Do you use your SAC for anything? POLL

[300bar]

RMV? not sure I know what that stands for SAC can be worked out no matter what cylinder you are using. We have two sized Cylinders and work out SAC each dive depending on the cylinder.

We have a pretty clear idea of what we can do on each cylinder for a given dive, depth and fill pressure.

In Oz RMV (Respiratory Minute Volume) is a medical term & almost never used in diving. If it is, it is interchangeable with the term SAC (Surface Air Consumption). They are both expressed in terms of volume/minute at 1 bar.

In the US they also measure surface consumption rates in terms of pressure/minute.

Because of the variations in the ways tanks are marked for US imperial & international metric, the variation in the use of SAC, RMV, & SCR, some confusion can arise.

I uderstand what you mean, we use the same system on O2 usage.
But for those whe are NOT medicaly trained we just use SAC.

 

[LakeCountyDiver]

I think it's very sad that so many divers see absolutely no need to understand thier breathing rate when diving. How in the hell can you PLAN a dive if you don't know how long your tank will last. "Oh I'll just jump in and come up when I reach 700psi" is not dive planning.

You should know your 3 SAC rates. resting (aka deco), normal, and stress.

Well you would have to do those "Oh I'll just jump in and come up when I reach 700psi" a few time before you can get a real SAC right??? If you took your SAC off your first 5 dives dont you think it would have changed by now? Just sayin.

How do you calculate SAC/volume? I dive a XS HP100 (first one on the page) if that helps.

 

[Kevrumbo]

Better Terminology:

SCR (Surface Consumption Rate) --in either volume per minute or pressure per minute for a particular tank size, referenced to surface or standard ambient atmospheric pressure of 1 ATA.

DCR (Depth Consumption Rate) --similar to above, but now multiplied by the working depth factor in ATA. For example, you are at 30m/100' which is equivalent in Atmospheres Absolute to 4 ATA; you have SCR of 22 litres/min or 0.75 cuft/min at the surface. Therefore your DCR at 4 ATA is 4 times 22 or 88 litres/min [4 times 0.75 or 300 cuft/min].

People, please read this great monograph on gas calculations and the terminology used: http://www.5thd-x.com/pdfs/battlefieldcalc.pdf

 

[fire_diver]

Well you would have to do those "Oh I'll just jump in and come up when I reach 700psi" a few time before you can get a real SAC right??? If you took your SAC off your first 5 dives dont you think it would have changed by now? Just sayin.

How do you calculate SAC/volume? I dive a XS HP100 (first one on the page) if that helps.

OK, assuming that you aren’t being asinine here is how you would do it.

Divide the volume by the working pressure. For this you would divide 100 by 3300 which give you .03 CF of gas per PSI. Next, you have to measure your start and end psi at a constant depth. If your computer gives an average depth you can use your begin and end pressure for the entire dive.

So lets pretend your average depth was 33 foot (2 atmospheres) and you used 2000 psi during your dive.

2000 psi x .03 = 60 cubic feet of gas used. Divide 60 by 2 = 30 cf of gas equivalent use during that time on the surface. If the total dive time was 30 minutes, divide volume by time = 1 cf/minute of dive. This is your SAC.

That was for one dive, with one gear set, in one type of dive condition. Do this for every dive and you will learn what you should be breathing as an average for each type of dive you do. Now you don’t need to check it every dive because you should know what to expect for certain conditions.

Now that you know what that dive was, you can plan that if you are going to 3ATA on your dive tomorrow, in similar conditions, you will be breathing down 3 cf every minute. After 10 minutes you could expect to be down 30cf or roughly 30% of your total tank.

As for the “come up at 700” dives, this is why new divers are recommended to stay SHALLOW. They don’t yet know what they don’t know.