When does "Gas Management" get taught?

[lamont]

The metric equivalent is "thumb the dive at 50 bar" - even if a diver has a whopping SAC of 30l/min, that means that he is able to come up from 30m to the surface and do a safety stop. I agree that "surface with 500 bar" is a bit more vague, as it doesnt make it very clear on what the thumb pressure should be.

"Battlefield calculations"? For reef dives? Is it just me or does that seem to be a bit of overkill? I have had students who struggle with basic math - I can just see them sitting there, running out of air while trying to do these calculations.

A more complex answer is not always the better one. And "everything tech" isnt always needed for recreational diving.

Here are my "battlefield calculations" for reef divers:

1. Rock Bottom: 100psi per 10 fsw for LP104/LP95/HP120s/HP130, 100 psi per 10 fsw + 300 psi for Al80s/HP100s/LP72 -- 500 psi minimum for all calcuations.
2. 0.75 SAC: 300 psi per 10 mins per ATA for Al80/HP100/LP72, 200 psi per 10 mins per ATA for LP104/LP95/HP120s/HP130.

So, for a 30 min dive to 100 fsw on an HP130, I expect my SAC rate to be 800 psi / 10 mins (actually these days I expect my SAC rate to be 600 psi / 10 mins or better, but for planning purposes lets use 0.75 SAC) and I expect to have used 800 psi at 10 mins, 1600 psi at 20 mins and 2400 psi at 30 mins. 3500 - 2400 psi is 1100 psi which is above my rock bottom, so the gas plan is solid and I can dive and I know where I expect to be with gas at various checkpoints on the dive. Similarly, if I'm diving with a relatively newer diver as a buddy that I've never dove with before who is on an HP100 and we go to 100 fsw, I know that at 10 mins they could have burned through as much as 1200 psi, and could burn up to 2400 psi 20 mins in. I'll be planning on a max bottom time at 100 of 20 mins and I'll check 10 mins in to see how close they are to 2300 psi and if they're under that value I know that we need to leave sooner than that. Everything figured out with very simple math, on the surface, before the dive.

 

[TheRedHead]

Are those calculations for a square profile or a multilevel dive, Lamont?

 

[lamont]

Are those calculations for a square profile or a multilevel dive, Lamont?

Well, if you want to multi-level it, just add in the levels:

20 mins @ 100 = 800 psi * 3 = 1600 psi
20 mins @ 60 = 600 psi * 2 = 1200 psi

total is 2800 psi for that dive, leaving 700, which is right about the rock bottom at 60 fsw.

realistically, for recreational dives on HP130s I only care about the gas planning for the deep section, and I usually come back with plenty to spare because my SAC is better than the 0.75 that I plan on (0.45 is my personal best so far). So I'll typically come up to 50 fsw and take 30-50 mins gradually coming out of the water, and all I have to do is make sure that I stay above my rock bottom and I don't bother much with SAC rate calcs.

also, for wall dives to a relatively constant 60 fsw, I've found 500 psi / 10 mins to be a really useful and easy SAC rate to monitor on HP130s that makes on-the-fly calculations in the water pretty trivial.

if you can consistantly hit much better SAC rates than 0.75, just memorize the value at 60 fsw and 100 fsw that you tend to consume gas for the tanks that you use and use those numbers. things are easier if you standardize on tank sizes and dive them consistantly.

 

[vkalia]

A lot of people cannot be trusted to just watch their pressure gauges - and you expect them to do all this before and during diving???

I am not knocking your approach here, btw - it is a very sensible and well-thought out option. The 10-20% of the diving population who cares about improving will find it very useful - the remainder will either forget it or find it far too complex to handle. Hell, I can think of a few tech divers who'd be hard pressed to do air calculations without a computer program.

Cynically,
Vandit

 

[darkpup]

The metric equivalent is "thumb the dive at 50 bar" - even if a diver has a whopping SAC of 30l/min, that means that he is able to come up from 30m to the surface and do a safety stop. I agree that "surface with 500 bar" is a bit more vague, as it doesnt make it very clear on what the thumb pressure should be.

"Battlefield calculations"? For reef dives? Is it just me or does that seem to be a bit of overkill? I have had students who struggle with basic math - I can just see them sitting there, running out of air while trying to do these calculations.

A more complex answer is not always the better one. And "everything tech" isnt always needed for recreational diving.

That being said, I agree that gas planning is completely ignored and need to be covered in a little bit more details (I generally cover it in the Deep Dive of the AOW course). I find it particularly ironic that the OW videos devote more time to the merits of dive bags than to gas planning.

