This is a spin-off from my other recent thread, based on some OT (for that thread) thoughts that were shared.
I want to specifically talk about gas switches in the context of an open circuit dive to a depth requiring a hypoxic gas. I do not want this to be about the specific gases used. Just the process of doing the gas switches.
To make the discussion a little easier (hopefully), let's just say you're using these gases:
10/70 (bottom mix)
21/35 (lean deco)
EAN50 (intermediate deco)
O2 (rich deco)
First stop depth on ascent is 140. Again, just for the sake of discussion.
The question is, what is your protocol for your gas switches and why? Based on the other thread, I will start by throwing out 3 options:
One depth w/Air Breaks:
- Arrive at your depth for your switch.
- If not already breathing back gas, you switch to back gas and clean up the cylinder you were breathing from.
- Switch from back gas to the new deco gas.
Two depths w/Air Breaks:
- Arrive at the last stop before you switch to the next deco gas. E.g. arrive at 30', before switching to O2 at 20'.
- If not already breathing back gas, you switch to back gas and clean up the cylinder you were breathing from.
- Ascend to next stop.
- Switch from back gas to the new deco gas.
One depth, no Air Breaks:
- Arrive at your depth for your switch.
- Switch from the gas you're breathing to whatever new gas you want to breathe.
- Clean up the cylinder you were breathing from. If it was back gas, that just means clipping off the primary 2nd stage.
Note: "no Air Breaks" does not mean that you would not actually do "air breaks" while on O2. It just means you're not switching to your bottom mix in between deco mixes. Once on O2, you could/would still do whatever "air break" procedure you use. My current training would have me breathe O2 for 15 minutes, then switch to back gas for 5 minutes. But, in this particular example, rather than switch to 10/70, I think I would switch to 21/35 for the "air break". Breathing 10/70 at 20' seems inherently risky, since it would only have a ppO2 of 0.16.
In the other thread, it seemed that the SB Communal Wisdom is that one of the first two protocols is the preferred approach. A couple of people said or implied that switching directly from one deco gas to the next is problematic because of the number of regulators that would be in your "golden triangle" (to pull in a sport diving term) - i.e. 4 versus 3. I have tried doing the direct switch, while just on a couple of shallow practice dives, and it didn't seem any harder than switching to back gas, cleaning up, then switching from back gas to the next deco gas. But, that was just a couple of practice dives.
So, which way do you do it? And, what specific things about your process do you think make it superior to the other processes I outlined?
At this point, I am not trying to advocate a specific process. I have tried them all and have a leaning. But, I think I am insufficiently experienced to have a strong feeling on which way is better. I'm curious about the subtle points that make some of you prefer a certain way, since most of you are vastly more experienced with this stuff than I am.
Thanks!
I want to specifically talk about gas switches in the context of an open circuit dive to a depth requiring a hypoxic gas. I do not want this to be about the specific gases used. Just the process of doing the gas switches.
To make the discussion a little easier (hopefully), let's just say you're using these gases:
10/70 (bottom mix)
21/35 (lean deco)
EAN50 (intermediate deco)
O2 (rich deco)
First stop depth on ascent is 140. Again, just for the sake of discussion.
The question is, what is your protocol for your gas switches and why? Based on the other thread, I will start by throwing out 3 options:
One depth w/Air Breaks:
- Arrive at your depth for your switch.
- If not already breathing back gas, you switch to back gas and clean up the cylinder you were breathing from.
- Switch from back gas to the new deco gas.
Two depths w/Air Breaks:
- Arrive at the last stop before you switch to the next deco gas. E.g. arrive at 30', before switching to O2 at 20'.
- If not already breathing back gas, you switch to back gas and clean up the cylinder you were breathing from.
- Ascend to next stop.
- Switch from back gas to the new deco gas.
One depth, no Air Breaks:
- Arrive at your depth for your switch.
- Switch from the gas you're breathing to whatever new gas you want to breathe.
- Clean up the cylinder you were breathing from. If it was back gas, that just means clipping off the primary 2nd stage.
Note: "no Air Breaks" does not mean that you would not actually do "air breaks" while on O2. It just means you're not switching to your bottom mix in between deco mixes. Once on O2, you could/would still do whatever "air break" procedure you use. My current training would have me breathe O2 for 15 minutes, then switch to back gas for 5 minutes. But, in this particular example, rather than switch to 10/70, I think I would switch to 21/35 for the "air break". Breathing 10/70 at 20' seems inherently risky, since it would only have a ppO2 of 0.16.
In the other thread, it seemed that the SB Communal Wisdom is that one of the first two protocols is the preferred approach. A couple of people said or implied that switching directly from one deco gas to the next is problematic because of the number of regulators that would be in your "golden triangle" (to pull in a sport diving term) - i.e. 4 versus 3. I have tried doing the direct switch, while just on a couple of shallow practice dives, and it didn't seem any harder than switching to back gas, cleaning up, then switching from back gas to the next deco gas. But, that was just a couple of practice dives.
So, which way do you do it? And, what specific things about your process do you think make it superior to the other processes I outlined?
At this point, I am not trying to advocate a specific process. I have tried them all and have a leaning. But, I think I am insufficiently experienced to have a strong feeling on which way is better. I'm curious about the subtle points that make some of you prefer a certain way, since most of you are vastly more experienced with this stuff than I am.
Thanks!