BackMounted Doubles and mixed gas - is that technical?

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A different scenario: The "buddy" that wanted you to descend with them goes with you to the bottom. They then go OOA due to equipment issues. You quickly donate primary and breath your necklace. As you ensure they are ok and try to calm them, you start convulsing. They really panic, 124' down, OOA, on the long hose of a convulsing diver that just tried to help them. You both die.

(I also checked we were in the advanced forum before posting that scenario and result.)

You said you had three cylinders, where were they? Back air long, back 40 necklaced, second air where? Sizes? Not that it changes the get training before diving toxic gasses story. Was the "buddy" solo trained and equipped?
 
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So I planned my dive on the Stolt Dagali of the NJ Coast. Sand is about 125 feet and the wreck goes up to about 70 feet.

I used Subsurface software which I have used before and calculated my dive times and gas usage. I was going to just use air for the entire dive but realized my second dive would be cut short due to my Nitrogen load (NDL driven - I am not AN/DP certified) - but I do have my Nitrox certification.

I dive Independent doubles and used air in one tank with the long hose and used 40% in the other under my chin. 40% at 82 feet is 1.4 PPO at 100 feet it would be 1.6 PPO- my plan was only to use it after I get to 80 feet and use half the tank. Saving the other half for the second dive.

I got some questions from fellow divers as to what I was doing and someone mentioned the fact that you are switching gases makes this a technical dive. To be fair I never really thought about it. I used air to get to the deep stuff and used 40% which I am allowed / certified to use and extended my dive due to the nitrox - getting me the longer NDL on both the first and second dives.

I happen to have a Perdix so I marked 21% and 40% did the gas switches and just followed my NDLs. No harm no foul. I did not go into deco and no one was checking my dives - I dove solo but went down the line with a "Buddy" because he wanted to make sure he was ok - I had no problem with the arrangement.

I brought 3 tanks - two filled with air and one filled with 40%. Other than OxTox if I made some kind of stupid mistake - it seemed to work for me and my diving style.

Would you consider this a technical dive? I am not a qualified technical diver and I am using the tools that are available to me - it did not seem to me like I was breaking any rules and the dive boat had no issues but I did not announce what I was doing either.
to clarify you had 3 tanks -2 on your back and one extra ? im not sure why you didn't just put the Air in your twins and carry the 40% in the third bottle is this the correct as @MichaelMc says in extremis your muscle memory will revert to your necklace

I would call this a technical dive but mostly because i think you've created unnecessary risks as others have stated
 
I believe he used 3 tanks for both dives ie one air one nitrox on dive one, changed air tank and used other half of nitrox for dive 2.

So only 2 tanks per dive, with one second stage on each.

That means no bottom redundancy thus not a solo dive, no donatable gas on the bottom except by buddy breathing.

One failed first stage between the 2 of them on the bottom and this thread might have been started by DandyDon.
 
Toxic gas on your necklaced reg was a major concern! Given how much the primary donate set of actions is ingrained into us. And the death by gas switch prevalence in those trained on multiple gases.

Stupid question, perhaps: Are there situations where you would have an unbreathable gas on your necklace as part of a properly planned dive? (The described dive is definitely not one!) But how is this handled, for instance, when you dive hypoxic mixes and are on your travel gas during decent? What's on your necklace reg then, and how do you handle an air-share situation then? I'm not trimix trained, but curious. Hope to take normoxic soon...
 
Stupid question, perhaps: Are there situations where you would have an unbreathable gas on your necklace as part of a properly planned dive? (The described dive is definitely not one!) But how is this handled, for instance, when you dive hypoxic mixes and are on your travel gas during decent? What's on your necklace reg then, and how do you handle an air-share situation then? I'm not trimix trained, but curious. Hope to take normoxic soon...
yes as you say hypoxic on necklace at start - switch from travel gas (or say 50% deco ) on descent to bottom gas on the fly
 
Technical ...... not technical ........ ?????? Is that really a point ? Maybe a better question is it may not be the best practice and increases the possibility of a bad out come . I would have concern with the easy access to your travel gas at depth . The main reason for the necklace is for hands free immediate acccess of gas . Do you really want a travel mix on your neck? Again as others have pointed out the OOA could also be a set up for failure. Again technical ..... not technical question really won't make much difference with travel / bottom gas mix up . Maybe the question could be what's a better practice to increase the chance of a successful dive with this profile and minimize risk.
 
Hey Basking Ridge, please don't take the comments here as "beating up on you." It's really easy to feel that way when you have a text discussion over the internet...a lot gets lost. Despite how it feels on some threads, I really think most folks here on SB have the well-being of all our community members in mind; that is certainly how I took it for the folks posting in this thread. The short of it is that there are a set of well-developed procedures that make the kind of dive you did much safer. AND, these procedures can be done without incurring a huge set of costs for gas, etc. I honestly believe that all recreational divers can truly benefit from an AN/DP course. If you then want to skirt the rec-tech boundary (however you want to define it), you'll be completely prepared for that kind of dive and it will increase your overall skill set, making your basic recreational dives that much more enjoyable.
 
I believe he used 3 tanks for both dives ie one air one nitrox on dive one, changed air tank and used other half of nitrox for dive 2.

So only 2 tanks per dive, with one second stage on each.

That means no bottom redundancy thus not a solo dive, no donatable gas on the bottom except by buddy breathing.

One failed first stage between the 2 of them on the bottom and this thread might have been started by DandyDon.
yes I see that now - and I agree no redundancy -if he had an extra valve on his air and second reg he could do it that way but 40% should not be on necklace
 
https://www.shearwater.com/products/perdix-ai/

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