Investigating the invisible threat: An exploration of air exchange rates and ultrafine particle dynamics in hospital operating rooms

The air exchange rate (AER), defined as the number of times the air is fully replaced per hour in an indoor space, is an important parameter affecting indoor air quality (IAQ). Hospital operation rooms (ORs), one of the indoor environments with relatively high health risks, should maintain high AERs to quickly remove surgical smoke during surgery. This study aimed to investigate the characteristics and transmission of pollutants in ORs through on-site measurements and numerical simulations. To determine actual AER (AERactual), both exponential decay and concentration variations, resulting in a more precise representation of indoor air pollutant residence time, were considered. Our results revealed that gaseous pollutants exhibited lower AERactual values compared to particulate pollutants due to their higher diffusibility. Notably, the AERactual of total volatile organic compounds (TVOC) was found to be greater than that of carbon dioxide (CO2) due to the higher reactivity of TVOC. Furthermore, this study also investigated the characteristics of surgical smoke particles and observed variations in emission factors (EF) depending on the surgical procedure, ranging from approximately 1010 to 1011 particles per minute. Moreover, coarse particles (>2.5 μm) were primarily influenced by drag forces, resulting in lower AERactual values. Additionally, the AERactual of ultrafine particles (UFPs) was examined, revealing that smaller particles exhibited lower AERactual values, potentially due to stronger Brownian motion. By combining measurement and simulation analysis, the spatial distribution of lung deposited surface area (LDSA) concentrations could be evaluated, providing accurate exposure concentrations for health risk assessments.