Performance of low-volume air cleaner and local exhaust in mitigating airborne transmission in hospital outpatient rooms

This study intends to explore the effective and flexible solutions to cope with airborne transmission in hospital outpatient rooms. Such solutions might be used as an additional measure during pandemics and as an independent measure in regions with incomplete health facilities and limited resources. It first investigates the dispersion characteristics of exhaled pollutants during typical expiratory activities and then evaluates the effectiveness of a low-volume air cleaner and local exhaust in reducing the risk of cross infection using a newly proposed index, i.e., personal exposure reduction effectiveness (PERE). The results show that, though wearing a face mask largely obstructs the horizontal dispersion of exhaled particles and thus avoids short-range direct transmission, the influence of particles leaked from the edges of a face mask on the doctor and the next patient cannot be ignored. Under the conditions without wearing a face mask, a background ventilation rate of 60 m3/h plus a 50 m3/h desk-mounted air cleaner is effective to prevent the direct exposure of the doctor from the patient's exhaled particles, with the PERE reaching 90.1%. Under the conditions with wearing a mask, a background ventilation rate of 60 m3/h plus a 30–50 m3/h local exhaust above the patient's head removes 85.7%–88.5% of leaked particles, achieving a PERE of 96.6%–100%. The aforementioned PERE value during the two types of conditions is 137% (or 70.4%–71.4%) higher than that under only a background ventilation of the stipulated 120 m3/h by standard. These findings should provide ideas and information for improving the mitigating system of airborne transmission in hospital outpatient rooms.