FluShields Gives Latest Insights About Aerosols And How The Corona Virus Is Spread
Exactly how the coronavirus is spread – whether above all via a droplet infection or rather about aerosols in the breathing air is not yet definitively defined. When a corona patient coughs, speaks, or sneezes, a beam of different sizes is produced that penetrates and spreads into the room air. That is why you need to protect yourself as much as possible with a face mask or face shield.
All these different sized droplets and aerosols potentially contain viruses. A research topic by Prof. Dr. Martin Kriegel, head of the Hermann Rietschel Institute at the TU Berlin, studied 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.
How long do virus particles stay in the air?
"In various projects, we investigate the time for the virus particles to spend in the air under a wide range of conditions," says Martin Kriegel. For these experiments, his team "Contamination Control" has two research cleanrooms, several indoor airflow laboratories, and a research operating room at his disposal. In connection with the corona pandemic, scientists are investigating how the spread of the virus depends on the composition and size distribution of the particles within the exhaled air - aerosols. An aerosol is the smallest, liquid, or solid particle - 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, human hair has a thickness of about 100 microns.
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The size of the carrier aerosols is crucial for the behavior of viruses in the air.
"For the coronavirus, it seems to be that both droplet infections and airborne transmission, i.e. via aerosols, are relevant," says Martin Kriegel.
So what is the difference between a droplet infection and an airborne transmission? 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," says Martin Kriegel. Again, that is why it is crucial for everybody to wear N95 face masks to protect others and protect themselves as much as possible.
Particles from 0.01 microns to 1500 microns occur when speaking, coughing, or sneezing.
The spread in the space 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. Various studies have shown that particles from 0.01 microns to 1500 microns occur when speaking/coughing/sneezing. If you wear an N95 face mask you actually protect others so that your virus particles do not reach them.
"After the beam has been completely mixed with the room air, the distribution takes place," explains Martin Kriegel. "The smaller particles largely follow the airflow of the room, while larger particles gradually fall to the ground. The fact that humans emit very large particles only when spelled is 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.
In various projects, 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. "Another study 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 emitted in the stream of heat sources. They rise, spread horizontally, and only then begin to deposit. Possible horizontal air movements further enhance the distribution effect," says Martin Kriegel.
And what is the situation in a multi-person office?
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In connection with the resumption of day-to-day work in an office occupied by 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," says Martin Kriegel.
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."
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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