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National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Health Sciences Policy; Giammaria C, Yost O, Nicholson A, editors. Current Issues in the Assessment of Respiratory Protective Devices for Occupational and Non-Occupational Uses: Proceedings of a Workshop. Washington (DC): National Academies Press (US); 2020 Dec 22.
Current Issues in the Assessment of Respiratory Protective Devices for Occupational and Non-Occupational Uses: Proceedings of a Workshop.
Show detailsRespiratory protective devices (RPDs) are assessed and approved through various pathways, but there are large gaps in regulation where certain populations are using devices that have not been subjected to any assessment. In this session, moderated by planning committee member Daniel Shipp, retired from the International Safety Equipment Association, three speakers explored how existing conformity assessment (CA) processes may be used to provide respiratory protection for non-occupational use, specifically the use of these devices by the general public. They also discussed classifications and testing requirements for general-purpose face coverings and described extant opportunities to develop or support CA processes that address the requirements of nontraditional users. Before beginning the session, Shipp commented that current events have rapidly changed our perception concerning the use of RPDs and cloth masks by the public. As such, he said, it is critical to understand how mask performance can be assessed against requirements and who should regulate this.1 These topics would be explored by the expert panelists in their presentations and during the discussion period.
CHALLENGES IN PROVIDING RESPIRATORY PROTECTION TO THE PUBLIC
Jim Johnson, a principal for JSJ & Associates, discussed the critical questions and challenges associated with providing non-occupational respiratory protection to the public. He highlighted several critical issues, including (1) to whom should this protection be provided, (2) the hazards from which protection is needed, and (3) how protection will be provided. RPDs have typically been designed for use in occupational settings by healthy workers, he said, but the need is growing for respiratory protection among the general public, children, and at-risk populations (e.g., elderly, physically challenged, immunocompromised). Unique issues may arise in offering respiratory protection to members of each of these groups, he said.
Defining the hazards to be addressed by RPDs has long been challenging due to the broad range of potentially hazardous chemicals (e.g., chemical spills, pesticide spray, leaded gasoline), air pollution (e.g., smog, ozone particulates, smoke from wildfires), and biological agents (e.g., mold, viruses). He said that in addition to the nature of the hazard, the source of the hazard is also an issue that must be considered. In the context of the coronavirus disease 2019 (COVID-19) pandemic, for example, the major source of the hazard is the presence of other infected people.
Some of the mechanisms through which respiratory protection can be provided include engineering controls, administrative controls, and the use of personal protective equipment (PPE), Johnson said. For instance, protection may be provided through ventilation systems, high-efficiency particulate air filters, electrostatic filters, increasing the frequency of air changes, or using large air volumes to help control or dilute the hazard source. An example of administrative control would be using social distancing to reduce the hazards of COVID-19 transmission. Johnson said that PPE has typically been regarded as the last line of defense or the last resort to protect against hazards that cannot be avoided through other controls. However, he said, during the COVID-19 pandemic, PPE has emerged as a major focus of the pandemic response, underscoring the need for better education about the appropriate use of RPDs to reduce the spread of disease.
Defining Respiratory Protective Devices
Johnson explained that RPDs are devices that have been designed to provide the wearer with a specified level of respiratory protection against a defined hazard. RPDs can be divided into three types based on design and performance: (1) respirators, which are a recognized type of PPE; (2) masks, like surgical masks, which can be a type of PPE; and (3) facial coverings, which are not a type of PPE. For respirators, the National Institute for Occupational Safety and Health (NIOSH) and the Food and Drug Administration (FDA) define the CA process, and the Occupational Safety and Health Administration (OSHA) defines the elements of the respiratory protection program for use by management. For masks, FDA defines the performance of surgical and non-surgical face masks, but face masks for non-medical use by the general public have no FDA requirements. “Facial covering” is a new designation that is currently being defined, with specific performance requirements being identified and developed. Johnson shared images of three common examples of NIOSH-approved half-facepiece respirators, including elastomeric half facepieces, filtering half facepieces, and surgical N95s, that would pass fit-test requirements. One of the filtering half facepieces pictured featured an exhalation valve. Johnson commented that exhalation valves are a type of impactor, which when opened can remove some of the particulate, especially large droplets, from an individual's exhaled airstream. He also presented images of various types of masks and facial coverings, including a surgical face mask, non-surgical procedure face mask, comfort mask, and several types of facial coverings (see Figure 6-1). FDA has some oversight over the two types of face mask and sets performance criteria for the protection these provide the wearer. Johnson reiterated that work is under way to develop a standard for facial coverings.
