It is well known that several viruses, as well as SARS-CoV-2, can be transmitted through airborne diffusion of saliva micro-droplets. For this reason, many research groups have devoted their efforts in order to gain new insight into the transport of fluids and particles originated from human respiratory tracts. This paper aims to provide a contribution to the numerical modeling of saliva droplets' diffusion produced by coughing. It is worth noting that droplets' diameters of interest in this work are such that represent typical emission during a cough. Aerosolization effects are neglected since emitted droplets' diameters are greater than 10 m. In particular, the well-known problem around the safety distance to be held for avoiding virus transmission in the absence of external wind is further investigated. Thus, new indices capable of evaluating the contamination risk are introduced, and the possibility to inactivate virus particles by means of an external ultraviolet-C (UV-C) radiation source is studied. For this purpose, a new model which takes into account biological inactivation deriving from UV-C exposure in an Eulerian-Lagrangian framework is presented.