It’s easy to assume that something as simple as a mask wouldn’t pose much of a risk. Essentially, it’s just a covering that goes over your nose and mouth.

But masks are more than just stitched-together cloth. Medical-grade masks use multiple layers of nonwoven material, usually polypropylene, designed to meet specific standards for how big and how many particles they can block. And they are tested and certified to determine how well they do that job.

Healthcare and other frontline workers usually use either a surgical mask or an N95 mask. Both protect the patient from the wearer’s respiratory emissions. But where surgical masks provide the wearer protection against large droplets, splashes, or sprays of bodily or other hazardous fluids, an N95 mask is designed to achieve a very close facial fit and very efficient filtration of submicron airborne particles.

The “N95” (or “KN95”) designation means that the respirator blocks at least 95 percent of very small (0.3 micron) test particles. If properly fitted, the filtration capabilities of N95 respirators exceed those of face masks.

In the case of an N95 mask, there are several potential points of failure to be concerned with. First, the mask must be designed and manufactured so that the entire perimeter of the mask fits firmly where it comes in contact with the face, in order to block entry to pathogens around the mask’s edge. And the mask material itself must block 95 percent of particles of 0.3 microns or larger. Masks are also tested for fluid resistance, filtration efficiency (for both particulate and bacterial substances), flammability, and biocompatibility (masks must be nontoxic and nonallergenic).

The danger of fake PPE failing any of these tests could range from simply being uncomfortable (e.g., a skin irritation) to death, if the mask fails to prevent organisms from passing through the mask.

To ensure a proper fit, legitimate N95 masks have elastic bands that go around the head and not ear loops. So-called N95 masks that have ear loops are an immediate giveaway that they are fake. Ear-loop masks are cheaper to make than the headband variety, and thus the design of choice for cheap fakes. The fact that fake masks are easy to produce compounds the counterfeit problem.

The CDC has posted a web page showing the various types of fake PPE and their manufacturers that it has found. Note that almost all of them have ear loops.

Mask safety? There’s a test for that.

In the United States, the CDC’s National Institute for Occupational Safety and Health (NIOSH), along with NIOSH-certified labs, are the certifying bodies for both disposable respirators, like N95 masks, and hospital-grade surgical masks. Because the two are not the same in terms of reducing particle exposure, tests for their reliability are slightly different as well. Both, however, must meet specifications for filtration efficiency and penetration, among other criteria.

Respirator filters must meet certification tests (42 CFR Part 84) established by NIOSH that are based on worst-case parameters. To achieve this, aerosol tests are performed under specific requirements for aerodynamics and relative humidity. A mass-median aerodynamic diameter particle of about 0.3 µm is considered to be in the “most penetrating particle size” (MPPS) range for most filters. Tests are performed for air flow, resistance, and filter efficiency. Test results help establish safety benchmarks for fiber diameters, porosity, and filter thicknesses.

On a more granular level, standards developed by ASTM International’s committee on personal protective clothing and equipment come into play. These include:
• F2101—“Test method for evaluating the bacterial filtration efficiency (BFE) of medical face mask materials, using a biological aerosol of Staphylococcus aureus.” Evaluates the ability of a mask to keep aerosol droplets away from the wearer’s mouth and nose.
• F2299/F2299M—“Test method for determining the initial efficiency of materials used in medical face masks to penetration by particulates using latex spheres.” This measures submicron particulate filtration efficiency.
• F1862/F1862M—“Test method for resistance of medical face masks to penetration by synthetic blood (horizontal projection of fixed volume at a known velocity).” Determines whether the mask would effectively protect user from blood spatter.
• F1671/F1671M—“Test method for resistance of materials used in protective clothing to penetration by blood-borne pathogens using Phi-X174 bacteriophage penetration as a test system.” Determines penetration in protective clothing using a very small virus.

In the European Union, specifications for face masks are set out in the European standards EN14683 (for medical masks) and EN149 (for PPE masks). For medical masks, four tests are required, of which bacterial filtration efficiency (BFE) and air permeability are most important. An aerosol test is performed to determine BFE. The aerosol, containing droplets loaded with bacteria, is sent through the masks and collected on agar inside an Anderson impactor, which sorts the droplets according to size. The bacteria are then grown and counted.

To test air-permeability, an air flow of 8 liters per minute is sent through the sample, and the pressure difference is measured.

Tests for personal protective equipment (PPE) are more complicated and require specialized test equipment. An aerosol test is required as well as another involving paraffin.