What happens if a Covid patient coughs in an emergency room? We know that the largest salivary droplets (droplets) fall to the ground by gravity within two meters, but the microscopic ones that we emanate not only with coughing, but also just talking or breathing (aerosols) remain longer in the air before evaporate. A 3D simulation created by researchers from the Bambino Gesù Pediatric Hospital, which joins numerous other studies on the same content, exactly reproduces the movement of biological particles in the environment and the impact of aeration systems on their dispersion. The results of the study, conducted with the university spin-off Ergon Research and the Italian Society of Environmental Medicine (SIMA), were published in the scientific journal Environmental Research. What emerges is that a crucial role is played byforced ventilation to disperse potentially contagious particles. Attention, the machines must be “to convey the external air inward” like those generally mounted in large environments such as hospitals. Almost all the air conditioners and heat pumps installed in homes and shops are instead of the split type: they do not convey fresh ara but recycle the existing one.
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The study
The researchers used “computational fluid dynamics simulation” (CFD – Computational Fluid Dynamics) tools to virtually recreate the waiting room of a pediatric emergency room equipped with an aeration system, with 6 children and 6 adults inside without bezel. In this virtual environment, the behavior of the droplets and the aerosol in the 30 seconds following the cough was traced in three different scenarios: with the ventilation system switched off, at standard speed e at double speed, to assess how much contaminated air each person present would breathe. Using the series of physical parameters that regulate the airborne dispersion of biological particles (velocity, acceleration, quantity, droplet diameter, turbulence, connective motions generated by air conditioning), the researchers obtained a 3D simulation that reproduces what exactly would happen in a real environment.
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The results
The results of the study confirm that air conditioning systems play a key role in controlling the dispersion of droplets and aerosols produced by breath in closed environments. In fact, it has been documented that the doubling of the air flow conditioning (calculated in cubic meters per hour) inside a closed room reduces the concentration of contaminated particles by 99.6%. At the same time, the double speed causes airborne dispersion of droplets and aerosols faster and at greater distances than standard air conditioning or switched off. With the air conditioner off, the people closest to the coughing child (1.76 meters in the simulation) breathe 11% of contaminated air while the farthest (4 meters) are not reached by the infected “cloud”. With the double speed system reduces the concentration of contaminant and the closest people breathe 0.3% of it, but even those furthest away are quickly reached who in this case breathe 0.08% of contaminated aerosol, very low percentages and essentially irrelevant for the purposes of contagion. ‘The activity has shown that, if used correctly, these tools can foster a greater understanding of the phenomenon and lead to an effective use of mechanical ventilation to improve indoor air quality,’ explain the researchers.
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The crucial role of ventilation
“The virus infection SARS-CoV-2 – said prof. Carlo Federico Perno, head of Microbiology and Diagnostics of Immunology of the Infant Jesus – is transmissible through the breath in relation to three fundamental elements: the immune status of the person, the quantity of pathogen present in the air, measured in particles per cubic meter, and the aeration of the environment. All other elements being equal, therefore, the higher the concentration of virus, the greater the likelihood of contagion“. «The air exchange in the rooms – underlines the professor Alessandro Miani, president of SIMA – also through theactivation of scientifically validated systems of aeration, purification and controlled mechanical ventilation, is fundamental in the dilution of the virus and in its transfer, as far as possible, to the outside, ie in the mitigation of the airborne biological pollutants present in the droplets, significantly reducing the concentration of the pathogen in the air. This, together with the use of barrier means (masks, spacing and hand hygiene), today represents the main tool to reduce the risk of contagion in neighboring environments “.
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A solution for schools and public transport
The airborne transmission of the coronavirus through the aerosol of tiny particles suspended in the air indoors it is a widely discussed way of contagion since the beginning of the pandemic. A large debate is underway among scientists around the world. Studies are piling up and various evidence shows that the risk exists above all if we are talking about closed and poorly ventilated environments, or even outdoors in crowded conditions. The US Centers for Disease Control CDC recently included particle aerosol in the list of possible transmission routes for Sars-Cov-2, while WHO still hasn’t. Staying a few minutes in a closed environment with a Sars-CoV2 positive person with mild symptoms, keeping your distance, will probably not expose you to a high risk of contagion. But if the stay is longer and the environment is not ventilated, things change. In school classrooms or in public transport, controlled ventilation could really be the solution to reduce the risk of contagion.
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October 29, 2020 (edited October 29, 2020 | 16:15)
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