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AFNOR Test

AFNOR NFT 72-28

AFNOR NFT 72-28 is the name of a French test standard. It has established itself as the standard method for testing the effectiveness of autonomous room disinfection systems. It is known for its particularly strict compliance conditions. Many suppliers of disinfection systems are deterred by this rigorous and expensive test; it is therefore not surprising that only about 30% of the systems offered on the market have passed the test. It is important in this context that the entire system, i.e. the disinfectant and the device are tested together.

A distinction is made between “automatic application” and “directed spraying”.

Direct spraying

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The disinfectant is sprayed onto a test surface from a predetermined distance. The sample plates are located on this surface. The test germs are applied to these sample plates. Germs can be bacteria, fungi, yeasts or viruses.

Automatic application

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The device to be tested is placed in a defined room. The disinfectant is fogged fully automatically into the room, an thus onto all surfaces. In contrast to directional spraying, the sample plates are located on the back of the test surface. (see picture above). The aerosols generated by the device must therefore be applied in such a way that they not only touch the test surface facing the device, but also the test surface facing away from the device.  The sample plates are placed somewhere in the room.

The AFNOR test is very close to reality, if one compares the set up of the test and, for example, a patient’s room  in which furniture, equipment, etc. is placed randomly.

Systeme with UV-light and AFNOR

Disinfection systems that are operated with UV-C light can never fulfil the AFNOR test. Because the sample plates are on the dark side of the test surface, the emitted UV rays never reach the test germs. Even automatic or autonomous movement of the device does not help, because the sample plates are placed so close to the wall that they are always in the shadow.

aseptobot

The aseptobot, which we developed recently passed the AFNOR test successfully. The disinfectant fog-it plus was used in the test.
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Contact transmission of SARS-CoV-2

There is extensive literature on the transmission routes of SARS-CoV-2. Essentially, two transmission routes are distinguished: airborne and contact transmission via contaminated surfaces.

Airborne

Transmission occurs through larger droplets and small aerosols, which are transferred from one person through breathing, coughing, talking, singing and sneezing to another person who inhales the droplets or aerosols.

Droplets fall to the ground relatively quickly, while aerosols “stay” in the air for a relatively long time. What does “relatively” mean?

The air we breathe consists of droplets between 0.2-20 µm. [1] It can be shown that for a person 175 cm tall, it takes about 20 seconds for the large droplets of breath to fall to the ground. The small aerosols reach the ground only after a very, very long time (days). These are theoretical considerations which do not take into account environmental influences such as temperature (evaporation), speed of the ambient air and pollution of the air.

When sneezing and coughing, the horizontal velocities of the aerosols are much higher than the sinking velocity, i.e. during the descent these aerosols are also carried very far. The video at the following link shows impressive pictures of how aerosols can be carried up to 8m. These droplets settle on surfaces and can lead to contact transmission.

SARS Cov aerosol
Picture from [7]

Contact transmission

The authorities in Switzerland, Germany and Austria therefore do not rule out contact transmission:

FOPH, Switzerland: When infected persons cough and sneeze, infectious droplets get onto their hands or onto neighbouring surfaces. Another person could become infected if they pick up these droplets with their hands and then touch their mouth, nose or eyes. [2]

RKI (Robert Koch Institute), Germany: Transmission through contaminated surfaces cannot be ruled out, especially in the immediate vicinity of the infectious person [3].

Federal Institute for Risk Assessment: Furthermore, transmission via contact or smear infections cannot be ruled out. In this case, pathogens that are on the hands reach the mucous membranes of the nose or the eye, where they can lead to an infection [4].

Austrian Health Office: the novel Corona virus can also adhere to the skin and on objects (e.g. door handles, telephone) and be transmitted via hands (smear infection) – especially if hands with virus particles come into contact with the eyes, nasal or oral mucosa. [5]

How long do viruses that reach surfaces via droplets remain infectious?

The much-cited reference literature [6] on this point can be found under the following link. The authors have investigated how long SARS-CoV viruses remain infectious on different materials. Copper, cardboard, stainless steel and plastic were examined. The pure aerosols in the air were also examined. The summary of the results can be seen in the following graphs:

SARS Cov Materials

The result of the study in brief:

  • SARS-CoV viruses remained infectious in the air for the entire experiment duration of 3 hours.
  • On the tested materials, the viruses remained infectious for up to 72 hours, although the viral load decreases significantly over time.
  • On copper and cardboard, the viral load decreases faster than on plastic or stainless steel.

Literature

  1. https://www.aerzteblatt.de/archiv/217048/SARS-CoV-2-und-Aerosole-(1)-Was-wir-bis-heute-wissen
  2. https://www.bag.admin.ch/bag/de/home/krankheiten/ausbrueche-epidemien-pandemien/aktuelle-ausbrueche-epidemien/novel-cov/information-fuer-die-aerzteschaft/schutzmassnahmen.htmlübertragung
  3. Epidemiologischer Steckbrief zu SARS-CoV-2 und COVID-19 Stand: 19.4.2021
  4. https://www.bfr.bund.de/cm/343/kann-das-neuartige-coronavirus-ueber-lebensmittel-und-gegenstaende-uebertragen-werden.pdf
  5. https://www.gesundheit.gv.at/krankheiten/immunsystem/coronavirus-covid-19/uebertragung
  6. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1, N Engl J Med 2020; 382:1564-1567