How to switch with 2 deco bottles?

[RGU]

It occurs to me that many of the dives over the years have required keeping the 50% around for "air" breaks.

[kitsap_diver]

I'll add my voice to the ones who have already stated that they go back to the BG reg between the two bottles. It's not so much about the air break as it is the simplicty. There are a few other things I would mention considering in this whole equation though. Such as where do you position the bottles? I have all my bottles on my left side. I try to think ahead with regard to bottom stages, 02 and any other deco gas and consider where I'll be placing them so that I can stow the hose for the bottle I'm coming off of cleanly and properly be able to verify the labeling on the bottle that I'm switching to. For instance a more common scenario for me would be returning to my 02 bottle at the end of a dive and breathing from a stage. I would come off the stage before I picked up the 02 bottle to ease in stowing the hose and then pick up the bottle (now on BG) and stow it outboard of the stage so that when I get up to 20 feet I can easily read the labeling on the 02 bottle and verify my gas before switching on to 02.

With just two gasses it doesn't make sense to be moving bottles around too much if you're not in a cave where you're dropping them on the line. On a recent OW dive I used 2 deco gasses and a bottom stage. I had the deep deco gas inboard, and the stage outboard in front of me. I had the 02 bottle clipped on a leash. When I came off the stage I was able to stow it easily. When I began my ascent I used the time at a deep stop (before my first gas switch) to clean up my bottles a little bit and I took my leash out clipped the empty stage to the leash and took the 02 bottle off the leash. I clipped the leash off and actually clipped the 02 bottle inboard of the deep deco gas. When I got up to the deep deco gas switch I was able to easily read the bottle deploy the hose and switch off back gas. When I came up to my 02 stop I switched off the deep deco gas at 30' was easily able to stow the hose and get onto O2 at the end of the dive. I surfaced with the O2 reg still in my mouth.

I could see someone making an argument that another way to do the sequence above would be to wait until after I was on the deep deco gas to rearrange the bottles. I could still verify the deep deco gas with the stage outboard, and it keeps the O2 completely out of the picture at that first gas switch. I think that's a valid argument.

Again with only two bottles it makes sense that you wouldn't want to have to rotate bottles if you didn't have to so thinking about the arrangement ahead of time to make sense for your dive is important. I know a lot of instructors teach a rule of some sort, rich on one side, and lean on the other or rich inside of lead or vice versa. It's important that the diver understand the "why" behind those rules, and that they are able to meet all the real necessary and important aspects of the gas switch (verifying the bottle you're breathing from, verifying the regulator you're about to breath from is connected to the bottle you've verified, stowing unnecessary hoses, etc)

[Maxpcf]

Switch to BG, stow the deep deco reg, switch to O2.

Cleaner, minimizes risk of switching to incorrect mix, minimizes clutter/complications.

[tbone1004]

Out of curiosity - why leash the 3rd bottle to the hip d-ring and not butt d-ring?

not scalable when you get more bottles, and I find the leash easier than the butt d-ring. All "dead" bottles go on the leash which makes surfacing a lot easier.

[lord1234]

You guys haven't picked it up yet. This is a guy who is trying to use the internet to train him. He has repeatedly come in here asking questions that should be answered by an *INSTRUCTOR*. Check his post history.

[tbone1004]

You guys haven't picked it up yet. This is a guy who is trying to use the internet to train him. He has repeatedly come in here asking questions that should be answered by an *INSTRUCTOR*. Check his post history.

yeah, but this is one of the only interesting discussions we have had in a long time on this forum, so whether he's trying to use the forums to train himself or not, it has us discussing useful things

[rddvet]

You guys haven't picked it up yet. This is a guy who is trying to use the internet to train him. He has repeatedly come in here asking questions that should be answered by an *INSTRUCTOR*. Check his post history.

Idk why people get so upset and just tell people to call their instructor. People like to have a knowledge base before they take a class (be it good or bad) and the internet is one of the places to do it. I had a ton of mentors that helped guide me before I took certain classes. One instructor actually even set me up with the mentor as he knew he?s teach me how the instructor wanted.
If the guy takes advice here then konks himself so be it. Its not going to fall back on you.
I just wish the immediate shutting these things down with call your instructor would stop. I even think the op said that was his goal. But I?m too lazy to go back to the top to confirm.


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[mrki]

As far as minimizing risks goes - you deploy your O2 reg, show your buddy the tank, follow the full length of the hose with your hand to confirm reg/tank. You know you have the O2 reg in your left hand. No matter which reg (backgas or 50%) you take out of your mouth with your right hand, you know which one you'll put in your mouth with the left. I don't see how there's more risk of switching to incorrect mix if it's the 50% that you've just pulled out of your mouth.

[Randall]

I prefer to switch directly from the deep deco gas to the next deco gas. If you follow your verification procedures correctly it would be very difficult to switch to the wrong bottle. Your BG long hose should be clipped off, your secondary BG reg is on your necklace, richer O2 mix is in your hand current leaner O2 mix is in your mouth. You switch from leaner to richer then stow the leaner. Your hoses should not get tangled up, even if they did it would not be a big deal to untangle the two deco hoses. Personally i feel if you switch to back gas you would be adding a bit of risk, as it would be possible for you to not have your next deco gas in you hand at all times after the verification with your buddy. To do it safely you would have to reach your next stop depth, switch to BG, stow the lean mix, verify the rich mix, deploy the rich mix, then stow the BG reg. This seems more complicated to me than just verifying the rich mix, deploy, and stow the lean mix. Either way if done properly is safe, i think it mostly comes down to how you were trained and what you are most comfortable doing. Just my two cents.

[Jim Wyatt]

One issue that has been described to me by hyperbaric physicians is the nitrogen "slam" when going from a low N2 mix to a higher N2 mix, then back to a low N2 mix.

Swapping from BG EAN32 to EAN50 and then to BG again - has PN2's of: 1.29 to .95 then back to 1.29 before switching to PN2 0.