Guidance Document for

Manufacturing Masks and Respirators for protection against

COVID-19

Updated May 21, 2020

The purpose of this document is to provide open source

guidance, resources, references, ideas, and information to

improve the manufacturing of DIY masks.

The ultimate goal is to make recommendations on best

materials and manufacturing methods for a variety of technical

and non-technical capabilities.

We welcome your collaboration. Document originators: Jeffrey Ott, Biorez Jacob Komenda, Biorez Justin Bendigo, Biorez Kevin Rocco, Biorez Document collaborators: Michael Plumley, Ph.D, P.E., US Coast Guard Academy Christopher Wiles, D.O., UConn Anesthesiology

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1: Purpose of this Guidance Document 2

2: Role of PPE & Transmission Mechanisms of COVID-19 3 2.1: Transmission Mechanisms of COVID-19 3 2.2: What is a Mask versus a Respirator? 4 2.3: How Masks and Respirators Work? 6

3: Guidance for Make-at-Home Masks 9 3.1: Purpose of Masks and User Needs 9 3.2: Overview of Primary, Secondary and Tertiary Mask Structure 10 3.3: Types of Fiber (Primary Structure) 10 3.4: Types of Fabric (Secondary Structure) 13

3.4.1: Commercially Available Material Table 17 3.4.2: Expanded Section on Materials 19

3.4.2.1: Fabrics 19 3.4.2.2: Other Materials 20

3.5: Mask Assembly (Tertiary Structure) 22 3.5.1: Design Features 22 3.5.2: Design Criteria 25 3.5.3: Published Methods of Assembly 25 3.5.4 Other Manufacturing Methods 27

3.6: Tips for Fit, Function, Cleaning & Re-Use 30 3.7: Lab Testing and Regulatory 32

4: Other Teams, Projects and Resources to Consider 35

APPENDIX A - SEM Imaging 36

APPENDIX B - Filtration Efficiency Figures 36

APPENDIX C - www.n95decon.org 43

APPENDIX D - Overflow 48 D.1: Polypropylene Background and Usage in Respirators 48 D.2: Production Techniques and Tips 49 D.3: N95 Respirator Testing Expanded 51

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Executive Summary The COVID-19 virus is primarily transmitted between people through respiratory droplets and contact routes, with airborne transmission still a topic of research. This document provides open source guidance, resources, references, ideas, and information to improve the manufacturing of Do It Yourself (DIY) masks. Discussion of progress toward development of DIY respirators is also discussed. It is intended to be collaborative. Research about the current Covid-19 pandemic is moving at a rapid pace, and this document provides current information regarding materials and manufacturing methods for a variety of technical and non-technical capabilities. Masks and respirators are key PPE for protection against COVID-19, and have different purposes. The CDC recommends that simple masks including cloth face coverings (home-made masks) be worn when in public instead of N95 respirators. A respirator’s job is to filter airborne aerosol droplets from the user’s air supply. Made-at-home masks are not intended to prevent the transmission of Covid-19 but provide a low level of protection and ease of manufacture. Careful selection of materials and methods will lead to higher quality and more effective made-at-home masks without increasing the difficulty of manufacturing. The ideal mask is easy to manufacture, tight fitting, highly breathable, traps and/or deflects particles, and is cleanable and reusable. Mask design may be discussed in terms of primary (fiber type), secondary (fabric type), and tertiary mask structure. While high thread cotton is commonly used, the best mask filters would consiste of mats of nonwoven fibrous materials, such as wool felt, fiberglass paper, and polypropylene. Nonwoven materials are dense, create a tortuous path, and adhesion of particles to the fibers without blocking open porous spaces, allowing air to flow easily. Furnace filter paper and sterilization wrap offer commercial sources for nonwoven materials, and flow properties of these are still being studied and reported in the media. Ideally, a hydrophilic outer layer (such as cotton) canl be used to absorb respiratory droplets, while the hydrophobic inner layer (such as nonwoven furnace filter or polypropylene) prevents droplets from entering the fiber and prevents the trapping of moisture. Mask structure may be created through sewn pleats or form fitted filtration material, or constructed plastic frames or hard shells which hold filter material. They are all often held by some sort of elastic. Respirators are highly regulated. As such, care should be taken when choosing an “N95 replacement”, as strict NIOSH testing procedures have likely not been carried out to ensure the same protection. Hard shelled fitted respirators require testing. Both the development of locally manufactured models through procedures like 3D printed, and methods to test such PPE, are the subject of considerable ongoing study by the DIY community and collaborators. The design space for masks and respirators is rapidly evolving as the SARS-CoV-2 pandemic is met by solutions developed in an unprecedented era of online collaboration and maker

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technology, in a race to eliminate PPE shortages in hospitals and the community. As such, this and other documents will also evolve rapidly to keep pace with innovation.

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1: Purpose of this Guidance Document Whether working in a supply-limited healthcare environment, or just going to the grocery store, we believe there should be a more scientific approach to manufacturing your own PPE. The purpose of this document is to provide open source guidance, resources, references, ideas, and information to improve the manufacturing of DIY masks. It is intended to be collaborative. Research about the current Covid-19 pandemic is moving at a rapid pace, and this document serves to represent the best of what we know of the situation in real time. The ultimate goal is to make recommendations on best materials and manufacturing methods for a variety of technical and non-technical capabilities. We welcome your collaboration. This document is intended as a primer to discuss the fundamental specifications and testing required for development of Do-It-Yourself (DIY) design and manufacturing of Personal Protective Equipment (PPE) intended to prevent the transmission of or infection with Covid-19 and similar viruses. This document is not intended to provide detailed manufacturing instructions, declare particular designs or processes superior, or to replace accepted Codes or Standards.

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2: Role of PPE & Transmission Mechanisms of COVID-19

2.1: Transmission Mechanisms of COVID-19 According to the WHO, SARS-CoV-2, commonly referred to as Covid-19 or novel

coronavirus, is primarily transmitted between people through respiratory droplets and contact routes. Currently there are three mechanisms of transfer being investigated in relation to the Covid-19 outbreak: Respiratory droplets, airborne transmission, and contact routes.(WHO Scientific Brief Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations)

Respiratory droplets originate from an infected person sneezing, coughing, spitting, etc.

They can be in the form or water vapor or mucus droplets that are expelled from the infected individual. These droplets are 5-10 microns large and are currently believed to be the primary transmission mechanism of COVD-19. Transmission occurs when someone comes into direct contact with these droplets and they get into the mouth, nose, or eyes after a cough or sneeze, or through indirect contact when an individual touches their mouth, nose or eyes after touching an object that had respiratory droplets resting on it. Surfaces and objects that transmit the virus are called fomites and droplets may stick around for hours and possibly days after falling there. (WHO Scientific Brief Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations)

Typically, respiratory droplets do not remain suspended in the air and fall quickly due to their size. Sometimes it may take a couple seconds, sometimes minutes, and sometimes even longer depending on the air flow in a room and the actual sizes of the droplets. The 6 foot radius that has been established as a minimum safe distance for social distancing is based on research of these patterns. However, in reality there is no imaginary wall 6 feet away from a person that prevents further spread droplets. They can likely travel much farther when propelled by an uncovered sneeze or cough. (Turbulent Gas Clouds and Respiratory Pathogen Emissions)

Airborne transmission typically refers to conveyance of virus through respiratory droplets which are under 5 microns in diameter. These originate in a similar manner, being expelled through mechanisms including breathing, coughing and sneezing. These very small droplets are referred to as aerosols or aerosol droplets. Particles of this size can be suspended in the air for several hours or by some accounts, indefinitely. This again depends on the airflow conditions and the actual size of the droplets. Additionally, in some instances, droplets under 5 micron diameter will fall quickly and droplets larger than 5 microns may stay in the air for hours. The

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length of time it takes for a particle or droplet to fall out of the air is referred to as the settling time. (Review of Aerosol Transmission of Influenza A Virus)

It is generally believed that the coronavirus is not airborne, or that it does not transmit through aerosol droplets that remain suspended in the air for long periods of time. This is currently a subject of contention among researchers. Though there is evidence that researchers have found parts of the viral genetic code in the air and in some ventilation systems, it is unclear if it is enough to actually infect an individual with the virus. It seems likely that at close proximity to an infected individual it is possible to be infected via airborne transmission. (Is the coronavirus airborne? Experts can't agree; Rapid Expert Consultation on the Possibility of Bioaerosol Spread; Transmission Potential of SARS-CoV-2 in Viral Shedding ; Features, Evaluation and Treatment Coronavirus)

The virus itself is quite small, measured to be as small as 70-90 nm (0.07-0.09 microns) with the average size reported as 125 nm (0.125 microns). It is unclear if the virus carries a charge. By nature the molecular structure of the virus relies on electrostatic and intramolecular forces to operate. One researcher has tried to identify electrostatic features within the virus structure, but this is likely only useful for designing small molecules as potential therapeutic candidates for treating the virus. As described above, the virus is typically attached to or within droplets expelled by an infected individual, though it is unclear how exactly they are attached or contained with these droplets. (Identification of Coronavirus Isolated from a Patient in Korea with COVID-19;)

2.2: What is a Mask versus a Respirator?

