A few days ago, the CDC announced that all Americans should be wearing face coverings when out in public to prevent spread of COVID19.  This announcement is widely recognized to mean that masks (rather than the vague “face covering”) are necessary to prevent, or slow, additional spread of the disease.  This comes after weeks of the CDC and other authorities discouraging the public from obtaining and wearing masks, in a perhaps misguided effort to preserve resources for healthcare workers.  These early comments emphasized the ineffectiveness of facemasks in preventing transmission of SARS-CoV-2 (the virus that causes COVID19), while at the same time championing the value of these items for healthcare workers.  Many commentators and individuals at that time saw the dissonance in this paradoxical position, and many others have been quick to point out the airborne transmission potential of SARS-CoV-2.

We have known for weeks that SARS-CoV-2 could be transmitted on airborne particles, and not just through contact droplets.  Keen observers will have made the connection for themselves that some type of mask is not paranoia but prudence.  The announcement simply confirms what we have known for weeks, while simultaneously weakening faith in government management of the COVID19 pandemic.

The decision to discourage the American public from wearing respiratory protection seems to have been made in order to preserve capacity for healthcare workers.  However, this failed to properly inform the public about the nature of their risk, and failed to account for the respiratory protection already in the hands of non-medical people or on store shelves and not in hospital stockrooms.  Many businesses and workers outside of healthcare came into this pandemic with a supply of respiratory protection.  Stocks of surgical masks, dust masks, N95 (and better) respirators on store shelves were bought up almost as fast as toilet paper, despite official efforts to discourage use.  These items were never going to be available to hospital stocks in any circumstance, and discouraging individuals with access that didn’t impact hospital stocks was likely a mistake.  The early and routine use of respiratory protection by the public could have had an impact on SARS-CoV-2 spread, and could have helped to flatten the curve even further.  This would have in turn protected healthcare workers by reducing case load and exposure, or at least spreading it out enough for manufacturing to begin to catch up to the mask demand.

We can guess that it might have been so, at any rate.  It is impossible to say for certain if this alternative would have created a better outcome, and now we must live with the decisions that were made.  There are no truly good answers, and every decision comes with consequences.

Consider that the theme for this discussion of respiratory protection for SARS-CoV-2/COVID19.  There are no good answers, and every decision comes with consequences.  Welcome to 2020, a pandemic year in which we can look back at years of predictions that called for millions of face masks and respirators.  Millions that were never stockpiled, never produced, and do not exist in our time of need.  We have put ourselves in the position of having no good choices left.

What is Respiratory Protection?
In short, respiratory protection is any measure or device undertaken to prevent the inhalation (breathing in) of harmful materials.  In particular, we are interested in face coverings which offer respiratory protection.  Masks, respirators, N95s, N99, PM2.5, bandannas, face coverings, surgical masks, dust masks: What are all of these things, and what are the differences?

There are many types of masks designed to offer the wearer at least some protection from inhaled hazards in their environment.  The most common are simple dust masks, which cover the nose and mouth with a thin layer of fabric or non-woven material to help filter dusts generated during cleaning, certain types of work, or manufacturing.  The highest levels of protection are provided by masks called respirators, which come in several forms.  Let’s run all of these down in brief.

  • Dust Masks or Comfort Masks – Simple masks that provide the lowest levels of protection, filtering out only the largest of particles such as dust.  Largely for increased wearer comfort in dusty environments, while affording no meaningful protection
  • Surgical Masks and Procedure Masks – Loosely fitting, and allowing air to pass around the sides of the mask, surgical masks serve more as a physical barrier against large droplets, splashes, and sprays, than as any kind of filter.  Surgical masks are designed to protect everyone but the wearer, by blocking exhaled particles from reaching other people are surfaces.  Surgeons wear these not to protect themselves from pathogens you may carry, but to protect you from their snot dripping into your open body compartments during surgery.  According to the CDC, in medical settings surgical masks are only used to prevent spread of aerosol particles from the mask’s wearer.  They do not confer any protection to the wearer from particles from other people.  To protect wearers from pathogens from others, N95 or better respirators must be used
  • Air Purifying Respirators – Closely fitting masks which force inhaled air through a filter, to filter out the smallest of particles possible while still allowing breathing.  This type of respirator is known as an Air Purifying Respirator, as it uses filtration to purify inhaled room air.  The most common are N95 respirators, which filter out >95% of particles 0.3 microns or larger.  Other grades, such as N99, filter out closer to >99%, while still others such as P95 filter out >95% while being oil-proof.  (For a full list of respirator ratings, and more information on additional types, see Wikipedia).  There are some types of air purifying respirator which fully enclose the wearer’s head in a full-face mask, providing eye protection as well.  Some of these, Powered Air Purifying Respirators (PAPR) use forced air systems to draw air through filters into the enclosed head-piece
  • There are additional categories of respirator called Air-Supplied Respirators, which amount to a self-contained-breathing-apparatus that provides purified air from a canister or supply, rather than drawing room air through a filter.  For the purposes of this article, we are going to be discussing Air Purifying Respirators, and specifically filtering face-pieces
  • There are other types of filtering face-pieces called pollution masks, which are relatively uncommon in the United States but very common in some other countries.  Some of these are little more than a Comfort Mask, while others are often a washable close-fitting fabric mask, with disposable filter inserts.  These masks are often marketed as PM2.5 masks, meaning they are designed to filter pollution particles 2.5 microns in size or smaller.  However, the filters used for these masks are often N95 filters, designed to filter 0.3 micron particles.  Not all pollution masks are N95-equal, however, and it’s important to know which masks of this type use filters, and which are true PM2.5, just fabric, or N95 or better.  Many pollution masks also cannot pass fit testing, and provide ineffective filtration 
  • (Important note: Although many sources use the terms interchangeably, respirator and ventilator are not the same thing.  A ventilator is a device used to push air into the lungs of a critically ill patient.  A respirator is a filtering device that someone breathes through, to protect themselves from the finest of inhaled particles)

For our purposes, we are going to skip over respirators that fully enclose the face, and focus on respirators which cover the nose and mouth, called half-mask filtering face-piece respirators (FFR).  FFR respirators can come in different forms, such as the classic N95 respirator mask intended to be disposable, and rubber half-mask face-pieces with removable filter cartridges (elastomeric respirators) designed for multiple uses.  Our primary focus here is on single use filtering face-piece respirators and fabric masks that can offer filtration.  Many things in this article will apply to the cartridges of elastomeric respirators as well, however.

