Deco with too less air, options from the book

[Reg Braithwaite]

You could just not answer

That's the most insightful meta-comment on the thread, IMO. Not to rag on people who answered in whatever way thy felt appropriate, but it's good to be reminded that when we see a question or a statement we find repellant/repugnant, it's always our option to ignore it.

p.s. SB also helpfully provides an ignore this thread feature and an ignore this user feature (a/k/a "Plonk") if you find your fingers drifting towards he "flame" button on the keyboard.

 

[Reg Braithwaite]

And now, from the comfort of my warm home during a blizzard, and speaking with all the confidence my complete inexperience provides...

Playing "what if" for impossible scenarios is an important part of the learning and testing process in every other endeavour. Imagine, for example, you and your buddy sign up for an operator to take you out on a deco dive. At the shop, they look over your certification cards.

The DM speaks. "Do you mind if I ask you a few questions to get a feel for your experience?" Of course you don't mind.

"You're doing a dive of XXX with planned deco of YYY. You suddenly realize you are short of deco gas. Do you cut the deep stops, the shallow stops, or shave a little off the entire profile?"

You are not fazed: "For starters, I have planned the dive and have back gas reserves to handle the loss of a deco bottle and deco bottle reserves to handle both divers. Furthermore, I have contingency tables."

The DM nods. "Excellent, but just so I can understand the depth of your knowledge about the subject, let's hand wave and say you don't have enough gas. What now?"

You can't be fooled. "I send up the yellow SMB for another bottle." The DM is pleased. "I am marking you down as being very solid on procedure, but I'm drawing a blank on your knowledge of theory. In other words, you are showing me that you know what to do but not that you know why we do it.

"Let's say there is no alternative but to do less deco. Given your knowledge of deco theory, what is the least risky way to modify your deco? To be clear at no time will we ever need to cut our deco short in this manner, but I do need to understand a little about you before we get on the boat, and this is a fairly simple question to answer if we can just think about the theory and accept that I am very pleased with your practical and safe approach to procedures."

Now what do you say?

 

[Steve SDI/TDI HQ]

"Let's say there is no alternative but to do less deco. Given your knowledge of deco theory, what is the least risky way to modify your deco?

Now what do you say?

With all due respect, there is no such thing as least risky way to shorten required decompression obligations. This whole thread is built on a faulty premise. Shortening a decompression obligation in any way heightens risk... all the crap about one option or another being more likely or less likely to result in a type one or type two hit is simple nonsense because there is no context for analysis. Certainly, modern decompression practices have us stopping deeper in the water but there are studies that repudiate that.

It may be that each of us has a comfort zone within which we'd modify our behavior but we should also know that we have not managed risk in any way shape or form.

The simple answer is there is no answer and I'd have a problem with a "divemaster" who thinks there is... at least one working for me.

A problem with this type of thread is that some poor bugger reads it and believes that it's message is correct... oh, if I do deep stops and cut the shallow ones that's less risky. NO IT IS NOT. It does not alter the risk. All this stupidity about I'd rather be bent at 20 feet than at 60 comes from what... experience or bull****?

I've done a few decompression dives and touch wood have never been to the chamber... I have run out of gas and I have cut schedules short... alarmingly short... I have also modified ascent profiles on the fly... but it would be ridiculous of me in a public forum to make a statement that one was safer than the other... they are both risky and there are no guarantees that one or the other is "right." The OP asked a question and got several good answers.

 

[Reg Braithwaite]

all the crap about one option or another being more likely or less likely to result in a type one or type two hit is simple nonsense because there is no context for analysis. Certainly, modern decompression practices have us stopping deeper in the water but there are studies that repudiate that.

That is an interesting point that adds value, thanks.

 

[HowardE]

This gets my vote for the worst thread I have ever read on SB - 45 posts before someone actually addressed the OPs question in a concise, realistic & non-condescending manner

Is this comment not condescending?

 

[seaducer]

I agree ... the question is not a low on gas problem , it's a shortening of my dive problem and what to do about my deco obligation?
Thank you for the responses that answer that question

As a rec diver who has no interest of persuing deco at this time, thanks for trying to drag this back to a reasonable discussion.

Personally I am interested in thoughts about why people would skip certain stops as opposed to others, not because I am planning to implement that information in my dive planning, but so that I can have a better grasp of deco theory, and what is going on in my body while I am diving to the depths and times I enjoy.

Discussions like these, with "real world" scenarios to paint a relevence picture and trained divers debating the merits of a schedule in plain language can be alot easier to follow than a dry medical journal.

Many thanks to those who have given and defended real answers.

 

[imasinker]

Not trying to hijack this thread, but keep in touch with the subject. OK...I plan to take the courses so don't start off by telling me to do so. I am researching the subject so that when I do take the course I will have some knowledge about what they are talking about. Now with saying that, I have used V planner. I did what I think is a basic deco dive, could someone who has experience with deco, look at this and tell me is this a safe plan. Opinions and if these safety stops / times are reasonable, non conservative or over conservative.
Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 110ft (s)
Conservatism = Nominal

Dec to 110ft (2) Nitrox 32 50ft/min descent.
Level 110ft 42:48 (45) Nitrox 32 1.36 ppO2, 90ft ead
Asc to 30ft (47) Nitrox 32 -30ft/min ascent.
Stop at 30ft 1:20 (49) Nitrox 32 0.60 ppO2, 21ft ead
Stop at 20ft 5:00 (54) Nitrox 32 0.51 ppO2, 12ft ead
Stop at 10ft 10:00 (64) Nitrox 32 0.41 ppO2, 4ft ead
Surface (64) Nitrox 32 -30ft/min ascent.

Off gassing starts at 64.2ft

OTU's this dive: 72
CNS Total: 28.6%

151.5 cu ft Nitrox 32
151.5 cu ft TOTAL

 

[Doppler]

Imasinker... on first blush, I would not do the dive you outlined... number of reasons, and in the briefest answer possible, they include, wrong gas for decompression, tables cut with pure algorithm and no level of conservatism which may be why the first stop is more than 1 bar above the off-gassing ceiling... something I tend to avoid in both my teaching and practice.

Please don't ask for a lesson on decompression theory here. If you have questions, call me, I am not that hard to find.


P.S. You have a very good planning tool there with Ross's V-Planner... run the same profile with the conservatism set to five... If you are anything like most of us, that will make you ask yourself the question... "hold on, same gas, same depth, same time... so which ascent profile is the right one?"

 

[imasinker]

Imasinker... on first blush, I would not do the dive you outlined... number of reasons, and in the briefest answer possible, they include, wrong gas for decompression, tables cut with pure algorithm and no level of conservatism which may be why the first stop is more than 1 bar above the off-gassing ceiling... something I tend to avoid in both my teaching and practice.

Please don't ask for a lesson on decompression theory here. If you have questions, call me, I am not that hard to find.


P.S. You have a very good planning tool there with Ross's V-Planner... run the same profile with the conservatism set to five... If you are anything like most of us, that will make you ask yourself the question... "hold on, same gas, same depth, same time... so which ascent profile is the right one?"

Thank you your answer makes a lot of sense to me, I ran a few through the planner trying to come up with a scenario, it won't work that way. I did try it on level 5 as you said, i am looking at the differences in time and start of deco. I am afraid I may have just confused the hell out of everyone. Your response is well noted and again thank you.

 

[Reg Braithwaite]

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html