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Protection factor for N95 filtering facepiece respirators exposed to laboratory aerosols containing different concentrations of nanoparticles.

Rengasamy S; Walbert G; Newcomb W; Coffey C; Wassell JT; Szalajda J
Ann Occup Hyg 2015 Apr; 59(3):373-381
A previous study used a PortaCount Plus to measure the ratio of particle concentrations outside (Cout) to inside (Cin) of filtering facepiece respirators (FFRs) worn by test subjects and calculated the total inward leakage (TIL) (Cin/Cout) to evaluate the reproducibility of the TIL test method between two different National Institute for Occupational Safety and Health laboratories (Laboratories 1 and 2) at the Pittsburgh Campus. The purpose of this study is to utilize the originally obtained PortaCount Cout/Cin ratio as a measure of protection factor (PF) and evaluate the influence of particle distribution and filter efficiency. PFs were obtained for five N95 model FFRs worn by 35 subjects for three donnings (5 models × 35 subjects × 3 donnings) for a total of 525 tests in each laboratory. The geometric mean of PFs, geometric standard deviation (GSD), and the 5th percentile values for the five N95 FFR models were calculated for the two laboratories. Filter efficiency was obtained by measuring the penetration for four models (A, B, C, and D) against Laboratory 2 aerosol using two condensation particle counters. Particle size distribution, measured using a Scanning Mobility Particle Sizer, showed a mean count median diameter (CMD) of 82 nm in Laboratory 1 and 131 nm in Laboratory 2. The smaller CMD showed relatively higher concentration of nanoparticles in Laboratory 1 than in Laboratory 2. Results showed that the PFs and 5th percentile values for two models (B and E) were larger than other three models (A, C, and D) in both laboratories. The PFs and 5th percentile values of models B and E in Laboratory 1 with a count median diameter (CMD) of 82 nm were smaller than in Laboratory 2 with a CMD of 131 nm, indicating an association between particle size distribution and PF. The three lower efficiency models (A, C, and D) showed lower PF values than the higher efficiency model B showing the influence of filter efficiency on PF value. Overall, the data show that particle size distribution and filter efficiency influence the PFs and 5th percentile values. The PFs and 5th percentile values decreased with increasing nanoparticle concentration (from CMD of 131 to 82 nm) indicating lower PFs for aerosol distribution within nanoparticle size range (<100 nm). Further studies on the relationship between particle size distribution and PF are needed to better understand the respiratory protection against nanoparticles.
Respirators; Respiratory-equipment; Respiratory-protection; Respiratory-protective-equipment; Filters; Laboratories; Aerosols; Nanotechnology; Particulates; Chemical-properties; Physical-properties; Surveillance; Exposure-levels; Risk-factors; Author Keywords: count median diameter; CMD; filter penetration; N95 filtering facepiece respirators; particle size distribution; protection factor; PF
Samy Rengasamy, National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratory, 626 Cochrans Mill Road, PO Box 18070, Pittsburgh, PA 15236
Publication Date
Document Type
Journal Article
Email Address
Funding Type
Fiscal Year
Identifying No.
Grant-Number-T01-OH-008431; M112014
Issue of Publication
NIOSH Division
Priority Area
Healthcare and Social Assistance
Source Name
Annals of Occupational Hygiene
Performing Organization
West Virginia University
Page last reviewed: September 3, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division