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Covid-19 and ventilation: how best to prepare for autumn and winter?

With autumn approaching in Europe, people are likely to work and gather again more frequently inside. As badly ventilated indoor places were proved to be the cause of Covid-19 superspread events in the early phase of the pandemic, the question is how to deal with proper ventilation in the coming months. Is there a need for nation-wide ventilation programmes and do tools exist for individuals to measure the ventilation rate of indoor places?

The low number of infections in Europe during summer, when weather allows people to spend more time outside, seems to confirm findings earlier this year that the vast majority of infections take place in public indoor spaces. This is due to aerosols, which can remain floating for a long time in rooms with poor ventilation and without the right humidity. One of the most remarkable aspects of the Covid-19 crisis so far is the slow acceptance, despite strong evidence, that aerosols rather than direct contact are responsible for transmission of the virus. While some governments still seem to be in denial regarding the role of aerosols, Angela Merkel stressed their importance in a speech given mid-August.

Given the importance of aerosols, the coming months will tell whether precious time has been lost during summer to properly adjust ventilation systems in indoor places where large numbers of people are present. The virus can easily be transmitted in places where ventilation systems bring in too little fresh air and no provisions are made to remove the virus from the air. According to Dutch researcher Maurice de Hond, the installation of a proper ventilation system can in fact make a room “Coronaproof”. With reference to a database that has mapped Covid-19 superspread events, de Hond points out that the commonality between these events is that they took place in enclosed spaces without a sufficient supply of fresh air. Notorious events where this happened are during rehearsals of a choir in Seattle and work in a slaughterhouse in Germany.

Thus, what is more important than the social distancing protocols, in de Hond’s view, is thatnational ventilation plans are set up. There is wide scientific support for this strategy, including by expert José-Luis Jiménez, who notes that “when it comes to Covid-19, the evidence overwhelmingly supports aerosol transmission, and there are not strong arguments against it”.

However, he also remarks that determining a realistic ventilation rate for a space can be difficult – even for commercial buildings and trained maintenance personnel. Jiménez explains that by knowing the ventilation rate of an indoor space, one can estimate the infection rate through aerosols in that location. The ventilation rate can be measured using CO2 analyzers, which are available at prices starting around $150. Therefore, using this equipment in conjunction with instructions and a spreadsheet provided by Jiménez, it is within financial reach for most professionals to measure the ventilation rate in shops and restaurants as well as for individuals in their own homes.

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