Air Consumption

[Rick Inman]

I'll piggyback on a couple of others.

I would suggest totally ignoring how much gas you breath, and focus on the skills that TSandM talked about, and the gas consumption will take care of itself.

 

[Sas]

Since I have obtained an air-integrated computer I have noticed how a number of things affect my SAC:

-firstly, slow down. When I have dived with more experienced divers they go very very slowly and when I do the same my SAC drops. Also when my buddy has taken his camera and we are going slow for pictures, my SAC drops then too. Most new divers go *way* too fast. I know I used to swim around really fast but there is no need really and you miss a lot of stuff.

-Stay warm. On my second dive of the day in cold water my SAC has always increased as I am in a wetsuit in 12C water so am quite chilled on repetitive dives.

-If you start getting stressed about anything such as equalising, your SAC will probably go up significantly. When I had an ear clearing issue my SAC jumped to 60L/s, so three times what it usually is. So yea, descend slow if you have ear problems, it isn't a race. I'd often use up 30bar just descending to 20L as I found it so stressful equalising. Anyway, after learning more about equalising and also taking Sudafed I have fixed that issue.

-Don't breathe deep IMO (though I am guessing a lot of people would disagree with me). For one thing it means you need better skills in buoyancy, which you might not have as a new diver. Just breathe as normal, like you do on land! Don't think about your breathing really, it should come naturally. Also don't hold your breath or breathe shallow and quick. Apart from the obvious reasons, you can also give yourself a nasty C02 headache holding your breath or breathing too rapidly.

-Do you mess around with your BC often? If you are constantly deflating and inflating, that will contribute a lot to air consumption also.

-Get properly weighted if you aren't already. I am overweighted at the moment so I am sure that is not helping my SAC (about 18L-20L/min which is not good but not terrible). Finally got some smaller weights yesterday so will see how I go next weekend

-Relax! That is the biggest thing as anything that slightly stresses me will mean my breathing rate jumps. Like I've been tangled in a fishing line before, had equalising issues, or I've gotten lost and it always means my breathing rate goes up significantly. I don't feel particularly stressed at the time mentally but obviously it impacts on my breathing. Having an air integrated computer has really helped that as it shows me when my breathing rate has gone up, so I now know the things that trigger an increase in SAC so just remind myself to calm down and relax. So yea, these days my breathing rate is a lot more stable. So yea, even if you feel more relaxed diving like you mentioned, you might have little things that trigger an increase in breathing rate for a few minutes here and there that might cause your gas consumption to increase.

After trying out all the suggestions here and if you still have a high rate compared to your buddies, don't worry about it. It isn't a competition so just use a bigger tank Good luck!

 

[emttim]

Since I have obtained an air-integrated computer I have noticed how a number of things affect my SAC:

-firstly, slow down. When I have dived with more experienced divers they go very very slowly and when I do the same my SAC drops. Also when my buddy has taken his camera and we are going slow for pictures, my SAC drops then too. Most new divers go *way* too fast. I know I used to swim around really fast but there is no need really and you miss a lot of stuff.

-Stay warm. On my second dive of the day in cold water my SAC has always increased as I am in a wetsuit in 12C water so am quite chilled on repetitive dives.

-If you start getting stressed about anything such as equalising, your SAC will probably go up significantly. When I had an ear clearing issue my SAC jumped to 60L/s, so three times what it usually is. So yea, descend slow if you have ear problems, it isn't a race. I'd often use up 30bar just descending to 20L as I found it so stressful equalising. Anyway, after learning more about equalising and also taking Sudafed I have fixed that issue.

-Don't breathe deep IMO (though I am guessing a lot of people would disagree with me). For one thing it means you need better skills in buoyancy, which you might not have as a new diver. Just breathe as normal, like you do on land! Don't think about your breathing really, it should come naturally. Also don't hold your breath or breathe shallow and quick. Apart from the obvious reasons, you can also give yourself a nasty C02 headache holding your breath or breathing too rapidly.

