How much gas in case of accidental deco.

[waterpirate]

As an example, the other year I conducted a multi-day series of repetitive (2-3 dives per day) deep (100-140ft) dives. On the last dive of the series, I dove to only 50ft depth and noticed a 30 minute NDL. I made the decision to exceed my NDL, on the basis that I was a technically trained diver and had ample gas supplies for any deco that arose (I was on double AL80s). I was aware when I exceeded the NDL on my computer (a Suunto Vyper) and had predicted (wrongly) that a further 5 minutes bottom time wouldn't cause a major deco obligation. Only a minute later, I glanced at my computer and was shocked to see that the deco obligation was already at ~8 minutes. This wasn't as I expected, so I began my ascent there and then. As I ascended from 50ft to 15ft, the mandatory deco continued to rise...quickly. By the time I reached my stop at 15ft, I was owing around ~25 minutes of deco time.

LOL!!!

Anyone who has been tech diveing any amount of time who will not fess up to that bone head move is lying! I can remember begging for that one minute of bottom time to be taken back, when observing my time to surface jump from 30 minutes to allmost an hour on my puter. Assumeing what your puter will say in regard to deco is a slippery slope.
Eric

 

[Gilldiver]

What happens if you do some agressive diving, on air, each day for a week or two? Not even 180 feet but say, 110-120 feet?

Well when I was in my 20's and early 30's wreck diving in NC 2 dives a day in the 90 to 160 range on air for 20-25 minutes each would have me feeling beat to hell by the end of the day on Friday. Made the 12-14 hour drive home on Saturday a bit tough.

 

[lowviz]

What happens if you do some agressive diving, on air, each day for a week or two? Not even 180 feet but say, 110-120 feet?

Here I go with advice, again...

Take IANTD's "Decompression Procedures" course. Said course has no requirement to do a deco dive, or even a get-wet dive for that matter. With your background, you will find this couse most enlightening and empowering. Especially so, in that you do multi-day, slow tissue loading dives.

---------- Post Merged at 09:19 PM ---------- Previous Post was at 08:48 PM ----------

...//... I can remember begging for that one minute of bottom time to be taken back, when observing my time to surface jump from 30 minutes to allmost an hour ...//...

Depth?

---------- Post Merged at 11:28 PM ---------- Previous Post was at 08:48 PM ----------

OK, seems like the honcho divers are circling their wagons.

I don't take much on faith when it comes to my own ass.

Here is what I have been able to understand about deco. Maybe someone who knows WTF they are talking about (like DiveNav, maybe) can grade my current progress.

Novel work, nobody will find this anywhere...

First dive, no loading, step one. The calcs give a number that corresponds to a letter of the alphabet. Pressure group.



Bottom line: First order understanding of a non-linear clock that determines my future health.

 

[waterpirate]

Depth?

Please do not take this the wrong way but I do not talk about depth freely anymore. It sounds like bragging, and it puts to much emphasis on it for aspireing tech trainees. It was at the outer limits of my current cert card. That bone head move comes when you get all comfy doing deco, and fly your puter more than cut tables. It is an occurance that happens to everyone eventually except the most disceplined in regard to following the dive plan.
Eric

 

[cascas]

I'm not sure the best place for this topic...move as you see fit.

If you were on a no deco dive and for whatever reason (inattention, dealing with a situation, etc) ran your NDL down and clipped the edge of the deco envelope, how much gas should you have to safely clear your obligation without pushing an out of air situation?
I try to stay in the habbit of using my air in 3rds. So (for simplicity sake) I start with 3300psi, turn at 2200, with the intention of being out of the water with 1100. I want to stress that I have no intention of planning deco dives without formal training, But I have seen a few Rec divers lock out their computers because they clipped that envelope and didnt know it, or didnt know what to do about it. I am also putting togeher a stage kit to carry a sling bottle, but for redundancy, NOT for increased air supply. What I mean by this is if I have 100cf of back gas, and an 80cf sling bottle, I my intention would be to use 33cf, turn, and finish with 33cf of back gas plus 80cf in the sling. NOT breathe my 100 down to 40, and then switch to the sling when the back gas runs out.

Instead of buying stuff to bail you out (or get you in more trouble than you're capable of handling), why not invest in understanding deco ( which you can easily do by reading a good book about it) so you know what to do and understand why you are doing it. That approach is way safer than "slinging extra gas" AND it will benefit you in possible further courses you do.
This investment I am sure will give you a greater return than anything else...



Bottom line for this thread is that although you might know what the numbers on your screen tell you, that does not mean you understand deco. When doing deco dives understanding what deco is, what it does to you and hou you should act to prevent it hurting you comes first.
A computer (or preferably a bottom timer) should be there only to help you. It should not be used as an allmighty know-it-all on deco matters because it is ultimately not smarter than an egg timer.
The smart part should be in your head. Then and only then are you really ready to do deco dives.

