Abstract Many governments have instructed the population to wear simple mouth-and-nose covers or surgical face masks to protect themselves from droplet infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in public. However, the basic protection mechanisms and benefits of these masks remain controversial. Therefore, the aim of this work is to show from a fluid physics point of view under which circumstances these masks can protect against droplet infection. First of all, we show that the masks protect people in the surrounding area quite well, since the flow resistance of the face masks effectively prevents the spread of exhaled air, e.g. when breathing, speaking, singing, coughing and sneezing. Secondly, we provide visual evidence that typical household materials used by the population to make masks do not provide highly efficient protection against respirable particles and droplets with a diameter of 0.3–2 μm as they pass through the materials largely unfiltered. According to our tests, only vacuum cleaner bags with fine dust filters show a comparable or even better filtering effect than commercial particle filtering FFP2/N95/KN95 half masks. Thirdly, we show that even simple mouth-and-nose covers made of good filter material cannot reliably protect against droplet infection in contaminated ambient air, since most of the air flows through gaps at the edge of the masks. Only a close-fitting, particle-filtering respirator without an outlet valve offers good self-protection and protection against droplet infection. Nevertheless, wearing simple homemade or surgical face masks in public is highly recommended if no particle filtrating respiratory mask is available. Firstly, because they protect against habitual contact of the face with the hands and thus serve as self-protection against contact infection. Secondly, because the flow resistance of the masks ensures that the air stays close to the head when breathing, speaking, singing, coughing and sneezing, thus protecting other people if they have sufficient distance from each other. However, if the distance rules cannot be observed and the risk of inhalation-based infection becomes high because many people in the vicinity are infectious and the air exchange rate is small, improved filtration efficiency masks are needed, to take full advantage of the three fundamental protective mechanisms these masks provide.

中文翻译：

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口罩对抗飞沫感染的基本防护机制


摘要 许多政府已指示民众佩戴简单的口鼻罩或外科口罩，以保护自己免受公共场所严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) 的飞沫感染。然而，这些口罩的基本保护机制和好处仍然存在争议。因此，这项工作的目的是从流体物理学的角度展示这些口罩在什么情况下可以防止飞沫感染。首先，我们表明口罩可以很好地保护周围区域的人们，因为口罩的流动阻力有效地防止呼出空气的传播，例如呼吸、说话、唱歌、咳嗽和打喷嚏时。其次，我们提供的视觉证据表明，人们用来制作口罩的典型家用材料无法对直径为 0.3-2 μm 的可吸入颗粒和飞沫提供高效防护，因为它们在很大程度上未经过滤的情况下穿过材料。根据我们的测试，只有带有细尘过滤器的吸尘器袋才能表现出与商用颗粒过滤FFP2/N95/KN95半面罩相当甚至更好的过滤效果。第三，我们表明，即使是由良好过滤材料制成的简单口鼻罩也不能可靠地防止受污染的环境空气中的飞沫感染，因为大部分空气流经口罩边缘的缝隙。只有不带出口阀的贴身、颗粒过滤式呼吸器才能提供良好的自我保护和防止飞沫感染。尽管如此，如果没有颗粒过滤呼吸面罩，强烈建议在公共场所佩戴简单的自制或外科口罩。 首先，因为它们可以防止脸部与手的习惯性接触，从而起到预防接触感染的自我保护作用。其次，由于口罩的流动阻力，可以保证呼吸、说话、唱歌、咳嗽、打喷嚏时空气紧贴头部，从而在人与人之间保持足够距离的情况下保护头部。但如果不能遵守距离规则，附近人多、空气交换量小，有传染性，吸入性感染风险较高，则需要提高过滤效率的口罩，充分发挥“三基”作用。这些面罩提供的保护机制。