Criticism of Workplace Protection Barrier Face Covering Article Mischaracterizes ASTM Standard and its Potential Utility

Abstract

Editor's Note: This is a response to “Why a Workplace Barrier Face Covering is a Bad Idea” by Mark Nicas. DOI: 10.1177/10482911231193771

A commentary mischaracterizes the paper “Barrier Face Coverings for Workers.” The American Society for Testing and Materials (ASTM) Barrier Face Covering (BFC) F3502-21 standard established performance criteria for face coverings as source control. While the standard states that BFCs may offer some personal protection, this was never its primary goal. We described a proposal for BFCs to be worn in low-risk (nonhealth care) workplaces for the purpose of source control, not respiratory protection. We did not recommend BFCs as respiratory protection for any worker in any workplace. A BFC is not “another term for a cloth mask”; many higher performing products are based on nonwoven high-efficiency filter media. Our “time to infectious dose” table was included to illustrate the impact of different degrees of inward and outward leakage, not to describe a dose-response relationship, which includes time and airborne particle concentration.

A commentary ¹ mischaracterizes the paper “Barrier Face Coverings for Workers” ² in several ways. In particular, we disagree with the author's main point that the American Society for Testing and Materials (ASTM) Barrier Face Covering (BFC) F3502-21 standard is a backward step and a bad idea.

First, the standard established performance criteria for face coverings as source control, not respiratory protection. While it states that BFCs may offer some degree of personal protection, this was never the primary goal, as the standard itself makes clear.

The pandemic highlighted the importance of wearing a face covering the purpose of source control, never before seriously considered or addressed by respirator experts. Respirators have their place, especially in settings where exposures to infectious particles are likely. Outward leakage may also be important in health care and other workplaces where people spend extended time together. A well-fitting respirator can prevent inward leakage and is likely to prevent but is not currently evaluated for outward leakage.

Early in the pandemic the Centers for Disease Control and Prevention (CDC) suggested that the public could wear any type of mask. There was considerable uncertainty about what that meant and over time the word “mask” came to describe anything worn on the face. Many subject matter experts realized there should be better guidance about masks for preventing emission of infectious particles. In May 2020, the ASTM F23 Committee on Protective Clothing and Equipment determined that a standard for barrier face coverings was needed. After an intensive series of meetings, sometimes with more than 100 participants, a new ASTM F3502 standard was published in February 2021 (record time for such an effort).

The standard included metrics to address performance attributes considered necessary for the principal function of source control, although there is no validated method for measuring outward leakage of particles from a facepiece. Consequently, the detailed product specification included performance criteria for particulate filtration efficiency and breathing resistance, with an optional assessment of fit as a surrogate for outward leakage.

It is noteworthy that this standard applies the same test methodology the National Institute for Occupational Safety and Health (NIOSH) uses to evaluate filtering facepiece respirators (FFRs). ³ This was deliberate because a variety of different methods are currently used to describe filtration performance, which is confusing to end users. Moreover, the selected test method is validated and in use at multiple laboratories.

Our paper describes how a scientific panel developed a proposal for BFCs that could be worn in workplaces for source control, not respiratory protection. As Table 3 shows, a BFC with 80% outward and inward leakage (typical of most cloth masks) offers very limited protection for the wearer and people nearby. Only with something like a respirator, with less than 20% leakage, does the time extend to an 8h day and only if worn by everyone and not just those who may be infectious.

Second, the commentary author criticizes what he calls our “dose-infection response model.” That was not the purpose of our paper or Table 3. We never discussed a specific dose-infection relationship and were clear that the CDC's 15 min contact tracing time is not scientifically derived.

Both “time” and “concentration” play a role in the dose of infectious particles someone inhales. Concentration is a function of many factors, including the number of sources, source activities (e.g., breathing, talking, singing, etc.), ventilation, etc. A table that considers only time has many limitations but offers a useful illustration of how reducing inward or outward leakage of particles can reduce the likelihood of infection.

Third, we agree with the commentary author that barrier face coverings should not be expected to offer any degree of respiratory protection but disagree that a BFC is “another term for a cloth mask.” The ASTM F3502-21 standard established no requirements for the material used to construct a BFC. While a cloth mask may be able to meet ASTM F3502-21 performance levels for filter efficiency and breathing resistance, it could not meet the NIOSH workplace performance levels for outward leakage.

Fourth, the author incorrectly characterizes the purpose of the NIOSH workplace performance designations. We made no statements recommending their use as respiratory protection for any worker in any workplace setting.

Higher-performing BFCs were meant for low-risk and medium-risk settings where workers were wearing any type of face covering for source control. We did not mean to imply that respirator shortages in health care, which are high-risk settings, were the impetus for either the BFC standard or for higher performance BFCs. We agree that there are many other types of respirators, including elastomerics, that could and should have been used by health care workers during supply shortages. ⁴

NIOSH recently updated its designation of “workplace performance/plus” to “enhanced performance/plus” to broaden the utility of BFC products. These new notations will be updated on its PPE Info web site.

The Occupational Safety and Health Administration (OSHA) emergency temporary standard (ETS) for nonhealth care workplaces considered ASTM F3502-21 and the NIOSH workplace performance levels but found “insufficient evident to make a general finding of feasibility” for their requirement in lieu of vaccination. ⁵ However, the agency stated that the purpose of a face covering worn by an unvaccinated worker was for source control, not personal protection. OSHA defined a “face covering” as something that completely cover the nose and mouth, is constructed of two or more layers of breathable fabric, is secured to the head with ties, ear loops or elastic bands, fits snugly over the nose, mouth, and chin with no large gaps, and consists of a solid piece of material without slits, exhalation valves, visible holes, punctures, or other openings.

The OSHA ETS for health care clearly stated that “Face coverings, facemasks, and face shields are not respirators” and made no mention of face coverings for any purpose in a health care setting. ⁶

The ASTM F23 Committee recognizes that the BFC standard is not perfect. A subcommittee is currently working on an outward leakage test method standard.

ASTM remains the best forum for open and transparent discussion and a robust consensus process to develop standards that address emerging needs. We encourage everyone with expertise in the design, manufacture, and use of facepieces to join ASTM and actively participate in its efforts to develop state-of-the-art testing and specification standards.