key: cord-0998104-mbiuwnvz
authors: Kumkrong, Paramee; Scoles, Ludmila; Brunet, Yvan; Baker, Scott; Mercier, Patrick H.J.; Poirier, Dominique
title: Evaluation of hydrogen peroxide and ozone residue levels on N95 masks following chemical decontamination
date: 2021-02-25
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2021.02.018
sha: 507c075fd5470e72d1e5f5bca135a4558f184645
doc_id: 998104
cord_uid: mbiuwnvz

BACKGROUND: Hydrogen peroxide and ozone have been used as chemical decontamination agents for N95 masks during supply shortages. If left behind on the masks the residues of both chemicals are representing a potential health hazard by skin contact and respiratory exposure. AIM: Characterization of hydrogen peroxide and ozone residues on mask surfaces after chemical decontamination. METHODS: Various N95 masks were decontaminated using two commercial systems employing either aerosol spray or vaporization of hydrogen peroxide in the presence of ozone. Following the decontamination, the masks were aired out to eliminate moisture and potential chemical residues. The residual hydrogen peroxide and ozone were monitored in the gas phase above the mask surface, and hydrogen peroxide residue directly on mask surfaces using a colorimetric assay. FINDINGS: After decontamination, hydrogen peroxide and ozone were detectable in the gas phase in the vicinity of masks even after five hours (h) of aeration. Hydrogen peroxide was also detected on all studied masks, and levels up to 56 mg per mask were observed after 0.5 h of aeration. All residues gradually decreased with aeration, likely due to decomposition and vaporization. CONCLUSION: Hydrogen peroxide and ozone were present on N95 masks after decontamination. With appropriate aeration, the gaseous residue levels in the vicinity of the masks decreased to permissible levels as defined by the U.S. Occupational Safety and Health Administration. The reliable assays to monitor these residues are crucial to ensure the safety of the mask users.

Background 10 Hydrogen peroxide and ozone have been used as chemical decontamination agents for N95 masks during 11 supply shortages. If left behind on the masks the residues of both chemicals are representing a potential 12 health hazard by skin contact and respiratory exposure. 13

Aim 14

Characterization of hydrogen peroxide and ozone residues on mask surfaces after chemical 15 decontamination. 16

Methods 17

Various N95 masks were decontaminated using two commercial systems employing either aerosol spray 18 or vaporization of hydrogen peroxide in the presence of ozone. Following the decontamination, the masks 19

were aired out to eliminate moisture and potential chemical residues. The residual hydrogen peroxide and 20 ozone were monitored in the gas phase above the mask surface, and hydrogen peroxide residue directly 21 on mask surfaces using a colorimetric assay. 22

After decontamination, hydrogen peroxide and ozone were detectable in the gas phase in the vicinity of 24 masks even after five hours (h) of aeration. Hydrogen peroxide was also detected on all studied masks, 25 and levels up to 56 mg per mask were observed after 0.5 h of aeration. All residues gradually decreased 26 with aeration, likely due to decomposition and vaporization. 27 The masks were decontaminated according to the condition prescribed by the equipment manufacturers. 77

Two decontamination processes were compared as follows: 78

Process I: Aerosol spray system delivered three ingredients; a maximum of six masks were arranged by 79 facing up on a tray and placed on a flat top belt conveyor driven by a motor. The tray carrying six masks 80 was driven to a closed chamber. The masks were exposed to UV-C, ozone (minimum 2 mg/L) and 3% 81 hydrogen peroxide aerosol (generated from a spray nozzle) at a flow rate of 40 ml/min for 30 to 40 82 seconds at room temperature. Before exiting the chamber, an excess amount of ozone was removed via an 83 activated carbon filter. 84

Process II: Dual chemical decontamination system; masks were loaded in a chamber following a pre-85 condition at a vacuum pressure of 1 torr for 10 min. A 50% hydrogen peroxide solution was injected into 86 the chamber as a vapour form and continuously injected (40 mg/pulse/s) until a different pressure of 19 87 torr (the difference between the actual chamber pressure of 20 torr and the initial vacuum of 1 torr) was 88 reached. Later an excess amount of hydrogen peroxide was removed by adding ozone (2 mg/L) and left 89 for 5 minutes (min) dwell time. The process was repeated for another cycle before evacuation and 90 ventilation in a total of 90 min [13] . 91

After decontamination, the masks were aerated at room temperature before the residue analysis. The time 92 profiles of the residue concentrations were monitored in this study to determine optimal aeration time. 93

