sac rate converting

[stairman]

I had a hard time finding info on calculating sac rate.Which I had to calculate and use to plan dives in my apprentice class.The NSS-CDS workbook has nothing about the subject.I think its time for them to upgrade.Ive finally learned that you should see how much gas you consume in 10 minutes at an average depth.Convert psi to cubic feet from a convertion chart.Divide c.f used by bottom time for c.f per minute.Find atmospheres [atm] for the depth,and divide c.f per minute by atm's.Example;[steel lp 95]in 10 minutes used 200psi,at 45ft. 200psi on the chart under steel 95 shows 7 c.f. Double that for twin tanks is 14c.f used.14divided by10=1.4c.f per minute.45ft.=2.3atm's[depth divide by33+1]so 1.4 divided by 2.3=.6[sac rate]since sac stands for surface air consumption,it seemslike you could figure that while sitting in your living room,or maybe walking around the house while breathing off your tank.

[andrebasso]

This is an easy formula to convert your breathing rate from one ATA into a breathing rate at any other ATA..... As it is a formula, it is VERY easy to remember. I fashioned this simple equation after the General Gas Law. The format is almost the same as the General Gas Law but with a slght tweak. Let "G" stand for Gas consumption. Let "P" stand for the Pressure or ATA....

The algebraic formula is -
G/P = G/P

Let's say your gas consumption was 4cf per minute at 6ATA, the equation would then read....
4/6 = G/P

If you wanted to find out what that would be at the surface (1ATA), Change the right side of the equation to read....
4/6 = G/1

On the right side, G is not changed because you are trying to solve for G, so you leave it alone. Now that all your known data is plugged into both sides, you begin to solve the equation by isolating the variable. Anything divided by 1 equals a whole, so the equation on the right then reads....
4/6 = G

The next step is to divide out the left side of the equation to fully solve for G.
0.66 = G

You have solved for G at a P of 1ATA. Your SAC is 0.66 which means you breathe 0.66 cft per minute at the surface. To use this for dive planning, you simply reverse this process. You start with the SAC and solve the equation to find what SAC translates into at any given depth. What's really fun is that you can completely disregard the surface and plug in different depths to see what your gas consumption would be like at 9' or at 900' and so on... This is the organized and accurate way of doing it on paper, the easy way though is to just remember - multiply down, divide up. Multiply your SAC by the target ATA when you want to find how much gas you would consume at lower depths. Divide your (G) gas consumption by the target ATA when you want to translate your gas consumption at depth to a shallower depth or to the surface.
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[john]

it seemslike you could figure that while sitting in your living room,or maybe walking around the house while breathing off your tank.

You would think. but there are many other factors involved when underwater.
its best to calculate from and actual dive while your swimming. like say stop at 33ft and swim around and measure yor consumption over 5 minuted.
then figure your sac rate.

[skip]

Best to take two measures. One while swimming for 10 minutes and one while resting for 10 minutes (five minutes is ok for the adhd types). Record time, psi, and depth, before and after the 10 minute period. Keep your depth constant during the 10-min swim. You can then use the data to calculate your working and resting SAC rates.

-skip

[MengTze]

...(five minutes is ok for the adhd types)...

-skip

I would suggest the ADHD types do the 10 mins... just to be sure that when they are actually in water and are all over the place, they have an accurate sac at hand.....

I would suggest the ADHD types do the 10 mins...

Those of us with OCD can do each test for ten minutes - then do it again, for reliability - then once again to make sure we got it right - then once more, for safety's sake - then again, in case anything went wrong...

[DeWayne]

I would suggest the ADHD types do the 10 mins...

Those of us with OCD can do each test for ten minutes - then do it again, for reliability - then once again to make sure we got it right - then once more, for safety's sake - then again, in case anything went wrong...

And then go back and do it all over again the next day just to make sure that you did not overlook any factors