Hygiene management
10.02.2021

Reduction of aerosols containing SARS-CoV-2

Regularly opening windows or an efficient ventilation system can significantly reduce airborne coronaviruses in hospitals and other facilities, according to the experts.

So-called aerosols are one of the main transmission routes of COVID-19. The solid or liquid particles in the air that we exhale provide the viruses with a convenient “means of transport”. These particles remain in the air for a long time and can spread throughout the entire room in a matter of minutes. At the same time, just the heat emitted by the human body is sufficient to keep the virus-containing particles suspended in the air.

Ventilation concepts to reduce the viral load

The “Aerosols Expert Group” carried out an investigation into which ventilation methods can reduce the concentration of coronaviruses in, for example, patient rooms and waiting areas. This group of scientists includes the Deputy Chair of the Commission for Hospital Hygiene and Infection Prevention (KRINKO) at the Robert Koch Institute (RKI), Prof. Dr. med. Heike von Baum.

In practice, it is not possible to actually measure the viral load in the air in a room. However, one way to track the virus-carrying aerosols is by measuring the air quality by means of the CO2 concentration. Although the amount of carbon dioxide emitted does not provide a specific measure of the number of virus particles, a low CO2 content is nevertheless indicative of a smaller aerosol load.

The expert panel of engineers, scientists and physicians recommends indoor air quality with a CO2 concentration of less than 800 parts per million (> 800 ppm). According to the scientists, this technical guide value is currently the best means of assessing the amount of aerosols in a room.

The CO2 level, and therefore the viral load, in the air can be reduced by:
  • Opening windows
  • Ventilation and air conditioning (VAC) systems
  • Air purifiers (in addition)

This is how the experts of the Aerosols Working Group evaluate the various ventilation concepts:


5 facts about ventilation by opening windows 

  1. Tilted windows only have a limited ventilation effect.
     
  2. The required air flow can only be achieved by pulse ventilation (windows wide open for short periods) or cross-ventilation with windows/doors on opposite sides of the room.
     
  3. Low outside temperatures reduce the ventilation time required. Example: a 20 m2 room with an open window takes 3 minutes to ventilate at outside temperatures between 0°C and -10°C. At 15°C, it would take twice as long.
     
  4. This type of natural ventilation is not appropriate everywhere, as it can cause a major temperature drop in the room, which affects the well-being of the occupants. Windows fitted with security restrictors are another factor.
     
  5. If there are several people infected with SARS-CoV-2 in the room, ventilation has only a limited effect.

 

5 facts about ventilation and air conditioning systems (VAC)

  1. VAC systems use fans to draw in outside air, then filter it and adjust its temperature before blowing the conditioned incoming air through openings into the room.
     
  2. If the openings are placed appropriately, a large-volume, room-wide air flow is created, regardless of the outdoor temperature.
     
  3. Aerosols are also removed from the room with the extracted air.
     
  4. VAC units should be operated without recirculation and should be equipped with filters.
     
  5. So-called HEPA (High Efficiency Particulate Air) filters with an efficiency of >99.95% or >99.995% are recommended. These have a H13 or H14 (outdated) rating, as well as classes ISO 35 H or ISO 45 H.
 

5 facts about air purifiers

  1. Air purifiers have a fan that draws in the indoor air, passes it through filters and returns it to the room as purified air.

  2. These portable devices can reduce or keep the viral load low over time.

  3. But even air purifiers are not a substitute for the “hands, face, space” + ventilation rule. If two people come together in a room without wearing masks and social distancing, they will be exposed to aerosols even if an air purifier is used.

  4. The device must be large enough and suitably equipped. The decisive factor is the clean air delivery rate (CADR) rather than the filtering efficiency.

  5. Limiting factors for their use are power consumption, noise emission and maintenance costs.

 

Proper ventilation of patient rooms during the coronavirus pandemic at 20 m2

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Proper ventilation of patient rooms during the coronavirus pandemic at 40 m2

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Sources:

Dittler A et al. (12/2020). Stellungnahme: Aerosole&SARS CoV2 – Entstehung, Infektiosität, Ausbreitung & Minderung luftgetragener, virenhaltiger Teilchen in der Atemluft. (Letzter Zugriff 02.02.2021) Aerosole_SARS_CoV2.pdf" target="_blank">https://www.baden-wuerttemberg.de/fileadmin/redaktion/m-mwk/intern/dateien/Anlagen_PM/20201204_Stellungnahme_Aerosole_SARS_CoV2.pdf

Positionspapier der Gesellschaft für Aerosolforschung zum Verständnis der Rolle von Aerosolpartikeln beim SARS-CoV-2 Infektionsgeschehen vom 07.12.2020. Letzter Zugriff 02.02.2021. https://www.tropos.de/aktuelles/pressemitteilungen/positionspapier-der-gaef-zum-verstaendnis-der-rolle-von-aerosolpartikeln-bei-covid-19

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