-Do you mess around with your BC often? If you are constantly deflating and inflating, that will contribute a lot to air consumption also.

-Get properly weighted if you aren't already. I am overweighted at the moment so I am sure that is not helping my SAC (about 18L-20L/min which is not good but not terrible). Finally got some smaller weights yesterday so will see how I go next weekend

-Relax! That is the biggest thing as anything that slightly stresses me will mean my breathing rate jumps. Like I've been tangled in a fishing line before, had equalising issues, or I've gotten lost and it always means my breathing rate goes up significantly. I don't feel particularly stressed at the time mentally but obviously it impacts on my breathing. Having an air integrated computer has really helped that as it shows me when my breathing rate has gone up, so I now know the things that trigger an increase in SAC so just remind myself to calm down and relax. So yea, these days my breathing rate is a lot more stable. So yea, even if you feel more relaxed diving like you mentioned, you might have little things that trigger an increase in breathing rate for a few minutes here and there that might cause your gas consumption to increase.

After trying out all the suggestions here and if you still have a high rate compared to your buddies, don't worry about it. It isn't a competition so just use a bigger tank Good luck!

As far as breathing deeply goes, the reason you want to do so while on scuba, is that on land your air volume is roughly 700 mL, and about 350-400ish of that is dead space. Now, when you add a regulator to the mix, the dead space in your lung volume increases slightly. Since dead space is essentially air that is not used, after each breath, dead space tends to have a fairly high amount of carbon dioxide since a lot of it will be exhaled air. When you do not breath deeply, you risk breathing too much dead air and not enough "fresh" air from your tank, and as a result, you can increase your body's carbon dioxide levels. What will this do? Well, for one, you might get a headache. Two, your body's respiratory drive is driven by your CO2 levels, so if you have increased CO2 levels, you'll breath more often which defeats the entire purpose. Three, and this should be most obvious, if you're not getting enough oxygen with each breath, then again you will be breathing faster and generally your body gets pretty agitated over a lack of oxygen.

Due to the reasons mentioned above, I would strongly advise against breathing normally and especially do not breath shallowly as Sas already mentioned. Breathing deeply will waste a lot of air though if you do it quickly. Don't suck in a bunch of air and then blow it out just as fast. Inhale slowly (and deeply), and exhale out slowly.

Concerning deep breathing for buoyancy, unless you're diving warm water, the alternative is cold which means buoyancy is going to be an issue regardless of how you breath due to the fact that you may need to adjust your buoyancy either through altering your breathing or adjusting the air in your BCD with any depth change or another change that may affect buoyancy (such as your tank starting to get empty at the end of a dive).

Weighting is definitely a big issue...do a buoyancy check before you drop down, you should be at eye level while holding a normal breath of air. Especially check trim by stopping all movement while being horizontal underwater and see if you tilt to either side then adjust accordingly. I had to do this myself and I now dive with 2 pounds less on my right side for example.

Avoid anything such as caffeine that will increase your heart rate and/or respiratory rate. Aside from the obvious predisposing factor to DCS, caffeine will cause you to breath faster and your body will require more oxygen as a result of increased circulation and muscle activity since caffeine's obviously a stimulant.

Slowing down definitely makes a huge difference. I finally dived with someone off here who goes at a much slower pace than my regular buddy, and as a result, my bottom time quite literally doubled.

Lastly, I agree with getting a big tank. Until your air consumption gets better, it will help you stay down as long as everyone else in the meantime, and once your air consumption improves, you'll be getting some pretty nice bottom times with a 95 or 100.

 

[Sas]

Due to the reasons mentioned above, I would strongly advise against breathing normally and especially do not breath shallowly as Sas already mentioned. Breathing deeply will waste a lot of air though if you do it quickly. Don't suck in a bunch of air and then blow it out just as fast. Inhale slowly (and deeply), and exhale out slowly.

