COVID-19: Respiratory Personal Protective Equipment Research and Online Resources

The following list of research related to decontamination, manufacturing, and/or reuse of Respiratory Personal Protective Equipment (PPE) is provided as a resource for members of the MIT community currently engaged in PPE research related to COVID-19. Note that some of these articles are relatively recent or written in response to COVID-19, and not all of them have been peer-reviewed. At this time, neither MIT nor MIT Environment, Health & Safety (EHS) endorse the decontamination, reuse, or use of homemade masks for respiratory protective equipment. This content is meant for informational purposes only and does not represent an endorsement of any of these approaches or research.

Listed under each citation are highlights from the article. This list is not all-inclusive, and new research is being published daily. While neither MIT nor MIT EHS is the source of this information, MIT EHS is maintaining this list. To propose the addition of studies or research to this list, please send a citation to environment@mit.edu.

The MIT governance team on PPE manufacturing opportunities is led by Peter Fisher, Marty Culpepper, and colleagues in various departments, including Aeronautics and Astronautics, and is sponsored by Maria Zuber. In consultation with Tolga Durak and Michael Yaffe, MIT has also formed a task force charged with examining PPE sterilization and reuse. Please contact manufacture‐ppe@mit.edu if you would like to contribute resources or skills to these efforts.

For further information and guidance about PPE, see the Centers for Disease Control and Prevention (CDC).

Masks

This section provides references discussing protective mask long-term use and decontamination, as well as using homemade masks when there are no alternatives, such as Food & Drug Administration (FDA) cleared masks or respirators, are available. The FDA enforcement policy for face masks and respirators is provided below.


Article Highlight: “Turbulent gas cloud dynamics should influence the design and recommended use of surgical and other masks. These masks can be used both for source control (i.e., reducing spread from an infected person) and for protection of the wearer (i.e., preventing spread to an unaffected person). The protective efficacy of N95 masks depends on their ability to filter incoming air from aerosolized droplet nuclei. However, these masks are only designed for a certain range of environmental and local conditions and a limited duration of usage.”9 “Protective and source control masks, as well as other protective equipment, should have the ability to repeatedly withstand the kind of high-momentum multiphase turbulent gas cloud that may be ejected during a sneeze or a cough and the exposure from them. Currently used surgical and N95 masks are not tested for these potential characteristics of respiratory emissions.”

Article Highlight: When properly fitted, selected, used, and maintained, tight-fitting particulate-removing respirators have been demonstrated to reduce the amount of aerosols – both bioaerosols and non-biological aerosols – that are inhaled by the wearer. In contrast, most surgical masks are not designed to seal tightly to the face, and research has shown that they do not achieve the level of contaminant reduction provided by a certified respirator that is used correctly.

Effectiveness of Homemade Masks

Article Highlight: In settings where facemasks are not available, HCP might use homemade masks (e.g., bandana, scarf) for the care of patients with COVID-19 as a last resort. However, homemade masks are not considered PPE, since their capability to protect HCP is unknown. Caution should be exercised when considering this option. Homemade masks should ideally be used in combination with a face shield that covers the entire front (that extends to the chin or below) and sides of the face.

Article Highlight: Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection. Masks worn by patients may not offer as great a degree of protection against aerosol transmission.

Article Highlight: This study examined homemade masks as an alternative to commercial face masks. Several household materials were evaluated for the capacity to block bacterial and viral aerosols. Homemade masks capture about 60% of sub-micron particles, compared to 95-99% for surgical masks and N95 masks. Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was three times more effective in blocking transmission than the homemade mask. Findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection

Long-term Use of Masks

Article Highlight: N95 and surgical masks were just as effective after 3 hours as they are new.The study also found that median protection factors increased over the 3-hour period for those wearing the homemade masks, decreased for those wearing filtering facepiece (FFP2) masks that lower the wearer’s exposure to airborne particles by a factor of 10, and showed no consistent pattern for those wearing a surgical mask. The materials used in this published study were fresh and previously unworn. It is likely that materials conditioned with water vapor, to create a fabric similar to that which has been worn for a couple of hours, would show very different filtration efficiencies and pressure drops.

Article Highlight Extended use is favored over reuse because it is expected to involve less touching of the respirator and, therefore, less risk of contact transmission.

