The spread of the dangerous infectious disease COVID-19 indicates that asymptomatic carriers can be transmitted by airflow. Many diseases can infect human bodies with tiny droplets or particles carried by various viruses and bacteria that are generated by the respiratory system of infected patients. This article presents the numerical results of particle propagation in a room. The proposed numerical model in this work takes into account the sedimentation of particles or droplets under the action of gravitational sedimentation and transport in the room during breathing, sneezing or coughing. Three different cases are numerically investigated, taking into account normal breathing and coughing, sneezing, respectively, and three different rates of ejection of particles from the mouth are considered. The Navier-Stokes equations for incompressible flows were used to describe three-dimensional air flows inside ventilated rooms. The effect of ventilation rate on social distancing is also investigated through calculations. It was found that particles can move up to 5 m with a decrease in concentration in the direction of the air flow. In summary, given the environmental conditions, the two-meter social distance recommended by WHO is not sufficient.