Particle inflow characteristics in airborne infection isolation rooms: Effects of airflow rate difference induced by pressure difference and door leakage area

Airborne infection isolation (AII) rooms are designed to maintain negative pressure relative to adjacent spaces to prevent the spread of emerging infectious diseases. However, contaminant inflow through door leakage can deteriorate indoor air quality and increase secondary infection risks for patients. Current guidelines emphasize maintaining pressure differences but do not address airflow rate differences, which directly influence contaminant inflow. This study evaluated the impact of airflow rate differences on particle inflow through full-scale chamber experiments. Experimental conditions were established by varying door undercut heights and pressure differences. Particle concentrations were monitored at the exhaust diffusers of the AII room and anteroom. The results showed that as the airflow rate difference increased from 117 to 500 m ³ /h, the particle inflow rate increased from 257 × 10 ⁶ to 1327 × 10 ⁶ counts/s (linear correlation, R ²  = 0.999), and the particle inflow ratio increased from 71.0% to 86.5% (logarithmic correlation, R ²  = 0.994). Furthermore, cases with identical airflow rate differences showed similar particle inflow ratios regardless of pressure differences or door leakage areas, confirming airflow rate difference as the key factor. These findings underscore the limitations of pressure-focused guidelines and suggest that airflow rate differences should be incorporated into AII room design and operational guidelines.