The ideal among all of these types of masks, for protection against SARS-CoV-2, is an N95 (or better) rated filtering face-piece respirator, that properly fits the wearer.  To work, the respirator must have a close, tight, fit to the face that does not allow any air to pass around the edges of the mask.  All inhaled air must pass through the filter, for the filter to protect the wearer.

There are some design differences between these types of FFR’s that are worth noting.  Many disposable N95 masks have a valve in the center of the mask, that allows exhaled air to directly exit the mask.  This is a one-way vale that seals during inhalation. Strap design is also important, as dual-strap designs are the most effective at sealing against the wearers face.  Single strap designs have more potential for improper fit. 

In ideal circumstances, an N95 or better respirator should be properly fitted to the individual wearer in a process called fit testing. During the COVID19 pandemic, many users are not going to be able to receive a proper fit testing. Please see the section on respirator fitting and wear later in this article.

Risk Attenuation
Respiratory protection is used to reduce the inhalation risk of harmful or infectious particles, to the individual wearing that protection.  We must recognize that there are different levels of need, based on the risk of exposure to harmful particles.  At this point in the game, the average person is confronted with two distinct possibilities that should provoke the use of respiratory protection.  Possibility one, any person, surfaces, or air they interact with outside the home could be infected or contaminated with SARS-CoV-2.  Possibility two, they are an asymptomatic carrier of (or, not yet symptomatic with) SARS-CoV-2.  In the first case, the use of masks or respirators is to protect the individual from infection.  In the second case, it is to protect anyone around, or who comes along behind, the wearer from infection.  It is this latter case that the CDC is focusing on in their recommendation to all Americans to wear a facial covering or mask.

Moving from the realm of possible into probable, healthcare workers are faced with the greater threat of exposure to SARS-CoV-2, where many of them can fully expect to have an infected patient directly in front of them, or in close confines in their shared air, on a typical day at work.  Their risk is significantly greater, because of the environment.  The infected they encounter aren’t moving through a space briefly, nor are healthcare workers themselves highly transient.  They are encountering infected people at a higher rate, in a more confined setting where the infected have more time to deposit viral load into the space.  Along with this comes a greater likelihood of droplet transmission, as infected sneeze and cough not just into the shared space, but directly in the physical workspace of care providers.

The risk level informs what we need from respiratory protection.  The average person needs little more than protection from incidental exposure in the process of going about their routine.  Those dealing with the public in closer quarters on a daily basis, from retail workers to law enforcement, need more from their respiratory protection.  Healthcare workers, facing the highest (almost guaranteed) risk need the highest levels of protection available.  Home caregivers need a similar level of protection to healthcare workers.

Crisis Capacity Strategies for Use of Respiratory Protection

In an ideal world, we would have enough N95 (or better) available that everyone could have a sufficient supply.  Obviously, that is not the case.  Filtering face-piece respirators are in short supply, if available at all, and are likely to remain so for the duration.  Stocks on store shelves were depleted quickly, and hospital systems have been picking up what they can from conventional and unconventional sources (while, at the same time, not taking up offers from the firearms industry to supply more equipment, including respirators). 
With the pandemic having critically strained the capacity of existing stocks of respiratory protection, health authorities have been investigating optimal strategies for extending the existing reserves of N95 and other masks.  Many efforts are being made to reduce the amount of masks required by reducing patient contact and infection risk through various controls, such as telemedicine use and patient cohorting.  In the environments where patient contact still must happen, there are two leading respiratory protection conservation strategies currently, extended use and reuse.

Extended use is the prolonged wearing of one properly fitted N95 or other filtering face-piece.  This means wearing the same mask over a shift, through multiple patient contacts, either without removing it until the end of your shift (or of your outing from your home) or with careful doffing and re-donning procedures (which are iffy, and repeated doffing and donning of the same FFR has been shown to cause fit issues).  Whereas in conventional use, a new N95 would be worn for each patient contact, crisis shortages make that untenable, as supplies would be quickly exhausted.  Extended use, the wearing without removal, of N95s and similar relieves some of the pressure on the stock of masks.
Reuse is the decontamination and return to service of N95 and similar masks after they’ve been worn.  This has been proposed and evaluated in the past for pandemic scenarios, with COVID19 bringing new focus on solutions to allow it.  Reuse following disinfection can be done up to 20 times with some of the available decon methods (discussed in the section below), and may go even further than extended use alone to preserve stocks.

Reuse without extended use will rapidly deplete masks, at least in the short term, as individual masks may be used at a faster rate than they can be decontaminated.  Extended use without reuse decontamination removes one mask per user per shift, depleting the inventory until it can be restocked.  Many institutions seem to have opted for a combination of these solutions, mandating extended use and then cycling each mask through decontamination.  Although we have heard reports from several individuals that their institution can’t support even this, and is pushing extended use out across multiple shifts without decontamination in between.

Many healthcare workers, first responders, and others who are regularly risking exposure to COVID19 are wearing a cloth mask over their filtering face-piece during extended use, to prevent the worst of heavy contamination from affecting their mask. For those who have the least resources, the final crisis capacity strategy is the use of homemade masks from fabric or other ad-hoc materials.

