The Development of an Alternative Methodology to Measure the Particle Size Allowed Passing Through Face Masks Using a...

Area of Science:

• Materials Science
• Nanotechnology
• Public Health

Background:

• The COVID-19 pandemic highlighted the critical need for effective respiratory protective equipment.
• Depletion and variable quality of face masks necessitated reliable testing methodologies.
• Existing methods like wind tunnels may not fully emulate real-world scenarios of particle expulsion.

Purpose of the Study:

• To develop and validate a complementary methodology for assessing face mask particle filtration efficiency.
• To evaluate the performance of different types of face masks, including N95 respirators and common commercial masks.
• To quantify the size and passage rate of particles through face masks under simulated respiratory events.

Main Methods:

• A novel technique using a gravity-feed airbrush gun at 60 PSI to spray 20% NaCl solution onto face masks.
• Simulated a cough or sneeze event with a 1-second deposition time.
• Collected particles that passed through the masks using sample holders with slides for scanning electron microscopy (SEM).
• Analyzed particle sizes (0.2–1.0 μm) using field-emission SEM (FSEM) after gold sputtering.

Main Results:

• K95 and KN95 masks allowed 85% and 88% of NaCl particles (0.2–1.0 μm) to pass through, respectively, with low deposition density (0.1 particles/μm²).
• Commercial two-layer polypropylene masks permitted particles larger than 5 μm to pass.
• Commercial three-layer face masks allowed particles down to 2 μm to pass.

Conclusions:

• The developed methodology provides a complementary approach to traditional wind tunnel testing for face mask filtration.
• N95-type masks demonstrated significant passage of sub-micron particles under the tested conditions.
• Commercial masks offer limited protection against smaller airborne particles, with three-layer masks performing better than two-layer ones.