Several places across the world are experiencing a steep surge in COVID-19 infections. Face masks have become increasingly accepted as one of the most effective means for combating the spread of the disease when used in combination with social-distancing and frequent hand-washing. However, there is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields and with masks equipped with exhalation valves. One of the factors driving this increased adoption is improved comfort compared to regular masks. However, there is a possibility that widespread public use of these alternatives to regular masks could have an adverse effect on mitigation efforts. To help increase public awareness regarding the effectiveness of these alternative options, we use qualitative visualizations to examine the performance of face shields and exhalation valves in impeding the spread of aerosol-sized droplets. The visualizations indicate that although face shields block the initial forward motion of the jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances. Visualizations for a mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control. Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves.

中文翻译：

---

可视化带有呼气阀的面罩和面罩的液滴扩散


全球多个地区的 COVID-19 感染人数急剧增加。当与保持社交距离和经常洗手结合使用时，口罩已被越来越多地接受为对抗疾病传播的最有效手段之一。然而，人们越来越多地用透明塑料面罩和配备呼气阀的口罩代替普通布口罩或外科口罩。推动这种普及的因素之一是与普通口罩相比舒适度的提高。然而，公众广泛使用这些普通口罩的替代品可能会对缓解努力产生不利影响。为了帮助提高公众对这些替代方案有效性的认识，我们使用定性可视化来检查面罩和呼气阀在阻止气溶胶大小的液滴传播方面的性能。可视化结果表明，尽管面罩阻挡了喷射流的初始向前运动，但排出的液滴可以相对轻松地在面罩周围移动，并根据周围环境光的干扰散布到大面积区域。配备呼气口的面罩的可视化结果表明，大量液滴未经过滤就通过呼气阀，这大大降低了其作为源头控制手段的有效性。我们的观察表明，为了最大限度地减少 COVID-19 的社区传播，最好使用设计简单的优质布口罩或手术口罩，而不是面罩和配备呼气阀的口罩。