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Recreational Scuba Deco Diving

Discussion in 'Advanced Scuba' started by rx7diver, Dec 22, 2020.

  1. rx7diver

    rx7diver Solo Diver

    EDIT: Changed the definition of RSDD to allow the use of EAN32 (or EAN36) as both the bottom gas and the single deco gas (rather than limiting to air only).

    EDIT2: Changed the definition to allow for EANx (since NOAA has published tables for more than simply EAN32/36. For example, link to the download here: NOAA No-Decompression Tables for Nitrox Dives | Office of Marine and Aviation Operations).

    A recent thread has me wondering who among us engages in what I am calling "Recreational Scuba Decompression Diving (RSDD)" by which I mean, "Making a planned decompression dive in a non-overhead environment, using open-circuit scuba, and using EANx for both the bottom gas and a--the only--deco gas." (No stage bottles can be used for extending the dive.)

    One of my posts in that thread is: Wanna stay down longgerrr.

    If you do this type of diving, please describe the particulars. For example:

    1. Seldom, occasionally, or often?
    2. Shore diving, or boat diving?
    3. Fresh water, or marine?
    4. Buddy diving, or solo diving?
    5. Rig? (For example: Single cylinder, no pony/backup/bailout? Single w/ pony? Back-mounted independent doubles? Back-mounted isolation-manifolded doubles? Side-mount independent doubles? Something else? What is/are the cylinder capacity/ies?)
    6. Exposures you typically plan for (i.e., planned max depth, planned bottom time, and planned deco stops and times)?
    7. Typical activities? (For example: Simple sightseeing? Photography? Food hunting? Artifact hunting? Scientific/research diving? Something else?)

    I am looking forward to your responses. (NOTE: I am NOT interested here in PSD-type nor commercial diving.)


  2. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    backgas deco, not necessarily air.

    1. often
    2. boat diving
    3. marine mainly, but occasionally in the lakes
    4. buddy mainly
    5. doubles
    6. depends on where I am
    7. simple sight seeing.

    I set my dive plans based on what I want to do, with the gradient factors that I want to dive. Whatever the deco profile ends up being, it ends up being. I am OK with 10-20mins of backgas deco with the gradient factors that I use, especially diving doubles. If I was diving single tank, it would be limited by whatever GF99 is.
  3. johndiver999

    johndiver999 Solo Diver

    # of Dives: 500 - 999
    Location: Gainesville FL
    I think you might get more "hits" if you expanded your definition to include nitrox (as both a bottom gas and deco gas). Perhaps there was a reason you see the criteria as 21% ??
    rx7diver likes this.
  4. JonG1

    JonG1 Barracuda

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
    I do, bit pretty much only training tho

    1. Often at moment under Covid
    2. Shore (quarry)
    3. As above
    4. Solo mainly
    5. SM
    6. SKILLS, drills and loosely surveying the local quarry
    Brett Hatch and rx7diver like this.
  5. mac64

    mac64 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 5,000 - ∞
    Location: Ireland
    Wreck dived for years on air to 75 meters. This year 67 meters max.
  6. rx7diver

    rx7diver Solo Diver


    Well, I wanted to exclude dives where divers needed to do worry about computing CNS and whole-body oxygen toxicity numbers. However, I know there are NOAA Nitrox I and Nitrox II dive tables that show decompression schedules and repetitive dive schedules, and, so, take this kind of thing into consideration behind the scenes. And nitrox dive computers would automatically take care of these kinds of calculations.

    So, yes, I'll go back and revise my definition for RSDD to allow for EAN32/36 as both the bottom gas and the single deco gas.


  7. jadairiii

    jadairiii Solo Diver

    Not to nitpick here, but once you have a decompression obligation, you are now essentially in an "over-head" environment, since you cannot ascend directly to the surface. Once you accept that fact it makes planning much more important and precise.

    Ascending through that fixed obligation can kill you just as quick as the roof of a cave or in a wreck.
  8. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO

    I am sure lots of people hang out for an extra 10 minutes of deco, and this "soft ceiling" means they are more likely to suffer DCS if they have a catastrophic gas loss and have to go to the surface before they have done their decompression.

    In very general and overly simplistic terms, the difference between recreational diving and technical diving is that "ceiling," meaning that on a recreational dive, you can go to the surface at any time, but in technical diving, you have a "ceiling," either a physical barrier ("hard") or a decompression obligation ("soft") preventing you from ascending. A huge portion of technical dive training is ensuring that all problems can be solved at depth. Being out of air cannot be solved at depth, so redundant gas is required for technical diving.
    DogDiver, inquisit, tursiops and 2 others like this.
  9. JMBL

    JMBL Solo Diver

    # of Dives: 1,000 - 2,499
    Location: France
    Well, as far as I'm concerned :

    1. Most of my dives
    2. 100% of my diving is made from a boat
    3. Marine
    4. Buddy diving
    5. Rig : single 15L air tank, no pony, no deco tank, 2 independent regulators (2 computers now, before it was 1 computer + bottom timer)
    6. Plan : max depth, max bottom time, and planned deco stops and time
    7. Simple sightseeing and wrecks

    I would add this kind of diving is what any agency linked with CMAS teaches.
  10. rx7diver

    rx7diver Solo Diver


    You're quite correct, of course. However, this is the "Advanced" forum, so I am assuming everyone here knows this already.

    My definition is attempting to describe decompression that is done in open water and doesn't involve high-octane deco gasses (so, no EAN50 and no oxygen deco cylinders, and no overboard oxygen, etc.) No stage bottles. No travel bottles either. Just "simple" decompression.

    I didn't want to belabor things by being too wordy. Oops, I guess I just did.


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