When does "Gas Management" get taught?

[Web Monkey]

I suspect the total number of people who read the board is representitive of most of the recreational diving community, however I also suspect that the people who actually post are not.

There are probably a lot of lurkers.

Terry

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

 

[Web Monkey]

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.
Vandit

I do 1/3's for deep dives and wrecks, but 50 bar/750 PSI really is enough to get a couple of average divers to the surface from not-too-deep, assuming nothing bad happens and there's no overhead or entanglement.

Of course that depends on the "hoover" factor. My buddy and I are pretty evenly matched, and about average on air, so it works out well. If one of us was in the 1.x SAC rate range, it would be a different story, as it would be for 90-pound girls who could probably dive the Andrea-Doria on what's left in my tank after a dive.

Maybe part of the OW final exam should be given after the last dive, and should be for the student to calculate their own rock bottom and SAC rates given the data from their own checkout dives.

Terry

 

[MXGratefulDiver]

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

Vandit

Actually ... no.

But it was interesting to receive PM's from a substantial number of people who were from relatively new (0-15 and 15-50) divers.

I'm not suggesting that the majority of divers would be interested in learning, much less practicing, this information ... but it is evident to me that there's an unfulfilled demand for it out there ...

... Bob (Grateful Diver)

 

[limeyx]

You know my answer ...

It's part of my NAUI AOW class ...

... Bob (Grateful Diver)

It was part of my PADI AOW class too, but certainly not *required* as part of that.
I am just fortunate that my PADI instructor is a GUE diver, and so included a bunch of extra skills etc. into the AOW classes.

 

[limeyx]

My OW instructor talked about turn around pressure when planning a dive, but told us that turning around at 1500 psi (when you start with 3000) wasn't good planning in his opinion. He told us that planning by thirds is safer...one third out, one third back, and one third reserve...but you can definitely snoop around under the boat until you're down to 500-700 psi, then up to the boat.

I see a lot of mention of "thirds" diving, which is kind of odd since it's not really too useful for OW diving in general. I think however the most important point to understand is *where* the numbers come from and why.

Rules of thumb are all good and well, untill you
a) start diving a smaller tank -- is it sill 100psi for each 10 feet on an AL 80 compared to a Steel 120 ?
b) have a buddy that breathes way more than you do ...

also thirds by itself doesnt get you out of the water, it just gets you back to your starting point. You still need "minimum gas" or Rock bottom or whatever to actually get to the surface.

Lastly, 1/3's might sound conservative but could be extremely dangerous if you get an OOA at your 1/3 limit -- it assumes you are both breathing at the same rate on the way back (while Out of gas) as you did on the way in -- maybe not a good assumption -- and no current etc.

 

[limeyx]

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

But the gas is for your buddy and not just yourself, so 50 bar might not be enough (especially if you are diving a smaller tank than normal)

And most calculations should be done *before* you get in the water (when not imparied by N2 and stressed).

I think it absolutely ought to be taught in open water classes, and I think it's dangerous that it's not (amazing really given all the other concerns about "liability" )

 

[lamont]

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

that's about 800 psi? that isn't bad for recreational OW divers on Al80s above 60 fsw. but if you're being told in BOW over there that you should leave depth at 50 bar, that beats what american BOW trained divers are typically told which is to "be back on the boat with 500 psi" and no tools for how to even do that, much less any idea that if you find yourself down at 100 fsw that you need a lot more than that... and at 100 fsw the 50 bar figure is not going to be a sufficient rock bottom, so it *is* a bad rock bottom for a lot of AOW-certified divers...

 

[darkpup]

and at 100 fsw the 50 bar figure is not going to be a sufficient rock bottom, so it *is* a bad rock bottom for a lot of AOW-certified divers...

That depends. If you include pauses starting at 75% of your depth every 10', and 1 minute saftey stops starting at 50% of your depth every 10', then yes, 800 psi on a single al80 tank won't be enough for rock bottom.

However, if you skip the pauses and stops for the standard 30' per minute ascent, then 800 psi would be plenty for rock bottom.

Not everyone follows the deep stop model and required saftey stops during an emergency.

~ Jason

 

[scubatexastony]

It was part of my PADI AOW class too, but certainly not *required* as part of that.
I am just fortunate that my PADI instructor is a GUE diver, and so included a bunch of extra skills etc. into the AOW classes.

Good for Bob for teaching it in AOW, and others for repeating it in all classes, but for the record, NAUI Standards and Policies states for the Scuba Diver Course...
"Planning Skills:
Measure, record and calculate individual air consumption (as surface air comsumption rate) using a submersible pressure guage, depth guage and timing device.
Plan and make a no-decompression stop dive to a depth between 40 and 60 feet. Planning is to consider at a minimum; adequate breathing gas suppy for descent, time at depth, ascent, precautionary stop and safety margin."

Right there in B&W.

tony

 

[lamont]

That depends. If you include pauses starting at 75% of your depth every 10', and 1 minute saftey stops starting at 50% of your depth every 10', then yes, 800 psi on a single al80 tank won't be enough for rock bottom.

However, if you skip the pauses and stops for the standard 30' per minute ascent, then 800 psi would be plenty for rock bottom.

Not everyone follows the deep stop model and required saftey stops during an emergency.

~ Jason

Yes, but I have serious doubts that standard AOW-trained divers will only spend a 1 minute at depth before ascending in an emergency as well. Our RecTriox class highlighted how terribly insufficient (or non-existant) the training was in standard scuba classes to just get off of the bottom as fast as you can. For example, 3 mins at 100 fsw + 3 min 30 fpm ascent at a 1.5 combined SAC rate is 13.5 cu ft + 8.40 cu ft = 21.90 cu ft which is 900 psi.