Doubles configuration

[MonkSeal]

Ok, why not have a small SPG on the backup regulator primary? I realize it is an extra hose but wouldn't it provide redundancy and eliminate the "How much gas do I have?" worry if the unthinkable happens? Hmmm...might be a place where that dreaded air integrated dive computer might be handy...

Mike

Your primary SPG is your bottom timer. You know at any moment of the dive how much gas you have by checking time. Comparing what you guess with what real SPG shows keeps you updated. Virtualy you have two SPGs. When failure happens you have pretty good idea of what you have and you can continue to track it by your bottom timer.

 

[MonkSeal]

Let's say I'm in a cave or wreck. Burst disk fails on the left. Isolated doubles. Unknown quantity on the right.

Unknown? In Europe we don't have burst disks so I don't know how much gas you can loose in time needed for shut isolator.

Do I share gas with my (let's say one) buddy or not? Like right now?

I say share now.

AFAIK standard procedure is: isolate, contine to breath long hose, thumb the dive, re-position yourself as a weak diver, try to estimate your gas supplies.

 

[rjack321]

Unknown? In Europe we don't have burst disks so I don't know how much gas you can loose in time needed for shut isolator.

AFAIK standard procedure is: isolate, contine to breath long hose, thumb the dive, re-position yourself as a weak diver, try to estimate your gas supplies.

A heck of alot. Think blown tank neck o-ring, or cracked cross-over threads, bubble city. There's an old study in ADM I think where they cut hoses and loosened burst disks. A cut LP hose drained an AL80 very fast. I'll look for a link.

Anyway, the problem with not sharing when its easy to do so (e.g. on the bottom) is that you may be forced to share when its challenging, inconvenient or more dangerous.

Why leave the diver with a failure to bear the burden of risk when it can be shared? By using a teammate's backgas for awhile. 1) Keep the right tank as a reserve by using the buddies long hose, 2) estimate remaining gas while starting to terminate the dive, 3) use the right tank when it makes sense to do so.

 

[cerich]

SO is Argon used on the wing or just for the dry suit (when used?)

I may try to swing by for the gear config night. Let me know. Most of next week I will be in Southern California. Of course my doubles won't be ready until next week (Monday at the earliest) anyway. Will you be doing the webbing/backplate or just doubles and regulator setups?

Kraken and I dive together all the time, I am getting my SS backplate from him.

Mike

Everything from bp,webbing, fins, wings, regs on doubles and stage/deco bottles, exposure, etc. We are waiting for AL to delivers some regs that 2 of the students ordered. let me know when you get back from CA and I'll schedule the class for then.

 

[cerich]

Let's say I'm in a cave or wreck. Burst disk fails on the left. Isolated doubles. Unknown quantity on the right.

Do I share gas with my (let's say one) buddy or not? Like right now?

I say share now. You have some amount that may or may not get you out and to the surface in that right tank. E.g. failure at 1/3rd into a cave and you definately don't have enough since you might only have 1/2 or less of the right tank remaining - not 2/3rds. Some amount was lost.

The way Murphy works, that right tank will run out at a bad time, like when you are single file and can't turn around to ask for gas easily. Or on ascent when you are trying to hold the 70ft stop and some of the gas went in but then you didn't realize it ran out and you're dropping.

Yes sharing gas will slow you down a touch, but after the first couple minutes you should hit a groove and move at a good clip. Save the right tank's remaining gas for awhile for:
1) bouyancy (in your wing not DS), and
2) in case you need to or its dramatically faster/easier to breath you own tank for a short while.

E.g. On a tech dive you might consider sharing on the bottom but going back onto your own right post for ascent and you can both better control bouyancy vs. having an OOA midway up.

In a cave you might share for a few minutes maybe until you get to a narrowing (like the lips - based on what I've heard) then go back to your right tank for the constriction(s) or once back in the cavern zone.

I would not remain on the right tank for the entire exit/ascent of that dive. But I wouldn't necessarily share the whole way either.

That's how I would manage this failure, YMMV

I disagree.

