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Ceiling/Deco obligation in recreational diving

Discussion in 'Basic Scuba' started by nick73, Aug 29, 2017.

  1. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Manassas, VA
    9,689
    5,490
    For my clarity, can you please confirm: Your computer was NOT showing you to be in deco when you started your ascent? You had NDL time left on your computer when you began your ascent? Then a rapid ascent resulted in the computer giving you a mandatory deco stop (of 1:00 at 20')?
     
  2. uncfnp

    uncfnp Solo Diver ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: North Carolina
    6,598
    5,381
    But does the ceiling on a Suunto, based on rapid ascent, occur in association with NDL or is it triggered at any point in the dive when a rapid ascent occurs?
     
  3. Charles2

    Charles2 Contributor

    # of Dives: I just don't log dives
    Location: Montgomery, Texas
    523
    319
    Hope you meant 63 ft/min?
     
    gfaith and Lorenzoid like this.
  4. Lorenzoid

    Lorenzoid ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: Atlanta, USA
    9,790
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    Yep, I'm familiar with this. Suunto refers to it as a "mandatory safety stop" and the computer displays a "ceiling," just as it does if you exceed the NDL, even though Suunto makes it clear that this "mandatory safety stop" is triggered by exceeding the ascent rate and is not related to exceeding the NDL.
     
  5. gfaith

    gfaith Solo Diver

    # of Dives: 100 - 199
    Location: Desert SE of NM
    444
    168
    Exactly. Here is a brief dive description that shows how stupid I can be. Diving at CCV on the drop off Newton's Wall. Wife/buddy and I drop off I told her I wanted to go to 100 foot as I had not bounced to 100 foot in a while. She said nope and stayed above at 50 foot. I drop to 100' and thought "now what would I do if she or I had a problem" (stupid I know) bad buddy. No where near NDL and I stupidly zipped up to be close to her exceeded 60ft/min. So in effect I violated 2 things fast ascent and bad, bad buddy.

    The Viper assigned the mandatory stop during the fast ascent. I knew it was coming at that point, but not a real issue as one minute has easily cleared in ascent. Then we also did a very slow ascent. I can post the Subsurface plot if needed.
     
    stuartv likes this.
  6. Lorenzoid

    Lorenzoid ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: Atlanta, USA
    9,790
    6,475
    From my Suunto (D6) manual:

    When the ascent rate exceeds 10 m/33 ft per minute continuously for more than 5
    seconds, the microbubble build-up is predicted to be more than is allowed for in the
    decompression model. The Suunto RGBM calculation model responds to this by
    adding a Mandatory Safety Stop to the dive. The time of this Mandatory Safety Stop
    depends on the severity of the ascent rate excess.

    The STOP sign appears in the display and when you reach the depth zone between
    6 m and 3 m/20 ft and 10 ft, the CEILING label, ceiling depth, and the calculated Safety
    Stop time also appear in the display. You should wait until the Mandatory Safety Stop
    warning disappears. The total length of the Mandatory Safety Stop time depends on
    the seriousness of the ascent rate violation.
     
    uncfnp likes this.
  7. gfaith

    gfaith Solo Diver

    # of Dives: 100 - 199
    Location: Desert SE of NM
    444
    168
    Yeah Charles I edited that .. I did mean ft/min..
     
  8. KenGordon

    KenGordon Rebreather Pilot

    3,842
    2,627
    Stuart, I think you (and DevonDiver) are claiming that you can be at a depth x and have a ceiling of 1mm (meaning you could not reach the surface with the exact tissue loadings you have now, at depth x - ie assuming teleportation to the surface) and not be in deco because if you ascended at 10m/s then by the time you got to the surface you'd have reduced your tissue loadings below the limit and have a ceiling of zero. Further you are saying that computers will call that you are still within the NDL in that case and only set NDL to zero when an ascent at 10m/s would still exceed the maximum saturation on arrival at the surface.

    What I claim is that calculating the projected saturation is expensive and pointless and might lead to the issue that the OP is concerned about, so in fact counter productive.

    The Baker code to calculate the ceiling doesn't take the time of ascent into account, it does not project forward to see how much you have OFF gassed in the ascent. You see there are no time or speed factors below. ONCE he has a ceiling he does check to see if the ON GASSING will make it too shallow, using the code whose comments you have reproduced, but only to make the stop deeper. So if planning a slow GF ascent you will still get stops planned, even if they are gone when you get to them. In the case above of being at depth x with a ceiling of 1mm by the tissue saturation you will still get a stop at 3m even if the ceiling would be gone by the time you got there.

    Code:
    C===============================================================================
    C CALCULATIONS
    C===============================================================================
     DO I = 1,16
     Gas_Loading = Helium_Pressure(I) + Nitrogen_Pressure(I)
     Coefficient_A = (Helium_Pressure(I)*Coefficient_AHE(I) +
    Gradient Factor Decompression Program in Fortran
    18
     * Nitrogen_Pressure(I)*Coefficient_AN2(I))/
     * Gas_Loading
     Coefficient_B = (Helium_Pressure(I)*Coefficient_BHE(I) +
     * Nitrogen_Pressure(I)*Coefficient_BN2(I))/
     * Gas_Loading
     Tolerated_Ambient_Pressure = (Gas_Loading - Coefficient_A*
     * Gradient_Factor)/(Gradient_Factor/Coefficient_B -
     * Gradient_Factor + 1.0)
    C===============================================================================
    C The tolerated ambient pressure cannot be less than zero absolute, i.e.,
    C the vacuum of outer space!
    C===============================================================================
     IF (Tolerated_Ambient_Pressure .LT. 0.0) THEN
     Tolerated_Ambient_Pressure = 0.0
     END IF
    C===============================================================================
    C The Deco Ceiling Depth is computed in a loop after all of the individual
    C compartment deco ceilings have been calculated. It is important that the
    C Deco Ceiling Depth (max deco ceiling across all compartments) only be
    C extracted from the compartment values and not be compared against some
    C initialization value. For example, if MAX(Deco_Ceiling_Depth . .) was
    C compared against zero, this could cause a program lockup because sometimes
    C the Deco Ceiling Depth needs to be negative (but not less than absolute
    C zero) in order to decompress to the last stop at zero depth.
    C===============================================================================
     Compartment_Deco_Ceiling(I) =
     * Tolerated_Ambient_Pressure - Barometric_Pressure
     END DO
     Deco_Ceiling_Depth = Compartment_Deco_Ceiling(1)
     DO I = 2,16
     Deco_Ceiling_Depth =
     * MAX(Deco_Ceiling_Depth, Compartment_Deco_Ceiling(I))
     END DO
    C===============================================================================
    C END OF SUBROUTINE
    







     
  9. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Manassas, VA
    9,689
    5,490
    That is correct.

    And I did not see anything in the rest of your post that refutes that.
     
  10. KenGordon

    KenGordon Rebreather Pilot

    3,842
    2,627
     

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