Overview of Chemical Disinfection of N95 FFRs

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Introduction

Disinfection and re-use of N95 full facepiece respirators is of critical interest during supply shortages. The following overview summarizes what has been published in peer-reviewed scientific literature, especially with respect to disinfection performance and the effects on the usability of the N95 FFR. This material is provided for informational purposes, and no recommendations are given or implied for any specific users or circumstances.

The studies summarized below were done using specific materials and conditions. Care should be taken to consult the original publications for details before attempting to reproduce the process.

Hydrogen Peroxide

The use of hydrogen peroxide (H2O2) has primarily been tested in a vapor form, or vaporized hydrogen peroxide (VHP). There are some commercial systems that use this approach for disinfection of equipment and other items, and some healthcare facilities may already have such equipment at hand.

A variant of vaporized hydrogen peroxide is “hydrogen peroxide gas plasma” (HPGP), often known by the commercial name “STERRAD”.

Disinfection Performance

• Wood et al. (2020) found essentially complete disinfection for 25 ppm VHP with 2 or more hours of exposure, with MS2 and Phi6 phages (possible surrogates for Ebola virus) on N95
• Kenney et al. (not peer reviewed, 2020) noted complete inactivation of three SARS-CoV-2 surrogates on N95s (T1, T7 and Phi-6 phages) after treatment in a room with an approximate 205 minute

N95 Performance Impacts

• Hao et al. (2019) treated positive pressure respiratory protective hoods with VHP for up to 60 minutes and concentrations between 100 and about 400 ppm. After 10 cycles, no physical or performance changes were noted for the
• Salter et al. (2010) determined that small amounts (about 1 mg) of hydrogen peroxide residues remain on N95 FFRs (after off-gassing for 18 hours), but that such amounts would pose no significant health hazards according to occupational exposure
• Bergman et al. (2010) noted that 3 cycles of HPGP degraded the filtration performance for 9 of 36 FFR samples. This degradation may have been related to the way the FFRs were stacked in the Sterrad
• Viscusi et al. (2009) noted no effect on physical appearance or performance (filtration or airflow resistance) for a single STERRAD process on a 55 minute
• Kenney et al. (not peer reviewed, 2020) noted no changes in appearance after 5 cycles, although performance was not

Ethylene Oxide

Ethylene oxide (EO) is a well-known disinfectant especially for equipment and heat-sensitive materials. It is also flammable and explosive, requiring special handling and facilities for its use.

Disinfection Performance

• Although EO is well-known as a disinfectant, no studies on its efficacy for N95 FFRs were readily

N95 Performance Impacts

• Salter et al. (2010) detected no remaining EO on FFR materials. However, a compound was detected (HEA, or 2-hydroxyethyl acetate) which is listed as a possible carcinogen and mutagen. HEA was hypothesized to form from EO reactions with elastomeric materials in the mask. Further study was
• Bergman et al. (2010) noted no effects of 3 cycles of EO processing on the filtration
• Viscusi et al. (2009) noted no effect on physical appearance or performance (filtration or airflow resistance) for a single 5 hour processing

Sodium Hypochlorite (“Bleach”)

Sodium hypochlorite, also known as bleach, is generally available at a concentration of between 5 and 6%, and is normally diluted by a factor of 10 or more before use for disinfection. It is well known as a disinfectant for surfaces and other materials.

Disinfection Performance

• Lin et al. (2018) reported no survival of bacterial spores (Bacillus subtilis) on N95 pieces after exposure to controlled amount of 0.54% hypochlorite or higher for 24
• Lai et al. (2005) found no survival of SARS-CoV-1 on paper, a disposable gown and a cotton gown material after 5 minutes exposure to 500 mg/L hypochlorite

N95 Performance Impacts

• Salter et al. (2010) noted that a chlorine smell remained on mask materials, even after off-gassing for 18 hours. Although the concentration was below industrial hygiene action levels (exposure limits), the odor may be problematic for some users and might cause adverse effects to users with asthmatic and similar conditions. Treatment in their work was with 0.6% (6,000 mg/L) bleach for 30 minutes.
• Bergman et al. (2010) noted no effects of 3 cycles of 0.6% bleach treatment (30 minutes each) on the filtration
• Viscusi et al. (2009) noted no effect on physical appearance or performance (filtration or airflow resistance) for a single 30 minute soaking in 0.6% bleach followed by air drying. The bleach odor was noted

Alcohols

• Viscusi et al. (2009) described that the use of 70% isopropyl alcohol caused significant degradation of filter

Alcohols or other organic solvents should not be used on N95 FFRs for disinfection or cleaning purposes.

References

Bergman, Michael S., Dennis J. Viscusi, Brian K. Heimbuch, Joseph D. Wander, Anthony R. Sambol, and Ronald E. Shaffer. “Evaluation of multiple (3-cycle) decontamination processing for filtering facepiece respirators.” Journal of Engineered Fibers and Fabrics 5, no. 4 (2010): 155892501000500405.

Hao, Limei, Jinhui Wu, Enlei Zhang, Ying Yi, Zongxing Zhang, Jinming Zhang, and Jiancheng Qi. “Disinfection efficiency of positive pressure respiratory protective hood using fumigation sterilization cabinet.” Biosafety and Health 1, no. 1 (2019): 46-53.

Kenney, Patrick, Benjamin K. Chan, Kaitlyn Kortright, Margaret Cintron, Nancy Havill, Mark Russi, Jaqueline Epright, Lorraine Lee, Thomas Balcezak, and Richard Martinello. “Hydrogen Peroxide Vapor sterilization of N95 respirators for reuse.” medRxiv (2020).

Lai, Mary YY, Peter KC Cheng, and Wilina WL Lim. “Survival of severe acute respiratory syndrome coronavirus.” Clinical Infectious Diseases 41, no. 7 (2005): e67-e71.

Lin, T‐H., F‐C. Tang, P‐C. Hung, Z‐C. Hua, and C‐Y. Lai. “Relative survival of Bacillus subtilis spores loaded on filtering facepiece respirators after five decontamination methods.” Indoor air 28, no. 5 (2018): 754-762.

Salter, W. B., K. Kinney, W. H. Wallace, A. E. Lumley, B. K. Heimbuch, and J. D. Wander. “Analysis of residual chemicals on filtering facepiece respirators after decontamination.” Journal of occupational and environmental hygiene 7, no. 8 (2010): 437-445.

Viscusi, Dennis J., Michael S. Bergman, Benjamin C. Eimer, and Ronald E. Shaffer. “Evaluation of five decontamination methods for filtering facepiece respirators.” Annals of occupational hygiene 53, no. 8 (2009): 815-827.

Wood, Joseph P., William Richter, Michelle Sunderman, M. Worth Calfee, Shannon D. Serre, and Leroy Mickelsen. “Evaluating the Environmental Persistence and Inactivation of MS2 Bacteriophage and the Presumed   Ebola   Virus   Surrogate   Phi6   Using   Low   Concentration    Hydrogen    Peroxide   Vapor.” Environmental Science & Technology (2020).