N95 Mask Decontamination and Reuse Webinar

April 29, 2020

With limited availability of N95 masks, many institutions have been forced to develop their own policies and procedures for mask decontamination and reuse. This April 24 webinar reviews three decontamination methods supported by academic research and provide clear and unbiased explanations of the pros and cons of each.

Hosts: N95DECON, AAMI, the Association of periOperative Registered Nurses (AORN), and the International Association of Healthcare Central Service Materiel Management (IAHCSMM).


  • Amanda Benedict, acting vice president of standards, AAMI (host and moderator)
  • Samantha M. Grist, Ph.D., UC Berkeley and N95Decon.org
  • Margaret L. Gardel, Horace B. Horton Professor, Physics and Molecular Engineering Director, Materials Research Science and Engineering Center University of Chicago
  • Jill R. Crittenden, Research Scientist with Prof. David E. Housman and Institute Prof. Ann M. Graybiel Massachusetts Institute of Technology

Amanda Benedict: Everybody is certainly keenly aware that the COVID-19 pandemic has created an unprecedented and extreme need for respirators that is far outpacing supplies. Recently, AAMI and IAHCSMM hosted a sterilization and COVID-19 webinar and one of the biggest areas of concern we were hearing was how to respond to shortages of N95 masks—a big issue for hospitals and healthcare providers—and at that time, the panelists for that webinar were really pointing to the existing standards and the guidance received per manufacturer, so IFUs, and letters that manufacturers had sent to customers. Many institutions have also been forced to develop their own policies and procedures for mask decontamination and reuse while they're trying to balance the needs to protect their staff and their patients with a very unpredictable supply of respirators. And we know also that some manufacturers are collaborating with companies and hospitals to evaluate the impact of various decontamination systems on the fit and effectiveness of N95 masks.

In recent weeks, the FDA has released a number of emergency use authorizations pertaining to N95 mask decontamination. Some examples are STERIS, Stryker, ASP, Sterilucent, Battelle. They've all had EUAs released. In the U.S. Centers for Disease Control and Prevention or CDC has laid out strategies to optimize the supply of personal protective equipment, which also includes limited reuse of disposable N95 respirators as a strategy to address the crisis. So I would encourage our audience to check out those resources. Go to the FDA website, go to the CDC website, and read the EUAs and the guidance that's available.

So to provide some framework for this webinar, we will review the three most commonly recommended decontamination methods and provide clear and unbiased expectations of the pros and cons of each. This webinar is intended to be informational and educational and with the understanding that there's no replacement for using new masks. This information can serve as the foundation to help organizations develop a risk management strategy for mask reuse, and this can also be adapted for any crisis situation. Please note, however, that this presentation does not constitute a recommendation for practice.

Margaret L. Gardel (00:08:34): The three speakers you'll hear from today are all representatives of the N95DECON consortium. We are 105 scientists from over 10 different institutions. We self-organized approximately a month ago in order to provide unbiased interdisciplinary approach to evaluating what's known in the peer reviewed literature on decontamination approaches for N95 masks. We do not have any financial conflicts with any of the advice or the technical information we're providing, and our group consists of PhDs, MDs, registered nurses, and as well as students representing these different skillsets. So our goal is to evaluate existing literature on N95 decontamination and publish technical reports and fact sheets on our website, N95DECON.com and coordinate and execute research to fill in the gaps of knowledge.

So as was referred to earlier, our group also knows and recognizes the best practice is to use new N95 masks and unfortunately, that's not a possibility in the current pandemic. The decontamination approaches that we'll be discussing today do not solve this PPE shortage crisis. It is an emergency practice to be considered only during the COVID-19 pandemic. So today, you'll hear three summary statements on the decontamination methods that have been evaluated by a consortium. Heat and humidity approach, which I'll be giving; decontamination by UV-C, by Dr. Samantha grist of UC Berkeley; and hydrogen peroxide approaches from Dr. Jill Crittenden at MIT. And the techniques we're discussing pertain only to NIOSH-certified N95 respirators. There may be variation between mask manufacturers and models and these recommendations do not apply to surgical masks.

