If staying indoor is suddenly dangerous

The indoor space matters. We spend an average of 90% of our time there (Allen & Macomber, 2020). At best, how we experience space makes us happy and healthy and ensures that we can perform. But what if that space can suddenly just be life-threatening? And what causes this is also invisible?

Staying indoors was never really associated with acute danger. It was unpleasant at best because it was too cold or too warm, or exhausting due to lack of fresh air. How different is the situation today, with a coronavirus disease (COVID-19) that currently has over 13 million confirmed infections worldwide and over 580,000 deaths? Now that public life is slowly but surely getting going again and companies are preparing for a controlled return of their employees to the office, the discussion about a healthy indoor climate is flaring up. And for a good reason.

Viral transmission

In early 2020, a fairly unexpected and new viral disease broke out in Wuhan, China. The outbreak of this 2019 coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been sweeping the world ever since. The virus that causes COVID-19 is mainly spread through moisture droplets released when an infected person coughs, sneezes or exhales. The droplets are too heavy to remain in the air and quickly drop to the ground or other surfaces. Therefore, to date, the main focus in the fight against COVID-19 is protection against close and direct contact with infected persons and surfaces. This has also led to public health guidelines for social distancing, washing hands, disinfecting surfaces, staying home with complaints and encouraging respiratory protection (mouth masks).

However, recent studies show that SARS-CoV-2 remains viable for several hours in so-called aerosols (van Doremalen et al., 2020). This means that another potential route for viral contamination is via the inhalation of these minuscule moisture droplets into the air (Lewis, 2020; Morawska and Cao, 2020). While the evidence for COVID-19 airborne transmission is currently still incomplete, several studies at least demonstrate a potential risk for air transmission (Chia et al., 2020; Jiang et al., 2019; Liu et al., 2020; Santarpia et al., 2020) in addition to direct contact and droplets. In any case, there is strong evidence for the transmission of viruses by indoor air in general, especially in crowded, poorly ventilated environments (Coleman et al., 2018; Distasio et al., 1990; Knibbs et al., 2012; Li et al., 2005; Moser et al., 1979; Nishiura et al., 2020).

Indoor air measures

To reduce the risk of indoor contamination by air, the advantages of an effective ventilation system are obvious (Eames et al., 2009). Ventilation plays a critical role in removing exhaled virus-contaminated air. Good ventilation replaces polluted air with clean air and thus protects against air transmission. The recirculation of air, on the other hand, is not without danger. It can transfer air pollutants (and therefore infectious viruses) from one room to another connected to the same system. This may increase the risk of airborne infection in those areas. Particulate filters and disinfection, while reducing this risk, may not always provide adequate protection against the entire spectrum of virus particles.

As homestay measures are gradually relaxed, a large proportion of the population can increasingly spend time in public buildings and other shared spaces, such as shops, offices, elevators, meeting rooms, schools, restaurants or public transport. The chance that infected persons share air with others is high. When these areas are not adequately ventilated, non-infected individuals are at risk of contracting a viral infection by inhalation (Morawska et al., 2020). If effective ventilation is not possible or rooms have a closed air treatment system, air purification offers the solution. A previous study showed that air purifiers can significantly reduce exposure to aerosols and droplets (Chen et al., 2020).

Air purification is also a "visible" solution that can promote the well-being and health of employees and customers. The visible distancing and contact measures do not prevent aerosol contamination with COVID-19. Without proper ventilation, hand washing and disinfection of surfaces provide false safety in confined spaces where (small) groups of people come together for a more extended period. Offices, schools and restaurants can cause a second wave of infection before you know it. In addition to air purification, viruses above a specific dose of UV-C radiation are completely inactivated in seconds (García de Abajo et al., 2020; Buonanno et al., 2020). Likewise, sunlight which inactivates about 90% of the number of viruses within a few minutes (Ratnesar-Shumate et al., 2020).



inside with covid


There are a few important recommendations to make the stay in buildings safe and to control the further spread of COVID-19 (see figure above). It concerns a combination of the use of high-tech and low-tech measures. First, we must recognize that contamination with SARS-CoV-2 is possible via air inhalation. Building managers should therefore be aware that appropriate indoor air measures are effective in controlling and reducing infection risks through this route. Increasing ventilation rates or at all ventilation is one of them. Ideally, the spaces are like the houses with a through-room at the front and back that can be opened.

Recirculation of the indoor air must be prevented in order to supply as much fresh (outdoor) air as possible. In addition to existing ventilation or in areas where ventilation is poor, portable air purifiers are required (with mechanical filter systems to trap the micro-droplets in the air). In addition to air purification, treatment of the air with UV-C light prevents the further spread of SARS-CoV-2.


 The most important lesson we learn from the corona crisis is to change the way you think about air. For a long time, the air was top of mind with temperature, humidity and odour among users of the space. It is the air conditions that trigger a certain sensation in humans. Corona is now catalyzing attention for air conditions that do not immediately trigger a reaction, such as CO2, particulate matter, non-odorous chemical components and above all viruses. In the future, the sustainability of buildings will, therefore, have to be more than circularity, energy-neutral and otherwise a footprint. Good for the environment, but bad for people in relation to buildings is no longer possible! Sustainability without a health claim is actually meaningless. Space has never been more popular than it is now. Macomber and Allen (2020) believe that in future buildings with a “good health story” will get sufficient tenants and good rental rates. Buildings with a lagging health story will be left behind.

Dr Herman Kok is lecturing Facility Management at Wageningen University and CEO of Shign. Shign is a scientific research company that focuses on policy issues surrounding housing and services and researches the influence of surroundings on people. He was asked by i-team Solution BV (part of i-team Global) to record his view of the current indoor situation.