New Diver: Drift Diving Dives 5-15 & Nitrox Cert

[inquis]

where else, other than Cozumel, is routine air sharing practiced?

I have seen it in both of my visits in Cozumel with (three? fuzzy memory) different DMs and two different operators. AL80 tanks. I have also seen it in Hawaii, on a leisurely journey back to the anchor line with the group. There, the guy went back to his own reg for the ascent. Granted, it's hardly a comprehensive sampling.

I don't make a habit of it, primarily because I'm usually ready to get out of the water when my buddy or I hit reserve. However, I would have no problem sharing (reserves permitting) if something cool showed up. For me, "standard practice" is don't violate reserves unless it's an emergency. On no-stop dives with no navigational constraints, what happens up to that point is a bit flexible. Perhaps I'm a deviant. Doubly-so since I don't adhere to the "standard practice" of "Never hold your breath while scuba diving." (Since we're in the New Divers area, I should clarify there are definitely times when that rule applies. If you don't know when it doesn't, following it to the letter is the safe choice.)

 

[arkstorm]

@arkstorm, your drive-by, buzzword post indicates your opposition to the practice. In the interest of discussion, can you elaborate as to why (beyond "standard practice is...")? Do you not find it inconsistent that it's OK for both divers to be at their reserve pressures in one case, but not in the other?

By way of example...

Diver 1 (the "DM") = lowest SAC rate
Diver 2 = moderate SAC rate
Diver 3 (the "Air Hog") = highest SAC rate

Scenario 1:

Dive begins with all divers at 3,000 psi.
@10 minutes, Diver 1 at 2,500 psi, Diver 2 at 2,250 psi. Diver 3 at 2,000 psi.
@ 20 minutes, Diver 1 at 2,000 psi, Diver 2 at 1,500 psi, Diver 3 at 1,000 psi.
Group makes safe ascent (air consumption decreases as depth decreases)
Surface @ 30 minutes, Diver 1 at 1,750 psi, Diver 2 at 1,125 psi, Diver 3 at 500 psi.
Dive ends safely.
All divers finish dive with adequate reserve pressure.

Scenario 2:

Dive begins with all divers at 3,000 psi.
@10 minutes, Diver 1 at 2,500 psi, Diver 2 at 2,250 psi. Diver 3 at 2,000 psi.
@ 20 minutes, Diver 1 at 2,000 psi, Diver 2 at 1,500 psi, Diver 3 at 1,000 psi.
Diver 1 shares air with Diver 3 to extend dive.
@ 30 minutes Diver 1 at 500 psi, Diver 2 at 750 psi, Diver 3 at 1,000 psi.
Group makes safe ascent (air consumption decreases as depth decreases)
Surface @ 40 minutes, Diver 1 at 250 psi, Diver 2 at 375 psi, Diver 3 at 500 psi.
Dive ends safely.
Diver 1 and Diver 2 finish dive with inadequate reserve <500psi.

Scenario 3:

Dive begins with all divers at 3,000 psi.
@10 minutes, Diver 1 at 2,500 psi, Diver 2 at 2,250 psi. Diver 3 at 2,000 psi.
@ 20 minutes, Diver 1 at 2,000 psi, Diver 2 at 1,500 psi, Diver 3 at 1,000 psi.
***Emergency occurs costing the dive team 10 minutes worth of air***
@ 30 minutes Diver 1 at 1,500 psi, Diver 2 at 750 psi, Diver 3 at 0 psi.
Diver 1 shares air with OOA Diver 3 for ascent.
Surface @ 40 minutes, Diver 1 at 750 psi, Diver 2 at 375 psi, Diver 3 at 0 psi.

Scenario 4:

Dive begins with all divers at 3,000 psi.
@10 minutes, Diver 1 at 2,500 psi, Diver 2 at 2,250 psi. Diver 3 at 2,000 psi.
@ 20 minutes, Diver 1 at 2,000 psi, Diver 2 at 1,500 psi, Diver 3 at 1,000 psi.
Diver 1 shares air with Diver 3 to extend dive.
@ 30 minutes Diver 1 at 500 psi, Diver 2 at 750 psi, Diver 3 at 1,000 psi.
***Emergency occurs costing the dive team 10 minutes worth of air***
@ 40 minutes, Diver 1 at 0 psi, Diver 2 at 0 psi, Diver 3 at 0 psi.
3/3 team members OOA. No reserve available.

. . .