Masks and Respirators are key personal protective equipment (PPE) for protection against transmission of Covid-19, and they have different functions and purposes. The Centers for Disease Control and Prevention (CDC) does not recommend that the general public wear N95 respirators to protect from Covid-19. Instead, it recommends the public wear cloth face coverings (here-to-for described as home-made masks) when in a public setting. (N95 Respirators and Surgical Masks (Face Masks)) Masks (both surgical and home-made cloth) function as a physical barrier between the wearer and others, blocking direct transfer of respiratory droplets and other bodily fluids. They are loose fitting; they do not form a seal around the wearer’s face. This means that droplets can get around that physical barrier and still contact the wearer, especially if those droplets are smaller aerosol droplets (N95 Respirators and Surgical Masks (Face Masks)). Some online references may draw a distinction between “surgical” and “home-made cloth” masks. For obvious reasons there may be greater variability in the quality and effectiveness of home-made products.

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Respirators, such as a N95 respirator, function as a filter between the wearer and the air around them. In general, the purpose of these filters is to eliminate very small particles such as aerosol droplets, and have a close, sealed fit around the wearers face that prevents particles from going around the filter barrier. The N95 in particular is called an N95 because it eliminates 95% of small 0.3 micron testing particles. More information on this test is described later in this document. (N95 Respirators and Surgical Masks (Face Masks))

Table 1: Comparisons of masks and respirators.

(Reusability of Facemasks During an Influenza Pandemic)

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Table 2: Functions performed by masks and respirators.

(Reusability of Facemasks During an Influenza Pandemic)

2.3: How Masks and Respirators Work?

The mechanisms in which masks and respirators block and filter particles are key to understanding how the function of masks and respirators differ. There are 4 mechanisms by which particles are captured or filtered. These are: Inertial impaction, interception, diffusion, and electrostatic attraction. Inertial impaction refers to a larger particle being unable to follow an airstream due to momentum. It collides directly with filter fiber instead of travelling around it with the airstream. Interception is when a particle does follow an airstream but runs into a filter fiber anyway, loses inertia, and stops. These first two mechanisms are typically how larger particles are stopped. Then there is diffusion, which is when smaller particles constantly bump into air molecules and other smaller particles, causing them to eventually contact a filter fiber. Lastly, there is electrostatic attraction, where charged particles flowing through an airstream are attracted to charged filter fibers. (Reusability of Facemasks During an Influenza Pandemic;N95 Respirators and Surgical Masks)

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Figure 1: Illustrations of the four mechanisms of filtration.

Another key difference between masks and respirators, is the presence of charged filter fibers in respirators, which significantly increase the effectiveness of filtration by allowing respiratory to filter using electrostatic attraction. Common masks do not have this capability. In one study, a surgical mask was found to block 40% of all particles, while an N95 blocked 95% of particles. This is likely to be from a combination of the electrostatic attraction and sealing well to the user’s face that the N95 has over its surgical mask counterpart. (Comparison of Filtration Efficiency and Pressure Drop in Anti-Yellow Sand Masks, Quarantine Masks, Medical Masks, General Masks,)

Understanding how the virus is transmitted is important for understanding how an individual or healthcare provider can protect themselves. Each type of transmissions described in the previous section has varying levels of precautions that have been recommended when dealing with disease. For both respiratory and airborne transmission, the CDC recommends putting a normal mask on the patient, but only recommends wearing an N95 respiratory or better for providers when airborne transmission is a risk. The CDC additionally recommends protecting the eyes for multiple forms of transmissions. (Transmission-Based Precautions | CDC)

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Figure 2: Droplet and airborne precautions as recommended by the CDC.

The job of the mask on the patient is to catch all of the infectious droplets leaving their system. The job of the respirator on the provider is to filter airborne aerosol droplets from their air supply. Since the virus is primarily transmitted through respiratory means, the goal of any PPE should be to prevent contact with droplets 5-10 micron in size. However, since droplet size is by no means limited to this range, PPE should be able to filter larger and smaller sized droplets. Wearing PPE also prevents an individual from touching their hands to their mouth, nose and eyes.

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3: Guidance for Make-at-Home Masks

3.1: Purpose of Masks and User Needs The typical made-at-home cloth masks are not intended to prevent the transmission of Covid-19 but provide a low level of protection and high ease of manufacture. It may be possible to improve made-at-home by optimizing the materials and manufacturing, without increasing the difficulty of manufacturing. Below is a series design criteria for an ideal mask.

User Needs Explanation

Protect the user from the virus and virus-carrying particulates

Materials used should block transmission of the virus during inhalation and exhalation

Block transmission of fluids and blood PPE must block inhalation and respiration of fluids ie blood and water vapor

Fit snugly but comfortable against the side of the face

A tight fit will reduce inhalation and exhalation transmission between the mask and the user’s skin

Allow for breathing without restriction The mask materials must allow the user to breath properly primarily through the material, not around the material

Comfortable for extended periods of time The mask must be made of materials that do not irritate the users skin, and fit must not create pressure points

Not create condensation while wearing Materials should not collect condensation on the inside of the mask during extended use which may cause irritation to users or collect contaminated fluids which can then be transferred.

Have ability to attach to users face Mask should have an adjustable method of attachment, ie elastic or tie string

Reusable and cleanable Ability to clean and reuse will decrease the strain on sourcing quantities

Made from easily sourceable materials Off-the-shelf materials and fabrics should be used

Fabrication technique suitable for home or hobbyist manufacturing

Assembly techniques accessible to the majority of people, like sewing and glueing

Electrostatic attraction Negatively charged materials will attract viral

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particles and repel liquids, while positively charged materials will attract liquids

Table 3: Design Criteria of an Ideal Mask.

3.2: Overview of Primary, Secondary and Tertiary Mask Structure The construction of a mask can be broken down into three tiered categories, which all have influence on mask performance. Selection of fabric material, design and construction technique influences filtration effectiveness. Mask makers should strive to create a mask with the highest filtration and best seal possible. While DIY masks are not intended to be respirators or surgical masks, there are plenty of readily available materials for an individual to create their own masks that come close to the filtration capabilities of those worn by healthcare professionals. More detailed information on attempts to make DIY respirators, or N95 replacements, are given in section 4.

3.3: Types of Fiber (Primary Structure)

The below table describes a number of different fiber materials that are used to create various fabrics, benefits to each fiber material, and common places where those fiber materials are found.

Fiber Material Reason to Consider Where it is used

Cotton Readily available, absorptive properties and hydrophilic, breathable

Clothing, bedding, some filters, quilts,

Polyester Readily available, more dense and heavier than cotton, more durable, hydrophobic, natural tendency to gain electrostatic charge

Clothing, bedding, furniture, filters, towels

Nylon Hydrophilic, strong, readily available, durable Clothing, bedding, some filters, seat belts, parachutes

Polypropylene Hydrophobic and chemically inert, natural tendency to gain electrostatic charge, strong

Respirator filters, pharmaceuticals, food containers

Polystyrene Low weight, natural tendency to gain electrostatic charge

Food containers, packaging, styrofoam

Wool Readily available, more insulation, thicker than cotton, natural tendency to gain electrostatic charge

Clothing, furniture, bedding

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PTFE Hydrophobic, strong, dense, good resistance to chemicals and temperature

Non-stick coatings, Teflon, lubricant, pharmaceuticals

Polycarbonate Hydrophilic, unique pore structure and capture, strong, flexible

Insulator, eye wear, pharmaceuticals, impact-resistant windows

Silk Strong, durable and comfortable, also absorbent

Clothing, bedding, furniture, parachute

Polyethylene Hydrophobic, strong, natural tendency to gain electrostatic charge

Films, tubing, laminates, insulation, sandwich bags

Cellulose Hydrophilic, readily available Cotton, paper, wood, insulation

Table 4: Material Characteristics/Fiber Types (Primary) An important factor in obtaining electrostatic charge, certain materials are naturally more likely to transfer their charges when coming into contact with other materials. The triboelectric series refers to a list of material organized by their tendency to gain or lose electrons when coming into contact with other materials on the list. A version of this list is below, with more complete/detailed versions located here (The Triboelectric Series) and here. More information on the triboelectric series and how to measure surface charge can be found in Appendix D.2. Of note on this list is the location of polypropylene, the most common material found N95 respirators, and other common household materials such as cotton, polyester, styrene, glass, wool and human hair and hands.

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 Figure 3: Materials organized by their tendency to gain or lose electrons when rubbed together.

