Average Gas Consumption

[scubadada]

Hi @BLACKCRUSADER

I'm assuming your pulse oximeter is incorrect. 88% saturation is at the very low end for people with severe lung disease such as COPD. That level, or a little lower can be dangerous. Perhaps your pulse ox needs calibration or is defective.

 

[scubadada]

Just a reminder, you can change your vote in this poll if your average RMV changes, as @RayfromTX recently did.

Make sure you are using the correct cylinder characteristics in your RMV calculations, volume and service pressure.

Average RMV is very useful in gas planning. It can also be useful to look at dives that vary significantly from your average. My RMV is most commonly elevated when I am cold, exertion also plays a role, particularly when prolonged. @dirkhh Average Gas Consumption and then I Average Gas Consumption recently plotted RMV vs dive temperature and demonstrated the relationship. EDIT: See follow up posts regarding the appropriateness of this evaluation

Imperial/metric conversion was posted at the beginning of this thread, here is is again:

1 cu ft = 28.3 liters
1 liter = 0.035 cu ft

<0.3 cu ft/min = <8.5 l/min
0.3-0.39 cu ft/min = 8.5-11.0 l/min
0.4-0.49 cu ft/min = 11.3-13.9 l/min
0.5-0.59 cu ft/min = 14.2-16.7 l/min
0.6-0.69 cu ft/min = 17.0-19.5 l/min
0.7-0.79 cu ft/min = 19.8-22.4 l/min
0.8-0.89 cu ft/min = 22.6-25.2 l/min
0.9-0.99 cu ft/min = 25.5-28.0 l/min
>1.0 cu ft/min = >28.3 l/min

From @dirkhh and others, we have now all learned about the nonlinear compression of gas and the error it can introduce in the RMV calculation. The error is just a few percent with a 3000 psi/207 bar cylinder, but can be much greater with a 4350 psi/300 bar cylinder. If using a high pressure cylinder, you might consider using the Subsurface dive log, that takes nonlinear gas compression into account. A basic discussion is available on the Dive Gear Express website Calculating SCUBA Cylinder Capacity | Dive Gear Express®

Thanks to everyone for contributing to this thread, 416 poll responses now. Good diving to all

 

[tursiops]

I personally know two divers whose average is below .3 - one of them is a ~100lbs female, the other one a >220lbs male in his 50s with around 13k dives. I have been on quite a few dives with both of them, so these are real numbers, not made up bragging... that said, I'm a 250lbs male in my 50s and in warm water my average is below .4
View attachment 657547
Note that all of these numbers are Subsurface data, so taking gas compressibility into account, which depending on your tank type will give you slightly lower (but, in fact, more accurate) numbers than what you'd get with naive calculations

Hey @dirkhh

Your graph was a great idea. I have known that my RMV was adversely affected by colder water for a long time, but I have never taken the time to prove it. My graph is not as pretty as yours, did it with Excel. The scattergram represents my last 533 dives from the beginning of 2018 until the present. The line is the linear trend. Clearly, as the temperature goes down, my RMV goes up. My RMV for these dives was 0.35 +/- 0.03 (mean +/- std dev). This needs to be taken with a grain of salt as many of my colder dives were also more strenuous. Revillagigedos and Galapagos were more challenging dives than those in Bonaire or Grand Cayman. Florida represents nearly the entire temperature range.

View attachment 658273

You guys are deluding yourselves if you think that linear fit line has any meaning.

 

[Blackcrusader]

Hi @BLACKCRUSADER

I'm assuming your pulse oximeter is incorrect. 88% saturation is at the very low end for people with severe lung disease such as COPD. That level, or a little lower can be dangerous. Perhaps your pulse ox needs calibration or is defective.

Works fine when my wife uses it her pulse is much faster and 95% plus for oxygen. I have always had low readings.

 

[dirkhh]

You guys are deluding yourselves if you think that linear fit line has any meaning.

I'm always impressed with the constructive and polite tone in these forums.

And while you are a "Master Instructor" with thousands of dives, in the context of that friendly comment I'd be more interested to here about your doctorate in statistics.

The line you are commenting on is actually a regression line that you can use to estimate the relationship between an independent (temperature) and a dependent (gas consumption) variable. And we such it is indeed quite meaningful.

 

[tursiops]

I'm always impressed with the constructive and polite tone in these forums.

And while you are a "Master Instructor" with thousands of dives, in the context of that friendly comment I'd be more interested to here about your doctorate in statistics.

The line you are commenting on is actually a regression line that you can use to estimate the relationship between an independent (temperature) and a dependent (gas consumption) variable. And we such it is indeed quite meaningful.

My PhD is in engineering and applied math, Dude.
Your regression line has no statistical significance.

 

[scubadada]

Hi @tursiops

Is there a better way to analyze the scattergram or is there no value? I only see that there may be a trend toward a lower RMV with higher water temperature, consistent with my personal observation. You are correct, the coefficient of determination for my plot is low. There are many other variables for each dive, exposure protection worn (personal warmth), exertion...

I redid my plot for my last 540 dives starting in 2018. Regardless, I have fun looking at my dive data when I am not lucky enough to be diving

 

[dirkhh]

My PhD is in engineering and applied math, Dude.
Your regression line has no statistical significance.

I will of course not argue with a person of such high education and polite manners.

To those actually interested in the math behind this, it's in the code. Other than that, my mute file has a new entry...

 

[tursiops]

I will of course not argue with a person of such high education and polite manners.

To those actually interested in the math behind this, it's in the code. Other than that, my mute file has a new entry...

So sorry you take offense at facts.

 

[Storker]

Hi @tursiops

Is there a better way to analyze the scattergram or is there no value? I only see that there may be a trend toward a lower RMV with higher water temperature, consistent with my personal observation. You are correct, the coefficient of determination for my plot is low. There are many other variables for each dive, exposure protection worn (personal warmth), exertion...

I redid my plot for my last 540 dives starting in 2018. Regardless, I have fun looking at my dive data when I am not lucky enough to be diving

View attachment 663471

Throw the 95% CI limits into that graph, then we can talk. Or the 99% CIs. Eyeballing those data, even the 95% CI could go either way.

With a datapoint spread like that, the best fit linear regression line doesn't mean crap unless you start including confidence intervals into the discussion.