How can a cloth stop a small virus? What is the best fabric? Do they protect the wearer?

Face mask Reduce the spread of the virus It is inherited from respiratory secretions. Cloth masks are imperfect, but widespread use of imperfect masks can make a big difference in viral infections.

We started reading the study of cloth masks and face covers at the beginning of the pandemic and looked for ways to protect us Vulnerable dialysis patients And our dialysis staff. A total of 25 studies were found. Advocate the use of masks And Summarized the survey results In a peer-reviewed publication. We have also created a website in plain language based on evidence (www.clothmasks.ca) To help people navigate this area.

The use of masks is widely adopted, but many people still have doubts about them.

You can see the space on the cloth. How can I stop the particles?

About the virus that causes COVID-19 0.1 micrometers in diameter.. (Micrometer (µm) is 1/1000 millimeter.) The holes in the woven fabric are visible to the naked eye. 5 to 200 micrometers in diameter.. It is counterintuitive that cloth is useful in this setting. This is compared to installing a wire mesh fence to stop mosquitoes. But that analogy is wrong in many ways.

According to aerosol science, it is an aerosol whenever a liquid is hanging in the air, but in other areas the term “droplet” is used to mean coarse particles of 5 micrometers or more, with an effective diameter of 5 micrometers. Reserve “aerosols” for fine particles less than a meter.

Particles are released when you breathe, talk, eat, cough, sneeze, or sing. Size range, Both coarse and fine, and The virus is in those particles.. There are gaps between the threads of the fabric, but the threads are usually wider than the gaps.

Also, at this microscopic level, the gap is a tunnel rather than a window because the thread has a thickness or depth.Microfilaments from broken or irregular threads Project into the gap.. Particles are not like mosquitoes that can redirect themselves to avoid obstacles. Momentum particles hit the fibers, even though the air flow circumvents them like a ball hits a wall. This is called a collision.

But at the microscopic level, two additional processes are working. Particles also fall out of the air — called sedimentation. Some particles move randomly, and this random movement makes contact with fibers called diffusion. Finally, you can use the cloth in multiple layers to add second and third gauntlets to run before the particles reach the other side.

The important thing is not that some particles can penetrate the fabric, but that some are blocked.

What is the best material for a cloth mask?

Based on us Summary of 25 different studies, Cotton fabric, at least 100 threads per inch. Flannel, cotton or polycotton blend, at least 90 threads per inch.Tea towel material; heavy and fine cotton T-shirt material all worked well.. This recommendation is based on available public data and does not cover all possible mask materials. For example, I didn’t find much information about synthetic materials, so I don’t know how to compare them.

We recommend that you create your mask in at least two layers, as all the studies that looked at layering showed differences. Three or four may be even better. Evidence of sandwiches with multiple layers of the same dough and different materials was found. We have not found good evidence of filtration levels useful for disposable filters such as coffee filters, so we recommend that you do not use them.

For example Two-layer T-shirt mask with sewn edges — Prevents stretching — Prevented 79% of oral bacteria from reaching the environment during a cough.. In the same experiment, the latest disposable medical masks performed 85% in the same range.

Two studies of surgical masks in the 1960s and 1970s distinguished between coarse particles (sometimes called droplets) and fine particles (sometimes called aerosols). A 4-layer cotton mask Mask made with Cotton and flannel sandwich 99% reduction in oral bacteria of all size particles reaching the environment during conversation, and oral bacteria in the particles 89 percent..

This is all good evidence that the cloth surface cover can prevent respiratory secretions from reaching the environment. All coarse or fine particles trapped in the mask cannot hang in the air or fall to the surface and contaminate them. “My mask protects you, your mask protects me”: If many people wear face covers, we expect the chances of infection to decrease I will.

Can a cloth mask protect the person wearing it?

Four studies on inward filtration were found. All of these showed useful levels of filtration using the same widely accepted technique for measuring salt particles in the fine particle range (0.02-1.0 micrometers). A Study of single layer tea towel mask And Research on two-layer masks made of T-shirt material Both showed at least 50% protection against particulates. Two cloth masks of unknown material Random purchases from street vendors worked as well. For comparison, two of these studies used exactly the same method to see how well the latest disposable medical masks work when tested in volunteers. Approximately 80% of the fine particles were filtered.

Three researchers at the University of Pittsburgh 8 layers of high quality cotton T-shirt before shrinkage Fits Your Face: Each provides a proof of concept for the idea of ​​filtering over 90% of the inner aerosol-sized particles to design a better cloth mask.

Ann Animal experimentation More insights can be gained with M. tuberculosis. Tuberculosis is usually considered an “air” disease, a disease that has an important route of transmission through aerosols and microparticles. When caring for a tuberculosis patient, healthcare professionals wear a high level respiratory protection N95 mask to protect themselves and prevent transmission to others. When rabbits were exposed to tuberculosis aerosols under controlled conditions, tuberculoma (infected abscess) was found in rabbits wearing a tightly fitted 3-6 layer gauze mask compared to rabbits not wearing it. It decreased by 95%.

Therefore, many of the cloth masks in use today can provide a useful level of filtration for the wearer, and there is a proof of concept to improve the material and design of the cloth mask.

How effective is the mask?

Two modeling studies predict that adopting 50% of 50% effective masks has a significant effect on transmittance, and increasing either percentage will further reduce transmittance. Cloth masks need to be more effective, but the masks at hand can change the progression of the pandemic, especially if most people wear them.

Mask obligations were imposed at different times in different states of the United States and produced natural experiments. COVID-19 daily growth rate After the mask mandate was imposed, it decreased by 1% in the first 5 days and decreased by 2% in 21 days...These effects are not small: they are 16-19 percent of the effectiveness of other much more invasive measures (School closures, bans on large gatherings, shelter-in-place orders, restaurants, bars and entertainment venues closed).

Taken together, this suggests that currently available types of fabric covers can reduce transmittance and, if fabric covers are required, reduce growth rates.Seattle Institute for Health Metrics Forecast on September 3 Reduce global deaths by three-quarters by the end of 2020 by increasing mask usage from the current 60% to 95% and, if necessary, increasing the social distance of the region can do.

Are there any other benefits to wearing a mask?

A New hypothesis Cloth masks proposed by researchers at the University of California, San Francisco suggest that not only do they reduce the chances of infectious microbes reaching humans, but they also reduce the number of infectious microbes. The lower the number of infectious microorganisms, the lower the severity of the disease.

Accumulation of epidemiological evidence This pandemic suggests that wearing a mask reduces the severity of the overall illness. The proportion of infected people who remain asymptomatic is high and the chances of death are low.In animal experiments well known Inoculation material (infection amount) is related to the severity of the disease. The threshold for 50 percent of animals in the same dose of infected group to die from infection is Lethal dose 50 (LD50)..

Experiments with mice using coronavirus MERS-CoV (Middle East Respiratory Syndrome) And SARS-CoV-1, which caused the SARS outbreak in 2003, It showed a dose response and established LD50 with MERS-CoV. In hamsters infected with SARS-CoV-2 and isolated between cages by a surgical mask, The severity of infection has been reduced Compared to hamsters that are not mask protected.

Further research on better cloth masks will be helpful.so Center of excellence of protective equipment and materials At McMaster, we want to play a role in that job. However, incomplete intake and even incomplete use of incomplete masks can have a surprisingly large impact during this pandemic. Perfection should not be the enemy of good.