“Supplies of N95 respirators can become depleted during an influenza pandemic (1-3) or wide-spread outbreaks of other infectious respiratory illnesses. (4) Existing CDC guidelines recommend a combination of approaches to conserve supplies while safeguarding health care workers in such circumstances. These existing guidelines recommend that health care institutions:

  • Minimize the number of individuals who need to use respiratory protection through the preferential use of engineering and administrative controls;
  • Use alternatives to N95 respirators (e.g., other classes of filtering facepiece respirators, elastomeric half-mask and full facepiece air purifying-respirators, powered air-purifying respirators) where feasible;
  • Implement practices allowing extended use and/or limited reuse of N95 respirators, when acceptable; and
  • Prioritize the use of N95 respirators for personnel at the highest risk of contracting or experiencing complications of infection.”
  • Reusability of Facemasks During an Influenza Pandemic: Facing the Flu, National Academies Press (2006)

Article Highlight: If an individual user needs to reuse his or her own N95 filtering facepiece respirator, the committee recommends it be done in the following manner:

  1. Protect the respirator from external surface contamination when there is a high risk of exposure to influenza (i.e., by placing a medical mask or cleanable face shield over the respirator so as to prevent surface contamination but not compromise the device’s fit).
  2. Use and store the respirator in such a way that the physical integrity and efficacy of the respirator will not be compromised.
  3. Practice appropriate hand hygiene before and after removal of the respirator and, if necessary and possible, appropriately disinfect the object used to shield it.

Decontaminating Masks

Article Highlight: The five decontamination methods used included using a rice cooker to provide dry heat, an autoclave to provide moist heat, ethanol, bleach, and isopropanol. Decontaminating an N95 mask in a dry rice cooker (160 C for 3 minutes) or an autoclave (120 C with 1.06 kg/cm2 for 15 min) resulted in no degradation to the mask’s filtration performance. Ethanol, bleach, and isopropanol significantly damaged mask performance. The tests only examined the effect on the N-95 filter media.  They did not examine the impact of any of the decontamination methods on changes to the fit of the N95 mask or quality of the seal against the face.

Article Highlight: Research suggests that UVGI could be used to disinfect disposable respirators for reuse effectively, but the maximum number of disinfection cycles will be limited by the respirator model and the UVGI dose required to inactivate the pathogen.

Article Highlight: Healthcare workers experienced nearly identical flu virus infection rates when wearing either surgical masks or N95 masks.Given the likelihood that N95 respirators will be in short supply during a pandemic, understanding the relative effectiveness of personal respiratory protective equipment is important. There are few comparative studies of respiratory protective devices, and data comparing the surgical mask with the N95 respirator among health care workers are sparse. Researchers hypothesized that the surgical mask, which is less expensive and more widely available than the N95 respirator, offers similar protection to the N95 respirator among health care workers at highest risk for exposure to influenza. Data show that the incidence of laboratory-confirmed influenza was similar in nurses wearing the surgical mask and those wearing the N95 respirator. Surgical masks had an estimated efficacy within 1% of N95 respirators.

Article Highlight: The researchers evaluated five decontamination methods for nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) N95masks.  Their test showed that bleach and microwaves were failures at point of care because the bleach gases (skin and respiratory irritants) remained after multiple strategies were used to remove them. Using the microwave melted the masks, and soaking them first led to reduced filtration. Ethylene oxide (EtO), Ultraviolet germicidal irradiation (UVGI), and hydrogen peroxide decontamination were safe and effective in the models tested, but it is not known if they would retain filtration, material strength, and airflow integrity with repeated use. EtO, UVGI, and hydrogen peroxide limitations include time from decontamination to reuse and available space and materials to decontaminate in an Operating Room setting. 70C /158F heating in an oven for 30min, or hot water vapor from boiling water for 10 min, are additional effective decontamination methods.

Article Highlight: In an effort to extend the stockpile of N95 FFRs and reduce risks associated with reuse of untreated, contaminated N95 FFRs, this team developed a surface decontamination procedure involving the delivery of ultraviolet germicidal irradiation (UVGI) to used N95 FFRs. The paper suggests hanging respirators on wires and exposed to UVGI towers containing eight 254 nm bulbs and, in a room, coated with UV reflective coating.

The paper outlines a very detailed process for the collection, storage, tracking, decontamination, post decontamination tracking, and storage, and return to users.  Each respirator is tracked individually, and paper has images and roles and responsibilities for each type of person (including healthcare profession, in-house staff, ambulatory clinic staff, immediate care clinic staff, and UVGI associate. The paper suggests Use respirators hung on wires and exposed to UVGI towers containing eight 254 nm bulbs and in a room coated with UV reflective coating.

Article Highlight: The team’s research shows a very slight degradation of N95 mask efficiency due to charge loss after 70C heat for 24 hours.  Also, a slight degradation of medical mask efficiency after 70C for 24 hours.  Alcohol liquid or vapors will erase charges.  This paper recommended heating masks in hot air (70C for at least 30 minutes) to inactivate “COVID-19”.  Charge loss is unnoticeable by steam sterilization of 125 C for 3 minutes.  Boiling for 3 minutes doesn’t affect charge, but stirring isn’t recommended because it can damage the mask.  Immersing in water for 3 days doesn’t affect the charge as they’re quasi-permanent charges, but laundering isn’t recommended due to physical damage to the mask.

