防病毒戴口罩保持社交距離還不夠 New research says that anti-virus wearing masks to maintain social distancing is not enough

新研究發現通過戴口罩和保持社交距離預防新冠病毒(COVID-19)效果沒有過去認為的那麼好。在新冠肺炎(武漢肺炎、COVID-19)全球持續流行期間,戴口罩、保持社交距離是普遍防範方法。但一項新研究發現,這兩種措施雖然有效,但是還不夠。對飛沫傳播的認識是基於數十年前研究。戴口罩和保持社交距離來防範飛沫傳播的科學基礎,是基於數十年前的研究。近期,維也納工業大學、佛羅裡達大學、索邦大學和麻省理工學院的研究團隊利用流體動力學,共同研發了新的飛沫傳播模型。

「我們對於飛沫傳播的認識,是源於1930和1940年代的測量結果。」維也納工業大學流體力學與傳熱研究所教授阿爾弗雷多·索爾達蒂(Alfredo Soldati)說。「在那時,測量方法沒有今天這麼好,特別是對小飛沫的測試,可能沒有那麼準確可靠。」過去的測量方式認為,當感染者噴出飛沫後,大飛沫會因重力落到地面,小飛沫直線噴到前方,但是很快就蒸發掉。 

「這個描繪太過簡單了」,索爾達蒂表示。病毒飛沫進入空氣會傳播更遠、停留更久。實際上,飛沫噴到空氣中後的情況相當複雜。索爾達蒂指出,小飛沫的水分雖然蒸發了,但是空氣中還殘留著氣溶膠微粒,這些顆粒中可能包含病毒。這使病毒能夠傳播幾米遠,而且會在空氣中停留很長一段時間。一般來說,小飛沫的直徑平均為10微米,大約要15分鐘才能落到地面。因此,即使遵守社交距離,也可能接觸到病毒,譬如搭乘感染者剛搭過的電梯。濕度高的環境就更有風險,譬如通風不好的會議室。 

維也納工業大學表示,雖然戴口罩能阻隔大飛沫,保持社交距離也是有用的,但不能因此而有錯誤的安全感。因為即便戴口罩,噴出的病毒在空氣中飄移的距離和時間,都比想像中的更久。而利用研發的新模型,將能夠計算出不同時間、不同距離病毒飛沫的濃度。

 

The new study found that by wearing masks and maintaining social distancing prevent new crown virus ( COVID-19 ) the effect of the past that is not so good. During the ongoing global epidemic of new coronary pneumonia ( Wuhan pneumonia , COVID-19 ), wearing masks and maintaining social distance are common prevention methods. But a new study found that although these two measures are effective, they are not enough. The understanding of droplet transmission is based on research decades ago. The scientific basis for wearing masks and maintaining social distancing to prevent droplet transmission is based on research decades ago. Recently, research teams from the Vienna University of Technology, the University of Florida , the Sorbonne University and the Massachusetts Institute of Technology have jointly developed a new droplet propagation model using fluid dynamics.

“Our understanding of droplet propagation is derived from measurements in the 1930s and 1940s ,” said Alfredo Soldati , a professor at the Institute of Fluid Mechanics and Heat Transfer at the Vienna University of Technology . “At that time, the measurement method was not as good as it is today, especially the test for small droplets, which may not be as accurate and reliable.” The past measurement method believed that when an infected person sprays droplets, the large droplets will fall to the ground due to gravity. The droplets spray straight ahead, but they evaporate quickly. 

“This depiction is too simple,” Soldati said. Virus droplets entering the air will spread farther and stay longer. In fact, the situation after spraying droplets into the air is quite complicated. Soldati pointed out that although the water in the droplets has evaporated, there are still aerosol particles in the air, which may contain viruses. This allows the virus to spread several meters and stay in the air for a long time. Generally speaking, the average diameter of small droplets is 10 microns, and it takes about 15 minutes to fall to the ground. Therefore, even if you observe social distancing, you may be exposed to the virus, such as taking an elevator that an infected person has just taken. Environments with high humidity are more risky, such as conference rooms with poor ventilation. 

The Vienna University of Technology stated that although wearing a mask can block large droplets and maintain social distancing is also useful, it should not give a false sense of security . Because even if you wear a mask, the distance and time that the sprayed virus travels in the air is longer than expected. The new model developed will be able to calculate the concentration of virus droplets at different times and distances.

 

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