 

[waterpirate]

Disagree with the above. A puter is a tool, like your brain. Both are prone to sudden short term failure. The trick is implementing multiple tools to accomplish one goal. That comes with edumacation, and the understanding that no one singular tool is the only one to get a given result.
Eric

 

[cascas]

Disagree with the above. A puter is a tool, like your brain. Both are prone to sudden short term failure. The trick is implementing multiple tools to accomplish one goal. That comes with edumacation, and the understanding that no one singular tool is the only one to get a given result.
Eric

Disagreeing is allowed..

But... If you are able to manage you deco using only your dive plan, your bottom timer and your brain, you will be far more flexible to handle unexpected events than you would be if you put your trust entirely in a "puter".

If your puter somehow shows a reading that does not make sense ( read various threads on this board about that) you will be lost and not know what to do.

A bottom timer is far less likely to show readings that puzzle you (except if narced like crazy). Those readings together with your diveplan and knowledge of deco ( ratio deco or deco on the fly) will get you to the surface safe. Just take a look at ratio deco, it is simpeler than your average recreational dive planner...

 

[freeclimbmtb]

Instead of buying stuff to bail you out (or get you in more trouble than you're capable of handling), why not invest in understanding deco ( which you can easily do by reading a good book about it) so you know what to do and understand why you are doing it. That approach is way safer than "slinging extra gas" AND it will benefit you in possible further courses you do.
This investment I am sure will give you a greater return than anything else...



Bottom line for this thread is that although you might know what the numbers on your screen tell you, that does not mean you understand deco. When doing deco dives understanding what deco is, what it does to you and hou you should act to prevent it hurting you comes first.
A computer (or preferably a bottom timer) should be there only to help you. It should not be used as an allmighty know-it-all on deco matters because it is ultimately not smarter than an egg timer.
The smart part should be in your head. Then and only then are you really ready to do deco dives.

While I agree fully, what I need is training and comprehension of decompression stop diving, I think I need more milage first. (But lets be honest, that is clearly the direction I will end up going. There are 1000's of recreational divers that stop right there, it is highly unlikely I wll fall into that category forever.) Now I am going to continue to read and learn as I can, but I think a course in intro to tech or decompression might be premature for me at this point. I will also remind you that as I noted before, I am an experiencial learner...not to say history, knowlege, and theory are useless to me, but I know myself fairly well and I can tell you, I wont learn decompression unless I practice decompression...and as I said, Im just not there.

I will also point out that my interest in slinging a bottle was not exclusively for a deco reserve, but also for a redundant air source in case of other incident. In response to just simply carying doubles or a big 130, I like the idea of the redundnacy of an isolated tank, AND, if its not manifolded or connected directly to my primary kit...then I have to make an intentional concious decision to use that air. Lastly, should the situation involve someone other than myself, I cant break a manifold and hand off half a doubles kit, but I can quite easily hand off a sling.

 

[mathauck0814]

In response to just simply carying doubles or a big 130, I like the idea of the redundnacy of an isolated tank, AND, if its not manifolded or connected directly to my primary kit...then I have to make an intentional concious decision to use that air. Lastly, should the situation involve someone other than myself, I cant break a manifold and hand off half a doubles kit, but I can quite easily hand off a sling.

If you're that afraid of consciously using the air in the other tank, you can always dive with the isolator closed. It's unnecessary because you're checking your pressure constantly and you'll always have more than enough should the ka ka hit the fan. And while, no, you cannot pass off half of a set of doubles, this is precisely why you have a long hose. You have your buddy's spare gas on your back, he has the tool he needs to receive it and you both benefit from having the gas system that is fault tolerant. Should one post or the other fail while you're air sharing on your doubles you would close whichever valve was offending and then switch to a buddy-breathing scenario.

 

[freeclimbmtb]

If you're that afraid of consciously using the air in the other tank, you can always dive with the isolator closed. It's unnecessary because you're checking your pressure constantly and you'll always have more than enough should the ka ka hit the fan. And while, no, you cannot pass off half of a set of doubles, this is precisely why you have a long hose. You have your buddy's spare gas on your back, he has the tool he needs to receive it and you both benefit from having the gas system that is fault tolerant. Should one post or the other fail while you're air sharing on your doubles you would close whichever valve was offending and then switch to a buddy-breathing scenario.

Ah. I see what you did there. That would certainly make using all your air a concious decision...but if you dive with the isolator closed...isnt that gonna throw your list all outta whack? Especially if you have something like doubled up AL80s? (not saying this is the best combination, but Ive heard it mentioned in the past) Isn't this one of the complications divers face when sidemounting? (except UTDs crossover setup for sidemount) if you dont manage your gas in both tanks correctly you float one side and sink the other yes?



I just realized I keep coming up with reasons why other ideas are worse than mine. Subconcious I swear to god...not trying to troll...