SAC Rates - The Good, The Bad, The Average

[j2s]

Don't worry about SAC rates..There are so many variables that effect it, it's almost meaningless.... I've seen people w/average to high rates last longer than those w/low rates.......I have a relatively low one, I'm in shape and dive weekly...I get 1hr45mins to 2 hrs out of an AL80....Occasionally I dive w/a woman who never works out, dives once in awhile and is a 'chain smoker' [2-2 1/2 packs a day !!!].........she gets 2 1/2-2hrs45min on her AL80 and usually comes back w/800-1000psi left....It's just not fair !!!!!....Maybe she'll will her lungs to me when she dies :O !!!!!!

 

[dumpsterDiver]

We can all manipulate our SAC rates by changing our breathing pattern, but we really should resist the temptation. Breathing through a reg underwater is not natural, but we should try to do it as naturally as possible.

I find that the more I dive, the less I think about my breathing. When I am teaching and working underwater, I breathe normally, naturally and as required. With challenging students my SAC goes way up, with easy students or just diving for fun in easy conditions' the SAC goes way down. As long as I plan ahead and carry appropriate back gas, I really don't worry about it or try to change it.

Solid buoyancy, perfect trim, moving slowly, effective finning, a calm demeanor, and relaxed rhythmic breathing, make the SAC rate level off where it is supposed to be.
IMO experienced divers lower their SAC rates because they are more comfortable underwater, more relaxed, and their bodies are demanding less O2. At some point, no matter how relaxed and efficient, we breath what we breath and the SAC fits the individual.

As TS&M suggests, the best way to prolong a dive or to increase the safety margin with a planned minimum reserve, is to use a higher volume tank. It worries me that some suggestions on Scubaboard could encourage risky diving habits. Improper breathing and the resulting CO2 buildup can significantly increase the risk of DCS.

Those seeking advice should research the advisor's profiles, previous posts and even then, draw a bell curve to see where the concensus lies. Look to a trusted outside source. DAN has some excellent articles on their website.

Please be careful.

I think you should compare what you are saying versus TSM's advice. She seems to be advocating a slightly deeper and slower breathing rate than "normal". You seem to be advocating a "normal" breathing pattern.

I strongly favor TSM's advice because it is consistent with my personal experience. Most people who have spent a lot of time scuba diving, DO change their breathing pattern to an underwater one and I think it is generally slower and deeper. Since you are an instructor and have hundreds of dives, I suspect that you also are breathing in a manner that feels "normal", but may not be the same as on the boat.

I don't think new divers should try to make a huge effort to manipulate their breathing (and trying to breath less is not good), but the advice to initially breath a little slower and deeper works.

 

[Divedoggie]

I think you should compare what you are saying versus TSM's advice. She seems to be advocating a slightly deeper and slower breathing rate than "normal". You seem to be advocating a "normal" breathing pattern.

I strongly favor TSM's advice because it is consistent with my personal experience. Most people who have spent a lot of time scuba diving, DO change their breathing pattern to an underwater one and I think it is generally slower and deeper. Since you are an instructor and have hundreds of dives, I suspect that you also are breathing in a manner that feels "normal", but may not be the same as on the boat.

I don't think new divers should try to make a huge effort to manipulate their breathing (and trying to breath less is not good), but the advice to initially breath a little slower and deeper works.

I think that we are splitting hairs.
I prefaced the paragraph that you highlighted with the statement that breathing through a reg underwater is not natural, but we should strive to breathe as naturally as possible. I can't disagree with your assessment of a slightly deeper and slower breathing pattern than "normal". It is likely that when I am working hard, and not thinking about my breathing pattern underwater, it remains slightly deeper and slower than normal.

The main point that I wanted to make, and that you make as well.... people shouldn't breathe "unnaturally" in order to attempt to lower their SAC rate. I think that people underestimate how breathing patterns can influence the likelyhood of hypercapnia and DCS.

I also wanted to reinforce the flexibility that bigger tanks give divers.

 

[dumpsterDiver]

I think that we are splitting hairs.
I prefaced the paragraph that you highlighted with the statement that breathing through a reg underwater is not natural, but we should strive to breathe as naturally as possible. I can't disagree with your assessment of a slightly deeper and slower breathing pattern than "normal". It is likely that when I am working hard, and not thinking about my breathing pattern underwater, it remains slightly deeper and slower than normal.

The main point that I wanted to make, and that you make as well.... people shouldn't breathe "unnaturally" in order to attempt to lower their SAC rate. I think that people underestimate how breathing patterns can influence the likelyhood of hypercapnia and DCS.

I also wanted to reinforce the flexibility that bigger tanks give divers.

Sounds like we are in agreement then, however the knowledge that deeper and slower is better can become a non-trivial issue if the diver finds themselves deep and over exerted and out of breath.

And I completely agree, trying to lower the sac is not good, trying to relax and maintain an efficient breathing pattern is.

 

[waterpirate]

Don't worry about SAC rates..There are so many variables that effect it, it's almost meaningless.... I've seen people w/average to high rates last longer than those w/low rates.......I have a relatively low one, I'm in shape and dive weekly...I get 1hr45mins to 2 hrs out of an AL80....Occasionally I dive w/a woman who never works out, dives once in awhile and is a 'chain smoker' [2-2 1/2 packs a day !!!].........she gets 2 1/2-2hrs45min on her AL80 and usually comes back w/800-1000psi left....It's just not fair !!!!!....Maybe she'll will her lungs to me when she dies :O !!!!!!

This is cruel reality that should motivate your buddy to "clean up". Her sac rate is better cause 1/2 her lungs are pre-plugged by smoking. Her body functions with less volume and less o2 content than a healthy persons lungs. Same thing happpened to a tech buddy of mine. He finally kicked his butts and sac rate went through the roof as his lungs repaired themselves.
Eric

 

[ajduplessis]

SAC is not important, I make sure I take enough and do my planning accordingly.

 

[Tigerman]

SAC is not important, I make sure I take enough and do my planning accordingly.

Thats actually WHY its important and the ONLY reason its important.. To know how much gas to bring..

 

[waterpirate]

To further simplify:
If you have to do a sac rate calc for a ndl dive, you need bigger tanks.
Eric

 

[scubajo007]

My SAC rate from the last 10 dives (tropic water) varies between 0.62 to 0.83. Correct me if I do wrong, I use average depth when I calculate the rate.

 

[Bob DBF]

SAC is just another number and only important if you need it. Mine usually runs from .7 to .9 and that is in cold water and I like to move around underwater and I have some long surface swims. I did have a .5 on a slow camera trip through a kelp forest, and on the other end, a 1.7 which was quite high but I was filling lift bags at the time.

So I guess that gives me the good, the bad, and the average.

The good news is that I can use 1.0 for any calculations so I can do them in my head to get a rough idea quickly.



Bob
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I may be old, but I’m not dead yet.