It occurs to me there have been several recent accidents which involved using a gas mixture at an inappropriate time/depth. In theory, the decompression gases are the most risky gas you're dealing with (assuming bottom mix is normoxic or greater ). Considering these factors, it is my opinion that I want to see those bottles during a NOTOX [gas] switch. Placing highly enriched gases in a position that is out of view removes my ability to confirm the gas prior to sucking it down, and worse I'm now relying on a buddy almost completely for a gas swich. These ideas do not align with my approach to technical diving. Accordingly, I would encourage you to seek a qualified instructor and discourage you from assembling your kit in this manner.
Sidemount with back mounted deco gas?
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victorzamora
Contributor
That would make me start diving doubles, that's for sure!!Good points about not being able to identify the tank/gas. Although with one deco gas it's not that hard if you use a distinctive regulator and back it up with a distinctive hose that you can identify by touch (ex- The only braided hose.) Also pretty easy to notice if a reg clipped off in front of you somewhere is freeflowing. Nonetheless, I understand the safety concerns.
Yeah a couple a dozen people died doing that before it finally sunk in that marked regs don't actually verify the gas. (regs get put on the wrong tank or you put the reg on an O2 tank instead of a EAN50% tank or its an air tank instead of an O2 tank or various other permutations on breathing the wrong gas through the "right" regulator.
There are a whole lot of things that went wrong there....
Will your brilliant idea work? Probably, but only until you forget about putting the reg with your braided oxygen flavored mouthpiece on the miss labeled deco bottle. It seems like you've already made up your mind about doing this despite the replies of several very knowledgeable and experienced divers. I just hope that your luck hold out and we don't have an "I told you so" moment in the passings forum.
Really? You can read my mind?
Since you can read my mind.... Why do you think I asked for opinions if my mind was made up?
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It doesn't seem to me that you have made up your mind. You had an idea pop into your head, thought it would make an interesting discussion, and it did. Keep in mind we are discussing this on an internet forum, and not during a pre-dive briefing 
I have heard the argument before that you shouldn't rely on color coded regs to identify gas because you might accidentally put it on the wrong tank. I never really cared for this argument as I find it a bit of a stretch to say that a diver can't be trusted to put the right regulator on the right tank, but can be trusted to put the right label on the right tank. Even though my regulators all look very similar, they still always end up on the same tanks.
However, I do think that a gas switching procedure should involve having your buddies read the MOD markings on the tank and verify that you have the right reg. It would likely be difficult for your buddies to remember which regs go with which tanks for your configuration, and reading the MOD label is just easier.
As for backmounting the deco tank, I do see a few issues. For one, how to you store the hose? I guess the reg could be clipped off on the d-ring, and be a short enough hose like the bungied backup, but then what if you had to buddy breathe with a teammate due to lost deco gas?
I understand that there is an advantage to getting the tank out of the way, but not sure this advantage outweighs the potential for problems.
I have heard the argument before that you shouldn't rely on color coded regs to identify gas because you might accidentally put it on the wrong tank. I never really cared for this argument as I find it a bit of a stretch to say that a diver can't be trusted to put the right regulator on the right tank, but can be trusted to put the right label on the right tank. Even though my regulators all look very similar, they still always end up on the same tanks.
However, I do think that a gas switching procedure should involve having your buddies read the MOD markings on the tank and verify that you have the right reg. It would likely be difficult for your buddies to remember which regs go with which tanks for your configuration, and reading the MOD label is just easier.
As for backmounting the deco tank, I do see a few issues. For one, how to you store the hose? I guess the reg could be clipped off on the d-ring, and be a short enough hose like the bungied backup, but then what if you had to buddy breathe with a teammate due to lost deco gas?
I understand that there is an advantage to getting the tank out of the way, but not sure this advantage outweighs the potential for problems.
It doesn't seem to me that you have made up your mind. You had an idea pop into your head, thought it would make an interesting discussion, and it did. Keep in mind we are discussing this on an internet forum, and not during a pre-dive briefing
I have heard the argument before that you shouldn't rely on color coded regs to identify gas because you might accidentally put it on the wrong tank. I never really cared for this argument as I find it a bit of a stretch to say that a diver can't be trusted to put the right regulator on the right tank, but can be trusted to put the right label on the right tank. Even though my regulators all look very similar, they still always end up on the same tanks.
However, I do think that a gas switching procedure should involve having your buddies read the MOD markings on the tank and verify that you have the right reg. It would likely be difficult for your buddies to remember which regs go with which tanks for your configuration, and reading the MOD label is just easier.
As for backmounting the deco tank, I do see a few issues. For one, how to you store the hose? I guess the reg could be clipped off on the d-ring, and be a short enough hose like the bungied backup, but then what if you had to buddy breathe with a teammate due to lost deco gas?
I understand that there is an advantage to getting the tank out of the way, but not sure this advantage outweighs the potential for problems.
Well said. 100% agreement. Whew!
I've done it once. I had two tanks of air, one on each side, and a tank of 33% on my back, which was the deco gas for the dive. My dive rite xt regs were on my air tanks and my scubapro mk17/a700 on my 33. They are distinctively different in every way, including the molded mouthpiece on the a700. The 33% tank was clearly marked and my buddy could easily see it and the reg coming from it to verify the gas switch.
Why? I didn't have a SM rig or another set of tank rigging with me. I used my bp/w and 40lb single tank wing. 2lb of lead on the band of each air tank. We did a shake-down dive to 100' (the day before) with this configuration prior to the technical dive. We had lift bag, smb, spools, etc should we have a wing fail, but I can easily swim that rig up without them - yes we checked that too.
-I had enough air to do the dive & enough to give air to my buddy if he had an issue without needing the 33% on my back.
-When we did our gas switch we both signaled and checked each-other as normal.
Now, I don't think it was the smartest dive in the world, but I don't think it was hugely dangerous either. It's not like we used 50 or 100.
Later in the week, we did an extended range no deco dive with three AL80 full of 33% set up the same way. I breathed down the tank on my back first, leaving plenty to donate. Getting to spend time on the far side of Bonaire's double reef (off Plaza) was amazing and well worth the 97min swim with all those tanks!
Why? I didn't have a SM rig or another set of tank rigging with me. I used my bp/w and 40lb single tank wing. 2lb of lead on the band of each air tank. We did a shake-down dive to 100' (the day before) with this configuration prior to the technical dive. We had lift bag, smb, spools, etc should we have a wing fail, but I can easily swim that rig up without them - yes we checked that too.
-I had enough air to do the dive & enough to give air to my buddy if he had an issue without needing the 33% on my back.
-When we did our gas switch we both signaled and checked each-other as normal.
Now, I don't think it was the smartest dive in the world, but I don't think it was hugely dangerous either. It's not like we used 50 or 100.
Later in the week, we did an extended range no deco dive with three AL80 full of 33% set up the same way. I breathed down the tank on my back first, leaving plenty to donate. Getting to spend time on the far side of Bonaire's double reef (off Plaza) was amazing and well worth the 97min swim with all those tanks!
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