Big danger is the air in small rooms

Room air cleaners and fresh air free indoor rooms from virus-containing aerosols

Six renowned German scientists, such as Professor Hendrik Streeck, Director of the Institute for Virology at the University Hospital in Bonn, and Professor Dieter Köhler, a pneumologist from Schmallenberg, have proposed measures to reduce indoor infections with the Covid-19 virus in a public statement. A major role is assigned to indoor air purifiers, such as the X-Series from UlmAIR. This is because it is a "scientifically undisputed finding" that "indoor spaces are the central sites of infection".

Here we give you an excerpt of the information available, among others, on the websiteäge
among others. You can read the entire text on the pages under "The Air Hygiene Check - Safe Rooms in a Pandemic".

The eight concrete measures proposed by the consortium of scientists to prevent infection by the Covid 19 virus indoors:

In der Außenluft gibt es keine relevante Ansteckungsgefahr (<0,01% im Vergleich zu Innenräumen). Die Ursache ist in dem vom Menschen durch die warme ausgeatmete Luft und die Körperwärme erzeugten Vertikalflow zu finden (bis zu 100m³/h). Dieser verdünnt die abgeatmeten Aerosole stark. Windströmung draußen im Freien verdünnt die Konzentration zusätzlich.
Der Lufthygienecheck setzt sich aus den folgenden Parametern zusammen:

1. the number of people who are currently in an unventilated room or have been until recently. As the number of people increases, so does the likelihood of an infected person being in the room, and the more people in the room, the more can potentially become infected.

2. residence time. An infectious person in the room increases the concentration of viruses in the room air over time and the longer uninfected people stay in the room, the more viruses they inhale.

3. volume of the room. The larger the room, the lower the concentration of viruses in the room.

4. room height. Thanks to the vertical flow generated by humans, high rooms are particularly safe because the exhaled virus-containing aerosols move upwards.

5. effectiveness of ventilation. The amount of fresh air supplied to the room dilutes the aerosols. In the case of window ventilation, this depends in particular on the temperature difference inside/outside and the wind movement. The greater the temperature difference, the greater the effect. However, the energy consumption also increases due to the cooling.
Effectiveness of indoor air purifiers: The practically aerosol-free air delivered into the room by an air purifier determines the CADR = Clean Air Delivery Rate or blown-off purified air (m³/h).

6. durability and effectiveness of masks worn by people in the room. Shields are ineffective because they do not prevent the infectious aerosols from spreading in the room.

7. breathing rate and depth of breathing of infected and non-infected persons in the room. Increased ventilation occurs, for example, during physical work, sports and singing.
Particularly unfavourable are small rooms with little or no ventilation (small offices and recreation rooms, lifts, toilets, motor vehicles, public transport, etc.) Here, a concentrated infectious aerosol cloud can remain in the air for a long time (similar to cigarette smoke) and then infect people who enter the room (e.g. cleaning staff). Sometimes virus spreaders and infected persons have never met.

So there are a number of measures that can be taken to reduce indoor infection through aerosol transmission:

- Limit the number of people in a room;

- Limitation of the time people can stay in a room;
Priority use of large and high rooms (e.g. many gymnasiums, auditoriums do not usually need additional special protective measures);

- Increase the supply of fresh air. Here, a control by means of CO2 measuring devices is an option;

- Use of effective room air purification devices. Here, control via aerosol measuring devices is possible.

There are essentially two ways to rid a room of virus-containing aerosols. Both are ventilation measures:

Supply of fresh air (outside air) through suitable ventilation technology.

Room air cleaning with suitable air filter devices.

To check the effectiveness of the respective measure, we propose a control by a combination of two measuring devices. On the one hand, a sufficient supply of fresh air is measured by means of a CO2 monitor, on the other hand, the air purification measures are checked by means of an aerosol measuring device. Both should be placed centrally in the room, without direct proximity to people, because exhaled air can greatly increase the CO2 concentration locally. Both hosts and visitors to a room can see for themselves how good the indoor air is in a facility.


The six authors
Dr. Ing. Achim Keune, VDI, DGUV Test certified RLQ Manager, Hamburg;
Prof. Dr. med. Dieter Köhler (Dipl. Ing. FH), Schmallenberg;
Prof. Dr.-Ing. Rüdiger Külpmann, Lucerne University of Applied Sciences and Arts, Institute for Building Technology and Energy;
Dr. rer. nat. Gerhard Scheuch, PhD Gemünden;
Prof. Dr. med. Hendrik Streeck, Director of the Institute for Virology at Bonn University Hospital;
Dr. med. Thomas Voshaar, Chief Physician Lung Centre Foundation Hospital Bethanien Moers.

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