He said that a general rule of thumb is: ‘If you have a mask and you can see through it in the light and you can blow through it, it’s probably not such a good mask.’ A knitted mask also performed poorly in the study.
The study also said that “talking through certain masks (especially the nape of the neck) seemed to disperse the largest drops into a number of smaller drops, which explains the obvious increase in the number of drops compared to no mask in that case. Given that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask can be counterproductive. “
The researchers tried to determine if masks blocked droplets from being released into the air, not if they blocked the virus from entering. Public health officials say people should wear masks to prevent the spread of the virus, and worm orders are in effect in dozens of states.
“I think most people really want to do the right thing” and prevent the spread of the virus, “Warren said. “If you’re really going to try to do that … you need to think a little bit more about what kind of worm style you wear.”
The study also offered some good news, and found that a paper surgical mask that was tested worked almost as well as an N95 mask to block the outflow of drops, and a number of homemade fabric masks also did a good job.
“What we really see is that most homemade solutions, if you fit them right so that there are no big gaps, they do a pretty decent job, work as good as medical disposable masks,” Warren said.
The researchers studied the effectiveness of the mask by asking people who wear masks to say the words “Stay healthy, people”, in the direction of an expanded laser beam in a dark enclosure. Drops in the laser beam then scattered light, which was recorded with a mobile phone camera. A computer algorithm was used to count the drops, say researchers in the study.
The researchers said the equipment needed was “usually available”, inexpensive, and “the experimental installation is simple and can be easily built and operated by non-experts.”
The researchers noted that they conducted “proof-of-principle experiments” that involved 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 under all possible circumstances,” Warren said. But he said researchers wanted to get some information, rather than “get a paper out in the fall of 2021”, when it might be too late to be of any help.
The researchers suggested that the measurement method could be used to guide “mask selection and purchasing decisions.” They said their method had already been used to guide a machine purchase decision 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 think it’s great that they want as many people as possible to test.”
The study shows that “masks vary greatly in how much they protect other people,” she said.
She also said she found some of the findings shocking, including the discovery of the neck fracture. “You can imagine that some really large droplets essentially pass through a sieve essentially and become smaller particles, which are known to travel longer, so it’s worse than nothing,” she said.
She also stressed that “the fit of the mask is important.” The study looked at drops that were banished in a forward direction, but “if you have large gaps on the side, for example, it can blow out the side of the face,” she said.
Martin finucane can be reached at [email protected]