If you have the choice, N95 or better should be your first choice no matter your risk profile.  We aren’t here to say that anyone should risk their own well being by sacrificing their N95s (though if you are hoarding, you’re an asshole).  If you have N95’s and have chosen to donate them, we absolutely support you and laud your decision.  However, if able to choose, no one should feel bad for choosing the best option.  This is especially true for people at the highest risk of serious infection, even if they aren’t healthcare workers.

For most of us who didn’t come into this well stocked, or who are running out of stock, our options are narrowing to fabric face masks, primarily DIY efforts.  That is also becoming the situation for many healthcare workers.  Many hospitals have been reduced to reusing N95 respirators to extend their stocks, or because their stocks are already depleted.  Various hospitals, researchers, and companies are rushing to develop methods for decontaminating used respirators, to keep the limited stock functional as long as possible.  Many decon methods are extremely damaging, and nearly all of them cause at least some degradation.  N95s and the like were never meant to be reused.  The best systems we have come up with so far can only get about 20 uses out of them, and they decrease efficiency with every cycle.  When those respirators, never intended for reuse, finally become too degraded, what replaces them? DIY fabric face masks.

Fabric and DIY Masks
Starting in mid-March, hospital systems and other official groups began calling for donations of fabric masks from their communities, for use in keeping with the CDC’s guidelines for shortages of masks, where untested and homemade masks are the very last tier.  Deaconness Health was the first we observed, putting out not just the call but a pattern and instructions for making a simple surgical mask style fabric mask.  Many individuals had already begun making masks, or talking about it at least, due to already evident shortages.

Around the same time, a study started being spread around social media that suggests that cloth masks cannot provide protection from infectious particles, and may in fact increase infection risk.  While the data is worth considering, especially the findings about how moisture effects filtration efficacy of cloth, it is also important to note, the study is terribly designed.  It never even asks (or answers) what kind of cloth they’re talking about, and speaks as if all cloth (or means of constructing a cloth mask) are the same for dry filtration.  Further, the study was funded by 3M, perhaps the largest manufacturer of N95 respirators and other types of masks.  Now, we love 3M and do business with them regularly, but the conflict of interest disclosure for this study has 3M all over it.  This is, in the trades, what they call “a clue”.

Now, nothing other than a properly fitted and properly used respirator is going to offer truly good levels of protection.  However, as the COVID19 situation deepens, that has become less of an option not just for individuals, but for many healthcare workers as well.  We are still under 1,000,000 cases in the US, and many systems are already completely out of proper respirators, and turning not just to commercial surgical and fabric masks, but calling for donations of homemade fabric masks as well.  This situation has been long predicted by epidemiologists and others who study epidemics and viral diseases.

The study linked above is not the only work done to evaluate the efficacy of cloth masks, or homemade masks.  These papers should be looked at together, and balanced against one another.  One 2013 study evaluated homemade masks, primarily from the view of preventing patients from spreading influenza during a pandemic.  This study evaluated different materials, and then a single mask design made of one material.  The materials evaluation is particularly useful information.  Their results on the fit of different materials are particularly interesting: Vacuum cleaner bags are too stiff to form good face masks (though that doesn’t negate potential for making filter inserts from them), while more comfortable materials such as double layers of tea towel displayed similarly high levels of filtration efficiency.  They chose a homemade surgical mask style, rectangular, design for their test masks, constructed of t-shirt fabric.  This may have been a poor choice, as this design is one of the worst fitting among several we have tried recently (see more details further down this post), The study concluded “An improvised face mask should be viewed as the last possible alternative if a supply of commercial face masks is not available, irrespective of the disease against which it may be required for protection.  Improvised homemade face masks may be used to help protect those who could potentially, for example, be at occupational risk from close or frequent contact with symptomatic patients.  However, these masks would provide the wearers little protection from microorganisms from others persons who are infected with respiratory diseases.  As a result, we would not recommend the use of homemade face masks as a method of reducing transmission of infection from aerosols.”  Again, this is based on a potentially poor mask design, but it reinforces the notion that, no matter how effective, homemade masks are a last resort.

That 2013 study references a 2008 study from the Netherlands, that also evaluates homemade masks against professional masks.  The principal finding of this study was “All types of masks reduced aerosol exposure, relatively stable over time, unaffected by duration of wear or type of activity, but with a high degree of individual variation.  Personal respirators were more efficient than surgical masks, which were more efficient than home-made masks.  Regardless of mask type, children were less well protected.”  Again using an influenza pandemic as the example, this group researched homemade masks from tea towels against both surgical masks and N95 type filtering face-piece mask.  Particularly interesting in this study, is that they researched the performance of the masks both in short duration wear and several hours of wear.  They concluded “It is also clear that home-made masks such as teacloths may still confer a significant degree of protection, albeit less strong than surgical masks or FFP2 masks.  Home made masks however would not suffer from limited supplies, and would not need additional resources to provide at large scale”, while also noting that “Home made masks, and to a lesser degree surgical masks, are unlikely to confer much protection against transmission of small particles like droplet nuclei”, but that the reduction in transmission afforded could be critical none the less.

A 2010 study examining different materials that could be used in cloth masks, found as much as 60% protection but also as little as 10%, depending on material and particle sizes.  They noted that “fabric materials tested in our study might also be expected to provide marginal levels of respiratory protection for 20–1000 nm aerosols (droplet nuclei).  Fabric materials may provide respiratory protection levels (i.e. total inward leakage) similar to the levels obtained using some surgical masks […] Thus, the use of improvised fabric materials may be of some value compared to no protection at all when respirators are not available.  Moreover, fabric materials would not suffer from limited supplies unlike respirators and surgical masks for emergency protection”.  It’s important to read the whole paper, as “some value” is, without a doubt, less value than a proper respirator.   The authors say, “The use of fabric materials may provide only minimal levels of respiratory protection to a wearer against virus-size submicron aerosol particles (e.g. droplet nuclei).  This is partly because fabric materials show only marginal filtration performance against virus-size particles when sealed around the edges.  Face seal leakage will further decrease the respiratory protection offered by fabric materials.”  This issue of leakage, as created by a poor fit, is important, as many improvised/homemade mask designs are not tight fitting to the face. It’s also worth considering that this paper relies on tests done with single layers of fabric.

