When does "Gas Management" get taught?

[Hoyden]

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...

In the PADI Open Water manual, gas planning/management is first mentioned in Ch 2, covered in Ch3 and again in Ch5. OW gas management according to PADI is “exit the water with 300-600 psi or more if the dive conditions warrant an extra margin of conservatism.” Since open water divers are only certified to make no decompression dives that allow you to ascend directly to the surface (no deeper than 60 feet) that seems to pretty well cover it. To quote the book, “To keep from running excessively low on or out of air, make a habit of checking your spg frequently. Obviously, your spg only works if you look at it.” In advance open water, gas management is covered in the deep dive section (which is one of the mandatory dives) – SAC rate calculations are covered in that chapter. You should be taught how to figure out how long a given volume of gas will last you at depth. That certifies you to 100’. That was certainly covered in my classes. I can't comment on PADI Deep Diver since I didn't take it and don't have a book. In DSAT Tec 1, gas planning is covered in great detail. In this class you are limited to 130’. By the time PADI allows you below 130 (DSAT Tec Deep), you have had plenty of gas planning and you are wearing doubles and carrying a deco bottle.

I don't see a need for more complicated gas planning for a no-deco open water dive of 60 feet or less.

Jackie

 

[Jason B]

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 ...

While I agree that diving thirds in OW is strange, I do want to comment on a few points.
Your buddy breathing more than you doesn't cause a problem with diving thirds. If he breathes more, then he reaches his turn pressure early and you turn the dive (and you have a crap load of gas left because you never even reached your turn pressure). If your buddy breathes more than you and you reach your turn pressure, your buddy is not a buddy because he has dipped into your third in his tanks. And of course, this all assumes proper 'gas matching' was done. Diving thirds without gas matching is pointless (not that you were suggesting otherwise).

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

I was taught that calculations were made once in the water to allow your tanks to cool (or heat as they do in cave country in the winter months ) which will change your pressure.

 

[darkpup]

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.

In the eternal words of Keanu Reeves as Ted, Whoa....

After my RecTriox class, I have serious doubts that standard GUE RecTriox divers will only spend 1 minute at depth before ascending in an emergency, let alone hit all of their stops. Come on, how many times were you able to hit the surface from 60' in 5 minutes while your instructors were messing with you? Do you think that would change if you were at 100' with 800 psi and your buddy goes OOA?

This point has been driven home during my Wreck Penetration and part 1 of my Tech class over and over. You run into a silt out inside a wreck on a NDL 1/3s dive with a conservative RB, I guarantee you your pucker factor is going to be high.

Even with GUE training, Rock Bottom may not be enough to solve the problem and head to the surface while hitting all of your stops. In that event, you have the choice of drowning or blowing your stops. I can recover from a DCS hit under these conditions, and the same is true for most NDL recreational dives.

But the question was is 800 psi going to get two divers to the surface safely given 1 minute for emergency and 30' per minute ascent. I'd say yes under those circumstances.

Would I feel comfortable with that amount of RB on a 100' dive? No, but that's my personal choice.

~ Jason

 

[darkpup]

While I agree that diving thirds in OW is strange, I do want to comment on a few points.
Your buddy breathing more than you doesn't cause a problem with diving thirds. If he breathes more, then he reaches his turn pressure early and you turn the dive (and you have a crap load of gas left because you never even reached your turn pressure). If your buddy breathes more than you and you reach your turn pressure, your buddy is not a buddy because he has dipped into your third in his tanks. And of course, this all assumes proper 'gas matching' was done. Diving thirds without gas matching is pointless (not that you were suggesting otherwise).

I don't think that's what Nick was trying to convey.

I agree that if your buddy breathes more than you on the way in, they'll hit their turn pressure before you do. However, if you have a similar consumption rate as your buddy at your turn pressure, and your buddy goes OOA with increased consumption due to stress, you won't have enough gas to get back to the surface without a reserve of some kind. Although most OOA experiences occur because people aren't paying attention to their gas, it's also possible to lose gas due to a failure.

However, since the main focus of the conversation is on Recreational Dives, you should be able to always go to the surface. You'll just have a longer swim back.

~ Jason

 

[Jason B]

I don't think that's what Nick was trying to convey.

I agree that if your buddy breathes more than you on the way in, they'll hit their turn pressure before you do. However, if you have a similar consumption rate as your buddy at your turn pressure, and your buddy goes OOA with increased consumption due to stress, you won't have enough gas to get back to the surface without a reserve of some kind. Although most OOA experiences occur because people aren't paying attention to their gas, it's also possible to lose gas due to a failure.

However, since the main focus of the conversation is on Recreational Dives, you should be able to always go to the surface. You'll just have a longer swim back.

~ Jason

Could very well be. Since he closed saying this...

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.

I took the first statement differently.

I think we all three agree with each other and this typing crap is interfering.

 

[rjack321]

In a lot of ways, typical gas planning instruction is somewhere back in the 60'/min ascent, maybe a safety stop at 15', possibly even J-valve era.

E.g. if you left 75' with 600 psi remaining and ascended at 60' per min to 15' and stayed there a couple of minutes I could see someone surfacing with 'about" 500 psi. Typical gas planning is "I'm close to that magic amount so I better ascend." This is light years ahead of, boy its hard to breath better pull the magic lever and ascend. But as demonstrated in the incidents section of this and other boards, its time for a better way.

And obviously, some instructors are better than others in this regard. But the fact that the manuals cited above don't give an example calculation suggests that they aren't very useful manuals.

 

[kickadyscuba]

gas management should start in basic open water. SACR and DACR begin in NAUI scuba diver(basic Open water) classes at least in mine and I am sure they do in all NAUI classes Hint it is a test question

JP NAUI 43957

 

[Adobo]

Sadly, "exit the water with 300-600 psi or more if the dive conditions warrant an extra margin of conservatism" is perceived by many as "gas planning."

It's a good thing all open water recreational divers dive the size tanks and all dive the same profiles. Or do we?:headscrat

 

[rjack321]

I would really like to know what IDCs are teaching re: this issue. Are instructors just re-iterating what they learned in BOW about "back on the boat with 500 psi"?

Just what are the teachers being taught? Seems like its not the type of calculations Delia, Lamont and others have posted on how to calculate minimum gas properly.

I don't really know and would appreciate someone who's been through a non-GUE IDC recently to chime in and provide some insight.

In other words, are IDCs teaching new instructors how to teach beyond the book?

 

[ShakaZulu]

Can't you guys read, PADI does NOT teach "Gas Management", end of story!!!!!!!!!