Pengfei Gao

Estimating historical respirable crystalline silica exposures for Chinese pottery workers and iron/copper, tin, and tungsten miners

Collaborative studies of Chinese workers, using over four decades of dust monitoring data, are being conducted by the National Institute for Occupational Safety and Health (NIOSH) and Tongji Medical University in China. The goal of these projects is to establish exposure-response relationships for the development of diseases such as silicosis or lung cancer in cohorts of pottery and mine workers. It is necessary to convert Chinese dust measurements to respirable silica measurements in order to make results from the Chinese data comparable to other results in the literature. This article describes the development of conversion factors and estimates of historical respirable crystalline silica exposure for Chinese workers. Ambient total dust concentrations (n>17000) and crystalline silica concentrations (n=347) in bulk dust were first gathered from historical industrial hygiene records. Analysis of the silica content in historical bulk samples revealed no trend from 1950 up to the present. During 1988-1989, side-by-side airborne dust samples (n=143 pairs) were collected using nylon cyclones and traditional Chinese samplers in 20 metal mines and nine pottery factories in China. These data were used to establish conversion factors between respirable crystalline silica concentrations and Chinese total dust concentrations. Based on the analysis of the available evidence, conversion factors derived from the 1988-1989 sampling campaign are assumed to apply to other time periods in this paper. The conversion factors were estimated to be 0.0143 for iron/copper, 0.0355 for pottery factories, 0.0429 for tin mines, and 0.0861 for tungsten mines. Conversion factors for individual facilities within each industry were also calculated. Analysis of variance revealed that mean conversion factors are significantly different among facilities within the iron/copper industry and within the pottery industry. The relative merits of using facility-specific conversion factors, industry-wide conversion factors, or a weighted average of the two are discussed. The exposure matrix of the historical Chinese total dust concentrations was multiplied by these conversion factors to obtain an exposure matrix of historical respirable crystalline silica concentrations.

Evaluation of Nano- and Submicron Particle Penetration through Ten Nonwoven Fabrics Using a Wind-Driven Approach

Existing face mask and respirator test methods draw particles through materials under vacuum to measure particle penetration. However, these filtration-based methods may not simulate conditions under which protective clothing operates in the workplace, where airborne particles are primarily driven by wind and other factors instead of being limited to a downstream vacuum. This study was focused on the design and characterization of a method simulating typical wind-driven conditions for evaluating the performance of materials used in the construction of protective clothing. Ten nonwoven fabrics were selected, and physical properties including fiber diameter, fabric thickness, air permeability, porosity, pore volume, and pore size were determined. Each fabric was sealed flat across the wide opening of a cone-shaped penetration cell that was then housed in a recirculation aerosol wind tunnel. The flow rate naturally driven by wind through the fabric was measured, and the sampling flow rate of the Scanning Mobility Particle Sizer used to measure the downstream particle size distribution and concentrations was then adjusted to minimize filtration effects. Particle penetration levels were measured under different face velocities by the wind-driven method and compared with a filtration-based method using the TSI 3160 automated filter tester. The experimental results show that particle penetration increased with increasing face velocity, and penetration also increased with increasing particle size up to about 300 to 500 nm. Penetrations measured by the wind-driven method were lower than those obtained with the filtration method for most of the fabrics selected, and the relative penetration performances of the fabrics were very different due to the vastly different pore structures.

Change in Tensile Properties of Neoprene and Nitrile Gloves After Repeated Exposures to Acetone and Thermal Decontamination

This study investigated the change in tensile properties of neoprene and nitrile gloves after repeated cycles of exposure to acetone, followed by thermal decontamination. The glove was exposed to acetone (outer surface in contact with chemical), subjected to thermal decontamination, and tested for the tensile strength and the ultimate elongation. Thermal decontamination was carried out inside an oven for 16 hours at 100°C. The exposure/decontamination procedure was repeated for a maximum of 10 cycles. For neoprene versus acetone, the mean tensile strength consistently decreased after each exposure/decontamination cycle. Multiple comparisons indicated that the mean tensile strengths between the new swatches and each exposure/decontamination group were significantly different (p < 0.05). The loss of either tensile strength or ultimate elongation was less than 23% compared with new swatches after four exposure/decontamination cycles. Swatches with out acetone exposure were then cycled through the oven in the same manner. It was found that both the heat used for thermal decontamination and acetone exposure significantly affected the tensile strength and ultimate elongation. For nitrile gloves exposed to acetone, the mean tensile strength remained virtually unchanged (p > 0.05). The mean tensile strength for the new swatches was 37.1 MPa and the mean tensile strength after nine exposure/decontamination cycles was 36.0 MPa, with a loss less than 3%. The largest single cycle loss for ultimate elongation occurred during the first exposure/decontamination cycle for both glove materials. In our previous study, decisions regarding the effectiveness of the decontamination process were based on having no discernible change in the breakthrough time and steady-state permeation rate. The results of this study indicate that the effectiveness of the decontamination process cannot be based on permeation parameters alone but must also take into account the change in physical properties.

