Infrared Thermography Study of Thermal Footprints Generated by Ordinary and Extraordinary Respiratory Activities in Persons Wearing Face Masks

The airborne diffusion of saliva droplets during respiratory activities is one of the major factors in the spread of infections. During the COVID-19 pandemic, the use of protective face masks was essential to reduce the risk of infection and spread of SARS-CoV-2. The face mask is able to significantly reduce the saliva droplet emission in front of the person. However, the use of masks also produces a particle leakage towards the back of the person, which could increase the infection risk of people behind the subject. Most of the experimental investigations applied invasive and/or complex experimental techniques to evaluate the face masks leakage. The primary objective of this study is to develop a novel, non-invasive methodology for assessing rearward droplet emission associated with the use of protective face masks. Specifically, a thermographic analysis of the thermal footprint released during ordinary and extraordinary respiratory activities is presented, evaluating the maximum temperature, the detection time, and the spread area of the thermal footprint. Both surgical and FFP2 face masks were tested. Two different subjects were involved in the experimentation to evaluate the influence of face conformation. The findings indicate that the area influenced by droplet dispersion is larger when wearing a surgical mask compared to an FFP2 mask, with the highest recorded temperatures observed for the surgical mask. The thermal footprint was found to be strongly dependent on individual facial morphology and mask fit. Notably, the FFP2 mask also altered the position of the thermal footprint, which was primarily confined to the region near the neck.