[Johan]

This forum is to discuss my article "How to dive deep" ( http://www.rebreatherworld.com/gener...-deep-50m.html ).

[jradomski]

Quote: (Originally Posted by Johan)

This forum is to discuss my article "How to dive deep" ( http://www.rebreatherworld.com/gener...-deep-50m.html ).

I don;t agree on your choice of bailout gases.. Choosing a lean mix and Oxygen gives you the least amount of options.. this raises the amount of a deep mix you have to carry..

INMHO carrying a deep mix and 50% is a better choice.. all along the "bailout" deco curve (time) you are ahead of the curve of the lean/02 curve. If your bailing because of an electronics problem, you still effectively have the use of oxygen when shallow...

Using lean and 50% allows you to closer match the size of your required bailout talks.. If team planning with 2 people, I would still do a lean and a 50% mix, if I'm planning with a tem of 3, then one team member will car o2 instead of 50%..

We are talking about a BAILOUT plan, not a normal decompression schedule, The goal should be what can I carry to give me the best chance of surviving .. If you run out of deep gas before you reach a depth you can use oxygen you can be in really bad shape and getting to your o2 stop may not help... If I carry 50% I know its much less likely I am ghoing to have an issue with the deep mix, I can get on 50% at a reasonable depth, and if I run out of gas I am much further along on my decompression at the same point in time..

Run your necessary gas calcs.. for even a 60m dive using lean and o2 requires you to carry an 80 for deep so you might as wall balance that with an 80 of o2, but if I carry 50% I can usualy get away with team members carrying 40s instead sionce the gas required is more balanced between the 2 mixes..

[NickK]

Simple and informative. Well done Johan!

Thanks,
Nick

[Mark Chase]

Obviously a lot of work went into this article and your efforts are to be applauded. However I would have a serious rethink about using air as a bailout gas for a trimix dive. Doing a 70m dive on something like 18/45 diluent and getting a problem so bad that bailout is required at depth I would not like to be hitting the narcosis of air and I don't fancy the DCI risk of the nitrogen spike either.

Personally I would have something like 21/35 as bailout for a straightforward clear ascent dive and i would use 18/45 for an overhead penetration dive or back to shot dive.

On a 70m dive we would have 80% staged on the deco station and a drop tank on the boat. As a result we would carry a 10 of bottom mix and a 10 of intermediate deco ranging from 32/30 up to 50% depending on the deco commitment. 50% is a good gas but often you will exceeded the capacity of the 10ltr on the deep mix unless you can switch deeper than 21m.

No deco station? then i would carry a third gas or operate team bailout.

ATB

Mark Chase

[jhaaja]

Quote: (Originally Posted by Mark Chase)

Obviously a lot of work went into this article and your efforts are to be applauded. However I would have a serious rethink about using air as a bailout gas for a trimix dive. Doing a 70m dive on something like 18/45 diluent and getting a problem so bad that bailout is required at depth I would not like to be hitting the narcosis of air and I don't fancy the DCI risk of the nitrogen spike either.

Personally I would have something like 21/35 as bailout for a straightforward clear ascent dive and i would use 18/45 for an overhead penetration dive or back to shot dive.

On a 70m dive we would have 80% staged on the deco station and a drop tank on the boat. As a result we would carry a 10 of bottom mix and a 10 of intermediate deco ranging from 32/30 up to 50% depending on the deco commitment. 50% is a good gas but often you will exceeded the capacity of the 10ltr on the deep mix unless you can switch deeper than 21m.

No deco station? then i would carry a third gas or operate team bailout.

ATB

Mark Chase

I would second this. It sounds a really stupid thing to change to air from a good trimix. The narcosis will hit you bad and you are allready excited because of the shit flying around because of the bail-out.

I like to have nearly the same amount of helium in my deep bail-out mix.

JH

[schford]

Great article - loads of work obviously went in to it :-) I too am with the no no on air as a bailout at depth though....

[ScubaDadMiami]

I enjoyed reading your article. Thanks for writing it.

Leaving the bailout gas issue aside, I would like to point out that my locality has some of the strongest prevailing currents on the globe. So, for that reason, our protocol is to shoot a lift bag as soon as one clears the wreck rather than doing so later in the ascent. This way, the dive boat can keep track of the divers drifting while ascending and doing decompression stops.

Nice job, and thank you.

[Johan]

Thanks for all your excellent comments! It sounds like it now is time to update the article based on the feedback. I'm planning to add a section called "Bailout configuration". This is such a big topic that I intend to narrow it down to configurations that one can carry by one self. That means that team bail-out, deco stations, staged bottles and other fun things will be left for the next article.

It appears that factors such as availability and price of helium, quality of filling station, type of analyzers and the amount of mixing efforts has an impact on gas choice. It seems natural to boil it down to three choices (or combinations of them)

1. No mixing
This is what currently is in the article. The pros and cons seem to be:
+ No mixing needed
+ No extra helium needed (cheap)
- Narcosis will hit you hard when you want it the least
- You have to get up all the way to 6m before your oxygen becomes usable

2. Simple mixing
This option is to use mixes based on air which means Nitrox as rich mix and HeliAir as lean mix. A natural choice seem to be to use Nitrox 50 and HeliAir with as little helium as possible that still keeps you away from narcosis. The pros and cons seem to be:
+ Simple to mix
+ Can be analyzed with O2 analyzer
+ Rich mix can be used twice as deep as pure oxygen
- More mixing and analyzing efforts than option 1

3. Advanced mixing
This is custom trimix combinations. In the most extreme case this would mean using only Heliox such as 50/50 as rich and say 15/85 as lean. In reality one would probably allow more deco obligation in exchange for less need of helium.
+ Minimal deco obligation
- Most expensive option
- More mixing effort than option 2
- Needs helium analyzer to analyze if not heliox is used

What do you guys think?

[andibk]

Johan,
If I am not mistaken those pictures you have on the site where off of Lung Tong's boat out of Samae San Thailand. Am I right???

andibk

[Johan]

andibk,
Good spot and you are quite right that it is outside Samae San. It was on the only boat that took tech divers out so I think it was Lung Tong's even though my memory is a bit vague about the owner's name since I flushed the brain with Singha after the dive