Air Consumption

[Squishy]

Hello Everyone,
I have a question about air consumption. I am a relatively new diver. I have a total of 14 dives. I am in reasonably good shape and do aerobic activity 4 days a week for 30 to 60 minutes a day.

I seem to use air faster than the people with whom I dive. If we all start at 3000 pounds, when I am down to about 500 pounds, everyone else is still at about 1000.

I consciously breath deeply as we learned to do in class. Above water, I tend to breath much shallower. I watch others to see if I am exhaling more frequently than the others, but it does not seem that I do, but it's hard to judge. I feel relaxed when I dive. In fact, it seems that this is where I feel most relaxed.

So what is the secret to using less air? Am I breathing too deeply? The only problem is that I end my dive (and my dive buddy's dive) before everyone else. My buddy has never complained about it at all, (Couldn't ask for a better dive buddy), but I would like to learn how to increase my bottom time.

Thanks!
-Mike-

 

[on_two_wheels]

I think you'll find most responses say this is completely normal. Even in good health, when your underwater your brain will fight itself since breathing in that environment isn't normal. As you (and brain) get conditioned to the normalcy, it will slow down. Granted, there are breathing techniques that allow for less consumption, gear placement, amount of movement, etc. All will be honed with more experience.

 

[1_T_Submariner]

Get a bigger tank and your air will last as long as your buddies. Don't mess with breathing other than how you are breathing. Your air consumption should go down with time.

 

[joji]

For an extend, yes, with more log time underwater, your air consumption will improve, but we have also to consider the fact that different person has different lung sizes, like for example, a man almost always will be heavier in gas usage than a woman diver, a known active, athletic, busy body kind of person will used more air than a passive person,so, in short, we just practice and then get our real gas consumption, then plan our dives accordingly.

 

[everlasting]

No one has mentioned this so far, but how is your trim? Are you overweighted? If you're more streamlined and if you're weighted correctly, you reduce drag and you'll need less energy for every movement you make, which translates into using less air. An overweighted diver who has to fight to maintain correct trim will use more air than a correctly weighted, streamlined diver.

But. As others said, relax. Your air consumption will go down. I have 40 dives now (so I'm still a new diver too), and my last few dives have been the first where my air consumption was as good as my buddy's.

 

[scubamickey]

What is your SAC rate?

 

[TSandM]

This is a very common problem for new divers!

There are really two answers to this question, and they are interrelated. One is relaxation, and the other is efficiency.

When you are a new diver, the very mechanics of being underwater and managing your buoyancy, navigation, and all your equipment use up a lot of bandwidth, and very new divers are rarely completely relaxed. Tension causes you to breathe inefficiently, keeping your lungs fairly full and just exchanging a small amount of gas with each breath (this contributes to the difficulties with buoyancy that new divers have, too!) Because a large part of each breath is only ventilating the trachea and major bronchi, structures which do not participate in gas exchange, a lot of the breath is wasted as far as getting oxygen into the bloodstream and CO2 out are concerned. Therefore, you have to breathe at a higher rate, wasting a lot of your consumed gas into the water.

But a major thing that contributes to tension, and massively contributes to gas utilization, is inefficiency. What do new divers do that's inefficient?

To begin with, they often do not have their equipment properly balanced. Especially when diving in cold water, where a lot of weight is necessary, it's important to distribute that weight so that the diver in a horizontal position will tend to REMAIN in a horizontal position. If you are carrying a lot of weight low on your body, as the integrated weight pouches of many BCs will place it, then you will always tend to float in a feet-down position. Once you think about it, it becomes pretty obvious that, if you are feet down, every kick drives you UPWARD. In order to stay at the same depth, the diver has to keep himself negative, so the upward drive of the fins is countered by the sinking created by the negative buoyancy. What that means is that a good portion of the effort expended in every kick results in no net motion at all! Since muscle activity uses more oxygen and creates more CO2, this means that all that useless motion is sucking gas out of your tank.

In addition, because of the lack of balance, new divers often swim with their hands. The hands are not an efficient means of propulsion underwater, especially not compared with fins, so again, this is largely wasted motion.

When you are not balanced so that you can remain still, you must swim constantly. I can remember my own beginning days -- it irritated the daylights out of me that my buddies could simply STOP and look at something, when I would have to swim circles around them, because I simply couldn't be still. Achieving a good, flat body posture and balancing my equipment allowed me to learn just to hang in the water, which is not only a great way to look at things, but is great fun in its own right.

