Average Gas Consumption

[tursiops]

I use memorized values to gauge stress level during the dive.

Memorized values of what?
Stress is different than air consumption.

 

[scubadada]

0.26? That's a crazy low SAC - you must have gills ! The best I've achieved to date was on my November Aruba trip where I was consistently below 0.4 and got as low as 0.35.

I'm lucky, my average RMV over the last 1669 dives is 0.36 +/- 0.04 cu ft/min (mean +/- std dev) I attribute my low gas consumption to having been a competitive swimmer from the age of 4 through high school. I don't really know the answer. I did learn an effective breathing pattern for scuba. My gas consumption has always been on the low side, 1970 to now. I am not svelte, 5'10", about 180-5 lbs. I have exercised about 6 days/week for my entire adult life. I'll be 68 years old next week, I'm doing just fine.

 

[scubadada]

I have understood that RMV (as a correctly define technical term) is independent of depth; it is a physiological concept that describes the uptake in the lungs, at the surface, for example 0.7 cuft/min or 20 l/min. If I increase my ambient pressure to (say) 3ATM, it isn't RMV that changes, it is just the amount of gas I breathe in 1 minute. So I can't say my RMV has tripled...it stays the same. It is my gas need that triples.

In a perverse sort of way, SAC also doesn't need to be stated as at 1 ATM; the S in SAC does that. Similarly to RMV, if I go to 3 ATM, my SAC doesn't change, only my gas needs.

Perhaps all would be clearer if Shearwater -- and others -- did not display SAC (or RMV, for that matter) during he dive but rather displayed psi/min or cuft/min AT DEPTH, so you can more easily see that you are using gas up faster if you are deep. If I glance down and see that SAC stays at 31 psi/min while I am diving, perhaps I might misinterpret that.

As you correctly point out the SRMV is useful in predicting gas use at any depth, its major value in gas planning.

 

[tursiops]

I've thought it should be SRMV, but we already have enough miscommunication as it is

As you correctly point out the SRMV is useful

Nevertheless, he persisted.

 

[scubadada]

As you correctly point out the SRMV is useful in predicting gas use at any depth, its major value in gas planning.

Nevertheless, he persisted.

I can never tell what you are doing, you are older than me., and even more obtuse

Ah, maybe I got it, it's the S, right? I like the S, just too confusing to everyone else

 

[tursiops]

I can never tell what you are doing, you are older than me., and even more obtuse

Ah, maybe I got it, it's the S, right?

Right. Completely unnecessary, and potentially even more confusing, as you suggest.

 

[Dan]

Since lung volume doesn’t change when you are scuba diving, do we need that “S” in SRMV?

 

[scubadada]

Right. Completely unnecessary, and potentially even more confusing, as you suggest.

OK, let's just all agree on the definition of SAC and RMV and use them in our effective communication

 

[Dan]

Pressure and gas density change at depth. That’s why we need to put “S” on SAC.

 

[scubadada]

@Dan

Both SAC and RMV are adjusted for surface consumption using average depth/atm of your dive, right?