Ventilation

Partly because of these recent insights, the Dutch National Institute for Public Health and the Environment "RIVM" amended the ventilation directive. Now they recommend supplying as much fresh air as possible in systems that use recirculation. Recirculation systems recycle the exhaust air rather than expelling it from the home. Reason for this recommendation is the survey into a number of infections in a nursing home in the Dutch city of Maassluis late June, linking the ventilation system to the infections. The surveys have not yet fully been completed, but the health authority concluded that, on second thoughts, the ventilation system probably was not a factor. RIVM confirmed this: though COVID-19 RNA was found on the ventilation system filters, it was no longer contagious. In addition, it became clear that staff had also been in direct contact with each other and that this infection route is far more likely than transmission through the air.

Yet it is a good thing that much research has been carried out in the way the virus may spread through the air, for all infection rates must be known to eventually be able to curb the virus. Right from the start we all assumed that maybe the virus could spread through moisture droplets that are released by coughing and sneezing, but also when talking, singing, and yelling. As a rule, these moisture droplets do not carry further than 1.5 m before they evaporate or settle, and that is why we duly keep our distance.

Today, there is much attention for aerosols as potential virus transmitters. Aerosols are small dust particles or moisture droplets that are light enough to hover in the air for hours, which gives them a much wider range. Although most scientists agree that it has not yet been established beyond any doubt that aerosols really contributed to the spread of the Coronavirus, there are indications that it could well be the case. There is a lot of talk about it and, in fact, the conclusion is that there still is a lot we do not know about the way the virus spreads. How much of the virus is needed to infect someone? Theoretically, just one virus particles suffices, but when infected with a single particle, the immune system has more time to respond before the virus has been able to multiply.

In the meantime, as long as there is a lot of discussion and uncertainty, we had still be better safe than sorry and do what we can to prevent infection on through the air. Effective ventilation is crucial here. When the number of virus particles determines whether an infection may take place, it helps to dilute the air as much as possible with clean air and to carry off used air as much as possible. This means that ventilating extensively reduces the risk of infection. Since prevention is always better than cure, our advice is: ventilate as much as possible and with maximum direct outdoor air supply.
 
“Since prevention is always better than cure, our advice is: ventilate as much as possible and with maximum direct outdoor air supply”.