How to determine the filtering capacity of mask materials

How to determine the filtering capacity of mask materials

SARS-CoV-2 travels through the air as particles of various sizes, such as droplets and aerosols, and can remain in suspension for hours. Hence the importance of wearing masks in people with the virus. Spanish experts have designed a system to establish the filtering capacity of the materials to manufacture them.

Scientists from the Higher Council for Scientific Research (CSIC) have written a report that compiles the available scientific information on how the SARS-CoV-2 virus, which causes COVID-19, is emitted and transmitted through the air, and on what requirements it has to have a mask or half mask to be effective.

Researchers have presented a non-approved system that can be useful both for the administration that makes decisions about what type of masks to test and for the laboratories that do the standardized test.

The report has been written by María Cruz Minguillón, researcher at the Environmental Geochemistry and Atmospheric Research (EGAR) group, at the Institute for Environmental Diagnosis and Water Studies (IDAEA-CSIC), with the collaboration of other researchers from the team and from the University from Colorado-Boulder and from Huelva.

SARS-CoV-2, about 100 nanometers in size, travels through the air. Various studies show that these particles that are emitted when breathing, vocalizing, coughing, sneezing and breathing are initially similar”, Says María Cruz Minguillón, from the IDAEA-CSIC.

But when they are emitted into the air, they become smaller when the water they contain evaporates. Coarse particles tend to settle quickly, but finer particles remain in suspension for hours or even days. The virus can remain active in air suspension for more than three hours", Add.

The concentration of virus in the environment varies depending on the location. A study conducted in Japan, based on contact tracing, has concluded that contagion is 19 times more likely indoors than outdoors.

Alternative in emergency situation

The effectiveness of the protection devices depends on three factors: the filtration efficiency of the material; the fit of the device to the face; and the purpose of filtration, either to filter the emission of particles from a sick person, or to filter particles from the ambient air inhaled by a healthy person.

In the current emergency situation, there is approved protective material in Europe that meets a standard for surgical masks, regulated by the EN 14683: 2019 standard, and personal protective equipment (half masks FFP2, FFP3), regulated by the EN standard 149: 2001, in which reference is made to the EN 13274-7: 2019 standard to evaluate the filtering capacity of the material with which they are produced.

Faced with the inability to manufacture sufficient approved material, IDAEA-CSIC researchers have designed a non-approved system to determine the filtering capacity of materials that may be candidates for the manufacture of filter masks or half masks.

The report compiles the information to assess what requirements a mask must have to be effective, both for commercial and artisan devices. It could be useful for both administration and laboratories.

This system is not intended to be an alternative to the certification protocols or a replica of the standardized systems, but has been designed according to the scientific and technical knowledge on particle filtration and SARS-CoV-2 and considering the viability of the means of those that are available.

Complete and detailed information is available on the IDAEA, CSIC and Ministry of Science and Innovation web pages.

But how do we solve it at home? With what material is it best to make the masks?

The effectiveness of each one is given by the ability to filter viral particles of 0.02 microns. A micron is one thousandth of a millimeter.

In this context, it stands out that the surgical mask has 89% filtration. They are made of cellulose or synthetic materials. It has five very thin layers.

The vacuum bag filters 86% of the particles. However, it is very heavy. It is difficult for someone to last many minutes with something like this, he limited on this type of fabric.

The cotton kitchen towel has the ability to filter 73% of particles. With a double layer you get an almost surgical quality mask, but it only lasts a few hours. You have to keep changing, he specified about this material.

The cotton or polyester t-shirts filter 70% and the pillowcase 57% of the viral particles.

In last place is silk with 54% filtration, cotton T-shirts (51%) and wool scarves (49%).

Also, the Centers for Disease Control and Prevention of the United States, recommends the use of bandanas. It is always better to cover your mouth and nose with something than nothing. Everything works.

With information from:

Video: The Best Materials for Face Masks According to Research (January 2022).