The importance of proper fit, and potential value of multiple-layers (and different types of fabrics) is highlighted in this review from the International Journal of Infection Control which looks at several different papers (including those above) and provides both historical analysis of cloth mask usage, and suggestions on what approaches work best, as well as pointing out areas for further research.  In looking at the available data, the authors of this paper have this to say “Three factors were highlighted in these studies in regards to the filtration capacity of a cloth mask: 1) closeness of the gauze/cloth threads; 2) number of gauze/cloth layers and 3) type of gauze/cloth.  Generally, the filtration capacity improved when the number of threads increased in the gauze and the mesh become finer compared to course [sic] gauze with lower thread counts.  Similarly, the number of layers was found to be directly proportional to the filtration capacity in most of the laboratory studies.  In these studies, the filtration effectiveness significantly improved with increasing the number of layers in the mask.  Certain types of cloth provides better protection than other; e.g. fine muslin (loosely-woven cotton fabric) was better than the gauze, gauze padded with cotton were better than simple gauze or paper masks and towels were more effective than other fabrics.  Cloths masks were generally found to be effective against large particles (>4 um), however some evidence exists against small particles as well.  Presence of moisture, distance traveled by the droplets and the design of mask were some other factors affecting the filtration capacity.  In summary, the filtration capacity of wet masks has been reported as being lower compared to dry masks.  The distance traveled by the droplets is associated with the filtration capacity and filtration capacity is generally decreased by decreasing distance”.  These suggestions could be used as the beginnings of a guideline for producing homemade masks for in extremis use, recognizing their inherent shortcomings: Tightly woven fabrics, multiple layers, and thicker/denser fabrics.  This also points out that moisture saturation, as from exhaling, can compromise the already limited efficacy of the masks, suggesting that masks should be rotated often for clean, dry, ones.

While woven fabrics are more accessible to most home-sewers, there is evidence that non-woven fabrics are more ideal for creating masks.  Non-wovens are used in the production of filtering face-pieces and other filtering materials such as sterilization wrap and HEPA filters, and have a great ability to capture viral particles than woven materials.  Non-wovens are also often hydrophobic, meaning they resist saturation with moisture which could transport viral particles across the barrier. 

Doctors have telling people in some parts of the country to use/make masks with a pocket for inserting a filter to be cut from HEPA-filter vacuum bags (as described in the 2013 study linked).  Some doctors are even making their own.  Other mask designs call for the use of PM2.5 filters commonly used in pollution masks.  Yet others simply use dual layers of fabric, as suggested by the available data.

Recent innovations, that appear to have started at the University of Florida, have suggested using a product called Sterilization Wrap to make masks from.  This is a nonwoven synthetic fabric that is used to wrap instruments and other reusable medical equipment prior to sterilization, which stays on both through and after the sterilization process.  It stays on because in layers it serves as a barrier against pathogens, keeping the instruments within sterile.  There is reason to believe that, when properly used, it will function as a better filter material than cotton or any of the suggested fabrics for making homemade protective masks. UF doctors have told the media that filtration provided by “steriwrap” equals that of N99 mask material.  There is a paucity of data on steriwrap material for use in masks, but it is a well known barrier for preventing contamination of sterile instruments.

Sterilization wrap is a synthetic non-woven material, typically either identified as SMS or SMMS standing for Spunbond-Meltblown-Spunboud or Spunbond-Meltblown-Meltblown-Spunbond.  Spunbond fabric is created by fibers of polypropylene being spun and dispersed into a web by directed airstreams and then thermobonded.  This creates a strong, but soft and flexible, fabric.  Meltblown fabric is created by forcing molten thermoplastic through a die containing multiple tiny holes, as it is blown by heated air, to create a nonwoven web of extremely fine self-bonded fibers.  Meltblown is fairly delicate.  SMS or SMMS fabrics are a layered fabric, with Spunbond on the exterior and one or two layers of Meltblown on the interior.  This creates a soft, breathable, moisture repellent fabric that has excellent filtering properties.  Excellent enough to be used to wrap sterile instruments, and keep them that way.  Excellent enough that the anesthesiologist at UF who has spearheaded the creation of masks from sterilization wrap has said that two layers of SMS/SMMS fabric is equal to N99 respirator material.  This is the most promising ad hoc mask material we are aware of, that is readily accessible.

Sterilization Wrap and Tin Ties (for Nose Pieces)


There are many designs for homemade face masks.  In recent days many patterns have been made available from different sources.  Some are good, some are terrible, and none are perfect.  We have been experimenting with homemade mask designs, with the help of a seamstress, and have found that all of the designs we’ve looked at needed some tweaking.

Some designs fit better than others.  Classic surgical mask style rectangular patterns have been the least successful, with poor fit, more slip, and less comfort than face contouring designs.  Pleated surgical mask designs are somewhat better, as they expand to offer more appropriate coverage and contour to the face.  Contoured designs work better overall.  Many patterns needed to be adjusted to give full coverage to adult wearers.  The design must extend over the nose, and underneath the edge of the wearers chin, and fit tightly along the entire edge, to offer protection.

Commercially produced masks and respirators often have a nose-piece, a flexible aluminum strip that can be bent to hold the mask in place over the nose.  Most DIY designs lack this element, and provide no measure for achieving the same fit without it.  Consequently, most DIY designs gap around the sides of the nose, ruining the efficacy of the mask.  This must be dealt with, and a flexible nose-piece of some kind integrated into the design.  Some sources have proposed using copper wire, which is narrow and may not fit as well or be as adjustable as a flat malleable nose-piece.  We had our best success using tin ties (commonly found on coffee bags, to close them after folding the top down) cut to length and sewn inside the edge of the mask across the nose.