Heat and humidity approach (00:10:56)

Margaret L. Gardel: So I will be talking about the use of a thermal cycle of heat in a human environment as an approach for N95 decontamination and reuse. In my day job, I'm a professor at the University of Chicago in the physics department. And this is just a brief summary of what I'll be speaking about today. I'll be talking about the approach, the technical considerations for this approach, and its requirements for inactivating SARS-CoV-2, and the impact of a thermal cycle on N95 performance. I'll then briefly discuss strategies for implementation as well as primary risks and unknowns.

The idea of elevating the temperature of N95 masks as a way to decontaminate them for reuse is an approach that has been used in the past, both for influenza outbreaks and then the SARS-CoV-1 outbreak in past years. Heat is effective at inactivating viruses on N95s. It's less effective for bacterial and mold spores. Based on the literature, we expect that an elevated temperature in the range of 70 to 85 degrees Celsius in a human environment that is elevated to 50–85% relative humidity over a time of 60 minutes should be effective at both inactivating SARS-CoV-2 as well as preserving the integrity of mask filtration.

So the target temperature of 70 to 85 degrees was determined from thinking of two considerations. If we go to lower temperatures, the risk of reduced viral inactivation increases, but if we go to higher temperatures, the risk of mask damage also increases. So now we look at a range in between these two, considering weighting the ill effects of these two risks, and 70 to 85 mitigate these risks. The relative humidity is a measure of the amount of moisture in the air and it's been known in literature that a high relative humidity is more effective than dry heat for inactivation of viral strains.

So just to give you a sense of what relative humidity and the importance in considering its temperature dependence, today is a nice cool day out in Chicago. It's about 50 degrees Fahrenheit or 12 degrees centigrade with about 45% relative humidity. If I now took the ambient air and increased the temperature to 65 degrees Celsius, that would pertain to a less than 5% relative humidity. So if we just take the ambient air and increase the temperature, it ends up being a dry heat situation. So in order to achieve this high relative humidity for N95 decontamination, the mask would need to be placed into, added moisture would need to be made for the masks to achieve this at the higher temperatures.

So it's been shown that elevated temperature of as low as 60 degrees is effective for inactivation of SARS-CoV-2, but this is in solution and this does not pertain to the surface of an N95 mask. We also know that elevated temperatures at high relative humidity inactivates influenza strains on N95 masks, and this gives a hint that higher relative humidity is effective at inactivating envelope viruses.

Two recent studies have pointed to the possibility that dry heat at 70 degrees could be used for N95 decontamination. However, it only gives a 3 log reduction of viral efficacy and it's insufficient on the metal nose piece. So that leads us with the current status of what's known in the literature of recommending the 70 to 85 degrees Celsius for over 60 minutes with this high relative humidity is likely to be effective. And we know that this temperature that will not inactivate all possible bacteria and spores, and we need more information on this, which should be forthcoming very soon.

As I mentioned, the other consideration with mask decontamination is the effect on any decontamination process on the mask filtration and the N95 mask seal. On this slide is a summary table, which you can see on our website at n95decon.org, just summarizing what's known about different mask models and the impact of the filtration and seal performance in response to different thermal cycles. As a summary, many common N95 models keep fit and filter performance for one to three cycles of 60 degrees C with high relative humidity, and some of these models even keep fit and filter for even higher temperatures of 85 degrees C with a high relative humidity.

As a note of caution, different N95 makes and models may respond differently to heat, and repeated thermal cycles may damage N95 fit and filtration. Again, if you want to see the impacts on specific N95 masks that you may have, you should go to our website and look at the full details of this table.

Several weeks ago, the CDC released guidance on the use of the approach for heat humidity for N95 mask decontamination. I should emphasize that there is still no FDA-approved process that has been validated for this approach as of yet. But we know that there are many commonly available devices in the healthcare settings that can maintain the desired temperature range, including warming cabinets, convection ovens, water baths, bacterial incubators, and these may reflect a simple, low-cost approach for achieving that desired temperature range.

