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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)
  2. >10-12 lpm (0.36 - 0.42 cf/m)

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

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

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

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

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

    7 vote(s)
  1. DeepScuba

    DeepScuba Manta Ray


    It's funny you mention that some folks do the "PSI per minute" calculation instead.

    When I'm doing a deco dive (and sometimes even a Rec one) what I will do, as triple redundancy while I'm doing my bottom time (I know it's totally NOT required, but I do it anyways, for kicks) is, after I've figured out the entire dive plan (B/Time, Air Consumption, 1/3rds etc etc) I will calculate, using "PSI per minute" my "turnaround PSI" which should, if the time and PSI happen at the same time, give me my over/under, of my calculated SAC rate. That way I know if my SAC rate was different for a particular dive, and possibly, why.

    I'll just jot it down on my slate to keep track.

    It's especially useful when I'm doing mulitple dives off of one set, and easily helps, with no calculators on board, if I have over used dive 1's air requirements, to find out if dive 2's still got enough air for my "planned" dive, and maybe dive # 3 too!!!

    It's a quick reference, as we always know our tank PSI at a moments notice.

    YES, there's enough padding everywhere to make this a mute point, but there's nothing better than knowing the precise PSI turnaround for subsequent dives off of 1 set.

    Yes, I love doing Math.

  2. sharpenu

    sharpenu Solo Diver

    # of Dives: I just don't log dives
    Location: Orlando, Florida
    I live here in Florida and I pretty much dive every other weekend or so. I am 5'10" and 230#. Well, my diving has been infrequent this year due to work and school, but any way, my average SAC for last year (2002) is 0.54 with a low of 0.35 and a high of 0.72. I dive steel 120's and have no problem doing 65-70fsw drift dives of over 75 minutes.

    That being said, my SAC is poor compared to my ex-GF. (She is also a member of this board- Just Jules) Her SAC is incredible. Diving 80's, she still beats me in the SAC category. She routinely comes up with more PSI than I do, that is why I got the 100's to start with, b/c I got tired of always cutting her dives short. I believe IIRC, that her SAC is around 0.30 or less. I remember 1 dive in particular where she had a dive with a SAC of 0.18.

    It can be done.
  3. James connell

    James connell Barracuda

    i like singles not twins - if i could figure out how to get it in the water i'd go for one of those propane storage/fill tanks.
  4. crispos

    crispos Instructor, Scuba

    I find this kind of poll really useless because a big person uses less air than a little person. Not to mention a few other variables you have to hold constant, like activity level, cold, current, age, etc etc.. My Pontiac Trans-Am sports car gets 20 mpg on the highway and alot less in the city. So what does that mean about it or me or my driving or the condition of the car? No much. By the way, Europeans, that is 5,700 cc pr about 3 times the size of engine commonly seen in your territory.
  5. phree337

    phree337 Solo Diver

    I've only been diving since July '03, but I've been tracking my SAC on every dive. What I do is take my max depth and compute the dive as a square profile--i.e., all the air was consumed at that depth, and only that depth. This to me is not as accurate as being able to track the whole dive profile and computing air consumption at all the different depths, but hey, I'm new to the sport and a rough idea is just fine for me as an OW diver.

    So as for results...I averaged 0.6 cfm during my training dives, had over a 0.7 cfm my first dive after that, and have been decreasing toward 0.5 cfm since then. Yesterday I had a 0.41 cfm sitting on the bottom of a river looking for fossils and shark teeth--truly a 'resting' SAC. All these numbers were computed using a 77.4 cu.ft./3000psi factor for Luxfer AL80's.

    When planning gas consumption for future dives, I'm using 0.6 cfm as a starting point, and adjusting from there depending on dive conditions.
  6. DeepScuba

    DeepScuba Manta Ray

    I reiterate.......for Sharpenu.......

    quote...I remember 1 dive in particular where she had a dive with a SAC of 0.18..........endquote


    Argue all you want, pretty soon you'll get down to "Got off the boat with 3000, got back on with 3300"............

    0.18, yeah right, Now THAT'S Padding, and has nothing to do with any amount of diving.

    We ain't fish, and we gotta breathe. Now, if she's 2'6" and 50lbs, I might reconsider her SAC rate of 0.18 as reasonable..........


    I agree with Crispos, warm fuzzy water will make a nice difference, but not THAT nice.

    Current, warmth, activity and exposure suit, age and sex (M/F) not the ACT of it! makes a difference, but 0.30 or whatever it is, is almost dead :)

    Here's what I'm gonna do......hang an ALU80 in my tub tonight, slip a mask on, and stick my face in the water and breathe.......

    I couldn't get any more relaxed (bored) than that.

    The stuff I do for science.
  7. DeepTechScuba

    DeepTechScuba Nassau Grouper

    Just remember that no matter how good your math is underwater, when things go bad, and then go from bad to worse, the likelihood of blowing off all your calculations and pooping in your suit will probably skyrocket your SAC rate more than you ever thought was possible.

    We call that an "oh sxxt" moment.

    A friend of mine had one of those during a Northwest Coast wreck penitration dive. He is a pretty good tech instructor. And even he then started "breathing a lot." :)
  8. Boogie711

    Boogie711 Loggerhead Turtle

    I have a friend who spent 2.5 hours on the bottom of his pool, with a single AL80, in a drysuit, scrubbing his pool. So it was hardly hazardous, but it was 'somewhat' exerting. He was using a hand brush and scrubbing the vinyl liner.

    This guy is also over 6' tall and well over 200 pounds.

    So - assuming he breathed the tank dry (he didn't)...

    77 cf in 180 minutes = .427 cf/minute

    8 feet = approx 1/4 of an atmosphere. So total pressure = 1.25 atmpospheres pressure.

    .427/1.25 = .34

    And he's an airhog compared to some divers I know.

    DeepScuba - Have fun in the tub.
  9. DeepScuba

    DeepScuba Manta Ray

    SO who's gonna tell him that it's 150 minutes, so it 0.42? (I also used 7' since he wasn't on the bottom, quite possible 6 ft). And lets assume that he's scrubbing the sides, and his depth averages less than even 6 ft, then we start to approach 0.50 very quickly.

    She's a shell game.

    It'll gonna be boring as hell, but I'll do it for you guys (the tub project).
  10. Boogie711

    Boogie711 Loggerhead Turtle

    But then again, you're also assuming he breathed the tank dry.

    And your bathtub experiment won't tell us very much, sir. You'll either get hypothermia from sitting in a tub for 3 and a half hours or more, or you'll be an airhog and tell us we're all wrong.

    Save yourself the trouble, and if you REALLY want to get scientific about it, go do a quantitative research study (formal poll with verified results in a variety of conditions.)

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