[jahnu]

> divers are trained to breath out during an emergency swimming ascent

To add a little more detail to this. You should ascend as slow as you can given the emergency situation but gently hum out your air rather than breath out. This slows it so you avoid the panic of empty lungs when not near the surface and also allows air to escape if it’s expanding quicker than you are humming :)

[hunter2_]

Instinctually (well, once you overcome the most naive instinct of holding your breath) one might think they need to exhale fast enough that the expansion of volume in the lungs doesn't outpace the rate of exhalation, but in reality even the slightest bit of intended exhalation will keep the airway open enough to prevent lung issues, right?

[orestis]

Yes, the point is to keep the airways open, but that’s hard to demonstrate hence the suggestion to “make a stream of small bubbles as you ascend”

[jahnu]

That was what I was taught at least when I learned recreational diving.