Disinfection of N95 Respirators with Ozone

Abstract

The coronavirus disease 2019 crisis is creating a shortage of personal protective equipment (PPE), most critically, N95 respirators for healthcare personnel. Our group was interested in the feasibility of ozone disinfection of N95 respirators as an alternative for healthcare professionals and organizations that might not have access to other disinfection devices. We tested the effectiveness of ozone on killing Pseudomonas aeruginosa (PsA) on three different N95 respirators: 3M 1860, 3M 1870, and 3M 8000. We used an ozone chamber that consisted of: an airtight chamber, an ozone generator, an ozone destruct unit, and an ozone UV analyzer. The chamber was capable of concentrating ozone up to 500 parts per million (ppm) from ambient air, creating an airtight seal, and precisely measuring ozone levels within the chamber. Exposure to ozone at 400 ppm with 80% humidity for two hours effectively killed bacteria on N95 respirators, types 1860, 1870, and 8000. There were no significant changes in filtration efficiency of the 1860 and 1870 type respirators for up to ten cycles of ozone exposure at similar conditions. There was no change in fit observed in the 1870 type respirator after ozone exposure. There was no significant change in the strap integrity of the 1870 type respirator after ozone exposure. Tests for filtration efficiency were not performed on the 8000 type respirator. Tests for fit or strap integrity were not performed on the 8000 or 1860 type respirators. This study demonstrates that an ozone application achieves a high level of disinfection against PsA, a vegetative bacteria that the CDC identifies as more difficult to kill than medium sized viruses such as SARS-CoV-2 (Covid-19). Furthermore, conditions shown to kill these bacteria did not damage or degrade respirator filtration. This is the first report of successful disinfection of N95 PPE with ozone of which the authors are aware. It is also the first report, to the authors' knowledge, to identify necessary conditions for ozone to kill organisms on N95 masks without degrading the function of N95 filters.

A systematic review of mask disinfection and reuse for SARS-CoV-2 (through July 10, 2020)

“…Overall, 16 studies measured disinfection and durability 12, 15, 19, 20, 22, 27-30, 33, 36, 47, 49, 51, 62, 64 , 16 studies measured only disinfection 13, 18, 23, 24, 31, 38, 40, 41, 43, 44, 48, 56, 63, 65-67 and 26 studies measured only durability 7, 14, 16, 17, 21, 25, 26, 32, 34, 35, 37, 39, 42, 45, 46, 50, 52-55, 57-61, 68 . Thus, 32 studies measured disinfection and 42 measured durability.…”

“…In total, 159 individual mask reuse tests were conducted in 42 studies 7, 12, 14-17, 19-22, 25-30, 32-37, 39, 42, 45-47, 49-55, 57-62, 64, 68 . The masks tested included: 114 tests with N95s (72%), an additional four tests with KN95s (2.5%), seven tests with folded or molded or HKYZ N95s (4.4%), four tests with FFPs (2.5%), and two tests with respirator fabric (1%).…”

Measurement of filtration efficiencies of healthcare and consumer materials using modified respirator fit tester setup

“…Much of the work to date has focused on sterilization of respirators for subsequent reuse. While a few studies have been completed and submitted to preprint servers after waiting for data from extant labs [24][25][26][27][28][29], a number of other preprints [30,31] and publications [32][33][34] have developed apparatuses to measure filtration efficiency as best they can independently. There is significant heterogeneity in these setups; some are built with assistance from labs which study aerosols, others with equipment found on hand.…”

Decontamination and Reuse of N95 Filtering Facepiece Respirators: Where Do We Stand?

“…In an initial report, ozone was used to inactivate Pseudomonas aeruginosa on multiple N95 models with no significant change in filtration for up to 10 cycles. 109 Further study is required to establish its promise for FFR.…”