swapping 1st stages while at depth; emergency only

[Cave Diver]

Consequently, you absolutely *need* to manage the gas so that the gas remaining in either tank is enough to get you out of the cave, and that includes the deco.

If you can't do that then you have seriously &%$*ed up the gas planning.

Totally agree. Unfortunately, I think a lot of people's idea of gas planning is "turn when we hit thirds" and I don't think that's always conservative enough.

 

[String]

Thirds falls apart once you start taking longer to get out than you do going in. Ie anytime you start running up deco.