ABSTRACT
In light of the COVID-19 pandemic, the importance of protective measures against infectious aerosols has drastically increased, as the transmission of diseases via airborne particles is impacting many aspects of everyday life. The protective measures against such infections are determinant in the operation of schools and kindergartens, hygiene in hospitals and medical facilities, in offices, administrative and production facilities, hotels, and the event industry, among others. To test these protective measures, suitable test aerosols and processes are needed. These aerosols ought to be similar to aerosols exhaled by humans as those carry the pathogens and thus need to be removed from the air or inactivated. The exhaled aerosols of several healthy test subjects were characterized by their particle concentration and size distribution. In previous studies, it was found that exhaled particle concentration varies significantly from subject to subject and most of the particles can be found in the submicron size range. Aerosols technically generated through nebulization were emitted by the generators in particle concentrations several orders of magnitude higher than those exhaled by humans, independent of the aerosol generation method and nebulized fluid. The particle size distribution generated by the two nebulizers used, however, was quite similar to the measured size distributions of the human aerosols, with most of the particles below 1 µm in size. Consequently, the used aerosol generators are not suitable to mimic single individuals as active aerosol sources, but rather to provide a sufficient amount of aerosol similar to human aerosols in size distribution, which can be used in the testing of air purification technologies.
Subject(s)
COVID-19 , Pandemics , Humans , Particle Size , Respiratory Aerosols and Droplets , COVID-19/prevention & control , Nebulizers and VaporizersABSTRACT
This paper focuses on simultaneous, time- and space-resolved measurements of particle size distributions in three different closed indoor environments (small office room, elementary-school classroom, and seminar room) applying mobile air filters in four scenarios (decay curves, filtration while people are present, a temporal strong point source, impact of filter orientation & cross-flow ventilation). The experiments reveal, that mobile indoor air filters, equipped with high-performance filter media (HEPA - quality), remove particles in the investigated rooms in relevant submicron size classes (x < 1 μm) efficiently and uniformly over time. For the description of the local decrease in particle concentration a simple mathematical model based on a transient continuous stirred tank reactor was applied. The local decay curves obtained in the different room-types were compared to simulated ones assuming ideal mixing of the indoor air. The real-room scenarios show a slower particle decay than the predicted ones assuming ideal mixing of the indoor air. The experiments reported in this contribution demonstrate, that indoor air filters, operated with a filtration rate of 3.5 h−1 and positioned correctly, are capable to lower the particle concentration in all relevant size classes in real-world closed indoor environments slowly over time (e.g. a reduction in particle concentration of 50% after 30 min in a classroom w/o particle sources). In the investigated set-ups, at filtration rates above 9 h−1, the filters’ performance is close to cross-flow window-ventilation. The experiments reveal, that mobile air filters cannot avoid close distance transmission of submicron aerosols from one person to another. Therefore, they do not replace any of the well-known methods to avoid aerosol-driven infection (like wearing an efficient face mask correctly, limiting the number of people and time of stay in closed indoor environments, frequent ventilation). Mobile air filter devices may represent an additional component in an entire prevention strategy, especially when rooms cannot be ventilated regularly, efficiently or the constellation of people changes frequently (e.g. waiting areas).
ABSTRACT
Aerosols are currently seen as one of the main transmission routes for SARS-CoV-2, but a comprehensive understanding of the processes and appropriate action/adaptation of protection concepts requires the exchange of information across interdisciplinary boundaries. Against this background, the Baden-Württemberg state government launched in October 2020 a multidisciplinary "Expert Group Aerosols" comprising engineers, natural scientists and medical professionals. In its statement, the group has compiled the current state of knowledge in all relevant disciplines in the context of airborne SARS-CoV-2 infection. In addition to the well-known hygiene and social distancing rules, the importance of the correct use of effective masks is emphasized. Furthermore, the necessity for dynamic and correct ventilation is pointed out and illustrated with ventilation intervals and periods for different scenarios as examples. The effectiveness of stationary or mobile cabin air filters as an important component in the protection concept is discussed. The first opinion of the expert group makes it clear that the existing hygiene and social distancing rules offer the best possible protection against SARS-CoV-2 infection only when correctly applied in combination.
Subject(s)
COVID-19 , SARS-CoV-2 , Aerosols , Germany , Humans , MasksABSTRACT
During the current COVID-19 pandemic, filtering-face-pieces and their certification get great attention from society. The determination of total filtration efficiency according to DIN EN 149/DIN EN 13274-7 (European standard for FFP1, FFP2 and FFP3 masks) has several drawbacks, making reliable certification of filtering-face-pieces difficult. This note analyses two of these drawbacks, namely the ambiguous definition of the total filtration efficiency and the broad range of the test aerosol particle size distributions allowed. The range of total filtration efficiency values for individual masks resulting from rather wide or missing specifications in the standard is calculated using size resolved penetration curves of 11 FFP2 masks from literature and 11 FFP2 masks from own measurements. From the 22 FFP2 masks regarded in this analysis, two would either pass or fail certification in dependence of the applied definition of the total filtration efficiency and the test aerosol applied.