Likewise, there are also approaches for enhancing the humidity of the N95 mask. You can put the mask in a sealed box, a plastic container, or humidify the chamber. To mitigate the risks of cross-contamination, masks should be kept separate and returned to individual users. And I should say that is still an area of research whether autoclaves that are common in hospitals that masks can withstand this thermal cycle because autoclaves are a known sterilization technique. Data suggests that the mask could only withstand up to five cycles before their integrity is compromised, and this must be considered in the decontamination process.

Some key considerations to take into account is that data from one model of N95 mask may not apply to others, that N95 mask should be isolated and returned to the original user, and a seal check should be performed before each reuse, and the temperature used should be stable and uniform. The risks are that these methods are still an untested protocol for coronavirus inactivation on N95 masks, and the virus may survive if there's improper thermal cycle conditions, and that N95 fit and filtration may be damaged by the thermal cycle conditions.

We also have to consider cross-contamination of resistant bacteria and mold spores. However, if these risks can be overcome, this is an approach that can be used as a promising low-cost method that could be easily implemented in many different types of healthcare settings, and this merits a potential for future FDA feasibility studies.

Again, if you want to see any of the information that I talked about in more detail, please see our website n95decon.org.

Ultraviolet light approach (00:20:46)

Samantha M. Grist: I'm a representative of the UV-C team of N95DECON. Now, before I say anything else, I really just want to communicate my, as well as my team's, gratitude to all of the healthcare workers and everyone else on the front lines of this crisis.

Now, you might be wondering about me and how I got involved with N95DECON. I have a PhD in electrical engineering, partly on optics, and my postdoc research in bioengineering involves ultraviolet light. And so at the start of the COVID-19 crisis, I started working with N95DECON to study the evidence for ultraviolet decontamination of N95s.

Now, as Margaret mentioned, the members of N95DECON 100% believe that decontamination does not solve the PPE crisis, and the best choice is always a new, unused N95. But during this crisis when that might not be available, our goal is to use our scientific training to review the evidence and provide an independent, scientific view to help connect decision makers to the information, the resources, and the expertise that they need to make crucial risk management decisions.

With that context in mind, my talk will focus on ultraviolet light for decontaminating N95s. I'll present the evidence supporting this approach as well as some of the risks and limitations. I do want to highlight a couple of things. The majority of the sources that we cite in this presentation have either gone through peer review or been implemented by hospitals, and those that haven't have been scrutinized in detailed by our team and do come out of groups that have been working in the relevant areas for many years.

Now, we do want to communicate a word of caution regarding preprint studies as they're widely ranging in terms of rigor and quality, and that's why for this presentation as well as in our technical reports posted on N95DECON.org, we've focused as much as possible on peer-reviewed evidence.

Now, when we speak about ultraviolet decontamination, what we're really referring to is this germicidal UV-C region of the electromagnetic spectrum highlighted in purple on this slide here. Now, when we look at the electromagnetic spectrum, longer wavelengths and lower energy radiation is on the right, so you can see visible light, and then as we move down in wavelength and up, so increasing the energy, we pass through the UV-A region of the spectrum, the UV-B region, and then the germicidal UV-C region of the spectrum before we reach a shorter wavelength ultraviolet light that has the potential to generate ozone, which is hazardous to humans.

Typically, when we speak about the germicidal UV-C region, we speak about that because if you look below the electromagnetic spectrum, you can see the germicidal action spectrum, and that is basically how effective light of different wavelengths is at decontamination. There's a peak in that spectrum at about 260 nanometers. The reason for that is that UV-C irradiation inactivates pathogens by damaging their genomic material, and DNA and RNA have a maximum UV absorption peak at around 260 nanometers.

We've summarized the evidence here as well as in our technical reports on n95decon.org, and the summary of the evidence suggests that a dose of ultraviolet C irradiation, a minimum dose of greater than or equal to one Joule per centimeter squared within this germicidal UV-C region, inactivates viruses similar to SARS-CoV-2 on the majority of tested N95 face pieces.

There's three main points that I want to highlight here. First, that that one joule per centimeter squared dose, or how much light the N95 respirator sees, is much higher than typically used for surface decontamination, so one or even two orders of magnitude higher doses than are used in typical surface decontamination protocols. It's important to note that large discrepancy in dose.