FIGURE 6-1
Examples of respiratory protective devices, masks, and facial coverings. Top: NIOSH-approved half facepiece respirators. Bottom: Masks and facial coverings. NOTE: FDA = Food and Drug Administration.
Ensuring the Effective Use of Respiratory Protective Devices by the Public
Johnson discussed several strategies to support the effective use of RPDs—specifically, facial coverings—by the public. The first strategy was to assign the responsibility for the overall program to a single organization with the authority to delegate responsibilities as appropriate. This organization could be a government or private-sector entity; Johnson suggested that NIOSH could be a good candidate for this role because it has the history, skills, and knowledge that could help expedite this effort. The second strategy was to develop an education program for the general public that could help to clarify the distinctions between respirators, masks, and facial coverings and the levels of protection they provide. A third strategy would be to evaluate, quantify, and communicate information about the hazards and risks clearly and accurately (e.g., whether droplets or particles are the major COVID-19 inhalation hazard). Finally, Johnson suggested implementing consensus standards that define RPD performance and include a CA program. He noted that multiple publications from the Institute of Medicine and the National Academies of Sciences, Engineering, and Medicine provide a wealth of information about RPDs and other topics related to the use of PPE (IOM, 2006, 2011a,b; NASEM, 2019).
To conclude, Johnson emphasized that the development of a CA program for RPDs and other PPE for civilian use needs to be assigned to a single organization with the authority to delegate as appropriate. He suggested that this CA program could follow the successful models currently used by NIOSH and OSHA. Finally, he underlined the major challenge of developing systems to identify and characterize hazards and quantify the risks encountered by the public when they use RPDs or other PPE.
CLASSIFICATIONS AND TESTING REQUIREMENTS FOR GENERAL-PURPOSE FACE COVERINGS
Emiel DenHartog, an associate professor and an associate director of the Textile Protection and Comfort Center at North Carolina State University, provided an overview of classifications and testing requirements for general-purpose face coverings. He said that during the early stages of the COVID-19 pandemic, he and his colleagues at the North Carolina State University's Wilson College of Textiles received numerous requests from textile manufacturers who wanted to begin producing general-purpose face coverings and wanted a better understanding of surgical masks and N95 respirators; however, at that time only limited guidance and standards were available for general-purpose masks. This catalyzed a group of volunteers from the American Association of Textile Chemists and Colorists and other institutes and organizations to help guide the textile industry in developing a voluntary standard.2 Their efforts, DenHartog said, focused on helping manufacturers understand what they would need to do to help serve the public by making general-purpose face coverings, a category that is distinct from N95 respirators and surgical/medical masks.
Because of the nature of existing requirements for PPE for occupational use, DenHartog said, general-purpose masks need a separate requirement. The extant RPD certifications primarily target occupational use (3M, 2020), and most, if not all, standards for protective masks are focused on occupational health settings and protecting people while they work. In contrast, few standards or requirements exist for general-purpose masks, although several voluntary guidance documents are available, especially from Europe (e.g., AFNOR, BSI, CE, NEN).3 As a PPE scientist, he said, he is concerned about the common adage “Anything is better than nothing” when it comes to respiratory protection because he knows of many examples in which inappropriate use of a protection product worsened the user's exposure or risk. This can result in a false sense of security associated with the use of respiratory protection, he said, and poorly designed RPDs may be made with materials that actually contribute to the risk of exposure.
