VO2 is a
difficult concept. The metabolic usage of a SCR diver strongly depends on
the workload. In general, this value is approx.
0,5 - 0,8 l/min, however when the
diver works under water a usage up to 4 litres is possible.
This variable has influence on the
inhaled gas fraction.
Since there is a variation in the metabolic use of oxygen
during the dive, there will be a variation in the inhaled oxygen fraction.
This has a direct impact on the decompression obligation because the
nitrogen fraction varies with the oxygenfraction.
calculate the fraction of the oxygen content the diver is breathing we need
to know a couple of things:
1. The gas in the bottle
2. The metabolic oxygen consumption of the diver
3. The gas injection with this particular gas
OK, suppose we dive a Dolphin rebreather fitted
with a 50% Nozzle (intended to be used with EAN 50) the flow is
fixed at 7,3 ltr/min. This value has to be found in the manual.
The 50% nozzle is a orifice that allows a fixed mass of gas when
certain parameters are OK. If you want to know more about
orifices and how they work search for "gas flow through an
orifice" on this website. Also we presume the diver has a
metabolic consumption of oxygen of 0,9 ltr/min, we than find the
Gas choice =
Dolphin injects 7,3 ltr/min with the 50% jet
When filled in the formulae we find:
The diver will breath a Nitrox mixture of