Without and With External Tin Tie Nose-Piece

The means for holding the mask to the face have required refinement as well. Elastic ear-loop designs made with flat elastic have proven uncomfortable, or unstable, for extended periods, often popping off the ears. Using 2mm hair-ties proved more effective for both comfort and retention than sewn loops of flat elastic.

Hair Tie and Flat Elastic Ear Pieces

For prolonged wear, however, any ear loop design is going to cause discomfort and possibly injury to the ears.  An “ear saver” can be made that attaches from the back of one ear loop to the other, distributing force across the back of the head instead of the ears, without changing the mask fit.  Several designs for these have been proposed, including 3d printed adjustable designs.  We expirimented with using simple ties of soft shoe-lace material, which worked, and with making a simple formed Kydex (thermo-formed plastic) piece consisting of a narrow (1/2” or so) strip of Kydex with each end curled over into a hook.  The Kydex piece worked best of the two.

Kydex Ear Saver

Single strap (elastic or tie) designs do not fit the face as well as dual strap designs.  A dual strap design that crosses behind the head, with the upper left strap connecting at the lower right and vice versa,proved very stable, but the most difficult to don and doff safely.  Dual straps that route straight are the best fit, for the easiest/safest handling. 
As we have gone through the process of refining this, another issue has also emerged: An elastic shortage.  Stores are sold out, online retailers are back-ordered, as homemade masks have begun to be churned out en masse.  Using hair ties has partially relieved this issue, for now, but those are getting more difficult to purchase as well.  Moving to a design using upper and lower ties of bias tape, strong ribbon, or similar material would resolve the issues presented by this shortage.  These have the advantage of being easiest to fit to individual users, but as they are not providing the same active tension as elastic they requiring more careful donning.

There is no good substitute for proven N95 (or better) face-piece respirators.  All of the “solutions” proposed to combat this crisis are the lesser of multiple evils, but are absolutely not an ideal and shouldn’t be anyone’s first choice where a choice exists.  This has to be absolutely understood, but it doesn’t change the circumstance we find ourselves in where these homemade (or industry made) fabric mask alternatives are the best of bad choices, the only thing left.

However, some mask designs are worse than others.  There are many DIY patterns being offered right now by sewing blogs, healthcare organizations, employers, etc., and there are many homemade and small business made masks being offered for sale right now, very suddenly.  What most of these have in common is that they aren’t going to protect you.  Many of them are made with single layers of material, or are made with the wrong kinds of material.  Many of them are poor designs which do not create a tight seal against the face, but instead leave gaps around the nose, on the cheeks, or around the chin.  While folks should be applauded for trying to help, many of these DIY’ers and small businesses aren’t helping – They’re selling false confidence.  While these simplest, thinnest, worst fitting of masks might help an infected person from spreading the SARS-CoV-2 virus, even that is in doubt when thin single layers, and large gaps around the side, can allowed expelled particles to escape.  If you endeavor to make your own mask, or you go to purchase already made masks from someone, please be aware of these kind of shortcomings, and of the intended use, and make appropriate selections.

Based on the available data, these are our internal recommendations for DIY face-pieces with at least some filtration capability:

  • Find or make masks (plural) that are made of multiple layers of recommended fabrics, ideally sterilization wrap (at least two layers).  Or, find/make masks (plural) that can use filter inserts and stock up on those inserts either by purchasing or making them (from sterilization wrap or HEPA bags)
  • Ensure that the masks are a contouring design, which has dual straps or ties, and a flexible (moldable) nose-piece, to get the closest fit possible
  • Wear the mask properly, at all times
  • Do not touch the mask while wearing it
  • Take precations handling the mask, especially when doffing it after wear, to avoid touching the outside.  Doff the mask by handling only the elastics or ties
  • Wash your hands before removing your mask
  • Rotate masks throughout extended periods of wear (this is why multiple masks is recommended) to prevent saturation of any one.  Especially with woven fabrics, a wet mask is not a filtering mask.  Two – four hours seems to be the limit for woven fabrics, before materials are saturated.  Remove the worn, contaminated, mask safely, and then throw away any filter insert (if they are’t being reused), and move the mask to a closed container to be washed/deconed
  • Wash your hands after doffing and storing a used mask, and before donning a clean mask
  • Store clean masks in a container which provides a barrier against transmission. Store dirty masks in a separate container which also provides a barrier

And, to be thorough, here is what we recommend against:

  • Single layer masks of any material
  • Masks without any filtering capability
  • Masks that do not provide a tight seal to the face
  • Masks made from bandannas, shemaghs, scarves, etc. that confer no protection to the wearer
  • Single strap/elastic masks
  • Touching the front of your mask
  • Scratching underneath your mask
  • Wearing your mask below your nose, or above your chin
  • Rewearing un-decontaminated masks
Tight Woven Lining and Tight Woven Lining with Filter Pocket

Decontamination of Commercial and DIY Filtering Face-Pieces
As the COVID19 crisis has deepened, reuse of masks has emerged as an obvious answer to shortages, but once you get past wearing (and not removing) one mask all day, they can only be reused further if they can be decontaminated.  This has received some study in the past, with an eye toward pandemic preparedness, but is getting far more attention now. 

Different methods have been proposed, and are being adopted by healthcare systems and various end-users, as possible.  The overall goal of these methods is not to sterilize the masks, but to decontaminate them of SARS-CoV-2 virus and reduce the infection risk, while maintaining their structural integrity to preserve proper fit.  True sterilization may be achieved by some methods, but not all, and it is not the goal of crisis capacity decontamination strategies.

The CDC is now providing rough guidelines for decontamination processes that hospitals can consider, as well as on what to avoid doing.  The CDC guidelines give the most credit to systems that aren’t going to be available to many individuals, and might even be a struggle for some hospitals, such as ultraviolet germicidal irradiation and vaporous hydrogen peroxide.

