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Can someone analyze this incident please?

Discussion in 'Near Misses & Lessons Learned' started by CAPTAIN SINBAD, Aug 14, 2011.

  1. CAPTAIN SINBAD

    CAPTAIN SINBAD Contributor

    # of Dives: 200 - 499
    Location: Woodbridge VA
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    I was doing a 100 ft plus dive on a wreck this Friday and got paired up with this other diver. Through out the dive we were fairly close to each other, diving a similar profile but then my tank started to run low as it was an AL 80 and we swam towards the end where the anchor line was. I swam my way up from sand towards the anchor line while she swam parallel to the floor. When we got to the anchor line I was hanging to it 15 feet higher than her. I started moving up the anchor line for my first deco stop but it seemed as if her computer was asking her to do a safety stop much earlier and deeper than mine was. In my training we were taught to stay close to the buddy but I was diving an AL-80 and she was wearing a bigger tank. If I had stuck with her at that depth I would have pushed it on gas. So while keeping her in view I rose up the rope until my computer showed my safety stop which was much higher than where she was hanging. Even when my stop was over I noticed that hers was not. I dive a Suunto Gecko which is a very conservative computer. I was thinking why the hell would she not come up? Is everything ok? I used a sign signal to which she gve me a thumbs up but still wont come. I prolonged my safety stop a few minutes more just so that she could climb up the rope and meet me. By the time we came out I was almost empty on gas.

    Later on I was thinking, what could I have done differently? I mean firstly is it possible that two dive computers would show this much of variation in ascent that following them would cause buddy separation of tens of feet? Secondly if that happens to you listen to your computer and abandon your buddy or do you ignore your computer and stick with your buddy? :idk:
     
  2. JahJahwarrior

    JahJahwarrior ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: West Palm Beach, Fl
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    You should both have figured out what your decompression obligation would be before you entered the water, and stuck to it.

    You should have planned your gas accordingly. Sounds like you massively violated thirds and did not have enough gas to do the dive safely.

    Just because the buddy has a larger tank is NO reason to have no emergency gas for them.
     
  3. Codiak

    Codiak Contributor

    # of Dives: 200 - 499
    Location: Beaver Lake, Nebraska
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    Was this a deco dive or a rec dive? You seem to be interchanging t,he terms.

    In either case it appears you didn't bother discussing the dive plan and actions before the dive, an important step for every dive but critical for pickup buddies.

    If this was and expected deco dive then an you better review gas planning quick.

    If this was a rec dive you still need to look at better gas planning. Leaving your redundant air source below you isn't wise, and breathing your buddies redundant air isn't friendly.
     
  4. Rescue Diver68

    Rescue Diver68 PADI Pro

    # of Dives: 500 - 999
    Location: NJ
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    Sounds like she was doing a deep safety stop at maybe half the max depth of the dive which some divers just do and not neccessarily required by computer. I could be wrong and it might have been something her computer required but I doubt it. Did you ask her on the boat? Did she do another stop at 15'? I don't see anything wrong with what you experienced though if I might have let my insta-buddy know that I would be doing a deeper safety stop prior to entering the water. I think you did the right thing by managing your gas and following your computer.
     
  5. Rescue Diver68

    Rescue Diver68 PADI Pro

    # of Dives: 500 - 999
    Location: NJ
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    I am assuming your "deco stop" stmt was meant as "safety stop" if not then I have a much different answer for you.
     
  6. divereh

    divereh Contributor

    # of Dives:
    Location: Ontario
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    In our world of high tech computers, we now can incorporate adeep stop function, ther is various concervatism settings, different computers use different algarythms. Maybe a predive discussion on what the dive plan is going to be.
    Also going into deco on an AL 80 is probably not the smartest thing you could have done, quit obvious your lacking any type of technical knowledge. Using your computer as your sole source of deco diving in wrong, there are many things that have to be considered, such as gas management calculations which would have prevented you lack of gas issue.
     
  7. divereh

    divereh Contributor

    # of Dives:
    Location: Ontario
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    dep stop is half the depth from the bottom to you first deco stop.
     
