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跑在瘟疫蔓延時 — 別跟車太貼,應拉遠距離

2020/4/11 — 17:02

荷蘭教授 Bert Blocken 出於好意,在推特「偷步」分享了其團隊趕工完成的飛沫流動力學分析結果,提醒跑友,跑在瘟疾蔓延時,所需的社交距離比靜態為多,最理想是肩並肩跑,或交錯地跑(見上圖),避免跑在前面跑友的滑流(slip stream)之內。在單排跑道上,動態社交距離要增加數倍,視乎跑者的速度、風向和風力。

飛沬隨跑者身後的滑流擴散。在無風環境下,要達到標準抗疾措施要求的 1.5 米靜態社交距離效果,時速 4 公里(逛街速度)時距離要增至 5 米,時速 14.4 公里(快跑速度)時則需要 10 米。

特別要指出,這是流動力學研究,並非病毒學,只提供跑者身後的飛沫落地和蒸發後,減弱到等同靜態距離 1.5 米的水平所需距離。

廣告

推持發出後,學者接受傳媒採訪,博客 Jurgen Thoelen 撰文 [1] 傳播至全球跑友社群。Vice 文章回應 [2],這個網紅「研究」不單並非嚴謹的學術期刋論文,亦非有待同行審批的預印本。

教授隨即在推持聲明,「偷步」分享研究結果,全因疫情嚴峻,公共健康為重。他鄭重聲明,跑步沒有問題,他本身亦堅持遠離人群騎單車,今次模擬乃其實驗室多年研究的成果,對飛沫的滑流分佈分析甚有信心,但表明並非病毒學研究,沒有對飛沫流動和染病關係作出任何判斷。

廣告

我做了基本查證。Bert Blocken 是行內資深專家,信譽良好。今早他和團隊已將研究寫成論文預印本公開發佈。跑友仍有疑慮,可直接看論文,或文後附錄的總結 [3]。

 

[1] Jurgen Thoelen, "Belgian-Dutch Study: Why in times of COVID-19 you should not walk/run/bike close to each other". April 8 2020.

[2] Jason Koebler. "The Viral ‘Study’ About Runners Spreading Coronavirus Is Not Actually a Study". Apr 9 2020.

[3] B. Blocken , F. Malizia , T. van Druenen , T. Marchal. "Towards aerodynamically equivalent COVID-19 1.5 m social distancing for walking and running". Preprint paper accessed 10:00 am, 11 April 2020.

Summary and conclusions

…This suggests that avoiding substantial droplet exposure in the conditions of this study can be achieved by one of two actions: either by avoiding to walk or run in the slipstream of the leading person or by keeping larger social distances, where the distances increase with the walking or running speed. The equivalent social distance for walking and running in the slipstream is defined as the distance that should be kept between the leading and trailing walker/runner to avoid substantial exposure to slipstream droplets, similar to the case where two people are standing still at 1.5 m distance. In the absence of head wind, tail wind and cross-wind, for walking fast at 4 km/h this distance is about 5 m and for running at 14.4 km/h this distance is about 10 m. Further work should consider the effect of head wind, tail wind and cross-wind, and different droplet spectra.

 

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