Fundamental protective mechanisms of face masks against droplet infections
Fundamental protective mechanisms of face masks against droplet infections
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DOI：
10.1016/j.jaerosci.2020.105617
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发表时间：
2020-10-01
影响因子：
4.5
通讯作者：
Hain, Rainer
中科院分区：
文献类型：
--
作者：
Kahler, Christian J.;Hain, Rainer
许多政府已指示民众在公共场合佩戴简单的鼠鼻罩或外科口罩，以保护自己免受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益处仍然存在争议。因此，这项工作的目的是从流体物理学的角度来看，在哪种情况下这些口罩可以防止飞沫感染。首先，我们展示了口罩对周围人群的保护作用，因为口罩的流动阻力有效地阻止了呼出的空气的传播，例如呼吸，说话，唱歌，咳嗽和打喷嚏。其次，我们提供的视觉证据表明，人们用于制造口罩的典型家用材料不能有效防护直径为0.3-2 μ m的可吸入颗粒和飞沫，因为它们基本上未经过滤地通过材料。根据我们的测试，只有带有细尘过滤器的真空吸尘器袋的过滤效果与商用颗粒过滤FFP2/N95/KN95半口罩相当，甚至更好。第三，我们表明，即使是由优质过滤材料制成的简单的鼠鼻罩，也不能可靠地防止被污染的环境空气中的飞沫感染，因为大多数空气都是通过口罩边缘的缝隙流动的。只有贴身的颗粒过滤式呼吸器才能很好地保护自己免受飞沫感染。然而，如果没有颗粒过滤呼吸口罩，强烈建议在公共场合佩戴简单的自制或外科口罩。首先，因为它们可以防止习惯性地用手接触脸部，从而起到防止接触性感染的自我保护作用。其次，因为口罩的抗流性保证了呼吸、说话、唱歌、咳嗽和打喷嚏时空气保持在头部附近，如果彼此之间有足够的距离，就可以保护其他人。但是，如果不能遵守距离规则，并且由于附近的许多人具有传染性并且空气交换率很小，吸入性感染的风险变得很高，则需要提高过滤效率的口罩，以充分利用这些口罩提供的三种基本保护机制。
Many governments have instructed the population to wear simple mouse-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 mu m 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 mouse-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 offers good self-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 remains 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.