Ultraviolet Decontamination – Ultraviolet Germicidal Irradiation (UVGI) is widely used in many healthcare settings already,  and low level UV sterilizers are available for water and common electronic devices, but presents challenges for use with filtering face-pieces.  Firstly, for the resource limited users (those likely to be dependent upon ad hoc solutions), the common UV water and device sterilizers are likely not powerful enough to decontaminate a SARS-CoV-2 contaminated FFR, as none of them produce a dose as high as the lowest sterilization doses.  Another issue is that not all FFRs studied were fully decontaminated by UV, particularly the elastics.  The next issue is that UV causes some degradation of both N95+ filter material, and of the elastics.  This degradation is not significant enough to rule out this method in settings where it can be done, as the degradation is largely low per cycle.  Current thinking is that no more than 20 cycles of UV decon should be performed before a mask is finally disposed of.  Hospitals that already have this resource have begun using it, and providing guidelines for doing so.  For resource limited and home users, this isn’t the most accessible technology, thoughthere are ways

Hydrogen Peroxide Vapor – This method has also been recommended by the CDC as an effective means of decontaminating FFRs.  In this process, vaporized hydrogen peroxide is circulated in a closed container at levels between 140 and 1400 parts-per-million (75ppm is considered dangerous to humans), for the necessary length of time to destroy a given pathogen.  The h2o2 is then pulled from the chamber and broken down into component water and oxygen by a catalytic converter.  This is an intensive process, requiring specialized equipment, but evidence supports its use where possible.  Some hospitals are already equipped for this process and research non-profit Battelle has received emergency authorization from the FDA to produce and deliver their own vaporous hydrogen peroxide system, something Battelle has worked on for several years.  These systems are going to be delivered to several states, but realistically will not be able to be produced in enough numbers to serve every institution.

Other methods of decontamination that have been suggested, which might have more meaning for resource limited and home users, are microwave steam, steam, boiling, and both moist and dry heat.

Microwave Steam – Microwave generated steam has been proposed as a method of deconing filtering face-pieces.  Much like steaming some vegetables in the microwave this method is simple, requiring only a microwave and a container for water that allows steam to escape directly onto the mask.  Microwave generated steam has proven successful in studies but, it does not come without risks of damage to the mask.  In at least one study, microwave generated steam caused damage to FFRs.  Another study, using microwave steam bags was more successful, and reported no significant change to filtration performance.
Even if effective, this method will only work with FFRs which do not have any metal components, such as nose-pieces or elastic attachments.  This rules out its use for many designs, especially the homemade designs we have proposed.

Warm Moist Heat – This method uses heat and intermediate humidity to inactivate the virus.  As discussed in this paper from N95 Decon, viruses have been shown to more readily deactivate at intermediate humidity values than at either high humidity or low.  The decon concept is simple, the masks to be deconed are “baked” at a temperature high enough to inactivate the SARS-CoV-2 virus but low enough to not damage masks (65-80C, roughly 150-175F), along with a moisture source that provides humidity and evaporation.  It is suggested that a 30 minute soak at those temperatures, with intermediate humidity (50-80%), is sufficient to inactivate the SARS-CoV-2 virus.  The low end of the temperature range is enough to deactivate the SARs-CoV-2 virus and the high end is the limit most N95’s can tolerate.  The CDC’s guidelines recommend 15-30 minutes at 60C with 80% relative humidity, based on successful inactivation of H1N1 virus.  Other sources have suggested a design for a chamber to provide warm moist heat, which consists of an enclosed box, partially filled with water, with a rack to hold the masks to be decontaminated above the waterline. 

Steam – Actual steaming has also been considered.  The previously cited work by Dr. Tsai at the University of Tennessee says that steam decontamination of masks at 125-degrees C for three minutes has an unnoticeable effect on the electrostatic charge of N95-type masks.  InstantPot brand pressure cookers have been getting a lot of attention recently for this use, with support for the idea that they are a superior improvised method to other types of steam pressure cooker.  However, studies done have pointed out that the temperatures used maycause other physical damage to N95 masks.  3M recommends against steam for decontaminating N95 masks, due to damage caused by the temperatures.  Temperature used may be key, as a study from the Netherlands suggests that slightly lower steam temperatures did not reduce effectiveness of the masks used.  However, aStanford review of decontamination methods found that even if initial damage wasn’t found, more than five steam cycles degraded the mask too much. 

Oven/Dry Heat Decontamination – This has been suggested for various filtering face-pieces, as a means to decon them for reuse.  Many hospitals are setting up large scale dry heat decontamination systems (i.e. ovens) to decon a days worth of used N95’s at once.  It has been suggested that this is a viable means for home decontamination as well, though concerns have also been raised.

One study evaluated using a rice cooker, without water, to provide dry heat decontamination.  They found that no decrease in filter performance arose from the cycle they used.  For this method, heat should be within the same ranges previously discussed for warm moist heat, between 60 and 80 degrees Celsius.  Higher heats will damage masks and decrease filtration provided. 

To decontaminate an N95 or mask of SARS-CoV-2 you need to soak it at around 160-degrees Fahrenheit for 30 minutes (158F, or 70C, destroys SARS-CoV-2 virions) and the soak time lets the heat reach deeper parts of the material). This is slightly detrimental to the face-piece, although the degradation per soak has been determined to be low when done properly.  Cumulatively, this 1-2% degradation will add up, however.  The number being tossed around for this decontamination processes (as with some others) is that it allows for up to 20 uses of a single mask, before it is unacceptably degraded.  For DIY masks, this point may be reached sooner, or later, depending on the materials used, and we don’t have good data to say either way.  We can probably safely assume that masks made from non-woven fabrics like sterilization wrap will have similar properties to N95’s in this regard.

In the oven, masks should be suspended with a heat safe clip, so that they are not resting against any metal components or racks of the oven.  Direct contact with the metal can cause distortion of the materials as heat is concentrated in the area of contact.  Free hanging allows heat to evenly soak into the mask at the set temperature. 

