During the COVID-19 pandemic, in South Korea, several inpatient wards were converted to temporary negative pressure isolation (TNPI) wards by using portable high-efficiency particulate air filter units (PHUs). This study proposes improvements to the TNPI ward to prepare for airborne infections.

Existing air-conditioning systems were investigated during the pandemic in 4 hospitals through a document review and field investigation with staff interviews. On-site experiments and measurements were conducted under vacant conditions. Differential pressure ( P) between spaces was measured in all 4 hospitals, while tracer gas tests were carried out in 2 hospitals.

The investigation revealed that thermal discomfort caused the existing systems remaining perpetually active. Additionally, the noise generated by the PHU caused an unexpected shutdown of that equipment. Furthermore, the  P of over −2.5 Pa was measured as a result of the operating status of equipment. These situations can cause duct backflow and gas diffusion through unsealed diffusers. Moreover, low airtightness of existing facilities can affect indoor environment, pressure difference, and gas diffusion.

When using existing facilities as TNPI wards, the airtightness and existing systems should be considered. We concluded that it is important to increase the airtightness and seal unused diffusers in order to prevent cross-infection by unpredictable airflow.