Air consumption rates.

[clownfishsydney]

Lots of confusion here, so much so I cannot even work out what some are saying.

Anyway, over the past 563 dives on my current computer, my SAC/RMV has been 10.9 litres per minute. Generally it is in the range 9.5 to 11 for reef dives above 30 metres. Below this it increases to around 13.5 due to carrying extra tanks and gear and also because these dives are generally done on wreck where there is a current most dives.

From my experience, a few people have consumption rates about the same as me (my wife for example), most who I dive with are about 12-13 l/min on reef dives. A few are about 15 l/min and I have encountered a few who are more than 20 l/min, but these have been mostly (but not always) brand new divers. I see very few, if any divers, who use less than me, but I have seen a couple of small females who do.

Of course, diving in warm water most people's consumption is lower than in average temperature and more in colder water. Gear configuration also has a great impact. Size of the person does not necessarily impact on the rate.

I actually breath a lot slower in the water than on the surface, even when in bed. I do not deliberately slow my breathing, it just happens. I breath about once every 12 to 14 seconds when on a normal dive. I have seen videos of people breathing every 1.5 seconds!!

 

[scubadada]

Lots of confusion here, so much so I cannot even work out what some are saying.

Anyway, over the past 563 dives on my current computer, my SAC/RMV has been 10.9 litres per minute. Generally it is in the range 9.5 to 11 for reef dives above 30 metres. Below this it increases to around 13.5 due to carrying extra tanks...

Hi clownfishsydney, please enter your RMV into the poll in the other thread it you have not already done so Average Gas Consumption

 

[clownfishsydney]

Hi clownfishsydney, please enter your RMV into the poll in the other thread it you have not already done so Average Gas Consumption

Hard to do as it is in imperial and I personally cannot be bothered to find the conversion figures to convert it to metric that 99.9% of countries use!

 

[scubadada]

Hard to do as it is in imperial and I personally cannot be bothered to find the conversion figures to convert it to metric that 99.9% of countries use!

Sorry, there was an imperial-metric conversion table on page 1, just below the poll. I reposted it and include it below. Your 10.9 l/min would be 0.38 cu ft/min, in the 0.3-0.39 cu ft/min range

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

Good diving, Craig

 

[Kharon]

My RMV is 0.37 cu ft/min, I dive for 60 minutes at an average depth of 60 ft. I use 63 cu ft of gas

If you dive for 60 minutes and use 63 cf of gas your actual gas usage for that dive per minute is 63 cf divided by 60 minutes - 1.05 cf/minute. It makes no difference what depth, what conditions, what other factors. The fact is that you breathed through 63 cf of gas in 60 minutes. It's simple arithmetic, not algebra, not calculus - simple freaking division. Amount of gas used by time in using it.

If your actual gas usage were 0.37 cf/min you would have a dive time of 170 minutes.

From a similar thread (bold and underline my addition):

You didn't list your dive depth. But you burned 83 cuft, In 50 mins =1.6 cfm. I will compute it using an average of .55, I calculate your dive depth at 63 fsw. If your dive depth is more shallow, your air consumption number heads towards .8 quickly.

The poster calculates the actual rate to be 1.6 cf/min then does the artificial calculation using an assumed SAC/RMV to derive depth. It's artificial because the guy actually used 1.6 cf/min during the dive independant of depth not 0.55 if the depth was 63 fsw and something else if it was not.

 

[scubadada]

If you dive for 60 minutes and use 63 cf of gas your actual gas usage for that dive per minute is 63 cf divided by 60 minutes - 1.05 cf/minute. It makes no difference what depth, what conditions, what other factors. The fact is that you breathed through 63 cf of gas in 60 minutes. It's simple arithmetic, not algebra, not calculus - simple freaking division. Amount of gas used by time in using it.

If your actual gas usage were 0.37 cf/min you would have a dive time of 170 minutes.

Kharon,

We really do have a communication problem. You seem to forget that RMV is at the surface, 1 atm. It can be used to predict gas consumption on any dive, adjusting for dive depth and time ((avg depth/33 +1) x RMV x dive time). My RMV is 0.37 cu ft/min, I use 1.05 cu ft/min because I was at 2.8 atm, 60 feet.

