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Advanced training questions

Discussion in 'Basic Scuba Discussions' started by Donpedro, May 4, 2014.

  1. EFX

    EFX Solo Diver

    # of Dives: 200 - 499
    Location: North Central Florida
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    I dove the Duane and the Spiegel in January and my buddies and I had a dive plan as I outlined above and we did just fine. You don't need gas planning and what kills divers is not the lack of a gas plan but not monitoring your SPG. Any dive to recreational depths can be done on an 80 without gas planning. You don't need to know your SAC or SRV. The example I gave of ascending with 700 was not meant to be a plan for all dive depths so cut me some slack.
     
  2. BCSGratefulDiver

    BCSGratefulDiver Mental toss flycoon ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: On the Fun Side of Trump's Wall
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    ... if you begin an ascent with an inadequate amount of air in your tank, you'll be watching your SPG go down into the red zone. That may have several impacts, depending on the diver. It may cause you to hurry your ascent, so that you reach the surface before it reaches zero. It may make you start stressing out ... which will only cause you to breathe harder, making the problem worse. Or it may cause you to decide to go to your buddy and ask for a donation ... which could be good or bad depending on how much air your buddy has left to share at that point. But it really doesn't do much to address the real issue ... which is that watching your gauge is only as useful as knowing how much air you need at any given point in the dive ... your SPG will never be able to tell you how much air you need, only how much you have.

    Oh dear ... gas planning has EVERYTHING to do with planning for something going wrong ... unless you've figured out a way to survive underwater without breathing ...

    DAN statistics simply don't support that claim ... roughly 40% of all diving accidents list lack of proper air management (OOA or LOA) as either the primary or proximate cause of the accident ... in other words, if people managed their air supply better the accident would not have occurred. This encompasses both "serious" divers and "vacation" divers ... since regardless of how often you dive, you will have to be able to breathe once your head goes below the surface.

    While the divers taking my AOW class tend to be committed divers ... they seek me out precisely because they know what kind of class I teach ... those who attend my seminars include divers from all points on the spectrum. And since the seminars are completely voluntary, they're not attending because they're polite ... they're attending because they're interested. The most common question I've gotten ... particularly from the occasional divers ... over the years is "why didn't I hear about this in my class?" It's a very good question.

    But if you think there's no interest in the greater diving community I'll challenge you to do a little exercise. Go Google the term "Gas Management" ... and see what comes up at the top of the list ...

    ... Bob (Grateful Diver)
     
    eelnoraa, Jim Lapenta and TSandM like this.
  3. rivers

    rivers PADI Pro

    # of Dives: 500 - 999
    Location: Bristol, UK
    1,467
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    So what happens if the current picks up, changes direction, a mask gets knocked off, or any of a number of other things that can cause your SAC rate to increase? You've only got 700 psi, your buddy is blowing through his gas and you're stuck at 100ft for some reason. Guess who's making it to the surface? My bet is neither of you. That is why gas planning, even at the basic open water level, is not only important, but necessary. If I'm doing a 100ft dive and I'm on a single HP100 (equivalent to a standard size single tank in the UK), we are starting the ascent at 1500 psi. That is minimum gas. Why? Because if my buddy has an issue, I know we can both make back to the boat safely, complete with stops.
    You are going to end up getting yourself or someone else killed with a plan like that. it may work if everything goes to plan, but the second something goes wrong, you will be up a creek without a paddle.
     
  4. EFX

    EFX Solo Diver

    # of Dives: 200 - 499
    Location: North Central Florida
    759
    352
    63
    I think I'm being misunderstood. It's coming down to semantics again.

    What you are describing above is what I called a dive plan. You are providing an example with a specific depth where I was providing a general case without a depth. If you are still having trouble with my example plan then substitute the required depth for ascent or keep the 700 and let's set the depth to say 25 feet. I agree with you that at 100 ft you need to ascend with more than 700.

    Going back I made these specific definitions:
    Gas planning: used to make a specific time or goal oriented dives where specific SAC/SRV rates are needed to determine tank size to accomplish the goal. The goal in this case excludes trivial exploring.
    Dive plan: a dive that doesn't require gas planning.

    I call your example above a dive plan because you have no minimum time or goal like bringing up an object therefore SAC/SRV aren't required. We watch our SPG's and agree to ascend when one of us reaches whatever minimum psi we set. Notice I didn't say we shouldn't take into account our buddies breathing rate (SAC) but that a specific SAC number and hence we need this tank (gas planning) are not required.

    Now, let's beat that dead horse:

    Dive 1: wreck penetration to explore a room midway into the ship. This is a specific goal that requires a minimum amount of time to accomplish and therefore we need (REQUIRE) gas planning.

    Dive 2: same as above but the is not required. If we make it fine. If we don't fine. Our dive plan calls for turning our dive at 2000 (assume an 80 and rule of thirds). We're not going to calculate SAC/SRV so we don't even know if an 80 is enough air. There is no gas planning. On this dive we only make it a 1/3 of the way in when we reach 2000. So we turn the dive. All we did is dive the plan and watch our SPG's.

    Let's also beat the dead horses brother:
    What all of you are doing is conflating my definitions of dive planning and gas planning into one lumpy definition and confusing what's needed with what's nice to know and then providing exceptions to disprove my argument. What does a PADI AOW or a vaction diver REQUIRE to make any dive within rec limits: watch your SPG and apply common sense and your basic training. No gas planning needed (as I've defined it). Thousands of divers are doing just that.
     
