He said a general rule of thumb is, ‘If you have a mask and you can see through the light and you can blow through it, it’s probably not a very good mask.’ A knitted mask also performed poorly in the study.
The study also said that “speaking through some masks (especially the neck fleece) the largest droplets appear to disperse into a lot of smaller droplets, which explains the apparent increase in droplet count relative to no mask in that case. Given that smaller particles are carried in air longer than large droplets (larger droplets sink faster), the use of such a mask can be counterproductive. “
The researchers tried to determine if masks were blocking droplets released into the air, not whether they were blocking the virus from entering. Public health officials say people should wear masks to prevent the spread of the virus, and mask orders are in force in dozens of states.
“I think most people really want the good thing,” and prevent the spread of the virus, Warren said. “If you’re really going to try to do this … you need to think a little bit more about what kind of mask style you wear.”
The study also offered some good news, and found that a paper surgical mask that was tested almost worked like an N95 mask in blocking the outflow of drops, and a number of homemade canvas masks also did a good job.
“What we really see is that most of the homemade solutions, if you fit them exactly so that there are no big holes, they do a pretty decent job, work just like the medical masks for once,” Warren said.
The researchers studied the effectiveness of masks by asking subjects wearing masks to speak the words “Stay healthy, people”, in the direction of an extended laser beam in a dark closet. Drips in the laser beam then scattered light, which was recorded with a mobile camera. A computer algorithm was used to count the drops, researchers said in the study.
The researchers said the necessary equipment was “generally available”, inexpensive, and “the experimental setup is simple and can be easily built and operated by non-experts.”
The researchers noted that they performed ‘evidence-of-principle experiments’ involving only a small number of speakers, but suggested that their method could serve as a basis for future studies.
“It’s worth understanding that this is not a clinical trial with 10,000 people in all possible circumstances that you can do,” Warren said. But he said researchers wanted to get some information, instead of “getting a paper from the fall of 2021”, when it might be too late to be of help.
The researchers suggested that the measurement method could be used to guide ‘machine selection and purchasing decisions’. They said their method was already being used to lead a decision to purchase a mask for the “Cover Durham” initiative in Durham, NC
Jill Crittenden, a researcher at MIT who is a member of the mask expert group N95cdecon.org, said: “I find it great that they want as many people as possible to test it.”
The study shows that “masks differ a lot in how much they protect other people,” she said.
She also said she found some of the findings shocking, including the finding about the fleece of the neck. “You can imagine some really large droplets essentially going through a sieve and becoming smaller particles, which are known to travel further, so that’s worse than nothing,” she said.
They also emphasize that the ‘fit of the mask is important.’ The study looked at drops that were driven in a forward direction, but, “if you have large holes on the side, for example, it can blow the side of your face,” she said.
Martin finucane can be reached at [email protected]
