AS&T Article Highlight: The influence of mechanical ventilation and portable air cleaners upon aerosol spread in a hospital outpatients clinic

By: Qian Zhang, UL Research Institutes

Authors of the Manuscript Featured: Jacob Salmonsmith, Andrea Ducci, Liwei Guo, Ryo Torii, Ramanarayanan Balachandran, Catherine Houlihan, Ruth Epstein, John Rubin, Manish K. Tiwari, Laurence B. Lovat

The utilization of mechanical ventilation and potable air cleaners (PACs) has been acknowledged as a major mitigation strategy to reduce exposure to airborne infectious aerosols based on lessons learned from the SARS-CoV-2 global pandemic. However, the resulted alteration of air flow dynamics may create highly complex environmental conditions and potentially lead to unintended spread of contaminations through the building systems. Therefore, it is important to evaluate the effects of built-in mechanical ventilation and/or PAC usage with consideration of air flow complexities in a broad building system.

Center for Aerosol Science and Engineering

This study investigated the spread of aerosols in a typical outpatients’ clinic with varied locations of aerosol sources and operations of ventilation and PACs. Aerosols were generated at a constant rate with a mass median aerodynamic diameter of 3 µm and at equivalent height of an adult sitting down to simulate a subject with an airborne respiratory disease. The clinic had a total volume of 470 m3 with five consulting rooms, two waiting rooms (hallway), a nurses’ station and a storage room, facilitated with an overall of 6 air changes per hour of fresh air supply. Airborne aerosols were measured with handheld laser diode particle counters for concentration.

The results showed that closing doors significantly reduced aerosol migration to nearby areas. However, operation of PACs in neighboring rooms seemed unlikely to reduce the aerosol concentrations at any locations compared to without running PACs. With the operation of building mechanical ventilation and open doors, aerosols were translocated throughout the clinic, with four out of the seven consulting rooms showed elevated aerosol levels than the source room. In addition, adjacent waiting areas in the hallway and the room at the far end from the source room all showed increased aerosol levels. PACs in all locations seemed to have minimal to moderate effect on reducing aerosols with different ventilation settings. Overall, this study indicated that the combination of PACs and mechanical ventilation may not always succeed in reducing exposure to aerosols but could result in unintended migration of aerosols, without carefully mapping out the building scenarios.

Further reading:

Salmonsmith, J., Ducci, A., Guo, L., Torii, R., Balachandran, R., Houlihan, C., Epstein, R., Rubin, J., Tiwari, M. K., Lovat, L. B. (2025). The influence of mechanical ventilation and portable air cleaners upon aerosol spread in a hospital outpatients clinic, Aerosol Sci. Technol., 1–12. https://doi.org/10.1080/02786826.2024.2446587.