OC Gas switch protocols?

[lv2dive]

I don't know anyone doing dives on a regular basis in the 200-300ft range, who worries about ICD until the dives are deeper than 300'+

 

[divezonescuba]

One of my instructors taught method 1. It was because you did not have to have so much going on around your neck at one time among other things. Going from backgas and then to a deco bottle is the same process for both gas switches. We returned to backgas just before the ascent to 20 feet. The only difference is identifying and using a different tank. Even though I took PADI TEC 50 with him, he was also GUE instructor so, I don't know if that had anything to do with it.

 

[PfcAJ]

One of my instructors taught method 1. It was because you did not have to have so much going on around your neck at one time among other things. Going from backgas and then to a deco bottle is the same process for both gas switches. We returned to backgas just before the ascent to 20 feet. The only difference is identifying and using a different tank. Even though I took PADI TEC 50 with him, he was also GUE instructor so, I don't know if that had anything to do with it.

Why return to backgas for the final ascent?

Imo it's smart to stay on your deco gas through the final ascent for offgassing and also because should you move to hypoxic gases you don't want to be breathing those shallower than about 20ft. Even 15% is noticeable (to me at least) if you're doing anything except sitting still.

 

[divezonescuba]

In TEC 50 you can't use hypoxic mixes.

So, its something like backgas to 70 ft, gas switch to 50% at 70 ft., stops at 60, 50, 40 ft, 30 ft, return to backgas just prior to the ascent from 30 ft to 20 ft, and then 100% at 20 ft.

 

[PfcAJ]

In TEC 50 you can't use hypoxic mixes.

So, its something like backgas to 70 ft, gas switch to 50% at 70 ft., stops at 60, 50, 40 ft, 30 ft, return to backgas just prior to the ascent from 30 ft to 20 ft, and then 100% at 20 ft.

Gotcha I read your post wrong. I thought you meant switch from deco gas to backgas for the final ascent. My mistake.

Your procedure you describe is a good one.

 

[stuartv]

@PfcAJ I still have one question unanswered. We plan air breaks independently from deco stops for things like long hangs at 20'. So, why wouldn't you keep air break planning separate from the ascent plan and gas switches for the whole ascent?

In other words, why not explicitly plan air breaks and do them per their own plan, instead of just saying "we'll just do our air breaks any time we do a gas switch"?

Separating them would then mean one could do gas switches directly from deco 1 to deco 2 - and still do air breaks on a thought-out, planned schedule.

Tangentially related question: At what depth (or other relevant dive parameter) would you be likely to carry 3 deco gases. From what I have seen, it seems like most people doing dives even as deep as, say, 240' are still only carrying 2 deco gases. It also seems like 150' is about the depth where people would typically (obviously not always) change from carrying 1 deco gas to carrying 2. But what depth is the cutoff where, below that, you start carrying 3 deco gases?

 

[tbone1004]

@PfcAJ
Tangentially related question: At what depth (or other relevant dive parameter) would you be likely to carry 3 deco gases. From what I have seen, it seems like most people doing dives even as deep as, say, 240' are still only carrying 2 deco gases. It also seems like 150' is about the depth where people would typically (obviously not always) change from carrying 1 deco gas to carrying 2. But what depth is the cutoff where, below that, you start carrying 3 deco gases?

it depends.... OW is very different than cave diving where the gas mixes are often determined by the cave profile. I.e. if you have a big long stretch at 100ft, then a drop down to 200ft, you're probably going to bring some EAN32 for the way in and way out for that stretch at 100ft which could be considered deco gas, and/or stage gas.
In OW, it is going to depend a lot more on what your ascent profile looks like and what benefit you get from those extra deco gases. If you have a low gf-lo with lots of deep stops, you're going to grab that deep deco mix earlier than you would running a high gf-lo without deep stops because you aren't below 70ft for long enough for it to matter

 

[PfcAJ]

@PfcAJ I still have one question unanswered. We plan air breaks independently from deco stops for things like long hangs at 20'. So, why wouldn't you keep air break planning separate from the ascent plan and gas switches for the whole ascent?

