Monday, August 3, 2020

Virus concentration: fresh air? How the room air is as corona-free as possible

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Office, restaurant, school or university: There is often little air exchange in closed rooms. Those who spend a long time indoors with many other people have an increased risk of becoming infected with the corona virus, for example.

Like this, many other pathogens spread through the air. The large corona outbreak at the Tönnies plant in Rheda-Wiedenbrück could also be due to air transmission. In order to bring the air there to low temperatures, it is pulled out of the room, cooled and brought back, said hygiene expert Martin Exner from the University of Bonn. He proposed high-performance filters and UV rays to prevent viruses from being distributed via such a system in the future.

At the latest based on these findings, the question arises: How can interiors really be made corona-free and remain so?

HIGH-PERFORMANCE FILTERS: The high-performance filters recommended by Exner, also known as Hepa filters, have been used in operating rooms of hospitals for many years, for example. They consist of synthetic fibers that are stacked on top of each other in several layers, explained hospital hygienist Michael Pietsch from the University of Mainz. According to him, particles are separated from the filter by various physical effects on the fibers and remain there. Corona viruses could also be filtered out in this way.

DISINFECTION BY FOGGING: Some companies and organizers disinfect rooms by fogging disinfectants. Various means are used, some of which are not entirely safe. Hospital disinfectant using formaldehyde diffusion has been used for over 100 years, Pietsch explained. However, the effort for this is very high, and formaldehyde can also cause cancer, which means that a room cannot be entered immediately.

Alternatively, hydrogen peroxide is also used. One advantage is the residue-free decay in water and oxygen, says Pietsch. However, this method also has to wait a long time, since hydrogen peroxide can be harmful if inhaled.

The agent that the Berlin Ensemble is trying out for disinfecting rooms should be tolerable and naturally degradable for allergy sufferers. The disinfectant Amoair, which is harmless according to the theater, is distributed in the air via a nebulizer or an existing ventilation system. A first test run showed that about 99 percent of the bacteria and viruses in the room could be destroyed by the fog.

UV RADIATION: Bacteria and viruses can be killed by UV rays. The method is hardly suitable for room disinfection: In order for the rays to work at all, the distance between the radiation source and the object should be 10 to 30 centimeters, according to Pietsch, the hygiene expert from Mainz. “A room air disinfection would only be possible if the air is moved and germs are repeatedly guided past the radiation source.” In the food industry, the process can still be used sensibly, for example for disinfecting packaging films.

AIR CONDITIONING: Air conditioning systems are more common than complex disinfection processes. They provide fresh air from the outside and cool or warm it: the old air is extracted and then either released to the outside or brought back into the interior together with fresh air. “In any case, there is a reduction in the concentration of germs in the indoor air,” said Pietsch.

The Federal Industry Association for Technical Building Equipment (BTGA) recommends air-conditioning systems with high-quality filters for cooled rooms with recirculation, such as those found in slaughterhouses. For systems in offices, hotels, shopping malls or congress centers, a high proportion of outside air offers the best protection against infection. “Especially in situations as we are currently experiencing, we recommend keeping the proportion of air circulating in air conditioning and ventilation systems as low as possible,” advises BTGA President Hermann Sperber. According to the association, the transmission of corona viruses via ventilation or air conditioning systems can almost be ruled out if the systems are operated properly and regularly maintained.

VENTILATION: But even without large technical equipment, the risk of infection indoors can be reduced: Impact ventilation with the windows wide open is the quickest way to exchange air. “Usually, indoor spaces are warmer than the outside air, so there is a draft from the inside out. This can reduce the possible virus concentration in the interior, »explained hygiene expert Pietsch. It also reduces the risk of infection through aerosols. However, an infection cannot be ruled out completely.

MASKS AND DISTANCE: Even if everyone has heard it countless times, wearing masks and complying with the distance rule continue to be important measures to protect against corona infection. Wearing a simple mouth-nose guard can also significantly minimize airflow.

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