 

[MonkSeal]

Anyway, the problem with not sharing when its easy to do so (e.g. on the bottom) is that you may be forced to share when its challenging, inconvenient or more dangerous.

Bottom and the moment when you thumbing the dive is last place and time when and where you want to start sharing. Of course, more challenging situations can wait for us (like restrictions) but we can predict them and pay more attention when approaching. But as a general rule I believe that continuing to breath your supplies is better choice.

Why leave the diver with a failure to bear the burden of risk when it can be shared? By using a teammate's backgas for awhile. 1) Keep the right tank as a reserve by using the buddies long hose, 2) estimate remaining gas while starting to terminate the dive, 3) use the right tank when it makes sense to do so.

Using non-standard procedure can put more stress to the team resulting with more less-then-optimal choices and making wrong decisions.

 

[rjack321]

Where did this standard procedure concept come from??? My Tech1 instructor taught me to think.

IMO The biggest risk is having someone go OOA and being forced to share. Optional/discretionary sharing is a lessor risk than obligatory sharing. So when a buddy has only a vague idea of how much gas is in that right tank use some of the team's gas to mitigate the worst threat which is an obligatory OOA share and potentially a rough ascent because they are manually inflating or slowed exit because they have constrictions to pass through.

If you know you have enough to exit, like it was a small scale reg failure, sure stay on your own long hose. But if the right tank may be significantly depleted and run out mid-exit - then share gas prophylacticly within the team to avoid an obligatory share.

 

[MonkSeal]

Ok, we can agree that thinking an estimating the situation are the key points. Both ways can be correct depending on situation.

 

[DIR-Atlanta]

If you know you have enough to exit, like it was a small scale reg failure, sure stay on your own long hose. But if the right tank may be significantly depleted and run out mid-exit - then share gas prophylacticly within the team to avoid an obligatory share.

I'll address this from a cave diving standpoint, since that is what I know best.

In theory, if someone has to isolate their tanks, then there should be enough gas in the remaining tank to get that diver out of the system without having to share gas. However, there may have been some gas lost dealing with the incident, and if it was the left post that had to be shut down, then you have no idea how much gas actually remains. So there is at least some chance that the diver will run OOA before you reach your stage or deco bottles.

In terms of "what to do", it is definitely easier and quicker for two divers to travel while breathing from their own back gas, so that might seem like the way to go. However, you always have to keep in mind that the diver with isolated manifold might run out of gas without warning, and at any time during the exit. So the biggest potential risk in this scenario is having a diver run OOA in a situation where you cannot get gas to him immediately - for example, swimming through a single file restriction or a tight passage where there is limited room to maneuver without destroying the viz.

It's probably OK to have the afflicted diver breathe his own back gas when you are traveling through large passages where you have more room to manuever. Any time you enter a tight area however, you need to make sure he is sharing gas with someone. This allows you to take advantage of the gas in the accessible tank (which seems prudent in this situation), while mitigating the chances that the diver will run OOA in a tight spot.

And of course, the decision of when/whether to do that needs to be made based on the particulars of the dive, the team, and the state of mind of the person who is OOA. That's where the "thinking diver" thing comes into play.

FYI, this is one of the reasons why DIR gas management procedures dictates preserving a little more gas in the doubles than in the stages - it gives you just that much more of a cushion in situations like this.

 

[rjack321]

I agree, although you could also play it the other way...

Your pretty sure you have enough gas to get out of some place but maybe not 100%positive its enough. Share when its easy/fast to do so like it the big passages.

Go back to your own backgas that you now know is adequate for the short constricted area where sharing would be slower.

Also works for tech dives where the option of doing a direct ascent is iffy. And you really need to return to the upline. Share a bit when its easy on the bottom so you don't have a escalation of the problems on ascent. Of course you need to be sure the donating diver does not run low (keeping their gas well above RB) since there is nobody (in a team of 2) to donate him/her gas.

Regardless, there's no "one way" IMO. Good discussion here, I've broadened my horizons.