These scenarios are necessarily hyperbolic to illustrate the need for margins of safety in risk management but you see why the standard of practice is to rely on the diver with the highest SAC rate to plan margins of safety rather than the diver with the lower SAC rate. I.e., when the Air Hog runs low on air, end the dive. The DM gratuitously donating air to the Air Hog to extend the dive increases the risk to all three divers.

Of course, this practice in Coz and other places (I've even seen this done in Bonaire) can occur hundreds of thousands of times without any adverse outcomes which is why this is a textbook example of normalization of deviance, because of the lack of consequences. But then there's that one in a million occurrence which we call a fluke, but was it really??

BTW - I would just hate to be a drive-by buzzword poster.

 

[arkstorm]

One more point, because this is posted in the forum for new divers and those considering diving...

In your dive training you will learn standard/best practices and you should follow those.

If you ever find yourself deviating from the rule, at the very least, make sure that you have a thorough understanding of why the rule exists and the cost vs. benefit of breaking it.

 

[inquis]

First of all, thank you for the additional detail. From that, I can see you're considering cases other than that we've been discussing. In prior discussion, at no point was (non-emergency) sharing to consume reserve gas. In Scenario 2:

30 minutes Diver 1 at 500 psi, Diver 2 at 750 psi, Diver 3 at 1,000 psi

The DM sets the minimum pressure for everyone at a level to get two people to the surface. If he sets that at 1000 psi (as it appears he did from Scenario 1), he would only share until he is also at the reserve pressure of 1000 psi. Diver 2 would also not go below 1000 psi. Everyone ascends long before you describe.

I won't disagree with the examples taking 10 minutes to resolve, as one can always postulate a worse emergency that will exceed whatever reserves are present. That's not the topic of discussion.

Again, my primary point in commenting was to point out the inconsistency that is present. Unfortunately, you didn't address my specific question, so to rephrase:

GIVEN that reserves are sufficient, what difference does it make how they get to reserve level before an emergency mandates sharing? They could a) share/extend, b) happen to have the same SAC, c) the lower SAC diver could blow a LP hose or similar malfunction, or even d) the higher SAC diver brings a larger tank. At no point did anyone take their pressure below reserve level. They both ascend on the remaining tank without issue. And yet, one of these cases is condemned by some.

 

[arkstorm]

I think "condemned" is too strong a word.

The "best practice" is for the group to ascend with the greatest amount of air remaining in the aggregate.

And when it comes to new divers, we always want to teach and instill the established "best practice".

That does not mean that anyone's head will explode if your dive leader in Coz wants to do something a little differently as long as you understand the reason for the rule and the cost vs. benefit of deviating from it.

 

[inquis]

The "best practice" is for the group to ascend with the greatest amount of air remaining in the aggregate.

No one died from having too much air, to be sure. There is always a balance to be found between air used during the dive and that reserved for emergency ascent, and this should be discussed among the dive team. I will note of the several ways I mentioned to arrive at the same place (i.e., both divers at reserve pressure), it is only the one which is a choice by the diver with "excess non-reserve" air that is contentious. If the universe conspires to arrange for both to be at reserve (i.e., one of the other paths), then everyone seems to accept that.

Anyone wondering about a best-practice for how much reserve to consider would benefit from reading this thread:

Why Surface with 500 PSI?

(Author Update) This old thread discusses the fallacy of "dive planning" which consists merely of "Return to the boat with 500 psi." It gives you a tool to do deeper dives safely as you increase your diving experience after getting your OW certificate... Every boat trip, the crew will brief the...

scubaboard.com

 

[Chavodel8en]

Just noting that this thread is no longer really responsive to the OP's initial questions.

 

[scubadada]

Just noting that this thread is no longer really responsive to the OP's initial questions.

@SeaBunny88 has not been here since post #4

 

[SeaBunny88]

@SeaBunny88 has not been here since post #4

Sorry! I have a job that sometimes requires remote travel, but I'm back and reading the thread!

 

[SeaBunny88]

This is literally it. I wouldn't be too intimidated as there will be others of a similar skill level and of the times I have been to Cozumel I have never found the current to be too much of an issue. They're going to drop you in together and then you'll all be relaxing while you ride the same drift. It's just diving on a conveyor so can be the easiest dive of your life. Typically in the operations there will be ratio of 4:1 divers per DM or better if there are a lot of new divers and they will just send you up with one of the staff if you happen to be OOA early. As mentioned though everyone will be grouped together with the dive guide out front.

@boulderjohn and @NauticalNick thank you for these responses! This was really helpful, I like to have an idea of the general flow of events. I'm sending an email in to Scuba Tony today.

Their website notes that more experienced divers tend to go in the morning, so an afternoon trip can be a good choice for new divers. Why is this?