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And not meant that way
Redundancy Required for Decompression Diving?
- Thread starter dumpsterDiver
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That's an interesting question and I find the answers so far even more so.
A few years back I needed to get certified for deco O2. I looked at my options. I wanted AN/DP but among the concerns was my ability to manage doubles both weight but more so valve drills. And at that time I knew I would likely never be in BM doubles. If ever I went true tech it would be SM cave.
To that end I participated in a thread that among other things explored less common routes to complete the AN/DP course. I was largely castigated even for the suggestion. So much so that I dropped the DP portion of the course but still bought and completed the course material and was fortunate enough that the instructor I chose for AN covered a large portion of the DP classroom information.
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You can ge
I've been following this thread but haven't responded up to now because I am not a technical instructor... I think Andy probably explained the party line as well as can be expected. I do have, however, 14 years of technical diving experience (50-odd "technical" dives per year) and I have a "take" on what you are saying. I may break with the heard on this a bit......
My initial technical training was via IANTD. In order to perform the skills that were required in the course (I think it was called Advanced Nitrox), the student would require dual 1st stages that can be manipulated blindly behind the diver's back. A Y valve on a single tank allows for that, an H valve normally would not. Manifolded twins allow for that but I don't recall that there was a requirement for an isolation manifold. Moreover, there were no skills involving isolation in my initial training.
Subsequently I took other technical specialties from IANTD. In particular I specifically remember the ice diving course requiring manifolded twins with an isolator (and in the initial training we were drilled to manipulate it). I do not know if this was a requirement of the agency or if the instructor was simply uncomfortable running the course with anything less but given the number of failures we had during the course I literally would not consider diving under ice in sub zero air temperatures without it. For example, on the last day of training the air temperature was -15C and one dive we had 2 divers (out of the 3 who were diving) with problems under the ice, both of which were frozen inflators, and 4 out of the 6 with problems above water (frozen inflators, frozen regulators and even a torn trilam suit). Before diving we literally had to lay for 5 minutes in the water first to let the gear thaw out enough to dive with it (at 4C the water was a LOT warmer than the air). In this kind of context you would be completely out of your mind to assume that your buddy's gear is a sufficient redundancy. Even diving in 3 man teams where everyone's gear was fully redundant, we were making contingency plans for 2 total system failures.
So that's where I am on this thread.... context. I've seen some of your videos so I have an idea of the context of your diving. You dive in clear warm water and while a diver can still drown in clear warm water, the chance of a total systems failure in the context is a LOT lower than in other technical contexts, as described above.
If you look at risk as a calculation of "chance" times "effect" then the lower the chance, the lower the risk. I think this is what your friend was saying on, perhaps, an intuitive level.
The courses are designed to teach students how to manipulate the redundancy that they have but after that the diver him/her self is responsible for making the risk evaluation and the contingency plan. These things are covered in various courses. In particular TDI is very explicit about it in their written materials. If you choose to take a risk then consciously CHOOSE to take the risk...... TDI does not suggest to "avoid all risk" as perhaps some other agencies do, but they lay the responsibility firmly in the hands of the diver and say (strongly paraphrasing), "if you WANT to be an idiot and it is a conscious CHOICE then who are we to be moralistic about it?".
Tying this in to your OP, what do I think? I think IF (and that's a big IF)
a) the diver understands deco theory very well
b) the diver estimates (or better yet, calculates) that their buddy's air supply offers a sufficient contingency for the intended deco obligation
and
c) the *chance* of buddy separation is next to zero
then I think there is reason to see this as 'under control'.
Obviously I don't know the details of your dive but what I am saying is that there is more than one way to skin this cat and I wouldn't automatically declare your buddy insane for taking his buddy's air supply in to account in his contingency plan.... in fact.... every recreational diver on the planet does this. If you look at what the buddy system really is.... it is the ASSUMPTION (and I'm not going to open that can of worms right now) that YOUR back up is on your buddy's back!
This is the reason you haven't been able to get a straight answer to your question yet. Because the answer is CONTEXT dependent.
To take it one step further..... and this is the point where I may break from the heard...... I don't think what your buddy said is even very shocking and I could see myself saying the same things... and maybe for the same reasons...... I'll speak only for myself in this case but becoming a technical diver was the best thing that ever happened to me because I no longer fear the NDL AT ALL. This is the most liberating thing that I've ever experienced in diving.