  5. nimoh

    nimoh Public Safety Diver

    # of Dives: 500 - 999
    Location: Rochester, MN
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    You are taking in to account SAC rates. You might be guessing what they are, but when you set a minimum psi, you are (presumably) setting it at a point where you have enough gas to make the ascent.

    An improvement to this might be to ensure you each have enough gas to share with the other (i.e. double what you would normally set for one person). Another improvement might be to determine your SAC rate and make a fairly accurate calculation.
     
  6. rivers

    rivers PADI Pro

    # of Dives: 500 - 999
    Location: Bristol, UK
    1,467
    539
    113
    How do you think I came up with 1500 psi as minimum gas? It's not some number I plucked out of thin air and thought "gee that sounds about right". I calculated using stressed sac rates, depth, time, etc based on the dive information. It's something that takes about 10 minutes to teach and a few minutes pre-dive to calculate. Once you start doing enough diving, you don't even need to calculate it anymore because you just know, including on dives where you have mandatory deco. Hell, if you don't want to do the maths yourself, I'm sure there's a smartphone app that can do it for you.
    What gas planning teaches you is how much gas you need in your cylinder to get yourself and another diver to the surface (or next available air source if on a technical dive) while both of you are breathing from it at the most critical point in the dive (which is from the bottom).
    A dive plan (to me anyway) is something like 30 minutes at 30 m on 32%, or until someone hits minimum gas (which for a 30m dive on a single 12L is 100 bar). Or it could be something along the lines of: We're going to start surveying X wreck at 15m. We're all on twins and on 32%, so gas, not time will be the limiting factor. It's only 15m, so minimum gas is 40bar. Again, that 40 bar is enough gas in a twinset to get 2 divers to the surface in case someone is OOG.
    Minimum gas will get 2 divers to the surface, but you need to know how to calculate it.
     
    Jim Lapenta likes this.
  7. TSandM

    TSandM Missed and loved by many. Rest in Peace

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    EFX, what you are describing works pretty well for basic, shallow dives. It falls apart once you reach the AOW level and start going deeper, because the part of the dive that's ignored is what happens if there is a major gas loss (eg. freeflow) or a significant delay in surfacing.

    If you go look at NW Grateful Diver's gas management article, you will see a discussion of what's called "Rock Bottom", or "minimum gas". The idea is that you need to reserve a certain proportion of your tank to ensure that you AND your buddy can ascend while sharing air. There is a simple formula for calculating that amount, but it can be surprisingly large if the dive is deep or the tank is small. For example, the minimum gas reserve for a 100 foot dive on an Al80 can be over 1000 psi, and that's making some assumptions that the divers involved have enough experience to have average gas consumption rates. It can be far more for a novice who is still hoovering! If such a diver remains at depth until he has only 700 psi left, and has to share gas, the two will not make it to the surface without running out, and what we know from the DAN studies (as well as cases a lot of us have seen) is that running out of gas underwater is a powerful inciter of panic.

    CAN you do years worth of shallow reef diving without ever developing a gas plan? Sure. Many guided dives are planned to result in a fairly predictable gas consumption, and the guides are trained to keep track of people and make sure they are checking their gauges. But this IS a form of gas plan, because the plan includes the assumption that the guide, whose SAC rate is probably miniscule, will have enough gas to share with a client, should that necessity occur. In this case, the guide is a form of pony bottle, and the math has already been done :)
     
  8. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
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    I don't know where you are from or who trained you but I do feel sorry for you. Any dive without a gas plan is a disaster waiting to happen. Especially when it's a dive on the Duane or the Grove or similar site.

    I will though thank you for your posts as I will use them in my classes as examples of poor dive planning and what not to do. They will also be especially useful to show why I teach the classes that I do and why they are so much longer and more involved than many others. If you know your SAC rate you don't need to constantly monitor your spg. You made a couple dives on the Grove and got away with it. Nice. Good for you. Just hope that the next time nothing goes wrong and someone has to put themselves at risk for your stubborn refusal to properly plan a dive.

    "Any dive to recreational depths can be done on an 80 without gas planning.":shakehead::shakehead: :confused: Really? This is just plain scary and the instructor who gave you that impression should be flogged.
     
  9. BCSGratefulDiver

    BCSGratefulDiver Mental toss flycoon ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: On the Fun Side of Trump's Wall
    74,364
    59,556
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    I wouldn't put it that strongly, but it is clearly incorrect.

    I just last evening did a recreational dive with a former student. He was carrying 120 cubic feet of gas on his back and used almost 100 of it.

    It totally depends on the dive profile, the water conditions, and the consumption rate of the diver ...

    ... Bob (Grateful Diver)
     
  10. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
    16,919
    8,688
    113
    Agreed. He was though expressing that opinion in the context of dives done on the Spiegel Grove and the Duane. On those dives, that are within recreational depths, not planning gas is foolhardy. Hell not planning gas on any dive is nuts. I personally witnessed two divers on Molasses Reef in an AOW class go out of air after 40 minutes. The instructor had his hands full. Knowing their SAC rates before that 35 ft dive would have avoided that scenario.
     

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