The second point that I want to make is that while that dose is effective for the majority of tested N95 models, as you can see in the summary table, it was not effective—it did not yield a 3-log reduction in virus—for all of the respirators. When I say 3-log reduction, of course, that means, as many of you probably know, that for every thousand starting active virus particles, 999 will be inactivated.

The third point that I want to make is that even when the face pieces of the respirators are effectively decontaminated, you can see from the table that the straps of the respirator are less effectively decontaminated using these UV-C protocols, and so the straps require a secondary decontamination method such as wiping with a compatible disinfectant.

At this one joule per centimeter squared dose, which, as we've discussed, is higher than typically used for surfaces, you might be wondering whether the N95s are damaged by that process. There is evidence showing that at the N95 keep fit and filter performance after 10 to 20 cycles of this dose alone. Damage to the respirator materials is seen at higher doses of greater than a hundred joules per centimeter squared or a hundred times that minimum dose. From that evidence, we anticipate that the limiting factor for reuse is actually just going to be fit degradation due to the repeated donning and doffing because fit factor below the OSHA standards has been measured after five don and doff cycles

That evidence summarizes the UV-C piece of the decontamination approach, but as I'm sure most or all of the audience already knows, UV-C, like all N95 decontamination approaches, really requires a robust sterile processing workflow. I want to highlight this because there are UV sources like you can see on this slide that looked like microwave ovens, and so the temptation can be there to think that you can just pop it the N95 respirator into that device and have it come out clean and safe. Unfortunately, that's not the case, and this robust workflow surrounding the actual decontamination process is required.

Some examples of the important considerations for that process are safety. So, UV-C light is hazardous to humans, so people cannot be in that treatment area. N95 donning and doffing procedures for use with decontaminated respirators have to be modified from regular protocols. You can see at the bottom of this slide, the University of Nebraska Medical Center has provided guidance as well as training videos on some of the modifications to these donning and doffing procedures.

The full workflow must avoid any cross-contamination between N95 respirators, and N95s should be labeled and tracked throughout this process in a way that minimizes physical damage as well as returns each N95 to its original user. For all of those reasons, it's critical to work with trained hospital personnel like many of yourselves for implementation.

Several hospitals systems have implemented UV-C protocols for N95 decontamination. One great example of this is the University of Nebraska Medical Center. Their process uses a commercial room-scale UV-C system, so they have systems on either side of clotheslines that are set up to hold N95 respirators. Their process involves 51 steps, including collection, decontamination, and redistribution over that full protocol. They use a return-to-index-user method, which is exceedingly important for UV-C decontamination because, as it's been discussed, it's decontamination only, not sterilization.

In the summary of the evidence, we discuss the importance of that minimally acceptable dose that is required for inactivation, and that is absolutely crucial because UV-C is only able to inactivate pathogens that see that minimal dose required for their inactivation. For that reason, we see it as absolutely critical to validate that that dose has been reached and characterize any UV-C illumination system.

To do that, it's necessary to measure UV-C irradiance, which is optical power per unit area, or UV-C dose, which is the integration of irradiance over time, and that measurement needs to be performed within this traceable calibrated sensor that is specific to the UV-C germicidal wavelengths and matched to the emission of the source. This is important because irradiance and dose are going to vary over space as well as over time. It's necessary to illuminate all surfaces of the N95, so illuminate both sides of the N95 with this minimal dose of one joule per centimeter squared, or flip the N95s mid-treatment, and if flipping is performed, it's really important not to cross-contaminate or recontaminate N95 surfaces during that process.

Finally, because UV-C only decontaminates what it can see, you need to be very aware of any shadows and creasing in the material as well as other materials that can block UV-C from reaching the respirators. Some examples of that are that glass blocks UV-C light, and cosmetics, sunscreen, and other materials deposited on the N95s, like dirt and debris, could also block the UV-C.

