Surface Air Consumption

Surface Air Consumption/Respiratory Minute Volume Work Sheet


Calculate your own SAC/RMV rate by collecting some data.

Resting (no movement), moderate work (easy swim) and hard work (kicking hard against stationary object).

You must know the size tank you are using; Beginning pressure and ending pressure; Depth at which readings are taken.  Try to do at least 5 minutes at rest, 5 minutes at moderate work and at least 2-3 minutes hard work.


Tank size      ______          pressure     ______          cylinder value       ft³ ÷ psig = ft³/psig (cylinder value)

Rest                     Moderate                     Hard      

depth          ______          depth          ______               depth          ______

begin time     ______          begin time     ______               begin time     ______
begin pressure     ______          begin pressure     ______               begin pressure     ______


end time          ______          end time          ______               end time          ______
end pressure     ______          end pressure     ______               end pressure     ______


total psi for each segment
____________               ____________                    ____________

total time for each segment
          ____________               ____________                    ____________

Convert the depth to absolute pressure ATA          Pressure (ATA) = (Depth ÷ 33) + 1
          
____________               ____________                    ____________


Now multiply total psi used by the cylinder value to find total ft³ used.

80 ft³ ÷ 3000 psig = .027 ft³/psig     63 ft³ ÷ 3000 psig = .021 ft³/psig     40 ft³ ÷ 3000 psig = .013 ft³/psig

PSI used× cylinder value  (.027if an alum 80 used)  = total ft³

___________               ___________                    ___________     


Now divide the total ft³ used by the number of minutes for each segment, to give ft³ per minute (at depth) or respiratory minute volume (RMV) at rest, moderate and heavy work.


total ft³ ÷  min = ft³/min          total ft³  ÷  min = ft³/min               total ft³  ÷  min = ft³/min

Rest                     Moderate                     Hard

___________RMV (depth)          ___________RMV (depth)               ___________RMV (depth)

To find out what this value is at the surface, you must divide the RMV at depth by the absolute pressure ATA of that depth.  This will give the Surface Consumption Rate / Respiratory Minute Volume.
RMV (depth) ÷ ATA = Surface Respiratory Minute Volume

___________RMV               ___________RMV                    ___________RMV

REST                    MODERATE                    HARD