Vandit

Vandit,

You and I have had this discussion before, and the last time we walked away agreeing with each other, in that, RB calculations on dives above 60' are basically the same thing as saying thumb the dive at 500 psi (run the numbers people, they're very close). I'm glad we're still in agreement here, and that we both see the value of teaching gas management early on.

The analogy of a diver dying while trying to run SAC rate numbers is a bit rough around the edges though. Come on, that's like saying an OW student would drown while attempting to use their table because tables are more difficult than using a computer. You don't stop teaching the tables because students will have a hard time remembering it, and OW students that use only tables (like myself for the first 16 years I dove) aren't dropping like flies.

It's odd that you assume Sac rates, remaining gas calculations, and EAD calculations (i.e. the Battlefield Calculations I posted) are a more complex answer. More complex to a computer, maybe. More complex to tables, not sure about that. Look at how many people have responded that they were taught these types of calculations in their OW courses from PADI, NAUI, and SSI. They didn't die from receiving this information.

IMO, the more information you have, the better decisions you and your buddies will make. I just don't see how a 1 hour introduction lecture on SAC rates, reserve gas, and gas management is that hard for OW students to handle. Let alone kill anyone because it might be difficult for some to grasp at first.

Hopefully I'm just beating a dead horse here, because this seems so obvious to me. Let me know if I'm missing something, which happens more times than I'd like to admit.

~ Jason

 

[darkpup]

A lot of people cannot be trusted to just watch their pressure gauges - and you expect them to do all this before and during diving???

I am not knocking your approach here, btw - it is a very sensible and well-thought out option. The 10-20% of the diving population who cares about improving will find it very useful - the remainder will either forget it or find it far too complex to handle. Hell, I can think of a few tech divers who'd be hard pressed to do air calculations without a computer program.

Cynically,
Vandit

Wait a minute. There's a huge difference between introducing students to this material, and students actually doing what they were taught. Take the tech divers you know, they have been introduced to this material, and choose instead to use their computers. More power to them.

Not introducing students to this material because they'll ignore it isn't the right solution IMO. If this mindset were the norm, why teach students how to use tables since they're going to ignore it and use computers?

~ Jason

 

[MXGratefulDiver]

A lot of people cannot be trusted to just watch their pressure gauges - and you expect them to do all this before and during diving???

I am not knocking your approach here, btw - it is a very sensible and well-thought out option. The 10-20% of the diving population who cares about improving will find it very useful - the remainder will either forget it or find it far too complex to handle. Hell, I can think of a few tech divers who'd be hard pressed to do air calculations without a computer program.

Cynically,
Vandit

Judging from the number of ScubaBoard members who've requested gas management info from me in the past 16 hours or so (about 30 so far), I'd guess that there's some interest in this information ...

... Bob (Grateful Diver)

 

[jepuskar]

I have invited George to stop by and say a couple things regarding this topic...

 

[vkalia]

Heya Jason,

Yep, we have had this discussion before, havent we? You'll note in my original post that I didnt disagree with the concept of teaching gas planning. I actually teach it myself, as I indicated.

My general belief is that it is preferable to teach a method that is simpler, but will be used by more people (as opposed to a more rigorous approach that fewer people will follow) You say that not introducing students to this material b/c they'll ignore it isnt the right solution - that isnt quite what I was saying (as I said, I dont disagree with the idea of teaching gas planning; quite the contrary). My thrust is that it is better to teach them something that they *can* remember and use.

Unlike a tech diver who has the option of using a different tool (ie, a computer), a casual diver who doesnt remember the air calculations will either not use it at all, or screw up and do something wrong. Isnt it worth even *considering* the idea of a simpler method?

I am merely pointing out that if something simple accomplishes the same goal, it is worth considering. You (speaking generally, not you specifically) may or may not agree that a simple rule of thumb accomplishes that goal - that is fine, as long as you consider both angles before reaching the conclusion, as opposed to blindly assuming that "more info is always better"

A secondary factor driving this post was "having-it-till-here" with the mindset which tries to make recreational diving far more complex than it really is. Call it the "tech groupie" effect where every element of tech diving is adopted for recreational diving, regardless of whether it is needed or no. But that is a different rant.

So in short, my point is: think about the diving one does, and ask yourself what the simplest/most effective approach to dive planning is - and follow that, whatever it is.

In a lot of cases and for a lot of people, "50 bar" isnt a bad rock bottom air pressure.

Cheers,
Vandit

 

[vkalia]

Judging from the number of ScubaBoard members who've requested gas management info from me in the past 16 hours or so (about 30 so far), I'd guess that there's some interest in this information

I dont doubt that at all. Do you think SB is representative of the total diving community, however?

Vandit