Hydrogen peroxide gas was measured using a handheld detector X-am 5100 from Drager, Germany. The 95 detection range of the instrument was 0.1 to 20 part per million (ppm) by volume with a precision of 14%. 96 A hydrogen peroxide detector was calibrated by the manufacturer and in-house calibrated using 10 ppm 97 sulphur dioxide gas. 98 instrument detection range was from 0.001 ppm to 0.50 ppm with a precision of 8%. The detector was 100 calibrated by the manufacture. Gas-phase measurements were carried out by placing one mask in an 11 L 101 closed chamber (Figure 1 ), equilibrated for 3 min then headspace concentrations were read and reported 102 as ppm. Before placing a new mask, the plastic chamber was flushed with nitrogen gas to remove all gas 103 residues and reduce carryovers. Table S2 and S3 in Supplementary material). Higher levels of hydrogen peroxide were detected for N95 138 masks treated with the decontamination process II compared to process I. As expected, the concentration 139 of hydrogen peroxide rapidly decreased with aeration time. After a two-hour aeration, the concentration 140 was less than a permissible limit of 1 ppm TWA in all masks treated by process I. However, the 141 concentration of hydrogen peroxide released from process II was depended on the types of masks, and it 142 could take two to five hours to be reduced to below the TWA limit. 

The amount of residual hydrogen peroxide on the mask depends on the mask type and decontamination 149 process (raw data in Table S4 and S5 in Supplementary material). The concentration of hydrogen 150 peroxide ( Figure 4 ) ranged from 1.01 mg/mask to 4.84 mg/mask for process I and 7.12 mg/mask to 55.9 151 mg/mask for process II after 0.5 h aeration. Interestingly, only less than 0.2 mg was detected on mask C 152 from both processes, and therefore mask C was not presented in Figure 4 . A high amount of hydrogen 153 peroxide was observed in mask E and mask F, particularly from process II. The differences are likely due 154 to the materials used for the mask construction and not to the shape of the masks (cupped vs. folded type). It was observed that all masks after decontamination were visually dry. However, our study showed that 177 residual hydrogen peroxide and ozone were detectable in the gas phase in the masks' vicinity. 178

Surprisingly, the elimination of residual ozone from both decontamination processes takes much longer 179 compared to the hydrogen peroxide (Figure 2 and 3) , which is counterintuitive considering a higher vapor 180 pressure of ozone. 181

After the masks were aerated for longer times, both residues in the 11 L chamber has decreased to safe 182 levels, compliant with TWA limits of 1.0 ppm for hydrogen peroxide and 0.1 ppm for ozone. Obviously, 183

it is not claimed that the 11L exposure chamber study design provides data that is directly applicable to 184 gas exposure risk assessments, as the chamber volume is a small fraction of that of inhaled air by a mask 185 user during typical daily use. Nevertheless, it provides useful information on the residue elimination 186 trends during mask processing. 187

Hydrogen peroxide extracted from N95 masks 188

Not surprisingly hydrogen peroxide was detected after decontamination (Figure 4) , particularly from 189 process II on the mask materials. An exponential decrease of hydrogen peroxide concentration was 190 observed during aeration at room temperature. The scatter plot of residual hydrogen peroxide vs. aeration 191 time with the correlation function is shown in Figure S3 and S4 in Supplementary material. Using the 192 exponential function an "aeration half time" could be calculated for any residue levels. In our study, it 193 takes three hours by process I and nine hours by process II to reduce residual hydrogen peroxide below 194 0.5 mg/mask (Table S6 and ozone. Overall, ozone used in these concentration regimes is unlikely to pose a significant exposure risk 202 to the masks' users after an appropriate aeration protocol is observed. 203

Higher amounts of hydrogen peroxide were detected in the gas phase and on the surface of N95 masks, so 204 respiratory and skin contact risks should be considered. From the gas phase experiments, it is evident that 205 the hydrogen peroxide concentration in the 11 L confined space after three hours of aeration falls below 206 the TWA level of 1.0 ppm. However, at the same three-hour aeration, the amount of hydrogen peroxide 207 residue on the mask surface was relatively high, particularly for the decontamination process II. 208

The results from this study demonstrated that hydrogen peroxide deposited on the mask was eliminated 209 rapidly during aeration. Overall dermal exposure from properly aerated masks to hydrogen peroxide is 210 likely minimal, especially at the 0.5 mg/mask levels targeted in this study, compared to other household 211 hydrogen peroxide applications which are ranging from 720 mg per application for hair bleaching to 15 212 mg in mouth wash (see list in Table S8 in Supplementary material) [15] . 213

From this study, we conclude that: (i), monitoring of residues resulting from decontamination process is 215 important to ensure user safety; (ii), both ozone and hydrogen peroxide present as residues after 216 decontamination; (iii), ozone and hydrogen peroxide levels in the gas phase above the mask are 217 measureable but could be eliminated with proper post decontamination aeration; (iv), hydrogen peroxide 218 on the mask surfaces represent potential skin contact concern, however it could be eliminated with

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