Advanced Gas Switching

[stuartv]

2 day class for hypoxic dives?
No offense and it’s just my opinion but maybe you should just do the class before asking about it on an internet dive forum as you might get different inconsistent opinions from internet divers who aren’t qualified in that area.
Good luck and enjoy

3 day class. More, if I don't get it right...

I like to get a variety of opinions before class. It gives me more context for understanding what my instructor is teaching me and helps prepare me with better questions than I would probably come up with all on my own.

 

[jale]

In this context, we're talking about being on back gas in between being on 2 different deco gases. If your buddy suddenly needs gas right then, why wouldn't you give them one of the 2 deco gases you are currently working with (instead of the bottom mix reg in your mouth)? In which case, being on your necklaced alternate right then seems like it would be okay?

Because when you are in this situation your priority is to give a breathable gas to the one who needs it. You can make adjustments after but at least you are sure that the breathable gas is the one in your mouth and the one you need to give to your buddy.

 

[jale]

Even the ISE protocol (and GUE, I think) starts with a switch to a deco cylinder that is one of two that are slung on your left. I haven't seen anybody teaching that you always only have 1 deco cylinder on your left. So, I don't think your comment about never having a chance to mix up the order of the gases is really valid.

On the other hand, everyone teaches some process that is designed so that you select the cylinder you're switching to and confirm it is correct as well as get your buddy to confirm it is correct, and then switch to it in a way that ensures you do actually switch to the chosen cylinder. With that process in place, having 2 cylinders slung on the left for all gas switches, versus just the first gas switch, does not seem like a safety hazard that needs additional mitigation. Does it?

I understand your point about not being the number of steps, but making sure the task is done correctly. But, I also think that the number of steps can have a direct correlation to the ability to accomplish the task correctly. Every step is an opportunity to make a mistake. Twice as many steps is twice as many chances for error.

I have always heard/read that the biggest risk for an OC tech diver is switching to the wrong gas. So far, in all the protocols I have identified, the first gas switch is to one of 2 cylinders slung on the left. So, they all have equal risk for that first gas switch.

After that first gas switch, the shorter protocol I outlined seems like it does at least as much to mitigate the risk of switching to the wrong gas as any other option. When you switch, there is only one reg on your left side to switch to. As long as you have managed your cylinders correctly (which is true for all the processes), you can't really switch to the wrong gas.

If you are using a protocol where you always have 2 cylinders slung on your left, then switching to back gas in between deco gases results in MORE risk, because when you go to switch from back gas to your deco gas, there are 2 regs slung on your left to choose from. All the protocols have this risk at the first gas switch. But, only some (one?) of the protocols maintains this risk through each and every gas switch.

You misread me or better to say I didn't say it correctly. I meant "to have the deco tank (you are about to use) in the proper position".
Of course checking hoses, mod, buddy validating,...need to be done.
The number of steps is not really an indication of level of complexity as you can break in a thousand steps a simple action and divide a complex action in a few steps. It is about perspective.
Yes switching to the wrong gas is the biggest risk...have you also thought about how you are going to do down as your backgas is not breathable on surface?
Good to have all these chalenges to think about and in fact beside this or that protocol, the most important thing is to be able to have this kind of questions. Whatever you do, you have the mindset of doing this kind of dives

 

[ChuckP]

I just don't get the concept of back gas between deco gasses - I was taught to get off the bottom and deco as efficiently as possible. The frizzle fracking around of bottle rotation, multiple reg changes - to me it all seems uneeded task loading.....

I was taught LL RR
We prepped our 1st deco gas (confirmed) while on the bottom, gas on, reg pulled out and draped over neck
Gas change on the fly at safe depth on the way to the first stop, clipping secondary off
Computer change before first stop if you have time
First stops are generally short so I spend time at each stop getting settled in checking computers checking buddies
Once settled in and squared away, I'll turn on and prep my last gas (confirm) by dangling that reg over my neck
Switch from 1st deco to 2nd deco, make the change on my computer
Clean up first deco bottle

I would never think about rotating bottles, I would never think about switching to anything but the next gas I should be breathing - this method is clean and simple, allows me no extra tasks and really allows me more time to evaluate my buddy, surroundings and computer. The only "dirty" part is the few minutes my first deco reg isn't stored but dangling - I'm in the open ocean, not a cave where it could be dragging the floor.