Now, you might be wondering why that one joule per centimeter squared dose is necessary when it's so much higher than required on surfaces. One of the answers for that is that the ultraviolet light is attenuated as it passes through the layers of the respirator material, so the inner filtration layers see a much lower dose—three to 400 times lower than is delivered to the surface of the respirator. It's really important to note that that attenuation process is highly dependent on the model of N95 respirator, so it's important to be conscious of the model that is being used and compare that to models that have been studied in the literature. The second point is that the straps are not as effectively decontaminated as the face pieces as I had mentioned previously, and so they require a secondary method of decontamination. That is thought to be because the straps themselves can twist in a way that shields them from UV-C light during that decontamination process.

The other important note is that not all pathogens may be inactivated with this minimally acceptable dose of one joule per centimeter squared, so nonenveloped viruses, bacterial spores, and vegetative fungi can all require higher doses for inactivation than viruses similar to SARS CoV-2. And so for that reason, these kinds of pathogens may not be inactivated from the inner layers of the respirator. And finally, there are a number of appropriate ultraviolet sources, but there's also a number of inappropriate ultraviolet sources that we urge caution, and I guess rigor, in choosing. So we spoke about being in this germicidal UV-C region of the electromagnetic spectrum.

However, some sources that do output this correct wavelength of light have insufficient power or insufficient uniformity in order to deliver that minimally acceptable dose during a reasonable treatment time. If we move to lower wavelengths, radiation between 175 and 210 nanometers can generate ozone, which as I mentioned, is hazardous to human health and does not go away when the lamp is shut off. And then finally, other sources of ultraviolet light such as tanning beds, nail polish, curing lamps, and sunlight do not deliver a sufficient dose of this germicidal UV-C range in order to be predicted to have a sufficient germicidal efficacy for N95 decontamination.

And so from these points, I do want to stress again how crucial it is to validate that greater than or equal to one joule per centimeter squared of UV-C dose reaches all surfaces of all N95 respirators in that treatment area using a calibrated sensor that is specific to those germicidal UV-C wavelengths. Next slide, please.

And so, to summarize, the literature evidence indicates that ultraviolet light in that germicidal region at this minimally acceptable dose of one joule per centimeter squared delivered to all N95 surfaces inactivates viruses similar to SARS CoV-2 on most N95 models. But there are some limitations and caveats that we discussed such as the model-to-model dependency, the fact that the straps likely require a secondary decontamination method, and that not all pathogens will be inactivated at this dose. And some of the important implementation considerations that we discussed include a careful dose validation with a UV-C-specific sensor as well as a robust industrial hygiene workflow supporting a return-to–index user system.

Hydrogen peroxide approach  (00:34:52)

Jill R. Crittenden: I would like to thank everyone for attending today and particularly for your important work on the front lines and protecting us, all of us, from this common enemy. I got involved in this because I work with viruses and bacteria in the lab, nonpathogenic forms. And when my laboratory closed down because of the epidemic and my friends were on the front lines in the hospital, I joined two groups that were involved in N95 decontamination because of the realization that my friends and you are required to reuse N95s in the absence of the availability of new ones, which is what we all hope for in the near future.

Today, I'm going to talk about hydrogen peroxide, which is a well-known sterilant. Some advantages of hydrogen peroxide are that it's a very powerful sterilant that's widely used in hospitals, and it has the ability to be used in many hospitals that already have the machines for delivering hydrogen peroxide to sterilize medical instruments. A major disadvantage is that it generates dangerous vapors, and so it needs to be used with caution, both in the decontamination process where it needs to be applied in aerated rooms, and also to be sure that the N95 masks that are going to be breathed through are completely aerated and free of hydrogen peroxide vapors that could be a respiratory hazard if breathed in.

So in the talk today I’ll describe the method of hydrogen peroxide decontamination, examples of how it's currently being implemented in hospitals to decontaminate and reuse N95 masks, what the primary risks and unknowns of hydrogen peroxide for decontamination of these masks are, and finally conclude. So as I said, hydrogen peroxide when it's in a bottle is not reactive. But when it's exposed to biological materials, it interacts with proteins, membrane lipids, for example the lipid coating of the SARS CoV-2 virus that causes COVID-19 is interactive, as well as DNA and RNA can be destroyed by interacting with hydrogen peroxide.