Monograph Specifications for General-Purpose Face Coverings
The collaborative efforts described by DenHartog led to the development of a voluntary draft monograph4 for the textile industry that offers basic design guidance and construction suggestions.5 DenHartog highlighted two of the technical specifications provided in the monograph: particle filtration and air permeability. The monograph attempts to offer some guidance regarding fit, but there is no available standard, so the document provides general guidance about what indicators should be considered to address the fit of a face covering. He noted that the monograph is now being further developed by ASTM International to provide more technical detail, background, and guidance.
Particle Filtration Efficiency
The voluntary draft suggests that for particle filtration efficiency,6 face coverings shall demonstrate a particle filtration efficiency of greater than 70 percent with maximum 3-micron particle size at a velocity of 10.4 cm/s. Testing is to be performed on “as-received” samples after a specified number of washes. DenHartog characterized this target filtration efficiency as a low bar that would primarily guarantee only the filtration of larger droplets. In the future, he said, a target filtration efficiency of 70 percent with maximum particle size of 2.5 microns may be suitable for protecting against smoke or pollution. The filtration efficiency of 70 percent was chosen based on European standards (ASTM F2299 or technical equivalent).
Breathing Resistance: Air Permeability
Ensuring the appropriate technical specifications for breathing resistance is important for ensuring that people can actually breath through the face covering, DenHartog said. The three international standards for air permeability—EN 14683,7 ASTM D737,8 and ISO 93279—are each associated with basic air permeability tests to assess how air flow will pass through a fabric or a fabric assembly at a certain pressure. The monograph provides guidance on how manufacturers can test their materials and understand how their results correspond with the various standards, including the EN standards and the requirements for NIOSH-certified products. DenHartog suggested that if these requirements can be fulfilled by those manufacturing face coverings, it might be appropriate to say that “anything is better than nothing” with respect to the risk–benefit ratio.
Variation in Fabrics Used in General-Purpose Masks
DenHartog said that the fabric used to manufacture non-medical, general-purpose masks for use by the general public varies widely and affects the filtration properties of the masks. The fabric used in general-purpose cloth masks differs in important ways from the fabric used in N95s, he said. N95s are manufactured with non-woven, technical-filtration fabrics that have a different structure than woven fabrics and have additional electrostatic functionality to enhance filtration efficiency. The structure of non-woven, technical-filtration fabric is made of a random fiber net that is created by the intersection of fine, rod-like segments of fibers. Because of the distribution of these fine fibers and other features of technical-filtration fabrics, they work well as effective yet inexpensive filter materials. In contrast, DenHartog said, woven fabrics and knit fabrics have a structure that is less random, so they must be designed carefully to provide any degree of filtration. In fact, he added, due to its standardized and patterned structure, woven cloth may function more like a sieve than a filter. Furthermore, the same basic structure can provide different filtration properties depending on the type of yarn that is used. Yarn can be made of different types of fibers that can be spun in various ways and thus affect a textile material's filtration efficiency (Ghosh et al., 2008). Fabric finishing techniques such as brushing, pilling, or raising can also affect surface hairiness and roughness, in turn influencing filtration efficiency.
General-purpose mask manufacturers must understand that “one cloth does not equal another” in terms of filtration efficiency, DenHartog said. Given the wide variation in textile materials, it is not yet possible to provide manufacturers with clear, simple guidance regarding fabric structure. Filtration efficiency should be measured, but it cannot yet be predicted, he said. For instance, the description of a fabric (e.g., “one-layer knit,” “layer jersey knit,” “two-layer jersey knit”) can capture some of a fabric's physical properties, but descriptions of a fabric's property are not sufficient to predict its filtration efficiency. He said that the textile industry is generally receptive to shifting production toward the materials best suited for filtration, but there is not yet sufficient evidence to make specific recommendations to manufacturers. In part, this is because the focus has been on understanding the filtration properties of non-woven fabric rather than of woven or knit fabrics. Although filtration efficiency can be improved by adding layers of fabric, this improvement comes at the expense of breathing resistance. DenHartog added that various woven and knit fabrics will need to be tested for any evidence-based claims to be made about their filtration efficiency.
