Covid-19 Pandemic Face Mask

Covid-19 Pandemic: Face Mask Disinfection & Sterilization for Viruses

CSS_Scott Mechler_Headshot
Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

UPDATED 04/10/2020

New information regarding Covid-19, SARS-CoV-2 (the virus that causes COVID-19) and the reuse of N95 masks is being released at an increasing rate. CSS will attempt to update this page in a timely manner to reflect important changes. However, as information is rapidly changing, CSS is not able to guarantee that the information provided here reflects the most current guidance and/or literature.

Important Update: As of 4/1/2020, CDC has released guidance on the decontamination processes for reuse of N95 masks. This information can be found on the CDC website:

With the global Covid-19 pandemic everywhere in the news, many healthcare professionals and concerned citizens are grappling with the shortage of respirator masks, vital tools for ensuring that healthcare workers are not infected by the people they’re trying to help. There has also been a large amount of confusion from the general public about what types of masks are useful for what, as many people are considering wearing masks in public for the first time due to news coverage about the Coronavirus.

In this blog post, we will briefly explain the various types of masks useful for infection control, and the different procedures available to help reduce some of the risk involved with the reuse of masks and respirators. None of the methods found remove all risk associated with mask reuse.

Broadly, there are three different types of masks usable for infection control:

  • Surgical Masks
  • Elastomeric Respirators (1).
  • N95 Type Respirator Masks

Of these three types, only some Elastomeric Respirators are designed for steam sterilization in an autoclave – neither Surgical Masks nor N95 Masks are designed for steam sterilization.

Surgical Masks

Surgical masks (see Image 1) are loose, single use cloth masks designed to provide protection against large droplets, splashes or sprays of bodily or other hazardous fluids. These types of masks experience leakage around the edges when the user inhales, and do not provide a reliable level of respiratory protection against smaller airborne particles. The primary recommended medical function of these types of disposable masks is for infected individuals who want to decrease the risk of transmitting the disease to others in their vicinity, and they are not a substitute for a respirator mask and their primary function is not to protect the wearer of the mask.

In professional healthcare settings, these masks are generally treated as single-use disposable items. As of this writing, we found no published literature regarding decontamination processes of used surgical face masks. It is possible that since they are not meant to protect the user against transmission of air-borne diseases and that are inexpensive enough to be treated as single use disposable items, no studies have been performed on their decontamination for reuse.


Image 1: Surgical Mask


Recently the CDC has issued guidance (17) regarding the creation and use of homemade layered cloth face coverings that would provide an initial barrier to aerosolized droplets, the primary mode of transport for SARS-CoV-2. Further, the use of a face mask also acts as a deterrent to touching one’s face, another vector for viral infection. This recommendation (18) replaced previous guidance that was intended to preserve masks for those who were at highest risk and needed them most – frontline healthcare workers and those working in public safety. Now that surgical masks and N95 masks are largely unavailable for personal purposes, a recommendation to use cloth face coverings no longer carries this risk. Additionally, some hospitals have begun accepting homemade masks produced by volunteers, and understandably many private citizens are concerned about potentially infecting frontline healthcare workers with homemade masks they create should they turn out to be asymptomatic carriers of the virus (20). The international World Health Organization (WHO) has also issued some guidance regarding the use of cloth face coverings, emphasizing that they should never be used in place of proper hand hygiene and social distancing guidelines (21).

The CDC recommends laundering homemade face masks regularly depending on use. Soap and other liquid detergents are quite effective at inactivating all kinds of viruses (19), particularly with the long exposure times and agitation provided by a standard laundry machine washing and rinsing cycle.

Further down in the blog, we will be reviewing literature currently available regarding decontamination methods available for N95-type respirators. The critical reason for such involved and precise methods for N95 type respirators specifically lies not in the difficulty of inactivating the virus but in attempting to preserve the function of the delicate electrostatic filtration element present in N95 type respirators which will not exist in homemade cloth masks. Immersion in liquid disinfectants and detergents that would severely compromise this N95 filter element is not a concern with homemade masks, which can be soaked through and washed much more thoroughly without damaging the mask or appreciably reducing its effectiveness.”

Elastomeric Respirators

Elastomeric Respirator masks (see Image 2) are larger, full or partial face-covering masks with removable filter elements designed to be re-usable. Some types of removable filters can be sterilized in an autoclave, however, most studies recommend that other decontamination methods are faster, damage the mask elements less, and are sufficient in eliminating influenza-like agents such as Coronavirus (2)(3).

