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Air Consumption Rates for Scuba Diving - SAC Rates, RMV Rates, Easy Calculations


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Formula for Calculating Your Respiratory Minute Volume Rate (RMV Rate)
A female scuba diver calculates her RMV rate on a jetty after a dive.

A calculator or computer is useful for calculating an RMV Rate after a dive.

©istockphoto.com, Spanishalex
Plug your SAC Rate (calculated on the previous page) and other necessary information into the appropriate formula below. Metric RMV Rate calculations are much simpler than Imperial RMV Rate calculations.
• Imperial Method:

- Step 1: Calculate a "tank conversion factor" for the tank you used when gathering data. To do this, you will need the tank volume (in cubic feet) and the working pressure (in psi) this information is stamped on the tank neck:
Tank Volume in Cubic Feet ÷ Working Pressure in PSI = Tank Conversion Factor
- Step 2: Multiply your Imperial SAC Rate by the Tank Conversion Factor:
Tank Conversion Factor x SAC Rate = RMV Rate in cubic feet/minute
- Example: A diver who has a SAC Rate of 25 psi/min when diving with an 80 cubic foot tank with a working pressure of 3000 psi has an RMV Rate of . . .
First, calculate the tank conversion factor:
80 cubic feet ÷ 3000 psi = 0.0267

Next, multiply the diver's SAC Rate by the tank conversion factor:
0.0267 x 25 = 0.67 cubic feet/ minute

The diver's RMV Rate is 0.67 cubic feet/ minute! Easy!
• Metric Method:

Simply multiply your Metric SAC Rate by the volume of the tank you used when gathering data in liters. This information is stamped on the tank neck.
Tank Volume in liters x SAC Rate = RMV Rate
- Example: A diver who has a SAC rate of 1.7 bar/minute when diving with a 12-liter tank has a RMV Rate of . . .
12 x 1.7 = 20.4 liters/minute

It's that easy!
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