Spray characteristics and penetration of the human cough, and the effectiveness of masks to prevent its dispersion

Abstract

Air-transmitted pathogens have become of particular interest for the general population during the COVID pandemic. Coughing is one of the most important spreading vector for air transmitted pathogens. To prevent and stop the transmission chain, it is of great importance to understand the characteristics of this phenomenon, assess the distance up to which the virion particles are transported and how effective the available masks are to stop the exhaled air. The Schlieren method stands as a proper non-intrusive methodology to study density variations such as the ones produced by the cough. An intubation dummy was instrumentalized to exhale CO2 at realistic cough flow-rates and ambient conditions. General spray characteristics were obtained for a free cough, while effectiveness of a cloth, surgical and FFP2 masks were assessed by analysing the penetration and the angle of the exhaled fluid into the surrounding air. The differences between the propagation distances with and without mask were quantified. The characteristics of a free cough where firstly assessed, and later, the effectiveness of wearing a mask is shown, a cloth one reduces the cough penetration a 50%, while a surgical and FFP2 one reduces it more than an 75%, to less than 10cm.