Evaluation of aerosol transmission risk during home quarantine under different operating scenarios: A pilot study

Abstract

SARS-CoV-2 has been recognized to be airborne transmissible. With the large number of reported positive cases in the community, home quarantine is recommended for the infectors who are not severely ill. However, the risks of household aerosol transmission associated with the quarantine room operating methods are under-explored. We used tracer gas technique to simulate the exhaled virus laden aerosols from a patient under home quarantine situation inside a residential testbed. The Sulphur hexafluoride (SF₆) concentration was measured both inside and outside the quarantine room under different operating settings including, air-conditioning and natural ventilation, presence of an exhaust fan, and the air movement generated by ceiling or pedestal fan. We calculated the outside-to-inside SF₆ concentration to indicate potential exposure of occupants in the same household. In-room concentration with air-conditioning was 4 times higher than in natural ventilation settings. Exhaust fan operation substantially reduced in-room SF₆ concentration and leakage rate in most of the ventilation scenarios, except for natural ventilation setting with ceiling fan. The exception is attributable to the different airflow patterns between ceiling fan (recirculates air vertically) and pedestal fan (moves air horizontally). These airflow variations also led to differences in SF₆ concentration at two sampling heights (0.1 m and 1.7 m) and SF₆ leakage rates when the quarantine room door was opened momentarily. Use of natural ventilation rather than air-conditioning, and operating exhaust fan when using air-conditioning are recommended to lower exposure risk for home quarantine. A more holistic experiment will be conducted to address the limitations reflected in this study.

Keywords: Aerosol transmission risk; Air conditioning; COVID-19; Fans; Home quarantine; Natural ventilation.

Fig. 1

(a) A snapshot of the master-bedroom; (b) a plan view diagram identifying the experimental setups both inside and outside the master-bedroom (i.e., the quarantine room). Information about in-room and hall-side samplers is highlighted in red. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Detailed indication of experimental procedures for actions being taken, status of the test room, and exhaust fan operation schedule.

Fig. 3

Time series SF_6,conc under different ventilation scenarios with/without window exhaust. (a) Air-conditioning (AC) only, (b) AC with ceiling fan, (c) AC with pedestal fan, (d) Natural ventilation (NV) with ceiling fan, and (e) NV with pedestal fan. The three sampling locations are: hall-side at 0.1 m height (red line), in-room at 0.1 m height (green line), and in-room at 1.7 m height (blue line). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

SF_6,conc distribution comparison for window exhaust On and Off status at: (a) In-room sampler at 0.1 m, (b) In-room sampler at 1.7 m and (c) Hall-side sampler at 0.1 m height.

Fig. 5

Plan view of the airflow patterns in air-conditioned scenarios together with the operation of (a) pedestal fan, (b) ceiling fan, and (c) window exhaust fan.

Fig. 6

Schematics of the airflow pattern in naturally ventilated scenarios with windows and toilet door open: (a) plan view operating with pedestal fan, and (b) side view operating with ceiling fan.

Fig. 7

Illustration diagrams of (a) a plan view and (b) a side vide for airflow generated by ceiling fan passing through the door gap (door between quarantine room and living room). The dotted blue arrows represent the turbulence incurred by the rebound airflow from the door. The grey line and arrows over the door are, respectively, indicating the air pressure gradient and the pressure direction initiated by the fans' airflow. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 8

Time series outside-to-inside (master-bedroom) SF_6,conc ratio. (a) AC only, (b) AC with pedestal fan, (c) AC with ceiling fan, (d) NV with pedestal fan, and (e) NV with ceiling fan.

Fig. 9

Boxplot on the steady state outside-to-inside (quarantine room) SF₆ concentration (i.e., O/I_SF6) for the conditions with/without window exhaust under five different operating scenarios.