If you stay long enough to incur a mandatory deco obligation it's technical. You will no longer have direct access to the surface.
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BackMounted Doubles and mixed gas - is that technical?
- Thread starter Basking Ridge Diver
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If you stay long enough to incur a mandatory deco obligation it's technical. You will no longer have direct access to the surface.
OP
Basking Ridge Diver
Contributor
So - I failed to mention I have access to Grade E air - as much as I want -40% in a 72 cu ft is about $9.
Last time I rented 4 Nitrox tanks it cost $120 - gas only - not including boat and tip...
And Yes my intention was to hit 124 feet or the bottom - I did want to explore... I came close to NDL but at 80 feet I switched to 40% and the NDL cranked back up - at no point did I encounter a deco obligation.
Last time I rented 4 Nitrox tanks it cost $120 - gas only - not including boat and tip...
And Yes my intention was to hit 124 feet or the bottom - I did want to explore... I came close to NDL but at 80 feet I switched to 40% and the NDL cranked back up - at no point did I encounter a deco obligation.
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beester
Contributor
It's this kind of experimentation without good mentoring (course or mentor in the know) that gets people in trouble. The fact that you worry more about NDL and deco than the unbreathable gas in your back mounted set shows me that you urgently need to take a course.
OP
Basking Ridge Diver
Contributor
Nope not worried - I did not want this to turn into a rant of no deco without instruction debate. Maybe I overstated it - so it would not be that thread again...
Other than what I mentioned (OxTox by stupidity) - I have not heard a solid argument for why this is a bad idea. I was throwing it out there to see if I was missing something like the elephant in the room... I dont intend on using this method every dive but it sounds like from what I heard - caution and process are key to safety which if you read my OP seems to me to be top of the list.
Jack Hammer
Contributor
Every thing is easy til you have a problem...
MichaelMc
Working toward Cenotes
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.
It does sound very much like accelerated 'off gassing', which is useful stuff for which there is a set of classes.
It does sound very much like accelerated 'off gassing', which is useful stuff for which there is a set of classes.
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I would consider it a dangerous and non-scientifically (i.e. poorly) planned dive.
1) Gas switching for accelerated deco without relevant training (presumably).
2) Riding your computer's NDL up - risky even within rec limits - instead of just planning your deco and doing it.
3) Doing a solo dive without redundant air - your deco mix wasn't breathable at the bottom.
4) Not announcing what you were doing.
It could have been executed as a rec dive (with short BT) or as an entry level technical dive (in a team with deco). Instead it was executed as just one of those... things where people don't seriously consider what they're doing. Plenty of people get away with it. People have gone to 60m+ on a single tank of air, solo, no computer, no training past OW, and come back. Just been talking to one a week ago - declined the invitation to repeat.
Not to take it personally, but that was an unnecessarily dangerous dive that could've been done easier and safer. Two tanks of air or 28% and planned deco would've provided real redundancy, only a little deco, less DCS risk than skirting computer limits, and overall considerably fewer things to go wrong.
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Scared Silly
Contributor
Other than what I mentioned (OxTox by stupidity) - I have not heard a solid argument for why this is a bad idea. I was throwing it out there to see if I was missing something like the elephant in the room... I dont intend on using this method every dive but it sounds like from what I heard - caution and process are key to safety which if you read my OP seems to me to be top of the list.
You have not heard why your planning was a bad idea because you are not listening. Several people have already said this but let me give you the exact scenario where you are dead.
You wanted to hit the bottom at 124. You proceed with caution but Davey Jones is there to meet you. He takes that nice air cylinder of yours and makes it his. Being the quick thinking diver you immediately switch to your cylinder of 40% and start sucking on it while trying to calm your nerves. But wait at that depth the PPO2 for 40% is 1.9 and soon you are convulsing like an electrified chicken. Being solo at the stern of the wreck while everyone else went to the bow no one notices your chicken dance. Soon you are napping in the sand.
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beester
Contributor
Nope not worried - I did not want this to turn into a rant of no deco without instruction debate. Maybe I overstated it - so it would not be that thread again...
Other than what I mentioned (OxTox by stupidity) - I have not heard a solid argument for why this is a bad idea. I was throwing it out there to see if I was missing something like the elephant in the room... I dont intend on using this method every dive but it sounds like from what I heard - caution and process are key to safety which if you read my OP seems to me to be top of the list.
Basking Ridge Diver (BRD), I'm sorry but apparently you are not reading what is being posted by many people here.
I'll repeat... it is NOT the NDL or DECO that you need to be afraid of at this stage. It's running out of air (ie not a good gas plan) or breathing the wrong gas at the wrong depth.
We are in "advanced scuba discussions" so I can post this... DECO probably won't kill you (certainly not in these kind of limited deco dives), not being able to breath or breathing a "hot" mix will, and very very fast. I recently posted my experiences in a deep tech dive where a teammember ascended and skipped about 40 minutes of deco... this did not kill him... however switching solo to a wrong gas would have killed him within minutes. Deco is the least of your problems.
When you take an AN/DP (or any other entry level tech diving) course, you'll notice that a lot of thought has gone into mittegating the risk of running out of air/gas and breathing the wrong gas. That's why we start carrying redundancy like manifolded double tanks, double regs, long hoses, etc etc...You are taught procedures how to calculate sufficient reserve air/gas to get you and a buddy safely to the surface and you are taught procedures how to safely switch to a deco mix with enough checks built in to minimize the risk of switching to a non breathable gas.
To your specifics:
- You want sufficient gas reserves for the dive.
- You want redundancy in your gas supply and your regs (ie if for any reason your main gas supply/ reg becomes compromised you can isolate your gas supply and switch regulators)
- You want your deco gasses (non breathable at certain depths) clearly identified and a clear switching procedure so you don't by accident breath a "hot" gas.
To be very frank... I see a clear case of dunning-kruger (Dunning–Kruger effect - Wikipedia), cognitive bias.
I hope you take the time to talk to your peers and evaluate your options.
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