Impulse dispersion of aerosols during singing and speaking

Abstract

Group singing events have been linked to several outbreaks of infection during the CoVID-19 pandemic, leading to singing activities being banned in many areas across the globe. This link between singing and infection rates supports the possibility that aerosols are partly responsible for person-to-person infection. In contrast to droplets, the smaller aerosol particles do not fall to the ground within a short distance after being expelled by e.g. a singer. Aerosol particles hover and spread via convection in the environmental air. According to the super-spreading theory, choir singing and loud talking (theater and presentations) during rehearsals or performances may constitute a high risk of infectious virus transmission to large numbers of people. Thus, it is essential to define the safety distances between singers in super-spreading situations. The aim of this study is to investigate the impulse dispersion of aerosols during singing and speaking in comparison to breathing and coughing. Ten professional singers (5 males and 5 females) of the Bavarian Radio Chorus performed 9 tasks including singing a phrase of Beethovens 9th symphony, to the original German text. The inhaled air volume was marked with small aerosol particles produced via a commercial e-cigarette. The expelled aerosol cloud was recorded with three high definition TV cameras from different perspectives. Afterwards, the dimensions and dynamics of the aerosol cloud was measured by segmenting the video footage at every time point. While the median expansion was below 1m, the aerosol cloud was expelled up to 1.4m in the singing direction for individual subjects. Consonants produced larger distances of aerosol expulsion than vowels. The dispersion in the lateral and vertical dimension was less pronounced than the forward direction. After completion of each task, the cloud continued to distribute in the air increasing its dimensions. Consequently, we propose increasing the current recommendations of many governmental councils for choirs or singing at religious services from 1.5m to the front and 1m to the side to a distance between choir singers of 2m to the front and 1.5m to the sides.

From classic to rap: Airborne transmission of different singing styles, with respect to risk assessment of a SARS-CoV-2 infection

“…Therefore, the risk of infection is higher while coughing rather than singing. This is a finding that is also supported by Asadi et al [13] and Echternach et al [6].…”

“…Hence, significant airflows were measured only at 1m, with low measurements at the 1.5m sensor, which decline within or below the usual room air velocity of 0.1 – 0.15 m/s, a finding supported by Becher et al [15], Kähler & Hain [14], Mürbe et al [8, 12] and Echternach et al [6].…”

“…The study by the Ludwig-Maximilians-Universität München and the University of Erlangen [6, 7] investigated different forms of speaking and singing with 10 professional singers of the Bavarian Radio Choir. They made respiratory flows visible by exhaling the smoke of e-cigarettes (not containing nicotine).…”

Airflow and air velocity measurements while playing wind instruments, with respect to risk assessment of a SARS-CoV-2 infection

“…Furthermore, they found out that the escaping air ascends due to natural convection or mixes with the surrounding room air [3]. A study by the Ludwig-Maximilians-Universität München and the University of Erlangen [4], pre-published in July 2020, investigated different forms of speaking and singing with 10 professional singers of the Bavarian Radio Choir. They made respiratory flows visible by exhaling smoke of e-cigarettes (not containing nicotine).…”

CO2 measurements in instrumental and vocal closed room settings as a risk reducing measure for a Coronavirus infection

“…In addition, the near region of infection risk with heavy droplets must also be considered by taking specific distancing for singing and playing instruments into account. [23, 24, 31]…”