Effectiveness of N95 facepiece respirators in filtering aerosol following storage and sterilization

The use of electret N95 filtering facepiece respirators (N95FFRs) after prolonged storage or treatment can reduce the expense of buying non-expired N95 and thus enable developing and developed countries to optimize their use of limited resources to against airborne particles and diseases, such as coronavirus disease 2019 (COVID-19). The filtration performance of five N95FFR models following long-term storage, removal of charge using isopropanol alcohol (IPA), autoclaving, or treatment with gamma-radiation was assessed using a TSI 8130 automated filter tester. Statistically significant differences were found in the penetration (P), pressure drop (Δp) and quality factor (qf) between non-expired and expired N95 models 3M-8210 and 3M-8511. A statistically significant linear correlation was also obtained between the N95 penetration ratio (PR) and the difference between year of manufacture and time of test (DYM). The PR of N95 was more strongly influenced by eliminating the charge (for extremely out-of-date respirators) on the electret filter than by the DYM. Sterilization by gamma irradiation increased the P into non-expired and expired N95FFR models (p < 0.05), reducing their qf. The qf of all N95FFR models, except UVEX-3200, was strongly affected by gamma irradiation, the removal of charge using IPA, autoclaving, and storage in that order. All expired models maintained acceptable filtration performance and still could be used to collect aerosol effectively, even though models 3M-8511 and 3M-1860 had been manufactured up to 13 years previously. As the COVID-19 outbreaks in 2019 and is getting worse in 2020, these data are useful in developing a global stockpiling strategy to maximize the longevity of N95FFRs for public health and healthcare workers. However, the aging of the straps and seal materials (rubbers, plastics) of the N95FFRs may affect their fit factor and effectiveness.