Elastomeric respirator mask
Image 2: Elastometric Respirator Mask

The standard reprocessing procedure recommended by OSHA and the manufacturers of these elastomeric respirator mask elements is:  Cleaning followed by disinfection. Filter cartridges should be removed from the masks, and the filter cover, straps and any other surfaces should be subjected to the full reprocessing procedure. OSHA’s cleaning guideline recommends the use of a mild detergent at 110°F maximum followed by rinsing and draining with cold water. For disinfection, immersion in a solution of water and 0.1% household bleach for 2 minutes, then rinsing and drying is recommended. To disinfect cartridges, wiping all external surfaces with an alcohol quaternary microbial cloth and allowing to dry is recommended. When properly implemented, a reprocessing procedure for elastomeric respirator masks can take 7-8 minutes per mask.

Cleaning and disinfecting elastomeric respirator surfaces was shown to result in a 4.66 log reduction in a viable influenza-like virus. (2) Any bleach concentration over 1,000ppm has been shown to inactivate influenza viruses. Other studies have shown the importance of standardized, easy to read and implement SOP procedures for disinfection of elastomeric respirators, since they may be unfamiliar devices to the healthcare professionals required to reprocess used masks, such as the one below.(3)

Respirator Cleaning Procedure

FOLLOW INSTRUCTIONS EXACTLY.  Do not don PPE until instructed.


Protective equipment: Nitrile gloves- 2 pairs, 1 mask with eye shield, and 1 liquid-resistant gown

1 canister of hospital-approved bleach disinfectant wipes

1 bottle of mild dishwashing liquid such as Dawn, etc.

1 container of chlorine bleach (___% hypochlorite)

1 soft bristle brush

2 plastic medication cups or other graduated container to measure ml and/or ounces

Clock or timer

2-2 gallon buckets

1 pair of metal tongs

2 Chux pads 24″x16″

1 clean plastic container large enough to hold mask and components after cleaning

Hospital air and hose if available or clean, soft cloth


  1. Place unopened bag containing the contaminated respirator mask. near sink by instructions.
  2. On the other side of the sink, place opened Chux pad and lay tongs on top. Place the second opened Chux by the clean bin.
  3. Place the 2 buckets in the sink and run 1 gallon (4 quarts) of comfortably warm (not hot) water into the first bucket and 2 gallons (8 quarts) of warm water into the second bucket.
  4. Perform hand hygiene and then don protective equipment–gloves, gown, and mask with eye shield.
  5. Pour 15 ccs (1/2 oz) of DISHWASHING LIQUID in the first bucket containing 1 gallon of water.
  6. Pour ___ ccs (___ oz) of BLEACH in the second bucket containing 2 gallons of water. Mix bleach solution with tongs, and lay the back on the Chux.
  7. Open biohazard bag, remove the respirator and place it on the top of the bag.
  8. Pop off the splash guards (if equipped) on each side of the mask and immerse them in the soapy water.
  9. Remove the filters by unscrewing or turning them to the left.
  10. Wipe the filters with disinfectant wipes and place them in a clean bin.
  11. Without removing the straps, immerse the mask in the soapy water.
  12. Clean mask and splash guards (if equipped) with the brush and soapy water gently on the inside of the mask to avoid damaging the valves. Then rinse them well in running water.
  13. Place rinsed splash guards and mask (face up) into bleach disinfecting solution.
  14. Submerge mask completely into the solution; then while the mask is submerged, use the tongs to turn the mask over until it is facedown. This will avoid air pockets.
  15. Place the end of the tongs gently inside the maks to keep it submerged. Then lean the tong handles against the side of the bucket. Leave the tong handles submerged in the disinfectant solution.
  16. Set timer for 2 minutes.
  17. Discard biohazard bag. Wipe faucet handles with bleach wipe.
  18. Discard gloves and perform hand hygiene. Don a new set of gloves.
  19. After the 2 minute immersion (TIMED), remove mask and splashguards from the disinfecting solution with the tongs and set them on the Chux by the side of the sink, along with the tongs.
  20. Rinse mask and splashguard (if equipped) completely in running water and place them on the second Chux by the clean bin.
  21. Dry mask and splashguards with hospital air hose if available; if not available, dry with. clean cloth or allow to air dry.
  22. When dry, reassemble mask, filters, and splashguards. Check the integrity of the respirator and store in a plastic bag.
  23. Empty and rinse buckets, clean sink area with bleach wipes. Then remove PPE and perform hand hygiene.

Elastomeric Respirators would appear to be ideal for healthcare workers during a widespread pandemic, however their size, operational restrictions such as visibility and audible communication difficulty and price have lead to many organizations relying on the smaller disposable N95 type masks (4).

N95 Type Respirator Masks

N95 Respirator masks (see Image 3) are sealed, tight-fitting masks that force all air through a filter designed to block 95% or more of 0.3 micron test particles. Within the USA, N95 masks should be certified by and bear the appropriate markings required by NIOSH. They must be properly fitted and tested for leaks before they can be considered safe, and traditionally, have been considered to be single use. However, airborne disease outbreaks like SARS, MERS, H1N1 and various other viruses caused regional shortages of these masks, which led many researchers to look into possible disinfection procedures that might allow the masks to be reused (5). Unfortunately, many common decontamination methods such as high temperature steam sterilization (6)(8), alcohol washing, and bleach washing (12) have been shown to degrade these types of respirator masks.

