Protocol Development to Quantify Total Outward Particle Leakage of Face Coverings

Background: The covid 19 pandemic has brought to light the importance of quantifying the total outward leakage of particles circumventing face coverings. Most research to date has focused on filtration efficiency of different materials typically used in face coverings. However, there is a lack of literature surrounding the size and number of particles able to bypass face coverings through the openings between the covering and the face. To evaluate the effectiveness of universal masking recommendations a protocol needs to be developed. Face coverings have been universally recommended as a source control option but to date only research regarding filtration efficiency testing has been done. Methods: A sampling chamber consisting of a WalkingPod™ and portable air filtration units was constructed to fit over the researchers’ head and body. Using two optical particle sizers (TSI 3300) and two water-based condensation nuclei counters (novel TSI WRPAS device), aerosols ranging from 7.5nm to 10um were collected in order to characterize the space around the researcher’s head. Data was gathered from the front, back, left, and right side of the head during normal breathing and talking with and without a face covering. Data was analyzed using box plots and summary statistics to compare particles generated within the chamber with and without face coverings. Results: Protocol development: Instruments were calibrated to ensure outputs from different instruments were comparable when a sample was taken from a single probed location. A process was designed to eliminate particles in the collection chamber. This began with incorporating a portable air filtration unit between samples during the protocol, then a cleanroom suit was added to reduce particles generated from clothing to ensure particles counted were originating from only exhaled breath. Discussion: This project demonstrates the feasibility of protocol development to address total outward leakage of face coverings. There are implications for incorporation of this protocol to compare total outward leakage of different face coverings and/or total outward leakage into standards such as ASTM cloth barrier standard, and the OSHA emergency temporary standard to protect workers from Covid-19.