Air consumption rates.

[scubadada]

0.3 cu ft/min is a pretty extraordinary SAC, even in very benign conditions. I consider myself in the top couple of percentile points when it comes to gas consumption, and on my best, best day I can do 0.38 (according to my Suunto). Someone who can consistently do a full 25% better than that would be a very special (and very small) diver.

Guess you missed my recent post, I'm a 5'10", 180 lb man. My average RMV is 0.37 cf/min based on my last 750 dives. Maybe you are still in the top couple percentile, I wouldn't worry about it. Let me know if you are ever in SE FL, I'd be very happy to dive with you, we'd be pretty well matched.

 

[Iralub]

For the dives since I started downloading computer data, my average sac is about 10l/min. It varies between 8l/min on a very relaxed dive with an Al63 tank and close to 14 l/min on a dive where we spent most of the time kicking against the current. It may be pretty low, but doesn't have much to do with my skill as a diver - it's just because I'm so small and have small lungs.
Between diving with someone who's a good diver with a higher SAC rate and someone who's not good, but will match my air consumption, I prefer the former

 

[scubadada]

So, my average RMV is about 10.5 liters/min, with a range of about 8-12.5 liters/min. We would be well matched.

 

[Iralub]

So, my average RMV is about 10.5 liters/min, with a range of about 8-12.5 liters/min. We would be well matched.

lol, yes, in SAC rate at least. I am about half your size It is amazing how some people who are not small manage such low consumption rates. I guess you can take credit for having achieved it, rather than it being a fluke of nature.

 

[KenGordon]

So, those of you with low SAC rates, could you do me the favour of measuring it on the surface at complete rest?

The question is - are you a small person with less need to ventilate (eg your Tv watching SAC is very low) or are you a person either deliberately limiting their breathing or who is insensitive to CO2.

 

[scubadada]

So, those of you with low SAC rates, could you do me the favour of measuring it on the surface at complete rest?

The question is - are you a small person with less need to ventilate (eg your Tv watching SAC is very low) or are you a person either deliberately limiting their breathing or who is insensitive to CO2.

Or....are you an individual who has a combination of controllable and uncontrollable physiologic characteristics that gives you an RMV at the lower end of the normal distribution? There are other individuals who are on the higher end of the distribution, who post threads to SB, asking for hints on how to lower their gas consumption.

Clearly, RMV is not controlled only by body size or the RMV could be normalized somehow (BSA, BMI, weight or adjusted weight) and then, be nearly the same for everyone. I've never seen what the normal distribution of RMV is for divers. Perhaps someone will make the effort to collect this data, of course only a biased subset of divers would have their RMV to contribute to such a database. I have my RMV for my last 750 dives, I'd participate

 

[KenGordon]

I suspect those who are asking how to lower their sac/rmv may be led into unrealistic expectations of normal.

That is why it would be interesting to see consumption in a non diving environment where diving skill and comfort are taken out of the equation. If you breathe X in front of the telly it seems unlikely you can aim lower in the water without deliberately trying to breath less. I don't think we are supposed to be teaching people to deliberately breath less as that can lead to excessive co2 and the problems that go with it.

You rmv of actual dives isn't entirely the interesting bit, the difference between that and your resting, non diving rmv is.

 

[Kharon]

... The diving RMV is extremely useful in gas planning. ...

All this talk about SAC and RMV is interesting, but I'm not convinced it's all that helpful in gas planning. Keep in mind that the numbers are normalized for depth and altitude (by the computer). My SAC sitting on the sofa is 0.25 cf/min. My Icon usually reports a RMV about 0.6 to 0.7 for most dives. However, when I divide the tank volume by the dive length in minutes - which is the actual amount of gas used - the number is significantly higher. I put together a spreadsheet with dive length, max depth, average depth, computer calculated RMV, and actual gas used. I graphed every pair of data points and found there is no corellation with dive length, max or average depth. Even the computer reported RMV doesn't corelate perfectly. Here is a table of some Roatan dives with computed RMV (col 1)and actual gas used (col 2):
0.52, 0.83
0.58, 1.16
0.6, 1.2
0.6, 1.2
0.61, 1.2
0.61, 1.18
0.61, 1.41
0.61, 1.23
0.63, 1.31
0.64, 1.16
0.67, 1.12
0.69, 1.19
0.7, 1.18
0.7, 1.28
0.7, 1.44
0.71, 1.29
0.72, 1.39
0.74, 1.35
0.83, 1.76
1.21, 1.98

Mean 1.29, Median 1.215, mode 1.2 - for me actual gas used is far more useful in gas planning than a theoretical calculation.

 

[Shotmaster]

Mine runs from .5 mild effort spearfishing to .8 for moderate constant finning looking around the reef for Lobster holes. I don't do much sight seeing diving, which should be lower consumption.

 

[Bob DBF]

Mine runs from .5 mild effort spearfishing to .8 for moderate constant finning looking around the reef for Lobster holes. I don't do much sight seeing diving, which should be lower consumption.

Sounds like your rate is similar to mine, however when I'm filling lift bags my rate is considerably higher.

Other than gas planning, I wouldn't track my SAC rate at all. I don't pay a lot of attention to lowering my SAC rate, I just grab a bigger tank, or make two dives if I need more air for the time I'm diving.


Bob