On the bright side, disinfection through warm humid heat and UVGI was found to be effective at inactivating the H1N1 influenza virus and caused the least degradation of mask integrity. The use of hydrogen peroxide vapor (HPV) was found to maintain mask integrity while achieving sterilization.

N95 Respirator Mask
Image 3: N95 Respirator Mask


When examining a decontamination process to permit N95 mask reuse, there are a number of key factors to consider. At the completion of any process, the mask must:

  1. Retain filtration efficiency of >95% (ie. capture at least 95% of test particles greater than 0.3 microns)
  2. Maintain breathability as the filter element may be damaged. Breathability must not be substantially reduced as determined by measuring the pressure drop across the mask.
  3. Not have visible damage or deformation to the filter, straps or sealing members. The mask must retain shape, fit and seal integrity. Straps must retain elasticity.
  4. Be successfully decontaminated of the desired organism(s), for example the virus SARS-CoV-2 that causes COVID-19. An ideal process would eliminate all organisms and pathogens rendering the mask sterile.
  5. Be safe to use for the wearer (no harmful chemical residues or toxic off-gassing).

If these 5 requirements can been repeatably achieved, then consider how many processing cycles the mask can withstand before all these conditions can no longer be met. It is important to consider that differences in mask construction and materials among various models and manufacturers can significantly impact test results. The ability of each make and model to achieve these requirements must be validated for whatever process will be employed.

Methods of Potential Viral Inactivation for N95 Masks

It is important to note that since SAR-CoV-2 is so new, much of the research has been performed on surrogate viruses, such as other types of coronaviruses as well as various strains of influenza. As of this writing, it is unknown whether inactivation of these surrogate viruses are indeed representative of inactivation of SARS-CoV-2. As such, available research and guidance must be interpreted with caution. Further, some methodologies achieve sterilization whereas others aim only for inactivation of the targeted virus. In the latter situation, other potentially harmful microbial life may remain active on the mask. All available regulatory guidance suggests that any mask that has undergone one of these procedures should be handled as if it was an infected mask, only touched wearing gloves, used by the same individual who initially wore it, and stored in a container or bag to avoid the mask being touched by any other individual.

Hydrogen Peroxide Vapor (HPV):

Hydrogen peroxide (H2O2) vapor has long been used as an industrial decontaminant and recent studies performed by the Dutch national institute of health have shown that this method is effective at inactivating similar viruses and does not damage N95 masks (16). Battelle has recently received approval from the FDA (14) for the use of their H2O2 vapor generator and system in decontaminating N95 masks. Similar approaches and technology have been validated by Duke University (15).

The Duke University facility contains a Bioquelltm Clarustm C system with a 35% concentration hydrogen peroxide solution and distribution system that is used to achieve a uniform concentration of 480ppm+ throughout the decontamination room. The HPV cycle included a 10 minute conditioning phase, 30–40 min gassing phase at 16 g/min, 25 min dwell phase, and a 150 min aeration phase (15). 100 N95 masks were hung from a metal rack in the center of the decontamination chamber while the cycle was run.

Biological indicators loaded with Geobacillus Stearothermophilus spores were used to validate this method, and a 6-log reduction was found, and no significant degradation of the respirator’s filter was found until 50 cycles were performed, making this an extremely robust method where available to be implemented. However, degradation of the straps was found after 20 cycles.

A major concern with H2O2  vapor decontamination is off-gassing of hydrogen peroxide from the inner layers of the mask following the completion of the decontamination cycle. The Duke university study also performed a qualitative and quantitative off-gassing study of the masks run through the procedure, and after four hours the level of detectable hydrogen peroxide emanating from the masks dropped below the detection level of the sensor used.

Heat & Moisture

There is a growing body of evidence that supports potential viral inactivation of SARS-CoV-2 through the use of heat, relative humidity and time.

Research performed autoclaving masks at typical sterilization temperatures of 121C showed inconsistent results. One study (9) found that a particular mask was able to be processed up to 5 times without loss of filtration efficiency or fit. Viral inactivation studies were not performed because tests were performed with commonly accepted steam sterilization parameters. However, when tests under similar parameters were performed on different masks (8), results showed unacceptable physical deformation preventing proper fit as well as degradation of filter efficiency below acceptable limits.

In a recent article (10), Peter Tsia, inventor of the electrostatic charging technology that makes the filter media of N95 face masks, discussed acceptable temperature ranges for the electret. Test data provided shows acceptable filter integrity after subjecting it to steam at 125C for 5 minutes; however, there is no experimental data provided on fit performance.