Particulate Filtration Efficiency of Different Materials
DenHartog presented findings about the particulate filtration efficiency of materials assessed through North Carolina State University's Textile Protection and Comfort Center's newly developed material-level evaluation (see Figure 6-2). For most filtering materials, particulate filtration efficiency was relatively low for particles ≤3 microns in size; only N95 mask material performed consistently when filtering such particles. Filtering very small particles and aerosols is a great challenge for most fabrics, he said, and this is a major issue when using fabrics for filtration. These findings suggest that general-purpose face masks are best suited to protect against large droplets that are ≥3 microns in size, which may not travel as far or be suspended as long as smaller particles.10 He added that cloth fabrics have poor filtration efficiency in the aerosol particle range; however, depending on the hazard, these face coverings may not require a highly protective level.
FIGURE 6-2
Particulate filtration efficiency of materials assessed through North Carolina State University's Textile Protection and Comfort Center's newly developed material-level evaluation. NOTE: Tests conducted using FLUKE 985 particle counter–0.1 cfm (more...)
Considerations for General-Purpose Face Coverings
DenHartog said that the protection offered by PPE is not merely about the fabric used, but about the final product and how it fits an individual. Mask fit is a major consideration because air follows the path of least resistance. Air that escapes from the mask perimeter is not passing through the mask. For instance, if a person's eyeglasses fog up while wearing a mask, it indicates that the mask is not appropriately fitted and that air is escaping around the mask perimeter. This effect is compounded by the fact that smaller particles (i.e., aerosols) are more likely to follow the flow of air. He noted that masks with transparent “plastic windows” to make the mask wearer's mouth visible will necessarily divert airflow, including aerosols, away from the impermeable plastic section and, as a result, they may not reduce the spread of a virus such as SARS-CoV-2.
To conclude, DenHartog explained that face coverings are not PPE, but they may help reduce the aerosol-exposure of the wearer to some degree, and, in the case of infectious diseases, they may help to reduce the spread of infectious droplets from the wearer. PPE scientists who are accustomed to dealing with filtration efficiencies of 95–99.9 percent may be concerned by the low filtration efficiencies of cloth masks, he said. However, the high filtration standards for extant PPE devices are designed to protect individuals who are entering known hazardous environments (e.g., first responders, chemical crews). From a public health perspective, however, there may be value in using less efficient filtering materials even though the minimal effective level is not yet known, DenHartog said. For example, he suggested that using a face covering with 20 percent filtration efficiency could represent a significant reduction that contributes to improved public health outcomes, even if that level of efficiency would be insufficient for use as occupational PPE. For instance, if 10 million individuals are exposed, then the use of a face covering with 20 percent filtration efficiency could potentially avoid exposing 2 million people. In a scenario with a 0.2 percent mortality rate associated with exposure, this device could save as many as 4,000 lives. DenHartog emphasized “not PPE” does not mean “not effective” from a public health perspective. This is because the objective of face coverings is to improve public health, not to protect individuals in hazardous environments. He suggested that in the context of the COVID-19 pandemic, this argument could help in public messaging about the potential benefits of using face coverings in addition to physical distancing.
DEVELOPING A STANDARD SPECIFICATION FOR BARRIER FACE COVERINGS
Jonathan Szalajda, the deputy director of the National Personal Protective Technology Laboratory (NPPTL) at NIOSH, discussed opportunities to develop or support CA processes for RPDs and for source control strategies, such as cloth face coverings, that are responsive to the specific requirements of nontraditional user groups. He focused specifically on the ASTM Work Item 73471–Standard Specification for Barrier Face Coverings (ASTM 73471).
