Air Flows in Opera

Clusters of contaminations have been identified within rehearsing choirs during the COVID-19 pandemic. In particular, singing and playing wind instruments are known to generate enhanced release of respiratory droplets, which are then transported by the expiratory flows. By tracking the air exhaled by professional opera singers and musicians from the MET Orchestra in New York City, we measure the spatial extent of the various air flows in opera. While loud singing is often associated with fast flows, professional opera singers and musicians are usually exhaling air flows slower than the air jets exhaled by a person breathing at rest. However, we identify a few situations leading to the release of rapid air jets that are able to enhance the transport of pathogenic droplets within an orchestra. Finally, we show how singing with a facemask and covering the bell of a wind instrument provide a strong reduction of the transport of respiratory droplets, in addition to the filtration features of a mask.

Figure 1

Air flows exhaled by an opera singer: (a) ${\mathrm{CO}}_2$ jet breathed out from the nose of the singer during respiration in a performance; the scale bar represents 20 cm; (b) ${\mathrm{CO}}_2$ jet exhaled while the singer speaks the lyrics of the song; (c) ${\mathrm{CO}}_2$ jet exhaled while singing “Casta Diva”; the warm exhaled air rises due to buoyancy; (d) ${\mathrm{CO}}_2$ jet exhaled while singing the “F” from “Tu Fai.” As the mouth is closing for the fricative “F” sound, the air jet reaches a distance of several tens of centimeters within 200 ms. (e) Expiratory flow rates $Q(t)$ measured during respiration at rest ($-60<Q<60\mathrm{L}/\min$, in green), when the singer speaks the lyrics (blue data), and during the performance (red). (f) Trajectories $y(x)$ of the front of the air jet exhaled by the singer during respiration (green diamonds), speaking (blue circles), singing with an open mouth (red squares), and singing the “F” from “Tu Fai” (orange triangles). When flow speeds are lower (red data), the exhaled warm air rises due to buoyancy as seen in panel (c). (g) Tracking of the horizontal front $x(t)$ of the air jet exhaled by the singer during respiration (green diamonds, initial velocity $V_0\approx 1$ m/s), speaking (blue circles, $V_0\approx 0.7$ m/s), and singing (red squares, $V_0\approx 0.35$ m/s). When the mouth is closing (singing the “F” from “Tu Fai”), the air travels faster (orange triangles, $V_0\approx 2-3$ m/s). All rapid jets continue their horizontal propagation at timescales larger than 1 s ($y\propto \sqrt{t}$ as seen on the blue, green, and orange dashed lines) whereas the singing with an open mouth saturates due to the rising buoyant flows (red dashed line).

Figure 2

Air flows emanating from a trombone. (a) Trajectories $y(x)$ of ${\mathrm{CO}}_2$ jets emanating from the bell of a trombone during a performance. The individual trajectories represent different sustained notes of various flow rates ranging from $9\mathrm{L}/\min$ (“High Piano,” yellow stars) to $80\mathrm{L}/\min$ (“Low Fortissimo,” red triangles). All trajectories can be fitted by a parabolic shape (solid lines). The scale bar represents 20 cm. (b) Radius of curvature ${\kappa }^{-1}$ of the jet trajectory as a function of the exhaled flow rate $Q$ during different sustained notes. Here ${\kappa }^{-1}$ is measured by fitting the trajectories by a quadratic equation as shown in panel (a). The flow rate $Q$ is measured as the musician plays through the mouthpiece of the instrument connected to a flow meter by a medical tubing (see Supplementary Figure S4). Data are averaged on a minimum of three measurements. Error bars represent the standard deviations. The solid line represents ${\kappa }^{-1}\propto Q^2$. (c) Horizontal front $x(t)$ of the jets emanating from the bell ($x=0$, $t=0$). All sustained notes lead to air jets of initial speeds 0.1 m/s $\le V_0\le 0.45$ m/s, which is slower than standard breathing exhaled from a human at rest (green diamonds, $V_0\approx 1\text{m/s}$).

Figure 3

Air flows around an oboe. (a) Sequence of images (timestep of 333 ms) of a ${\mathrm{CO}}_2$ jet emanating from the bell of the instrument during the performance. The position of the front of the jet is tracked (blue arrows). The horizontal position $x(t)$ of the jet front is highlighted with the vertical blue dashed lines. The scale bar represents 3 cm. (b) Tracking of the exhaled air from the musician’s mouth during a swift exhalation (see Movie S11). The air front is tracked (red arrow) within an artificial fog illuminated by a laser sheet (green area). The scale bar represents 10 cm. (c) Expiratory flow rates $Q(t)$ measured during a respiration at rest ($-40<Q<40\mathrm{L}/\min$, in green) and during the performance while the musician successively releases a constant small flow rate of air during the notes ($Q\approx 3\mathrm{L}/\min$, in blue) and breathes out air during respirations (in red) made of swift exhalations (up to $100\mathrm{L}/\min$) followed by rapid inhalations ($Q<0$). (d) Tracking of the horizontal front $x(t)$ of the air jet from the bell during the performance (blue data, initial velocity 0.07 m/s $\le V_0\le 0.3$ m/s), from the mouth during a standard respiration (green diamonds, $V_0\approx 1$ m/s), while blowing (orange squares, $V_0\approx 2$ m/s), or during a swift expiration during the performance (red squares, $V_0\approx 3$ m/s). Solid symbols are measured during a musical performance and open symbols on a human subject at rest. Dashed lines are guides for the eyes based on linear fits of the data. Here “LF,” “HF,” “LP,” and “HP” denote “low fortissimo,” “high fortissimo,” “low piano,” and “high piano,” respectively.

Figure 4

Mitigation of musical air flows. (a) Trajectories $y(x)$ of ${\mathrm{CO}}_2$ jets emanating from the bell of a trumpet while playing a “low fortissimo.” The exhaled air is rising and limited in terms of horizontal propagation when the bell is covered with a tissue (filled symbols) compared to the trajectories from an uncovered bell (open symbols). The scale bar represents 20 cm. (b) Trajectories $y(x)$ of ${\mathrm{CO}}_2$ jets emanating from the bell of a trombone while playing a “low fortissimo.” The exhaled air is rising and limited in terms of horizontal propagation when the bell is covered with a tissue (filled squares). The scale bar represents 20 cm. (c) Horizontal position $x(t)$ of the front of the ${\mathrm{CO}}_2$ jet emanating from the bell of a wind instrument. Both trombone (blue squares) and trumpet (red circles) show the same behavior: the spatial extent of the jet is limited by the use of a cover (filled symbols). (d) The ${\mathrm{CO}}_2$ exhaled by a soprano singing “Brunhilde’s Immolation” forms a turbulent jet (red arrow) reaching several tens of centimeters within a second. The scale bar represents 10 cm. (e) The ${\mathrm{CO}}_2$ exhaled by an opera singer wearing a face mask during a performance only propagates horizontally over few centimeters (blue dashed line). Leaks of ${\mathrm{CO}}_2$ from the edge of the mask induce a rising flow (green arrow). The scale bar represents 10 cm. (f) Horizontal position $x(t)$ of the front of the ${\mathrm{CO}}_2$ jet during a performance. The face mask restricts the horizontal propagation of the jet to a few centimeters (blue filled circles). The saturation seen for the blue data (circles) corresponds to the rise of the buoyant jet.