Adding a third bottle into the program, the deco gas would be close to my chest or on top, the travel gas would be on the bottom. The only possible change I see to my taught method would be butt clipping the travel gas at some point to make it easier to stow the first deco reg when that gas is completed. That's the only bottle movement I see needing - it's clean, neat and safe????

Is there not any concern about ICD when switching from backgas to any deco gas?

The idea that your long hose is trapped while carrying a bottle on your right is really a lost argument, when you carry three bottles, ones on your right.... we teach arm locked air share in OW, there's no reason that two experienced Tec divers can't get a situation under control and slip that long hose under the right side cylinder.

 

[stuartv]

For reference, this is the ISE video on how to do gas switches while carrying 3 deco bottles:


@ChuckP: Until I got in the water with 3 bottles, I did not fully appreciate the PITA that it is. I tried it with 1 80 on the left and 1 80 + 1 40 on the right. It was a pain. I think 2 80s on the left (which I have done before) and 1 40 on a leash will be a lot easier.

Also, with one or 2 bottles on the right, I think the long hose is an issue. But, I think the issue is compounded when carrying a battery canister on the right that has a light cord and a heat controller cord coming off of it. Having all 3 of those cords/hoses on the right to manage is okay when there is no deco cylinder getting in the way. But, a slung cylinder on the right plus a long hose and 2 other cords, all on the right (and I like to carry my primary reel/SMB on my right waist D-ring, too)... well, at this moment I feel like that is just too much. Too busy. I think having 2 on the left and one on a leash addresses all that and makes it all very manageable.

At least, that's my opinion now, when I have not actually tried the bottle on a leash part....

Also, I think your point about the long hose and being able to get a situation under control and then sort out the long hose really goes out the window if you think about divers in anything other than open water. If they're inside a wreck or in a cave, that doesn't necessarily work. And even in open water, if one diver suddenly needs his buddy's long hose, then stuff has really gone awry. I mean, that should NEVER actually happen, right? Even if a diver has a tank valve O-ring blow out, they should shut down their isolator and still have one tank to breathe (or be in sidemount and have one tank to breathe). So, if they diver really does need his buddy's long hose, then they probably really do not want to spend a minute or two extra dealing with getting the long hose out from under a clipped off tank or whatever. At that point, it is time to start exiting/ascending, post-haste. In other words, I think a system that does not yield that extra requirement/work is really preferable. I have only carried a deco cylinder on the right when diving CCR (where I don't have a long hose to worry about), or last weekend, when practicing for my upcoming class (where I decided I really don't like it). I think GUE, ISE, and all the tech instructors I have personally worked with in the past, have it right on that. For OC diving, carry all the deco on the left (or on a leash to the left side).

 

[tbone1004]

Even the ISE protocol (and GUE, I think) starts with a switch to a deco cylinder that is one of two that are slung on your left. I haven't seen anybody teaching that you always only have 1 deco cylinder on your left. So, I don't think your comment about never having a chance to mix up the order of the gases is really valid.

On the other hand, everyone teaches some process that is designed so that you select the cylinder you're switching to and confirm it is correct as well as get your buddy to confirm it is correct, and then switch to it in a way that ensures you do actually switch to the chosen cylinder. With that process in place, having 2 cylinders slung on the left for all gas switches, versus just the first gas switch, does not seem like a safety hazard that needs additional mitigation. Does it?

I understand your point about not being the number of steps, but making sure the task is done correctly. But, I also think that the number of steps can have a direct correlation to the ability to accomplish the task correctly. Every step is an opportunity to make a mistake. Twice as many steps is twice as many chances for error.

