Modeling of inhalation exposure to transmitted droplets at different interpersonal distances and postures in indoor environments

Understanding droplet dispersion in indoor environments, subsequent inhalation, and dermal deposition is the basis for controlling airborne transmission. In this study, we investigated the risk of inhalation and dermal exposure to droplets exhaled from infected persons at different interpersonal distances (IPDs), close-contact postures, and face orientations, using a realistic human model with a respiratory tract. We modeled the droplet and its nuclei dispersions under stagnant indoor airflow conditions (0.05 m/s). Our results corroborate the analytical findings that short-range inhalation dominates exposure at an IPD ≥ 0.3 m. In the examined close contact postures and IPDs, there was greater inhalation exposure during coughing than during speaking in the standing–standing posture (4.8 % and 2.9 %, respectively). The face-to-side (cheek) orientation reduced inhalation exposure during speaking but not during coughing. The inhalation and deposition fractions varied inversely with an increase in IPD. Inhalation exposure was higher in the standing-standing close contact posture than that in the standing-sitting posture at the same IPD due to high velocity magnitude at the nose. During the speaking scenario, higher fraction of inhaled particles with a wider diameter of ≥ 15 µm before evaporation were deposited in the nasal cavity. For the coughing scenario, most inhaled droplets of pre-evaporation sizes < 10 µm passed through the pharyngeal end, with minimal deposition in the nasal cavity. The aspiration efficiency is dependent on the timing of the inhalation period and droplet concentration in the breathing zone. This study can inform the unsettled discourse on safe IPDs and other novel measures for infection control.