Because when hydrogen peroxide reacts with these materials, it produces dangerous free oxide radicals and other very reactive oxygen compounds, and finally degrades into water and oxygen. So it doesn't produce materials that are damaging to the environment. In hospitals, it's often used because it doesn't require heat and so it can be used to decontaminate plastics, for example, that are heat sensitive. And it's also useful because it can penetrate very small spaces because it can be used as a vapor or a gas form, so it can get into tight-bore medical equipment with small bores.

Some disadvantages are that it's not available to everybody because it requires expensive equipment, which is now in shorter supply because this has been FDA approved as a way to decontaminate N95 masks, and it also requires trained personnel who know how to operate the machinery. Also, there are a number of different machines available that can be used for hydrogen peroxide decontamination and specific protocols need to be used, particularly when applying them to N95 masks that have particular features, that are different from how these methods are normally applied to surgical instruments, for example.

And so the correct protocol needs to be applied depending on the equipment that you have available in your hospital. Also, as I mentioned, hydrogen peroxide is a respiratory hazard and so, when implementing it in a new space in particular, it needs to be done in a room or a chamber that has controlled airflow so that the vapor cannot escape and damage the lungs of people in the room. And also it must be sufficiently aerated from the N95 masks before the user breathes through them. Because of this, this decontamination method requires usually hours in order to be sure that the N95s are completely aerated prior to giving them back to the users.

So this slide summarizes many of the different types of hydrogen peroxide methods in use. So for one of the most common ones, because it's currently being implemented by Battelle as a system that you can mail away the N95s to, this uses what's called hydrogen peroxide vapor or vapor-phase hydrogen peroxide, just two names for the same method. So for this system, the high-concentration hydrogen peroxide is shot into a room or a chamber, and then it condenses. The vapor condenses on the surface of, for example, the N95 masks. And when it does that, it decontaminates the surface by interacting with any viruses or bacteria that might be on the surface of the mask.

Hydrogen peroxide gas plasma, HPGP, is another method that's used. And for this it's converted into an ionized plasma, which is highly reactive with biological specimens and is very short lived. And so the advantages of this are that because it's a short-lived, toxic molecule, it dissipates more rapidly than the vapor phase does and so does not need to be aerated for as long afterwards. In some cases, it requires application of electrical field to the vapor either before or during the vapor phase to generate this ionized plasma, and when that happens may be important for whether the mask is damaged or not.

Ionized hydrogen peroxide is also employed by the SteraMist system and I'll describe the application of that in one of the hospitals. So all of these methods have been described in papers and I'll show some examples of that.

A dry hydrogen peroxide vapor as opposed to the wet hydrogen peroxide vapor is used by the STERIS system and is known as vaporized hydrogen peroxide. This differs from the HPV BPHP Battelle system or Bioquell system simply because the vapor is simultaneously dehydrated. And so it, too, does not take as long to dissipate from the masks because they're simultaneously being dehydrated of the vapor so they don't get as wet.

The last two methods are known as aerosolized hydrogen peroxide. So it's just a larger droplet size than for the vapors. So for these, a nebulizer is used to shoot the hydrogen peroxide into the air and then similarly those droplets settle on the mask surface and decontaminate it. And this is a very effective method because the hydrogen peroxide is so saturating that it has a very high kill power.

So here I just wanted to highlight the methods that I'm going to go over. So I'd like to describe three of those methods. The Bioquell Clarus system, which is done in house because many places have these machines in their buildings and this is the wet hydrogen peroxide system. The same system is used by Battelle where you mail out the masks to be decontaminated. The SteraMist system has been described at the University of Iowa and Brigham & Women's Hospital in Boston, and both have published on this method where they use either a chamber or a room that has already been set up with nozzles that spray the ionized mist into the room. And also the STERIS system, which has been described in a preprint by the Mass General Hospital in Boston, and this is the dry hydrogen peroxide vapor that's typically used in biosafety cabinets.

So this is a picture of the Battelle system. So to use this system, it's important to start collecting masks right away, I'm told by hospital personnel that are using it, because your inventory is very important. And so it's important to have an inventory that you can ship away so that you still have some available in the hospital to use while these are sent out by a biohazard delivery service to the Battelle system, where they can decontaminate as many as 80,000 masks at one time. As shown here, they're put in the open air and exposed to this vapor. And in the upper right hand corner you can see an example of the PPE that's required for people who are in that room with vaporized hydrogen peroxide.

