香港理工大学创新产品与科技研究所所长梁焕方(Wallace Leung)称,医用口罩的材料是聚乙烯。他做的实验发现,在标准空气流速下,基本款的口罩只能过滤20%到25%直径在50到500纳米的细颗粒物。这种尺寸的颗粒物常见于柴油车尾气中,直径不到人体毛发的1%,因为能深入肺部进入血液循环而尤为令人担忧。这些数据还没有考虑口罩与面部之间漏气的情况,而这种空隙会进一步降低过滤效率。
"What it means is, if you wear a face mask, you get 75 to 80 percent into the body," Dr. Leung said. "So that's not good."
“这就意味着,如果戴的是一般口罩,就会有75%到80%进入人体,”梁博士说。“所以情况不太妙。”
A better bet, experts say, are respirators that guard against at least 95 percent of small particles. Sometimes known as N95 respirators, they use thick layers of polypropylene, according to Dr. Leung, and are designed to fit tightly to the face. In the United States, such masks get tested by the National Institute for Occupational Safety and Health and must be shown to keep out at least 95 percent of all tiny airborne particles to gain approval. They are often used by industrial workers and are generally disposable.
专家们表示,更好的选择是能阻挡至少95%细颗粒物的呼吸防护罩。这种产品有时被命名为N95防护罩,梁博士说它由厚厚的多层聚乙烯制成,采用紧贴面部的设计。在美国,此类面罩接受国家职业安全与卫生研究所(National Institute for Occupational Safety and Health)的检测,要想过关必须证明能过滤空气中至少95%的细颗粒物。它们常被工业工人使用,基本是一次性用品。
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