I have always heard/read that the biggest risk for an OC tech diver is switching to the wrong gas. So far, in all the protocols I have identified, the first gas switch is to one of 2 cylinders slung on the left. So, they all have equal risk for that first gas switch.

After that first gas switch, the shorter protocol I outlined seems like it does at least as much to mitigate the risk of switching to the wrong gas as any other option. When you switch, there is only one reg on your left side to switch to. As long as you have managed your cylinders correctly (which is true for all the processes), you can't really switch to the wrong gas.

If you are using a protocol where you always have 2 cylinders slung on your left, then switching to back gas in between deco gases results in MORE risk, because when you go to switch from back gas to your deco gas, there are 2 regs slung on your left to choose from. All the protocols have this risk at the first gas switch. But, only some (one?) of the protocols maintains this risk through each and every gas switch.

the chance to mix gases based on the bottles "loaded" is different than having multiple regulators deployed though. If you don't fully stow the regulator before you switch, then chasing the hose back is more complicated, thus introducing higher risk of a bad gas switch. For me though, it's just less clutter overall and I'm all about less clutter.

@ChuckP switching to backgas to stow the previously used bottle isn't going to affect your deco time and efficiency. When we do "air breaks" we don't switch off of the deco mix on the computers. I don't know if there has been any actual research studies done on air breaks vs. not, but the general understanding says that the breaks help to open everything back up as O2 is a vasoconstrictor and that actually helps improve deco efficiency.

ICD concerns are valid if you're on that bottle for a long time, but you're not. If you watch the video, which is admittedly from one of the most competent divers in the world. That said, let's look at the time stamps
3:51-start
3:58-backgas in
4:58-move up to 6m
5:25-start switch
5:53-O2 in
Total time on backgas is 2 minutes, 30 seconds of which was moving up to the next stop. If you double the time to stow, a "new diver" would be on backgas for 3 minutes and that really is inconsequential in the grand scheme of things, certainly not enough IMO to cause worry about ICD since you aren't intaking that much He.

@stuartv you should still have a long hose when tech diving a CCR IMO, but I don't know how you have yours rigged. With a bmcl unit like the Revo it's not difficult to deal with a long hose and I much prefer having it when in any overhead

 

[JonG1]

I'm on Achim's Patreon site, pretty sure when we discussed the 3 stage video, he did confirm that the o2 bottle wasn't full, hence why it behaves so well.

I've tried 3 bottles, with 2 on left 1 on a leash and I just can't get on with it, if the mixes are nitrox ie not floaty helium.

Achim did also advise that there are buoyancy characteristic differences between old/new bottles and Europe/US so that may also excuse my poor efforts with a leash!

 

[Wstern5]

Question for anyone who actually does OC dives using mix with 10% or less O2 for bottom mix and 100% O2 as one of the deco gases-

Is bottom mix back gas or in a stage? If bottom mix is back gas do you breath this at 20ft while preforming the switch to 100%?

I’m nowhere near this level but genuinely interested and curious. Thanks.

 

[ChuckP]

I was just taught a much different approach to deco than what's shown with those gas changes - and I do not want to get into what's right or wrong. That video is obviously a fantastic smooth method of gas changes.

The whole concept of carrying three tanks and making the gas changes effectively is something - I never thought about can lights and suit heaters as I don't dive that way. Lots of variables....

 

[ChuckP]

Question for anyone who actually does OC dives using mix with 10% or less O2 for bottom mix and 100% O2 as one of the deco gases-

Is bottom mix back gas or in a stage? If bottom mix is back gas do you breath this at 20ft while preforming the switch to 100%?

I’m nowhere near this level but genuinely interested and curious. Thanks.

I have the same question too - the video is a little different than I would expect as in it appears the stage tank is bottom mix and the doubles are travel gas - that's not what I would choose for a wreck dive. I'd think bottom mix in doubles and travel gas in a stage and I would not breathe my bottom gas during that gas change but I too defer to the folks doing that diving.