Article Highlight: Battelle evaluated the efficacy of hydrogen peroxide vapor (HPV) for the decontamination of N95 respirators against a single organism using the Bioquell Clarus C HPV decontamination system. The study established the parameters of the HPV decontamination cycle to ensure a 6-log reduction in organism viability, evaluated the mechanical integrity and performance of the N95 FFR following exposure to up to 50 cycles of HPV decontamination, and confirmed that decontamination was still achieved even after 50 repeated cycles of biological aerosol exposure/HPV decontamination.

The study established the parameters of the HPV decontamination cycle to ensure a 6-log reduction in organism viability, evaluated the mechanical integrity and performance of the N95 FFR following exposure to up to 50 cycles of HPV decontamination, and confirmed that decontamination was still achieved even after 50 repeated cycles of biological aerosol exposure/HPV decontamination.

Article Highlight:

Respiratory protective devices (RPDs) that protect first responders and workers from infectious disease outbreaks may be in short supply during public health emergency situations.

One type of respirator routinely used to protect workers from biological hazards is known as an N95 filtering facepiece respirator (FFR, pictured). These respirators protect the wearer by removing contaminants from the air. Currently, these respirators must be discarded after one use, but in emergency response circumstances such as an emerging infectious disease (pandemic influenza, for example) or intentional release of a biological threat agent, reuse of these respirators may be necessary to maintain adequate supplies.

Some RPDs, including filtering facepiece respirators (FFRs), are currently designated as single-use devices. Others, including half-mask elastomeric respirators (HMERs) and powered air-purifying respirators (PAPRs, pictured), are reusable and can be shared among multiple people.

In emergency response circumstances such as an influenza pandemic, decontamination and reuse of FFRs and more efficient decontamination processes for other types of respirators may be necessary to maintain adequate supplies.

Article Highlight: Duke University has a room dedicated to decontaminating equipment using VHP (vaporous hydrogen peroxide). They tested up to 50 cycles of decontamination before noticeable degradation of the elastic straps. They also plan to limit the cycles to 30 before disposal of the N95 to prevent noticeable degradation. The research team used biological indicators of geobacillus stearothermophilus spores to ensure decontamination efficacy. They also used H2O2 sensors to ensure operators wouldn’t be exposed to dangerous levels of H2O2 due to off-gassing of the decontaminated N95 post-cycle.  4 hours appeared to drop the levels below the threshold of the sensor (below 0 ppm).

Article Highlight: Battelle has a process to use VPHP (vapor phase hydrogen peroxide) to decontaminate tens of thousands of PPE per cycle.  Based on data, N95 respirators can be decontaminated up to 20 times without noticeable degradation or reduction in filtration efficiency.  Runs are verified by indicators to show 6 log reduction in bacterial contamination.  Process validated against SARS-CoV-2 in Battelle’s BL3 lab. The original process follows published procedures from the 2016 study Battelle did via an FDA funded study grant.  The 46-page final report summarizing process and results is available on the Battelle website.

Article Highlight: The CDC and NIOSH does not recommend decontamination and then reuse of filtering facepiece respirators (FFRs), but this option can be considered in a crisis and shortage. The article summarizes potential methods based on limited research available.  There are also strategies for extending use. Data suggests SARS-CoV-2 survives up to 72 hours, so one strategy is to issue 5 respirators to staff and then put them in a breathable bag and let sit for a minimum of five days before reuse by the same staff member. No manufacturer authorized methods are available for decontamination of FFRs prior to use. Battelle has an emergency use authorization (EUA) from the FDA for decontamination with VHP. Ultraviolet germicidal irradiation (UVGI), vaporous hydrogen peroxide (VHP), and moist heat are the most promising methods and should be considered. Other methods should not be used due to significant degradation of FFRs and particle penetration exceeding NIOSH standards.  These include autoclave, 160 C dry heat, 70% isopropyl alcohol, microwave irradiation, and soap and water wash, and disinfectant wipes. Ethylene oxide did not appear to impact filtration efficiency but was not recommended due to the potential to be harmful to the wearer if any residual gas is trapped in the FFR (long off-gas time).

Article Highlight: “Many methods of N95 mask sterilization have been studied and proposed with the hope of being able to safely reuse masks [2]. Two major considerations must be made when re-sterilizing masks: (1) the sterilization method effectively kills pathogens, penetrating into the fibers of the mask, and (2) the method does not degrade the operational integrity of the N95 filters.”  “The results of this study “suggest against ionizing radiation as a method of disposable N95 sterilization, and even more importantly, against using the qualitative fit test alone to assess mask integrity.”