I think that is the issue I was getting at. Often people interpret breathing deeply to be breathing deeply fast. That is always what I thought it meant and in my earlier dives ended up with a few very nasty headaches because of it. I think people tend to naturally breathe deeper on scuba anyway, so it is not something you should need to concentrate on. I guess what I meant by breathing normally is just not pay a huge amount of attention to it, I found when I stopped worrying about my breathing rate it got under control and now breathing is no different to when I am on land. I don't think about breathing on land and now I rarely do underwater unless my computer beeps at me when it detects a sharp increase! But yea, others might not have had the same experience.

 

[scubamickey]

no offense to the OP but do you really think they would know what that is?

They may not even know what SAC stands for being they are a new diver.

No offense taken. If they don't know what a SAC rate is then the only person who should take offense is their instructor for not teaching them. This is a basic calculation that every new diver should know. Otherwise, how the heck do they know how long of a dive they can do?

I learned about SAC rates in my OW class. If people aren't learning this as part of their basic training, then it explains why the rate of out of air situations is as high as is reported.

 

[scubamickey]

I'll piggyback on a couple of others.

I would suggest totally ignoring how much gas you breath, and focus on the skills that TSandM talked about, and the gas consumption will take care of itself.

You can't mean that. I agree with focusing on skills but knowing your gas consumption is vital to planning a dive. They are not mutually exclusive. It is insane to just go diving without having a clue how much gas you need to do the dive and safely ascend.

You can know your SAC rate and safely plan a dive. That doesn't mean that you can't concentrate on buoyancy and trim during the dive. One happens on the surface and the other in the water.

But you CAN NOT ignore how much gas you breath. You know better than that Rick, you were GUE trained. Please tell me that I am misunderstanding what you wrote.

 

[Rick Inman]

You can't mean that. I agree with focusing on skills but knowing your gas consumption is vital to planning a dive. They are not mutually exclusive. It is insane to just go diving without having a clue how much gas you need to do the dive and safely ascend.

You can know your SAC rate and safely plan a dive. That doesn't mean that you can't concentrate on buoyancy and trim during the dive. One happens on the surface and the other in the water.

But you CAN NOT ignore how much gas you breath. You know better than that Rick, you were GUE trained. Please tell me that I am misunderstanding what you wrote.

I wasn't meaning, don't know your consumption rate. I wasn't meaning, don't plan your dive based on gas consumption. I was meaning, that whatever it is, don't focus on improving it. Focus on improving your skills and the consumption rate will take care of itself.

I can see how the way I phrased it would be confusing. So yeah, ya gotta know your sac.

Thanks for the clarification.

 

[Cabbie]

I've been diving for a long time and had never heard of SAC rates until I joined SB. Maybe when I started it wasn't part of the course...it's all been very interesting reading.

 

[Riger]

Hello all,

(btw: 9 Days before Wifey and I leave on a Red Sea Liveaboard !!)

Back to the matter at hand, 2 things;

1. I was never taught about SAC rates on OW course, of course I soon realised what they are and that they have a valuable role in your planning ...

2. Someone in this thread mentioned that being fit increases your air consumption. I am presently a little chunky and not too fit, but I have recently started a fitness program and am choosing healthier culinary options, if this is going to be a disadvantage for my SAC rate, then ... ? I thought fit body = lower heart rate and therefore more efficient use of 02 therefore ..... you see where I am going. Anyone care to enlighten (ha ha see the pun) me?

Did I mention that its 9 Days before Wifey and I leave on a Red Sea Liveaboard !! Yaay

Regards
Richard

 

[Rick Inman]

2. Someone in this thread mentioned that being fit increases your air consumption. I am presently a little chunky and not too fit, but I have recently started a fitness program and am choosing healthier culinary options, if this is going to be a disadvantage for my SAC rate, then ... ? I thought fit body = lower heart rate and therefore more efficient use of 02 therefore ..... you see where I am going. Anyone care to enlighten (ha ha see the pun) me?

Again, just saying, I don't think the goal should be to improve your sac. The goal should be to be fit and improve your skills and technique, and let the sac take care of itself - which it naturally will.

Oh, and, how long did you say before your Red Sea trip?