The triboelectric series. (Triboelectric series) 

There is some concern whether the fibers should be hydrophilic (wettable and of low surface energy) or hydrophobic (nonwettable and of high surface energy). If the hydrophilicity of the fibers is high, liquid droplets will form film-wise collections on the fibers as shown in the figure below. If too hydrophilic the medium will become "waterlogged" resulting in high pressure drop, medium plugging, re-entrainment, and low separation efficiency. On the other hand, if the fibers are hydrophilic the collection will be dropwise as shown in the belfow. If the surface energy is

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too low to hold the droplets to the fiber surface, they will release and re-enter into the fluid stream. (Handbook of Nonwoven Filter Media)

Thus it may be beneficial to use a combination of hydrophobic and hydrophilic materials. In theory, a hydrophilic outer layer will tend to absorb respiratory droplets, while the hydrophobic inner layer prevents droplets from entering into the fiber and prevents the trapping of moisture. (Engineering of High-Performance Textiles; Are you wearing your mask properly? The ultimate guide of do's and don'ts for the coronavirus crisis.)

Figure 4: Droplet coalescing mechanisms for hydrophobic (a) and hydrophilic (b) fibers.

 

3.4: Types of Fabric (Secondary Structure) There are three basic types of fabric, and each can be found in everyone’s daily lives. There are knit fabrics, woven fabrics, and nonwoven fabrics. Each of these fabric types can be identified at home by looking at the fabrics up close. Each of these materials is readily available online for order at places such as Joann Fabrics, McMaster Carr and even eBay.

Construction Type Reason to Consider Where it is used

Woven

Woven fabrics are many yarns put together, criss-crossing over and under each to form a grain. These do not stretch in the directions parallel and perpendicular to the grain, and will likely form wrinkles when folded or crumpled up. Woven fabrics can have a smaller permeability than knitted fabrics.

Bedsheets, scarves, flannel, bandanas, reusable napkins, some uniforms

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Non-woven

A nonwoven fabric is created when fibers are bonded and/or interlocked using mechanical, chemical, thermal or solvent means. These fabrics can be soft and pliable or hard and stiff and will typically come apart when stretched. Felt is a good example of a nonwoven material. Nonwoven fabrics are typically used in filtration applications (such as the N95), since woven and knitted fabric have a tendency to be permeable and usually less dense.

Filtration media, disposable napkins, insulation, felts

Knitted

Knit fabrics are made up of a single length of yarn that is continuously looped. This may allow for stretching of the knit structure. These fabrics can be folded or crumpled up and return to their original shape. Knitted fabrics typically have a higher air and liquid permeability than woven fabrics. In general, knitted fabrics are less suitable than woven or non-woven fabrics.

Sportswear, t-shirts fleece, spandex, sweaters, socks, scarfs

Table 5: Fabric Manufacturing Methods (Engineering of High-Performance Textiles) Respiratory and medical masks filters typically consist of mats of nonwoven fibrous materials, such as wool felt, fiberglass paper, and polypropylene. Nonwoven materials are dense, create a tortuous path, and various mechanisms result in the adhesion of particles to the fibers without necessarily blocking the open porous spaces, which means air can still flow easily across the filter (Respiratory Protection Handbook). Nonwoven fabric, initially using natural fibers, came into greater prominence with the introduction of synthetic polymers, particularly polypropylene, about 40 years ago. There are a number of ways to make nonwoven materials, including but not limited to: electrospinning, melt-blown, and spun-bond. Each of these methods are described in the table below.

Additional Non-Woven Manufacturing Process

Description Example

Electrospinning Dissolved polymer is forced out of a spinneret with an electric field which then solidifies, creating nanometer fiber diameters.

Tissue scaffolds

Melt-blown Polymer is fed and extruded into filaments that are kept warm with hot air creating thin filaments that form a fiber web.

Respirator filter material

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Spun-bond Polymer is fed and extruded into filaments that are stretched and then cooled. These form a uniform fiber web that are then thermally bonded with heat and pressure.

Respirator filter material

Carding Compressing dry fibers in many orientations using a roller removed with a wire which are then bonded mechanically.

Felt

Air laid Compressing dry fibers in many orientations using a roller removed by blowing air which are then bonded.

Shoe inlays, diapers

Wet laid Compressing a wet random web of fibers and drying which are then bonded mechanically.

Surgical gowns, gloves, car filters

Needle punching/Needle Felt Fibers are layered into a loose web and then entangled by a series of needles penetrating through the fibres.

Certain carpets

Table 6: Various methods of manufacturing non-woven fabrics. (Nonwovens manufacturing process)

The salient advantage of nonwoven technology is the ability to produce fabrics or structures at significantly lower cost than the older fabric-generating techniques of weaving or knitting of spun yarns. Additional important advantages are the versatility of the process and the products in terms of properties and uses. There has been ongoing development of, and increasing sophistication in, spun-bonded, and the related melt blown, technologies, which have made these materials the optimal choice in many applications.

Surgical face masks are also made with non-woven fabric, which has better bacteria filtration and air permeability while remaining less slippery than woven cloth. The material most commonly used to make them is polypropylene, either 20 or 25 grams per square meter (gsm) in density. Surgical masks can also be made of polystyrene, polycarbonate, polyethylene, or polyester (How Surgical Masks are Made, Tested and Used). Polypropylene is also the most common material found in N95 respirators. Polypropylene is an ideal fiber for nonwoven fabrics due to its strength, its tendency to gain electrostatic charge, ability to be processed into micron and submicron diameter fibers, and cost (Reusability of Facemasks During an Influenza Pandemic). Other uses of non-woven fabrics are listed in the table below.

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Table 7: Overview of markets for basic types of non-woven media.

(Handbook of Filter Media 2nd Ed)

3.4.1: Commercially Available Material Table Below is a table describing readily available fabric materials that an individual may have access to, and what fiber type and fabric construction each consists of linked to evidence that supports its use as a filtration material.

Fabric Material

Typical Fiber Type

Typical Construction Source

T-Shirt Cotton, Polyester or blend

Woven or Knitted Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm

Bedding/ Pillowcase

Cotton, Silk, or other

Tight-weave, higher thread count better

Environmental engineers study fabrics, materials for face covers

Bandana Cotton/polyester blend

Knit Environmental engineers study fabrics, materials for face covers

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Scarf Cotton or Polyester Loose-weave or knit Environmental engineers study fabrics, materials for face covers

Vacuum Bags Fiberglass, polypropylene,

Woven or nonwoven Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

Paper Towels Cellulose Woven Reuse Mask? DIY Mask? | Consumer Council

Tea/dish Towel Cotton Woven Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

Coffee Filter Wood pulp fibers (cellulose)

Nonwoven Use Cloth Face Coverings to Help Slow Spread | CDC

Furnace Filter Fiberglass, polyester, cotton

Woven or nonwoven Environmental engineers study fabrics, materials for face covers

Sweatshirt Blend of Cotton and Polyester

Woven or Knitted Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm

Shop towels Polyester Knit Blue Shop Towel Masks

Reusable Grocery Bags

Polypropylene Nonwoven Make your own face mask—no sewing machine required

Swiffer Polyester and cellulose core, polypropylene outside

Nonwoven https://twitter.com/aaqrl_wustl/status/1247696679446425600

Sterilization Wrap

Polypropylene Nonwoven UF Health anesthesiology team devises respirator mask made from existing hospital materials

Table 8: Accessible Fabrics (Secondary)

3.4.2: Expanded Section on Materials The following section expands on each fabric material in Table 8 with descriptions and detail of evidence as a filtration material. Note that supporting data for each fabric material only reflects that of the experiment in which it was tested, some of which are unpublished or may be found to be different in other experiments.

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3.4.2.1: Fabrics T-shirt Many individuals are using 100% cotton or cotton/polyester mix shirts as masks as recommended by multiple sources including the CDC since it is a readily available material. A dense, thick or tight knit is optimal. Cotton is hydrophilic meaning it will attract and absorb respiratory droplets, but may also attract smaller droplets that aren’t able to be filtered out due to the knit fabric design. A more effective mask design may include wrapping the shirt around multiple layers of another fabric, such as a filter, towel or bed sheet.

● T-shirts have a relatively high penetrance to particulate ● Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks

and Common Fabric Materials Against 20–1000 nm Size Particles ● 100% cotton T-shirt not as effective at filtering aerosol bacteria as a cotton mix ● Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza

Pandemic? ● “Simple Respiratory Mask” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/

Sweatshirt Sweatshirts are made of similar materials as T-shirts: cotton or cotton/polyester mix, but tend to be a thicker material with somewhat better filtration. Cotton is hydrophilic meaning it will attract and absorb respiratory droplets, but may also attract smaller droplets that aren’t able to be filtered out due to the knit fabric design. A more effective mask design may include wrapping the sweatshirt around multiple layers of another fabric, such as a filter, towel or bed sheet or combining a normal shirt with a flannel shirt.

● Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles

Bedding/Pillowcase Bedding and/or pillowcase have been recommended as more readily available materials also by the CDC. A “high thread count” is recommended, with multiple layers stacked together to increase effectiveness. A more effective mask design may include wrapping the bedding around multiple layers of another fabric, such as a filter or towel, or within a cloth t-shirt.

● 600 count bed sheets filtered better than 400 count bed sheets layered 4 times ● Environmental engineers study fabrics, materials for face covers

Scarf Bedding and/or pillowcase have been recommended as more readily available materials also by the CDC. A dense, thick or tight knit is optimal. A more effective mask design may include wrapping the scarf around multiple layers of another fabric, such as a filter, towel or bedding.

