Contingency Deco Plan

[RyanT]

@RyanT Ive been called many things, insightful? Them's fighting words!

whoops, I mean

Packrat: I consider my required deco what I planned for at the start of the dive. If some dire circumstance required me to get out of the water early, changing my algorithm doesn't change my physiology. Sure, it might be nice to know that I got out of the water in accordance with a more aggressive profile than planned, but at the end of the day, you get out of the water when you do and you take a hit or don't. I like to dive a relatively conservative profile and I'll do everything I can to complete it. I realize that lots of folks fudge their profiles depending on the particular dive, I simply prefer to be conservative and do what I can to complete that profile.

Rainpilot, I've taken both Man-O-War and stonefish stings. I would still do everything I could to say in the water. Admittedly, the stonefish sting is pretty much the only time in my adult life that I've cried from physical pain. It's bad.

 

[Remy B.]

I will thank all of you for your inputs.

My conclusion with the 30@60m, is that I carry enough gas with that gear for contingency of an 20 min over-run at depth and still come up alive, with either Algorithm, but I see that the 35/95 will have me off-gassing longer at shallow than the VPM-B even if I cut it short due to depleting the 7L 80%, I have some little 50% over to stay a few minutes, there is no spare Deco gas to share in this case, but that will be a very unlikely event that you get in trouble down deep and then loose your Deco gas as well, if that happen then that was just your day to die or get a hit, your ticket number was called above, end of story.

 

[DevonDiver]

This is really a question I'd expect from some one who us taking or just completed AN/DP, not from some one planning a dive to 60m. Perhaps the internet isn't the best place gain experience.

Much of the OPs line of thinking illustrates significant inexperience relative to the dive level being debated (and God forbid, attempted!).

I've assumed his questions were hypothetical. 50-99 dives (as stated) is nowhere near enough learning and developmental time to be competent for trimix deep diving. Even assuming great training and diligent practice thereafter (which is shockingly rare in tech divers nowadays...)

Tech cards are handed out like candy nowadays. An over-ambitious, impatient, diver can always find some unethical tech instructor who'll empower them with junk c-cards for a quick buck.

Current deco technology also goes a long way to furthering delusions of competency. Download a copy of multi-deco and everyone becomes an instant deco expert. Strap on a Shearwater and the sky (or rather, the abyss) is your limit.

Welcome to the era of 'junk tech' and the 'insta-expert'...

 

[KenGordon]

Air on diver, 2x 12L-300 + 2x 6.8L-300 + 1x 5.6L-200 50%O2 + 1x 7L-230 80%O2

This is what I'm thinking about


Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 35/65

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 26:40 (30) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 36m (33) Trimix 18/40 -8m/min ascent.
Stop at 36m 1:00 (34) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 2:00 (36) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 2:00 (38) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 3:00 (41) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (44) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 2:00 (46) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 5:00 (51) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 6:00 (57) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 8:00 (65) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 40:00 (105) Nitrox 80 1.28 ppO2, 0m ead
Surface (106) Nitrox 80 -6m/min ascent.

OTU's this dive: 142
CNS Total: 54.6%

4834.6 ltr Trimix 18/40
681.9 ltr Nitrox 50
1349.5 ltr Nitrox 80
6866 ltr TOTAL

===========================================================================================

Backup Plan.

Decompression model: VPM - B

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = Nominal

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 46:40 (50) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 42m (52) Trimix 18/40 -8m/min ascent.
Stop at 42m 0:45 (53) Trimix 18/40 0.93 ppO2, 18m ead, 21m end
Stop at 36m 4:00 (57) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 3:00 (60) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 3:00 (63) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 6:00 (69) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (72) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 4:00 (76) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 6:00 (82) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 7:00 (89) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 10:00 (99) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 41:00 (140) Nitrox 80 1.28 ppO2, 0m ead
Surface (141) Nitrox 80 -6m/min ascent.

Off gassing starts at 46.8m

OTU's this dive: 184
CNS Total: 71.0%

8120.7 ltr Trimix 18/40
856.2 ltr Nitrox 50
1441.0 ltr Nitrox 80
10417.9 ltr TOTAL

That is a poor choice of gas to carry. I could not stand up with all those backgas cylinders, but I would not get in with so little deco gas for that dive.

