Environmental Health Laboratory, California Dept. of Public Health, Richmond, California.
Department of Mechanical Engineering, University of Colorado, Boulder, Colorado.
J Occup Environ Hyg. 2021 Oct-Nov;18(10-11):495-509. doi: 10.1080/15459624.2021.1963445. Epub 2021 Sep 13.
Minimization of airborne virus transmission has become increasingly important due to pandemic and endemic infectious respiratory diseases. Physical distancing is a frequently advocated control measure, but the proximity-based transmission it is intended to control is challenging to incorporate into generalized, ventilation-based models. We utilize a size-dependent aerosol release model with turbulent dispersion to assess the impact of direct, near-field transport in conjunction with changes in ventilation, exposure duration, exhalation/inhalation rates, and masks. We demonstrate this model on indoor and outdoor scenarios to estimate the relative impacts on infection risk. The model can be expressed as a product of six multiplicative factors that may be used to identify opportunities for risk reduction. The additive nature of the short-range (proximity) and long-range (background) transmission components of the aerosol transport factor implies that they must be minimized simultaneously. Indoor simulations showed that close physical distances attenuated the impact of most other risk reduction factors. Increasing ventilation resulted in a 17-fold risk decrease at further physical distances but only a 6-fold decrease at shorter distances. Distance, emission rate, and duration also had large impacts on risk (11-65-fold), while air direction and inhalation rate had lower risk impacts (3-4-fold range). Surgical mask and respirator models predicted higher maximum risk impacts (33- and 280-fold, respectively) than cloth masks (4-fold). Most simulations showed decreasing risk at distances > 1-2 m (3-6 ft). The risk benefit of maintaining 2-m distance vs. 1 m depended substantially on the environmental turbulence and ventilation rate. Outdoors, long-range transmission was negligible and short-range transmission was the primary determinant of risk. Temporary passing events increased risk by up to 50 times at very slow walking speeds and close passing distances, but the relative risks outdoors were still much lower than indoors. The current model assumes turbulent dispersion typical of a given room size and ventilation rate. However, calm environments or confined airflows may increase transmission risks beyond levels predicted with this turbulent model.
由于大流行和地方性传染性呼吸道疾病，空气中病毒传播的最小化变得越来越重要。保持身体距离是经常被提倡的控制措施，但它旨在控制的基于近距离的传播很难纳入到基于通风的通用模型中。我们利用具有湍流扩散的尺寸相关气溶胶释放模型来评估直接的、近场运输的影响，以及通风、暴露持续时间、呼气/吸气率和口罩的变化。我们将该模型应用于室内和室外场景，以估计对感染风险的相对影响。该模型可以表示为六个乘法因子的乘积，可用于识别降低风险的机会。气溶胶传输因子的短程（近距离）和长程（背景）传输分量的可加性意味着必须同时最小化它们。室内模拟表明，近距离的物理距离会减弱大多数其他降低风险因素的影响。增加通风可使进一步的物理距离下的风险降低 17 倍，但在较短的距离下仅降低 6 倍。距离、排放率和持续时间也对风险有很大影响（11-65 倍），而空气方向和吸气率的风险影响较低（3-4 倍）。外科口罩和呼吸器模型预测的最大风险影响（分别为 33 和 280 倍）高于布口罩（4 倍）。大多数模拟结果表明，距离大于 1-2 米（3-6 英尺）时风险降低。与 1 米相比，保持 2 米距离的风险收益在很大程度上取决于环境湍流和通风率。在户外，长程传输可以忽略不计，短程传输是风险的主要决定因素。在非常缓慢的步行速度和近距离通过时，临时通过事件的风险增加了高达 50 倍，但室外的相对风险仍然远低于室内。当前模型假设了给定房间尺寸和通风率的典型湍流扩散。然而，在平静的环境或受限的气流中，传输风险可能会超过该湍流模型预测的水平。