● “In recent tests, HEPA furnace filters scored well, as did vacuum cleaner bags, layers of 600-count pillowcases and fabric similar to flannel pajamas. Stacked coffee filters had

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medium scores. Scarves and bandana material had the lowest scores, but still captured a small percentage of particles.” What's the Best Material for a Mask for Coronavirus?

Bandana Cloth bandanas are a common item also recommended as an option by the CDC. Bandanas however are very thin with poor filtration and a poor fit to the wearers face and should only be used as a last option.

● “In recent tests, HEPA furnace filters scored well, as did vacuum cleaner bags, layers of 600-count pillowcases and fabric similar to flannel pajamas. Stacked coffee filters had medium scores. Scarves and bandana material had the lowest scores, but still captured a small percentage of particles.” What's the Best Material for a Mask for Coronavirus?

Tea/Dish Towel A Tea/Dish towel performed better than cotton, linen, silk, and pillowcases but not as good as a vacuum cleaner bag in terms of aerosol bacteria filtration. Recommended as an option due to the readily available nature of these towels by the CDC. These towels layered and in combination with a wrap of fabric are likely more effective than a single towel alone.

● Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

● To Buy: Tea Towels - Amazon

3.4.2.2: Other Materials Blue Shop Towels When tested against other materials (fabrics, coffee filters, and others, tested down to 0.3um particle size), a Los Angeles sew shop found blue shop towels to have the best filtration. These are recommended to be used as filler filter material for cotton masks.

● Inserting two of these towels into an ordinary cotton mask brought filtration up to 93% of particles as small as 0.3 microns, the smallest their machine could test. Meanwhile, the cotton masks filtered 60% of particles at best in their tests

● Using blue shop towels in homemade face masks can filter particles 2x to 3x better than cotton

● To Buy: ToolBox® Shop Towels - 200 Count at Menards® ● To Buy: ZEP Industry Towels - 75 Count at Home Depot

Paper Towels A chinese university recommends a simple DIY mask made from two paper towels and a tissue paper that has similar filtration to a surgical mask when tested. This design alone may have been shown to work well, but further protection by wrapping this design in a cloth may extend its life time and durability.

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● Reuse Mask? DIY Mask? | Consumer Council ● To Buy: Paper Towels: Health & Household - Amazon ● To Buy: Tissue Paper - Amazon

Filters Furnace Filter Furnace filters have been suggested as a potential filtration material, but they are demonstrably less effective than HEPA filters (although still more effective than materials like cotton for capturing nano-sized particles). These filters should be wrapped in a cloth fabric, as some filters have a tendency to shed particles that may be harmful to the lungs. Appendix B discusses them in greater detail. At a minimum, a MERV rating of 12 is recommended.

● A furnace filter captured 75 percent with two layers, but required six layers to achieve 95 percent.

● Environmental engineers study fabrics, materials for face cover ● MERV 13-15 materials can often be found without fiberglass. For example, MERV13

filters are easily found on EBAY. Also, 3M Filtrete MPR 1500 (=MERV12) is found at Walmart, MPR 1900 at Target, MPR 2200 (=MERV13) is found on amazon. MERV15 materials can be found online too. Be very careful purchasing MERV16. In fact, unless you know what you’re doing, MERV 16 is dangerous as it contains fiberglass and would need to be isolated by sealing inside layers of another material such as cotton. Here is an example of a highly effective but dangerous, if not used with caution, material: MERV 16 Rating Air Filter - Amazon

Coffee filters Coffee filters have been recommended by the CDC as a filler filter material placed within a cloth fabric mask. Additionally, stacking these coffee filters has been demonstrated to be more effective at filtering compared to scarves or bandanas alone.

● Use Cloth Face Coverings to Help Slow Spread | CDC ● What's the Best Material for a Mask for Coronavirus? ● To Buy: Brew Rite Natural Basket Style Coffee Filters 100 filters - Amazon

HEPA vacuum bag filters HEPA level filtration provides a similar level of filtration as surgical masks in terms of aerosol capturing aerosolized bacteria. However, there is concern due to some being constructed using microscopic glass fibers which can be harmful to the lungs if inhaled as the filter sheds.These filters should be wrapped in a cloth fabric.

● Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

● To Buy: EnviroCare Replacement HEPA Filtration Vacuum Cleaner Dust Bags 6 Pack (No Fiberglass) - Amazon

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Sterilization Wrap Sterilization wrap is often found in hospitals and is two-ply nonwoven polypropylene. According to one source it blocks 99.9% of all particulates. Prototypes are being developed using this material. The material itself can be used to form the mask and does require other fabrics to cover it. However, some testing laboratories including at University of Connecticut and at Cleveland Clinic indicate H600 filters suboptimally at higher flow rates users might see while climbing stairs or performing CPR, and that the 99.9% figure appears, unfortunately, to be a significant overestimation. Providing increased surface area, and therefore decreased peak flow rate during breathing, would improve this finding. Also, the correlation between flow rate and filtration efficacy is generally true for most fabrics, so this material should still be seriously considered.

● UF Health anesthesiology team devises respirator mask made from existing hospital materials

● https://www.infectioncontroltoday.com/environmental-hygiene/choosing-sterilization-wrap-surgicalpacks

● To Buy: Amazon Best Sellers: Best Sterilization Wrap ● Ask local hospitals or surgery centers to salvage material from surgeries that, as 1 4’ by

4’ sheet usually wraps every reusable sterile instrument try and it is typically thrown away, still clean.

Reusable fabric grocery bags Reusable grocery bags are typically constructed of nonwoven polypropylene and can be found in the non-laminated form. Often they are laminated, so look for a bag without the glossy laminated cover. They can be cut out and placed in a cloth fabric as a filter filler or used as is. No data currently on their filtration efficiency.

● Make your own face mask—no sewing machine required ● To Buy: Nonwoven 100% polypropylene fabric - Joann Fabrics

Swiffer Swiffer (the quicker picker upper) when layered, had better filtration than a number of other fabrics intended for filtration (MERV 14 and MERV 16 ratings). The mop pads are a polyester and cellulose core with a surrounding sheet of nonwoven polypropylene that uses electrostatic charge to remove dust and dirt. They’re a promising option for filtration, however they are not meant to be put to the mouth or face, and should thus be wrapped in a cloth fabric for usage as a DIY mask.

● https://twitter.com/aaqrl_wustl/status/1247696679446425600 ● To Buy: Swiffer Dry Sweeper Refills Unscented - Amazon

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3.5: Mask Assembly (Tertiary Structure)

3.5.1: Design Features Overall Mask Structure (Tertiary) The tables below describe different types of masks and respirators in terms of manufacturing, protection and face seal fit. An ideal mask should be as tight fitting as possible to the user’s face. This will reduce transmission around the mask. Methods of doing this include:

● Pleating of the mask - Allows wrapping around the face. Several examples may be found online showing pleated masks, both by DIY groups and commercially available

● Form fitting design- This typically constitutes a mask without pleats fitted to a wearer. Examples may be found online (https://www.prettyhandygirl.com/best-fit-face-mask/)

● Increasing tension of the mask - This can be accomplished with elastic straps. Ear straps are often used. Users are also growing fond of ‘earsavers’, which may be easily made or 3D printed, reduce irritation around the ears, increase tension and therefore fit to the face.

● A simple rubber band chain can be added to another mask to increase pressure of the mask against the face, reducing chance of an air leak (https://www.fixthemask.com)

● Plastic frames - typical of hard shell respirators, plastic or resin frames may be made into which filter cartridges are screwed or snapped into place. Examples of 3D printed and injection molded mask frames may be found online.

● Edges to the skin - Keeping filter material against the skin also affords a seal. Prints are available online of “face frames”, which are often thin bands of plastic which may be fitted on the user's face and hold some type of filter material.

Type of PPE Difficulty to Manufacture Protection against Transmission

Cloth Mask Easy Low

Surgical Mask Easy to Moderate Moderate to High

N95 Respirator Moderate to High High

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3D Hard Shell Respirator

Moderate to High High

Table 9: Various types of PPE and the relative complexity of the manufacturing processes and protection against transmission.

Mask

Respirator

3D Hard Shell

Respirator

Face Seal Fit Loose-fitting Tight-fitting Tight Fitting

Leakage Leakage occurs around the edge of the mask when user inhales

Minimal leakage around edges when user inhales

Minimal leakage around edges when user inhales

Table 10: Each type or PPE Face Seal Fit is described along with how each device is prone to airflow leakage.

(PPE Differences | CDC)

Figure 5: An example of a ‘face frame’, the plastic frame reinforces the seal of the mask to the face with tension provided by elastics around the head and neck. (https://today.uconn.edu/2020/04/farmington-storrs-team-make-needed-ppe-uconn-health/)

The ideal mask is easy to manufacture, tight fitting, highly breathable, traps particulate, and cleanable/reusable. Manufacturing, fit, and particulate trapping are covered in the sections above. Cleanable/reusable is discussed in section 3.6,and breathability is covered in the testing section 3.7.