ASTM Work Item 73471–Standard Specification for Barrier Face Coverings
Szalajda described how the development of ASTM 73471 began in summer 2020, when a fabrics industry association initiated a discussion about developing a “get back to work” product in response to the COVID19 pandemic. A committee of more than 45 representatives from industry, academia, and government was then convened to develop ASTM 73471. The “get back to work” product is not a respirator or a surgical mask, nor is it intended to replace those commodities. Instead, Szalajda said, the basic idea was to create a device that is superior to a simple cloth face covering—perhaps closer in caliber to an N95 or surgical mask—but that also addresses the issues of scalability associated with true respirators. One scalability issue relates to the amount of non-woven fabric required to produce respirators. To address this issue, Szalajda suggested identifying commonly available materials that would be accessible in larger quantities to create different designs for use as barrier face coverings.
Scope and Performance of ASTM 73471
The scope of the ASTM 73471 standard includes source control and the provision of some degree of inhalation protection. Emerging evidence suggest that face coverings may help to reduce transmission through source control, Szalajda said, and there is growing awareness that the types of face coverings currently being used vary in terms of effectiveness. The efficacy of face coverings for reducing transmission is dependent on how reliably individuals actually wear them, he said. Face coverings are not effective if they are not worn consistently or if individuals refuse to wear them. Citing historical accounts of non-compliance with policies regarding face covering during the 1918 influenza pandemic (Hauser, 2020), Szalajda said that neither face covering technology nor issues related to public compliance with face coverings have evolved substantially over the past century.
Szalajda recognized that the new ASTM 73471 standard could not be developed through the existing occupational approval or CA processes of NIOSH or NPPTL. Thus, ASTM International was engaged to initiate the work item and to develop a specification for barrier face coverings. The specification was intended to identify some minimum level of performance requirements, along with a standard that would provide improved source control while also preventing particles from being inhaled. Szalajda said the idea behind this approach was to afford the wearers of these face coverings greater control over their own safety, a greater incentive to wear their face coverings, and a higher degree of confidence in resuming normal activities.
ASTM 73471 has three main performance elements of concern: (1) if the covering has filtration capability, (2) if the covering “fits,” and (3) whether wearers can breathe while wearing the covering. “Fit,” Szalaida said, refers to a combination of factors, including how well a covering seals to the user's face and how well the covering prevents particles from entering the covering via its perimeter. Szalaida further explained that comfort is another aspect of performance that will be critical for public use, as face coverings must be comfortable enough to wear for long durations without requiring manipulation by the wearer to maintain comfort. Reusability is also an important feature of barrier face coverings, he added. The standard is intended to be flexible enough to address reusable products as long as those products still provide a degree of protection once laundered. For reusable barrier face coverings, Szalaida added, ASTM 73471 will require that the product will be tested after laundering.
Addressing Translational Gaps and Challenges
The committee developing the ASTM 73471 standard has been identifying performance-related research gaps, Szalajda said. He added that translating a process and procedure from well-defined occupational products to general use products is challenging. However, the committee is working to determine minimum performance criteria to be expanded on in the future following more comprehensive research efforts to fill critical knowledge gaps related to performance. He said that, thus far, the committee's focus has been on developing standards that use existing test methods for ASTM International or NIOSH processes. For instance, they are looking at filtration requirements using the ASTM F-2100 standard and the NIOSH test procedure for N95 filtering facepiece efficiency. They are also considering the forthcoming ASTM standard for measuring fit (expected to be released in late 2020) as well as the NIOSH breathing resistance test. Additionally, they are planning to reference the ASTM International CA method described by Jeff Stull, the president of International Personnel Protection, Inc., in Chapter 5 of this proceedings. Szalajda said that the committee has also considered a unique approach that involves looking at manufacturers' self-reported data about fit capability given that most of the users of these types of devices will not have the capability to fit test their own device. Szalajda suggested that integrating fit capability as part of the approval process could increase the probability that devices will appropriately fit users.
