Evidence-Based Methods For The Decontamination Of N95 Respirators

This document is meant for information purposes. Please review the CDC guidelines for N95 mask contingency planning.

FDA-approved methods

On March 29, 2020, the FDA issued an emergency use authorization for a proprietary hydrogen peroxide vapor (HPV) system for the decontamination of N95 FFR. This system allows up to 20 cycles of decontamination.

In a study performed by the manufacturer of this system, there was no loss of filtering capability and no change in air resistance through the respirator after 50 cycles. However, strap degradation occurred after 20 cycles, and there was variable loss of fit on the model mannequin that was being used. This loss of fit was similar to controls.

Non-FDA-approved methods for decontamination reported by health care facilities

Duke University has reported a method using HPV at 480+ ppm hydrogen peroxide with a dwell time of 20 minutes, followed by four hours of aeration to allow any off-gassing (evaporation of hydrogen peroxide) from the masks to occur. There was no apparent degradation in mask fit, but the investigators did not test filtering capability.

Duke University houses a regional National Institute of Allergy and Infectious Diseases Biocontainment Laboratory and has implemented its reported protocol.

The University of Nebraska Medicine has reported a method for decontamination of N95 FFR using ultraviolet germicidal irradiation (UVGI).

This method exposes masks to UVC at 300 mJ/cm2. UVGI has been evaluated for its effects on mask integrity, and a small decrease in filtering capability was found. All masks, however, remained within parameters necessary to maintain the N95 rating.
UVGI was found to cause loss of structural integrity in some masks.

The University of Nebraska has implemented its decontamination protocol (first developed when they were caring for patients with Ebola).

Other reported methods of decontamination

Warm, moist heat (water reservoir heated to 65°C for 3 hours then used to decontaminate mask for 30 minutes) has been reported to be effective to decontaminate FFR inoculated with influenza viruses.

This method did not cause degradation of filtering capability or changes in mask structural integrity.

The effect of dry heat on the inactivation of viral infectivity has also been reported. Coronavirus SARS-CoV-1 was completely inactivated when heated to 75°C for 45 minutes, but not when heated to 56°C or 65°C.

Unpublished data from Stanford University reported that N-95 FFR maintained their filtering capability after exposure to 70°C for 30 minutes.

Mask rotation with storage after use may be an effective method for reuse of N95 FFR. There are limited data available on the environmental persistence of SARS-CoV-2. In laboratory conditions, viable virus can persist for 3-4 days on stainless steel, and environment persistence was similar to SARS-CoV-1. Other coronaviruses have been found to remain viable for up to 5 days on cardboard and five days on silicon rubber. Survival decreases at higher temperatures.

Storage for four to five days before reuse may, therefore, be a viable method for reuse of N95 FFR.

Non-recommended methods that can degrade N95 FFR (N95 masks)

The use of home powered heating methods are not recommended for decontamination of FFR due to the risk of loss of structural integrity or incomplete viral inactivation. When heated to 160°C (320°F), masks lost their structural integrity. Under-heating can result in incomplete inactivation of coronaviruses (viable virus persisted after 90 minutes of dry heating at 65°C). The temperature at which polypropylene will begin to degrade is between 90° and 100°C necessitating strict control of exposure temperatures, which cannot be obtained with radiant heating devices (e.g., home ovens). Heating in a home oven or similar is not recommended for N95 FFR decontamination.

Immersion in isopropyl alcohol, ethyl alcohol, chlorine-based disinfectants, or soap and water has been shown to degrade the charged cotton layer of N95 FFR, resulting in a significant decrease in filtering capability. Immersion techniques are not recommended for N95 FFR decontamination.

Surface wiping of masks does not result in the decontamination of interior layers unless the entire mask becomes wet. As noted above, many cleaning solutions can degrade the N95 FFR filtering capability and are not recommended for N95 FFR decontamination.

Autoclaving and microwaving result in significant destruction of N95 FFR structural form and fit and are not recommended for the decontamination of N95 FFR.

James Chenoweth is an emergency physician.

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