How rare is extended range trimix?

[drice]

This, too, violates what you're taught in a normoxic trimix class. No well trained normixic diver would agree to a dive profile where they have to ascend 230ft before their first deco gas. The minimum gas requirements for a dive like that would be absurd. If you don't believe me, run a profile for that dive where the 100ft bottle fails and let me know how that works out.

I'll ask again, can you pick proper gases and still be at risk for ICD?

I completely agree. It's not a set of gasses I would ever pick for multiple reasons, but you asked for one that kept your END under 100 and so that's what I gave you at 1a when I couldn't sleep. But fine, I'll play one more time. Let's say you added another deco gas to switch to at around 200'; same other gasses. Off the top of my head, lets just say 18/45 (this will still keep your END under 100' and you can switch to it as early as 260'). What happens if you lose that gas when making your switch at 200'? Did you take in account ibcd risk in the event of lost gas during your planning/gas selection? I sure hope so.

Maybe you're right and maybe you did learn everything you need to know, and that 150' is just the same for you as 330'. Great, fantastic and good for you. Go ahead, dive to 330' heck dive to 500' treating it just like a 150' dive. I'm quite confident that you'll be just fine 99% of the time while you treat it like a 150' dive. I choose to dive with those that can understand the gravity of a deeper dive, and that the complexity increases as the depth does. Someone who isn't going to forgo training on behalf of what to be honest appears as arrogance.


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---------- Post added April 15th, 2015 at 09:24 AM ----------

Ibcd is a real thing, for sure. But if you pick smrt gases isn't not. It was briefly discussed in my t2 class, but the gue standard gases really make it a non issue.

Im in sure you can contrive some sort of gas plan that would put you at risk for it, sure.

Yeah but don't you want to know the "why" instead of just saying "well I'm just going to use these gasses because someone else told me they're the right ones"? What if you end up in a situation for some reason or another where you don't have access to those "perfect" gasses?


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[LiteHedded]

arguing that a 330' dive is the same as a shallow 150' dive and requires no more special consideration is a bit silly

 

[ucfdiver]

I completely agree. It's not a set of gasses I would ever pick for multiple reasons, but you asked for one that kept your END under 100 and so that's what I gave you at 1a when I couldn't sleep. But fine, I'll play one more time. Let's say you added another deco gas to switch to at around 200'; same other gasses. Off the top of my head, lets just say 18/45 (this will still keep your END under 100' and you can switch to it as early as 260'). What happens if you lose that gas when making your switch at 200'? Did you take in account ibcd risk in the event of lost gas during your planning/gas selection? I sure hope so.

Maybe you're right and maybe you did learn everything you need to know, and that 150' is just the same for you as 330'. Great, fantastic and good for you. Go ahead, dive to 330' heck dive to 500' treating it just like a 150' dive. I'm quite confident that you'll be just fine 99% of the time while you treat it like a 150' dive. I choose to dive with those that can understand the gravity of a deeper dive, and that the complexity increases as the depth does. Someone who isn't going to forgo training on behalf of what to be honest appears as arrogance.


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Why would losing a deco gas around a 200ft stop cause ICD issues? What I was taught in Normoxic trimix was that you 50% extra deco gas than required, so that if your buddy loses a deco gas you can share theirs. For instance, if you had 40min deco, you'd add 50% to that (now 60min deco) and then each do half of it on the next deeper gas (backgas if it's your first stop) and half on deco gas, so 30 min on bottle and 30min on bg.

I'm not trying to be funny, I just don't think that I'm understanding you right or something.

 

[PfcAJ]

I completely agree. It's not a set of gasses I would ever pick for multiple reasons, but you asked for one that kept your END under 100 and so that's what I gave you at 1a when I couldn't sleep. But fine, I'll play one more time. Let's say you added another deco gas to switch to at around 200'; same other gasses. Off the top of my head, lets just say 18/45 (this will still keep your END under 100' and you can switch to it as early as 260'). What happens if you lose that gas when making your switch at 200'? Did you take in account ibcd risk in the event of lost gas during your planning/gas selection? I sure hope so.

Maybe you're right and maybe you did learn everything you need to know, and that 150' is just the same for you as 330'. Great, fantastic and good for you. Go ahead, dive to 330' heck dive to 500' treating it just like a 150' dive. I'm quite confident that you'll be just fine 99% of the time while you treat it like a 150' dive. I choose to dive with those that can understand the gravity of a deeper dive, and that the complexity increases as the depth does. Someone who isn't going to forgo training on behalf of what to be honest appears as arrogance.


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---------- Post added April 15th, 2015 at 09:24 AM ----------



Yeah but don't you want to know the "why" instead of just saying "well I'm just going to use these gasses because someone else told me they're the right ones"? What if you end up in a situation for some reason or another where you don't have access to those "perfect" gasses?


