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What is your average Air Consumption?

Discussion in 'Basic Scuba Discussions' started by Diver0001, Sep 21, 2003.

Choose range for avg air consumption

Poll closed Oct 5, 2003.
  1. 6-10 lpm (0.2-0.35 cf/min)

    7 vote(s)
    8.4%
  2. >10-12 lpm (0.36 - 0.42 cf/m)

    11 vote(s)
    13.3%
  3. >12-14 lpm (0.43 - 0.49 cf/m)

    15 vote(s)
    18.1%
  4. >14-16 lpm (0.50 - 0.57 cf/m)

    22 vote(s)
    26.5%
  5. >16-18 lpm (0.58 - 0.64 cf/m)

    11 vote(s)
    13.3%
  6. >18-20 lpm (0.65 - 0.71 cf/m)

    10 vote(s)
    12.0%
  7. > 20lpm (0.72 or higher)

    7 vote(s)
    8.4%
  1. Charlie99

    Charlie99 Solo Diver

    # of Dives: 500 - 999
    Location: Silicon Valley, CA / New Bedford, MA / Kihei, Maui
    7,966
    160
    63
    It's not something to debate. I simply stated what I observed. 1 bottle. 95cf LP steel, pumped to ?? psi. 2 dives, 60 minutes runtime each. Inside ledge is 60-65' to the sand, about 10' profile. Reef top is 45' but not as interesting. His 60 minute runtimes are predictable enough that the boat will make a run to his ball for pickup based solely on time rather than waiting for him to surface. The diver in question is a smaller, skinner, older guy that dives almost every weekend. You can see a lot of his photos on the websites of Splashdown of Boynton Beach, FL; Seahorse of Pompano and probably others.

    Let's try these numbers: 95 pumped to 3500 is 126cf, assume he drains it down to 200psi (119 cf used). Also assume he does 5 minutes on reef top and 5 minute hang at 15' (actually that may be underestimate since the SI between dives is only 30 minutes).

    That results in a 0.37cu ft/min guesstimate. Very reasonable for the conditions -- warm water, drifting, and doing photography.

    His SAC and how much air he had was not my concern since he was diving solo, so we didn't bother discussing SACs or how high up he had jacked the 95's. I had noticed that he didn't seem to have a 2nd tank and inquired. He confirmed that he used only 1 tank for both dives. I also noted that the boat crew knew exactly when he would come up from dive 1 ---- exactly 60 minutes. End of story. The rest is conjecture.

    -----------------

    On a separate note ....... I think the big reduction in my SAC came about when I started consciously working on gettting closer to sea life. I'll bet a lot of the people with low SAC are the same ones that can swim into schools of fish and not scare them off. Hands need to be tucked away. You can't have any sudden movements. Calm, gentle motions only. Just a thought ....
     
  2. DeepScuba

    DeepScuba Manta Ray

    724
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    Yes Charlie, it's too much of a ballpark of made up numbers (At our end) to determine exactly his SAC. In this I agree. Alll I was doing was putting the Math to how high I would "jack-up" my steels and then ran the numbers you put forth, with some other very possible scenarios as well. (Not exactly 60min, not exactly 60ft)

    Yes, it makes for sloppy math at our end. Which is my point in this entire thread. It's too easy to over estimate (For ego's sake) our "prowess" in SAC rates.

    Regards.

    Flame throwers "ON"



    :flame:
     
  3. Drew Sailbum

    Drew Sailbum Instructor, Scuba

    # of Dives:
    Location: Grand Cayman
    2,188
    103
    63
    I lived in Wisconsin, and did much of my early diving on Great Lakes wrecks. Lake Superior was rather cold as I recall. The local ice dives were a touch cold too. So long as I used suitable exposure protection, SAC rates didn't double. Higher, yes. 0.40-0.45

    Don't know if you'll ever get to 0.18, but here's a start. Spend a minimum of three weeks per year underwater breathing from a scuba regulator. Not hard to do.

    3 weeks=21 days x 24hr/day = 504 hours. At a leisurely 45 minute average for a dive, that's a mere 672 dives per year, or a mere 2.3 dives per working day for this Cayman dive instructor. It's a start.

