[Image above] Credit: Mika Baumeister, Unsplash
In the distant past that was one very long year ago, wearing a face mask out in public felt strange in many parts of the world, including in the United States—even though we’ve known for more than a century that face masks are effective at controlling epidemics.
Fast forward to today, and many of us now have extra face masks dangling from the rear-view mirrors or stuffed into the glove boxes of our cars, hiding in our purses and backpacks, and strewn across our homes. Free face masks are distributed at public places and as promotional items. I even recently witnessed a discarded mask blowing across the pavement like a pandemic tumbleweed. Face masks are everywhere, and wearing them out in public has become routine for a large segment of the population.
Unlike lab supplies, semiconductors, and chicken wings, among many other goods and services over the course of the past year, there’s certainly no shortage of face masks. Shop at nearly any store, whether online or in person, and you’re bound to find face masks for purchase. Some even offer a dizzying array of options, with widely varying materials, designs, styles, patterns, colors, and intended uses.
Yet as I noted in a CTT post from last July, despite the vast array of choices in face masks, there is a disappointing lack of information about how effective each of those choices are.
That’s a problem because the effectiveness of masks can range “from 0 to 80 percent, depending on material composition, number of layers and layering bonding,” says Dale Pfriem, president of Protective Equipment Consulting Services and a member of the standards development working group addressing mask guidelines, in a NY Times article.
Now, those standards Pfriem and many others worked to develop were finally released by ASTM International, an international standards organization that develops standards for diverse products, materials, systems, and services as a means to ensure technical quality and uniformity.
The new ASTM International F3502 standard, released mid-February 2021, now provides a validated set of consensus metrics to evaluate the efficiency of consumer face masks.
While consumers previously had to rely largely on a manufacturer’s claims (if any) about how effective a mask is at blocking potentially disease-causing particles, the new ASTM standards set a uniform measure by which manufacturers can test their products and ensure they meet established standards for effectiveness.
If a product meets the minimum requirements outlined in the standard, the manufacturer can label the product as such—in that way, the new standards provide a sort of uniform seal of approval that can be placed on products, so that consumers can more easily and effectively evaluate how well a face mask works.
“If you go into a store and buy a mask, you generally have no idea what you’re getting,” Dan Smith, ASTM’s vice president of technical committee operations, says in an NBC News article. “But if you go into a store and purchase a face mask that’s labeled, saying it meets the ASTM standard, you can understand what you’re getting and that you’re getting a certain level of protection.”
While ASTM standards already existed for medical face masks and respirators, there were no previous standards by which to gauge standard consumer face masks, so the new standards apply to this niche particularly.
The F3502 standard establishes minimum performance, design, labeling, and care requirements for those face masks, termed “barrier face coverings.” In terms of performance, the standard specifies how products should perform in terms of both controlling what goes in and what comes out from a face covering—reducing disease transmission by catching expelled droplets and aerosols from the wearer’s mouth, as well as protecting the wearer from inhaling potentially infectious particles. The standard also address comfort of wearing a face covering, quantified via its breathability, as well as if the covering can be reused.
In addition, the standard also specifies how testing should be performed, including requiring testing at least 10 samples to ensure a product meets the standards.
So what levels do the standard set? F3502 establishes two specific levels of performance for face covering filtration efficiency and breathability:
Level 1: ≥20% filtration efficiency, ≤15 mm H2O airflow resistance
Level 2: ≥50% filtration efficiency, ≤5 mm H2O airflow resistance
Filtration efficiency measures how well the covering can filter out particles with an average diameter of 0.3 µm—so a level 2 face covering under the new standards filters out ≥50% of particles 0.3 µm or larger. For reference, the gold-standard N95 masks have a filtration efficiency of ≥95%.
While the SARS-CoV-2 virus has a diameter of only about 0.1 µm, droplets and aerosolized particles containing the virus—which are the most likely way for the virus to be transmitted from person to person—are much larger, more on the order of ≥0.5 µm. That means the actual filtration of face coverings that meet the new ASTM standard are in reality more effective than those measures may sound at actually preventing transmission of disease.
The other value—airflow resistance—is a measure of how breathable a face covering is, so it provides a sense of how comfortable it is to wear. A higher value indicates higher airflow resistance, which means it is more difficult to breath.
So an ideal face covering has a high filtration efficiency yet a low airflow resistance, which is usually a balancing act in terms of material characteristics. Level 1 sets minimum effectiveness for face coverings, and level 2 face coverings perform even better.
Importantly, the guidelines do not consider fit of the face covering even though fit is a critical component of how effective a mask performs. However, there are simple DIY ways to improve the fit of any mask, along with other upgrades to enhance effectiveness.
F3502 also does not account for more environmental and circumstantial factors that affect performance, “such as material degradation from wearer challenges including perspiration, talking, sneezing, and the length of time the barrier face covering is worn,” according to the standard.
Nonetheless, the new ASTM standard provides an important benchmark to help consumers evaluate effectiveness as they navigate the vast choices of face coverings. Because despite the quickening pace of vaccinations, wearing face coverings is likely to continue to be our new normal for quite some time still.