Differentiating between direct and indirect exposure to exhaled particles in indoor environments with mechanical ventilation systems

¹ Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T. 999077, Hong Kong SAR, China
² Shun Hing Institute of Advanced Engineering, The Chinese University of Hong Kong, Shatin, N.T., 999077, Hong Kong SAR, China
³ Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, 518057, China
⁴ Department of Building Services Engineering, The Hong Kong Polytechnic University, Kowloon, 999077, Hong Kong SAR, China

^* Corresponding author: chunchen@mae.cuhk.edu.hk

Abstract

Exhaled contaminants transported in the air can result in the transmission of many airborne infectious diseases in indoor environments. When the exhaled air from the infected person directly enters the breathing zone of another person, direct exposure occurs. When the exhaled contaminants disperse in the room and then are inhaled by another person, indirect exposure occurs. This investigation developed a method for differentiating the direct and indirect exposure to exhaled contaminants in indoor environments with mechanical ventilation. A literature review was conducted to collect experimental data for 191 person-to-person contaminant transport cases. With the analysis of the database, a mathematical method was developed to differentiate direct and indirect exposure in rooms with mixing and displacement ventilation systems. The proposed method correctly differentiated direct and indirect exposure for 120 out of the 133 mixing ventilation cases and 47 out of the 58 displacement ventilation cases. It can be used at the early design stage to quickly assess whether there will be direct exposure to exhaled contaminants in a room with mechanical ventilation systems.