Table 1.

Peak flow rates or flow velocities in human breathing and speaking reported in the literature

	Breathing	Speaking
Peak flow rates	0.7 L/s (22)	$0.3-1.6$ L/s
Or velocities	0.5 m/s (23)	(22, 24–28)
Peak Reynolds numbers	$7\times 10^2$ to $3\times 10^3$	$1\times 10^3$ to $7\times 10^3$

We assume a typical length scale for the orifice or mouth of diameter $2a=2\hspace{0.17em}\text{cm}$ for calculating the Reynolds numbers, $\text{Re}=2ua/\nu$, where $u$ is the average speed at the mouth or orifice exit and the kinematic viscosity of air $\nu \approx 1.5\times 10^{-5}$ m²/s.