This shows an example from the Duke University Medical Center publication of their method for using the same Bioquell wet hydrogen peroxide vapor. And so this gives you a sense also of what is necessary in order to send away the N95 masks to Battelle. And an example of that will also be on the N95DECON site. And so the masks need to be collected, they need to be shipped in a truck to the facility that has the rooms or large chambers for the hydrogen peroxide vapor decontamination, the masks need to be labeled to know where they came from, particularly if they're going to be returned to the index user. In some cases, they are returned to the index user, in other cases they are not. And then they're exposed to the decontamination process at the facility and they're quality checked, which is an important aspect of it—to be sure that they don't have a lot of Vaseline or makeup on them, for example, or any rips or tears—and then redistributed to individuals and retested for a seal to be sure that, if they're not returning to the same index user, in particular, that the new user still has an effective seal on the face.

This is an example of the STERIS system, and so these systems in fact can be rented and operated by safety-trained personnel and hooked up to biosafety cabinets. This system has been approved by the FDA for return to the index user only. And because it's not shipped away, it can have a shorter turnaround time than the Battelle system, for example, and cannot process very many masks at once. So, maybe as many as 100 masks can be processed at once in a large a biosafety cabinet.

This shows an example of the system being used at Brigham Women's Hospital where they're using a SteraMist that they already had set up in the hospital. You can see the room where it's being applied that has a nozzle. In fact, it has several nozzles that shoot the vaporized mist into the room, and before it's shot into the room, it's exposed to electrical frequencies to generate the highly reactive hydrogen peroxide gas plasma as opposed to the vapor is converted to plasma before it shot into the room.

And in this system, they put bacterial spores to ensure that they were getting good sterilization under the masks located in the various areas of the room, which is an important aspect to ensure that everything is decontaminated, and that is also part of the Duke process. They don't return the masks to the user until it's been confirmed that the spore-forming bacteria, which is a very hardy model for a pathogen, has been completely destroyed in that particular exposure of the N95 masks.

So, just to conclude, there are a number of different hydrogen peroxide decontamination methods that are available in different hospitals. It's important to read new research findings about them to see which masks they're most effective with, and what particular concerns might be. These FDA emergency use authorizations are changing rapidly. I believe there are now five different methods approved by the FDA that use hydrogen peroxide decontamination. So, it's important to keep an eye on what you have available in your facility, and whether it's FDA approved, and how it's approved. For example, how many decontamination cycles are possible with that method versus other methods? It varies depending on the particular hydrogen peroxide method that you're using.

You can check our website for the SOPs links to references of the SOPs that are being used by hospitals for these different methods, including the examples that I gave. And so, for each hospital it's important to evaluate what machinery you have available, what expertise you have in operating the machinery with the appropriate safety, and protocols for application to the N95 mask decontamination. Understanding the process limitations, for example, the number of times that it can be reused, and how much stockpile you need for being able to ship them away, or returning to index user.

It's important to confirm decontamination in all cases. And one particularly useful resource here from the NIST, that I've linked at the bottom, provides a checklists so that you can determine if you're going to be setting this up anew in your facility, how long the decontamination needs to be done for. For example, rooms that have absorbing materials like carpets, or absorbing portions of the ceiling may absorb some of the hydrogen peroxide and, therefore, require longer decontamination and aeration cycles.

Q&A (00:50:48)

Amanda Benedict: As we pivot into this portion of the webinar, I want to remind everybody that this session is intended to be informational. We're not intending to provide directives, or recommendations for practice, but rather points of consideration for your decision-making. And to get us started on question and answers, the first question to the panelists is related to UV-C.

If we're talking about N95 surface decontamination, why would surface UV protocols not be effective on N95? (00:51:27)

Samantha M. Grist: The reason why we talk about using higher doses for N95 decontamination is because we, as much as possible, want to inactivate virus, and other pathogens throughout the full volume of the N95 respirator. And so, typically these viral studies involve extracting the virus by immersing pieces of N95 respirator in a viral media. And so, what the assay reads out at the end is active virus from throughout that N95 respirator. And so, as much as possible, we do want to inactivate the virus throughout that volume and because of the UV-C attenuation as it travels through the respirator, that requires higher doses.

