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How to calculate total air consumption along ascent?

Discussion in 'Basic Scuba' started by magicfx, May 11, 2021.

  1. Wibble

    Wibble Contributor

    # of Dives: 500 - 999
    Location: UK
    725
    507
    You've discounted the difference in speed in the ascent: need to accelerate to 10m/min and slow down (else broach like a porpose when surfacing). Therefore ascent speed is not constant.

    Breathing will vary; it won't be exactly 1.5 litres of inspired gas (normalised to surface pressure).

    Breath intake will vary according to depth: one doesn't breathe a lungful in an instant, say taking 5 seconds meaning the start will be at a higher pressure than the end.

    In short, analysing consumption like this is meaningless. It can only be ascertained by an inline tidal flow device worn by the diver during the ascent.


    Back in the real world... we overcompensate to allow for margins of error. The penalty for not doing this is death by drowning.
     
  2. Raphus

    Raphus Assistant Instructor

    # of Dives: 100 - 199
    Location: Germany
    382
    298
    15l on surface,
    30l on 10m
    10m/min ascent rate

    Takes 1 minute to reach the surface.
    Average depth will be 5m.
    So it's the same as you would stay at 5m for 1 minute.

    Consumption at 5m:
    15l * 1.5 =22.5l/min

    Because you need 1 minute it's 22.5l
     
  3. Centrals

    Centrals Barangay Pasaway

    # of Dives:
    Location: Hong Kong
    9,656
    3,527
    Assuming everything is constant.
    No point to ask the question in the first place.
     
  4. clownfishsydney

    clownfishsydney Contributor

    # of Dives: 2,500 - 4,999
    Location: Sydney Australia
    1,550
    1,035
    So many people overthinking this!!!

    In any case, as someone mentioned, really no need to ever know the answer as if you are that close to running out you will be bolting to the surface as quick as you can.
     
  5. Centrals

    Centrals Barangay Pasaway

    # of Dives:
    Location: Hong Kong
    9,656
    3,527
    Excuse me. I am BORED!
    22.5L is the bare minimum if taking 5m as the average depth. How about if the average is breaking down to 2m increment ?
    (10, 8, 6, 4, 2, 0)m
    10m = 6L( 15 divide by 5 and x 2 = 3L)
    8m = 5.4
    6m = 4.8
    4m = 4.2
    2m = 3.6
    Total = 24L.

    I could be wrong entirely.
    Cheers.
     
  6. Raphus

    Raphus Assistant Instructor

    # of Dives: 100 - 199
    Location: Germany
    382
    298
    He wants to know this for a theoretical task.
    22.5l is the amount of air needed.
    It's not said the he has no air left.

    For example: when calculating min gas you want to know how much gas you consume during ascent. And of course you plan to have 50bar(or whatever) to have still left.

    So it's not about an emergency when only 22.5l air is left in the tanks. It's more about gas and dive planning.

    The calculation is easy, as I explained in me post above. There is not need for integrals or different test samples.
    It's just gas planning
     
  7. Centrals

    Centrals Barangay Pasaway

    # of Dives:
    Location: Hong Kong
    9,656
    3,527
    "22.5L" is the bare minimum required.
    In 2m increment the diver will take one more breath deeper than or = 5m. (10,8,6 vs 4,2)
    In 1m increment the diver will take two more breaths deeper than or = 5m. (10,9,8,7,6,5 vs 4,3,2,1)
     
  8. johndiver999

    johndiver999 Solo Diver

    # of Dives: 500 - 999
    Location: Gainesville FL
    1,653
    1,695
    If you assume a uniform breathing rate and a uniform ascent rate, then you do not need to integrate or use calculus, just use the average depth of the ascent and the SAC and the ascent time. Something like the area of a triangle is 1/2 bh. Actually, I think it is exactly that.
     
  9. Ayisha

    Ayisha DIR Practitioner

    # of Dives: 500 - 999
    Location: Toronto, Canada
    3,258
    1,594
    And here I thought that using GUE Minimum Gas and the CAT formula was enough math with a nice safety margin.

    But the OP wants it cut to the best case scenario with no margin of error? So if something goes wrong, your calculations are screwed from the get-go. Hmm... o_O
     
  10. broncobowsher

    broncobowsher Solo Diver

    1,974
    1,452
    But what if this is an altitude dive?
     
    Raphus likes this.

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