During the COVID-19 pandemic, the quality of medical masks has been a topic of public concern, with a high Degree of misinformation among the public and even among healthcare workers themselves.

Two scientists from the University of Navarra are evaluating the quality and efficacy of some protective masks used by health professionals. They are Arturo Ariño, director of department of Environmental Biology of the University of Navarra, and Jesús Miguel Santamaría, director of high school of research in Biodiversity and Environment (BIOMA) of the academic center. Although the first requests for analysis came from the Clínica Universidad de Navarra and from the University's own Occupational Risk Protection Service, more than 600 tests have already been carried out with samples provided by institutions, companies and individuals. 

The goal of this work, points out Ariño, is "toprotect those who protect us", that is, to analyze the filtering capacity of the masks -new and recycled- to find out which ones can reduce the possibility of contagion of healthcare professionals who provide front-line care to people infected by coronavirus. "Their work is fundamental for the well-being of everyone and we must do what we can to protect them," adds Santamaría.

Through this study, the aim is to find out what capacity the masks have to filter the passage of particles during actual use. "The droplets exhaled by people have a variable size, from microns to millimeters, and we check whether these particles, as well as those of the same size as viruses (less than a third of a micron), are able to pass through the protective barriers," Santamaría explains.

The experimental protocol developed by both scientists of the School of Sciences consists of using a medical mannequin to which they have adapted a suction pump to make it breathe through a mask, just like a person. The mannequin is placed inside a chamber where a carbon aerosol is generated that simulates a cloud of viral particles, and the researchers measure the concentration of this aerosol in the air and inside the pharynx of the mannequin at the same time. To do this, they use two identical infrared laser spectrometers capable of analyzing particles of different sizes (from nanometers, like viruses, to tens of microns, like droplets) at different concentrations continuously. In this way they can characterize how effective the mask is in different risk situations.

 

The versatile laser light is also used in a complementary experiment to measure the ability of the masks to retain the droplets of saliva exhaled during coughing, which are considered a likely source of contagion source . In this case, the mask is attached to another mannequin that is connected to a respirator that simulates a normal cough and a clinical dropper that simulates the generation of saliva in the mouth. During coughing, droplets of saliva shoot toward the mask, and lasers detect microdroplets that may pass through or escape. By comparing the light scattered by the lasers when the mannequin coughs with and without a mask, it is possible to deduce how much of the mask has been retained, or where the aerosol cloud has been dispersed.

 

The results of hundreds of experiments show that there are important differences between different types of masks. Ariño and Santamaría are forceful in their recommendation to use approved masks whenever you are in a high-risk environment such as the one that can occur in places where there are infected patients, since in general they can protect several times more than those that are not. "Although the vast majority of the masks manage to stop a significant proportion of the droplets that we disperse when talking or coughing, and are therefore useful for avoiding contagion during normal activity, the usefulness of the masks for self-protection is extraordinarily variable, and in the case of the handmade ones, there is really no comparison with those that carry the EN-149 homologation," Ariño points out. However, they insist that "we must avoid both the false sensation of safety that a mask gives, which can make us neglect other equally necessary measures, and the idea that they are useless: at least they reduce the probability of generating a contagious environment", they point out.

 

In addition to the characteristics of the fabric, one of the most important factors in ensuring the effectiveness of masks for self-protection is to fit them properly to the face. "We have found that very efficient masks are useless if they are not perfectly adjusted, so it is vital to make an effort to put them on correctly," concludes Santamaría.