R

esearch teams and government health officials are expanding the understanding of face coverings and the coronavirus by warning that two popular types of coverings may fail to inhibit virus spread as much as other choices and that one type may actually worsen it.

杜克大学的研究人员发现,风格of face covering popular among construction workers—thin fabric tubes with elastic ends called buffs, gaiters or fleeces—could send droplets into the air and may be worse than no covering at all. And the U.S. Centers for Disease Control and Prevention has recently pointed out in new guidelines that valved N95 face masks—the conical fabric masks that meet Occupational Safety and Health Administration and ANSI standards, and qualify as personal protective equipment for many dusty environments, are less effective than the unvalved variety.

The newest research arrives on an already cluttered landscape of virus-related protective practices for workers. Some of the different approaches involve workers and employers choosing between effective virus protection and comfort, convenience and productivity, and increased costs. Employers of all types have long been responsible for protecting workers from familiar respiratory hazards that include toxic gases, carcinogenic dust particles or oxygen-low air. The pandemic has put a new twist on that responsibility.

The Duke study’s most striking finding is that the popular thin fabric buffs could actually encourage virus spread. Valued for versatility and convenience, the buffs allow workers to easily drop the covering from their noses and mouths to cool faces, untrap carbon dioxide and allow eye protection to defog. Earlier this summer, such face coverings were distributed free to union bricklayers in a Northwestern local. The local’s business manager spoke of his members’ need for heat relief while doing heavy work.

在杜克大学的研究中，研究新利luck人员使用低成本系统来测量大于0.5微米的液滴的潜在扩散。志愿者在黑暗的室里说了几句话，并使用激光和相机，目视记录的液滴散布。为了衡量面部覆盖物之间的差异，科学家计算了以微米为单位测量的从面具中移动的呼出液滴。该病毒多次小，在液滴上搭便车。

该方法用于使用单个扬声器研究14种常见的面部覆盖新利luck设计。研究人员还用四个不同的扬声器测试了几种类型的口罩。面膜类型的范围从典型的三层手术口罩到阀门和未墙的N95口罩，再到棉花和聚丙烯的分层组合以及带有褶皱的面具。确定未置化的N95口罩是减少病毒扩散方面最好的。

羊毛中最轻的织物

To test the buffs or fleeces, the authors selected one made of a thin polyester and spandex, a product that provides a breathable fabric ideal for keeping cool. But the thin fabric, the Duke team found, transmitted numerous droplets and filtered them into smaller pieces. “That’s primarily why they got through” the protection, Martin C. Fischer, a research professor in the department of chemistry and one of the authors, said by email. By transmitting smaller aerosol micro-drops, the fleece also may send the virus farther than heavier, fasting-falling droplets would travel without a mask. “Considering that smaller particles are airborne longer than large droplets … the use of such a mask might be counterproductive,” the authors wrote in the journal Science Advances.

Different types of fleece masks, with different test subjects, could produce different results. “We expect there are variations of performance” and “there are just too many different mask types to test them all,” Fischer says.

到目前为止，通过不断变化的选菜菜单进行了与工作场所病毒传播的斗争，首先将面部覆盖物被视为社会疏远的一种替代方案。但是，随着人们对病毒传播的理解的增长，呼吸液滴比病毒大数千倍，但能够在房间周围旅行，这已成为重点。同时，公共场所和商店中的掩盖规则已演变为对个人自由和公共卫生的痛苦的文化和政治论据。

Research is refining the best options. In June, for example, two scientists wrote in the journal Physics of Fluids that the denser weaves of cloth face coverings held back more droplets and could cut in half the distance traveled by the droplets.

Digging Into Face Covering Data

While most of the news media concentrated on the fleece’s limitations, the Duke study held clues to what works and what doesn’t. “If you dig into the Duke study, the data clearly shows that an N95 mask with no valve is better for source control than an N95 with a valve,” which is only about as effective as the various cotton face covering, notes Chris Trahan Cain, executive director of CPWR, the Center for Construction Research and Training.

她说：“除了发现羊毛可能是一个不好的选择，数据表明，大多数布面具大大减少了液滴的数量，并且与阀门N95测得的减少相当。”

More new U.S. guidance is likely to come this year as more research is published. The CDC and OSHA have made it clear for months they don’t consider cloth face coverings personal protective equipment on a par with N95s, which meet safety standards. But CDC’s recent guidance about valved N95s adds another important detail in selecting what to use.

测试面部覆盖物时，许多其他变量都可以进入图片，包括在不同天气和工作环境中进行的呼气。杜克测试方法将如何与咳嗽和打喷嚏一起使用。但是现在很明显，某些面部覆盖在工作场所和关闭的面孔，在停止病毒传播方面优越。