How rare is extended range trimix?

[drice]

Wtf would you use 15/55 as a travel gas? The entire point is to have something normoxic at the surface...

The point of a travel gas is not to have something normoxic on the surface but to be able to maintain conscientiousness, which only requires a ppO2 of .16 ata. 15/55 has a ppO2 of .16 at 2' and is breathable JUST under the surface so not nearly as outrageous as you make it sound. One solution if the environment allows for it: reg out of mouth on the surface, take a breath, descend a few feet, put reg. Or just use a gas with 16% which can sustain conscientiousness on the surface =)

 

[LiteHedded]

The point of a travel gas is not to have something normoxic on the surface but to be able to maintain conscientiousness, which only requires a ppO2 of .16 ata. 15/55 has a ppO2 of .16 at 2' and is breathable JUST under the surface so not nearly as outrageous as you make it sound. One solution if the environment allows for it: reg out of mouth on the surface, take a breath, descend a few feet, put reg. Or just use a gas with 16% which can sustain conscientiousness on the surface =)

people get a little too loosey goose with that 15/55 gas. i go in on my deepest deco gas when i have 15/55 on my back. i've heard plenty of stories and dont mess around with hypoxic gases on the surface even if it's 15/55

 

[ucfdiver]

The point of a travel gas is not to have something normoxic on the surface but to be able to maintain conscientiousness, which only requires a ppO2 of .16 ata. 15/55 has a ppO2 of .16 at 2' and is breathable JUST under the surface so not nearly as outrageous as you make it sound. One solution if the environment allows for it: reg out of mouth on the surface, take a breath, descend a few feet, put reg. Or just use a gas with 16% which can sustain conscientiousness on the surface =)

I think you're missing what he's saying. Why would you use 15/55 to travel on instead of a 70/120ftbottle or something? Now you're lugging an extra tank around that is only useful during a brief period of the dive, as it's toxic at the depths being discussed and isn't all that efficient for decompression compared to gases you'd already have.

If you research aviation and mountain climbing accidents I think you'll see that the PPo2's you're describing are not a fantastic scenario for someone who's a bit excited or reaching a panic stage. Certainly not the gas I would want to rely on.

 

[drice]

I think I'm still missing something. Sure, you would have spent a bit of time on back gas before switching to your 100ft gas, but in no way are you switching to nitrox after being on 10/70 for an hour. You would have been sharing the deco gas you planned on using 50% of that previous deco step. Are you saying you'd be worried about ICD having spent 50/50 time with 10/70 (whatever bottom gas) and 18/45? It almost seems like, to me, that you're planning to be on back gas 100% of the time and not share your buddy's deco gas. If that's the case, I think we were just taught to plan dives differently.

That's an option and if it was available you bet I'd absolutely be borrowing my buddies left over gas. BUT I was also taught to plan for worst cases. What if something goes wrong? What if we get separated? I want to have planned my dive knowing that I can still execute my dive safely.

 

[LiteHedded]

That's an option and if it was available you bet I'd absolutely be borrowing my buddies left over gas. BUT I was also taught to plan for worst cases. What if something goes wrong? What if we get separated? I want to have planned my dive knowing that I can still execute my dive safely.

you're talking about a team separation AND a lost deco gas at this point.
that's one heck of a dive you're planning for. you should be carrying two of your deepest deco gases if that's the case

 

[ucfdiver]

That's an option and if it was available you bet I'd absolutely be borrowing my buddies left over gas. BUT I was also taught to plan for worst cases. What if something goes wrong? What if we get separated? I want to have planned my dive knowing that I can still execute my dive safely.

If you needed only 50cu ft of 120 gas for your planned deco you'd need 100cu ft of bottom gas or more (realistically more). At a certain point, planning to lose deco gas and your buddy results in planning yourself out of a dive.

 

[PfcAJ]

It can sustain consciousness but it CANNOT sustain a high activity workload. You will get winded and have a real bad time if you need to do something even a bit strenuous on the surface.

So no, 15% is not a good choice as a "travel gas". Get out of the books and get into real life, dude.

 

[drice]

I think you're missing what he's saying. Why would you use 15/55 to travel on instead of a 70/120ftbottle or something? Now you're lugging an extra tank around that is only useful during a brief period of the dive, as it's toxic at the depths being discussed and isn't all that efficient for decompression compared to gases you'd already have.

If you research aviation and mountain climbing accidents I think you'll see that the PPo2's you're describing are not a fantastic scenario for someone who's a bit excited or reaching a panic stage. Certainly not the gas I would want to rely on.

Fair enough and I see what he was actually saying now. No, I wouldn't lug something like that as a travel gas JUST to have it as a travel gas. I was just clarifying the purpose of a travel gas which is to be able to maintain consciousness not necessarily be normoxic. If you were using 15/55 as a bottom gas and the conditions in no way required you to need to have your reg in your mouth on the surface, one completely acceptable option to me would be to (keeping the reg out of your mouth) take a breath of outside air and descend. Put the regulator in your mouth at 10' and you're already at a ppO2 of .199 (pretty close to the same ppO2 as air on the surface). Again that solution is dependent on conditions.

 

[LiteHedded]

Fair enough and I see what he was actually saying now. No, I wouldn't lug something like that as a travel gas JUST to have it as a travel gas. I was just clarifying the purpose of a travel gas which is to be able to maintain consciousness not necessarily be normoxic. If you were using 15/55 as a bottom gas and the conditions in no way required you to need to have your reg in your mouth on the surface, one completely acceptable option to me would be to (keeping the reg out of your mouth) take a breath of outside air and descend. Put the regulator in your mouth at 10' and you're already at a ppO2 of .199 (pretty close to the same ppO2 as air on the surface). Again that solution is dependent on conditions.

agreed. it's a big boy decision. and one best made by people who have had hypoxic training

 

[drice]

you're talking about a team separation AND a lost deco gas at this point.
that's one heck of a dive you're planning for. you should be carrying two of your deepest deco gases if that's the case

Or you could make gas choices that would allow you to switch to your 2nd deco gas and not have a high risk of an ibcd hit. He asked for an example, I provided one. He asked for another, I provided that. I'm not going to continue to debate the fact that planning a 330' is a bit more involved than planning a 150' dive. There are more risks involved and more aspects that need to be accounted for, ibcd being one of them.