20 minutes late at 60m on OC is very likely dead. You are finding that the sort of dead with this configuration is not enough deco gas. You might as well plan for dead due to being out of back gas while stuck in the wreck and save your back carrying all those cylinders which will not save you.

As has been said above, gas planning with two deco gases is not a simple extension on a single deco gas dive. It is fairly subtle and needs to be discussed with someone that does it for the sort of dives you want to do.

 

[joe10540]

I'm not a deco diver but am fascinated with the physiology of it. As a healthcare provider I also understand that everything in medicine is an experiment of one and more so when it comes to the black magic of deco. Yes gf 99/99 is he THEORETICAL limit but are you telling me that you are in perfect shape with perfect conditions and with perfectly blended gas and someone standing by for the hit you might take if perfect isn't good enough in your experiment of one? Using a gf of 35/80 or any other more conservative profile is because most of us have extra bioprene and aren't quite hydrated enough and might be a little cold or have some minor niggle that requires just a little extra time, and still people get hit when they follow all the recommendations. It's ultimately your life and you are free to make whatever decisions you want but remember the life you save just might be your own.

 

[packrat12]

joe10540 - Keep in mind that everyone I see here is talking about an extreme emergency. If I was low on air because <insert reason here> and I stayed at GF 30/85, when I ran out of gas, I would eventually pass through the M-Value (theoretical, ideal what ever). Now it is not a question of being on the ideal M-Value line but rather passing through it. Using the GF99, I might not need to pass through it, can extend my time at 20' to make up the difference or if I do pass through it, it will be closer to the end and the Slow tissues rather then possibly the Fast tissues. DCS Type I hit vs a DCS Type II hit anyone? The idea of using GF99 to ascend is a trade off of bigger risks vs DCS. Ideally, we would all continue to dive the plan but circumstances may change.

As for gas emergencies, I had to share 40CF of my 120CF of bailout with 2 different divers on deco recently. If I needed to bailout, I would have had barely enough gas and would have used GF99 to get up - especially if I had a CO2 hit also!! Perfect planning with contingencies is a pipe dream. Even NASA cannot do it. Plans should work almost every time but there are situations where one needs to understand all options to them. With NASA, Sorb, duct tape and the LEM comes to mind. With a diver having a serious enough emergency, GF99 or other GF settings are a valid option.

Where our bodies are on the M-Value line - Who knows. But as you encounter in your medical field and me in my engineering, it is a starting point, a good baseline. I may be able to 'cross' it without issue. I may be far away from it and get a DCS hit. GF 30/85 my not prevent a DCS hit today. GF 110/110 (no it does not exist) might not case a DCS hit.... In an emergency, I will use it as a trade off point. BTW, many recreational computers use equivalent of 99/99 so divers are on the M-Value line a lot!

A flight example might be:
I can imagine flying a GA airplane IFR in IMC with a flight plan and lost radios. I do a missed approach at my first airport and am flying to my alternate airport. Along I go VMC and see a different airport. Believe me, my plan is going out the window and I will land there.

 

[kensuf]

RyanT - What is do you consider your required deco? Is it determined by a GF of 20/70, 30/85, 40/90, something different?? Why is 99/99 not the required deco after all it is the true M-Value line? I use a GF of 30/85. Everyone else does too right? It must be the only one out there..

I think it is proper to say that the 'required deco' is 99/99 for Buhlmann. The GFs are a 'conservative' margin to be determined individually. Why, in an extreme situation, am I going to not take the appropriate risk I decide to get out of the water as quick as I am willing to do? Maybe for some it is 99/99 while others it is 30/85....

Quite simply, the required deco is what's required to get out without being bent. That may vary on your own unique physiology, condition of the day, activity on the dive, profile, gases chosen etc.

99/99 may work for you, it doesn't work for me.

 

[Remy B.]

That is a poor choice of gas to carry. I could not stand up with all those backgas cylinders, but I would not get in with so little deco gas for that dive.

