Spread of viruses

Pathogens such as bacteria and viruses like COVID-19 need a carrier to spread. This can be a dropletor a solid particle. The transfer usually takes place via contact (directly from person to person or indirectly via a contaminated surface), but also through air. Measures such as good hygiene, sufficient distance, and wearing of protective equipment (such as a mouth mask and/or a face shield) ensure that direct contamination is prevented. However, also tiny droplets, known as aerosols, are released when coughing, sneezing, speaking and breathing. Due to their small size, these aerosols stay afloat for a long time, while they also may contain virus material.


Research has shown that aerosols can spread quickly over a room and therefore pose a potential risk for contamination. The extent to which these aerosols cause contamination is currently being investigated. For safe use of spaces in which several people are staying (while maintaining sufficient distance), it is currently recommended to ventilate abundantly and to avoid recirculation of exhaust air. Building design legislation determines the legal framework for minimum (forced) ventilation per type of building and use function, but is it known to which extent it is sufficient to minimize the risk of contamination? In addition, what are the roles in this of occupancy rate, technical condition of the building, size of spaces, but also the degree of physical exertion? It suggests that a one-size-fits-all approach is not adequate.

A group of international researchers with backgrounds in building physics, fluid dynamics and (sports) medicine have investigated the possibilities for occupancy rate in sports centers based on the factors mentioned above. Although sports centres are obliged to be ventilated extensively, there is also an increased emission of aerosols due to the physical effort. The researchers have  calculated how many people can exercise safely toegether in a room of a certain size in relation to the “refreshment rate” as a result of ventilation. The type of ventilation system also plays a significant role in this. Many sports centers have been equipped with a system that mixes in fresh air instead of a continuous one-way movement of refreshment. This has energetic advantages, but is detrimental to the spreading of aerosols.

Active air treatment

The researchers then examine the potential of air purification in such a situation. Herein, The Aufero from ENS Clean Air Solutions serves as an l example from practice. The Aufero has a wide application in spaces with medium to large content and is often applied to stimulate recirculation and mixing to optimize performance. Because aerosols are actively captured at a large flow capacity (7,500 m3/h), the degree of spreading is reduced. And it shows. For a range of room sizes and ventilation rates, it is calculated how many people can safely be present. Under certain conditions the amount of people may be doubled compared to the guidelines by using an air purifier like the Aufero!

Safety first

In addition to personal protective equipment, active air cleaning would provide additional safety against the spread of pathogens. The researchers offer technical tools to curb the complexity of the various specific circumstances and to provide targeted advice that may increase the possibilities when facilities are reopened. This offers social and economic perspective in the upcoming uncertain times.