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i agree with you, it needs to be taught.

My solution for if I don't have the gases I need? Stay on da dock.

 

[Makhno]

To the OP: a 100m/330" dive is rare but not that rare, because it is the pinnacle dive for most folks who take an advanced trimix or hypoxic trimix course. However, those are usually dives with short bottom times. A dive to 100m/330" with a bottom time of more than 10-15 minutes is quite rare for open circuit divers, because of the gas volumes needed and the expense involved in using that much helium. The rebreather divers I know also don't spend a lot of time at those depths because of (1) the bailout gas requirements and (2) the amount of hang time required to decompress from those kinds of dives.

A previous poster said that a lot of divers will do only 1 dive to that depth; that probably describes me. I've done exactly 1 dive to 100m (during training) and don't plan on another. The only reason I might do another 100m dive would be to touch a very rarely-visited, special piece piece of history, like maybe one of the Battle of Leyte wrecks which lie at about 100msw in Ormoc Bay.

There are so many wrecks, reefs and caves at shallower, safer, and cheaper depths that I just don't see much reason to dive so deep.

 

[PfcAJ]

Here's my take on 150 vs 300.

the principles are the same. The margins for error are not. The skills for a 300ft dive are more than a 150ft dive, but share many attributes.

I think they are different enough to warrant a class.

 

[ucfdiver]

Here's my take on 150 vs 300.

the principles are the same. The margins for error are not. The skills for a 300ft dive are more than a 150ft dive, but share many attributes.

I think they are different enough to warrant a class.

...and that's a point I won't argue. But to say that the dive planning is completely different makes me think that the expectation is that a normoxic class doesn't cover the basics.

 

[LiteHedded]

...and that's a point I won't argue. But to say that the dive planning is completely different makes me think that the expectation is that a normoxic class doesn't cover the basics.

the dive planning IS different though.
your trimix class included a hypoxic gas with multiple deco gases, so much of this likely doesn't apply to you.

 

[drice]

Why would losing a deco gas around a 200ft stop cause ICD issues? What I was taught in Normoxic trimix was that you 50% extra deco gas than required, so that if your buddy loses a deco gas you can share theirs. For instance, if you had 40min deco, you'd add 50% to that (now 60min deco) and then each do half of it on the next deeper gas (backgas if it's your first stop) and half on deco gas, so 30 min on bottle and 30min on bg.

I'm not trying to be funny, I just don't think that I'm understanding you right or something.

Let me elaborate a bit more now that I'm not responding via a phone. If you were diving the gasses that I mentioned last night/this morning - 12/65 for your bottom gas, 18/45, EANx36 and O2. These aren't the prescribed "perfect" gasses, but they meet the requirements that you've mentioned (since after all, you asked if I could give you a set of gasses that could pose an issue). If during your switch to your first deco gas 18/45 you have a lost gas scenario, you're now back to the scenario that I posted last night - trying to switch from your back gas to EANx36 at 100'. If you were to try to make this switch you have a risk of an ibcd hit. So, did you plan for that? In your planning did you look at switch and realize that it has risk? Did you decide to swap out the EANx36 for a different (most likely trimix) gas? If not, in your planning did you change your plan so that you're switching to the EANx36 later (shallower than 100') and add add some additional stops on your back gas to allow you to off-gas a bit more? You still will run a risk that you'd have to decide if you're comfortable with, but it would be less of one.


---------- Post added April 15th, 2015 at 11:40 AM ----------

i agree with you, it needs to be taught.

My solution for if I don't have the gases I need? Stay on da dock.

And that's definitely a very safe solution and not one that I ever would criticize you for making. I like knowing that if for some reason the gasses turn out to not be exactly what I had initially planned that I can still take what I know to (a) determine if a safe dive with the same goals can be made with those gasses and (b) create and execute a dive plan that is still safe.

 

[ucfdiver]

Let me elaborate a bit more now that I'm not responding via a phone. If you were diving the gasses that I mentioned last night/this morning - 12/65 for your bottom gas, 18/45, EANx36 and O2. These aren't the prescribed "perfect" gasses, but they meet the requirements that you've mentioned (since after all, you asked if I could give you a set of gasses that could pose an issue). If during your switch to your first deco gas 18/45 you have a lost gas scenario, you're now back to the scenario that I posted last night - trying to switch from your back gas to EANx36 at 100'. If you were to try to make this switch you have a risk of an ibcd hit. So, did you plan for that? In your planning did you look at switch and realize that it has risk? Did you decide to swap out the EANx36 for a different (most likely trimix) gas? If not, in your planning did you change your plan so that you're switching to the EANx36 later (shallower than 100') and add add some additional stops on your back gas to allow you to off-gas a bit more? You still will run a risk that you'd have to decide if you're comfortable with, but it would be less of one.

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.