Deco with too less air, options from the book

[TSandM]

5--so, like I learned about how long a tank really lasts, the answer is it depends but generally blow off or shorten the deeper stops and keep to the shallower ones.

That may roughly be the concensus here, but in my opinion (for what THAT's worth), Steve from SDI/TDI has the best post in the thread.

The models and programs we use to calculate decompression schedules have gone through a certain amount of validation, and we know that the majority of divers can surface safely using those tools. We have NO testing of shortening deco schedules. We have anecdotal reports of people abbreviating deco (see the Truk lagoon thread) and either surviving it, or getting hurt.

When someone says, "I'd do this," there are no data behind the statement. (Obviously, the experiment of blowing off a certain amount of deco deep or shallow and seeing if people get hurt, and if so, how, isn't going to pass anyone's IRB.)

My buddy and I were discussing this yesterday, talking about why it's good to understand a number of different models and what the shape of the decompression is that's generated from each one. You may plan a dive perfectly and have plenty of deco gas, but your buddy rips his drysuit and has a full flood in 45 degree water. There's a thermocline and the shallow water is 75 degrees. Can you reshape your deco to get shallow faster? Understanding the difference between bubble models and pure Buhlmann may allow you to reshape your decompression to salvage the situation. But there, we are still remaining within the total decompression required by the models, so it's still using a validated system. There is no approach to shortening the total decompression that can be said to be superior to any other, as the data don't exist.

 

[boulderjohn]

I had a thought while reviewing all of the posts that emphasized that a well planned dive should not encounter this problem. This concept (with which I agree, BTW) demonstrates a like-mindedness on the part of those who post about how deco dives should be done.

Not all people who routinely do deco dives are of that mind, however.

When you read The Last Dive or Shadow Divers, you find people who have a different appraoch to such dives. You will read, for example, about highly experienced divers who believe firmly that deep deco dives should be done solo, because they believe a buddy is more likely to kill you than save you. You will see them bring what they believe to be adequate gas, but because they don't keep it with them at all times, and because they have no buddies, they routinely dive without any redundant gas at hand. You will see examples of highly experienced divers who had to shorten or eliminate deco stops as a result.

In The Last Dive, author Bernie Chowdhury describes his near-fatal DCS experience while diving deep air solo. Almost certainly under the influence of narcosis, he started up the wrong ascent line off a wreck before realizing he was not on the line on which he had left his deco bottles. Because of a ripping current, he had to crawl to the other end of the wreck to get to the correct line, but he crawled completely around the wreck and found himself back on the wrong line. Now nearly out of air, he surfaced and prayed for a successful chamber experience. He got it.

Reflecting on this experience, he seems to feel the only mistake he made was not using a full-face mask so he could transmit a radio distress message to the surface. I don't recall that he even considers the idea that a buddy might have been helpful.

I think that I read recently that he is a tech instructor now. I could be wrong.

In that same book and in Shadow Divers, you meet the Rouse family, father and son. While diving the famed U-Boat, again on deep air, they had a problem within the U-Boat and struggled to find their way out. When they did, they came out a different hole than they went in, and apparently were not able to locate the bottles they had left at their entry point. They followed the same ascent plan as Chowdhury, although with less fortunate results.

I guess the lesson is that what some of us take for granted as a safe diving philosophy is not universally shared. For some people, planning what to do in such a circumstance is very important.

 

[Gilldiver]

You have the events of the U-869 deaths a bit wrong, they didn't come out of a diffrent hole as there was only one hole. They were in a bad air Narc, paniced, and just blew past their bottles.

Back to the original question. What can you do if you did a 160' dive for 20 minutes and are short of gas for your planed deco?

Assuming you were not using a He mix, You could fall back on to US Navy Air tables which give you a deco of:

3 minutes @ 20 feet
11 minutes @ 10 feet

This was a very standard dive on the USS Bass and we would pad it to:

5 minutes @ 20 feet
15 minutes @ 10 feet

The US Navy tables are not considered to be ideal anymore but houndreads of thousands of dives were done on them with accident rates of less then 1/10% or less. By getting to shallower water quicker, you also move your gas volume into the longer deco stops.

When in Hell, they can be your ticket out.

 

[boulderjohn]

You have the events of the U-869 deaths a bit wrong, they didn't come out of a diffrent hole as there was only one hole. They were in a bad air Narc, paniced, and just blew past their bottles.

I only have this description in The Last Dive to go by:

Chrissy apparently tried to use his cave-diving training and follow his guideline, which should have led them straight out of the wreck. But the guideline was later found strung back and forth across the debris littering the bottom of the U-boat's compartment, and parts of it were buried, indicating that the two had difficulty finding the way out. The line leads out of the wreck through a different opening than the one they had entered.... p. 273.