In other words, why not explicitly plan air breaks and do them per their own plan, instead of just saying "we'll just do our air breaks any time we do a gas switch"?

Separating them would then mean one could do gas switches directly from deco 1 to deco 2 - and still do air breaks on a thought-out, planned schedule.

Tangentially related question: At what depth (or other relevant dive parameter) would you be likely to carry 3 deco gases. From what I have seen, it seems like most people doing dives even as deep as, say, 240' are still only carrying 2 deco gases. It also seems like 150' is about the depth where people would typically (obviously not always) change from carrying 1 deco gas to carrying 2. But what depth is the cutoff where, below that, you start carrying 3 deco gases?

I don't think I really understand your question. Breaks are part of the plan. I plan to switch to backgas between switches and at interval at 20' during the oxygen stop. I don't count these against my deco time, either. If (for instance) I have a 30min oxygen stop and I take a 5min break in the middle, I still only stay at 20ft for 30min, not 35min.

Results are what matters to me. I think there's no impact to decompression from this in practice.

Regarding adding a 120 bottle, I do it on cave dives that are deeper than 200'.

There's kind of a fuzzy line related to depth and dive duration. Cave dives seem to have longer bottom times and call for a 120 in a way that ocean stuff just doesnt for me. I don't do a ton of deep ocean stuff, and when I do it's nearly always 240 or shallower and just doesn't require a 120.

Adding oxygen usually occurrs around 170 for me.

 

[stuartv]

it depends.... OW is very different than cave diving where the gas mixes are often determined by the cave profile. I.e. if you have a big long stretch at 100ft, then a drop down to 200ft, you're probably going to bring some EAN32 for the way in and way out for that stretch at 100ft which could be considered deco gas, and/or stage gas.
In OW, it is going to depend a lot more on what your ascent profile looks like and what benefit you get from those extra deco gases. If you have a low gf-lo with lots of deep stops, you're going to grab that deep deco mix earlier than you would running a high gf-lo without deep stops because you aren't below 70ft for long enough for it to matter

Right. So, first, I'm not really asking about cave scenarios because I know just enough about cave diving to know that gas planning for that is a whole different ball game than gas planning for deep wreck diving. I suppose I should have said up front that I'm talking about OC and OW. But, I didn't because I didn't really expect gas switch protocols to be any different between the two.

So, assuming OC and OW, at what depth do you start at least thinking about carrying 3 deco gases? I think 150' is about where I would be looking at carrying 2. So, where for 3?

 

[stuartv]

I don't think I really understand your question. Breaks are part of the plan. I plan to switch to backgas between switches and at interval at 20' during the oxygen stop. I don't count these against my deco time, either. If (for instance) I have a 30min oxygen stop and I take a 5min break in the middle, I still only stay at 20ft for 30min, not 35min.

What I'm saying is, your protocol for air breaks is they are done at switches AND they are done at intervals. So, you're mixing your air break protocol into your gas switch protocol, instead of keeping them separate. And you have mixed criteria for doing air breaks.

Why not make them completely separate and simple? Gas switch protocol is "this" and has nothing to do with air breaks. And air breaks are based on "this" (intervals) and are handled separately from gas switches.

That seems like it would really simplify gas switches. And you could still do just as many air breaks as you want. I don't know. I guess if you feel like always doing at least a brief air break every time you do a gas switch is beneficial, then just building it into the gas switch protocol makes sense. But, it sure does seem like a lot of people are doing "basic" dives in the 240 or less range without doing those extra air breaks and they're getting out okay. At least enough that a lot of agencies teach it that way.

Is there any agency that specifically teaches Method 1 (back gas between deco gases)?

Adding oxygen usually occurrs around 170 for me.

What does that mean? You usually add a 3rd deco gas when you plan for deeper than 170'?