Achieving good buoyancy control, which includes getting properly weighted, helps with gas consumption as well. You probably learned during OW that you could affect your buoyancy with your breath. This is very true, but if you overuse this mechanism, you waste a lot of gas (not to mention setting yourself up for a CO2 headache). In the beginning, when you aren't quick to detect changes in depth, and when you are perhaps not as judicious in adding and venting air from your BC, you will make many buoyancy adjustments, both with the BC and your breath. As you gain experience, you will learn how to anticipate the need to change buoyancy, and you'll learn to add or vent air in very small amounts, keeping your buoyancy from ever being far from neutral. Gas consumption will go down with this facility, as well.

Finally, there is a level of gas consumption that will be required by your body and your degree of fitness. My favorite dive buddy is one of the most beautiful divers you could hope to see -- He is relaxed, extremely still in the water, and VERY skilled with his buoyancy. But his gas consumption is almost twice mine, simply because he's about twice my size. It would be absolutely counterproductive for him to work on his gas consumption as an end in itself; we simply dive different sized tanks, and life is good for both of us.

Have fun with this, and don't get anxious about it. Do, if you can, spend some time in a pool working with the trim pockets on your BC, or some weight pouches on your cambands, and try to get your rig balanced so you can hover in a horizontal position. This will result in a very big reduction in your gas needs.

 

[Cabbie]

I've always loved my air (I pay for it, so I'm going to use it) and have 200+ dives.

Recently there does seem to have been an improvement, but to be on the safe side on a liveaboard recently, I had the crew top up my tank with a little bit extra

 

[Web Monkey]

Hello Everyone,
I have a question about air consumption. I am a relatively new diver. I have a total of 14 dives. I am in reasonably good shape and do aerobic activity 4 days a week for 30 to 60 minutes a day.

I seem to use air faster than the people with whom I dive. If we all start at 3000 pounds, when I am down to about 500 pounds, everyone else is still at about 1000.

1_T_Submariner and TSandM nailed it.

You'll use less air as you get better at diving, however until then, just get a bigger tank.

There are no prizes for using less air, other than the length of the dive, so if you start with a bigger tank, you should be able to hang out as long as your buddies.

If you're diving with an 80, try a 95, or possibly a 105.

Terry

 

[Trixxie]

What is your SAC rate?

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.

SAC = surface air consumption rate.
it's a mathematical formula to find your breathing rate:

The compressibility of gasses is also an important consideration for divers due to its affect on how long a diver can stay underwater. Scuba regulators are designed to deliver air to a diver at the same pressure as the surrounding water pressure, at ambient pressure. That means that when a diver fills his lungs at a depth of 33 feet, he is taking in the equivalent amount of air as two breaths at the surface. Obviously then, a tank will only last half as long at 33 feet as it would at the surface. And tank that would last 1 hour at the surface would only last 1/3 as long, or 20 minutes, at a depth of 66 feet, etc.

It can be beneficial to be able to estimate how long a scuba tank might last at a given depth when dive planning. To determine this, it is first necessary to determine a divers Surface Air Consumption (SAC) rate. For example, if you are diving at 33 feet, and use 500 lbs of air in 10 minutes, it is easy to determine that you are using 50 lbs per minute. This is only true for this depth however. How much air would you use at 66 feet, or 99 feet?

The first thing we must do is calculate SAC rate. In the preceding example, a diver using 50 pounds per minute at a depth, would use 25 pounds per minute at the surface. His surface air consumption rate is 25 pounds per minute. With our SAC number of 25, it is easy to calculate our consumption rate for depths of 33, 66, 99 feet etc. We know we are under 3 times the pressure at 66 feet, so we would use 3 times as much air, or 75 pounds per minute at this depth.

The process becomes slightly more complex if depth consumption rate (DCR) is determined at a depth that is not in even atmospheres. (Not at 33, 66, 99 feet etc.) For this situation we use a formula that is simply an adaptation of Boyle's Law to determine our SAC rate:

SAC Rate = (DCR x 33) / (Depth + 33)

Let's look at an example. Suppose you did a 50 foot dive for 25 minutes and used 1700 pounds of air. This would mean our DCR is 1700/25 or 68 pounds per minute. Using this in our formula we get:
SAC Rate = (68 x 33) / (50+33)

or: SAC Rate = 2244/88 or 25.5 pounds per minute.

We can then turn the equation around to determine our DCR for any depth.

It may be what some of the others have hinted at
Trim, weighting and just being new to the water. Most folks SAC rate improves with time and experience.