A Novel Home-Built Metrology to Analyze Oral Fluid Droplets and Quantify the Efficacy of Masks

TL;DR

This study introduces a low-cost, home-built metrology system using fluorescent tonic water and smartphone recording to visualize and quantify oral fluid droplets, evaluating mask efficacy effectively and affordably.

Contribution

A novel, inexpensive, and accurate home-built method for analyzing oral droplets and mask efficacy using common materials and smartphone technology.

Findings

Masks with smaller pores and thicker fabric block more droplets.

The method is low-cost, under $50, and highly accurate.

Droplet generation varies with speech loudness and phonics.

Abstract

Wearing masks is crucial to preventing the spread of potentially pathogen-containing droplets, especially amidst the COVID-19 pandemic. However, not all face coverings are equally effective and most experiments evaluating mask efficacy are very expensive and complex to operate. In this work, a novel, home-built, low-cost, and accurate metrology to visualize orally-generated fluid droplets has been developed. The project includes setup optimization, data collection, data analysis, and applications. The final materials chosen were quinine-containing tonic water, 397-402 nm wavelength UV tube lights, an iPhone and tripod, string, and a spray bottle. The experiment took place in a dark closet with a dark background. During data collection, the test subject first wets their mouth with an ingestible fluorescent liquid (tonic water) and speaks, sneezes, or coughs under UV darklight. The fluorescence from the tonic water droplets generated can be visualized, recorded by an iPhone 8+ camera in slo-mo (240 fps), and analyzed. The software VLC is used for frame separation and Fiji/ImageJ is used for image processing and analysis. The dependencies of oral fluid droplet generation and propagation on different phonics, the loudness of speech, and the type of expiratory event were studied in detail and established using the metrology developed. The efficacy of different types of masks was evaluated and correlated with fabric microstructures. All masks blocked droplets to varying extent. Masks with smaller-sized pores and thicker material were found to block the most droplets. This low-cost technique can be easily constructed at home using materials that total to a cost of less than $50. Despite the minimal cost, the method is very accurate and the data is quantifiable.