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Figure 6: An example of a multi-layer surgical mask.

Figure 7: An example of a multi-layer tight fitting respirator (with a ventilator fan to increase exhalation

airflow). Further description in Appendix D.1. (Assessment of a respiratory face mask for capturing air pollutants and pathogens ).

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3.5.2: Design Criteria The table below consists of a series of technical specifications surgical masks must meet to be designated as surgical masks. Making a mask that meets all of the specifications below would mean a mask is as effective as a surgical mask, even if it does not go through the necessary regulatory approval. Figure 7 provides information from ASTM F2100, the standard governing mask specifications. It may be noted that F2100 only evaluates the material used in the mask, and not the seal of said mask, which is the primary difference between masks and respirators as discussed in section 2.

Figure 8: From ASTM 2100-19 “Standard Specification for Performance of Materials Used in Medical

Face Masks”

Technical Requirement Performance Specification

Particulate filtration efficiency ≥ 95%

Bacterial filtration efficiency ≥ 95%

Electrostatic attraction Potential exists to attract positively charged particles

Synthetic Blood Penetration Pass at 80mmHg

Pressure Drop <5.0mm H20/cm2

Flammability Class 1 (flame spread time ≥3.5 seconds...)

Biocompatibility Must be non-irritating, non-toxic

Table 11: Design criteria for masks to be considered effective as a Level 1 surgical mask.

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3.5.3: Published Methods of Assembly There are a plethora of published methods on how to make a mask using common materials and household assembly methods. Below is a list of these designs as well as the material recommended by the publisher.

Published Designs Material (Equipment needed) Source

Simple cloth face covering Shirt, hand towel, or bandana (Non-sewing)

CDC: Recommendation Regarding the Use of Cloth Face Coverings | CDC;The CDC's Guide To Making A Face Mask In 45 Seconds | Mashable

Surgical-like mask Cotton fabric (Sewing machine) Jo-Ann Fabric: DIY FACE MASK TUTORIAL

Origami Masks Tyvek or Vacuum bags (Both non-sewing)

IndianaU: Origami Face Mask Pattern: Coronavirus Open Medical: ORIGAMI MASK

Simple face covering Cotton fabric plus a paper towel (Non-sewing)

Masks4all: How To Make A Homemade COVID-19 Mask In 2 Minutes

Surgical-like mask 100% cotton (Non-sewing) Maskbuilders: Make a mask

Simple face covering Cotton fabric (Sewing thread and needle)

NYT: How to Make a Face Mask With Fabric

Simple face covering Cotton fabric (Sewing machine) Deaconess: How to make a Face Mask

Respirator like covering A fabric plus vacuum bags (Sewing required)

PrimalSurvivor: Homemade N95 Respirator Mask Instructions (Using HEPA Vacuum Bag)

Respirator like covering Sterilization Wrap - Nonwoven polypropylene (Sewing required)

UFlorida: Second Life: Sterile Wrap Fashioned into Masks

Respirator like covering Nonwoven polypropylene (Sewing machine)

MakerMask: non-woven polypropylene mask design instructions

Respirator like covering Cotton fabric, flannel fabric, nonwoven fabric (Sewing thread and needle)

Yale: Support Our Caregivers

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Simple face covering Paper towels plus tissue paper (Non-sewing)

UHongKong: Reuse Mask? DIY Mask? | Consumer Council

Simple face covering Tightly woven cotton fabric (Sewing machine)

Michaels: DIY Face Masks & Coronavirus Face Shields | Michaels

Surgical like mask Nonwoven polypropylene, vacuum bags (Sewing and non-sewing options)

FastCompany:The 4 best mask designs you can make yourself

Surgical like mask Any Fabric (Sewing machine) Providence St. Joesph Health: Community Face Mask

Surgical like mask Tightly woven cotton fabric (sewing required)

Suay:SUAY COMMUNITY MASK COALITION

Respirator like covering Reusable grocery bag - Nonwoven Polypropylene (Non-sewing)

Popsci: Make your own face mask—no sewing machine required

Respirator like covering HEPA vacuum bag (Sewing machine)

Instructables: HEPA Vacuum Bag Mask : 7 Steps

Respirator like covering 3M Filtrete 2200 Air Filters Youtube: Wiles Pandemic Respirator

Table 12: Available methods on how to make DIY masks using a number of different materials with

varying filtration capabilities.

3.5.4 Other Manufacturing Methods 3D Printed Mask Structure: 3D printing allows for rapid iteration of designs using hard and soft polymers. The NIH is currently vetting a variety of PPE being created by 3D printing designers. Collections are designated by “For Community Use” and “For Clinical Use” and can be found at https://3dprint.nih.gov/collections/covid-19-response/. This provides some measure of review over designs simply posted on sites like Thingiverse and Instructables, however certifications do not currently rise to the level of NIOSH or FDA approvals for medical use. 3D printing has its limitations, and is a relatively new technology not previously used for this purpose. Several designers and prototypers are rapidly innovating concepts to introduce 3D printed masks and “N95 replacements” to the DIY community. It should be noted that even a posted STL file may print with different fits and tolerances on different 3D printer models, from different manufacturers, and with different settings. Settings such as fill rate, fineness (resolution

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or layer height), and material type can all have a significant impact on build quality and repeatability. 3D printing does offer a means to rapidly disseminate a design to remote areas. It is not possible to 3D print a fabric or a filter, but this manufacturing technique is being used to create frames to improve the fit of a mask to the users face, for containing filters, and for affixing face shields. 3D printing is time consuming and may take multiple hours per item. However, there is a potential for scalability, as a single design can be distributed to multiple users across the world, and these printers can create parts in a semi-automated fashion around the clock. However, volume cannot match that of more complex and expensive industry methods such as injection molding and thermoforming, if they are available locally. 3D printing has been used to manufacture 3D hard shell masks. These masks are a hard shell with a smaller breathing port where a filter is placed. This filter can be replaced making the 3D mask reusable. However, the hard shell masks may not be form fitting to the wearers face, and the type of filter being used is still the biggest factor in determining the efficacy of the mask. Filter material remains critical, as materials used in these masks should be evaluated for filtration efficiency prior to use. The seal around the mask, and around the parts of the mask holding the filter material, area also critical. The seal can often be improved with the addition of rubber trim, but may still not fit all faces, so designers often make 3D printed masks in various sizes. Filament plastics play an important role in design using Fused Deposition Modeling (FDM) type 3D printers. PLA is a common material, and is fairly rigid for a given fill rate and geometry. TPU, marketed under names such as ninjaflex, is more pliable and therefore form-fitting and comfortable, but may be too pliable and TPU is considered one of the more porous 3D printer filament options, raising concerns for air and virus making its way through micropores. PETG is considered to be more easily cleaned. ABS is another plastic filament type. PVA and Nylon may also be used. Stereolithography (SLA) printers do not use a filament, and instead use a light source to cure a liquid resin. Thermoformed mask structure: Thermoforming over 3D printed or machined molds allows for more rapid production of thin shelled hard and soft polymer components, and may be used for manufacturing 3D hard shell masks or face shields. This has promise for allowing rapid distribution of masks or respirators which use smaller, replaceable filters.

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Figure 8: 3D Hard Shell Mask with replaceable filter (credit to Tepha).

Figure 9: 3D printed and Thermoformed Assemblies (credit to Tepha).

3.6: Tips for Fit, Function, Cleaning & Re-Use Materials for making masks at home should be qualitatively evaluated for their ability to filtrate particles. Based on the details given above, here are general guidelines for choosing materials, design and fit:

● Materials chosen should not have visible transparency or openings between the knit or weave. A material that stretches may not be optimal as this may signify increased permeability when stretched. As discussed above, nonwoven materials are often best.

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Materials such as filter material and sterilization wrap, discussed above, are commercially available and the subject of current testing by labs.

● Material should provide a reasonable level of resistance to breathing to signify ability to block or capture particulates. This is also the subject of testing by labs as discussed in the next section.

● Although masks are not intended to provide a tight seal to the face, the mask should fit snugly but comfortably against the side of the face. Tips on tertiary structure above discuss different methods for achieving this.

● It is recommended a mask should capture water on the inside of the mask (hydrophilic) while repel water on the outside of the mask (hydrophobic). Dual material masks can achieve this. For instance, some DIY mask makers leave a pocket between pleated layers of cotton to allow for filter paper material to be replaced in between.

● Ideally ,a tightly fitted mask should block the user from smelling potent smells like vinegar, smoke, or incense. Fit tests of respirators are based on this principle, which is discussed in the next section.

Shortages in PPE due to the COVID-19 crisis are leading healthcare providers and consumers to find ways to reuse their masks, respirators, gowns and gloves. Disposable PPE are generally not approved for routine decontamination and reuse however it has become necessary for this to be considered and in many instances, carried out, in order to maintain supply. Two sources worth looking into are listed below.

