Laboratory of Multiscale Studies in Building Physics, Empa, Dübendorf, Switzerland.
Indoor Air. 2022 Aug;32(8):e13094. doi: 10.1111/ina.13094.
As virus-laden aerosols can accumulate and remain suspended for hours in insufficiently ventilated enclosed spaces, indoor environments can heavily contribute to the spreading of airborne infections. In the COVID-19 pandemics, the role possibly played by cable cars has attracted media attention following several outbreaks in ski resort. To assess the real risk of infection, we experimentally characterize the natural ventilation in cable cars and develop a general stochastic model of infection in an arbitrary indoor space that accounts for the epidemiological situation, the virological parameters, and the indoor characteristics (ventilation rate and occupant number density). As a results of the high air exchange rate (we measured up to 180 air changes per hour) and the relatively short duration of the journey, the infection probability in cable cars traveling with open windows is remarkably lower than in other enclosed spaces such as aircraft cabins, train cars, offices, classrooms, and dining rooms. Accounting for the typical duration of the stay, the probability of infection during a cable-car ride is lower by two to three orders of magnitude than in the other examples considered (the highest risk being estimated in case of a private gathering in a poorly ventilated room). For most practical purposes, the infection probability can be approximated by the inhaled viral dose, which provides an upper bound and allows a simple comparison between different indoor situations once the air exchange rate and the occupant number density are known. Our approach and findings are applicable to any indoor space in which the viral transmission is predominately airborne and the air is well mixed.
由于载有病毒的气溶胶可以在通风不足的封闭空间中积聚并悬浮数小时，因此室内环境可能会严重促进空气传播感染的传播。在 COVID-19 大流行期间，缆车在滑雪场发生的几次暴发后引起了媒体的关注，可能发挥了作用。为了评估实际的感染风险，我们通过实验对缆车中的自然通风进行了表征，并开发了一个任意室内空间中感染的一般随机模型，该模型考虑了流行病学情况、病毒学参数和室内特征（通风率和乘客密度）。由于空气交换率高（我们测量到高达每小时 180 次空气交换）和行程相对较短，因此在开窗行驶的缆车上感染的可能性明显低于其他封闭空间，如飞机客舱、火车车厢、办公室、教室和餐厅。考虑到停留的典型时间，缆车上的感染概率比其他情况下低两到三个数量级（在通风不良的房间中进行私人聚会的风险最高）。对于大多数实际目的，感染概率可以通过吸入的病毒剂量来近似，这提供了一个上限，并允许在已知空气交换率和乘客密度的情况下，在不同的室内情况下进行简单比较。我们的方法和研究结果适用于任何主要通过空气传播病毒且空气混合良好的室内空间。