Chrissy later told divers that he and his father searched along the U-boat's deck for eleven minutes, trying desperately to find their extra tanks....Because they had exited from a different hole than the one they had entered, they were inadvertently on the opposite side of the U-boat. When Chris found the one scuba tank he had dropped off just outside the opening he had swum through to rescue his son, he clipped the bottle to his son and signaled for them to ascend. p. 274.

You may have different information.

It's a small point, though. Chrissy was obviously in a situation where he had to figure out how to decompress without enough gas, which was what I was pointing out.

 

[Mambo Dave]

The US Navy tables are not considered to be ideal anymore but houndreads of thousands of dives were done on them with accident rates of less then 1/10% or less. By getting to shallower water quicker, you also move your gas volume into the longer deco stops.

When in Hell, they can be your ticket out.

Nice post!

Thank you

 

[HowardE]

I come to scubaboard because I don't know, but this is a tough crowd. I'd be afraid to ask a question of this group! We ceratinly don't want to get someone hurt with a bad answer but we want to learn and have fun while staying safe.

As I understood the answers (and my apologies to h90--all north americans aren't mean)

1--don't do it if you aren't trained for it
2--plan for it properly
3--if you screw it up you're an idiot
4--if you are an idiot you are still 100+ feet under water and short on gas
5--so, like I learned about how long a tank really lasts, the answer is it depends but generally blow off or shorten the deeper stops and keep to the shallower ones.

I'll probably never tec dive, but I am interested in learning more about the sport--everything I learn makes me a better (read safer) diver. The physiology of deco stops actually helps me understand my safety stop better so thanks to those who tried to answer the question. Some day when I have a question I hope some of you will help me learn.

This question (thread) is/was a tough one from the onset. The question itself may be flawed in some ways. When you talk about life/death situations, it causes people to get somewhat passionate. This particular thread is one of those cases.

Don't be afraid to post your questions on SB wherever they need to go... You may get a few jerk offs responding in less than favorable ways, but for the most part. People are helpful.


If you do learn about decompression theory... you'll find it's been a long - on going debate - both online and otherwise.

Also - for those interested... The US Navy tables are based on 100 dives performed by navy divers.... Of those 100 dives... 5 of the dives resulted in DCS. I guess 5% is acceptable?

 

[Rhone Man]

I only have this description in The Last Dive to go by:

I think in Shadow Divers Kurson indicated that Chris and Chrissie left through a different crack in the hull than that which they entered through, and mistakenly turned left instead of right, thereby going to the bow of the U-Boat instead of the stern where their tanks were (had they exited from the side that they entered on, they would have turned left to get to the tanks).

The thing I never understood from the book was why they did not at least try and do some kind of salvage deco using the surface supplied O2 that Kurson indicated was hanging from the Seeker instead of popping straight out of the water (or indeed, why they didn't go back down to it).

Monday morning quarterbacking at its very worst I know, but surely if they had stopped at (or gone back down to) 20 feet and breathed O2 they had to have a better chance...?

 

[Mambo Dave]

I believe that by the time they came up one of them was out of it, and the second was in very bad shape. I'm not sure either could have descended again without another diver's assistance.

Am I remembering it wrong?

 

[Rhone Man]

I certainly remember that the father reportedly died in the water at the back of the boat, so I suspect that your recollection is correct.

 

[MXGratefulDiver]

I wouldn't take what I read in Shadow Divers as anything other than entertainment ... Kurson admittedly took a bit of literary license to make the story flow. Also, he's not a diver ... and anyone who's ever read a newspaper account of a diving accident understands how wrong non-divers can get it, even when they're trying hard to report the facts.

Couple things to consider about using Navy tables ... they were created based on the experiences of very fit 20-something year old men ... who had ready access to an on-board hyperbaric chamber. So I'd be wary of considering Navy tables suitable for use by your typical recreational diver.

And finally, if Bernie Chowdhury chooses to take great risks with his decompression choices, my guess is that he's doing so based on experience and knowledge that most divers on ScubaBoard do not possess. An analogy ... if Jimmie Johnson or Jeff Gordon were to go on the internet and explain how to steer out of a high-speed spin, we'd be all ears. But if someone learning how to drive were to ask the same question of his driving instructor, the correct answer would be to not put yourself into a position where you'd have to do that.

Same applies here ... the "correct" answer really depends on who's asking the question.

... Bob (Grateful Diver)