A Recirculation Aerosol Wind Tunnel for Evaluating Aerosol Samplers and Measuring Particle Penetration through Protective Clothing Materials

A recirculation aerosol wind tunnel was designed to maintain a uniform airflow and stable aerosol size distribution for evaluating aerosol sampler performance and determining particle penetration through protective clothing materials. The oval-shaped wind tunnel was designed to be small enough to fit onto a lab bench, have optimized dimensions for uniformity in wind speed and particle size distributions, sufficient mixing for even distribution of particles, and minimum particle losses. Performance evaluation demonstrates a relatively high level of spatial uniformity, with a coefficient of variation of 1.5-6.2% for wind velocities between 0.4 and 2.8 m s(-1) and, in this range, 0.8-8.5% for particles between 50 and 450 nm. Aerosol concentration stabilized within the first 5-20 min with, approximately, a count median diameter of 135 nm and geometric standard deviation of 2.20. Negligible agglomerate growth and particle loss are suggested. The recirculation design appears to result in unique features as needed for our research.

Development of a Computer Program for Permeation Testing Data Analysis

A Microsoft Windows-compatible computer program, referred to as “Permeation Calculator,” was developed at the National Institute for Occupational Safety and Health (NIOSH) to automate and standardize permeation testing data analysis. The program imports the data file collected during a permeation test and calculates relevant permeation parameters within a few seconds, based on a series of algorithms, strategies, and automated decision-making processes. It allows calculations of all the permeation parameters related to American Society for Testing and Materials (ASTM) F 739, International Organization for Standardization (ISO) 6529, and ASTM D 6978 standards, including standardized breakthrough time, normalized breakthrough time, breakthrough detection time, steady-state permeation rate, cumulative permeation mass at a given elapsed time, and elapsed time at a given cumulative permeation mass for either a closed-loop or an open-loop permeation test. For open-loop permeation testing, the software also allows changing sampling flowrate and allows calculations of average permeation rate and maximum permeation rate to see if the rates ever reach the threshold maximum for decision making. On completion, the software displays all the permeation parameters together with relevant information and the permeation curve as a report file in Microsoft Excel and text file formats. This software helps industrial hygienists and researchers to avoid labor-intensive hand calculations of the permeation parameters. The software also prevents experimenter bias, thus ensuring identical permeation parameters will be obtained from a given permeation testing data file. The Permeation Calculator is available either on the NIOSH website or on CD by request.

Review of Chamber Design Requirements for Testing of Personal Protective Clothing Ensembles

This review focuses on the physical requirements for conducting ensemble testing and describes the salient issues that organizations involved in the design, test, or certification of personal protective equipment (PPE) and protective clothing ensembles need to consider for strategic planning. Several current and proposed PPE ensemble test practices and standards were identified. The man-in-simulant test (MIST) is the primary procedure used by the military to evaluate clothing ensembles for protection against chemical and biological warfare agents. MIST has been incorporated into the current editions of protective clothing and equipment standards promulgated by the National Fire Protection Association (NFPA). ASTM has recently developed a new test method (ASTM F 2588-06) for MIST evaluation of protective ensembles. Other relevant test methods include those described in International Organization for Standardization (ISO) standards. The primary differences among the test methods were the choice of test challenge material (e.g., sulfur hexafluoride, methyl salicylate, sodium chloride particles, corn oil, fluorophore-impregnated silica) and the exercise protocol for the subject(s). Although ensemble test methods and standards provide detailed descriptions of the test procedures, none give specific requirements for chamber design. A literature survey identified 28 whole-body exposure chambers that have been or could potentially be used for testing protective clothing ensembles using human test subjects. Median chamber size, median floor space, and median volume per subject were calculated from 15 chambers (involving human test subjects), where size information is available. Based on the literature survey of existing chambers and the review of the current and proposed standards and test methods, chamber design requirements will be dictated by the test methods selected. Due to widely different test conditions for aerosol/particulate and vapor ensemble testing, it is unlikely that a single chamber could accommodate all types of ensemble testing. With increasing use of the MIST protocol by NFPA for CBRN certification of structural firefighting gear and protective ensembles for first responders, the need for MIST laboratory capability is clear. However, existing chambers can likely be adapted to accommodate MIST with some modifications.