Finding: An N95 mask placed within a Biosafety Cabinet (BSC) with a manufacturer reported fluence of 100 W/cm^2 should be effectively sanitized for reuse after approximately 15-20 minutes per side. The author’s suggest that idle BSCs can be utilized to alleviate the PPE shortage by sterilizing PPE to allow safe daily re-use. Additionally, the author’s recommend testing on a larger scale, and confirming in a virology laboratory before adoption.

Article Highlight: Preprint, non-peer reviewed article discussing the potential for using the UV light inside a biosafety cabinet (BSC) to decontaminate N95 masks.  Since BSC’s are a common piece of equipment in research labs, there is potential to use them to decontaminate Personal Protective Equipment (PPE) in a crisis/shortage situation.  Researchers placed electrodes on the surface of masks to track the intensity of the UV light hitting different areas of the mask.  Based on the intensity readings from a handful of UV lights in different BSC’s combined with recommendations from the literature on inactivation of viral DNA, the authors suggested a 15-20 minute UV sterilization per side of the mask would be appropriate.  This is a conservative number and is only based on the intensity measured from a few BSC’s and averaged.

Article Highlight: The paper reviewed 21 laboratory studies on N95 reuse and extended use. Available studies support prioritizing extended use over reuse. In addition the following was found:

  1. N95 respirator contamination risks: 2 studies found that 4% to 18% of H1N1 virus particles and >10% of M2 bacteriophage particles were viable after 4 to 6 days on 3M 8210 filters at room temperature. 1 of the studies (Brady et al. 2017) reported that 2% to 15% of M2 particles transferred to the users who donned contaminated N95s. The other study (Fisher et al. 2012) reported minimal M2 aerosolization (<0.2%) from contaminated N95s in simulated cough tests. 
  2. N95 disinfection/decontamination: 3 studies reported that autoclaves, steaming, moist heat, bleach, benzalkonium chloride, and ultraviolet-C (UV-C) (1 to 2 J/cm2) achieved >10,000-fold reduction in H5N1 (Lore et al. 2012), H1N1 (Heimbuch et al. 2011), and S. aureus (Heimbuch et al. 2014) loads on contaminated N95s; however, Heinbuch et al. (2011) found UVGI ineffective on some N95 models, and 1 of the studies reported that inoculation patterns affected UCGI (Woo et al. 2012). 
  3. N95 integrity: 2 studies (Vuma et al. 2019, Bergman et al. 2012) reported that 7% to 8% of N95s failed fitting after 2 uses and >20% failed after 5 fittings. 1 study (Lin et al. 2017) reported reduced filtration in a N95 model cleaned with bleach, 70% ethanol, steaming, or autoclaving; however, 1 study (Bergman et al., 2010) reported that 6 models still filtered >95% of 300 mn particulate after 3 cleanings with bleach, hydrogen peroxide, steaming, moist heat (65 °C for 20 minutes), or UVGI (1 to 2 J/cm2). The same group (Viscusi et al. 2011) reported that cleaned N95s fit well, but 1 study (Lindsey et al. 2015) reported that filters and straps were damaged by UVGI doses >120 J/cm2. 
  4. Adverse event risks: 2 studies (Sinkule et al. 2013, Roberge et al. 2010) on more than 30 models found that covering respirators with surgical masks had no clinically significant effect on breathing effort and gas exchange. 1 study (Salter etal. 2010) reported no toxic residue in N95s detectable toxins. 

Article Highlight: Study which reviews existing evidence on SARS-CoV-2 survivorship and methods to disinfect PPE with an emphasis on N95 masks.  Due to the lack of current information on SARS-CoV-2, the study was conducted using data on SARS-CoV-1, a closely related virus.  From the outset, the study proposes a two-step disinfection process, which should be considered as conservative due to the lack of information that is available on SARS-CoV-2.  The study goes on to say that a four-day stand down storage period of the PPE followed by ultraviolet light exposure, dry heat treatment or chemical disinfection treatment; the type of PPE would determine which secondary measure is used.  In all cases, considerations should be made to ensure that any potentially reused PPE would fit as if it were previously unused.  

Other Resources

Article Highlight: “Some consumers and health care professionals are currently experiencing difficulties accessing alcohol-based hand sanitizers.  We are also aware of reports that some consumers are producing hand sanitizers for personal use; the Agency lacks information on the methods being used to prepare such products and whether they are safe for use on human skin.”

Because of the public health emergency posed by COVID-19, the FDA does not intend to take action against compounders that prepare alcohol-based hand sanitizers for consumer use and for use as health care personnel hand rubs for the duration of the public health emergency declared by the Secretary of HHS on January 31, 2020, provided [several] circumstances are present.”