triox vs. trimix?

[Miss Roxy Chablis]

The problem with teaching someone a deco / lost deco strategy that involves a buddy's deco gas is that if the buddy's lost you or vice versa then it becomes useless I guess. With GUE that isn't an issue but I can understand the problem with other agencies wanting their divers to be self contained and self sufficient. Most also seem to recommend a reserve of double your deco gas for similar reasons IIRC.

You simply won't have enough backgas under almost any circumstances to deco out by doubling up your stops IMO.

I use 25/25 as an ocean gas between 30-40m. Beyond that it's too hot on the PPO2 for me and 21/35 kicks in - but I understand others feeling differently. My own view is that when I can choose a gas that doesn't push the working PPO2 beyond 1.2 - why bother choosing one that does? 5 minutes extra deco if you believe the tables / software (I don't) is a tiny price to pay for reducing the risk of oxtox under water IMO. Many, many benefits to keeping the O2 down and the He up - cost unfortunately not being one of them

25/25 is a great gas for 30-40m. It's not stupidly expensive if you get remixes and with getting on for half the N2 in air - it makes a big difference to how you feel during and after the dive in my experience.

HTH

[Steve S]

Originally Posted by Howard Payne

The problem with teaching someone a deco / lost deco strategy that involves a buddy's deco gas is that if the buddy's lost you or vice versa then it becomes useless I guess. With GUE that isn't an issue but I can understand the problem with other agencies wanting their divers to be self contained and self sufficient. Most also seem to recommend a reserve of double your deco gas for similar reasons IIRC.

What would you do if you were diving as a buddy pair and had become separated from your buddy and lost your own deco gas?

Safe diving,
Steve

P.S. I know it is a double failure

[nickb]

Originally Posted by Howard Payne

...My own view is that when I can choose a gas that doesn't push the working PPO2 beyond 1.2 - why bother choosing one that does?...

Are you guys operating some sort of forced-labour chain gang down there?

There's hundreds, probably thousands, of people diving 32% to 35m using BSAC's max of 1.44 PPO2. I'm not reading about these guys ox-toxing on a regular basis.

[Clare Gledhill]

Originally Posted by nickb

Are you guys operating some sort of forced-labour chain gang down there?

There's hundreds, probably thousands, of people diving 32% to 35m using BSAC's max of 1.44 PPO2. I'm not reading about these guys ox-toxing on a regular basis.

We dive a maximum working partial pressure of oxygen of 1.4 so I have no argument with you on that score Nick. However, as I am sure you know, sometimes the wreck is deeper than we plan for so having a margin for error is no bad thing. I'll plan to be a bit leaner on the O2 so if I end up a little deeper for part of the dive it is no big deal. My MOD is still 1.4 but it is there for contingency not a planned exposure.

Longer dives however, it becomes more of a problem. If we add up the risks of getting an o2 hit they include....

Cold - well that often happens on UK dives.
Higher partial pressures of Oxygen - well yes.
Depth - well that too.
Work - well we never know how hard we are likely to have to work to the bottom in current are we?
Physical stress - tired, dehydration... not that I've ever seen any of that on a dive trip...
Oh - and Co2 retention is thought to play a part. Which is one really good reason why helium helps in this range.
And time. A higher exposure won;t hurt you for a few minutes but when dives in the 30 metre range go over 2.5 hours (which I have done several times) you get that clock ticking.

If I can wind back my exposure a little, back off from the limits a bit I just feel I'm loading the gun with a little less ammunition. Remember the pattern Donald found when studying O2 toxicity in divers?

None at all - like a shot gun had sprayed over the graph. Can't say I see a reason for pushing close to the established limits just to save a few minutes of deco especially as I probably wouldn't change my profiles anyway.

[Miss Roxy Chablis]

I totally accept its a line in the sand.

By a similar argument you could actually make rec tables like the PADI RDP way less conservative because a miniscule number of people get bent using them.

There was a time when a PPO2 of 2.0 was not considered excessive.

Its just personal choice. I'm not looking at someone who chooses to dive to 1.4 on a tech dive like they're a kiddy fiddler - I just see it as a a tiny risk that I can remove without any real consequence?

The risks are miniscule but the consequences are huge.

[Brian of Aquanauts]

Originally Posted by Steve S

What would you do if you were diving as a buddy pair and had become separated from your buddy and lost your own deco gas?

Safe diving,
Steve

P.S. I know it is a double failure

having decided that i'm totally useless as a diver and really ought to go back to diving in 20m of water until I can get my basic dive skills back in order, i'd now have to suddenly get my shit together and get myself out of that real idiotic position. Although if i were that bad a diver i doubt I'd have this skill either.

these are the choices:

Fix the rig so it's no longer "lost"
double all the stops on back gas and
send up an SMB with note attached for one of the support divers or other teams to bring spare gas down to me at 6m
Complete all stops (doubled) to 6m, do what I could at 6. Get out and keep monitoring for a sign of a bend. At least the chance of a CNS bend is low as the fast tissues should all be clear. Take ibuprofen, rest and breathe O2.

However your single deco gas loss isn't really so bad, as most of gas diving that I'm doing involves 2 or 3 deco gases, so I have lots of trained strategies that work using the reserve deco gases that I carry in the other bottles.

Our single deco gas to 45m example is actually possible to deco out on backgas quite easily by doubling stops, and reducing the conservatism that we planned in with our 30/85 gradient factors. Combine this with the above choices and you have lots of ways out of the problem if you can keep your wits about you.

[milldog]

FFS were off again



Ps my cats blacker than yours

Graham

[Miss Roxy Chablis]

PMSL Do I get a Lance? If I did - I'd have lanced you a long time ago Graham

[Brian of Aquanauts]

Originally Posted by milldog

FFS were off again



Ps my cats blacker than yours

Graham

I thought you had a Newfoundland Dog?

“An open mind leaves a chance for someone to drop a worthwhile thought in it”

[milldog]

Originally Posted by Howard Payne

PMSL Do I get a Lance? If I did - I'd have lanced you a long time ago Graham

your misses said the last lance you showed her she needed a magnifying glass

Graham