Dunker T, Tschudi J, O'Farrell M. Measurements of droplets from singing and some other activities. [Project memo]. (2020-09-07). https://www.sintef.no/contentassets/c443f8aad9324279a2c8734674dde6e9/memo_measurement_of_droplets_signed.pdf/

Dies ist ein „Project memo“ zu ersten Ergebnissen einer Studie der SINTEF, einer unabhängigen Forschungsorganisation in Norwegen, von der hier lediglich kleine, erste Ergebnisse präsentiert werden.

We present initial results from measurements of exhaled droplets by two female singers during singing, speaking, laughing, and recitation of poetry. We also conducted measurements with a flute, a clarinet, a tuba, and only the tuba's mouthpiece. This small project is motivated by the current distancing restrictions for choirs, musicians, and actors. To be able to image and track droplets, we have developed and built a portable measurement set-up. We have detected droplets with diameters of approximately 50 μm and above. We found that for a single subject, the largest amount of droplets are produced during singing, but that laughing can produce a comparable number of droplets. Speaking and recitation of poetry do not produce as many droplets. We repeated exercises at varying distances and found that the number of detected droplets decreased rapidly with increasing distance. However, the relative height difference between people, e.g. in a stage setting, must be considered when determining how far a droplet of a given size and velocity can reach. Most droplets we detected follow a ballistic trajectory, and hit the ground after a distance of approximately 1 m. In case of the musical instruments, we did not detect droplets exiting a tuba and only few single droplets from a flute and a clarinet. A clarinet usually points downwards, such that droplets follow a downward trajectory and hit the ground after a short distance. The situation was different when the tubist used only the mouthpiece (that is, detached from the tuba) during warm-up while partially blocking the opening with a finger: in this case, many droplets were ejected from the mouthpiece. These followed ballistic trajectories at different speeds, with some droplets exiting the measurement volume. Two important limitations of this study are that (i) the sample size is very small, such that a statistical analysis is beyond our scope; and (ii) that we cannot draw conclusions about a possible risk of infection with COVID-19 when performing any of the said activities.

An mehreren Stellen in der Veröffentlichung wird auf Limitierungen dieser Studie hingewiesen.

Auszug aus dem Disclaimer:

The purpose of this small project was building a set-up and demonstrating that the generation of droplets from a limited number of subjects, during different activities, could be measured and compared. The set-up was designed and built so that it could be used in different scenarios. However, for these initial tests, all measurements were performed in an ordinary room at SINTEF.

Due to limited time and budget, measurements were performed on only two subjects. We must assume that different people generate different amounts of droplets. Therefore, a complete study would require a larger number of subjects, measured in different situations/environments. Our observations must, therefore, be treated as preliminary, and the conclusions are subject to change upon expansion of the project - for example, with a more in-depth analysis of a larger, more statistically representative number of measurements.

Auszug aus der Einleitung, Abschnitt 1.1 Scope and limitations of this initial study:

From the measurements and results presented here, it is not possible to draw conclusions about a risk of infection with COVID-19. This is beyond the scope of this study.