Next Steps After the Development of the Standard
Szalajda suggested several potential ways forward after the development of the ASTM 73471 standard. A major translational challenge will be that nuanced terminological distinctions (e.g., N95, surgical masks, face coverings) are not readily apparent to the public. “They are all a mask as far as the public is concerned,” he said. Going forward, he added, how these concepts are introduced to the public will be critical. Szalajda went on to say it will also be necessary to identify the required protection for these types of products, and technical experts are working to synthesize existing literature and research to develop a standard for the performance of face coverings, to establish a baseline for identifying research gaps, and to identify hazards and appropriate levels of performance.
Szalajda also remarked on considerations related to the oversight associated with this type of product (e.g., determining which governing bodies have authority over such products and how oversight will be implemented at the national level). CA will be another important aspect of the success of this new product, he said. CA can provide needed assurance that a product meets the declared performance standard and helps to eliminate products from the market that do not offer any protection. He commented that this effect was demonstrated following the September 11, 2001, attacks, when many products came to the market that purported to provide users with protection from chemical, biological, radiological, and nuclear hazards. However, once a standard was established that identified the appropriate protections, many of these products disappeared from the market. Looking to the future, he raised the question of how performance can be presented to users in a way that helps individuals make informed decisions. He wondered whether information about the performance of face coverings—or any other types of products that may evolve to public use from occupational use—will need to be presented in a manner that allows for informed decision making by the public.
DISCUSSION
Conformity Assessment for Barrier Masks
Shipp asked the panel about the most critical elements or factors for a CA program to examine in assessing the performance of barrier masks. Johnson spoke of the need to address the hazard that a barrier mask is to be used for as well as the expectations of the wearer. Additionally, Johnson said, there should be a background of approval, CA, and test methods that ensure a certain level of protection and performance for an individual who decides to wear that barrier mask to reduce risk. DenHartog suggested developing some level of hazard assessment to determine appropriate standards and test methods, which would make it possible for certification to be conducted by private companies or through NPPTL. At that point public health and educational efforts could then support individuals in decision making related to the selection and use of products for different circumstances, he added.
Szalajda suggested that using an analysis of risk to identify the appropriate CA for face-covering products is an opportunity to apply the national framework developed by NIOSH. Face coverings, he said, should not be discussed as providing the same level of protection as a respirator or a surgical mask. However, these products do serve a role in providing a level of protection for the general public, he said, so he suggested that the development of a standard for barrier face coverings should determine and propose a CA level that is associated with the risks in the areas where these products are being used.
Shipp asked Szalajda whether he envisions (1) a set of standards or CA procedures for face coverings that are equivalent to what NIOSH currently has in place for respirators to assess different types of hazards, such as particulates, vapors, or gases, or (2) a broader set of requirements that would define, in general terms, factors such as filtration efficiency, breathing resistance, and fit. Szalajda replied that a more general set of requirements will be needed for face coverings because they are source control devices and not respirators. Whether through a third-party evaluation or some other mechanism, source control should be addressed as part of the standards development process, he said. He went on to explain that in settings where there is less certainty regarding the risk and the protection associated with those risks, more flexibility could be allowed in terms of how information is presented. A standard would allow manufacturers to report their filtration efficiency against the NIOSH requirement.11 Szalajda added that manufacturers will be allowed to present their “fit” or “leakage” for their products, depending on which term is ultimately agreed upon. The lingering issue, Szalajda said, will be determining how that information is translated to the public to assist decision making and it is unclear whether this would fall into the NIOSH framework or into a Safety Equipment Institute framework in association with ASTM International.
Barrier Face Coverings as Source Control
Shipp highlighted Szalajda's comments that barrier face coverings provide source control and, therefore, are only effective when everybody is wearing them. This differs from more typical RPDs, which are designed to protect the wearer. A participant asked whether a barrier face covering needs to perform similarly to a surgical N95—or perhaps at a lower protected factor—in providing protection to the wearer and providing source control as a barrier to outgoing pathogen flow. In addition, the participant asked whether a face covering should also protect from environmental hazards such as smoke and air pollution. Szalajda said he thinks the same requirement could be used for both the surgical mask and the face covering standard as the surgical mask standard has a national consensus already in place. Existing methods can be used to provide the source control element to ensure devices perform as they are intended to, he said.