A Multidomain Magnetic Passive Aerosol Sampler: Development and Experimental Evaluation

An innovative “quarter-sized” multidomain magnetic passive aerosol sampler (MPAS) has been developed, mainly for determining particle penetration through personal protective ensembles. The MPAS is a 28 mm disc with a height of 8.6 mm. It consists of 186 small magnets with about 140 on the collection area, arranged in an alternating N and S pole pattern. In contrast to conventional passive samplers, it uses magnetic force to collect a quantifiable amount of surrogate Fe3O4 particles within a substantially shortened sampling time. This article presents detailed design, principles of operation, performance evaluation, and the development of a deposition velocity model for the MPAS. Performance of the MPAS was evaluated under various test conditions, including different particle sizes ranging from 95 to 350 nm and wind speeds ranging from 0.48 to 1.17 m/s. A previously developed recirculation aerosol wind tunnel was employed to evaluate its performance. Experimental results show that the dimensionless deposition velocity increased with increasing particle size (e.g., about 5-fold greater for 300 nm particles than 100 nm particles at 0.48 m/s) and slightly decreased with increasing wind speeds. Our results show that this sampler is promising for the measurement of particle penetration through protective ensembles for which high collection efficiency is needed. Copyright 2013 American Association for Aerosol Research

Effect of multiple alcohol-based hand rub applications on the tensile properties of thirteen brands of medical exam nitrile and latex gloves

ABSTRACT Current CDC guidance for the disinfection of gloved hands during the doffing of personal protective equipment (PPE) following the care of a patient with Ebola recommends for multiple applications of alcohol-based hand rub (ABHR) on medical exam gloves. To evaluate possible effects of ABHR applications on glove integrity, thirteen brands of nitrile and latex medical exam gloves from five manufacturers and two different ABHRs were included in this study. A pair of gloves were worn by a test operator and the outside surfaces of the gloves were separately treated with an ABHR for 1–6 applications. Tensile strength and ultimate elongation of the gloves without any ABHR treatments (control gloves) and gloves after 1–6 ABHR applications were measured based on the ASTM D412 standard method. In general, tensile strength decreased with each ABHR application. ABHRs had more effect on the tensile strength of the tested nitrile than latex gloves, while ethanol-based ABHR (EBHR) resulted in lesser changes in tensile strength compared to isopropanol-based ABHR (IBHR). The results show that multiple EBHR applications on the latex gloves and some of the nitrile gloves tested should be safe for Ebola PPE doffing based on the CDC guidance. Appropriate hospital staff practice using ABHR treatment and doffing gloves is recommended to become more familiar with changes in glove properties.

Quantitative Analysis of Unique Deposition Pattern of Submicron Fe3O4 Particles Using Computer-Controlled Scanning Electron Microscopy

This study was designed to optimize particle counting of a unique deposition pattern of iron oxide (Fe3O4) particles that were collected by a multidomain magnetic passive aerosol sampler (MPAS). Fe3O4 is paramagnetic with a high magnetic susceptibility, rendering high collection efficiencies. The MPAS was designed exclusively for measuring particle penetration through protective clothing. To quantify particle deposition by size, two counting methods were employed with a computer-controlled scanning electron microscope (CCSEM). Based on a sequential set of measurements at known coordinates, particles were quantified across particle clusters collected by individual magnets. Because all magnets were of equal dimensions and strength, the particle concentration per cluster across the entire MPAS substrate was expected to be relatively uniform. However, since individual CCSEM fields are extremely small compared with the full sample, a randomized counting approach was used to determine how many fields were needed to obtain a representative subsample. Results by the sequential method show that particle numbers were higher toward the edge of the cluster, dominated by smaller particles; moderate at the center, dominated by larger particles; and null at the corners. The results additionally show that counting by the random method was comparable with the sequential method and repeatable for particle counts ranging from 3 to 383 particles per field, or 409,565–52,287,826 particles per substrate, taking between 25 and 53 min, respectively. The results suggest that with the random method, the CCSEM provided a powerful tool for quantitative analyses of particle numbers with unique deposition patterns. Copyright 2012 American Association for Aerosol Research

Performance Evaluation of 26 Combinations of Chemical Protective Clothing Materials and Chemicals After Repeated Exposures and Decontaminations

Effective decontamination of chemical protective clothing (CPC) is essential for reducing occupational skin diseases and disorders during a reuse scenario. To protect the workforce, the efficacy of decontamination methods and the reusability of CPC need to be evaluated. In this study, performance of 14 CPC materials against 12 liquid chemicals was evaluated based on standardized breakthrough time (BT) and steady-state permeation rate (SSPR). Thermal and water-detergent decontamination methods were used. Exposure/decon- tamination was repeated up to 11 cycles, or until the material failed, so that further testing became impossible. Changes in BT and SSPRs were determined for each material and chemical combination. There were 20 and 13 combinations that were able to complete 11 cycles with thermal and detergent methods, respectively. By comparing the beginning and ending cycles, mean BT increased 9% with the thermal method but slightly decreased (3.3%) with the detergent method, while mean SSPR decreased 2% with the thermal method, but slightly increased (1.4%) with the detergent method. Less than half of the changes were found statistically different (p < 0.05). Generally, the thermal method had higher decontamination efficacy than the detergent method.