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Deep stops for recreational diving

Discussion in 'Decompression Theory' started by scubadada, Jul 25, 2010.

  1. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    Hi Dr Deco,

    A recently resurrected thread on Basic Scuba Discussion brought up the topic of deep stops for recreational diving (130 fsw or less, no deco). I have read the Decompression and the Deep Stop Workshop Proceedings from 2008 and am aware that no consensus statement was produced regarding the value or routine implementaion of deep stops for this purpose.

    I would be very interested in the current thinking regarding deep stops in recreational diving.

    Good diving, Craig
  2. drbill

    drbill The Lorax for the Kelp Forest Scuba Legend

    # of Dives: 2,500 - 4,999
    Location: Santa Catalina Island, CA
    Wasn't there an article in Alert Diver within the last year or two on this subject? I seem to remember one.

    Although I've done many dives that some would consider technical, I still consider myself a recreational diver. I always use deep stops if diving beyond 100 ft, but it is built into my normal dive profile where I stop at different depths to film. If I'm doing a square profile, I will hang on the line at successively shallower depths on my way up.

    In nearly 50 years of diving, I've never taken a hit (yet).
    Jax likes this.
  3. DocVikingo

    DocVikingo Senior Member

    Hi scubadada,

    Courtesy of the 09.08 issue of Undercurrent (http://www.undercurrent.org/):

    "When Considering Deep Stops, Profiles Rule

    The concept of deep stops has been around for a long time. Yet it remains to be fully embraced by the diving community and likely won’t be until typical divers know the details.

    Deep stops have advocates in the science of dive physiology. Several published studies indicate that deep stops decrease bubbles detected over the heart, and can also reduce gas tensions in tissue compartments. NAUI recommends that a deep stop should be done for recreational dives deeper than 40 feet, with a one-minute stop incorporated at half of a dive’s max depth, followed by a two-minute safety stop at the 15- to 20-foot level.

    However, there is evidence suggesting that certain types of technical dive profiles may be inappropriate for deep stops. A study from the Norwegian University of Science and Technology, using pigs as subjects in simulated dives, found that deep stops significantly reduced vascular bubbles in a long, shallow dive (100 feet for 70 minutes), but dramatically increased them in a short, very deep dive (20 minutes at 215 feet).

    A U. S. Navy Experimental Diving Unit study with volunteers making training-tank tech dives to 170 feet on surface-supplied air also raised cautions regarding such stops on deep deco dives involving exercise. It reported that those who made deep stops had an increased incidence of DCS compared to those who didn’t. Researchers theorized that slower off-gassing, continued gas loading, or both, may offset the benefits of reduced bubble growth from deep stops.

    Clearly research on deep stops needs to be conducted in the actual recreational dive environment before meaningful conclusions can be drawn. If, how, and under what conditions deep stops may be of significant benefit are yet to be finally determined. In the meantime, the expert opinions and limited findings to date are of strong interest because they suggest that performing deep stops during routine recreational dives may reduce DCS risk. At the least, as PADI has stated, deep stops in typical recreational diving, “... probably won’t hurt anything.”

    Until the multiple, complex issues of deep stops are further clarified, recreational divers can feel secure by following the usual recommendations for reducing DCS. Limit the times and depths of profiles and do slow ascents. Take long safety stops and surface intervals, and dive EAN to air tables. - -Doc Vikingo”

    And here's DAN's take on the topic:

    Deep Stops: Can Adding Half the Depth of A Safety Stop Build in Another Safety Margin?
    DAN Divers Alert Network



    This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual and should not be construed as such.
  4. thetedinator

    thetedinator Guest

    # of Dives: 50 - 99
    Location: Valencia,CA
    Thanks DocVikingo. Good stuff.
  5. Dr Deco

    Dr Deco Contributor

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
    Hello scubadada:

    I have been looking over the reports for the past three days from the Deep Stops workshop held in June of 2008. It is really a collection of conflicting results in the few studies performed. Most studies had fewer than 20 divers. Doc. Vickingo gave a nice summary above.

    US NAVY Tests

    The US Navy study [in a wet-pot] did have a large number of subjects with 11 DCS events in 198 deep-stop divers. In shallow-stop dives, 3 DCS events occurred in 192 divers. The DCS incidence was greater in the Deep-Stop schedule and CNS problems were encountered.

    Other Studies

    Three other groups reported their work. Two groups found no difference between deep and shallow stops. Another indicated that deep stops were more effective at reducing Doppler-detectable bubbles in long, shallow dives and increased bubbles in short, deep dives.

    Historical Perspectives

    Very often, when differences are difficult to show, it indicates that actual differences are not really there. There is evidence that a single stop at half distance between bottom depth and the first stop, but a series of several deep stops is not clearly very obvious.

    Differences – or no differences - can result when few subjects employed. Some divers are bubbles-prone and some bubbles-resistant [and DCS resistant]. When few divers are utilized, chance selection can play a role. Scientists always hedge their bets and conclude their papers with the line, “These results are interesting, and they show that more studies need to be done.” Right....:idk:

    Microbubbles are squeezed when descending. In the absence of much physical activity at depth, new, larger ones are not created. If there is physical activity at depth, then deep stops could be valuable.

    As far as personal research, I have not done anything in this arena. My work at NASA involved depress to altitude. It was a wonderful model with which to work since gas uptake was not an issue. All of the subjects had the same gas load, i.e., sea level nitrogen. “Deep stops” were never an issue!

    That is how I see it.

    Dr Deco :doctor:
  6. philip.legrange

    philip.legrange Divemaster Candidate

    # of Dives: 50 - 99
    Location: South Africa
    I had a confusing experience on a dive recently ... we dived to around 110ft (34m) with max dive depth of 120ft (37m) when my computer showed me I was hitting the no deco limit I went up from 120ft to 20ft where I did a 5min safety stop and boarded the boat. Once the other divers surfaced they asked me why I had not done a deep stop in addition to the 20ft safety stop. Prior to this I had never heard of a deep stop. I have not been able to find clear guidance on this....

    - Is a deep stop necessary for no deco dives in the 100 to 130ft range?
    - If so at what depth and for how long would you recommend doing this?

    any advice would be helpful.
  7. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
    Is it "necessary": NO
    Will it help?: Maybe
    Wathdoc, DocVikingo and Jax like this.
  8. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

    Last edited: Jan 8, 2013
    SoggyPancake672 likes this.
  9. muzikbiz22

    muzikbiz22 Contributor

    # of Dives: I just don't log dives
    Location: Southern California
    Bill, perhaps, this is the one you are referring to ?
  10. philip.legrange

    philip.legrange Divemaster Candidate

    # of Dives: 50 - 99
    Location: South Africa
    Thanks will give the 15m deep stop a try next time.

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