● CDC guidance on decontamination and reuse: COVID-19 Decontamination and Reuse of Filtering Facepiece Respirators

● A great collaborative resource has been put together from a multitude of university researchers: N95DECON - A scientific consortium for data-driven study of N95 FFR decontamination

Other methods that have been investigated and may be worth further investigation::

● Hydrogen Peroxide Vapor Sterilization ○ Yale: Hydrogen Peroxide Vapor sterilization of N95 respirators for reuse ○ Batelle: Battelle CCDS Critical Care Decontamination System for PPE

Decontamination ● Humid Heat ● UV-C Radiation ● Dry cleaning (requires further review) ● Liquid Critical C02 (requires further review) ● Rice Cooker cleaning:

○ Taiwan FDA demonstrates how to use rice cookers to disinfect used face masks

● Laundering

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3.7: Lab Testing and Regulatory

3.7.1: Commercial Distribution For commercial distribution, medical and surgical masks are tested per ASTM F2100 (version -19 is the most current to date). These masks are considered medical devices by the US FDA and most typically follow the 510(k) regulatory pathway. Standards governing masks include:

● ASTM F2299/F2299M-03(2017) Standard Test Method for Determining the Initial Efficiency of Materials Used in Medical Face Masks to Penetration by Particulates Using Latex Spheres

● ASTM F2101-19 Standard Test Method for Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials, Using a Biological Aerosol of Staphylococcus aureus

● ASTM F2100-19 Standard Specification for Performance of Materials Used in Medical Face Masks

● ASTM F1862/F1862M-17 Standard Test Method for Resistance of Medical Face Masks to Penetration by Synthetic Blood (Horizontal Projection of Fixed Volume at a Known Velocity)

● ASTM F1494-14 Standard Terminology Relating to Protective Clothing Below are the tests required by ASTM F2100 and their descriptions from Nelson Labs. (Nelson Labs - Microbiology Testing Lab)

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Figure 9: Medical face masks tests and requirements from Nelson Labs.

Bacterial Filtration Efficiency (BFE%) Acceptance Criteria: 95% Nelson Labs Test Procedure: BFE110 Applicable Standard: ASTM F2101, F2100

The Bacterial Filtration Efficiency test determines the filtration efficiency by comparing the bacterial control counts to test article effluent counts. The test is conducted using Staphylococcus aureus as the challenge organism. After the filtration media is preconditioned, a liquid suspension of S. aureus is aerosolized and delivered to the filtration media at a constant flow rate of 28.3 liters per minute (LPM) or 1 cubic foot per minute (CFM). The aerosol droplets are drawn through a six-stage Andersen sampler for collection. The number of bacterial aerosol droplets contacting the filter media is determined by conducting challenge controls without filter medium in the test system. Challenge controls are maintained at 1700 – 3000 colony-forming units (CFU) with a mean particle size (MPS) of 3.0 ± 0.3 µm. This allows filtration efficiencies to be reported up to >99.9%. Particle Filtration Efficiency (PFE%)

Acceptance Criteria: ≥ 95% Applicable Standard: ASTM F2299, F2100 Nelson Labs Test Protocol: PFE115

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In Particle Filtration Efficiency testing, the filtration efficiency of filter media materials against sub-micron particles cannot be determined using viable challenge particles. This procedure involves the generation of a particle aerosol using NIST traceable polystyrene microspheres with a Particle Measurement Systems (PMS) Model PG-100 particle generator. The particles are counted with a PMS Model LASAIR II-110 or 310 laser particle counter. The latex particles used in this procedure have a narrow standard deviation and the design of the PMS particle generator produces a consistent particle challenge. Testing is conducted at a single particle size. Nelson Labs has the capability to perform the testing at 0.1µm, 0.3µm, 0.5µm and 1.0µm. ASTM F2100 specifies a challenge particle size of 0.1µm. The PMS particle counter is an optical laser based device and operates at a flow rate of 1 cubic foot per minute (CFM) or 28.3 liters per minute (LPM). Synthetic Blood Penetration

Acceptance Criteria: Pass at 80mmHg Nelson Labs Test Protocol: SBP210 Applicable Standard: F1862, F2100

2 mL of synthetic blood is sprayed through a small cannula onto the surface of the face mask. At the conclusion of the test, the back side of the medical face mask is observed for synthetic blood penetration. Face masks can be evaluated at three different velocities corresponding to a human blood pressure of 80, 120, and 160 mm Hg. If the mask passes at the highest pressure, there is no need to test the mask at a lower pressure. A single sampling plan providing Acceptable Quality Level (AQL) of 4.0% would require that 32 masks be tested and that 29 of the 32 masks pass the test. The surface tension range for blood and body fluids is approximately 42 – 60 dynes/cm. To simulate the wetting characteristics, the synthetic blood is adjusted to the lower end of this range (40 ± 5 dynes/cm). Differential Pressure Acceptance Criteria: <5.0mm H20/cm2

Nelson Labs Test Protocol: [NA] Applicable Standard: EN 14683, ASTM F2100 The Delta P test is performed to determine the breathability of masks by measuring the differential air pressure on either side of the test article using a manometer, at a constant flow rate of 8 L/mi Flammability

Acceptance Criteria: ≥3.5 seconds Nelson Labs Test Protocol: FTS101 Applicable Standard: 16 CTF Part 1610, ASTM F2100

The Flammability test determines the time of flame spread for the given material. All fabrics of natural or regenerated cellulose, as well as certain types of finished and unfinished fabrics made from other natural or synthetic fibers, are combustible. Some combustible fabrics are

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potentially dangerous to the wearer because of the speed and intensity of flame with which these fabrics burn and their ease of ignition. Biocompatibility

Applicable Standard: ISO 10993 Testing for Biocompatibility involves multiple analytical tests which characterize the risk of the materials used in the device construction.

3.7.2: Respirator fit tests  Respirators rely on a face to mask seal, and as such this often requires a proper fitting to the individual using OSHA guidelines, as well as positive pressure checks by the wearer during each use. Grainger provides a summary of requirements for qualitative fit tests, parts of which are repeated here (https://www.grainger.com/content/qt-qualitative-fit-testing-324). They are taken from the Occupational Safety and Health Administration’s (OSHA’s) Respiratory Protection Standard, 29 Code of Federal Regulation (CFR) 1910.134 Appendix A – Fit Testing Procedures (Mandatory). This is not to be confused with quantitative procedures which also exist to measure actual face seal leakage.   Qualitative fit test procedures rely on the senses (taste, smell) of the wearer to a particular test agent. OSHA recognizes four test agents: Isoamyl Acetate (Isopentyl Acetate or Banana Oil), Saccharin Solution, Bitrix™ (Denatonium Benzoate), Irritant Smoke (Stannic Chloride)  

3.7.3: Community use and other tests Efforts are underway to develop less stringent testing procedures for medical masks to allow hospitals and institutions to evaluate ‘emergency’ or ‘diy’ PPE that may need to be called upon in an unprecedented shortage of commercially approved equipment. An example of a team developing test procedures may be found at Yale University, where researchers are comparing flow impedance and particle counts between new filter material and N95 approved filter material. UCONN has a similar effort underway that compares mask and material approaches with respect to water aerosol filtration in realistic conditions. To Relieve a Critical Shortage, a Way to Test Face Masks

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Flow rate is a consideration in these tests. Inspiration rates appear to be a subject of debate among researchers. OSHA standards site test rates of 64, 85, and 100 lpm, with one study in 2006 noting peak instantaneous breathing rates were measured as high as 424 lpm, with a sinusoidal profile of 135 lpm likely capturing 99.9% of peak and instantaneous rates. In tests, flow is dependent on the area being tested. Pressure drops across filtration materials are specified in ASTM standards as noted in previous chapters, for instance for level 1 masks 4 mm

water is specified per square centimeter. https://www.ncbi.nlm.nih.gov/pubmed/16857648

3.7.3: Available Standards During this time ASTM is offering access to PPE standards free of charge. They may be found at ASTM Standards & COVID-19.

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4: Guidance for Make-At-Home Respirators

4.1 Purpose of Respirators and User Needs As discussed previously, respirators differ significantly from masks in that they require a seal on the user. For this reason fit, testing and regulatory requirements are more strict for respirators. As of 5/21/20, there is only one FDA approved design for make-at-home respirator, called the Stopgap mask, but there are other designs approved for clinical use by the NIH 3D print exchange. There are several designs appearing on the internet that are designated as “N95 respirator replacements”. A detailed listing of approved designs and procedures is beyond the scope of this edition of this document, however readers reviewing the previous chapters should have a sense of the differences in the requirements and needs associated with the different devices. As a result, care should be taken to investigate the specifications and build quality devices designated as replacements.

4.2: Lab Testing and Regulatory Procedures for applying for approval of respirator designs may be found at: Respirator Approval Information | NPPTL | NIOSH | CDC There are 7 types of approved respirator models. They are:

● N95 – Filters at least 95% of airborne particles. Not resistant to oil. ○ Surgical N95 – A NIOSH-approved N95 respirator that has also been

cleared by the Food and Drug Administration (FDA) as a surgical mask. ● N99 – Filters at least 99% of airborne particles. Not resistant to oil. ● N100 – Filters at least 99.97% of airborne particles. Not resistant to oil. ● R95 – Filters at least 95% of airborne particles. Somewhat resistant to oil. ● P95 – Filters at least 95% of airborne particles. Strongly resistant to oil. ● P99 – Filters at least 99% of airborne particles. Strongly resistant to oil. ● P100 – Filters at least 99.97% of airborne particles. Strongly resistant to oil.

