Do cloth masks work? Supercomputer Fugaku says yes
Nikkei -- Aug 25
Masks made of nonwoven fabric performed best in a Japanese supercomputer model of their ability to block virus-carrying respiratory droplets, but other types of masks also showed effectiveness.

Japan's Fugaku, which recently took the title of world's fastest supercomputer, modeled the performance of cotton, polyester and nonwoven fabric masks in blocking spray from cough by the wearer. The government-backed Riken institute announced the results Monday.

While nonwoven masks blocked nearly all droplets emitted in a cough, all three types stopped at least around 80% of spray, making them effective at slowing the spread of the coronavirus, the team behind the tests said.

"What is most dangerous is not wearing a mask" just because the weather is hot, said Makoto Tsubokura, a team leader at Riken's Center for Computational Science. "It's important to wear a mask, even a less-effective cloth one."

The nonwoven masks did allow more than 10% of droplets measuring 20 microns or less in diameter to escape through gaps between the fabric and the face, the computer model showed.

The Fugaku, which recently took the title of the world's fastest supercomputer, modeled the performance of cotton, polyester and nonwoven fabric masks in blocking spray from coughs. (Photo by Shoya Okinaga)

But polyester and cotton masks allowed up to 40% of these droplets to pass through, as their fibers are spaced more widely than those of nonwoven fabric. One micron equals one millionth of a meter.

The team also modeled the effectiveness of face shields in blocking a cough by the wearer. Though droplets of 50 microns or more stuck to the inner surface of the shield, those 20 microns or smaller were able to escape through gaps.

新型コロナウイルスの感染予防策について、理化学研究所などはスーパーコンピューター「富岳」を使ってマスクの素材や建物の構造によって飛沫(ひまつ)の広がり方がどの程度違うのかを検証し、その結果を発表しました。  これは富岳が計算したマスクをつけた際の飛沫の動きです。赤い点はマスクの内側にとどまった飛沫。青はマスクを通り抜けた飛沫。黄色はマスクと顔の隙間から出た飛沫を示しています。理研のチームリーダーを務める神戸大学の坪倉誠教授らが不織布とポリエステル製、綿製の3種類のマスクで比較したところ、一番飛沫が広がらなかったのは不織布で、飛沫の8割を抑えていました。一方、ポリエステルや綿のマスクでも7割から8割を抑えていて、リスク低減の効果は見込めるとしています。一方、フェースシールドは大きな飛沫はシールドに付着していますが、小さな飛沫は顔の下側や側面から漏れ出すとして換気の併用を勧めています。学校の教室の換気ついても検証しています。青が濃くなるほど換気が進んだことを示しています。真夏や真冬など窓を全開にできない時期でも対角線上の窓や扉を20センチ程度開ければ、一般的なオフィスビル程度の換気ができるということです。2000人規模の多目的ホールのシミュレーションです。赤は大きな飛沫を、青は小さな飛沫を表しています。マスクなしでは大きな飛沫も広い範囲に広がります。マスクをつければ大きな飛沫は防げますが、小さな飛沫が近くに座っている人に付着していることが分かります。坪倉教授は両隣と前の座席にはリスクがあると指摘しています。今後は、ショッピングモールや飛行機内の飛沫の動きを検証する予定です。
News sources: Nikkei, ANNnewsCH
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