    Take advantage of a tropical water advantage - no wetsuit means minimal use of my BCD, and less air being used that's not going through my lungs. I once had the corrugated inflation hose break in two, and didn't notice for some time.

    That got my SAC rate down to 0.35 cuft/min. It's about average to slightly high for instructors in our shop.

    To get to 0.18, I'd suspect that I would need to be much smaller physically. Being female with (on average) proportionally smaller lungs would help too. I suspect that those two differences account for a bit of the difference between my SAC rate and my friend's.
     
  4. Charlie99

    Charlie99 Solo Diver

    # of Dives: 500 - 999
    Location: Silicon Valley, CA / New Bedford, MA / Kihei, Maui
    7,966
    160
    63
    OTOH, you seem to have blinders on and feel that the range of SACs of you and your buddies is the complete range.

    You need to do some warm water drift dives. If you look back at my original post, the lowest entry was "0.35 while in a coma or relaxing drift dive". Whle you may not accept it, those are repeated, carefully noted results. Typical example: 2:07 dive in front of Scuba Club Cozumel using 2600 psi out of standard AL80. Average depth 20'. Gentle finning against 1/8-1/4 kt current. Thats only 0.53 cu ft/min before applying the 1.6 depth fudge factor to get 0.33cu ft/min SAC.

    Totally relaxed drift diving is a world apart from fighting a current in cold water.

    I'll be down in the Keys, Pompano, and/or Boynton Beach, FL for 10 days starting next Friday. PM me if you want to meet up for some dives (DeepScuba or any other ScubaBoard members. Right now my sked is completely flexible since I haven't booked anything other than flights).
     
  5. GreenDiverDown

    GreenDiverDown Instructor, Scuba

    3,138
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    There have been a few posts in this thread that suggest some pretty wierd respiratory physiology.

    First, a few definitions:

    Respiratory rate (RR): The number of breaths per minute. For an average adult at rest that rate is 12 - 16. Well at least according to the books. In my experience, an ER doc that looks at vital signs all day long, the average rate at rest is more like 16 - 20.

    Tidal Volume (TV): The amount of air entering or exiting the lungs during a normal breath at rest. For the average adult this is around 500 mls.

    Minute Respiratory Volume (RMV): TV x RR The amount of air passing into or out of the lungs at rest for one minute. For the average adult this is around 6 liters per min.

    Inspiratory Reserve Volume (IRV): The maximum amount of air that one can breath in after a normal inspiration. This is around 3300 mls for the average adult male and about 1900 mls for the average adult female.

    Expiratory Reserve Volume (ERV): The maximum amount of air that one can breath out after a normal expiration. This is about 1000 mls for the average adult male and about 700 mls for the average adult female.

    Residual Volume (RV): The amount of air that remains in the lungs after a complete and maximal expiration...the amount of air that you can't get out. For the average adult male this is about 1200 mls and a little less for females.

    Functional Residual Capacity (FRC): ERV + RV The amount of air that is remaining in the respiratory system after a normal expiration.

    Vital Capacity (VC): IRV + TV + ERV The total change in pulmonary volume between a maximal expiration and a maximal inspiration. The VC of a normal adult is about 4500 mls. This can be as high as 6500 mls in a trained athlete and as low as 3000 mls in a petite female.

    Dead Space: Air that is breathed in but is expired before it reaches the alveoli and is useless as far as oxygenation is concerned. This is the air that is in the pharynx, hypopharynx, trachea, and the primary and secondary bronchi and segmental bronchioles. Of a normal TV of 500 mls only 350 mls of air actually make it to the alveoli to participate in gas exchange.

    Alveolar Ventilation This is the most important measure of the effectiveness of one's respiration. It is the total amount of air that enters the alveoli in one minute. On average, this is about... 350 mls x 12 resp. per minute = 4200 mls per minute. I've seen figures approaching 200 liters per minute in well conditioned rowers. A person can remain alive, at least for a few hours, with an alveolar ventilation as low as 1200 mls per minute.

    I have attached a graph or a spirogram below to show the different phases of respiration. As you follow the line, breath as the line suggests. This will make it easier to understand.

    And since some of you guys laughed at DeepScuba's bathtub idea...let me suggest an experiment that will help you not only to understand some respiratory physiology but also help you figure out what might be your personal best possible SAC rate.