Your actual gas use calculation is completely dependent on the average dive depth for that dive. It cannot be used to predict gas consumption for any other dive except for one at the same average depth. There is no reason for RMV to correlate with actual gas use as per your previous analysis. RMV is independent of depth, actual gas use is dependent on depth.

Are we on the same page now?

Good diving, Craig

 

[gopbroek]

If you dive for 60 minutes and use 63 cf of gas your actual gas usage for that dive per minute is 63 cf divided by 60 minutes - 1.05 cf/minute. It makes no difference what depth, what conditions, what other factors. The fact is that you breathed through 63 cf of gas in 60 minutes. It's simple arithmetic, not algebra, not calculus - simple freaking division. Amount of gas used by time in using it.

If your actual gas usage were 0.37 cf/min you would have a dive time of 170 minutes.

From a similar thread (bold and underline my addition):


The poster calculates the actual rate to be 1.6 cf/min then does the artificial calculation using an assumed SAC/RMV to derive depth. It's artificial because the guy actually used 1.6 cf/min during the dive independant of depth not 0.55 if the depth was 63 fsw and something else if it was not.

I have to go with the 0.37 RMV number. Without depth weighting the number is meaningless, like comparing apples to oranges. For the kind of diving I do the RMV number is really not needed. Diving in Cozumel is multi-level drift diving where the entire column is usable dive space so if I wish to stretch my time I just go higher, pretty simple. If on the other hand I was wreck diving or deep square profile diving or going into a closed environment then gas planning would become critical and the RMV number becomes very important.

I do get a calculated RMV rate off my log software (Subsurface) expressed as ‘SAC’ not ‘RMV’ which is more appropriate. I do find this to be helpful after the fact to benchmark my breathing rate to see how my trend is after equipment changes.

 

[Kharon]

Bye

 

[Lorenzoid]

If you dive for 60 minutes and use 63 cf of gas your actual gas usage for that dive per minute is 63 cf divided by 60 minutes - 1.05 cf/minute. It makes no difference what depth, what conditions, what other factors. The fact is that you breathed through 63 cf of gas in 60 minutes. It's simple arithmetic, not algebra, not calculus - simple freaking division. Amount of gas used by time in using it.

If your actual gas usage were 0.37 cf/min . . .

It seems you people are going around in circles due to nothing but disagreements over terminology. When @scubadada says his "RMV" is 0.37, I believe he means his gas usage normalized to 1 ata, i.e., what I was taught to refer to as "Surface Consumption Rate" or "SCR." If you multiply 0.37 by the pressure in atmospheres at 60 feet as in his example dive in which he used 63 cf of gas, it comes out to roughly what you calculated: 1.05. So you're saying the same thing.

I was taught that the term "RMV" refers to gas usage that is not normalized to the surface pressure--it's a measure of gas usage at whatever depth (pressure) the gas usage was measured. Now, if I normalize an RMV data point to 1 ata, then I refer to the result as "SCR." To get a useful number for dive planning, I compute an average of such SCR data points over many different dives under different conditions.

 

[scubadada]

It seems you people are going around in circles due to nothing but disagreements over terminology. When @scubadada says his "RMV" is 0.37, I believe he means his gas usage normalized to 1 ata, i.e., what I was taught to refer to as "Surface Consumption Rate" or "SCR." If you multiply 0.37 by the pressure in atmospheres at 60 feet as in his example dive in which he used 63 cf of gas, it comes out to roughly what you calculated: 1.05. So you're saying the same thing.

I was taught that the term "RMV" refers to gas usage that is not normalized to the surface pressure--it's a measure of gas usage at whatever depth (pressure) the gas usage was measured. Now, if I normalize an RMV data point to 1 ata, then I refer to the result as "SCR." To get a useful number for dive planning, I compute an average of such SCR data points over many different dives under different conditions.

Vocabulary and terminology are key. We've all been taught something different, makes communication very difficult