When thirds are not enough....

[Cave Diver]

Going back to an earlier post:
I'm a newbie at this so please be kind:

If the non-breather diver has a catastrophic failure, then he goes on the 40 -- correct? Now that may not be enough gas but ONLY the buddy goes on the 40 since the 'breather diver has no issue.

OTOH, if the 'breather diver has an issue, he goes on the 40 and the OC guy still has full gas.

OTHER THAN 40 may not be enough, I don't see the issue. What am I missing?

OC = 2 x 84 or 168 cft gas. 1/3 = 56 cft of gas. So even if the 84's aren't cave filled, the 40 is 16 cft short of being a full third. If you turned at thirds of the OC diver and had a problem right then, the bailout out bottle is not enough to get either diver back out unless the CCR diver can go to SCR mode.

 

[SuPrBuGmAn]

I've never dived 1/3rds at Peacock, we always had plenty enough gas to make our plans happen, and simply exitted after never getting anywhere near a turn pressure of any sorts.

I dive mainline JB on thirds though.

 

[JahJahwarrior]

Me.

I have not dive 1/3rds at Peacock, Hole-in-the-Wall, Twin, and everything I've ever done in MX (maybe 40 different systems).

Really? Not even in huge mainline tunnel where you aren't going back too far? You are probably a rarity. Most do as UCFDiver says, using thirds for most dives at Peacock but backing off for some tunnels. I salute you sir for your safety, just remember that being conservative doesn't always save you-- recently had a conversation with UCFDiver and another diver where we discussed how some instructors imply that following all of the guidelines will keep you safe, and it doesn't always. I'm sure you know that, mostly posting that point for those who don't, not trying to imply that you are diving recklessly

There are specific tunnels where I don't dive 1/3rds at Peacock, but for the stuff that isn't tight, I'm fine with 1/3rds. If you want to amuse yourself, search for grand traverse reports, nearly everyone uses 1/3rds to do that. If you read past conversation (as well as an article about it in either nacd/nss journal) people basically admit to diving 1/3rds for that dive fairly often. Then in threads similar to this one, they later post that they drastically back off 1/3rds in no flow.
.

I dive thirds in most tunnels at Peacock. I do recognize that thirds is not conservative enough. I just view the risk as being very low and take it. But, if I go somewhere where I view the risk as growing too high, I back off thirds. I've never hit thirds while diving the Grand Traverse before I reach the other side

 

[rjack321]

Really? Not even in huge mainline tunnel where you aren't going back too far? You are probably a rarity. Most do as UCFDiver says, using thirds for most dives at Peacock but backing off for some tunnels. I salute you sir for your safety, just remember that being conservative doesn't always save you-- recently had a conversation with UCFDiver and another diver where we discussed how some instructors imply that following all of the guidelines will keep you safe, and it doesn't always. I'm sure you know that, mostly posting that point for those who don't, not trying to imply that you are diving recklessly



I dive thirds in most tunnels at Peacock. I do recognize that thirds is not conservative enough. I just view the risk as being very low and take it. But, if I go somewhere where I view the risk as growing too high, I back off thirds. I've never hit thirds while diving the Grand Traverse before I reach the other side

With 2 buddies I have dove 1/3rds in a no or low flow system a few times. That is 2x the reserve gas however. But I rarely have 2 buddies.

Usually its just me and 1 other in which case we dive 1/3rds minus _____ a fudge factor. Typically 200psi in a known system so we turn at 2200 (AL80s, depending on the fill). This would be your proverbial "huge mainline tunnel". Sometimes we just budget for 1/4ths so we're turning at 2300 but this is pretty conservative. Although in brand new-new overheads where I am laying new line I have retreated to 1/6ths.

If my instructor caught me diving 1/3rds with only 1 buddy in MX he'd have my card yanked for stupidity.

I wouldn't say that reserving more gas is in and of itself "safe" but I find it humorous that you think you have to tell me how you're being "just as safe" when you know you are violating the rules. Do you tell yourself that when you skip putting in a primary line too?

 

[LiteHedded]

The only time I'll dive thirds is when I'm diving in a cave. For internet diving, I religiously stick to 1/10ths. I write a post, then delete 9/10ths of it. Posting more than one tenth of what I write runs me into the risk of too much internet penetration also known as caring way too much about the internet and not enough about real life.



(on a serious note, how many people actually dive something more conservative than thirds at Peacock? I mean actually dive it, not just post that you dive it. And I mean full cave divers, not intro divers, even the intro divers that dive thirds because they think they are Big Cool People that are above the guidelines.)

i dive thirds there mostly

 

[JahJahwarrior]

I wouldn't say that reserving more gas is in and of itself "safe" but I find it humorous that you think you have to tell me how you're being "just as safe" when you know you are violating the rules. Do you tell yourself that when you skip putting in a primary line too?

You are going to have to help me out here...What exactly did I break?

1. They are guidelines, not rules
2. I don't break thirds.
3. I said you are being safer than other people and applauded you for it. I did not say "just as safe"
4. I put in a primary line when the cave requires it, using the safe exit standard. At times, there is no guideline required as the cave line runs to open water. At times, a line must be run from the surface, which is even more than the open water standard of some agencies.

 

[rjack321]

Nevermind. Carry-on diving 1/3rds in no flow systems.

 

[BabyDuck]

The esteemed DAN magazine committed this error this month. I forget the exact title of the article but its about deep dive "gas planning".

exactly. i saw red.

and i dive thirds in peacock. getting out somewhere like challenge wouldn't be fun, but is possible. times we've done something 'bigger' than an up & back, we take a stage or buddy bottle. which, as i recall, we've gotten sh!t for, so some of you make up your minds - is thirds reckless, or is having more gas stupid?

 

[JahJahwarrior]

Nevermind. Carry-on diving 1/3rds in no flow systems.

That doesn't break a guideline

Look at it this way: how many people dive Peacock on any given weekend? How many of those people survive? If we took a one weekend sample size, I can prove to you that diving thirds is 100% safe. We have to either pick a weekend with a fatality, or go out to multiple years to show that thirds is unsafe, and then it's not killing a huge percentage of divers. Infact, the last death was an intro diver, so she should have been diving 6ths, right? When was the last death of a diver diving thirds at Peacock, where diving something more conservative like 1/4ths would have probably saved them?

So if I'm doing an easy, mainline dive, I will often dive to thirds. I don't break thirds, and usually turn 50-100 psi early just because I don't trust my gauge. I've already told you that I frequently dive well less than thirds-- my last grand traverse, we went there AND BACK and I believe I was halfway back before I hit thirds.

If you want to tell me that thirds in Peacock, no matter where you are in the system, is not conservative, go for it, we both agree. If you want to tell me that I'm breaking a guideline by diving thirds in some parts of Peacock, then I'll have to admit that we must have different versions of the cave diving manual

I'm not trying to tell people to dive thirds in a low flow system. Divers should always use their own judgement. I'm just doing something a lot of people won't do: being honest about the fact that I don't consider the risk of diving thirds in some parts of Peacock to be excessive. Present, but not excessive.

 

[ucfdiver]

If my instructor caught me diving 1/3rds with only 1 buddy in MX he'd have my card yanked for stupidity.

Richard, if it put's your mind at ease, I've dove 1/3rds in a no flow cave with one of your instructors other students. He didn't fly over here to yank his card

(I've also done dives where we used 50cu ft going in, and left about 270 in reserve with that same diver, under different conditions)