(NPPTL - NIOSH-Approved Particulate Filtering Facepiece Respirators) OSHA provides a video to identify counterfeit versions of NIOSH respirators: Counterfeit & Altered Respirators: The Importance of Checking for NIOSH Certification A list of NIOSH approved N95 respirator manufacturers may be found at the CDC site: NIOSH-Approved N95 Particulate Filtering Facepiece Respirators - A Suppliers List

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The site also notes that some products that are approved by NIOSH as an N95 respirator and also cleared by the Food and Drug Administration (FDA) as a surgical mask. These products are referred to as Surgical N95 Respirators. Surgical N95s differ from NIOSH approved N95s in the form of increased fluid resistance as approved by the FDA. Surgical N95 respirators meet ASTM Test Method F1862 “Resistance of Medical Face Masks to Penetration by Synthetic Blood”. N95 respirator NaCl test details are covered in Appendix D.

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5: Other Teams, Projects and Resources to Consider This document is open for collaboration. Some areas that need assistance:

● Medical or manufacturing expertise to fact check, add detail, add sources ● Researching commercially available fabrics & coordinate testing for mask efficacy

○ Need a list of existing fabrics in bulk, viable candidates ○ Add to our growing list ○ Recommend test top online designs, such as top three masks from Joanne

Fabric, and test @ Yale ● Identifying and coordinating with existing mask making efforts

○ A source for 3D printed designs: https://3dprint.nih.gov/collections/covid-19-response/

● Coordinating with hospitals seeking information Other Teams, Projects and Resources worth mentioning:

● Reusability of Facemasks During an Influenza Pandemic: Facing the Flu ● N95DECON - A scientific consortium for data-driven study of N95 FFR decontamination ● COVID-19 Response – PRAKASH LAB ● Respiratory Protection Infographics | NPPTL | NIOSH ● The effectiveness of respiratory protection worn by communities to protect from volcanic

ash inhalation. Part I: Filtration efficiency tests

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APPENDIX A - SEM Imaging Knit

Woven

Non-Woven

Table B1. (Engineering of High-Performance Textiles)

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APPENDIX B - Filtration Efficiency Figures

Figure B1: Preliminary data of non-medical materials for filtration (Dr. Wang, Missouri

S&T, unpublished) (Yang Wang (@carlwangyang))

- The same study also shows that multiple layers stacked increases the effectiveness of filtration for all types or materials. A 600 thread count pillowcase captured nearly three times the particles when in four layers compared to two layers.

- Others have looked into blue shop towels that have 2-3x better filtration than cotton alone. Inserting two of these towels indo a cotton mask increased filtration up to 93% for particles as small as 0.3 micron. Meanwhile, cotton masks filtered 60% of particles at best. (Blue Shop Towels)

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- Effectiveness of filtrated volcanic ash of <1um diameter;

Figure B2. The effectiveness of respiratory protection worn by communities to protect from 

volcanic ash inhalation. Part I: Filtration efficiency tests

- Below are some WUSTL figures from their aerosol lab inspired by Dr. Wang's

research. Here, swiffer material and higher MERV materials are the most effective at

filtration.

- Filtration efficiency decreases from being high at very very small particles to less

effective at about 1 um for some materials, and then above 1 um, all efficiencies for

all materials are high. Seems counter-intuitive, but the reason 0.3 micron test

particles are used for the NIACH testing is that the range 0.3 micron particles are

supposed to be the most difficult to filter. Not big enough to be intercepted or

contact fibers due to inertia, and not small enough to be affected by diffusion.

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Figure B3 and B4: Filter efficiency of various materials. (AAQRL, WUSTL,

unpublished) AAQRL (@aaqrl_wustl)

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- and some figures from Prof. Marr at Virginia Tech.

Figure B5 and B6: Filtration efficiency of different materials (Prof. Marr, Virginia Tech,

unpublished)

Figure B7: Furnace filters vs HEPA filters effectiveness. (Kim et al. “Experimental study of nanoparticles

penetration through commercial filter media”Journal of Nanoparticle Research (2007) 9:117–125).

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https://www.researchgate.net/publication/226318339_Experimental_study_of_nanoparticle_penetration_through_commercial_filter_media

Figure B8: Particles blocked with various PPE. (Figure 2: Part Fibre Toxicol. 2009; 6: 8. )

In a study of the first randomized control trial of cloth masks, and the results caution

against the use of cloth masks. This is an important finding to inform occupational health and safety. Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection. Further research is needed to inform the widespread use of cloth masks globally. However, as a precautionary measure, cloth masks should not be recommended for healthcare workers, particularly in high-risk situations, and guidelines need to be updated. (A cluster randomised trial of cloth masks compared with medical masks in healthcare workers)

MERV stands for 'minimum efficiency reporting value' and is a standard that rates the overall effectiveness of air filters. A higher value means finer filtration. Dr. Yang Wang at Missouri U of Sci and Tech tested a number of everyday materials using what appears to be the same test used to rate the N95 filters. They found that an allergy-reducing HVAC filter captured 94% with two layers, and that a furnace filter captured 95% with six layers. In order to find a filter similar to the two that were tested, we should look for a MERV rating of 12 or higher (or a

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microparticle performance rating of 1900 or higher) on other types of filters. (What's the Best Material for a Mask for Coronavirus?)

Specific off-the-shelf materials worth investigating The following table is a list of materials that are likely effective in terms of filtration, however have a current lack of evidence to support their effectiveness in masks and should be tested if capabilities allow.

Material Reason to Consider Link

Lennox X5425 MERV 16 Filter

MERV 16 https://www.amazon.com/gp/product/B004X4UN9M/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1

Air Filter Rolls

Polyester, MERV 7 or 8, but may be too thick (1 or 2”)

https://www.mcmaster.com/air-furnace-filters/maximum-filter-efficiency~99-/air-filter-rolls/

Filter Felt 6376T1

Polyester, minimal thickness, filters as low as 5um particles

6376T1

Nonwoven polypropylene

Same fiber material and fabric construction as N95 respirator

https://www.joann.com/pellon-360-ez-stitch-tear-away-stabilizer-20/12043329.html#q=nonwoven%2Bpolypropylene&start=1

Table B2: Materials with a lack of data that may be useful as filtration materials in DIY masks.

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Table B3. What is a MERV rating? | Indoor Air

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APPENDIX C - www.n95decon.org Below are 4 fact sheets published by n95decon.org. From their website, N95decon is a volunteer collective of scientists, engineers, clinicians, and students from universities across the US (University of California, San Francisco; University of California, Berkeley; University of Chicago; Harvard University; Stanford University; Georgetown University; Seattle University; University of Utah; Massachusetts Institute of Technology and the University of Michigan) as well as other professionals in the private sector. N95DECON seeks to review, collate, publish, and disseminate scientific information about N95 decontamination to help in decisions about N95 decontamination and reuse. Another goal is to identify important missing information, then plan and carry out future joint research projects to address those knowledge gaps rapidly without unnecessary duplication of effort. N95DECON is not sponsored by any group nor does it represent the interests of any private/public organization or any specific technology.

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APPENDIX D - Overflow

D.1: Polypropylene Background and Usage in Respirators Polypropylene

Polypropylene is one of five major commodity plastic resins now produced in large quantities in many countries. It is readily converted into spun-bonded fabric and structures with a very wide range of properties. Some of the parameters that can be varied include fiber thickness (down to micron or submicron diameters), density of fibers per unit area or volume, density of bond points, and average orientation of fibers.

For filtration and trapping of aqueous particles (as in respirators and medical masks), polypropylene fiber surfaces require modification to render them more hydrophilic (water attracting) because polypropylene is inherently hydrophobic (water repelling). Several methods are known to impart the necessary degree of hydrophilicity to the surface. A process in which a droplet-attracting electric charge is applied to the surface has also been described, but it is not clear that such a charge could be maintained during storage of the respirator or mask, and the charge would dissipate with exposure to air with any degree of humidity.

