Air consumption?

[Lorie]

How much air would you use on a dive at say 30' for 40 mins?

 

[Sas]

836L approx.

 

[mts0628]

How much air would you use on a dive at say 30' for 40 mins?

Hi Lorie:

Read this by Lamont. All you ever wanted to know about gas calculations at the recreational level and made easy too. I hope this helps.

With kind regards,
Thomas

 

[The Kraken]

Without any other information, based upon a square dive profile:

With a SAC rate of:
0.40 cfm = 30.5 cubic feet
0.50 cfm = 38.2 cubic feet
0.60 cfm = 45.8 cubic feet
0.70 cfm = 53.5 cubic feet
0.80 cfm = 61.1 cubic feet
0.90 cfm = 68.7 cubic feet
1.00 cfm = 76.4 cubic feet

Hope this helps.

the K

 

[mts0628]

Without any other information, based upon a square dive profile:

With a SAC rate of:
0.40 cfm = 30.5 cubic feet
0.50 cfm = 38.2 cubic feet
0.60 cfm = 45.8 cubic feet
0.70 cfm = 53.5 cubic feet
0.80 cfm = 61.1 cubic feet
0.90 cfm = 68.7 cubic feet
1.00 cfm = 76.4 cubic feet

Hope this helps.

the K

With all due respect to the Kraken, Surface Air Consumption rate is reported in pounds per square inch per minute, while Respiratory Minute Volume is reported in cubic feet per minute. Substitute RMV for SAC in the above, and all is good. And as a good starting point, an average RMV is about 0.75 Ft³/minute.

 

[Crowley]

Me personally? between 600 - 800 litres of air depending on what I'm doing - that's approximately 40 - 70 bar on a standard 12 litre tank filled to 200 bar (you can do the imperial coversions yourself!).

A novice diver (or even an experienced diver, to be fair) could quite easily consume twice as much depending on their fitness, comfort level, and lung capacity (it can vary a great deal). I've known DMs and Instructors who've run out of air before their students! There are plenty of techniques to help improve your air consumption (posted here at some length so I won't do it here) - just think yoga!

Cheers

C.

 

[ivobj]

Without any other information, based upon a square dive profile:

With a SAC rate of:
0.40 cfm = 30.5 cubic feet
0.50 cfm = 38.2 cubic feet
0.60 cfm = 45.8 cubic feet
0.70 cfm = 53.5 cubic feet
0.80 cfm = 61.1 cubic feet
0.90 cfm = 68.7 cubic feet
1.00 cfm = 76.4 cubic feet

Hope this helps.

the K

I guess Kraken's table above says it all!

In my specific case, based on my average SAC of 14 L/min (0.51 cfm) and a squared profile, I would consume around 1060 L (38.5 cuf), meaning for an AL80 I would finish the dive with 590 L (21.5 cuf) + 550 L (20 cuf) of the reserve, a pretty confortable safety margin.

For gas calculation purposes, specially on deco dives, to add safety, I use SAC of at least 18 L/min ~ 20 L/min (0.65 cfm ~ 0.73 cfm), depending on the phisycal effort and stress levels antecipated for the dive, to find the total volume of gas needed.

 

[Teamcasa]

How much air would you use on a dive at say 30' for 40 mins?

I would use about 60% of the air in my HP100 tank.

 

[Drew Sailbum]

I would use about 22.9 cuft of air, or about 859psi from an 80cuft cylinder. My air consumption rate trends to the low end of the spectrum.

 

[The Kraken]

mts0628,

With all due respect, when I had my class "A" flight physical, was put on the treadmill and had a hose attached to my nose and mouth so that my air consumption could be measured, the unit of measure used by the doctors to describe the volume was in cubic feet of air per minute.

If you're breathing is measured in psi, how many psi of gas do you remove from the atmosphere every minute?

The psi method of determining gas consumption is based upon the size tank one is diving and varies with the size/working pressure of the tank.

The cubic foot method of determining gas consumption is based upon the amount of gas aspirated by the person. This method remains constant regardless of what size tank, or its working pressure is used.

the K