gas switch: backgas? move bottles?

[kwinter]

To those who always look for an opportunity to jump on someone, I will restate my case. No, I'm not really worried about ongassing for the minute or so it would take. But I also don't see any reason to go through 2 gas switches instead of one. Why add the complexity, no matter how minor? As for O2 toxicity, that's why I don't use 100% for deco. 80% gives you almost as short a deco schedule, is almost as efficient, and reduces O2 loading. I rarely do any OC deco diving anymore, but I use the same philosophy of limiting O2 exposure. AJ- if you really think that one minute of back gas makes that big a difference, be my guest. But stop spewing your crap about always offgassing when you haven't taken into account what mix there is and what the pressure gradient is. And if you think one extra minute at 1.4 is more dangerous than using 1.6 for deco, then leave me out of it. I guaranty I can come up with mixes that I've used at Eagles Nest where I would be ongassing helium if I switched to backgas at the log. I think I'm good enough at stowing hoses to not need a crutch. I see no harm in switching from middle gas to rich gas.


Please pardon any typos. Sent from my iPhone using Tapatalk

 

[PfcAJ]

Go nuts dude. I don't care what you do, but I sure as hell wouldn't dive with you.

Having two hoses out increases complexity when compared to putting one completely away then taking the time to do a proper switch with only one deco reg deployed.

I also dont don't break for "one minute" btw, and where is the po2 a 1.4 exactly? Sense. You're not making it.

 

[jadairiii]

..... As for O2 toxicity, that's why I don't use 100% for deco. 80% gives you almost . ....

1990 called....

 

[Dr. Lecter]

1990 called....

Aww, maybe you'll post an outdated, unsourced, and largely fallacious list of 10 wrong ideas about O2 and deco, "George."

 

[PfcAJ]

Aww, maybe you'll post an outdated, unsourced, and largely fallacious list of 10 wrong ideas about O2 and deco, "George."

Hard to argue with success, however.

 

[jadairiii]

Aww, maybe you'll post an outdated, unsourced, and largely fallacious list of 10 wrong ideas about O2 and deco, "George."

Actually I would like to see anyone of the "experts" do a numbered list of how/why 80% is safer/more efficient than 100% O2. It would be easier for me than playing "whack a mole". Then I (or anyone else) could go down the list and explain in detail why each one is wrong.

 

[Makhno]

Thanks for your replies, everyone.


Sorry, I thought my questions were clear from the title I gave to the original post and from the blog I quoted. I now think that my questions weren't clear enough. They led to some interesting discussion, but I am still left wondering about my original questions. Let me try again.



Suppose that the blog I quoted didn't say this:

. . . we prefer to switch directly to the second deco gas as switching to back gas during decompression is problematic with regard to DCS risk on deeper trimix dives.

Just ignore that part of the quote, as it isn't needed.

Suppose further that the deco gases I'll use will be EAN50 (with a switch at 21m) and O2 (with a switch at 6m).

Suppose also that I don't need a break from high partial pressure of oxygen before the 6m switch to O2.



Assuming all of those suppositions as given, why should I switch from EAN50 to backgas instead of switching directly from EAN50 to O2? And why should I go about clipping and unclipping deco bottles just so I can put the O2 on top before the 6m stop?


I know there must be some well-considered answers to those questions, but I don't remember having heard them.

Thanks in advance, and let's try to keep this a courteous discussion, please.

 

[Dr. Lecter]

Hard to argue with success, however.

Sucessfully skinning the cat one way is hardly proof of their being only one way to skin a cat.

 

[PfcAJ]

Thanks for your replies, everyone.


Sorry, I thought my questions were clear from the title I gave to the original post and from the blog I quoted. I now think that my questions weren't clear enough. They led to some interesting discussion, but I am still left wondering about my original questions. Let me try again.



Suppose that the blog I quoted didn't say this: Just ignore that part of the quote, as it isn't needed.

Suppose further that the deco gases I'll use will be EAN50 (with a switch at 21m) and O2 (with a switch at 6m).

Suppose also that I don't need a break from high partial pressure of oxygen before the 6m switch to O2.



Assuming all of those suppositions as given, why should I switch from EAN50 to backgas instead of switching directly from EAN50 to O2? And why should I go about clipping and unclipping deco bottles just so I can put the O2 on top before the 6m stop?


I know there must be some well-considered answers to those questions, but I don't remember having heard them.

Thanks in advance, and let's try to keep this a courteous discussion, please.

switching to backgas between deco gases helps minimize the potential confusion and tangled up hoses. I think the biggest reason though is the o2 break.

I dont see any reason to move the 6m bottle on top. Top or bottom, it
doesnt matter at all and gas switching based on position of tanks is bad news.

 

[mathauck0814]

The OP cited "T50/Extended Range" dives. ~165fsw you shouldn't need two deco gases anyway, moot point. I go from gas to gas, don't bother switching to back gas. By the time you're doing dives where you have complex gas switches you should be on CCR anyway (and if you find yourself on open circuit you've bailed out and have bigger problems).