Protecting others vs. protecting yourself against ballistic droplets: Quantification by stain patterns

TL;DR

This study uses a stain technique to quantify ballistic droplets from simulated coughs and sneezes, demonstrating that masks are more effective at protecting others than the wearer, especially when placed near the source.

Contribution

It provides quantitative evidence that masks worn by infected individuals are more effective at preventing droplet spread than masks worn by healthy individuals.

Findings

Masks block most ballistic droplets from source.

Masks near the source reduce droplet reach more effectively.

Protecting others with masks is more effective than self-protection.

Abstract

It is often accepted a priori that a face mask worn by an infected subject is effective to avoid the spreading of a respiratory disease, while a healthy person is not necessarily well protected when wearing the mask. Using a frugal stain technique, we quantify the ballistic droplets reaching a receptor from a jet-emitting source which mimics a coughing, sneezing or talking human: in real life, such droplets may host active SARS-CoV-2 virus able to replicate in the nasopharynx. We demonstrate that materials often used in home-made face masks block most of the droplets. We also show quantitatively that less liquid carried by ballistic droplets reaches a receptor when a blocking material is deployed near the source than when located near the receptor, which supports the paradigm that your face mask does protect you, but protects others even better than you.