    Here it is:

    You need a glass measuring cup. Borrow one from the kitchen and get one that is marked of in milliliters.

    Grab something like a short piece of hose with a diameter of at least 5/8".

    Now head to the bathtub. After relaxing in the tub for a while grab the measuring cup and hose. Put the cup under the water...allow it to fill completely then invert it...open end down. Place the hose up under the cup. After a normal relaxed inspiration, exhale into the hose. You'll have to practice several times to get it right...you don't want to force more air into the cup than you would with a normal expiration. Do it several times and then take an average. You have just measured your Tidal Volume.

    Now all you need do is count your respiratory rate (it is probably best to close your eyes and have someone else count your respirations per minute.)

    Now TV x RR = Respiratory Minute Volume

    It will be in mls per minute. Divide by 1000 to get Liters. Then multiply by .0353 to get cubic feet. You now have a resting RMV in cuft/min or your best attainable SAC rate! Of course, as soon as you get out of that warm tub your SAC rate will start to climb!

    You might find that .18 cuft per min is possible. Then again you might not!

    SA
     
  6. GeekDiver

    GeekDiver Manta Ray

    # of Dives: 500 - 999
    Location: Houston
    576
    1
    0
    On an avg dive it's .4 if I'm working a bit .5 if it's an easy slow dive .35
     
  7. Uncle Pug

    Uncle Pug Swims with Orca ScubaBoard Supporter

    13,768
    82
    48
    It does matter and for a very good reason:
    It is important to know your SAC for gas management purposes. It is also important to know not only your working SAC but your resting SAC. It is important to know how temp effects your SAC. It is necessary to take into consideration gas used (though this thread is in basic scuba and *the gas* is Air... other gases will take more or perhaps even less.)


    It doesn't matter and for a very good reason:
    It doesn't matter how *good* or *bad* your SAC is... you take the amount of gas you need based on what your SAC *is*... or you constrain the dive parameters to the gas available.

    Why compare SACs? The SAC bragging seems rather silly in this thread... however on a real dive it is important to compare SACs for gas management purposes... the dive plan to a certain extent will depend on the person with the highest SAC.
     
  8. DeepScuba

    DeepScuba Manta Ray

    724
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    That's right U/Pug, it's SAC bragging rights. It's not blinders. I know very good instructors, cave divers etc etc etc, with thousands of dives, they are as good as anybody in all areas, and UP HERE, IN OUR CONDITIONS, if you guys want me to be specific, there's no way in hell they do 0.35 even. And even they, with their ego's admit that!!

    I'm starting to believe that your "working" dives, are our "coma" dives.

    I guess it's true, what somebody here on this board has as their
    "catch phrase" If you can dive here (Canada) you can dive anywhere.

    Evidently, you guys have it too easy

    :D

    Enjoy breathing nothing :wink:
     
  9. divermasterB

    divermasterB Instructor, Scuba

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    0
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    Carribean, or warm lake not working .45 scfm
    Drysuit single tank not working .63 scfm
    Drysuit single tank teaching .7 scfm
    Drysuit doubles, single stage .77 scfm

    Conditions and workload come into play a LOT when it comes to air consumption.
     
  10. freedive

    freedive Barracuda

    200
    0
    16
    Ok being a newbie to diving (20 dives since being OW certified in June 2003), Iv'e been reading this thread carefully to understand further about SAC rates and how to calculate them.
    Thanks Atticus and Diver0001 for the info provided :) It shows me I'm averaging 0.57cf per min and still need quite a bit of improvement.
    Please correct me if my calculations are wrong here but on the subject of a 0.18 SAC rate, I dive with someone who (weather and current permiting) does it all the time. She consistently does 200 min at 25 feet with a AL80 with 3000 psi returning with 500 psi:

    2500psi or 83%
    83% of 76cf = 63cf
    at 25ft rate 63/200 = 0.315 c ft per min
    0.315cf/1.75ata = 0.18 per min SAC rate

    Again please correct me if my calculations are wrong but if they are not this SAC rate is not impossible. Her personal best is 210min which would make it a 0.1714285. She is the best example I know and have witnessed.
     

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