Johnson contended that the growing evidence base about facial coverings will demonstrate that no single universal facial covering can be effective for protection against the full spectrum of exposure hazards (e.g., wildland smoke, SARS-CoV-2, pesticide applications), so the public will need to be educated about different types of hazards. He added that local public health departments will need to help ensure that the correct equipment is specified when there is a public health emergency. “We [cannot] fall in the trap that this current barrier mask is going to take care of everything,” he cautioned.
DenHartog raised the issue of air speed as it pertains to source control, noting that sneezing has been found to produce higher speeds and larger droplet sizes than coughing, talking, and breathing. In terms of source control, he said, the impact of droplet size on the effectiveness of cloth masks is still unknown. DenHartog said that the device needed for protection against smoke will be different from a device needed for protection against COVID-19. However, DenHartog added, it is becoming increasingly clear that there is at least some beneficial effect of well-designed cloth masks as source control.
N95 Exhalation Valves
Workshop planning committee member Melissa McDiarmid, a professor of medicine, epidemiology, and public health at the University of Maryland School of Medicine, suggested that concerns about the use of N95s with exhalation valves have been minimized somewhat by the asymptomatic spread of COVID-19. She mentioned that there are other pathways through a mask through which transmission could occur from the mask wearer, such as through the face seal. She noted that 10 percent face seal leakage is allowable even for an N95, and she asked the panel to comment about exhalation valves on N95s as well as on elastomerics.
Johnson suggested creating a visualization to demonstrate the difference between coughing through an exhalation valve and coughing without an exhalation valve. He noted that different exhalation valve designs will remove different percentages of particles. The exhalation valve may not open very much when the wearer of a filtering face piece mask is in a sedentary state, because air is flowing out through the filter media and the pressure does not drop substantially. He added that the potential effects of exhalation valves come into play when the wearer has a higher breathing rate, which reduces breathing resistance. Elastomerics always open, he explained, as that is the mechanism for exhaled air to exit the elastomeric face piece.
Johnson gave the example of a medical center that put an embargo on any filtering face piece with an exhalation valve and instructed people to wear face coverings instead. He said that this decision does not reflect an understanding of aerosol physics or respiratory protection, which underscores the need for better communication about the scientific underpinnings of different types of RPDs. From his perspective, he said, the key questions are (1) how the exhalation valve affects source control, (2) how the exhalation valve works as an impactor,12 and (3) how the covering on most exhalation valves functions as another collector of droplets of any size that pass through the valve. He maintained that if the medical community determines that exhalation valves are not acceptable, then every person who wears a mask is a potential contaminated source. In that case, he said, all of the controls applied to respirators need to be applied in the same way to masks. Szalajda said that any respirator—including respirators with exhalation valves—is a source control device. He said that NPPTL is actively working to quantify anything that may be coming through the exhalation valve or through face seal leakage. He added that an exhalation valve is often misconstrued as a hose blowing air out, which is not the case.
Maryann D'Alessandro, the director of NPPTL, referred to preliminary data showing that the outward leakage from an exhalation valve is not significant under normal breathing situations. She added that NIOSH is conducting laboratory studies to compare elastomerics and N95s with exhalation valves as well as with surgical masks in order to produce quantitative data. D'Alessandro said that the current position of the Centers for Disease Control and Prevention is that the N95 respirator with an exhalation valve provides the same level of protection to the wearer as one without a valve, but the presence of the valve reduces exhalation resistance, making it easier to breathe. She suggested that wearers could opt to put a covering over the valve until more data are available. D'Alessandro added that NIOSH is also exploring how to work with manufacturers to develop devices to cover the exhalation valve, either to filter air or to serve as a covering to eliminate this issue.
