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Nitrogen load clearing overnight?

Discussion in 'Advanced Scuba' started by PACKRMAN, Jul 21, 2015.


    PACKRMAN Contributor

    # of Dives: 500 - 999
    Location: just north of Tulsa, OK
    You are on a liveaboard. After the third day of multiple dives your computer craps out. You make a safe accent using your B.U.D. You may even sit out the last dive of the day. The next morning you break out of your luggage the backup computer you brought along and jump in the pool.

    Is it all good? Or, is there residual nitrogen from the multi day, multi dives that the new computer is not aware of?
  2. whitefang21

    whitefang21 Divemaster

    # of Dives: 200 - 499
    Location: New jersey
    there is always residual nitrogen after a dive. The new computer wont know you have been in the water to factor in the residual nitrogen. If you have a backup computer you should carry it with you even it means putting in a bc pocket.
  3. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    that. if you are carrying multiple computers, they should be on every dive with you. Why own it if you aren't going to use it?
  4. GrandpaScuba

    GrandpaScuba Instructor, Scuba

    # of Dives:
    Location: Seattle, Puget Sound
    First - Your back up computer should be with you on every dive. The whole point of the b/up is to have another device that has up-to-date data in it if the primary craps out.

    That said, the rule you are referring to is from standard dive tables. But, you nitrogen loading doesn't clear "over night" it clears in 12 hours. If "over night" has only been 8 hours, then you are not clear.

    A live-aboard dive boat often offers a huge number of possible dives. It is not their intention that you are to make every single dive. They expect you to be a seasoned diver and dive according to your decompression status. You should choose one dive, nearly every day to stay back on the boat. If missing the last day of diving bothers you, then I suggest that you "go light" on the day before the last diving day. Either make only one dive that day, or even take that day off.

    I once went to a land-based operation that offered a large number of dives each week. They balanced this by taking Thursday off. They had no organized diving on Thursday. (You could still shore-dive, if you wanted to.)

    My point is, if you sit out an occasional dive when on intense diving vacation, you will have a better experience.
  5. Patoux01

    Patoux01 Solo Diver

    # of Dives: 100 - 199
    Location: Geneva
    I'd say it's "all good" and simply not go up to NDL, leaving some margin (basically as I always do, but leaving a bit more). But that's just me, and I'm definitely an unsafe diver.

    However, I don't see the use of a backup computer that doesn't come with me. There's space on my arms, I might as well use it.
  6. Diver0001

    Diver0001 Instructor, Scuba

    Most modern computers have a 720 minute compartment or something analogous, which means it will continue to calculate offgassing for 3.5 days.

    After 24 hours, the difference is likely to be marginal; however, the "new" computer will be unaware of what the other computer knew, which is that you had already made several repetitive dives over a 3 day period. Vacation diving with multiple dives over multiple days also tends to include a fair amount of relatively shallow time so the 720 min compartment could become relevant. Depending on the algorithm, there could be important differences in the NDL's if you only skipped one dive and started the next morning with a "fresh" computer.

    If you have a backup computer, then just throw it in the pocket of your BCD and forget about it. If you need it, then it's up-to-date on data.

    If I were in the position of having to fall back to a computer I hadn't been diving with then I would tend to wait 24 hours and then just not push the NDL's after that. Just to be clear, I don't think any agency has a standard recommendation for this scenario so what *I* would do for myself, may not be what you should do. The computer's user-manual may have some information about such a scenario and if it does then I would follow the manufacturer's recommendation.


    PACKRMAN Contributor

    # of Dives: 500 - 999
    Location: just north of Tulsa, OK
    Interesting, thank you for your answers. I had no idea about off gassing for 3.5 days. I think I will do a little experimenting next week along these lines. Definitely food for thought.
  8. Doppler

    Doppler Dive Equipment Manufacturer

    Just a little more info to add to Diver0001's post above.

    Chances are good that your computer is using a Buhlmann or modified version of a Buhlmann ZH-L16. Start your research there. You might want to research BEFORE experimenting! LOL!
    rhwestfall likes this.
  9. 100days-a-year

    100days-a-year Solo Diver

    # of Dives: 5,000 - ∞
    Location: NE Florida
    If you are really worried about a nanny computer beating you out of dives then remove the batteries at night or find one that is more liberal.
    A second computer in your luggage is a spare,a second computer in the water is a back-up,1 way of looking at it.
  10. Agility

    Agility Solo Diver

    # of Dives: 200 - 499
    Location: Austria
    You said you have a B.U.D so you might as well use its reading for your diving after your primary DC failed. just rig a bungee-mount and dive

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