20 minutes late at 60m on OC is very likely dead. You are finding that the sort of dead with this configuration is not enough deco gas. You might as well plan for dead due to being out of back gas while stuck in the wreck and save your back carrying all those cylinders which will not save you.

As has been said above, gas planning with two deco gases is not a simple extension on a single deco gas dive. It is fairly subtle and needs to be discussed with someone that does it for the sort of dives you want to do.

I dive with carbon bottles Ken, you don't know what are you talking about, the tanks are a lot lighter and smaller, I guess you are not familiar with the metric readings, it is enough gas, with 30min run and I can afford 20min over run and still complete Deco almost in two algorithms, and you say I don't have enough gas, but at the same time you will not enter the water with that many weight I can understand in the USA and ASIA tanks configurations here in the EU the carbon tanks are common and get away with all that.

What is wrong to start flushing deeper with 50%O2 ?

 

[Remy B.]

Much of the OPs line of thinking illustrates significant inexperience relative to the dive level being debated (and God forbid, attempted!).

Yes I don't have experience, I just don't put 1000-3000-5000 dives below my picture, at least I'm honest.
I don't have my trimix training yet that will take time, and I'm lacking my own gear to be in that position of 30@60, but I can conform my self with 30@45 and keep repeating anything from there up.

I've assumed his questions were hypothetical. 50-99 dives (as stated) is nowhere near enough learning and developmental time to be competent for trimix deep diving. Even assuming great training and diligent practice thereafter (which is shockingly rare in tech divers nowadays...)

Still learning, at least here I can see of what not to do and what are not good ideas, and ask more questions and think in alternatives that I had not considered.

Everybody has his own ways to count his dives, Since my AOW that was short after my OW, I don't count anything that is not deeper than 6m and shorter than 30min, good for the divers that splash in the water for 20min or less and count them as a dives, everybody his free to count as they wish, they will have their reasons, I only have 92 dives the way I count them, I only will consider me an apprentice when I get 500.

This comments above I know are for me, and below are general as are my answers.

Tech cards are handed out like candy nowadays. An over-ambitious, impatient, diver can always find some unethical tech instructor who'll empower them with junk c-cards for a quick buck.

I agree, they are out there for what I have seen for Rec diving, can't comment on the Tec diving side, but between you instructors you know who is who, but the agencies had set their requirements, I agree they are low, 5 or 6 dives for it, 50 dives for this, 100 for that, etc, etc, but all of you followed so it starts and ends in the same place, I bed you are handing OW's after 6 dives as well, does that diver really knows how to dive, NO he really doesn't, he just did what you told him to do, that does mean absolutely nothing, if you think he does, you are full of shaiit and I know you are not, but if the instructors don't hand over that OW card even if that person did what the book said had to complete, because in reality 5 or 6 dives aint shaiit , then there will be a shaiit load of less dives schools out there, that is not happening because you can't fight the system even that you know it is not correct because you live from it.

Current deco technology also goes a long way to furthering delusions of competency. Download a copy of multi-deco and everyone becomes an instant deco expert. Strap on a Shearwater and the sky (or rather, the abyss) is your limit.

I will trust more anything that has been tried than my self making guffy calculations that I can get wrong.

So we better don't ask question and opinions ?, great solution, Let a blind cross the highway by his own even if he ask how will you do it, bummer. Ego is strong in the Experts, but I will keep asking it doesn't bother me, it appears it does to others, to bad.

Welcome to the era of 'junk tech' and the 'insta-expert'

Be humble, take your self back in time and go thru the dump questions and wrong ideas you had when you started back in the days.

 

[RyanT]

I don't count anything that is not deeper than 6m and shorter than 30min, good for the divers that splash in the water for 20min or less and count them as a dives,

This seems very strange. Granted, 6 m is pretty shallow, but not counting any dive less than 30 min? I don't understand. I've done plenty of short, solo deco dives in the 35-50m range that had run times of just under 30 minutes. I gained a huge wealth of experience from those dives. Of course YMMV, but it seems to me that most people can learn and gain experience even from relatively short dives.