SAC terminology

Jef Driesen jefdriesen at
Thu Feb 13 23:18:14 UTC 2014

On 2014-02-13 15:58, Willem Ferguson wrote:
> I am doing a technical qualification with IANTD and they use SAC as
> the rate of decrease per minute in the pressure in the gas cylinder
> (units=bar/minute). Then I went back to some of my TDI and NAUI notes
> and came across the same definition. This use of SAC would remove the
> interchangeability that is often encountered between SAC and RMV, with
> RMV indicating the gas consumption in volume/minute (e.g.
> liters/minute). Is this something worth worrying about for the SAC
> rate given on the dive info panel?
> Kind regards,

If you ask me, SAC (Surface Air Consumption) defined as pressure/time is 
pretty useless because it depends on the tank volume. For example a SAC 
of 1 bar/min is equivalent to 10L/min for a 10L tank, but 15L/min for a 
15L tank. While, SAC defined as volume/time is a truly independent 
number that you can compare across dives, regardless of the tank size.

The term RMV (Respiratory Minute Volume) is less known and more 
difficult to grasp for the average diver (respiratory, what the hell 
does that mean?), so I would stick to the name SAC. When the units are 
shown, there is no confusion about which interpretation is used.


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