  8. Lee Taylor

    Lee Taylor Crusty old diver ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Charleston, South Carolina, United States
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    Hello Sinbad,

    Going by what you typed, it sounds like you overstayed your bottom time a little bit and was then in a hurry to get topside. Sounds like your buddy had plenty of air and was in no hurry. It does not sound like your buddy had any interest in rushing to the surface. How far off am I?
     
  9. Rescue Diver68

    Rescue Diver68 PADI Pro

    # of Dives: 500 - 999
    Location: NJ
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    My answer was given assumimg this was a No Decompression dive, therefore there would be no 1st deco stop.

    Copy and paste from DAN website
    Deep stops
    "Making A Stop Helps
    What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate. As can be seen from Table 2, a five-minute in-water stop is much more effective than simply slowing the ascent rate, even though the total ascent time is not much different (6.6 minutes vs. five minutes). That total ascent time also remains very short. We know the spinal cord has a 12.5-minute halftime. Thus, 6.6 minutes is an insufficient total ascent time for the spinal cord which is, by then, virtually fully saturated (as seen in Table 1).

    At 30 feet per minute (which is the ascent rate more commonly used today with a five-minute safety stop at 20 feet), the time to surface from 100 feet will be some eight minutes. This is better, but still a lot shorter than the 12.5-minute halftime of the spinal cord (not considering that gas elimination is slower than uptake). A plausible alternative might therefore be to ascend at 30 feet per minute but to add an additional "Haldanian" stop at about half the depth (remember, the depth is 100 feet / 15 meters) at 50 feet for five minutes. This gives 13.3 minutes of total ascent time2. "
     
  10. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

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    This is a case of poor gas management, and inadequate dive planning.

    Have a look at THIS article. It will tell you about developing a strategy for managing the gas in your tank, BEFORE you get in the water. You always want to have enough gas in your tank to get you AND your buddy to the surface (assuming, of course, that both of you are on single tanks and have no redundant gas source). Especially on a square profile dive, which it sounds as though this one was (meaning you aren't wending your way up a wall, but instead are spending your entire dive time at roughly the same depth), you have to think about these things. And on a deep dive like this where you need to get back to the anchor line, you need to have a plan for how far you are going to go away from it, and when you are going to turn back. You made a mistake in estimating when to return to the anchor line, and as a result, you ran low on gas. You did the right thing at that point, which is to get shallow so as not to run OUT of gas, but it forced you to default on the obligation you took on at the beginning of the dive, which was to be a dive buddy. One of the parts of that obligation, in the eyes of many if not most divers, is that you are carrying your buddy's spare gas, should she have a freeflow or any other malfunction that cuts off her gas supply.

    If you are going to meet that obligation, you must carry enough gas to get you AND your buddy back to the anchor line from any point in the dive, and then enough to get both of you to the surface . . . if you do the calculations as Bob has described them, you will discover that an Al80 is a woefully inadequate tank to do a square profile 100 foot dive where you must return to the anchor line. (An Al80 is bad enough for a square profile 100 foot dive where you DON'T have that additional constraint.)

    Now, the end of the dive didn't go as well as it should have, either. Assuming you had kept things within no deco limits, it was safe for your buddy to omit her deep stop to stay with you. Had you informed her you were low on air? Did she know that was the reason you were shallowing up? If so, she made what I think was a very poor decision, in allowing distance to open up between her (with the gas) and you (possibly needing it). In staged decompression diving, there comes a point where it's sufficiently unsafe to omit deco that doing so may create two victims (although the recent Jodrey accident shows that sometimes people will take that risk), but in recreational, no-deco diving, it is almost certainly safe to omit ALL stops in a situation of stress. So I'll criticize her decision to follow her computer, and I suspect that, like many people, she probably doesn't know very much about WHY the computer is telling her to do what it is, and how critical (or not) following its advice is.

    Imagine this dive going differently: On the boat, once you knew you were going to dive together, you sit down for a few minutes and talk about the upcoming dive. You compare gas supply, and warn her that you will be the gas limiting diver. You calculate your gas strategy and agree on it. Then you talk about where you want to go on the wreck, and then set up a plan for your ascent. At this point, you learn that she wants a different ascent profile, and you can negotiate that. By the time you get in the water, you're both on the same page . . . or maybe you've decided it isn't going to work for the two of you to buddy up. But either way, you won't discover the problems once you are underwater and they are harder to manage.
     

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