Abstract：
The building\'s toilet drainage system has been identified as a potential route for the transmission of SARS-CoV-2 during outbreaks. This study employed agar-fluorescein sodium semi-solid as trace particles to investigate the possibility of vertical transmission of the SARS-CoV-2 in drainage system. In both scenarios, where floor drains were all properly sealed or dried out, simulated faeces containing fluorescein sodium were flushed into the toilet bowl. Air sampling was conducted in each restroom, and differential pressure measurements at the floor drain locations were taken. The experimental results showed that when all floor drains were properly sealed, the differential pressure at each floor drain was 0. The fluorescein sodium-traced aerosol did not transmit through the drainage system to various floors, which significantly reduced the risk of infection for users through this route. However, when all floor drains dried out, toilet users above the neutral pressure layer (NPL) were at a high risk of virus infection. Due to the increasing maximum negative pressure at the floor drain above the NPL with ascending floor levels, users on each floor above the NPL faced an elevated infection risk in restrooms. Specifically, users on the top floor were exposed to infectious aerosols roughly 1.6 times that of the first floor above the NPL. Conversely, owing to the increasing maximum positive pressure at the floor drain below the NPL with descending floor levels, users below the NPL experienced a comparatively lower infection risk. This finding has important implications for understanding the vertical transmission dynamics of SARS-CoV-2 in residential or public building and can inform the development of effective control measures.
摘要：
建筑物的厕所排水系统已被确定为在爆发期间传播SARS-CoV-2的潜在途径。本研究采用琼脂荧光素钠半固体作为痕量颗粒，以研究SARS-CoV-2在排水系统中垂直传播的可能性。在这两种情况下，地漏都被适当地密封或干燥，将含有荧光素钠的模拟粪便冲入抽水马桶。每个洗手间都进行了空气采样，并在地漏位置进行了压差测量。实验结果表明，当所有地漏都被适当密封时，每个地漏的压差为0。荧光素钠追踪的气溶胶没有通过排水系统传播到各个楼层，这大大降低了通过这种途径感染用户的风险。然而,当所有地漏都干涸时,中性压力层（NPL）以上的厕所使用者面临病毒感染的高风险。由于随着地板水平的上升，NPL上方的地漏处的最大负压不断增加，NPL上方各楼层的用户在洗手间面临较高的感染风险。具体来说,顶层的用户暴露于感染性气溶胶，大约是NPL上方一层的1.6倍。相反，由于NPL以下地漏处的最大正压力随着地板水平的下降而增加，低于不良贷款的用户经历了相对较低的感染风险。这一发现对于理解SARS-CoV-2在住宅或公共建筑中的垂直传播动态具有重要意义，并可以为制定有效的控制措施提供信息。
