FluShields Takes Another Peek Into How Corona Virus Spreads Via Droplets and Aerosols
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Exactly how the coronavirus is spread – via a droplet infection or rather about aerosols in the breathing air, is not yet definitively clarified. When a corona patient coughs, speaks or sneezes, a beam of different sized aerosols are produced that penetrates and spreads into the room air.
In July 2020 Prof. Dr. Martin Kriegel, head of the Hermann Rietschel Institute at the TU Berlin, finished a study about all these different sized droplets and aerosols which potentially contain viruses. He and his team researched how these particles behave, if and when they sink to the ground, how far they are distributed, remain in the air, or where they sediment.
Here are his first findings:
The TU Berlin investigated the time for pathogens to spend in the air under a wide range of conditions: i.e. if the spread of the virus depends on the composition and size distribution of the particles within the exhaled air (aerosol). An aerosol is the smallest, liquid, or solid particles (these can be viruses, for example, individually or in combination with saliva) in a gas, usually air. The particle size ranges from a few nanometers – i.e. one-millionth of a millimeter – to several micrometers. By comparison, a human hair has a thickness of about 100 microns.
For the coronavirus, it seems to be that both droplet infections and airborne transmission, i.e. via aerosols, are relevant. In a droplet infection, the virus particles in a saliva droplet reach directly onto the mucous membranes of another human being. In an airborne transmission, the viruses enter the airways, bound in the smallest liquid particles. The size of the carrier aerosols is crucial for the behavior of viruses in the air, but also the indoor climate, the rate of air change, and the way in which it is ventilated. Larger particles sink to the ground faster.
Smaller particles follow the airflow and can remain in the air for a long time: a fact which makes them very dangerous for people working in open offices.
The spread of the mixture of particles, saliva, and air, which occurs during the speech, coughing, and sneezing, takes place in two steps.
First, coughing, speaking, sneezing creates a ray that penetrates into the room air and increasingly mixes with it. The course of the incoming beam depends on different boundary conditions such as speed, turbulence, the temperature difference between the beam and the ambient air, and the difference in humidity.
The first studies have shown that particles from 0.01 microns to 1500 microns occur when speaking/coughing/sneezing. "After the beam has been completely mixed with the room air, the distribution takes place. The smaller particles largely follow the airflow of the room, while larger particles gradually fall to the ground.
The fact that humans ‚sneeze‘ very large particles are often ignored. Normal speech and coughing generate almost exclusively small aerosols. More than 50 percent of medium particles can still be found in the air after 20 minutes.
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In the various tests, the scientists measured the so-called sedimentation time (deposit time) of particles of different size classes. Small particles (0.5 to 3 microns) are still almost completely present in the air after a measuring time of 20 minutes. The deposition of these particles is not or only slightly recognizable. For medium particles (3 to 10 microns) more than 50 percent are still to be found in the air after a measuring time of 20 minutes. It also shows that even larger droplets (>60 microns) can spread far in space under certain circumstances. This is the case, for example, when the particles are „sneezed“ in the stream of heat sources (for example, by one person). They rise, spread horizontally, and only then begin to deposit. Possible horizontal air movements further enhance the distribution effect.
And what is the situation in a multi-person office?
In connection with day-to-day work in an office with several people, the scientists also simulated the particle propagation in an office occupied by four people with and without mechanical ventilation. This shows that smaller particles under 50 microns, in particular, spread far in the room without mechanical ventilation and linger for a long time. In contrast, particles between 5 and 20 microns spread less widely in a room with mechanical ventilation and are largely discharged. Any increase in outdoor air supply makes sense.
The key questions that we will now explore in interdisciplinary projects are how large SARS-CoV-2 particles must be in order to be still infectious and how the length of stay of this particle size can be influenced by targeted supply and exhaust air systems or even simple ventilation of rooms.
The indoor climate also plays a role, because the aerosols become smaller very quickly due to evaporation and then behave differently. Basically, it can be said that at typical air change rates in residential and office buildings, the pathogens remain in the room for hours. The sinking speed and also the air renewal takes a very long time. Any increase in the external air supply is therefore generally useful.
Good news: You can improve your protection by wearing an N95 or KN95 respirator mask: Get your KN95 respirator masks for the whole family today.
Disclaimer: Please note that we can only pass on general information and cannot make any guarantees or be liable for any consequences of your decision making or behavior. Use good common sense and ask your healthcare provider or physician for advice.
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