) evaluate the applicability of the recently developed National Institute for Occupational Safety and Health (NIOSH) respirator fit test panels for Chinese workers and (ii) develop new respirator fit test panels using the Chinese survey data. Overall, 95% of the workers in the Chinese survey fall within the NIOSH bivariate and principal component analysis (PCA) panels, suggesting that these panels would also be appropriate for the Chinese population. However, distribution of the subject across the panels was not uniform; only 6.3% of survey participants fell into five cells of the bivariate panel and only 7.2% were found within three cells of the PCA panel. Therefore, new respirator fit test panels with subject dimensions and distributions specific to Chinese workers may be beneficial for certain applications. Two new respirator fit test panels were developed with the same techniques used to create the NIOSH panels. All measurements were weighted to match age and gender distributions of the Chinese population from the 2005 census. The bivariate approach used face length and face width measurements, and the PCA panel was developed using the first two principal components obtained from a set of 10 facial dimensions. Respirators designed to fit these Chinese worker-specific panels are also likely to accommodate >95% of Chinese workers.

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.

Impact of multiple consecutive donnings on filtering facepiece respirator fit.

BACKGROUND A concern with reuse of National Institute for Occupational Safety and Health-certified N95 filtering facepiece respirators (FFRs) is that multiple donnings could stress FFR components, impairing fit. This study investigated the impact of multiple donnings on the facepiece fit of 6 N95 FFR models using a group of 10 experienced test subjects per model. METHODS The TSI PORTACOUNT Plus and N95 Companion accessory were used for all tests. After qualifying by passing a standard Occupational Safety and Health Administration fit test, subjects performed up to 20 consecutive tests on an individual FFR sample using a modified protocol. Regression analyses were performed for the percentage of donnings resulting in fit factors (FFs) ≥100 for all 6 FFR models combined. RESULTS Regression analyses showed statistical significance for donning groups 1-10, 1-15, and 1-20. The mean percentage of donnings with an FF ≥100 was 81%-93% for donning group 1-5, but dropped to 53%-75% for donning group 16-20. CONCLUSIONS Our results show that multiple donnings had a model-dependent impact on fit for the 6 N95 models evaluated. The data suggest that 5 consecutive donnings can be performed before FFs consistently drop below 100.

Shape analysis of 3D head scan data for U.S. respirator users

In 2003, the National Institute for Occupational Safety and Health (NIOSH) conducted a head-and-face anthropometric survey of diverse, civilian respirator users. Of the 3,997 subjects measured using traditional anthropometric techniques, surface scans and 26 three-dimensional (3D) landmark locations were collected for 947 subjects. The objective of this study was to report the size and shape variation of the survey participants using the 3D data. Generalized Procrustes Analysis (GPA) was conducted to standardize configurations of landmarks associated with individuals into a common coordinate system. The superimposed coordinates for each individual were used as commensurate variables that describe individual shape and were analyzed using Principal Component Analysis (PCA) to identify population variation. The first four principal components (PC) account for 49% of the total sample variation. The first PC indicates that overall size is an important component of facial variability. The second PC accounts for long and narrow or short and wide faces. Longer narrow orbits versus shorter wider orbits can be described by PC3, and PC4 represents variation in the degree of ortho/prognathism. Geometric Morphometrics provides a detailed and interpretable assessment of morphological variation that may be useful in assessing respirators and devising new test and certification standards.