Air consumption

[kidspot]

http://www.spearfishing.org/bruces_tips/java/sac.html has several calculators, but more importantly they have the formulas for figuring things out for yourself...

 

[DTB1981]

http://www.spearfishing.org/bruces_tips/java/sac.html has several calculators, but more importantly they have the formulas for figuring things out for yourself...

I just went to that site and calculated my SAC's

.37 static rate
.47 to .49 on an easy dive at 40'

But my rates jump up when my average deapth is more than 70' it that normal
it goes to .70 or .72

 

[Blackwood]

I just went to that site and calculated my SAC's

.37 static rate
.47 to .49 on an easy dive at 40'

But my rates jump up when my average deapth is more than 70' it that normal
it goes to .70 or .72

While your breathing rate will be higher at higher depths, your SAC rate should not (since it is normalized to the surface). Attribute that to lack of comfort, etc., at depth.

 

[Blackwood]

I would be interested in the formula for adjusting for depth.

It is extremely simple.


(Pressure Used/Rated Pressure)*(Rated Volume/(Average Absolute Pressure Depth*Bottom Time))=SACrate (volume/time).

Assuming you are Imperial, it will be something like this when you work it out:

(2700PSI-500PSI)/(3000PSI) * (78CF/((50ft/33ft+1) * 25min)) = 0.91CF/min




It's usually written differently (as shown below):

[(Pressure Used)/(Average Absolute Pressure Depth*Bottom Time)]/[Rated Volume/Rated Pressure]

 

[The Kraken]

If one's breathing rate increases, given that the intake volume of air on each breath remains the same, the SAC rate will increase.

Given: SAC = .55 CFM
Given: Respiration Cycle = 10 cycles per minute
.55cfm/10 cpm = .055 cfm per cycle

Variable: Respiration Cycle increases 50%
Respiration Cycle is not 15 cycles per minute

.055 cfm X 15 cpm = .825 SAC

the K

 

[spectrum]

I just went to that site and calculated my SAC's

.37 static rate
.47 to .49 on an easy dive at 40'

But my rates jump up when my average deapth is more than 70' it that normal
it goes to .70 or .72

If you are less at ease, colder or otherwise stressed then you should expect an increase since you are now further from your relaxed surface check state. A 60% increase sounds like a lot. How did you feel?

Pete

 

[Blackwood]

If one's breathing rate increases, given that the intake volume of air on each breath remains the same, the SAC rate will increase.

Given: SAC = .55 CFM
Given: Respiration Cycle = 10 cycles per minute
.55cfm/10 cpm = .055 cfm per cycle

Variable: Respiration Cycle increases 50%
Respiration Cycle is not 15 cycles per minute

.055 cfm X 15 cpm = .825 SAC

the K

Of course.

When I said "breathing rate," I didn't mean frequency of breathing. I meant AC rate (as opposed to SAC rate).

 

[DTB1981]

I think I may have been a little stressed. It is not much cooler down there. I think I was messing with my bc alot more getting my boyancy right too.

 

[serambin]

On a recent dive trip, over three dive days and at depths between 40 and 60 feet, my sac rate varied from a low of .38 to .74. Go figure.

Guesses might include:

Wind direction, migration paterns of Monarch Butterflies, what I had for breakfast or what I had before breakfast. Who knows. But vary it does.

So, don't worry, be happy.

Stan

 

[The Kraken]

I think I may have been a little stressed. It is not much cooler down there. I think I was messing with my bc alot more getting my boyancy right too.

Constant fiddling with the B/C, especially at depth, will cause a significant increase in one's SAC. That's gas that's being used that is not being physically consumed.

the K