DenHartog added that masks with exhalation valves likely work better than many of the face coverings that people are wearing, such as gaiters or single-layer cloth masks. He also noted that masks need to be assessed in different ways. For example, cloth masks featuring a transparent window or cloth face coverings with filter pocket inserts to provide filtration in the center of the product could potentially increase air resistance and drive air around the filter. Instead of looking at the exhalation valve or at the fabric filtration in isolation, he suggested examining the mask overall and developing guidelines to certify masks.
Reflections on the Session
Shipp offered his reflections on the presentations and discussions of workshop Session 4B: Assessment Pathways for Respiratory Protective Devices and Other Options for the Public. First, he said, existing knowledge and experience about respiratory protection in occupational settings could be used and translated into a public health approach to respiratory protection. Respiratory protection for the public, Shipp said, needs to be properly situated among other health, safety, and administrative controls. For instance, Shipp added, in the response to the COVID-19 pandemic, administrative controls such as social distancing may have been incorporated into potential standards or guidance on the use of facial protection for the public. Given current circumstances, Shipp said, the typical process for standard development—which takes approximately 5 years—would need to be significantly accelerated to address the respiratory protection needs at hand. He highlighted the urgent need for information, both in terms of the public's need for information about how to communicate performance measures of respiratory products among suppliers, distributers, and sellers of respiratory products (e.g., community masks). He concluded that although he agrees that “the perfect should not be the enemy of the good,” particularly in terms of providing respiratory protection to the public, it is not necessarily the case that any protection is better than no protection.
Footnotes
- 1
In order to clarify terminology in this publication, masks, face coverings, facial coverings, and respirators are distinct terms with distinct meanings, but their use in this report depends on the speaker's choices. Every attempt has been made to limit the term “respirator” to a tight-fitting device that protects the user from inhaling airborne contaminants and “masks” to mean coverings that are loose, unfitted devices that cover the nose and the mouth of the user and provide protection for the environment from the user's cough and exhaled secretions. Respiratory protective devices (RPDs) include respirators as well as masks, face coverings, and facial coverings (Johnson, 2020; NASEM, 2019).
- 2
The voluntary standard is available at https://www
.aatcc.org /guidance-for-making-a-better-face-covering (accessed October 9, 2020). - 3
AFNOR = French Standardization Association; BSI = British Standards Institution; CE = Conformitè Europëenne; NEN = Royal Netherlands Standardization Institute.
- 4
The voluntary standard is available at https://www
.aatcc.org /guidance-for-making-a-better-face-covering (accessed October 9, 2020). - 5
DenHartog emphasized that while the monograph was not intended for the general public, education is needed among the public to ensure that RPDs are used correctly.
- 6
Specification is per ASTM F2299 or technical equivalent.
- 7
Using 8 L/min air flow, with standard diameter of 25 mm. Should exhibit a maximum of 36.7 Pa/cm2.
- 8
Using a standard 125 Pa pressure drop. Use the standard 38.3 cm2 test area. Should exhibit a minimum of a minimum of 37.5 ft3/min/ft2.
- 9
Using a standard 100 Pa pressure differential. Should exhibit a minimum of 0.91 L/min/cm2 (or 15 cm/s).
- 10
DenHartog clarified that technically it is small droplets rather than aerosols that would be suspended in air for a longer period of time and that assessment involves looking at the smaller micron particle size. National Personal Protective Technology Laboratory (NPPTL) tests are in the range of 0.1–0.5 microns because 0.3 microns is the most challenging size for technical media to filter.
- 11
More information about the 0059 test is available from https://www
.cdc.gov/niosh /npptl/stps/pdfs /TEB-APR-STP-0059-508.pdf (accessed September 16, 2020). - 12
Johnson clarified that exhalation valves are a type of impactor, which can remove particles when an airstream comes in contact with them earlier in the proceedings.
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