There is a concern about oven decontamination at home spreading infection, and health authorities are telling people not to decon masks or N95’s at home.  This is largely an attempt at covering their ass in case of misuse of their recommendations leading to infection, but there may be a legitimate concern hidden within.  Handling contaminated masks in the home may spread the infectious particles if great care is not taken, just from handling and contact.  Further, many home ovens have a fan, that can aerosolize material (viral particles) from the surface of the mask, and push them out of the oven before they are “killed”.

We have found a few potential solutions to this problem.  One, is to use a toaster oven that has no fan (particularly if you can set that up in a garage, closed off from the home, or even outside your home).  The second solution is to fabricate a simple bag from sterilization wrap, into which masks can be dropped, without contacting the outside of the bag.  The top of the bag is then rolled and clipped closed with a heat resistant clip.  This can be done before ever bringing a contaminated mask into your home.  That package can then be inserted into the oven, suspended or elevated on a low-heat-transfer rack such as hardwood, and soaked at the 160-175 temperature range for 30 minutes without risk of anything getting out of the bag.  This creates a package that can be left intact until the next time you need your mask, and will prevent any other contamination from reducing efficacy of your mask as well.

Mask Can Be Inserted Without Touching Outside
Sterilization Bag Rolled and Clipped

The other hitch to home decon in the oven is that many home ovens won’t go as low as 160.  Many won’t go under 200, and some will only go to 170.  Many toaster ovens, however, will go as low as 160, or 170, and they aren’t terribly expensive (and can commonly be found in thrift stores for just a few bucks).  Using a toaster oven also facilitates creating a “mask decon area” that’s not in the living space of your home.  If you are using an oven that won’t go lower than 200, use of a bag as described above and cracking the door of the oven can get you into a temperature range appropriate for decontamination, but low enough to not accelerate degradation of your mask.

Heat based methods offer a lot of potential for small-scale and home users.  We encourage you to read the cited (linked) sources thoroughly, run your own searches, and devise optimal strategies from the available data for your needs and FFRs. Useful meta-analyses of this subject are being done, evaluating multiple studies and their results at once, and will be beneficial for time constrained research.

Disinfectant Chemicals – Although many disinfectants are effective against SARS-CoV-2 on surfaces, that does not mean that they will work on masks.  Simply wiping the surface of any mask with a disinfectant will do nothing to penetrate between fibers and inactivate virus particles trapped within.  A mask would have to be soaked with a liquid disinfectant to achieve proper penetration.  This is a problem, as many disinfectants can seriously damage the masks materials.

Hydrogen peroxide can inactivate SARS-CoV-2 in very low concentrations (<1%) and has been shown to be fairly safe for using to disinfect N95 masks, though one study noted corrosion of steel staples on some masks.

Bleach has been found to damage masks, rendering them unusable or unsafe to use, as well as creating concerns about inhalation dangers for wearers of the bleached masks.  Alcohol destroys the electrostatic charge of N95 (and similar) mask materials, and reduces the filtration ability to far below safe levels.  Soapy water was also found to damage N95 type materials.

Washing with Soap and Water – Air filtration company Smart Air performed testing by washing N95 masks with soap and water, and found that this damaged the material, reducing filtration efficiency by 21%.  Homemade masks of cotton cloths can be washed in this method, as long as you are gentle, without risking damaging their limited filtration abilities (so long as they are dry again when worn).  Similarly, fabric masks that take a filter insert can also be washed with soap and water, or in a washing machine, safely – The filter insert cannot be, however.

Time – Where possible, simply letting the mask sit in an isolated, dry, environment for 72+ hours is likely sufficient to inact,ive any SARS-CoV-2 contamination.  Although fabrics, and non-wovens such as N95 and steriwrap materials, have not been specifically tested, SARS-CoV-2 survives the longest on plastic and stainless steel, remaining viable on those surfaces for around 72 hours.  Allowing the mask to decontaminate in a safe place, where spread of infectious particles from the mask is unlikely/actively prevented, is unlikely to cause degradation of the mask, preserving it for further reuse, and also conserves supplies/resources used for other methods of decon.

Lower temperatures can increase virus survival, as can relative humidity below 20% and over 80%, so the ideal environment for time decontamination would be warm and of moderate humidity.  Direct exposure to sunlight may also be beneficial to inactivation of the virus on masks, as SARS-CoV-2 has displayed UV sensitivity, and solar ultraviolet has been proposed as a factor in inactivation of other UV sensitive viruses.

Whatever decontamination strategy works for your needs, you must maintain strict procedures for performing it.  Until the mask is decontaminated, it remains a transmission risk and must be treated as such.  So must any containers used for storing the contaminated mask.  Similarly, poor handling or careless procedures for decontamination can damage the mask, and render it ineffective.  Too many decontamination cycles can also damage your mask.  Institute a set of procedures for identification and separation of clean and dirty masks, and for the handling, decontamination, and return to service of worn masks.  Label masks clearly, and use tally marks to track the number of decontamination cycles.

Masks that have visible damage must be immediately thrown away, as they will not serve their purpose.  Masks that have been heavily soiled by blood or other deposits of bodily fluids, mucus, etc. should also be immediately disposed of, as decontamination methods may not penetrate heavy soiling to fully inactivate SARS-CoV-2 or other pathogens.

Proper Wear and Storage of Commercial and DIY Filtering Face-Pieces
Filtering face-pieces cannot work, will not protect you or anyone else, if they are not worn properly.  As all of this has been going on, we’ve all seen people doing ridiculous things with their PPE, but many of you could be guilty as well.  Let’s go over this and make sure we’re all getting it right.
To begin with, masks must actually cover the parts of your face used to breathe.  This means your mouth, and your nose.  Don’t be one of these chuckleheads walking around with your mask below your nose because “it’s more comfortable.” That’s not how this works, that’s not how any of this works.  They must also actually seal tightly.  To do this, they must go over the chin, and fit tightly over the nose and across the cheeks.  This means that you can’t have anything on your face that gets in the way of this seal.  Beards are right out.  Piercings that might interfere as well.  Care must be taken with long hair to make sure you don’t entrap hair under the edge of the mask, violating the seal to your face.  Yes, guys, this means you’re gonna have to shave if you’re serious about this.

