Make a “mask house” really effective is not impossible, but it is far from simple…
June 2, 2020
Updated June 3, 2020 at 4h19
Not easy to do a real good mask…
The cotton or polyester? The coffee filters, is it “on”? Once one started, why not try the vacuum filters? The Institute for research in safety and health at work (IRSST) has tested a range of materials in common use (and less current) in recent weeks, with a conclusion a bit daunting : make a “mask house” really effective is not impossible, but it is far from simple…
“This is one of the great lessons of the notice : there are few materials that Mr. and Mrs. All-the-World will be able to find it in them to make masks of good quality,” says Loïc Wingert, a researcher at the IRSST and the senior author of the study. This is not a good new but at the same time, it is almost normal. If he had enough to take a bit of cotton to make good masks, 3M and other companies have not had need to do so much research to produce a N95 or masks surgical grade.
“This is an important point to get across, I think, not that people have a false sense of security, so that they know that this is not enough to put one or two layers of cotton in front of the mouth,” he continued.
Essentially, Mr. Wingert, and his colleagues tested three characteristics of the tissue. They have examined the filtration, i.e. the proportion of fine particles which is retained; a textile was judged to be good if he captured 60 %, “acceptable” if it filtered between 40% and 60%, and inadequate below this threshold. They have also pushed the gust of compressed air through (tests of the “spray”) to see if the materials left escape out of the droplets in the event of coughing or sneezing. And they have measured the “breathability”, is the extra effort that the lungs need to do to breathe through a mask.
Almost all of the materials tested have passed the test of the breathability, the most high in hand, but the other two proved to be another pair of sleeves, at least for the materials most easily accessible. Either the linen, for example, the wipes (and the whole series has been tested), felt, wool, merino, fleece, cotton woven to 200 or 600 threads per inch or the coffee filters, the fibres present in the daily life of Mr. and Mrs. All-the-World do not make very good masks. Almost all failed either at the test of filtration, or spray — often two, moreover — and it is not very advisable to filter the particles if it is to apply with spray droplets infected with the slightest cough.
However, some have shown an interesting potential for one or the other. The polar, for example, is not a good filter, but it prevents the spraying of the droplets. Conversely, a few models of wipes to retain the particles (as long as you put enough layers), but not the droplets. We can therefore imagine that a mask having a polar as an outer layer and a few layers of cloth to the inside could make a mask effective — still a little warm for summer, but that is another question. Other combinations are also possible (all the details and the names of the models tested are available in the report of the IRSST).
One other avenue possible, said Mr. Wingert, is to make an envelope machine fabric in which we would place a layer filter (washable or replaceable). In this regard, the IRSST has achieved good results — both in terms of filtration in spray — for a few materials that can be relatively easily available to the general public, as well as some vacuum bags, and air filters, and some sheets of absorbent. But even here, it should be noted that the performance varies greatly from one model to another, and some materials require more thickness to pass the tests of the IRSST.
“Then be a good mask house, this is feasible, said Mr. Wingert. Someone who will be well informed and read our notice in detail will be able to do. But it’s still a little bit technical and it demands attention in the development.”
“But even a good quality breathing mask does not replace other measures, such as the distancing, the correct way to put on and remove the mask, etc”, he says.
Note that the IRSST will continue its tests in the coming weeks and plans to update the information on the website, when new results are available.