Tests performed at lower temperatures of 65C with humid (85% RH) (8) or moist air (11) for 30 minutes, showed at least a Log 4.8 viral inactivation of two influenza strains. The CDC highlights the use of 60°C and 80% RH as well as 65°C and 85% RH. There are many potential ways to achieve this temperature and humidity range through the use of an incubator, environmental chamber or proofing oven. Research is currently ongoing on methodologies to use existing autoclave infrastructure to achieve these conditions.

Other moist heat methods found in literature are discussed below.

Microwave Generated Steam (MGS):

Plastic reservoirs with perforated tops as shown are filled with about 50 mL of tap water at room temperature, the contaminated N95 mask is placed atop the center of the assembly and loaded into a commercially available microwave oven and exposed to radiation for two minutes (one minute each side of mask). Use of this method resulted in an average log reduction of 5.06 of viable virus. Note that many designs of N95 mask feature metallic nosebands which when exposed to microwave radiation will melt the surrounding area of the mask, rendering it unusable (12). However, average aerosol penetration and airflow resistance was not shown to have changed significantly for masks subjected to this disinfection method that did not contain any metallic components. It is important to note significant potential issues with this approach. As noted, the metal noseband can damage the mask and can also create a fire hazard. Microwaves are available in a variety of wattages both with and without rotating carousels. This study also did not identify whether any of these are important parameters in order to achieve viral inactivation while maintaining filter integrity.

Microwave generated steam
Image 4: MGS Disinfection Setup

Warm Moist Heat (WMH):

A sealable container is filled with about one liter of tap water. A plastic support rack is placed in the container and this assembly is to be heated to 65℃ for 3 hours in an oven after which the mask is placed onto the support rack and returned to the oven for another 30 minutes. Use of this method resulted in an average log reduction of 4.81 of viable virus (5).

Warm Moist Heat WMH
Image 5: WMH Disinfection Setup


A UV-C lamp (80W, 254 nm) is used to expose the contaminated FFRs to UV radiation (≥1 J/cm^2 total dosage) for 15 minutes on each side of the mask (outer and inner). Use of this method resulted in an average log reduction of 4.81 of viable virus. Both dosage and wavelength of UV light are critical for inactivation, and when designing a procedure users must bear in mind that UV light is based on line-of-sight, and any part of the mask in shadow will not be disinfected. Further, it is vital to ensure that UV-C dosage is measured at the mask as dosage can be significantly reduced with increased distance from the source(s). One potential problem with implementing UVGI disinfection is penetration to the inner layers of some mask designs, which may not be exposed to the same dosage. Certain strap designs prone to twisting may also inhibit UVGI disinfection and a secondary disinfection step only applied to the straps of the mask may be necessary to counteract this.

While testing has shown that exposure to UVGI does not reduce the aerosol penetration to above 5%, statistically significant increases in penetration do occur meaning that repeated use of this method of disinfection will degrade masks over time (7). However, anecdotal evidence from facilities like the University of Nebraska where mask reuse has been fully implemented using UVGI light disinfection protocols suggests that the repeated usage of the mask leads to degradation far faster than the disinfection protocol does. At that facility the average number of times masks have been able to be reused is 3 times before fit testing failures are observed, whereas masks were run through the UVGI disinfection protocol 50 times before significant degradation of seal integrity was observed (13).

General Implementation

When using any disinfection procedure, healthcare providers should be aware that no known method is capable of achieving ideal levels of reusability (i.e. >6 Log reduction of viable virus and bacterial spores) while avoiding all forms of degradation. To reduce the risk of spreading any contagion, it is best practice to return the same mask to the same person for each use, rather than sharing reused masks between different people. This may also reduce the loss of seal integrity due to refitting the mask to differently shaped faces, though this is of course a secondary concern. Use of labeled masks and labeled individual bags can help to reduce the risk of cross-contamination between masks (14).

Image 6: An example of a marked, disinfected and reused mask from University of Nebraska, showing employee name, department, date of first use and number of decontamination cycles the mask has been run through (14).
Image 7: An example of individually labelled paper bags relaying the same information to decontamination personnel without exposing them to the potentially infected masks (14).

It is always best to use a new N95 mask whenever an N95 mask is required, however that may not be possible in all circumstances. As the fight against Covid-19 progresses, disinfection procedures and reuse may be necessary to combat acute shortages of respirators of all types.









8) Viscusi DJ, King WP, Shaffer RE. Effect of decontamination on the filtration efficiency of two filtering facepiece respirator models. J Int Soc Respir Prot. 2007;24:93–107.











19) Wolfe M and Lantagne D (2017). A method to test the efficacy of handwashing for the removal of emerging infectious pathogens. Journal of Visual Experiments Jun 7(124). DOI: 10.3791/55604.





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