In professional environments, N95 and better respirators are fitted to each wearer.  Yes, even those disposable N95’s are supposed to be fit tested.  By regulations, workers requiring filtering face-pieces need to be fit tested for the appropriate respirator annually.  This process involves using an enclosed hood worn over the head, into which a scented or flavored substance is aerosolized.  If the mask fits properly, the subject will not be able to detect the aerosolized substance (often saccharine or banana oil).  Every different model of respirator, even from the same manufacturer, requires separate fit testing.

In resource limited situations, from austere environments to crisis posture, this type of testing may be difficult to perform in adequate numbers.  Ad hoc, improvised, or homemade filtering face-pieces present a further challenge to this, as designs can have a wide variation and tolerances from handmade mask to handmade mask can vary widely.  If possible, and the provided masks are consistent enough in manufacture, fit testing should be performed.  Realistically, we can anticipate that it’s not going to be possible in great numbers.

However, it will remain critical that you individually seal check each mask that you wear.  Visually inspect each mask before wearing it, to ensure that it is free of damage, holes, etc.  When putting on the mask, ensure that the flexible nose-piece is properly adjusted for a tight fit, and that the mask is seated correctly on the face.  The edges of the mask should feel tight all around.  With the mask in place and secured, press your hands over the mask enough to block airflow without deforming it, and exhale fully. The mask should expand briefly, before allowing air to escape.  Similarly, inhale fully.  The mask should contract against the face, rather than pull air in around the edges.  You shouldn’t feel air moving past the edges of the mask.

Once the mask is in place and seal checked, leave it alone.  Don’t reach under it to scratch, don’t pull at it to adjust it, don’t touch it.  Touching it spreads contamination hands-to-mask or mask-to-hands.  Reaching under it violates the seal of the mask, spreading contamination inside and defeating the purpose of the mask.  And all of these actions risk breaking the seal and moving it out of position.  If you must adjust your mask, do so in isolation from others, do not reach under the mask, attempt to avoid directly touching the surface, touching the elastics/ties instead to pull/adjust, and wash your hands thoroughly before and after.

Donning your mask:

  • Wash your hands before handling, or donning, and clear mask
  • If using an N95 (or better), or other filtering face-piece with dual elastic straps, cup the front of the clean mask in the palm of your hand and place over your nose and mouth.  With your other hand, pull the lower elastic over your head and into place below your ears.  Repeat this with the upper strap, placing it above the ears towards the crown of your head
  • If using a mask with dual ear loops, grasp the mask by the loops, place the mask over the nose and mouth, and place the loops over each ear.  If using an “ear saver” or other comfort device, hook one end of the device into one ear loop, hold it in place, and then extend the other to loop over the opposite end
  • If using a mask with ties, grasp by the upper ties, place the mask over the nose and mouth and secure first the upper ties (to prevent the mask from flopping) and then the lower
  • Use your hands to adjust the mask, ensuring that it covers underneath the chin and over the nose, and that it isn’t folded under anywhere
  • Adjust the flexible nose-piece to fit tightly across the bridge of the nose

Masks should be removed when you are done wearing them, or when it is time to switch to another mask.  When it is time to take your mask off, you have to be extremely cautious.  The surface of the mask, during wear, may have collected infectious particles.  If you touch the surface, and then touch your face incidentally during the removal process, you’ve just defeated the entire purpose of wearing the mask.  You must avoid cross-contamination of this nature during doffing (removal) of the mask.
Here are the proper steps for removing your mask:

  • Wash your hands prior to removing your mask, to remove any viral particles from your hands
  • Reach behind your head or ears, and grasp the elastics, ties, or clip securing your mask, and unfasten them or stretch and lift them off over the top of the head
  • If using a mask with ties or elastics that go around the head, untie the lower tie or stretch and lift the lower elastic over the head first, and then remove the upper
  • Do not remove the upper first, and allow the front of the mask to flop down onto your chest/neck
  • Using the elastics/ties only, pull the mask forward off your face, and away from your face
    Avoid shaking, snapping, or violently moving your mask through the air, as this may aerosolize particles
  • Handling it only by the elastics/ties place the mask into a paper bag, steriwrap bag, or other container, and roll the top or close the container
  • Wash your hands thoroughly once more, to remove any viral particles picked up from handling the mask
  • Remove a clean mask from storage, and place it on the face, secure it, and perform a seal check while you have clean hands

Clean masks should be stored in a clean, dry, container that prevents dust, debris, or any pathogens from getting on them.  Even unworn, masks exposed to the environment can pick up pollutants or infectious material, compromising their effectiveness or safety.  If you have constructed bags of steriwrap, as described earlier, you can simply leave your masks in these awaiting use.  Masks should not be stored in containers that trap moisture, however.  This can degrade mask performance, and in the case of worn masks can preserve pathogens and increase the risk of their spread.

Masks Alone Aren’t Enough
Respiratory protection by itself is not enough to protect you from infection, from anything.  If you are not practicing proper hand hygiene, and not using other forms of PPE when necessary, your mask by itself isn’t much protection.  If you are in regular close contact with COVID19 patients, whether in a healthcare setting or caring for a family member recovering at home, you should (in addition to gloves and respirator) be wearing a face-shield when in contact with them.  Face shields, or goggles that fully seal to the face, protect you from particles expelled by coughing or sneezing, which can get into the eyes.

This is strictly a review of available literature, and none of the preceding is medical advice.  Do not take any actions without the direction of your personal physician, workplace medical director, or other healthcare authority.

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