Im trying to figure (internalize) the differences and usages in these two breathing consumption rates.
First, to baseline the discussion:[1]
SAC: Surface Air Consumption. Measure by taking a tank of known volume, wear a mask or nose plugs, note the starting pressure, breath for 10 to 20 minutes, then note the final pressure. Compute the cu ft (L) used. SAC Cu ft / minutes.
Surface RMV: Respiratory Minute Volume. Take an average from past dives, rework the figures of consumption at depth to extrapolate what the consumption would be at 1 atm (bar). Figure the consumption per minute.
The SRMV supposedly has other factors against it such as work during dive, cold, darkness, and other things that affect volume consumption. The SRMV is variable per dive.
The SAC is supposed to be a more-sure baseline as it is generally not affected much over time (except to vary with physical fitness).
Heres an interesting difference. The TDI Guide to Advanced Nitrox[2] has nothing about the SAC, but does all computations according to a divers RMV.
Q1: Why use a variable consumption rate?
Q2: What would be the general / average / expected difference in the SAC vs the SRMV?
Q3: What do you use to compute your gas use and why?
[1] SDI Solo Diving Manual 2007
[2] TDI Guide to Advanced Nitrox 2009
Lot of discussion on SAC here: http://www.scubaboard.com/forums/basic-scuba-discussions/344311-sac-rates.html but the definition of SAC doesnt seem to be the same.
First, to baseline the discussion:[1]
SAC: Surface Air Consumption. Measure by taking a tank of known volume, wear a mask or nose plugs, note the starting pressure, breath for 10 to 20 minutes, then note the final pressure. Compute the cu ft (L) used. SAC Cu ft / minutes.
Surface RMV: Respiratory Minute Volume. Take an average from past dives, rework the figures of consumption at depth to extrapolate what the consumption would be at 1 atm (bar). Figure the consumption per minute.
The SRMV supposedly has other factors against it such as work during dive, cold, darkness, and other things that affect volume consumption. The SRMV is variable per dive.
The SAC is supposed to be a more-sure baseline as it is generally not affected much over time (except to vary with physical fitness).
Heres an interesting difference. The TDI Guide to Advanced Nitrox[2] has nothing about the SAC, but does all computations according to a divers RMV.
Q1: Why use a variable consumption rate?
Q2: What would be the general / average / expected difference in the SAC vs the SRMV?
Q3: What do you use to compute your gas use and why?
[1] SDI Solo Diving Manual 2007
[2] TDI Guide to Advanced Nitrox 2009
Lot of discussion on SAC here: http://www.scubaboard.com/forums/basic-scuba-discussions/344311-sac-rates.html but the definition of SAC doesnt seem to be the same.