Gas factors into my mind set (you must be able to make the dive)..... total dive time factors into my mind set (I hate being cold)..... navigation factors into my mind set (I hate being lost) but the NDL is no longer a factor in my diving and hasn't been for 14 years. I look at TTS on my computer in order to judge when to turn the dive (within calculated parameters) but I literally do not remember the last time I looked at NDL on my computer. The water temperature is more relevant to me.
I suspect your buddy is in a similar mind set.
Does this help you put things in context a bit better?
R..
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This was probably the best reply yet. Good job.
sea_otter
Contributor
This is a great perspective, and I think it's one that is shared with many. I've started diving with a few people with a lot of technical experience, and most seem to feel the same way. I find myself being a limiting factor in wanting to stay within NDLs, and for me that limit is down to human factors alone. Despite the fact that I know I have redundancy (doubles), sufficient gas, warm clothing, a good directional sense, and have confidence that I won't be separated from my buddy, seeing a ceiling on my computer makes me nervous. And nervous is not something I'm willing to be in that situation.
This is a big part of what's prompted me to sign up for additional training. I want to be sure of the "me" part of the equation. I think those people who say "yes, this is okay" are those with sufficient training and experience to fully understand what they're agreeing to and their capacity to handle it. Those who are asking the questions, in many cases, may not have that level of understanding.
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that, that is what I advocate for and think is a huge let down in the industry right now by making NDL's scary.
lerpy
Contributor
Without trying to sound like a dick, I would suggest if you are interested in the standards of practices for technical diving to get training in the filed rather than learning from the internet and completing deco dives as it sounds like you have, without training or instruction on gear use and technique.
The principal of secondary life support is one of the things covered In the Padi Tec courses. This means two independent first and second stages, gas sources, bouyancy control methods, deco methods, etc.
100days-a-year
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DISCLAIMER
O NOT TRY THIS AT HOME decompression diving is serious and without proper training you are likely to get hurt,annoy everyone rescuing you and/or die.
PS to DISCLAIMER #1 in particular do not try to emulate any particular dive strategy(especially mine)you have read on the internet without first running it by an accredited technical instructor of the agency of your pleasure.
Unless I plan heavy deco in excess of 20mins or using multiple gasses,my redundancy consists of extra spearshafts
.I can do a lot of diving including deco on a single 120 and still get out within 1/3s.Diving tri-mix long and deep is different bird and I wear doubles,sling stages, carry spares etc... and have experienced support on the surface.
For most dives <200' and <20 min deco.....No H,no Y,no pony,no EPIRB or PLB,no signalling mirror,no backup mask,no raft,no reels,no second light etc.If everything fails,I can CESA (Having had to do so once when a SP gauge froze at depth while working deep and once when a DIN valve blew an o-ring),put on an 02/spare tank and get back in within a couple minutes as long as my ascent rate doesn't embolize me
.I prefer that to carrying a lot of extra gear that in an emergency has to be swam up and is a general PITA to wear,upkeep,don and doff etc...
Knowing and having dove with the OP,he is more than competent enough to make the right decision in any case.
O NOT TRY THIS AT HOME decompression diving is serious and without proper training you are likely to get hurt,annoy everyone rescuing you and/or die.PS to DISCLAIMER #1 in particular do not try to emulate any particular dive strategy(especially mine)you have read on the internet without first running it by an accredited technical instructor of the agency of your pleasure.
Unless I plan heavy deco in excess of 20mins or using multiple gasses,my redundancy consists of extra spearshafts
.I can do a lot of diving including deco on a single 120 and still get out within 1/3s.Diving tri-mix long and deep is different bird and I wear doubles,sling stages, carry spares etc... and have experienced support on the surface. For most dives <200' and <20 min deco.....No H,no Y,no pony,no EPIRB or PLB,no signalling mirror,no backup mask,no raft,no reels,no second light etc.If everything fails,I can CESA (Having had to do so once when a SP gauge froze at depth while working deep and once when a DIN valve blew an o-ring),put on an 02/spare tank and get back in within a couple minutes as long as my ascent rate doesn't embolize me
.I prefer that to carrying a lot of extra gear that in an emergency has to be swam up and is a general PITA to wear,upkeep,don and doff etc...Knowing and having dove with the OP,he is more than competent enough to make the right decision in any case.
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