Is it necessary to you use the secondary method to decontaminate the straps when using UVGI [ultraviolet germicidal irradiation]? If the straps are hung up on a frame, not twisted, is that sufficient? (00:52:40)

Samantha M. Grist: Even when the straps are hung up on a frame, they can potentially twist, as well as the points that make contact with that frame are a potential source for residual contamination. So, for that reason, some of the peer-reviewed literature evidence does suggest employing that secondary decontamination method. And potentially, also, decontaminating any hang points that the straps are making contact with just to reduce that risk of cross-contamination between respirators that might be decontaminated in subsequent cycles.

What do facilities need to do to prepare, if they're planning to use a mail-away decontamination process? (00:53:36)

Jill R. Crittenden: One aspect of the Battelle system is to have in place a biohazard transport company that can transport the masks, and also to start collecting masks as soon as possible because it might be some turnaround time before they're returned to you. And so, you want to start stockpiling right away. Also, make sure that everything is on the ground in place for Battelle. So, they need HVAC systems, they need internet, they need a site to set up. And so, you want to be sure that somebody in your vicinity is preparing the site for them to arrive.

What is known about the point impact on elastic bands given each of the decontamination methods discussed? (00:54:32)

Jill R. Crittenden: In terms of the hydrogen peroxide, one concern has been the metal points that may have toxic residue on them. People have said that they don't undergo much change in appearance. And so, those points are probably not an issue, but I don't know of particular studies that have directly addressed that.

Why are the N95s hung so sparsely? Why not fully decorate the room with higher throughput? (00:55:20)

Samantha M. Grist: There's a couple of main points that I'd like to make in response to that question. The first point is why are the N95s not packed closer together in those UV-C protocols? And the reason for that is really to mitigate any shadowing that could be introduced from one N95 to another N95. The N95s need to be exposed as much as possible to that UV-C light for effective decontamination. And that includes both the direct light that's coming from the UV-C source, as well as any reflected light. So, typically, these setups also require sort of reflective materials in the room to more uniformly irradiate the respirators and mitigate shadowing. So, that's why they're hung sparsely to avoid shadowing.

And why are they not in the entire room set-up? The reason for that is because, as I mentioned, the ultraviolet irradiation, and the ultraviolet dose coming from a source is going to be spatially dependent. And so, when you do that characterization with the UV-C sensor at the regions where the N95s will be hung, you need to characterize the irradiance throughout that field. And there will be a point at which the irradiance drops off to unacceptable levels. And so, that's why they can't be hung up throughout the entire extent of the room. That region has been characterized by careful UV-C irradiance measurements, and then the dose computed, or the exposure time computed so that the N95s that receive the lowest dose are still over that minimally acceptable dose of one joule per centimeter squared.

Another question we received is related to some facilities that are using KN95 masks. Can this decontamination information that's based on N95, can it be extrapolated to those masks, or is it very specific to N95? (00:57:51)

Jill R. Crittenden: One really important point to make about that is that the hydrogen peroxide methods are not compatible with cellulose because the cellulose absorbs the hydrogen peroxide. And so, it's harder to aerate, and also prevents hydrogen peroxide to getting to the other surfaces because it's being absorbed. And so, a key point is to be sure that you're not attempting to decontaminate any masks that have cellulose. And some masks, some KN95s do have cellulose, for example, in the straps. And so, that needs to be a feature taken into account for all N95s or KN95s.

Our last question was about the references for the calculations, particularly those that are related to UV-C transmission percentage. Is that information available through your website? Or another method for obtaining that? (00:58:54)

Samantha M. Grist: Yes. Our technical report for UV-C on the N95decon.org website does cite the literature that studied the transmission of N95 respirators. And there's two particular studies. One is a preprint and should be interpreted with caution, and one is a peer-reviewed study studying ultraviolet transmission of the different layers of the N95 respirator.

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