Covid-19 - everyday masks also effective against aerosols

According to flow experiments, cloth masks reduce the risk of infection with SARS-CoV-2 despite their large mesh size.

Social distancing and the use of mouth and nose protection (MNS) are currently the only measures to prevent SARS-CoV-2 infections in addition to a total lockdown. According to a study by the Canadian Simon Fraser

University, a mask requirement in public places reduces new infections by about 25 percent. According to Florida Atlantic University, the protective effect of different mask types differs significantly.

Now the German Aerospace Center (DLR) has investigated whether everyday masks made of fabric can actually protect against SARS-CoV-2 infection. Critics of the masks regularly claim that this is not possible because the mesh size of conventional everyday masks is so large that aerosols should easily penetrate them.

Flow experiments show movement of the aerosols

A twelve cubic meter chamber was used for the research project, in which otherwise aerospace flow experiments take place. During the Aeromask project, the scientists were able to use the room's 3D particle tracking technology to visualize the spread of potentially infectious aerosols and the protective effect of everyday masks.

Tiny soap bubbles were released in the chamber, which simulate aerosols with a diameter of only 350 micrometers. These helium-filled bubbles were illuminated by a row of LEDs and made visible in the air. A body warm doll in the center of the room with an artificial lung simulates a person and his breathing flow during the measurements. The effects of thermal and breath on the movements of the aerosols were recorded. Thanks to the high-resolution cameras, the movements of the simulated aerosols can be observed down to a few millimeters.

Masks slow down potentially infectious aerosols

The records show that everyday masks, although their mesh size is actually too large to filter aerosols from the air, have a protective effect against SARS-CoV-2. During the experiments it happened that the exhaled air flow through the MNS was slowed down. The aerosols are still released into the environment, but no longer spread as far through the mask, but form a cloud around the already infected person.

In closed rooms, the body heat also ensures that the exhaled air pulls the aerosols slowed down by the MNS with it as it ascends. These then float towards the ceiling and from there are distributed over a larger area. The local concentration of potentially infectious aerosols is therefore reduced by an MNS.

Nevertheless, according to the scientists, regular ventilation should not be avoided in order to prevent an accumulation of virus-containing aerosols. Alternatively, the aerosol pollution can also be reduced with room air purifiers, if these have appropriately fine filters.