These materials and processes have produced a viable material whose low cost permits a disposable, one-use culture to prevail in industrialized countries. Spun-bonded polypropylene masks have completely supplanted the woven cotton fabric masks previously used in the United States and predominate in the filtration components of commonly used respirators. (Reusability of Facemasks During an Influenza Pandemic)

Figure 6: Respirator Design Examples

The test mask in Figure 6 is an N95-rated respirator face mask comprised of the following layers, from outer to inner (Figure 2): an outer layer constructed of hydrophobic non-woven polypropylene that prevents external moisture from entering the mask material, followed by two layers of melt-blown non-woven polypropylene that capture oil and non-oil based particles through four key mechanisms. The next layer is a modacrylic support layer that provides rigidity and adds thickness to the mask, giving it more structure and adding to the feel of comfort. The innermost layer is another hydrophobic non-woven polypropylene layer which minimizes moisture within the mask from entering the mask material and adversely impacting filtration efficiency. (Assessment of a respiratory face mask for capturing air pollutants and pathogens) Alternative Materials

A membrane that is hydrophobic will have a greater tendency to being fouled, especially by proteins. Hydrophobic membranes require wetting, for example with alcohol, prior to filtration of water-based solutions: they are consequently good filtration media for gases. Three hydrophobic materials commonly used as microfiltration membranes are PTFE, PVDF

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(polyvinylidene difluoride) and polypropylene. These all exhibit excellent to good chemical stability. PTFE is insoluble in most common solvents and is produced by solvent casting. PVDF is less stable than PTFE, and is soluble in aprotic solvents such as dimethylformamide, and can be produced by solvent casting. Polypropylene is the least stable of the three and can be produced by stretching and phase inversion. (Handbook of Filter Media 2nd Ed)

D.2: Production Techniques and Tips The standard production technique for N95 respirators is melt blowing polymers into a

small fiber. Other production techniques could include electrospinning, melt-spinning, and rotary jet spinning to name a few. Each technique comes with different manufacturing challenges, which could be properly adding charge to the material or producing enough material or an expensive overhead cost. Adding Electrostatic Charge

The most important part of the process is adding the electrostatic charge to the fiber to create an electret. This is described briefly in 3Ms patent of the process (US4215682A - Melt-blown fibrous electrets) using corona (not the virus) charging and in an article about Peter Tsai, the inventor of this technique . An electric field is used to ionize neutral air which generates ions and electrons that charge the molten nonwoven fibers as they are melt-blown.(University of Tennessee - Nonwoven Peter Tsai) Some other versions of the N95 made by other companies include additives to the polymer that are supposed to help sustain the electrostatic charge, such as copper and zinc ions (BioFriend BioMask N95). The charges in the devices last throughout the shelf life of the device. According to a report summarizing the reusability of facemasks during an influenza pandemic,” the first electrostatic filters used resins added to natural wool fibers to retain an electrostatic charge.... However, the efficiency of resin electrostatic filters is degraded when they are exposed to airborne oil mists and other materials that shield the electrostatic charge. Manufacturers have been able to overcome this issue by incorporating synthetic plastic fibers, such as polypropylene which are said to be capable of holding a sufficiently strong electrostatic charge (electret) to effectively resist the shielding effects of oil.” (Reusability of Facemasks During an Influenza Pandemic)

There are however other methods to charge these materials that aren’t currently as widely used. This includes triboelectric charging (friction) or chemical enhancement, as suggested by one patent application (KR101160691B1 - Electrostatically Charged Filter Media Incorporating An Active Agent). Peter Tsai also invented another approach to apply electrostatic charge to fabrics, this time via friction (triboelectrification). In a nutshell he soaks the fabrics with water, and then draws them out with a vacuum which generates friction and adds charge to the fabric. The main triboelectric fibrer couple for some time was polypropylene and modacrylic, and this is still exemplified by Hollingsworth and Vose's Technostat media (formally Hepworth) 18t. A newer fibre grouping is polypropylene with polymetaphenylene isophthalamide, supplied as Tribo media by Texel (9~, with claims for superior performance. These fibre mixtures are well

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suited to needle punching technology, and there is evidence that they have much better charge characteristics than corona charged material. (Handbook of Filter Media 2nd Ed)

Figure D1: Triboelectric series of textile materials. (Handbook of Filter Media 2nd Ed)

One way to know whether the charge of a device is effective is to do the typical NIACH

tests and show that it is effective in filtering out a certain amount of a specific particle size. However, this is an indirect measurement of how much charge there is. A direct measurement can be made by measuring the surface voltage in the fiber web with an isoprobe electrostatic voltmeter (US4215682A - Melt-blown fibrous electrets). A measurement of this nature could be less accurate if the fibers contain a mix of opposite charges. This mix of charges is still good for filtering properties, it just won’t be fully represented by the net charge measured with this technique. In this 3M patent, fibrous electrets that carry a persistent charge of only one sign measured generally at least 10-8 coulombs per gram of melt-blown fibers. For fibrous electrets that include both positively and negatively charged fibers, the net charge will generally be at least 10-9 coulombs per gram of melt-blown fibers. Other measurements of electric charge are possible, but may not provide the quantification of charges brought about by this technique. Researchers in the Prakash Lab at Stanford have recorded their own observations of measuring electrostatic charge and surface energy using special voltmeters and have been able to make measurements on fibers they have created using a non-contacting electrostatic voltmeter. (Project 1000 x 1000 - Prakash Lab)

The following are types of medium that might be used in cabin air filters: (a) Electrospun nonwovens, which combine electrostatic effects with nanofiber filtration. (b) Triboelectrically charged needle-punched nonwovens. (c) Split charged fiber media. (d) Melt-blown media. (e) Spunbonded nonwovens. (f) Dry laid webs. (g) Wet laid webs. (h) Adsorptive media (activated carbon and activated alumina). (i) Composite structures of the above. (Handbook of Nonwoven Filter Media)

Activated carbon is the most frequently used adsorbent to remove dangerous chemical and fume components from the air. Usually advanced respirator canisters contain a bed of activated carbon granules or pellets. In some applications, the activated carbon is combined with nonwoven layers to form a composite structure. Other forms of nonwovens containing

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activated carbon are utilized, such as wet laid webs impregnated with carbon particles and webs coated with activated carbon particles. For severe chemical application.s the activated carbon may be treated with metal salts of copper, silver, zinc, and molybdenum (ASZM) and with triethylenediamine (TEDA) for enhanced chem-sorption properties. ASZM-TEDA produced by Calgon Carbon Corporation of Pittsburgh, Pennsylvania USA is an activated carbon of this type used for military gas mask applications

Some applications use hydrophilic layers to attract droplets instead of repel them. For example, This antiviral surgical face mask which was equivalent in all ways to a normal ASTM-F2100 surgical face mask used by hospitals and medical practitioners. Because the outer layer is hydrophilic, it absorbs sneezes and coughed droplets, and the compounds in the outer layer could inactivate a variety of respiratory viruses. The mask was tested against 15-plus strains of influenza type A and type B as well as swine, equine and avian influenza, all with 99.99% inactivation. They also worked to inactivate other respiratory and other common bacterial pathogens. (Are you wearing your mask properly? The ultimate guide of do's and don'ts for the coronavirus crisis.) Combinations of Polypropylene and Other Polymers

Typical of the media used in respirators are the needlefelts described in Table 5.17: relatively thick sheets of needlefelts, made mainly from a mixture of polypropylene and polyacrylonitryl fibres. These have low breathing resistances, allowing the making of a small mask, and avoiding the fitting of a bypass valve used when breathing resistance rises too high.

Figure D2: Needlefelt options for respirators.

D.3: N95 Respirator Testing Expanded

Sodium Chloride Aerosol Challenge

The Sodium Chloride Aerosol Challenge test is able to determine filtration efficiency measurements up to 99.999%. In this procedure, the TSI® CERTITEST® Model 8130

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Automated Filter Tester reservoir is filled with a 2% NaCl solution.* The sample is placed into the filter holder. Cone or molded masks and respirators are mounted to a test fixture and sealed into a cylinder filter holder to ensure that the mask is properly sealed.

Samples are subjected to aerosolized NaCl. The concentration of NaCl is measured before and after impact with the sample. The amount of NaCl that passes through the sample is used to calculate the filtration efficiency of the sample.

Respirators for NIOSH pre-qualification are required to be preconditioned at 85 ± 5% RH and 38 ± 2.5°C for 25 hours prior to assessing the filtration efficiency.

There are three categories for NIOSH-certified, nonpowered, air-purifying, particulate-filter respirators: N (Not resistant to oil), R (Resistant to oil), and P (oil Proof).

*Only N-series filters are evaluated using a NaCl aerosol, which is slightly degrading to filter medium. Test articles intended to be resistant to oil (R-series) or oil proof (P-series) must be evaluated using an oil-based aerosol.

Test articles submitted for testing according to NIOSH requirements will be tested according to 42 CFR Part 84 “Approval of Respiratory Protective Devices.”

Dioctyl Phthalate (DOP) Challenge

The DOP aerosol test is a widely accepted method for evaluating particle penetration and air flow resistance properties of a variety of filtration materials (e.g., breathing system filters, NIOSH respirators and face masks). The procedure employs an aerosol of DOP using a TSI® CERTITEST® Model 8130 Automated Filter Tester.

Test articles are challenged with particles of the most penetrating particle size range, 0.3 µm.

Filtration efficiency measurements can be determined up to 99.999%. Samples can be tested at flow rates up to 90 liters per minute (LPM). The filtration requirement for HEPA filters is 99.97% at 0.3 µm using the DOP test.

Inhalation, Exhalation, and Valve Leak Tests

In addition to NaCl and DOP tests, mask manufacturers may be required to demonstrate inhalation, exhalation, and valve leak tests in conformance with 42 CFR Part 84 and NIOSH procedures.

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